heat transfer in automoble radiators of the tubular type_Dittus_Boelter

Heat Transfer and Thermal Systems Heat transfer and thermal systems are crucial in various industries and applications, including power generation, transportation, and manufacturing. The ability to transfer heat efficiently is essential for the proper functioning of these systems. In this essay, we will explore the importance of heat transfer and thermal systems, their applications, and thechallenges associated with them.Heat transfer is the process of exchanging heat between two or more objects or systems. It occurs in three ways: conduction, convection, and radiation. Conduction is the transfer of heat through a solid material, while convection is the transfer of heat through a fluid. Radiation is the transfer of heat through electromagnetic waves. In thermal systems, heat transfer is crucial to maintain the desired temperature and prevent overheating or cooling.Thermal systems are used in various industries, including power generation, transportation, and manufacturing. In power generation, thermal systems are used to convert heat energy into electrical energy. This isdone by using a heat source, such as coal or natural gas, to heat water and produce steam. The steam is then used to turn a turbine, which generates electricity. Thermal systems are also used in transportation, such as inthe cooling systems of cars and airplanes. In manufacturing, thermal systems are used to heat and cool materials during the production process.One of the challenges associated with heat transfer and thermal systems is the efficiency of the system. The efficiency of a thermal system is determined by its ability to transfer heat without losing energy.Inefficient thermal systems can result in higher energy costs and decreased performance. To improve the efficiency of thermal systems, various techniques can be used, such as insulation and heat recovery.Another challenge associated with thermal systems is the environmental impact. The use of fossil fuels in thermal systems can result in the emission of greenhouse gases, which contribute to climate change. To reduce the environmental impact of thermal systems, alternative sources of energy, such as renewable energy, can be used. Additionally, the use of energy-efficient technologies and practices can help reduce the environmental impact of thermal systems.In conclusion, heat transfer and thermal systems are crucial in various industries and applications. The ability to transfer heat efficiently is essential for the proper functioning of these systems. Thermal systems are used in power generation, transportation, and manufacturing. However, there are challenges associated with heat transfer and thermal systems, such as efficiency and environmental impact. To address these challenges, various techniques and practices can be used, such as insulation, heat recovery, and the use of renewable energy sources.。

M.HEAT MASS TRANSFERVol.12, pp.3-22, 1985Printed in the United StatesHeat Transfer In Automobile Radiators Of TheTubular TypeF. W. Dittus and L. M. K. BoelterIntroductionHeat to be dissipated from water-cooled internal combustion engines is usually transferred to the atmosphere by means of devices commonly called radiators. The medium conveying heat to the radiator is generally water, the medium conveying heat away is air.In this article it is intended to discuss the fundamentals involve in the transfer of heat from water to the atmosphere in the simplest type of tubular radiator. No attempt will be made to discuss the effect of the rate of heat transfer when using fins, honeycomb section, or any type other than the plain tube.The unit of measure of heat transfer in heat exchange equipment is the “Overall Transfer Factor”, which is the heat transferred per unit area of heat transmitting surface per unit time per unit of temperature difference between the hot and cold fluids.Film Transfer Factor On The Liquid Side Of A RadiatorTypes of fluid flour through tubesOn the liquid side of a radiator heat is carried from the warm water to the colder tube wall by two methods:(1)Convection(2)ConductionIn the region of turbulent flow, most of the heat is transferred from the liquid to the tube wall by forced convection. Because of the low thermal conductivity of fluids, very little heat is transferred from the center of the stream to the tube wall by conduction. In forced circulation systems the fluid flow through the radiator is turbulent unless the tubes are of very small diameter.In the viscous flow region practically all of the heat is transferred from the interior of the stream to the tube wall by conduction.The rate of heat flow from the water to the air is retarded by(a)Film resistance on the water side of the tube surface,(b)Thermal resistance of tube,(c)Film resistance on the air side of the tube.If we denote the three resistances mentioned above by R w, R t, and R a, respectively, we may write the following equation:(1)o w t a R R R R =++where R o =overall or total heat flow resistance.Ordinarily, however, the term employed is not thermal resistance but thermal conductance, which is the reciprocal of resistance. Denoting thermal conductance by U we may then write:1111(2)o w t aU U U U =++where U o =overall transfer factor (BTU/sq.ft./℉./hr.).U w =film transfer factor on water side (BTU/sq.ft./℉./hr.).U a =film transfer factor on air side (BTU/sq.ft./℉./hr.).U t =thermal conductance of separating wall (BTU/sq.ft./℉./hr.).The value of U t can be readily calculated by the use of the following equation:(3)t kU t =wheret=thickness of separating wall (ft.).k=thermal conductivity of separating wall material (BTU/sq.ft./℉./hr.).Equation (2) holds when heat is transferred through a body with parallel heat-transmitting surfaces. In the case of heat flow through curved surfaces, for example, tube walls, a correction should be made for the face that the outer surface per unit length of tube is greater than the inner surface for the same length of tube. Equation (2) then becomes:1111(4)?o m a a t t w w U A U A U A U A =++ or, referred to the mean diameter of the tube, equation (4) becomes:1111(5)'o w t a U U R U U R =++whereA m =Mean area of heat transfer section based on mean tube diameter (sq.ft).A a =Area of heat transfer section on air side (sq.ft).A w =Area of heat transfer section on water side (sq.ft).R=Ratio of outer tube surface (air) to surface of tube at mean diameter per unit length of tube.R ’=Ratio of inner tube surface (water) to surface of tube at mean diameter per unit length of tube.R=2D/(D+d).R ’=2d/(D+d).D=Outside diameter of tube (inches).d=Inside diameter of tube (inches).The value of U t for a curved separating wall is:4(6)()ln /t kU D d D d =+Substituting equation (6) for the term U t and also substituting in equation (5) the equivalent values of R and R ’, the latter becomes:11ln /1()()(7)?22o o t D d D d U U D k U D +=++The type of fluid flow existing within a tube may be determined by calculating “Reynolds criterion ”, which is defined as follows:(8)/0.624r vd Vd C u s z ==whereC r =Reynolds criterionC r ’=Reynolds critical number (see following paragraph)v=mean linear velocity of fluid (ft./sec.)V=mean mass velocity (lbs./sq.ft./sec.)d=inside diameter of tube (inches)u=absolute viscosity of fluid at mean stream temperature (poises)z=absolute viscosity of fluid at mean stream temperature (centipoises)s=density of fluid (numerically equal to the specific gravity of fluid referred to water at 60℉.) (gram./cc.)If, upon substitution of the proper values in the above equation, the numerical result (Cr) is greater than 40, the flow is turbulent. If, on the other hand, the result is less than 25, the flow is non-turbulent or viscous. In the event that a ratio (Cr ’) having a value between the just mentioned numbers is obtained, the flow may be either turbulent or viscous depending to a great extent upon the entrance and exit conditions of the installation in question and roughness of the tube surface.Film transfer factors for turbulent flow —Most of the experimental work done on heat transfer covers the turbulent region for fluid flow inside of tubes. McAdams and Frost (1922) correlated all the published data and proposed the following equation for heat transfer existing at turbulent flow:0.7961()(9)/Ud vd B k u s = which is a simplified form of the following equation proposed by Nusselt (1910): 12()()(10)/Ud vd cu f f k u s k =WhereB1=constantc=specific heat of fluid (BTU/lb./℉)k=thermal conductivity of fluid (BTU/sq.ft./hr./℉./ft.),and all other terms as mentioned above.McAdams and Frost eliminated the third term of equation (10) because the correlated datafell along the same straight line when plotted on logarithmic paper according to equation (9). Most of the data plotted were results of heat transfer tests conducted with water flowing through tubes.Equation (9) was later modified by McAdams and Frost (1924) to include a correction for the increased heat transfer rate due to turbulence at the entrance of the tube. This modified equation is as follows:2(1)()(11)'/Ud N vd B f k r u s =+whereB2=constantN=empirical numberr=ratio of tube length to diameter=l /du ’=viscosity of fluid at film temperature (poises)Upon considering the results a number of experiments the equation proposed by the last mentioned authors was:0.80250(1)()(12)?'/Ud vd B k r u s =+As mentioned above, in most of the experiments performed the fluid used was water and the heat was generally flowing from the tube to the liquid, i.e., heating the liquid.Morris and Whitman (1928) conducted a series of experiments in which oils having a wide range of viscosities were used. In addition to this they studied the heat transfer rates for cooling as well as heating of the liquid flowing through the tube. The result of the investigation showed that film transfer factors may be expressed by the following equation:0.37()()(13)?Ud Vd cz f k z k =which is of the same form as the Nusselt equation previously mentioned, except that mass velocity (lbs./sq.ft./sec.) is used instead of linear velocity and absolute viscosity expressed in centi-poises instead of poises. The two just mentioned variables are denoted by “V ” and “z ” respectively. Figure 1 shows the experimental data of these investigators plotted according to equation (13). It will be noted that there are two separate groups of points, one for heating liquids and another for cooling liquids. As pointed out by Morris and Whitman, the film transfer factor for cooling a liquid is about 75 per cent of that for heating a liquid when the comparison is made at the same flow conditions.This variation is no doubt due to the fact that the physical properties of the fluid particles conveying and conducing heat are different for the two conditions, even though the mean fluid temperatures are the same. Perhaps a better procedure would be to plot the film transfer factoes as a function of the various thermal properties of the fluid at the film temperature instead of the mean stream temperature.The curves obtained when using the physical properties of the fluid at the tube temperature instead of at the mean stream temperature are in no better agreement than those shown by Morris and Whitman, nor is there a better agreement when the physical properties are taken at a mean temperature between the tube wall and mean stream temperatures. In every case a separate curve was obtained for heating and cooling, in some cases the cooling curve lying above and in some cases lying below the heating curve, depending entirely upon the temperature used to determine the physical properties of the liquid.In order to obtain a common curve for heating and cooling, it is suggested to use two different exponents in the term (cz/k)n for each process. Figure 2 shows the plotted results calculated from Morris and Whitman ’s published data, using n equals 0.4 and 0.3 respectively for heating and cooling a liquid flowing to a tube. Unfortunately, no other data are available to test the use of two different exponents for heating and cooling.The fluids used by Morris and Whitman in their experiments were water and oils covering a considerable range of viscosities. Neither these authors nor McAdams and Frost showed any experimental values for gases flowing through tubes.In order to determine whether or not the Morris and Whitman curve also applies to gases, the published results of a number of investigators using gases in their heat transfer experiments were analyzed and plotted according to the following equations:()()(14)z nUd Vd cz f k kwheren=0.3 for coolingn=0.4 for heatingall other variables as previously defined.The curves thus obtained for gases are shown in figure 3 together with others published by McAdams and Frost for liquids. The curves shown for gas flow cover a range of tube diameters from 1/2 inch to about 6 inches and a temperature range from 60℉ to 1400℉. The mass velocities varied from 0.2 to 6.6 lbs. per sq. ft. per second. The pressure within the pipe varied from 1.5 to 190 pounds per sq. inch absolute. Considering this wide variation in operating conditions, the agreement of the curves is remarkable, although it is somewhat difficult to draw a mean curve.The mean curve shown on figure 3 may be expressed by the following equation:19.5()()(15)m nUd dV cz k z k =where n is the 0.3 and 0.4 for cooling and heating, respectively, as mentioned above.The entrance correction factor (1+50/r) proposed by McAdams and Frost was omitted by Morris and Whitman in the equation proposed by the latter. The reason for the omission is that not sufficient data are available definitely to determine the end correction factor. For the same reason the factor is also omitted from equation (15).Film transfer factor for viscous or non-turbulent flow —Very little data have been published on heat transfer for viscous flow. McAdams (1925) published a curve having a slope of about 1/10 when the variable (l ’d/k)/(1+50/r) is plotted against (Vd/z) or, in other words,1/1150()(1)(16)?o Ud Vd B k z r=+No experimental data were shown to support this equation.Some experiments were conducted by Dittus at the University of California (1929) on the heat transfer from tubes to liquids in viscous motion. It was found upon plotting the experimental results according to the equation Ud/k=f(Vd/z) that the latter equation did not hold, but separate curves were obtained, each of which had a slope of roughly 1/12, for each diameter tube tested. It was apparent that some additional variables should be included in the above equation in order to obtain a satisfactory curve. When the experimental data were plottedaccording to Nusselt ’s equation (10), the results again did not fall along the same curve. Upon including the additional variables, specific heat and temperature difference, the following equation was derived by the application of the principle of dimensional homogeneity:3U [(),(),()](17)/d rd drsc k f k u s k dv s ∆=where △=logarithmic mean temperature difference between tube and liquid, and all other terms are the same as mentioned before.By combining the variables in equation (17) in a particular manner, it was possible to derive a new group of variables, which caused all experimental points to fall along the same curve when plotted accordingly.The final equation proposed is as follows:1/32/31/1220()()(18)/k vd U s c d u s ∆=Further information on heat transfer in the viscous or non-turbulent flow region is available in an article published by Thomas and Wadlow (1929) on the heat transfer performance of tubular radiators for automobiles. These investigators determined the overall transfer from water to air by maintaining a constant water velocity and varying the air velocity in one set of experiments. These tests covered both the turbulent and the non-turbulent or viscous flow on the water side of the turbulent and the non-turbulent or viscous flow on the water side of the radiator tubes. Because of the method employed of varying only one of either the air or water velocity, it is possible to calculate the film transfer factors from the overall transfer factors. The results are shown in figure 4.It will be noted upon reviewing figure 4 that results calculated from Thomas and Wadlow ’s data do not agree with the tests of Dittus. The reason for this may be that in the latter tests every effort was made to eliminate turbulence due to entrance and exit, disturbances, while in the former tests no such precaution was observed. For this reason, turbulence existed at the entrance to the radiator tubes, which may have resulted in a higher overall transfer factor.It will be remembered that McAdams and Frost suggested an end correction factor for the case of turbulent flow.Upon applying the same correction factors (1+50/r) to the results calculated from Thomas ’ and Wadlow ’s data and plotting the values thus corrected, it was found that the plotted points coincided remarkably well with those reported by Dittus (1929), as is shown in figure 5. The equation now proposed for heat transfer existing at viscous flow is as follows:1/32/31/125020()()(1)(19)/k vd U s c d u s r ∆=+As mentioned above, in the tests conducted by Dittus provisions were made to eliminate all disturbance due to entrance conditions. For that particular case the term r then becomes infinite and equation (19) will be the same as equation (18).It is true that the introduction of the end correction term is based on rather meager data, but until more data are available, it is advisable to employ the McAdams and Frost end correction factor as shown in equation (19).Film transfer Factor With Flow Transverse to TubesSingle row of tubes —Much work has been done on heat transfer from cylinders to fluids and vice versa with flow at right angles to the cylinder. Some experiments have been conducted with heated wires moving at a fixed velocity through liquids or air in order to obtain a relation of heat transmission and relative velocity and thus calibrate the device for velocity measurements. Some work has also been done with air flow transverse to tubes. The most recent data of the latter type of tests are those published by Reiher (1925) in which hot air was cooled by flowing transverse to cold tubes. Reiher proposed the following equation:()(20)/m m m mv D UD f k u s = which may also be expressed as follows: ()(21)m m m v D UD f k z =wherev m =average velocity between two adjacent tubes (ft./sec.)V m =average mass velocity between two adjacent tubes (lbs./sq.ft./sec.)D=absolute viscosity of fluid at mean of tube and fluid temperature (poises)u m =absolute viscosity of fluid at mean of tube and fluid temperature (poises)z m=absolute viscosity of fluid at mean of tube and fluid temperature (poises)k m =thermal conductivity of fluid at mean of fluid and tube temperatures (BTU/sq.ft./hr./℉/ft.)c m =specific heat of fluid at mean of fluid and tube temperature (BTU/lb./℉)and all other terms are as mentioned before.The term Vm may be calculated as follows:(22)4m o bV V d b π=-also max (23)o b D V V b -=whereVo=mass velocity of gas just before entering tube bundle (lbs./sq.ft./sec.)Vmax=maximum mass velocity of gas between two adjacent tubes (lbs./sq.ft./sec.) b=center to center spacing of tubes (inches)D=outside diameter of tubes (inches)Using the term Vm instead of either Vo or Vmax eliminates the use of another group of variables involving the ratio of tube spacing to tube diameter. Reiher found that upon plotted in that manner in figure 6. It will be noted that points obtained with air flowing at right angles to the cylinder fall along the same curve, while the points obtained from experiments using oil and water instead of air formed separate curves depending upon the liquid used.Expressing each curve according to the following equation:()(24)nm o m m V D UD B k z =It was found that the constant B 0 could be plotted as a function of the term (c m z m /k m ) and varied as the one-third power of the last-mentioned group of variables.Because of this fact all data were replotted as shown in figure 7 according to the following equation:1/3()()(25)n m m m m m m v D c z UD f k z k =Upon reviewing figure 7 it will be noted that all points, regardless of whether tests were conducted with water, oil, or air, fall along the same curve. It will furthermore be noted that for the region where V m D/z m is less than 0.25 the line has a slope of 0.4 while for the region above that the line has a slope of about 0.56. Apparently there is a change of film conditions at the intersection of the two curves. The equations for heat transfer with fluid flow at right angles to cylinders may then be written as follows:(a) for 0.25m mV D z < 0.41/383()()(26)m m m m m mV D c z UD k z k = (b) for 0.25m mV D z >0.541/3105()()(27)m m m m m m V D c z UD k z k =Several rows of tubes —A series of tests for the determination of heat transfer when several rows of tubes are involved were made by Reiher. In all these experiments the heat transfer took place from tubes to air; no data are available from experiments in which liquids were used. Furthermore, all of Rerher ’s results are for the region where V m D/z m is greater than 0.25 so that no data are available ta all for several rows of tubes in the region where the just mentioned criterion is less than 0.25. Until experiments prove otherwise, it may be assumed that Reiher ’s equation applying to air flow only may be modified to include liquid flow by introducing the term (c m z m /k m )1/3 as was done in the case of the equations for single tubes. The modified equations applying to several rows of tubes for the region where V m D/z m is greater than 0.25 are as follows:(1) staggered rows of tubes: 2 rows,0.691/3max 53()()(28)?m m m m mV D c z UD k z k = 3 rows, 0.691/3max 60()()(29)?m m m m mV D c z UD k z k = 4 rows, 0.691/3max 65()()(30)?m m m m mV D c z UD k z k = 5 rows, 0.691/3max 69()()(31)?m m m m m V D c z UD k z k =(2) rows of tubes directly behind each other: 2 rows,0.6541/3max 55()()(32)?m m m m mV D c z UD k z k = 3 rows, 0.6541/3max 57()()(33)?m m m m mV D c z UD k z k = 4 rows, 0.6541/3max 58()()(34)?m m m m mV D c z UD k z k = 5 rows, 0.6541/3max 59()()(35)?m m m m m V D c z UD k z k =It should be noted that in the two last mentioned groups of equations the term V max instead of V mean is used. Just why this was done is not explained in Reiher ’s paper; unless he assumes that in heat exchange equipment, when several rows of tubes are used, the bulk of the heat transfer takes place at the point of maximum velocity. Rerher also states that the above equations are valid only when the tubes are fairly clos together.Discussion and conclusionsAnalysis of published data on heat transfer in tubular radiators indicates that a large part of the total resistance to heat flow is due to the relatively low film transfer factors on the air side of the tubes. For this reason, any attempt to increase the overall transfer factor on the air side of the tube. Some improvements may also be made by decreasing the film resistance on the liquid side of the tubes, although the total gain will be slight unless the air film transfer factor is increased materially at the same time. The film transfer factor on the liquid side of a tubular radiator may be calculated readily with the aid of the equations (15) and (19) according as the flow is turbulent or non-turbulent respectively.The critical point at which the flow within a tube changes from non-turbulent to turbulent may be determined by application of Reynolds criterion listed as equation (8).It appears that there is also a critical region for flow transverse to tubes at which the flow changes from non-turbulent or viscous to turbulent; this is clearly shown in figure 7. The change of flow from non-turbulent to turbulent appears to take place at the point where V m D/z m is equal to 0.25.For the non-turbulent or viscous region of flow transverse to tubes the film transfer factor for single rows of tubes is expressed by equation (26) while for the turbulent region equation (27) applies.。

1.1工程热力学基础Thermodynamics is a science in which the storage, transformation, and transfer of energy are studied. Energy is stored as internal energy (associated with temperature), kinetic energy (due to motion), potential energy (due to elevation) and chemical energy (due to chemical composition); it is transformed from one of these forms to another; and it is transferred across a boundary as either heat or work.热力学是一门研究能量储存、转换及传递的科学。

能量以内能（与温度有关）、动能（由物体运动引起）、势能（由高度引起）和化学能（与化学组成相关）的形式储存。

不同形式的能量可以相互转化，而且能量在边界上可以以热和功的形式进行传递。

In thermodynamics, we will derive equations that relate the transformations and transfers of energy to properties such as temperature, pressure, and density. Substances and their properties, thus, become very important in thermodynamics. Many of our equations will be based on experimental observations that have been organized into mathematical statements or laws; the first and second laws of thermodynamics are the most widely used.在热力学中，我们将推导有关能量转化和传递与物性参数，如温度、压强及密度等关系间的方程。

汽车全球变暖英文作文英文：Global warming has become a major issue affecting the world, and the automotive industry plays a significant role in contributing to this problem. The use of fossil fuels in cars releases carbon dioxide and other harmful gases into the atmosphere, which traps heat and causes the Earth's temperature to rise.As a car owner, I am aware of the impact my vehicle has on the environment. I try to reduce my carbon footprint by carpooling, using public transportation, and driving afuel-efficient car. However, there is still a long way to go in terms of reducing emissions from cars on a global scale.One solution is the development and implementation of electric cars. These cars run on electricity rather than gasoline, which eliminates the emission of harmful gases.Electric cars are becoming more popular and accessible, but there are still some challenges such as the cost and availability of charging stations.Another solution is the use of alternative fuels such as biofuels and hydrogen fuel cells. These fuels have lower emissions compared to traditional gasoline and diesel, and they are renewable resources. However, the infrastructure for these fuels is not yet widespread, making it difficult for consumers to access them.In conclusion, the automotive industry must take responsibility for the impact it has on the environment and work towards sustainable solutions. As consumers, we can also make a difference by choosing eco-friendly options and reducing our reliance on cars.中文：全球变暖已成为影响世界的重大问题，汽车行业在造成这个问题方面扮演着重要角色。

Heat Transfer in the MoldHeat transfer from Steel, Mold to Cooling WaterHeat transfer in the mold is critical and complex. The predominant transverse heat transfer can be considered as a flow of heat energy through a series of thermal resistances, from the high-temperature source of liquid steel core in the mold to the sink of cooling water of the mold-cooling system. It includes:∙Heat transfer in the solidifying casting.∙Heat transfer from steel shell surface (skin) to inner copper-lining surface.∙Heat transfer through copper lining.∙Heat transfer from outer copper-lining surface to mold-cooling water.In the solidifying castingHeat transfer in the solidifying casting occurs in a complex way since the heat to be extracted originates from enthalpy changes in the steel strand both from temperature decreases and phase changes. The former is referred to as sensible heat change and the latter as latent heat. Moreover, phase changes involve not only the changes between solid phases, but also the conditions produced by the solidification of an alloy. For example, a "mushy zone" exists between theliquidus and solidus temperatures which depend on the carbon content of the steel. In addition, the thermal resistance increases as the shell thickness increases from the meniscus to the bottom of the mold. Heat transfer in this region is by conduction.From steel shell surface to inner copper-lining surfaceHeat transfer in this step is most complex and is the controlling step in the mold. It involves mainly two mechanisms of heat transfer: conduction and radiation. The salient feature of this heat-transfer step is the shrinkage of the solidifying steel (which is a function of steel grade and caster operating conditions), and the resulting tendency for an air gap to form between the steel shell and the mold surface.The formation of the air gap is complex and may vary both in the transverse and longitudinal direction. Thus, it has a variable effect on the heat-transfer mechanism and the magnitude of heat flux. For example, as the air gap is formed, the heat transfer proceeds mainly from conduction to radiation with a resulting decrease in heat flux. In general, this heat-transfer step represents the largest thermal resistance of all of the four steps, especially with respect to heat transfer through the copper lining and from the latter to the mold cooling water.The entire pattern of heat removal in the mold is dependent on the dynamics of gap formation. In general, gap width tends to increase with increasing distance from the meniscus as the steel shell solidifies and shrinks away from the mold surface. In addition, as the shell thickness increases with distance from the meniscus, it tends to withstand the opposing bulging effect of the ferrostaticpressure to reduce the gap.Heat transfer at the copper inner surface is further complicated by the effects of mold lubrication. Another factor influencing heat transfer at this mold surface is the mold taper, which tends to increase heat transfer because it opposes the effect of gap formation.In general, the local heat flux down the mold length reaches a maximum value at or just below the liquid steel meniscus, and decreases down the mold length. The average heat flux for the whole mold increases with increasing casting speed.Through copper liningHeat transfer in this step is by conduction. It is dependent on the thermal conductivity of the copper and its thickness; the greater the thickness, the higher the hot-face temperature of the copper lining.From outer copper-lining surface to mold-cooling waterHeat transfer in this step is accomplished by forced convection. Although the bulk temperature of the cooling water, typically about 40°C (90*F, is usually below its saturation temperature at a given water pressure, boiling is still possible at local regions at the mold outer surface if the local temperature of this surface is sufficiently high for water vapor bubbles to nucleate at the surface, pass to the colder bulk cooling water, and condense. This effect increases heat transfer. Nucleate boiling can result in cycling of the temperature field through the copper mold (both at the cold face and the hot face) and can result in deleterious product quality. Boiling can be suppressed by increasing the water velocity in the cooling system or by raising the water pressure. Incipient boiling is more likely in billet molds, which have higher cold-face temperatures than slab molds because of their thinner wall thicknesses. Typical values for cold-face temperature are in the range of 150°C (302°F) for billet molds and 100°C (212°F) for slab molds.Cooling Water SystemControl of heat transfer in the mold is accomplished by a forced-convection cooling-water system, which must be designed to accommodate the high heat-transfer rates that result from the solidification process. In general, the cooling water enters at the mold bottom, passes vertically through a series of parallel water channels located between the outer mold wall and a steel containment jacket, and exits at the top of the mold.The primary control parameters are:∙The volume of water at the required water temperature, pressure and quality.∙The flow velocity of water uniformly through the passages around the perimeter of the mold liner.Water Volume, temperature, pressure and qualityTypically, a pressurized recirculating closed loop system is employed. The rate of water flow should be sufficient to absorb the heat from the strand without an excessive increase in bulk water temperature. A large increase in temperature could result in a decrease in heat-transfer effectiveness and higher mold temperatures. For this same reason, the inlet water temperature to the mold should also not be excessive; a proper mold water pressure is also required. For example, as discussed previously, higher water pressures tend to suppress boiling but excessively high pressures may cause mechanical mold deformation.Water quality is an important factor with regard to scale deposition on the mold liner. Scale deposition can be a serious problem because it causes an additional thermal resistance at the mold-cooling water interface that increases the mold-wall temperature leading to adverse effects such as vapor generation and a reduction in strength of the copper liner. The type and amount of scale formed is mainly dependent on the temperature and velocity of the cooling water, the cold-face temperature of the mold, and the type of water treatment.Water flow velocityTo achieve the proper flow velocity, the cooling system is designed such that the velocity is high enough to produce an effective heat-transfer coefficient at the mold-cooling water interface. Too low a flow velocity will produce a higher thermal resistance at this interface, which may lead to boiling and its adverse effects. In general, the higher the cooling-water velocity, the lower is the mold temperature. The cooling system should also be designed to maintain the required flow velocity distribution uniformly around the mold and to maximize the area of the faces that are directly water-cooled. Uniform flow distribution can be achieved by the proper geometrical design of the water passages with the use of headers and bale plates. Monitoring the operating parameters of the mold cooling system provides an assessment of the casting process. For example, with a constant cooling-water flow rate, the heat removed from a mold face will be directly related to the difference between the inlet and outlet watertemperature, AT. Thus an excessively large DT may indicate an abnormally low flow rate for one or more mold faces, whereas an excessively small DT may indicate an abnormally large scale buildup for one or more mold faces. An unequal DT for opposite faces may result from an unsymmetrical pouring stream mold distortion, or from strand misalignment.Mold OscillationDuring casting as the strand moves down the mold, tensile forces are developed in the solidifying skin due to high friction and sticking of the casting skin to the working face of the mold. The friction and sticking can be further enhanced by increasing ferrostatic pressure. If these tensile forces exceed the cohesive forces of the solidifying steel, the skin will tear and a breakout may occur. Sticking can be exacerbated by local rough areas in the mold such as gouges.To reduce the mold-strand adhesion and the risk of breakouts, in which liquid steel breaks through the thin solidified shell either in or below the mold, the mold is oscillated and lubricated. Oscillation may be accomplished by:∙motor-driven cams∙levers and cranks∙hydraulic actuation∙etc.Motor-driven cams, which support and reciprocate the mold, are used primarily.Mold oscillating cycles are many and varied with respect to frequency, amplitude and form. Many oscillation systems are designed so that the cycle can be changed when different section sizes on steel grades are cast on the same machine. However, there is one feature that has been adopted, almost without exception, which applies a negative strip to the solidifying shell. Negative strip is obtained by designing the "down stroke" of the cycle such that the mold moves faster than the withdrawal speed of the section being cast. Under these conditions, compressive stresses are developed in the solidifyingshell which tend to seal surface fissures and porosity and thus enhance the strength of the shell. During the "up stroke" portion of the cycle, the mold is very rapidly returned to the starting position and the cycle then repeated. Thus the shape of the oscillating cycle is non-symmetrical with respect to time.Mold LubricantsMold oscillation alone is insufficient to prevent skin ruptures and the use of mold lubricants is essential. Mold lubricants can be divided into two categories:∙liquids (oil lubricants)∙ solids (mold fluxes or mold powders)Oil lubricants (used with open pouring) tend to wet the copper mold and permit greater heat transfer at the upper part of the mold. Liquid oil lubricants include those of mineral, vegetable, animal and synthetic origin. Rapeseed oil was commonly used but is being replaced bysemi-refined vegetable oils. Because of the casting environment, the oil lubricants require high- temperature properties, such as a high flash point, so that they can effectively lubricate the mold surface in contact with the steel. The oil is continually injected through a series of small holes or slots in the upper portion of the mold above the steel meniscus to form a thin continuous film over the surface of the mold walls. Oils are principally used in billet or bloom machines casting silicon-killed steels.Solid lubricants (mold fluxes or mold powders) are widely used with submerged refractory tube shrouds in casting aluminum-killed steels on slab and bloom casters. Both mold fluxes (used with refractory shroud pouring) and mold powders result in greater heat transfer.The powders serve not only as lubricants but also provide other functions:∙Enhanced heat transfer at the strand-mold interface.∙Protection of the liquid metal surface in the mold from reoxidation by surrounding air.∙Thermal insulation of the liquid metal surface to prevent unwanted solidification, particularly at the wall-meniscus interface and at the submerged shroud.∙Absorb non-metallic inclusions that float to the liquid surface.Mold powder is added to the surface of the liquid steel shortly after the start of casting either manually by rakes or by mechanical feeders. Powder in contact with the liquid steel melts forming a liquid slag that then infiltrates between the mold wall and surface of the solidifying steel. Additional powder is added continually to replace that removed on the surface of the cast section. Lubrication by mold powders is a complex phenomenon and depends not only on flux properties such as viscosity, but also on the operating conditions, such as steel grade, casting speed, and oscillation condition.In addition to viscosity, which is dependent on the silica and alumina content of the powder, the melting point or crystallization temperature characteristics of the powder are also important. Very "fluid" slugs with low viscosities and low crystallization temperatures tend to provide the most effective heat transfer in the mold.Additional characteristics affecting the other functional requirements of powders include: a minimal iron oxide content, for example, to protect the liquid steel surface from reoxidation; and a low density which, together with graphitic carbon to retard sintering, fusibility and melting, enhances the thermal insulation capabilities.Mold powders consist of a mixture of materials of which Si02-CaO-AI203-Na2O-CaF2 is the basic component with varying amounts of carbon and other coinpounds. They can be broadly divided into:∙fly-ash based powders∙synthetic powders∙prefused, fritted or granulated powdersReferences[1] The making, Shaping and Treating of Steel, 1985, US Steel.[2] The making, Shaping and Treating of Steel, 2002, AISE Steel Foundation.。

RadiatorRadiators are heat exchangers used to transfer thermal ener gy from one medium toanother for the purpose of cooling and heating. The majority of radiators areconstructed to function in automobiles , buildings, and electronics. The radiator isalways a source of heat to its environment, although this may be for either thepurpose of heating this environment, or for cooling the fluid or coolant supplied toit, as for engine cooling . Despite the name, most radiators transfer the bulk of theirheat via convection instead of thermal radiation. Spacecraft radiators necessarilymust use radiation only to reject heat.The Roman hypocaust, is an early example of a type of radiator for building spaceheating. The heating radiator was invented by Franz San Galli, a Prussian-bornRussian businessman living in S t. Petersbur g, between 1855 and 1857.[1][2]1Radiation and convection 2Heating 3Engine cooling 4Electronics 5Spacecraft 6 ReferencesHeat transfer from a radiator occurs by all the usual mechanisms: thermal radiation, convection into flowing air or liquid, and conduction into the air or liquid. A radiator may even transfer heat by phase change , for example, drying a pair of socks. In practice,the term "radiator" refers to any of a number of devices in which a liquid circulates through exposed pipes (often with fins or other means of increasing surface area). The term "convector" refers to a class of devices in which the source of heat is not directly exposed.Radiators are commonly used to heat buildings. In a central heating system, hotwater or sometimes steam is generated in a central boiler, and circulated by pumpsthrough radiators within the building, where this heat is transferred to thesurroundings.Radiators are used for cooling internal combustion engines, mainly in automobilesbut also in piston-engin ed aircraft, railway locomotives , motorcycles , stationarygenerating plants and other places where such engines are used.Water-air convective cooling radiatorContentsRadiation and convectionHeatingA Type 22 Convector Radiator ,typical of a standard central heating systemEngine coolingTo cool down the engine, a coolant is passed through the engine block, where itabsorbs heat from the engine. The hot coolant is then fed into the inlet tank of theradiator (located either on the top of the radiator, or along one side), from which it isdistributed across the radiator core through tubes to another tank on the opposite endof the radiator. As the coolant passes through the radiator tubes on its way to theopposite tank, it transfers much of its heat to the tubes which, in turn, transfer theheat to the fins that are lodged between each row of tubes. The fins then release theheat to the ambient air. Fins are used to greatly increase the contact surface of thetubes to the air, thus increasing the exchange efficiency . The cooled coolant is fedback to the engine, and the cycle repeats. Normally , the radiator does not reduce thetemperature of the coolant back to ambient air temperature, but it is still sufficientlycooled to keep the engine from overheating.This coolant is usually water-based, with the addition of glycols to prevent freezingand other additives to limit corrosion, erosion and cavitation. However , the coolantmay also be an oil. The first engines used thermosiphons to circulate the coolant;today, however , all but the smallest engines use p umps.Up to the 1980s, radiator cores were often made of copper (for fins) and brass (fortubes, headers, and side-plates, while tanks could also be made of brass or of plastic,often a polyamide). Starting in the 1970s, use of aluminium increased, eventuallytaking over the vast majority of vehicular radiator applications. The maininducements for aluminium are reduced weight and cost. However , the superiorcooling properties of Copper-Brass over Aluminium makes it preferential for highperformance vehicles or stationary applications. In particular MW -class installations,copper-brass constructions are still dominant (See: Copper in heat exchangers ).CuproBraze is a copper-alloy heat exchanger technology for harsh temperature andpressure environments such as those in the latest generations of cleaner dieselengines mandated by environmental regulations.[3][4] Its performance advantagesover radiators made with other materials include better thermal performance, heat transfer, size, strength, durability , emissions,corrosion resistance, repairability , and antimicrobial benefits.Since air has a lower heat capacity and density than liquid coolants, a fairly large volume flow rate (relative to the coolant's) must be blown through the radiator core to capture the heat from the coolant. Radiators often have one or more fans that blow air through the radiator . To save fan power consumption in vehicles, radiators are often behind the grille at the front end of a vehicle. Ram air can give a portion or all of the necessary cooling air flow when the coolant temperature remains below the system's designed maximum temperature, and the fan remains disengaged.As electronic devices become smaller, the problem of dispersing waste heat becomes more difficult. Tiny radiators known as heat sinks are used to convey heat from the electronic components into a cooling air stream. Heatsink do not use water, rather they conduct the heat from the source (high performance heat sinks have copper to conduct better). Heat is transferred to the air by conduction and convection; a relatively small proportion of heat is transferred by radiation owing to the low temperature of semiconductor devices compared to their surroundings.Radiators are found as components of some spacecraft. These radiators work by radiating heat energy away as light (generally infrared given the temperatures at which spacecraft try to operate) because in the vacuum of space neither convection nor conduction can work to transfer heat away . On the International Space Station these can be seen clearly as lar ge white panels attached to the main[5]Car engine bay , with radiator in frontAuto radiators with a double grid of tubes: staggered grids on the left,parallel grids on the right ElectronicsSpacecrafttruss. They can be found on both manned and unmanned craft.[5]1. "Family Sangalli / San Galli" (http://www .gruner-fam.de/SanGalli-E.html).Gruner-fam.de . Retrieved 2011-09-20.2. The hot boxes of San Galli (http://www /press/energyhistory/sangalli/) (in Russian)3. Vehicle radiators: Can CuproBraze turn copp e r into a bona fidecontender?; American Metal Market September 2008;/u/46572847/Perspectives-radiators.pdf4. Partanen, Juho (2011). Hot property: Heat exchangers that optimizeproduct reliability , decrease lifecycle costs an d improve profitability arejust the ticket for increasing the lifespan and performance of of f-highwaymachinery; Industrial V ehicle T echnology; March 2011;http://viewer /services/DownloadP DF5. "Radiators" (https://www /mission_pages/station /structure/elements/radiators.html#.VgcSEMtVhBc). International Space Station . NASA .Retrieved September 26, 2015.Retrieved from "https:///w/index.php?title=Radiator&oldid=808719777"This page was last edited on 4 November 2017, at 18:27.T ext is available under the C reative Commons Attribution-ShareAlike License ; additional terms may apply . By using this site, you agree to the T erms of Use and Privacy Policy . Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. A passive heatsink on a motherboardReferences。

SEISCOEndless Hot Water�Copyright © 2006 Microtherm, Inc.223 West Airtex, Houston, TX. 77090, Ph:888-296-9293, Fx:281-876-3338, 5-Year Limited Warranty*Features & BenefitsFor Additional Features See Inside PageChamber and PartsHigh Efficiency Compact Design Provides Unlimited Hot Water -Commercial models provideunlimited hot water while operating within their designed gallons per minute range, immediately heating water when a hot water outlet is opened. Seisco models install inside closets, or on almost any wall. Water is only heated on de-mand, virtually eliminating standby heat loss and providing over 99% efficiency.Microprocessor Control -On-board computer logiccontrols temperature through a modified proportional,integral, derivative (PID) control scheme. The control also provides self-diagnostics, signal the need for maintenance in case of a water leak inside the heater, incorporates an optional switch for local on/off power interuption, and intel-ligently controls power distribution to the heating elements while continuously monitoring critical functions in order to shut down the water heater if a failure occurs.PowerShare™ Technology -Patented power dis-tribution control technology utilizes computer algorithms and electronic triacs with patented cooling technology to pulse power on and off to all heating elements resulting in uniform temperature modulation between 1-100% of the element’s range. PowerShare along with constantly flowing water across heating elements ensure that heat-ing elements operate at the lowest possible temperature. When the elements are turned off, low sheath temperature prevents boiling minerals out of the water causing buildup on the heating elements, prolonging element life. Power-Share also eliminates electrical disturbances in the home from the water heater, such as flickering lights.Thermistor Temperature Sensing -Five thermis-tors continuously monitor inlet/outlet water temperature and the water temperature in each heating element cham-ber. Outlet water temperature is factory set to 120°F and is field adjustable between 90-145°F. In addition, water flow is sensed using the same thermistors, eliminating the need for troublesome flow switches.Heating Elements -Industry standard 1 ½” hexhead, direct immersion, heating elements utilizePowerShare technology to help eliminate scale build-up and prolong element life far beyond that of tank type water heaters. If an element fails, a replacement can be purchased from virtually any plumbing distributor.Redundant Safety Features -Two water levelsensors are located at the top of the water heater’s chambers to prevent powering on the heating elements if sufficient water is not detected inside the water heater. In addition, two safety cutoff switches, one manual and one automatic reset, shut down power to the heating elements should an unsafe condition occur.Built-in Leak Detector and Alarm -A switchlocated inside the water heater’s cover along thebottom of the mounting plate activates an alarm when contacted by water.Code Approvals -UL/CUL 499/64, HUD MobileHome, ISRAEL, NOM, and NEC. Hydrostatically tested to 300 psi.*Limited Warranty-See written warranty for details.Two & Four Chamber Models ShownSEISCOEndless Hot Water�Copyright © 2006 Microtherm, Inc. Do You Know?223 West Airtex, Houston, TX. 77090, Ph:888-296-9293, Fx:281-876-3338, 934567821181213141516171110Cold Water InletHot Water OutletHeating ElementsMicroprocessorThermistor Temperature SensorsSafety Cutoff SwitchesTemperature Control KnobOff Peak Control ConnectionWater Leak DetectorCleanout PlatesLED Indicator LightSpeakerService ButtonPower LugsTriacs3/4” Conduit ConnectionsNon-Ferrous Water PassagesHeavy Gauge Steel MountingPanelFour Chamber Design-Inside View... the majority of stan-dard tank type commercialelectric water heaters usesurface mounted thermostatsfor temperature sensing...Seisco models use thermis-tors immersed in the waterfor more accurate tempera-ture control.... most standard tank typecommercial electric waterheaters are limited to 12KWmaximum input, one 6KWelement located in the topof th tank, and one 6KWelment located in the bottomof the tank. At maximuminput, their recovery is reallynot equivalent to 12KW/hourbecause the top heating ele-ment turns off as soon as thetop 1/3 of the tank reachesthe set point of the upperthermostat...Seisco modelsalways perform up to 100%of their rated KW input.... most tank type commer-cial electric water heatershave a 3-year warranty...Seisco models include a 5-year warranty.... most tank type commer-cial electric water heatershave standby heat loss of ap-proximately 2-3% per hour...Seisco virtually eliminatesheat loss, conserving fueland saving money on waterheating.181414149817161615151515110105551347121165653333214SEISCOEndless Hot Water�Do You Know?223 West Airtex, Houston, TX. 77090, Ph:888-296-9293, Fx:281-876-3338, MICROAdditional Features & BenefitsService Button/LED Light/Speaker-While on the phone with a Microtherm technician, the service agent pushes a service button in order to activate an audible diagnostic sequence. The service agent can also diagnose a problem through observing an LED that indicates service issues through a series of flashes.Rust and Corrosion Resistant Engineering Composite Material- All water passages are constructed of a high temperature resistant DuPont® resin. Grades of the same resin family, but with lower properties, are so strong that they are used as the “header” for automobile radiators. Ability to resist extreme temperature changes far above those found inside Seisco models and superior chemical resistance make DuPont’s engineering composite material the ideal material for Seisco’s commercial tankless electric water heaters. Continuous Venting Design-As water is heated, dissolved gases are released. Tiny bypass air passages at the top of each water chamber allow air and dissolved gases to exit unnoticed through the hot water outlet as hot water is being used.Optional Demand Side Management Connection- Allows connec-tion of an on/off control to the water heater (specify this option when ordering). Cleanout Plates-Should sediment such as sand or silt from the water supply accumulate inside the water chambers, removable plates sealed with reusable gaskets allow access for cleaning without disconnecting wires or removing the heating module and control board.¾” Non-Ferrous Inlet/Outlet Connections-Factory installed ¾” MNPT thermoplastic nipples allow easy plumbing connections and eliminate the need for dielectric fittingsHeavy Gauge Steel Mounting Panel-Modular water passages, the control board, and other components are assembled and then mounted to a heavy gauge steel back panel that includes four tabs with rubber feet for mounting the unit to the wall. A decorative plastic cover encloses all components.¾” Electrical Conduit Connection-Standard ¾” electrical conduit connections allow fast wiring of the water heater.... large commercial elec-tric tank type water heaters sequentially step heating elements on at 100% of full power to avoid flickering lights and electrical distur-bances... Seisco models, even when installed in multiples, use PowerShare technology to modulate power to the heating elements from 1-100% of full power, elimina-teing electrical disturbances. ... due to space constraints in most commercial instal-lations, it is usually improb-able that more than four commercial electric tank type water heates can be plumbed together... Seisco’s compact design allows more units to be manifolded together in the same amount of space occupied by just one commercial electric tank type water heater.... the cost of professionally replacing a heating element in a commercial electric tank type water heater can easily exceed $150... Seisco reduces the cost of repairs by prolonging element life and eliminating a large tank to drain as part of the service call.... Seisco models can be used with one or more manifolded commercial storage tank(s) to provide hot water for a large hot water demand over a short periof of time.Copyright © 2006 Microtherm, Inc.SEISCOEndless Hot Water�Copyright © 2006 Microtherm, Inc.223 West Airtex, Houston, TX. 77090, Ph:888-296-9293, Fx:281-876-3338, Suggested Written SpecificationCommercial electric water heater(s) shall be Seisco tankless water heater model _______ as manufactured by Microtherm, or an approved equal and shall have a 5-year limited warranty* when installed in a commercial application. Heater(s) shall have a rated input of _____ KW at ____ Volts. Electrical control of the heater must be accomplished using an integrated microprocessor that employs a proportional/integral/derivative (PID) control scheme using thermistors for sensing temperature and flow. Heating elements must use PowerShare technology to simultaneously vary KW input across all heating elements from 1% to maximum input. Stepping individual elements on and off at full power is not acceptable. Flow switches that restrict the flow of water in any way are not acceptable. (Optioinal-Heater(s) shall include an electrical connection for demand side control). Heater(s) shall include dual water level sensors, high limit control via the microprocessor, and dual high limit cutoff switches, one manualthe status of all monitored functions. Heater(s) shall have a built-in water leak detector. All water passages must be constructed of a high temperature resistant DuPont ® resin. Clean-cut access for removing sediment must be provided without removing plumbing connections or exposing electrical components of the water heater. Heater(s) must be UL/CUL 499, CSA, NSF , HUD Mobile Home, ISRAEL, NOM, and NEC approved.CA 12/05 R1*Limited Warranty-See written warranty for details.*Limited Warranty-See written warranty for details.Recovery (gpm & gph) @ Temperature Rise (F)*Depth: Not Shown On Drawing **Optional: 1-60 amp. breaker, ***Optional: 2-60 amp. breakers. All models are 99+% efficient.Written specifications subject to change without notice.。