Research On Heat Transfer Characeristics Of The Deionized Water-Fe₃O₄ Nanofluid In Heat Pipe

Nano-fluid is a new stable suspension which is made by adding nanoscale metal,nonmetal or metal oxide particles into pure liquid in a certain way and proportion.The forces in the nanofluid are mostly van der Waals forces,Brownian forces,and electrostatic forces which cause random motion between nanoparticles.Such kind of random motion increases the internal disturbance of the fluid,which in turn enhances the thermal conductivity of the fluid and the effect of convection heat transfer.Therefore,the application of nano-fluid in the gravity heat pipe can significantly reduce the thermal resistance of the heat pipe and enhance the heat transfer characteristics of the heat pipe in the case of the least influence on the heat pipe processing technology.This paper designs and builds a gravity heat pipe system test platform.Based on different input powers Q(30W,35W,40W,50W,60 W),different liquid filling rates FR(35%,40%,50%,60%,70%),different nanoparticle mass concentration(0.2%,0.5%,0.8%,1%,2%),inclination angle of 90°,and air-cooling system wind speed of 6m/s,the outer wall temperature of gravity heat pipe is tested and the heat transfer characteristics of the gravity heat pipe filled with deionized water and deionized water-Fe3O4 nanofluid are studied in detail.The purpose is to guide the application of nanofluids in the gravity heat pipe and improve the heat transfer efficiency of heat pipes.The main contents of this paper are:(1)When deionized water is used as the heat pipe working medium,the external wall temperature of the heat pipe is tested under five input powers(30W,35W,40W,50W,60 W)and 5 liquid filling rates(35%,40%,50%,60%,70%).According to the test data,the test devise reliability,isothermal performance,and the equivalent calculation of the equivalent convective heat transfer coefficient and heat transfer resistance of the deionized hydrothermal heat pipe are studied and analyzed.The results show that when the deionized hydrothermal gravity heat pipe is Q=40W,FR=50%,the equivalent convection heat transfer coefficient is up to 3190.783 W.m-2.K-1,but the heat transfer thermal resistance is as low as 0.225?/W.The heat transfer performance is the best at this condition.(2)Taking lOnm nanometer,nanoparticles mass concentration 0.2%,0.5%,0.8%,1%and 2%of deionized water-Fe3O4 nano fluid as working medium,the gravity heat pipe of nanofluids was tested under the same conditions as deionized water.The equivalent convective heat transfer coefficient and heat transfer resistance of the heat pipe are calculated theoretically.(3)Comparing and analyzing the similarities and differences of the heat transfer characteristics between the nanofluid working fluid and the pure deionized water gravity heat pipe under the same conditions,the study shows that the outer wall temperature of the evaporation section of the nanofluid gravity heat pipe is lower than the outer wall temperature of the deionized water gravity heat pipe,while its temperature of the outer wall of the condensation section is higher.That is to say the average temperature difference between the evaporation section and the condensation section of the nanofluid gravity heat pipe is lower and better isotherm.When liquid filling rate of gravity heat pipe is 50%and imput power is 40W,the two kinds of heat pipes have the highest equivalent convection heat transfer coefficient and the lowest thermal resistance.Therefore,it is concluded that the gravity heat pipe has the best heat transfer performance at this time.In addition,compared with deionized water heat pipes,when the mass concentration increases from 0.2%to 1%,the equivalent convective heat transfer coefficient of nanofluid heat pipes continues to increase.The maximum increase is achieved at a mass concentration of 1%.When the mass concentration increases to 2%,the increase in the equivalent convective heat transfer coefficient decreases,but its value is higher than the equivalent convection heat transfer coefficient of the deionized water heat pipe.Similarly,the thermal resistance of the heat pipe decreases first and then increases,but the overall thermal resistance is smaller than the thermal resistance of the deionized water heat pipe.Therefore,when nanofluids are used in gravity heat pipes,the heat transfer performance can be improved effectively and when the mass concentration is 1%,equivalent convection heat transfer coefficient is even higher but the heat transfer thermal resistance is lower,which is more suitable for the application in the heat pipes.