A Study on Thermal Resistance over a Solid-Liquid Interface by the Molecular Dynamics Metho

工科英语考试题及答案一、选择题（每题2分，共20分）1. The most common method to measure the strength of materials is ________.A. Tensile testingB. Compression testingC. Impact testingD. Fatigue testing答案：A2. In engineering, the term "yield strength" refers to the point at which a material ________.A. BreaksB. Starts to deform permanentlyC. Returns to its original shapeD. Becomes elastic答案：B3. Which of the following is not a type of heat treatment used in metallurgy?A. AnnealingB. HardeningC. TemperingD. Electroplating答案：D4. The process of converting electrical energy intomechanical energy is known as ________.A. ElectromagnetismB. Electromechanical conversionC. ElectrolysisD. Electrostatics答案：B5. In fluid dynamics, the Hagen-Poiseuille equation describes the flow of ________.A. Gases in pipesB. Liquids in pipesC. Solids in fluidsD. Fluids in open channels答案：B6. The unit of power in the International System of Units (SI) is the ________.A. WattB. NewtonC. PascalD. Joule答案：A7. A ________ is a device that converts rotational motioninto linear motion.A. PulleyB. LeverC. GearD. Piston答案：D8. The study of the behavior of materials under various loads is called ________.A. Mechanics of materialsB. Material scienceC. Structural engineeringD. Civil engineering答案：A9. In electrical engineering, the term "ohm" is the unit of ________.A. VoltageB. CurrentC. ResistanceD. Power答案：C10. The process of creating a three-dimensional digital model of a physical object is known as ________.A. PrototypingB. 3D printingC. Computer-aided design (CAD)D. Virtual reality答案：C二、填空题（每题2分，共20分）1. The ________ of a material is its ability to resist deformation.答案：stiffness2. In mechanical engineering, ________ is the study of the forces and moments acting on rigid bodies.答案：statics3. A ________ is a type of gear system that allows for the transmission of motion and power between parallel axes.答案：spur gear4. The ________ is a device that uses a rotating magnetic field to convert electrical energy into mechanical energy.答案：electric motor5. The ________ is a type of sensor that measures the force exerted on it.答案：load cell6. The ________ is a principle stating that the pressure at a point in a fluid is equal in all directions.答案：Pascal's principle7. ________ is the process of joining two pieces of metal by melting their surfaces together.答案：welding8. A ________ is a type of circuit that allows current to flow in only one direction.答案：diode9. ________ is the study of the flow of electric current through conductors.答案：electrical conduction10. ________ is the process of removing material from a workpiece to shape it.答案：machining三、简答题（每题10分，共40分）1. Explain the difference between brittle and ductile materials.答案：Brittle materials are those that break or fracture without significant deformation before failure, while ductile materials can undergo significant plastic deformation before breaking.2. Describe the function of a capacitor in an electrical circuit.答案：A capacitor in an electrical circuit stores electrical energy in an electric field. It can smooth out voltage fluctuations and block direct current while allowing alternating current to pass.3. What is the purpose of a heat exchanger in a thermal system?答案：A heat exchanger is used to transfer heat from onefluid to another, either to cool down a hot fluid or to heatup a cold fluid, without the fluids mixing together.4. How does a transformer work?答案：A transformer works by using electromagnetic induction to change the voltage of an alternating current. It consists of two coils of wire wrapped around a common iron core, and it can either step up or step down the voltage.结束语：希望以上试题及答案能帮助你更好地准备工科英语考试。

Energy and Buildings 75(2014)60–69Contents lists available at ScienceDirectEnergy andBuildingsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e n b u i ldThe facade system with ventilated channels for thermal insulation of newly constructed and renovated buildingsM.I.Nizovtsev a ,∗,V.T.Belyi b ,A.N.Sterlygov aaLaboratory Problems of Energy Savings,Institute of Thermophysics,Russian Academy of Science,Siberian Branch,1Lavrent’ev Avenue,Novosibirsk 630090,Russia bThermoland Ltd.,38,Stantsionnaya Street,Apt.5,Novosibirsk,Russiaa r t i c l ei n f oArticle history:Received 4March 2013Received in revised form 29January 2014Accepted 1February 2014Keywords:Ventilated facadeHeat-insulating panel Ventilated channels Brick wallMoisture analysisa b s t r a c tIn the present paper,we describe a new thermal-insulating facade system for newly constructed and renovated buildings,based on heat-insulating panels with ventilated channels.The calculated data on thermal resistances of heat-insulating panels and on the reduced thermal resistances of brick walls with an external facade system,formed by the panels with ventilated channels,are reported as a function of panel thickness.Heat transfer performance uniformity factors of brick walls with different numbers of anchors used for mounting a panel on the brick wall are determined.The calculations show that the heat transfer performance uniformity factors of ventilated panels can be substantially increased in comparison with similar factors for traditional ventilated facade systems.Non-stationary thermal and moisture calculations of newly constructed and renovated buildings with brick outer walls were carried out to determine the humidity dynamics of heat-insulating and structural wall layers over a period of three years.The calculations prove that the examined configuration of ventilated channels is capable of providing for low moisture content and good heat-insulating properties of the walls.Photos and thermograms of building facades,thermally insulated with ventilated channels,are presented.©2014Elsevier B.V.All rights reserved.1.IntroductionIn recent years,ventilated facade systems have found widespread use in various climatic zones due to their high energy performance,rich variety of available design solutions,reduced effect of solar radiation on indoor microclimate,good noise reduction properties,and possibility of rapid building repair and reconstruction [1].Performance characteristics of ventilated facades are influenced by the outdoor conditions (the solar irradiance,the wind direction and speed,and the outdoor air temperature),and also by the indoor conditions (the temperature and humidity of the indoor air)and facade design features (air interlayer configuration,composition of used materials and their layout)[2].In recent years,the wide use of ventilated facades in civil engineering and involvement of many factors,affecting the per-formance of such facades,stimulated numerous simulation studies aimed at gas dynamics and heat–mass transfer analysis of venti-lated facades [3–6].Fundamentals of free-convection flows,moving∗Corresponding author.Tel.:+73833165336;fax:+73833165336.E-mail address:nizovtsev@itp.nsc.ru (M.I.Nizovtsev).along vertical surfaces under heating or cooling,were laid down in the classical works by Bar-Cohen and Rohsenow [7],Rohsenow et al.[8],and Sparrow et al.[9].It should be noted,however,that,in spite of the permanently increasing number of numerical studies of ventilated facades,the development of valid engineering procedures for simulating such facade systems still remains an urgent problem.This is why of much significance are also experimental studies of ventilated facades,aimed at verification and optimization of simulation procedures [10–12].In recently reported studies,special attention was paid to sev-eral design features of ventilated facades.For instance,it was noted in [13]that,although the external skin can play an important role in a facade system,the choice of external-skin material for venti-lated facades was previously given insufficient attention.In [14],results of the study of the effect of a heat-reflecting film,provided on the surface of ventilated air cavity,were described;and the high performance of the film,especially at night in the winter season was shown.In [15],attention was drawn to the necessity of tak-ing the building envelope mass into account while analyzing the performance of ventilated facades.The literature also contains the results gained in the studies of performance characteristics of various “active”facades with forced/10.1016/j.enbuild.2014.02.0030378-7788/©2014Elsevier B.V.All rights reserved.M.I.Nizovtsev et al./Energy and Buildings75(2014)60–6961Nomenclatured panel thickness(mm)D effective moisture diffusivity(m/s2)H enthalpy of the humid material(J/kg)h phase-transition heat(J/kg)k absorption coefficient for solar radiationn number of mounting anchors per panelP water-vapor pressure(Pa)R thermal resistance,reduced resistance to the trans-fer of heat(K m2/W)r heat transfer performance uniformity factors of the anchored panelt temperature(◦C)W V volume humidity(kg/m3)W relative mass humidityx,y coordinates(m)q t heat-flux density(W/m2)q m moistureflux density(kg/m2s)q s incidentflux of solar radiation(W/m2)Greek symbolstime(s)ϕrelative humidityvapor permeability coefficient(kg/m s Pa)˛heat-transfer coefficient(W/m2K)ˇmass-transfer coefficient(kg/m2s Pa)thermal conductivity(W/m K)Subscriptsair airb boundaryo structural layerp panelred reduced quantityreq required valuereq+reduced value with allowance for anchorssat saturated water vaporventilation and adjustable shading elements[16]or with solar bat-teries,installed on the external surface[17,18].In hot-climate regions,ventilated facades allow diminishing the influence of heating of external building-wall surfaces on the indoor microclimate[2,19].Since the thermal-insulating proper-ties of mineral wool heat-insulating materials are largely defined by the moisture state of the materials,in the region with low winter temperatures and with a long cold period,one of the main functions of ventilated facades is maintaining the outer heat-insulationlayer in a dry state[20].In ventilated facades with a heat-insulation layer,various mate-rials were used;nonetheless,as a rule,such facades normally feature a design common to all such facades.During installation of a ventilated facade on a building wall,an intersystem formed by metal outriggers and supporting profiles isfirst mounted.Then,at a certain distance from the heat-insulation layer,an external-skin layer is to be installed.Thus,in installation of a standard ventilated fac¸ade,all operations are performed on the construction site;this circumstance makes the inspection of work quality difficult and prolongs the time necessary for the mounting.In the present article,we describe a new facade system based on factory-produced heat-insulating panels with ventilated channels and report results of thermal and moisture calculations,performed for brick walls of newly constructed and renovated buildings,pro-vided with the new facade system.Fig.1.The facade system with ventilated channels.2.The facade system with ventilated channelsDeveloping the new facade system,we intended to design a high prefabrication system,suitable for thermal insulation of build-ing walls in both newly constructed and renovated buildings.Such a facade system with ventilated panels was developed.The new facade system(see Fig.1)is based on heat-insulating panels admit-ting their line production at factories[21].From the outside,each panel is provided with a thin metal cladding,covered with a special decorative coating.The cladding is glued onto a mineral wool layer,provided on the outer side with longitudinal venti-lated channels(Fig.2).The cross-section of the ventilated channels is20mm×40mm,the separation between neighboring channels being62mm.The latter dimensions were chosen based on the heat–moisture analysis,whose results are reported below.The total thickness of the panel heat-insulating layer d varies depending on the particular panel application.The dimensions of a standard panel are3000mm×1190mm.The panels are mounted on a newly constructed or renovated building wall with steel anchors(Fig.1).In mounting the panels, in between them,horizontal gaps are left to befilled with min-eral wool down to the bottom of ventilated channels;in this way, horizontal ventilation slits,covered from the outside with weather strips,are formed.3.Thermophysical analysisIn construction and renovation of buildings,whose structural layer has a reduced thermal resistance R0,there is a need to deter-mine the thickness of a heat-insulating panel,providing for the reduced outer-wall thermal resistanceR req=R0+R p,where R p is the panel thermal resistance.Using the computer program“Term5”[22],allowing2D sim-ulation of building structures,we carried out thermal calculations of ventilated panels of various thicknesses.In the calculations,for the thermal conductivity of the mineral wool layer in the panels,a value0.042W/m K,typical of a wide range of mineral wool thermal insulators,was adopted.Data for one of the analyzed designs are shown in Fig.2.From an analysis of the plots of R p vs d,it follows that this dependence is linear in the interval80mm≤d≥250mm; this linear dependence can be presented asR p=0.0238(d−80)+1.62162M.I.Nizovtsev et al./Energy and Buildings 75(2014)60–69Fig.2.Thermal data calculated for a 160-mm thick heat-insulating panel.Further,we carried out thermal calculations of the reduced resistance to the transfer of heat for brick building walls withclay brick layer thicknesses 250-,380-,and 640-mm (R 250red,R 380red,and R 640red,respectively)provided with external heat insulation,formed by ventilated panels of various thicknesses.The calcula-tions were performed with the computer program “Term 5”,taking into account a 20-mm thick cement-sand plaster layer,covering the inner surface of the wall.In calculations of the reduced thermal resistances,the total coefficients of heat transfer from the outside and inside were adopted to equal respectively 23and 8.7W/m 2K.These data can be generalized with the following dependences:R 250red=0.0238(d −80)+2.165R 380red=0.0238(d −80)+2.351R 640red =0.0238(d −80)+2.722From the results of thermal calculations,we were able to deter-mine the recommended thicknesses of heat-insulating panels withventilated channels for brick walls of various thicknesses on the condition of a 5–10%excess of the reduced thermal resistance of building walls,specified for Novosibirsk climatic conditions by Construction specifications and regulations [23].The recom-mended thickness of heat-insulating panels for 250-,380-,and 640-mm thick brick walls was found to be respectively 160,150,and 140mm.Mounting of heat-insulating panels on a brick wall with metal anchors entails an additional heat loss,whose relative measure is given by the heat transfer performance uniformity fac-tor;r =R red+/R red ,where R red +and R red are the reducedthermalFig.3.Calculated distribution of temperature in the anchor plane for 250-mm thick brick wall and for 15anchor/panel.M.I.Nizovtsev et al./Energy and Buildings 75(2014)60–6963Table 1Properties of materials.MaterialBulk density,kg/m 3Porosity,m 3/m 3Spec heatcapacity,J/kg KThermal conductivity,W/m 2KWater vapor diffusion resistance factorCement-sand plaster 19000.248500.819Clay brick masonry 19000.248500.610Mineral wool1100.958500.0423.3Fig.4.Heat transfer performance uniformity factors of thermally insulated brick wall for different numbers of mounting anchors per panel.1–640-mm thick brick layer,2–250-mm thick brick layer.resistances of the building wall,determined with and without allowance for the anchors.With the aim of determining the heat transfer performance uniformity factors of panel anchoring,we carried out thermal calcu-lations for the newly constructed brick walls (brick layer thickness 250mm,panel thickness 160mm)and renovated brick walls (brick layer thickness 640mm,panel thickness 140mm).In the calcula-tions,the inner surface of the brick walls was assumed to be covered by a 20-mm thick cement-sand plaster layer.The calculations were performed using the specialized com-puter program HEAT 3.5,intended for 3D thermal calculations of building structural elements [24].In the calculations,we treated the case of a standard 1.19m ×3m heat-insulating panel with ventilated channels,mounted on the brick wall with 8,12,or 15steel anchors of 8mm diameter.The dimensions of the computa-tional domain were defined by the panel area per one anchor.The indoor and outdoor air temperatures were assumed to be 21◦C and −39◦C,which case refers to the coldest five-day period in Novosibirsk [25].By way of example,Fig.3shows the distribution of wall tem-perature in the anchor section over a 250-mm thick brick layer,heat-insulated with a panel of 160mm thickness,fixed on the brick wall with 15anchors.According to the calculated data,the inner-surface wall temperature at the place opposite to the anchor location was rather high,19.1◦C,and differed by as lit-tle as 0.1◦C from the inner-surface wall temperature far from the anchor.Using the calculated data,we have determined the heat transfer performance uniformity factors of panel anchoring for brick walls of 250and 640mm thicknesses for different numbers of anchors per panel (Fig.4).The performed thermal calculations showed that the heat transfer performance uniformity factors for anchored panels with ventilated channels in the case of both newly constructed and renovated buildings fell in the range from 0.98to 0.93,those valuesbeing notably in excess of the heat transfer performance uniformity factors of traditional ventilated-facade designs [26].4.Moisture analysisTo identify the moisture state of walls in newly built or ren-ovated buildings,thermally insulated with ventilated panels,we carried out a moisture analysis of two facade designs:Design 1.A 250-mm thick clay brick wall of a new building is ther-mally insulated from the outside with 160-mm thick panels having ventilated channels.Design 2.A 640-mm thick clay brick wall of a renovated building is thermally insulated from the outside with 140-mm thick panel having ventilated channels.As a heat insulator in the panels,a mineral wool of 110kg/m 3density was used.The calculations were performed on the assump-tion that the inner wall surface was covered with a 20-mm thick cement-sand plaster layer.In the calculation of both designs,identical boundary conditions were adopted.The indoor temperature and the relative air humidity were assumed to be respectively 21◦C and 55%.From the outside,the air temperature,the relative air humidity,and the incident solar radiation intensity were specified at 1-h step for a typical year close to the climatic conditions of Novosibirsk.The calculations were performed for building walls oriented to the west.The coefficient of solar radiation absorption by the outer wall surface was taken equal to 0.4.The calculations were performed for a period of three years,starting from August 1.The calculations were performed using the computer program “Wufi2D-3”intended for 2D non-stationary heat–moisture calcu-lations of building structures [27].Properties of layer materials and their dependencies on tem-perature and humidity were taken from the library of materials properties of “Wufi2D-3”program,and the basic materials prop-erties,used in the calculations,are presented in Table 1.Air humidity and temperature in the ventilated channels were taken for the calculations,based on the parameters of the outdoor air,that is proved to be reasonable according to further estimates of air velocities in the channels,moisture flows through the walls and due to the horizontal slits present every 3m over the fac ¸ade height.In the calculations,we took into account the dependence of moisture storage capacity on relative humidity of all considered materials,including the mineral wool.The algorithm of the program is based on numerical solution of the equation system,involving the enthalpy conservation equation (1)and the moisture-mass conservation equation (2).The specified boundary conditions are certain values of heat-flux density (3)and moisture flow density (4)[28]∂H ∂t ∂t ∂ =∂∂xx∂t∂x+∂∂yy∂t ∂y+h∂∂xx∂ϕP sat ∂x+h∂∂yy∂ϕP sat ∂y(1)64M.I.Nizovtsev et al./Energy and Buildings 75(2014)60–69Fig.5.Variation of outer-surface wall temperature (250-mm thick brick layer).∂W V ∂ϕ∂ϕ∂ =∂∂xD x∂W V ∂ϕ∂ϕ∂x + x ∂ϕP sat∂x+∂∂yD y∂W V ∂ϕ∂ϕ∂y + y∂ϕP sat∂y(2)q =˛(t air −t b )+q s k(3)q m =ˇ(P air −P b )(4)4.1.Moisture state of a new building wallThe initial relative humidity of the brick and plaster layers in the newly built building wall was assumed substantial,equal to the sorption humidity of involved materials at 80%relative air humid-ity.In calculations with outer-wall surface temperature lowering in winter months (see Fig.5),the density of the heat flux through the wall showed an increase with the highest values running into 10W/m 2(Fig.6).Fig.7shows the variation of the average relative mass humid-ity of the panel mineral wool layer.According to the calculated data,in the first-year winter season after the wall was built,theFig.6.Variation of heat-flux density on the inner wall surface (250-mm thick bricklayer).Fig.7.Mean relative humidity of the mineral wool layer (250-mm thick brick layer).humidity was somewhat greater than 2%due to the enhancedmoisture content of the brick layer,and afterwards the humidity showed a decrease.In subsequent years in the winter time,the humidity increased to 1.5%.Such an increase of the humidity of the mineral wool layer can be considered insignificant,only weakly affecting the thermal insulating properties of the heat-insulation material.Thus,as calculations showed,the heat-insulation mate-rial in a panel with ventilated channels was in a rather dry state with no danger of fungus growth.This is evident from the data of Fig.8;in this figure,the dots indicate the hydrothermalconditionsFig.8.Hydrothermal conditions in the heat-insulator layer (250-mm thick brick layer).M.I.Nizovtsev et al./Energy and Buildings 75(2014)60–6965Fig.9.Mean relative humidity of the brick layer (250-mm thick brick layer).in the heat-insulation material at different times.The same figure shows the hydrothermal curve,over which the appearance of fungi becomes possible in the heat-insulation material.As it is evident from calculations,the relative humidity of the brick layer showed a sharp decrease during the first year after the construction of the building;later this humidity was at a level of 0.2%,showing insignificant rises to 0.3%in the periods from the end of summer to the beginning of autumn (Fig.9).Note that,on the whole,the humidity level of the brick layer was rather low.Fig.10shows distribution of average volume humidity in the brickwork and in the heat-insulating layer of the panel in the 3rd year after the construction completion in August,when there were maximal humidity increase in the brick masonry and some increase of humidity in the heat-insulating layer.According to the calculated results,humidity of brick masonry both in August and February decreased from the internal to external surface;and over its thick-ness,humidity in February was lower than in August.In panel heat-insulation layer,humidity of the outer layers in the considered months was higher than in the internal ones.In February,it wasdueFig.10.Month average humidity distribution (250-mm thick bricklayer).Fig.11.Moisture diffusion flux density at the brick layer/heat insulator interface:(a)over a three-year period,(b)during the winter season (250-mm thick brick layer).to the lower temperature of the outer layers,and in August –due to the higher humidity of the outer air at its rather high temperature.As a result of calculations,the density and the direction of the moisture diffusion flux across the brick layer/heat-insulation layer interface were determined (Fig.11a).An analysis of the data shows that in winter,the moisture flux is positive,directed from the brick to thermal-insulation layer,and in summer,it is predominantly negative,directed from the thermal-insulation layer into the brick wall.To judge whether the ventilated channels will be capable or not of providing for the necessary removal of the moisture,accu-mulated in the thermal-insulation material,we determined the average density of the diffusion flux of moisture during the win-ter months,¯qm =7.7×10−8kg /m 2s (Fig.11b).We performed a gas dynamics analysis of the ventilated channels in January for the mean outdoor temperature −18.8◦C and relative air humidity of 80%,the latter values being typical of the Novosibirsk climatic con-ditions.The evaluated velocity of the air flow in the channels was 0.2m/s.The calculations showed that,under the conditions with inter-storey air inlet and outlet openings into a ventilation chan-nel,each ventilated channel was capable of removing moisture at a rate of up to 0.3×10−7kg/s,the necessary rate of moisture removal being 0.2×10−7kg/s.Thus,the calculations showed that,with properly organized inter-storey air openings into the ventilated channels,the exam-ined configuration of the ventilated channels provides for efficient removal of moisture out of the heat-insulation material.66M.I.Nizovtsev et al./Energy and Buildings75(2014)60–69Fig.12.Mean relative humidity of the mineral wool layer(640-mm thick brick layer).4.2.Moisture state of a renovated building wallA640mm thick brick wall in a renovated building was assumed thermally insulated with140-mm thick panels with ventilated channels,installed using no wet processes;that is why in the calcu-lations,the initial moisture content of the brick and plaster layers was taken equal to the sorption humidity of the materials at50% air humidity.According to the calculated data,no accumulation of moisture in the mineral wool layer of the panel occurred during the annu-lar cycle,with just cyclic oscillations of mean relative humidity at the end of summer and in the winter season being observed(here, the relative humidity varied within1%(Fig.12)).During the whole calculated period,the mineral wool remained rather dry and,as hydrothermal calculations showed,no danger of fungi formation and growth occurred in the heat-insulation layer.The calculated data on the variation of brick layer humidity on average and over component layers are shown in Fig.13.From these data it follows that the mean moisture content of the brick wall is rather low,with an insignificant rise of material humidity at the end of summer and the beginning of autumn(Fig.13a).The analy-sis of the distribution of the moisture content over the component brick-wall layers reveals the fact that the most humid one is the inner brick-wall layer,while the largest amplitude of the annu-lar oscillations of material humidity is observed in the outer layer (Fig.13b).Distribution of average volume humidity for the month in the brick and heat insulating layer of the wall in August and February of the3rd year is shown in Fig.14.Similarly to the earlier considered calculation option for the wall with a brick layer of250mm thickness(Fig.10),humidity distribu-tion in heat insulation was similar to humidity increase from to the outer surface due to the abovementioned reasons.In the inter-nal part of the brick masonry,humidity in February turned out to be higher than in August,and for the wall with250mm brick masonry–vice versa;that was obviously bound with the lag effect of moisture transfer processes in the thicker brick layers.We also performed calculations of the variation of the moisture diffusionflux across the brick layer/heat-insulator layer interface. The calculation showed that,similar to the case of design1,in winter,the moistureflow is directed out of the brick layer into the heat insulator,and in summer,predominantly in the opposite direction,out of the heat insulator into the brick wall(Fig.15a).Fig.13.Mean relative humidity of the brick layer(a)in the whole brick layer,(b)in different component layers of the brick wall:Digits1–4enumerate the component layers from the outside to inside(640-mm thick bricklayer).Fig.14.Month average humidity distribution(250-mm thick brick layer).M.I.Nizovtsev et al./Energy and Buildings75(2014)60–6967Fig.15.Moisture diffusionflux at the brick layer/heat insulator interface,(a)over a three-year period,(b)during the winter season(640-mm thick brick layer).According to the calculations,in winter season,the mean mois-ture diffusionflux across the brick wall/heat insulator interface was 2.4×10−9kg/m2s(Fig.15b).The latter value is more than three times lower than the same quantity for a newly constructed build-ing(design1),so that the ventilated channels in the panels are quite capable of ensuring an efficient removal of this moisture.It should be noted that in these calculations,effect of solar radiation,falling on the outer wall surface,was considered only through the temperature increase on the external surface of the heat-insulating layer beyond the ventilation channels;therefore according to the calculated results,influence of solar radiation on materials humidity was weak.In real situation,solar radiation will also heat the outer walls of the ventilation channels,that will in turn increase air temperature in the ventilation channels;and this will lead to the decrease in relative humidity and growth of air veloc-ity in the ventilation channels.Consideration of these processes will result in even lower humidity of construction and heat insu-lation materials of the walls compared to the ones obtained in the calculations.4.3.Practical implementation and results of inspectionsPresently,the thermal insulating facade systems based on the ventilated channels panels were installed on more than ten new and renovated buildings in Novosibirsk and Novosibirsk Region; two renovated buildings are shown in the photos of Fig.16.The use of a broad assortment of decorative coatings allows real-ization of a multitude of design solutions in the thermalinsulation Fig.16.A building thermally insulated with the ventilated panels:(a)a dwelling house,(b)an office block.of buildings with the heat-insulating panels.The experience gained in installation of the new facade system on newly constructed and renovated buildings has proved the possibility of performing effi-cient,good-quality installation works.The thermal imaging inspections of several buildings performed in the winter time have confirmed the high thermal performance of the new facade system.Some results of thermal imaging study of the three-floored building with the outer walls,made of clay bricks with the thickness of510mm,partially covered by the panels,are shown in Fig.17as an example of efficient application of the pan-els with ventilated channels,used for heat insulation of previously constructed buildings.The outside air temperature at investigation was−14.5◦C.The picture and thermogram of the outer corner of the building,where one wall is covered by the panels and another is free of them,are shown in Fig.17a and b.According to investi-gation results,the temperature of the outer surface of the panels is 3.5–4◦C lower than the temperature of the outer surface of brick walls,which are not covered by the panels.This proves a significant (several times)decrease in the heat losses through the walls,cov-ered by heat insulating panels with ventilated channels.The similar conclusion is made by the results of the indoor thermal imaging. At the inner air temperature of26–27◦C the temperature of the inner surface of the outer wall in the room with a wall covered outside by the panels(Fig.17c)is more than4◦C higher than the temperature of the inner surface in the room without heat insula-tion of the outer wall(Fig.17d).Thus,thermal imaging confirms high efficiency of the panels with ventilated channels used for heat insulation of reconstructed buildings.。

基于液态金属的高热流密度电力设备冷却实验研究李振明;刘伟;赵勇青;刘赟甲;丘明【摘要】大功率电力设备的冷却方式成为制约电力设备集约化紧凑性的重要因素.常规水冷技术难以应对具有高热流密度的工况条件,而新兴的液态金属冷却技术具有解决该难题的潜力.为此,本文建立了基于液态金属的高热流密度电力设备冷却实验平台.在该平台基础上,开展了液态金属和水的对流换热系数和热导率对比实验.实验表明,在相同工况条件下,以液态金属替代水作为冷却介质,系统热阻可由0.033 K/W降低至0.019 K/W;若进一步以液态金属替代传统导热膏作为界面材料,则散热系统热阻可降低至0.014 K/W.%Cooling the electric equipment with high power is one of the important issues to limit the compactness and intensity of electric equipment. Traditional water cooling can not deal with the operating conditions of high heat flux, however, novel liquid metal cooling has the potential to solve the problem. Therefore, this paper presents a study based on liquid metal cooling system for high heat flux electric equipment. The contrast experiments of con-vective heat transfer coefficient and thermal conductivity between the liquid metal and water are carried out. Experi-mental results show that the system thermal resistance can be reduced from 0. 033 K/W to 0. 019 K/W when using liquid metal instead of water as the coolant. Moreover, if further using liquid metal as the thermal interface materi-al, the system thermal resistance can be finally reduced to 0. 014K/W.【期刊名称】《电工电能新技术》【年(卷),期】2017(036)004【总页数】5页(P66-70)【关键词】电力设备;高热流密度;液态金属冷却;水冷【作者】李振明;刘伟;赵勇青;刘赟甲;丘明【作者单位】中国电力科学研究院储能与电工新技术研究所,北京100192;中国电力科学研究院储能与电工新技术研究所,北京100192;中国电力科学研究院储能与电工新技术研究所,北京100192;中国电力科学研究院储能与电工新技术研究所,北京100192;中国电力科学研究院储能与电工新技术研究所,北京100192【正文语种】中文【中图分类】TM40随着电力工业的发展，大功率电力设备的热管理已成为影响电力设备集约紧凑性的关键难题之一。

电路 electric circuit电气工程electrical engineering 电机electric machine自然科学physical science电气设备 electrical device电器元件 electrical element正电荷positive charge负电荷negative charge直流direct current交流alternating current电压voltage导体conductor功work电动势electromotiveforce电势差potential difference功率power极性polarity能量守恒定律the law of conservation energy 变量variable电阻 resistance电阻率resistivity绝缘体insulator电阻器resistor无源元件passive element常数constant电导conductance短路short circuit开路open circuit线性的linear串联series并联parallel电压降voltage drop等效电阻equivalent resistance 电容器capacitor电感器inductor储能元件storage element电场electric field充电 charge放电discharge动态的dynamic电介质dielectric电容capacitance磁场magnetic field电源power supplu变压器transformer电机electric motor线圈coil电感inductance导线conducting wire绕组wingding漏电阻leakage resistance电子系统electronic system结构图block diagram功能模块functional block放大器amplifier滤波器filter整形电路wave-shaping circuit 振荡器oscillator增益gain输入阻抗input impedance带宽bandwidth晶体管transistor集成电路integrated circuit电力电子power electronics数字信号处理digital signal-processing 输出装置output device模拟信号analog signal数字信号digital signal传感器transducer采样值sample value模数转换器analog-to-digital converter 频谱frequency content采样频率sampling rate or frequendy扰动disturbance分立电路discrete circuit数字化信号digitized signal运算放大器operational amplifier有源电路active circuit电子部件electronic unit封装package管脚pin同相端noninverting terminal反相输入inverting input电路图circuit diagram压控电压源voltage-controlled voltage source 开环增益open-loop gain闭环增益closed-loop gain负反馈negative feedback正饱和positive saturation线性区linear region电压跟随器voltage follower等效阻抗equivalent impedance逻辑变量logic variable位bit数字字digital word字节byte半字节nibble与运算AND operation真值表truth table与门AND gate非门NOT gate或门OR gate加号addition sign与非门NANA gate异或运算XOR operation逻辑表达式logic expression 二进制binary system正逻辑positive logic负逻辑negative logic参考方向reference direction 理想变压器ideal transformer 电气绝缘electrical isolation阻抗匹配impedance matching电力electrical pewer绝缘变压器isolating transformer电压互感器voltage transformer电流互感器current transformer原边绕组primary winding工作频率operating frequency配电变压器distribution transformer 电力变压器power transformer磁通密度flux density磁场magnetic field铁芯变压器iron-core transformer大功率high-power空芯air-core磁耦合magnetic coupling小功率lower-power励磁损耗magnetizing loss磁滞损耗hysteresis loss涡流eddy current励磁电流exciting current漏磁通leakage flux互磁通 mutual flux线圈coil芯式core form壳式shell form高压绕组high-voltage winding 磁链flux linkage电动势electromotive force有效值root mean square value 匝数比turns ratio视在功率apparent power匝数the number of turns升压变压器step-up transformer 降压变压器step-down transformer 电动机motor发电机generator机械能mechanical energy电能electrical energy电磁的electromagnetic直线式电动机linear motor同步电机synchronous machine感应电机induction machine定子stator转子rotor气隙air gap轴shaft电枢armature励磁绕组field winding无功功率reactive power制动状态braking mode稳态steady-state相序phase sequence反响制动plugging滞后电流lagging current励磁电抗magnetizing reactance 启动电流starting current变频器frequency changer感应电势induced voltage逆变器inverter周波变换器cycloconverter换向器commutator自动控制automatic control控制器controller扰动disturbance期望值desired value压力pressure液位liquid level被控变量controlled variable 方框图block diagram传递函数transfer function 工程控制process control伺服系统servomechanism流率flow rate加速度acceleration前向通路forward path补偿correction反馈通路feedback path闭环closed-loop开环open-loop输出output增益gain手动调节manual adjustment变送器transducer误差error控制方式control mode比例控制proportional control 积分控制integral control微分控制derivative control 执行元件manipulating element 调节时间setting time残差residual error不确定度uncertainty观测数据observations采样sample算术平均arithmetic average 期望值expected value标准偏差standard deviation 下限lower range limit上限upper range limit跨度span分辨率resolution死区dead band灵敏度sensitivity阈值threshold可靠性reliability过量程overrange恢复时间recovery time过载overload过量程极限overrange limit 漂移drift准确性accuracy误差error重复性repeatability系统误差systemic error再现性reproducibility校准calibration线速度linear velocity角速度angular velocity弧度radian测速仪tachometer增量式编码器incremental encoder 定时计数器timed counter稳定性stability接口interface调节器conditioner开关switch执行器actuator电磁阀solenoid valve连续控制系统sequential control system 触点contact常开normally open常闭normally closed限位开关limit switch继电器relay延时继电器time-delay relay接通电流pull-in current开断电流drop-out current电机启动器motor starter接触器contactor自锁触点holding contact整流器rectifier变流器converter逆变器inverter二极管diode阳极anode阴极cathode正向偏置forward biased反向偏置reverse biased阻断block稳压二极管zener diode晶体管transistor集电极collector基极base发射极emitter共发射极common-emitter双向晶闸管triac正半周positive half-cycle 触发电流trigger circuit 功率容量power capability 功率器件power device晶闸管thyristor导通conduction正向阻断 forward-blocking通态on-state关断状态off-state反向击穿电压reverse breakdown voltage 漏电流leakage current电流额定值current rating漏极drain门极gate缓冲电路snubber circuit均流current sharing额定电压rated voltage可控开关controllable switch相控phase-controlled充电器charger工频line-frequency变换器converter整流rectification逆变inversion可逆调速revesible-speed再生制动regenerative barking关断时间turn-off time纯电阻负载pure resistive load脉动ripple感性负载inductance load周期time period带内部直流电动势的负载load witn an internal DC voltage 波形waveform换相commutation稳态steady state交流侧AC-side延时角delay angle交点intersection电力系统power system发电厂generating plant发电机generator负荷load输电网transmission nerwork 配电网distribution network 电electricity天然气natural gas原理图schematic diagram锅炉boiler热效率thermal efficiency 风力wind power断路器circuit breaker变电所substation故障fault过电压overvoltage击穿值breakdown value过电流over current可靠性reliability继电器relay触点contact电流互感器current transformer合闸线圈operating coil分闸线圈trip coilCircuit theory is also valuable to students specializing in other branches of the physical science because circuit are a good model for the study of energy system in general,and because of the applied mathematics,physics,and topology involved.电路理论对于专门研究自然科学其他分支的学生来说也十分有价值，因为电路一般可以很好地作为能量系统研究的模型，并且电路理论涉及应用数学、物理学和拓扑学的相关知识。

中考物理原理英语阅读理解15题1. What is the force that makes a ball fall to the ground?A. Magnetic forceB. Gravitational forceC. Electrical forceD. Frictional force答案：B。

解析：球落到地面是因为重力的作用。

选项A 磁力通常作用于磁性物体之间；选项 C 电力作用于带有电荷的物体之间；选项D 摩擦力是阻碍物体相对运动的力，与球下落无关。

2. Which of the following is an example of optical reflection?A. A magnifying glass enlarging an image.B. A prism splitting white light into colors.C. A mirror reflecting an image.D. A lens focusing light.答案：C。

解析：光学反射是指光线遇到表面后被反弹回来。

镜子反射图像是光学反射的例子。

选项A 放大镜放大图像是利用光的折射；选项B 棱镜将白光分成颜色是光的色散，也是折射现象；选项D 透镜聚焦光线也是光的折射。

3. When you push a box across the floor, what force opposes your push?A. Normal forceB. Tension forceC. Frictional forceD. Air resistance答案：C。

解析：当推箱子时，摩擦力阻碍箱子的运动，与推力相反。

选项A 法向力是垂直于接触面的力；选项B 张力通常存在于绳子等物体中；选项 D 空气阻力在一些情况下也会阻碍物体运动，但在这里主要是摩擦力起作用。

4. What type of lens is used to correct nearsightedness?A. Convex lensB. Concave lensC. Plane mirrorD. Prism答案：B。

Thermal resistanceThermal resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow. Thermal resistance is the reciprocal of thermal conductance.∙(Absolute) thermal resistance R in K/W is a property of a particular component. For example, a characteristic of a heat sink.∙Specific thermal resistance or specific thermal resistivity Rλ in (K·m)/W is a material constant.∙Thermal insulance has the units (m2K)/W in SI units or (ft2·°F·hr)/Btu in imperial units. It is the thermal resistance of unit area of amaterial. In terms of insulation, it is measured by the R-value.Absolute thermal resistanceAbsolute thermal resistance is the temperature difference across a structure when a unit of heat energy flows through it in unit time. It is the reciprocal of thermal conductance. The SI units of thermal resistance are kelvins per watt or the equivalent degrees Celsius per watt (the two are the same since the intervals are equal: Δ1 K= Δ1 °C).The thermal resistance of materials is of great interest to electronic engineers because most electrical components generate heat and need to be cooled. Electronic components malfunction or fail if they overheat, and some parts routinely need measures taken in the design stage to prevent this.AnalogiesElectronic engineers are familiar with Ohm's law and so often use it as an analogy when doing calculations involving thermal resistance. Mechanical and Structural engineers are more familiar with Hooke's law and so often use it as an analogy whendoing calculations involving thermal resistance.typestructuralanalogyhydraulicanalogythermalelectricalanalogy quantity... [...] m3 of water heat [J] charge [C] potentialdisplacement[m]pressure [N/m2]temperature [K=J/]potential [V=J/C] fluxload orforce [N]flowrate [m3/s]heat transferrate [W=J/s]current [A=C/s]fluxdensitystress [N/m2 =Pa]velocity [m/s]heatflux [W/m2]currentdensity [C/(m2·s) = A/m2]resistanceflexibility [...]fluidresistance [...]thermalresistance[...]electricalresistance [Ω]conductivitystiffness [N/m]thermalconductivity[W/(K·m)]electricalconductance[...]lumpedelementlinearmodelHooke'slawHagen–PoiseuilleequationNewton's law ofcoolingOhm'slawdistributed linearmodel...Fourier'slaw Ohm'slawExplanation from an electronics point of viewEquivalent thermal circuitsThe diagram shows an equivalent thermal circuitfor a semiconductor device with a heat sink:is the power dissipated by the device.is the junction temperature in the device.is the temperature at its case.is the temperature where the heat sink is attached.is the ambient air temperature.is the device's absolute thermal resistance from junction to case.is the absolute thermal resistance from the case to the heatsink.is the absolute thermal resistance of the heat sink.The heat flow can be modelled by analogy to an electrical circuit where heat flow is represented by current, temperatures are represented by voltages, heat sources are represented by constant current sources, absolute thermal resistances are represented by resistors and thermal capacitances by capacitors.The diagram shows an equivalent thermal circuit for a semiconductor device with a heat sink.Example calculationConsider a component such as a silicon transistor that is bolted to the metal frame of a piece of equipment. The transistor's manufacturer will specify parameters in the datasheet called the absolute thermal resistance from junction tocase (symbol: ), and the maximum allowable temperature of the semiconductor junction (symbol: ). The specification for the design should include a maximum temperature at which the circuit should function correctly. Finally, the designer should consider how the heat from the transistor will escape to the environment: this might be by convection into the air, with or without the aid of a heat sink, or by conduction through the printed circuit board. For simplicity, let us assume that the designer decides to bolt the transistor to a metal surface (or heat sink) that is guaranteed to be less than above the ambient temperature. Note: T HS appears to be undefined.Given all this information, the designer can construct a model of the heat flow from the semiconductor junction, where the heat is generated, to the outside world. In our example, the heat has to flow from the junction to the case of the transistor, then from the case to the metalwork. We do not need to consider where the heat goes after that, because we are told that the metalwork will conduct heat fast enough to keep thetemperature less than above ambient: this is all we need to know.Suppose the engineer wishes to know how much power he can put into the transistor before it overheats. The calculations are as follows.Total absolute thermal resistance from junction to ambient=where is the absolute thermal resistance of the bond between the transistor's case and the metalwork. This figure depends on the nature of the bond - for example, a thermal bonding pad or thermal transfer grease might be used to reduce the absolute thermal resistance.Maximum temperature drop from junction to ambient= .We use the general principle that the temperature drop across a given absolutethermal resistance with a given heat flow through it is:.Substituting our own symbols into this formula gives:,and, rearranging,The designer now knows , the maximum power that the transistor can be allowed to dissipate, so he can design the circuit to limit the temperature of the transistor to a safe level.Let us substitute some sample numbers:(typical for a silicon transistor)(a typical specification for commercial equipment)(for a typical TO-220 package[citation needed])(a typical value for an elastomer heat-transfer padfor a TO-220 package[citation needed])(a typical value for a heatsink for a TO-220package[citation needed])The result is then:This means that the transistor can dissipate about 18 watts before it overheats. A cautious designer would operate the transistor at a lower power level to increaseits reliability.This method can be generalised to include any number of layers of heat-conducting materials, simply by adding together the absolute thermal resistances of the layers and the temperature drops across the layers.Derived from Fourier's Law for heat conduction[edit]From Fourier's Law for heat conduction, the following equation can be derived, and is valid as long as all of the parameters (x and k) are constant throughout the sample.where:is the absolute thermal resistance (across the length of the material) (K/W)x is the length of the material (measured on a path parallel to the heat flow) (m)∙k is the thermalconductivity of the material(W/(K·m))∙A is the cross-sectional area (perpendicular to the path ofheat flow) (m2)Problems with electrical resistance analogy[edit]A 2008 review paper written by Phillips researcher Clemens J. M. Lasance notes that: "Although there is an analogy between heat flow by conduction (Fourier’s law) and the flow of an electric current (Ohm’s law), the corresponding physical properties of thermal conductivity and electrical conductivity conspire to make the behavior of heat flow quite unlike the flow of electricity in normal situations. [...] Unfortunately, although the electrical and thermal differential equations are analogous, it is erroneous to conclude that there is any practical analogy between electrical and thermal resistance. This is because a material that is considered an insulator in electrical terms is about 20 orders of magnitude less conductive than a material that is considered a conductor, while, in thermal terms, the difference between an "insulator" and a "conductor" is only about three orders of magnitude. The entire range of thermal conductivity is then equivalent to the difference in electrical conductivity of high-doped and low-doped silicon."[3] Measurement standards[edit]This sectionrequires expansion. (January 2015)The junction-to-air thermal resistance can vary greatly depending on the ambient conditions.[4] (A moresophisticated way of expressing the same fact is saying thatjunction-to-ambient thermal resistance is not Boundary-Condition Independent (BCI).[3]) JEDEC has a standard (number JESD51-2) for measuring the junction-to-air thermal resistance of electronics packages under natural convection and another standard (number JESD51-6) for measurement under forced convection.A JEDEC standard for measuring the junction-to-board thermal resistance (relevantfor surface-mount technology) has been published as JESD51-8.[5]A JEDEC standard for measuring the junction-to-case thermal resistance (JESD51-14) is relatively newcomer, having been published in late 2010; it concerns only packages having a single heat flow and an exposed cooling surface.[6][7][8]Resistance in CompositeWall[edit]Parallel thermalresistance[edit]Similarly to electrical circuits, the total thermal resistance for steady state conditions can be calculated as follows.Parallel Thermal Resistance in composite wallsThe total thermal resistance(1)Simplifying the equation, we get(2)With terms for the thermal resistance for conduction, we get(3)Resistance in series and parallel[edit]It is often suitable to assume one-dimensional conditions, although the heat flow is multidimensional. Now, two different circuits may be used for this case. For case (a) (shown in picture), wepresume isothermal surfaces for those normal to the x- direction, whereas for case (b) wepresume adiabatic surfaces parallel to the x- direction. We may obtain different results for the totalresistance and the actual corresponding values of the heat transfer are bracketed by . When themultidimensional effects becomes more significant, these differences are increased withincreasing .[9]Equivalent thermal circuits for series-parallel composite wallRadial Systems[edit]Spherical and cylindrical systems may be treated asone-dimensional, due tothe temperature gradients in the radial direction. The standard method can be used for analyzing radial systems under steady state conditions, starting with the appropriate form of the heat equation, or the alternative method, starting with the appropriate form of Fourier’s law. For a hollow cylinder in steady state conditions with no heat generation, the appropriate form of heat equation is [9](4)Where is treated as a variable. Considering the appropriate formof Fourier’s law, the physicalsignificance of treating as a variable becomes evident when the rate at which energy is conducted across acylindrical surface, this is represented as(5)Where is the area that is normal to the direction of where the heat transfer occurs. Equation 1 implies that thequantity is not dependent of the radius , it follows from equation 5 that the heat transfer rate, is a constant in the radialdirection.Hollow cylinder withconvective surface conditions inthermal conductionIn order to determine the temperature distribution in the cylinder, equation 4 can be solved applying the appropriate boundary conditions. With the assumptionthat is constant(6)Using the following boundary conditions, theconstants and can be computedand The general solution gives us andSolving for and and substituting into the general solution, we obtain(7)The logarithmic distribution of the temperature is sketched in the inset of the thumbnail figure. Assuming that the temperature distribution, equation 7, is used with Fourier’s law in equation 5, the heat transfer rate can be expressed in the following formFinally, for radial conduction in a cylindrical wall, the thermal resistance is of the form。

Journal of Materials Science and Engineering A 1 (2011) 71-75Formerly part of Journal of Materials Science and Engineering, ISSN 1934-8959Study on Friction and Wear Properties ofCu-Zn-Sn-Pb-Ni AlloyJianhua Liu, Yu Feng, Yaxue Kang, Ana Lu, Guirong Peng and Ruijun ZhangState Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China Received: November 29, 2010 / Accepted: December 17, 2010 / Published: June 10, 2011.Abstract: In order to improve wear resistance of copper alloy, a Cu-Zn-Sn-Pb-Ni alloy was prepared. The friction and wear properties of Cu-Zn-Sn-Pb-Ni alloy sliding against GCr15 steel were investigated by friction tester, and the morphologies of worn surface of the specimen were observed by scanning electron microscopy. The results show that the wear rate of Cu-Zn-Sn-Pb-Ni alloy increases with increasing load and friction speed, the friction coefficient decreases with increasing the friction speed, and first increases and then decreases with increasing load. The wear mechanisms of Cu-Zn-Sn-Pb-Ni alloy are mainly abrasive wear and adhesive wear.Pb phase in the alloy exhibited good lubrication, it is favorable to improve the wear resistance of the Cu-Zn-Sn-Pb-Ni alloy.Key words: Cu-Zn-Sn-Pb-Ni alloy, friction and wear, load, sliding speed.1. IntroductionCopper alloy was widely applied in many industries due to its good electric conductivity and thermal conductivity, high oxidation and corrosion-resistant. But the strength of copper alloys is not higher, the part made of copper alloy often generates wear and tear in poor lubrication conditions, even appears killed phenomenon [1], which leads to the parts obsolescence, resulting in many disaster and huge economic loss. Therefore, it is necessary to develop high wear resistant copper alloy [2-6]. Some studies show that the strength and wear resistance of copper alloy could be improved by adding multi-alloy [7-10]. However, these materials are not fit for making sliding bearing. Because sliding bearing alloy is composed of hard matrix and soft particle scattering into the hard matrix [11], Pb and Cu neither dissolve each other in solid state, soft particles Pb is scattered into the Cu matrix. These soft particles act as a certain degree of lubrication during the friction process, which can improve wear resistance of copper alloy. However, study on friction and wearCorresponding author: Ruijun Zhang, Ph.D., professor, characteristics of multi-component copper alloy containing Pb has scarcely been reported. Therefore, a Cu-Zn-Sn-Pb-Ni alloy as the experimental material, the friction and wear properties of the alloy was discussed by analyzing its friction coefficient, wear rate and friction and wear morphology.2. ExperimentExperimental material is Cu-Zn-Sn-Pb-Ni alloy, and oxygen-free copper (purity 99.99%), tin grains (purity 99.8%), zinc tablets (purity 99.99%), lead shot (99.8% purity) and Ni powder (purity 99.9%) are raw materials. The materials were prepared by smelting raw materials in a vacuum medium frequency induction furnace, and its chemical component (mass fraction, %) is: 85.4Cu, 6.59Sn, 3.14Pb, 3.08Zn, 1.20Ni, 0.59 others. The friction and wear experiments were carried out on a MMU-200 reciprocal friction and wear tester in ring-on-disc configuration, the upside specimen is GCr15 ring, its size of inner diameter and external diameter is Φ20 mm andΦ21.5 mm, respectively, and the hardness is 58~62 HRC. The below specimen is Cu-Zn-Sn-Pb-Ni alloy disk, its size is Φ45 × 5 mm. Before theStudy on Friction and Wear Properties of Cu-Zn-Sn-Pb-Ni Alloy72experiment, the surface of the specimen was polished with 1000# sand paper, and disk samples fixed and ring samples were circular motion during the experiment process, whose friction speed was 56, 112, 224, 448 mm·s -1, and external load applied on the samples was 50, 75, 100, 125 N, respectively, and friction time was 5 min. The samples were disposed by 5 min pre-grinding before entering into the normal experiment. Friction coefficient was automatically expressed by the tester. The change of the weight of the specimen before and after the experiment were measured with a ESJ205-4 photoelectron balance (precision is 0.1 mg), the data of wear loss weight is the average value of 3 samples tests’ results, and wear rate was expressed by wear loss weight per unit sliding distance. In order to evaluate effect of Pb in the Cu-Zn-Sn-Pb-Ni alloy, the friction coefficient and wear rate of the same ingredients of Cu-Zn-Sn-Ni alloy were measured, the results are compared with that of the Cu-Zn-Sn-Pb-Ni alloy. The microstructure and the worn surface morphologies of the specimen were analyzed by a NEOPHOT21 metallography microscopy and a KYKY-2800 scanning electron microscopy (SEM/EDS).3. Results and Discussion3.1 Friction CoefficientFig. 1 shows that relationship between load orsliding speed and friction coefficient. It can be seen that the friction coefficient of Cu-Zn-Sn-Pb-Ni alloy decreases with increasing sliding speed, and it firstly increases and then decreases with increasing load, but the effect of load on friction coefficient is less than effect of sliding speed on friction coefficient. Fig. 1 also shows that when load is 75 N, the sliding speed increases from 56 mm·s -1 to 448 mm·s -1, the friction coefficient decreases from 0.30 to 0.21, when sliding speed is 56 mm·s -1 and load is 100 N, the friction coefficient shows the maximum of 0.32. This may be the increase of the friction by reason of the increase of applied load, which will cause severe grinding abrasion, roughness increases, and lead to the increases of friction coefficient. But the external load is too large and the sliding speed increases, the friction heat increases during the friction process, making grinding surface easily generate a layer of oxide film, while the oxide film has some lubrication function, causing friction coefficient decrease. It can be seen from Fig. 2 that the friction coefficient fluctuates irregularly during the friction process. However, the friction coefficient of Cu-Zn-Sn-Pb-Ni alloy (0.30) is less than the friction coefficient of Cu-Zn-Sn-Ni alloy (0.31) when the applied load is 75N and sliding speed is 56mm·s -1. 3.2 Wear RateFig. 3 shows that relationship between load or slidingFig. 1 Relationship between load or sliding speed and friction coefficient (a) relationship between load and friction coefficient; (b) relationship between sliding speed and friction coefficient.Load/N F r i c t i o n c o e f f i c i e n tSpeed/mm·s -1F r i c t i o n c o e f f i c i e n tStudy on Friction and Wear Properties of Cu-Zn-Sn-Pb-Ni Alloy73Fig. 2 Curve of friction coefficient changed with friction time (75 N, 224 mm ·s -1), me(75 N, 224 mm ·s -1).speed and wear rate. It can be seen that the wear rate of Cu-Zn-Sn-Pb-Ni alloy increases with increasing applied load and sliding speed. When sliding speed is 56mm·s -1, load increases from 50 N to 125 N, and wear rate of the alloy increases from 1.82 mg·m -1 to 2.10 mg·m -1. When the load is 75 N, sliding speed increases from 56 mm·s -1 to 448 mm·s -1, and wear rate increases from 1.86 mg·m -1 to 3.23 mg·m -1. It can also be seen from Fig. 3 that the increases of wear rate of Cu-Zn-Sn-Pb-Ni alloy is not linear relation with load and sliding speed. When sliding speed is 56 mm·s -1, the applied load is over 100 N, and the applied load is 75 N, sliding speed is over 224 mm·s -1, the wear rate of alloy markedly increases. When the applied load and sliding speed are 75 N and 56 mm·s -1, the wear rate ofCu-Zn-Sn-Pb-Ni alloy (1.86 mg·m -1) is less than that of Cu-Zn-Sn-Ni (1.92 mg·m -1). This means that Pb can improve the wear resistance of the material. 3.3 Worn Surface MorphologyFig. 4 shows the microstructure of the Cu-Zn-Sn-Pb-Ni alloy. Combined with EDS results, it can be known that the Cu-Zn-Sn-Pb-Ni alloy iscomposed of Cu matrix and irregular Pb phase. It can be seen from Fig. 5 that there are obvious furrow and the adhesive thin sheet of debris on the wear surface under the low speed and low load conditions, with the increase of load and sliding speed, the furrows became deeper and wider and produced thin sheet exfoliation, and the lamellar debris also increases. Therefore, it can be concluded that the wear mechanism of Cu-Zn-Sn-Pb-Ni alloy are mainly adhesive wear and abrasive wear. With the increase of the load and sliding speed, abrasive wear increases and accompanied by delamination wear. The analysis results of adhesive thin sheet of the debris by EDS shows that Pb content of the debris is higher than Pb content of the matrix, which indicated Pb phase drags out from the matrix during the friction process. 3.4 DiscussionWhen Cu-Zn-Sn-Pb-Ni alloy is sliding against GCr15 steel, because many micro-convex on the surface ofFig. 3 Relationship between loads or sliding speed and wear rate (a) relationship between loads and wear rate; (b) relationship between sliding speed and wear rate.501001502002503000.00.10.20.30.40.5F r i c t i o n c o e f f i c i e n tTime/sW e a r r a t e /m g .m -1Speed/mm .s -1Load/NW e a r r a t e /m g .m -1Study on Friction and Wear Properties of Cu-Zn-Sn-Pb-Ni Alloy74Fig. 4 Microstructures of Cu-Zn-Sn-Pb-Ni alloy.Fig. 5 Morphologies of the wear surface under different sliding condition (a) 50 N, 56/mm.s -1; (b) 125 N, 448/mm.s -1.GCr15 steel ring directly compress into the surface layer of the softer sample. The cutting and extrusion of the contact area on the sample results in plastic deformation of the contact surface of the sample. When the stress occur in interface exceed the yield intensity of the Cu-Zn-Sn-Pb-Ni alloy, the adhesive wear occurs, while the friction process generate debris will be as a new wear particles of the subsequent friction process which can generate abrasive wear to the wear surface. With the increase of the load and sliding speed, thetearing action of the friction surface increases, and the friction heat increases during the friction process, causing the surface metal temperature rises and the material softening, which reduce its resistance to plastic deformation capacity and carrying capacity, and resulting in the wear rate increasing. Moreover, the sample sub-surface easily produce the micro-crack with increasing load and sliding speed [12], and then the micro-crack will gradually expand and converge under the repeated shear stress until the rupture of the friction layer, causing lamellar debris exfoliation, and the wear rate obvious increases. The increase of applied load and sliding speed will lead to the changes which were shear deformation of the friction surface of the material, between the adhesive and tear and surface roughness, and so on, resulting in friction coefficient change. As for the fluctuation of friction coefficient during the friction process, it may be mainly due to the friction surface roughness of the alloy which produce the instantaneous change, causing the contact area of the friction surface and wear and destruction way to change. Owing to Pb basically did not dissolve in copper, only as an independent phase exist, so Pb phase and Cu matrix are mechanical combination, adhesion between Pb phase and Cu matrix is weaker. Furthermore, the thermal expansion coefficient of Pb and shear modulus are lower [13], when the coupled parts are mutual friction, Pb easily is towed out from the Cr matrix. Because Pb is softer and its adhesion coefficient is larger, therefore, Pb will gradually form Pb film on the wear surface during the friction process, which can be confirmed by EDS analysis, thus it can be inferred that Pb phase in the alloy exhibited good lubrication, which can improve the wear resistance of the Cu-Zn-Sn-Pb-Ni alloy. Therefore, the wear resistance of Cu-Zn-Sn-Pb-Ni alloy is better than that of Cu-Zn-Sn-Ni alloy.4. Conclusions(1) The wear mechanism of Cu-Zn-Sn-Pb-Ni alloy are mainly abrasive wear and adhesive wear, and has50μm(b)50μm(a)50μmStudy on Friction and Wear Properties of Cu-Zn-Sn-Pb-Ni Alloy75good wear resistance,which is attributed to Pb in the alloy exhibited good lubrication.(2) The wear rate of Cu-Zn-Sn-Pb-Ni alloy increases with increasing load and sliding speed, and the friction coefficient decreases with increasing sliding speed, but firstly increases and then decreases with increasing load, when Cu-Zn-Sn-Pb-Ni alloy is sliding against GCr15 steel the sliding speed of 56~448 mm·s-1 and the load of 50~125 N.(3) The friction coefficient decreases from 0.30 to 0.21, and the wear rate increases from 1.86 mg·m-1 to 3.23 mg·m-1, when load is 75 N, and friction speed increases from 56 mm·s-1 to 448 mm·s-1.References[1] A.Q. Wang, R. Xu, C.Z. Chi, The friction characteristicand tensile properties of casting Al-bronze, Journal ofLiaoning Technical University (Natural Science Edition)19 (2000) 87-89. (in Chinese)[2]G. Straffelini, L. Maines, M. Pellizzari, P. Scardi, Drysliding wear of Cu-Be alloys, Wear 259 (2005) 506-511. [3]S.Z. Zhang, B.H. Jiang, W.J. Ding, Dry sliding wear ofCu-15Ni-8Sn alloy, Tribology International 43 (2010) 64-68.[4]K.S. Asadi, B.A. Zare, A. Akbari, The effect of slidingspeed and amount of loading on friction and wear behaviorof Cu-0.65 wt.%Cr alloy, Journal of Alloys andCompounds 486 (2009) 319-324.[5]M. Yasar, Y. Altunpak, The effect of aging heat treatmenton the sliding wear behaviour of Cu-Al-Fe alloys, Materials and Design 30 (2009) 878-884.[6]S.A. Kouhanjani, A. Zare-Bidaki, M. Abedini, Influenceof prior cold working on the tribological behavior of Cu-0.65 wt.%Cr alloy, Journal of Alloys and Compounds480 (2009) 505-509.[7]H. Turhan, Adhesive wear resistance of Cu-Sn-Zn-Pbbronze with additions of Fe, Mn and P, Materials Letters 59(2005) 1463-1469.[8]P. Liu, S.G. Jia, M.S. Zheng, F.Z. Ren, Effects of trace Zron the wear behavior of Cu-Ag alloy, Chinese Journal ofMaterials Research 20 (2006) 109-112. (in Chinese)[9]T. Higuchi, K. Yamamoto, M. Sakamoto,Effects ofNi-B compound addition on mechanical properties andwear resistance of Cu-Sn-Pb alloys, Journal of the JapanSociety of Powder and Powder Metallurgy 40 (1993) 780-783.[10]H.B. Cui, J.J. Guo, Y.Q. Su, Effect of Cr addition onmicrostructure and wear resistance of hypomonotectic Cu-Pb alloy, Materials Science and Engineering A 448 (2007) 49-55.[11]K. Cui, Iron and Steel as Well as Nonferrous Metals,Mechanical Industry Press, Beijing, 1986, p. 434.[12] D.L. Shu, Mechanical Properties of Metals, MechanicalIndustry Press, Beijing, 1994, pp. 196-197.[13]M. Wang, Z.Z. Zhang, Y.M. Zhou, Research on thetribological property of undercooled Ni-Pb-Cu solid self-lubricating alloy, Lubrication Engineering 14 (2006)50-52.。

温度漂移英语Temperature Drift。

Temperature drift refers to the phenomenon where the accuracy of a measurement or the stability of a system is affected by changes in temperature. It is a common issue in various fields, including electronics, physics, and engineering. In this article, we will delve into the concept of temperature drift, its causes, and its impact on different systems.Temperature drift occurs due to the dependence of certain physical properties on temperature. As temperature changes, these properties also change, leading to variations in the measurements or performance of a system. One of the most common examples of temperature drift is seen in electronic devices, particularly in resistors and capacitors.In electronic circuits, resistors are used to control the flow of current. However, resistors are not perfectly stable and can exhibit temperature-dependent variations in resistance. This means that the resistance of a resistor can change with temperature, leading to inaccurate measurements or calculations. Similarly, capacitors can also experience temperature drift, affecting the performance of circuits that rely on their capacitance values.The causes of temperature drift can be attributed to various factors. One of the primary factors is the thermal expansion of materials. When a material is subjected to temperature changes, it expands or contracts, altering its dimensions and properties. This expansion or contraction can introduce changes in the accuracy of measurements or the stability of a system.Another factor contributing to temperature drift is the change in electrical conductivity with temperature. Some materials exhibit a decrease in electrical resistance as temperature increases, while others show the opposite behavior. This change in conductivity can affect the performance of electronic components and systems, leading to temperature-dependent variations.Furthermore, temperature drift can also be influenced by the thermal coefficient of materials. The thermal coefficient represents the rate at which a material's properties change with temperature. Materials with high thermal coefficients are more prone to temperature drift, as small temperature changes can result in significant variations in their properties.The impact of temperature drift can be detrimental in many applications. In scientific experiments or industrial processes that require precise measurements, temperature drift can introduce errors and compromise the accuracy of the results. In electronic devices, temperature drift can lead to unstable performance, affecting the reliability and functionality of the system.To mitigate the effects of temperature drift, various techniques are employed. One common approach is temperature compensation, where the system is designed to account for the temperature-dependent variations. This can involve using temperature sensors to monitor the temperature and adjust the system accordingly. Additionally, the use of temperature-stable components and materials can help minimize temperature drift.In conclusion, temperature drift is a significant concern in various fields, affecting the accuracy and stability of measurements and systems. It is caused by the temperature dependence of certain physical properties, such as resistance and conductivity. Understanding the causes and impact of temperature drift is crucial in developing strategies to minimize its effects and ensure reliable and accurate performance in various applications. By implementing temperature compensation techniques and utilizing temperature-stable components, the adverse effects of temperature drift can be mitigated, leading to improved system performance and more accurate measurements.。

Thermal Science and Engineering Thermal Science and Engineering: A Comprehensive ExplorationThermal science and engineering is a multifaceted field that encompasses a wide range of disciplines, including thermodynamics, heat transfer, and fluid mechanics. It plays a crucial role in the development and optimization of various technologies, from power generation and refrigeration systems to aerospace engineering and environmental control. In this essay, we will delve into the intricacies of thermal science and engineering, exploring its significance, applications, and the challenges it faces.The Importance of Thermal Science and EngineeringThermal science and engineering is of paramount importance in today's world. It is the backbone of numerous industries and technologies that we rely on daily. For instance, in power generation, thermal engineering principles are used to convert heat into electricity, making it possible for us to enjoy a life powered by electricity. Similarly, in the automotive industry, thermal management is critical for the performance and longevity of engines and other components.Moreover, thermal science and engineering are essential for the development of sustainable technologies. As the world grapples with the challenges of climate change and the need for clean energy, thermal engineers are at the forefront of designing and optimizing systems that minimize energy consumption and reduce greenhouse gas emissions. For example, advancements in solar thermal energy and geothermal power generation are largely driven by the principles of thermal science.Applications of Thermal Science and EngineeringThe applications of thermal science and engineering are vast and varied. Some of the most notable areas include:1. Power Generation: Thermal power plants, which rely on the Rankine cycle or other thermodynamic cycles, are a primary source of electricity for many countries. These plants use the principles of heat transfer and thermodynamics to convertheat into mechanical work, which is then converted into electricity.2. Refrigeration and Air Conditioning: The refrigeration and air conditioning industry relies heavily on thermal engineering principles to design and optimize systems that provide cooling and dehumidification. These systems are crucial for maintaining comfortable living and working environments, as well as preserving perishable goods.3. Aerospace Engineering: In the aerospace industry, thermal management is critical for the performance and safety of aircraft and spacecraft. Thermal engineers design systems to manage the heat generated by engines, avionics, and other components, ensuring that temperatures remain within safe operating limits.4. Environmental Control: Thermal engineering plays a vital role in designing and optimizing systems for environmental control, such as heating, ventilation,and air conditioning (HVAC) systems. These systems are essential for maintaining comfortable and healthy indoor environments, as well as reducing energy consumption and emissions.Challenges in Thermal Science and EngineeringDespite the significant contributions of thermal science and engineering to various industries, the field faces several challenges. Some of the most pressing issues include:1. Energy Efficiency: As the world seeks to reduce its dependence on fossil fuels and minimize energy consumption, thermal engineers are tasked withdeveloping more efficient systems. This requires a deep understanding of thermodynamics, heat transfer, and fluid mechanics, as well as innovative design approaches.2. Material Selection: The selection of appropriate materials for thermal systems is crucial for their performance and longevity. Engineers must consider factors such as thermal conductivity, strength, and corrosion resistance when choosing materials for components like heat exchangers, pipes, and insulation.3. Environmental Impact: The environmental impact of thermal systems is a growing concern. Engineers must strive to minimize the emissions and waste generated by these systems, while also considering the lifecycle of materials and components.4. Advanced Simulation and Modeling: As thermal systems become more complex, the need for advanced simulation and modeling tools increases. These tools help engineers predict the performance of systems and identify potential issues before they arise, reducing the time and cost associated with design and testing.The Future of Thermal Science and EngineeringThe future of thermal science and engineering looks promising, with numerous opportunities for growth and innovation. As the world continues to face the challenges of climate change and the need for sustainable energy, thermal engineers will play a pivotal role in developing and optimizing technologies that meet these demands.Advancements in materials science, nanotechnology, and computational methods will likely drive the future of thermal engineering. These advancements will enable the development of more efficient, reliable, and environmentally friendly systems, paving the way for a more sustainable future.In conclusion, thermal science and engineering is a critical field that underpins many of the technologies we rely on today. Its applications are vast, and its importance cannot be overstated. As we look to the future, the challenges faced by thermal engineers will only grow, but so too will the opportunities for innovation and advancement. By embracing these challenges and leveraging thelatest technologies, thermal engineers can help shape a more sustainable and efficient world for generations to come.。