纳米颗粒强化热虹吸管换热特性的实验研究

http://www.paper.edu.cn Experimental studies of heat transfer enhancementin the thermosiphon by adding nanoparticles YE Xiang, HUANG Suyi, LI Zhongzhou（Department of Power Engineering Huazhong University of Science and Technology, Wuhan ,430074）

Abstract With the rapid development of nanometer technology, researchers have gradually applied the new and advanced technology to the traditional area of Energy & Power. A new method of enhancing heat transfer of the heating section of a two—phase closed thermosiphon has been proposed .And, theoretical and experimental studies have been carried out of the performance of the heat transfer enhancement by adding a proper amount of nanoparticles to the thermosiphon with water as the working fluid. Compared with the ordinary thermosiphon, results indicate that this heat pipes posses such advantages as good startup, lower tube wall temperature, and its heat transfer coefficient is increased by 47～96%, heat flux is increased by 7.6～15% in the range of the experiment. The performance of the heat transfer relates to the diameter and the volume fraction of nanoparticle. This new enhancing method is simple and easy to apply in industry. Keywords: nanofluid; nanoparticle; thermosiphon; intensify heat transfer

1 Introduction Nanoparticle ﹤ 100nm has a lot of unique features because of its very small particle size and much larger relative surface areas[1]. In recent years, with the rapid development of nanotechnology, researchers have gradually applied the new and advanced technology to the traditional area of Energy & Power [2]. A novel approach to engineering to fluids with better

heat-transfer properties, based on the rapidly emerging field of nanotechnology, has recently proposed [3] [4]. As we known, it has long been recognized that suspensions of solid particles in

liquids have great potential as improved heat-management fluids [5]. The key idea is to exploit the very high thermal conductivities of solid particles, which can be hundreds or thousands of times greater than those of conventional heat-transfer fluids such as water and ethylene glycol. In conventional case, the suspended particles are of μm or even mm dimensions. Although such suspensions do indeed display the desired increase in thermal conductivity, they suffer from stability and rheological problems. In particular, the particles tend to quickly settle out of suspension and thereby cause severe clogging, eroding pipelines, and severe pressure drop, etc, particularly in mini and microchannels. All those shortages limit the application of the conventional solid-liquid mixture. The nanofluids have a unique feature which is quite different from those of the conventional solid-liquid mixtures in which millimeter and/or micrometer size particles are added, a notable exception is provided by the Brownian motion, which appear to be stable because of their very small particle size. Applications of

1 http://www.paper.edu.cn nanoparticles provide an effective way of improving heat-transfer characteristics of fluids. Particles in diameter exhibit properties different from those of conventional solids. Compared with micron-sized particles, nanophase powders have much larger relative surface areas and a great potential for heat transfer enhancement. Some researchers tried to suspend nanoparticles into fluids. Choi is the first who used the term nanofluid to refer to the fluids with suspended nanoparticles. Some preliminary experimental results showed that increase in thermal consisting of water and 5 vol% CuO nanoparticles [6].

In this paper, author firstly proposed a new method of enhancing heat transfer of evaporator section of a two-phase closed thermosiphon by adding a proper amount of nanoparticles to the thermosiphon with water as working fluid. And, theoretical and experimental studies have been carried out of the performance of the heat transfer coefficients, heat flux, wall temperatures of the evaporator section.

2 Experimental system procedure 2.1 Experimental material The nanometer material we adopted in this experiment was provided by the Zhoushan Mingri Nanometer Material Co., Ltd. Its main parameter and the TEM photo of nanoparticle are as follows:

a γ phase Al2O3 b anatase phaseTiO2 c αphase Al2O3

Fig.1 TEM photo of nanoparticle

Item Purity(％) Average Particle Size（nm） Specific area（m2/g）

Specific Density（g/cm3）

γphase Al2O3≥99.99 30±5 180±30 0.2～0.4 Αphase Al2O3≥99.99 <150 10±5 0.3～0.5 anatase phase TiO2≥99.9 5 210±10 0.6～0.7 Table 1 Main technical index 2.2 Experimental apparatus A schematic diagram of the thermosyphon experiment is shown in Fig.2. The thermosyphon consisted of a 10-mm, 12-mm, 800-mm long copper tube. Its inner surface was finished with a roughness. Five chromel-alumel thermocouples of 0.5-mm theath diameter were embedded in 0.48-mm wide, 0.3-mm deep, 100-mm long grooves made on the outer surface of the tube to measure wall temperatures of the evaporator, adiabatic sections. Temperatures within the volumes