Experimental Study And Numerical Simulation Of Heat Transfer Performance Of U-shaped Heat Pipe Heat Exchanger

Clean workshops and other places need to control the temperature and humidity of the environment.U-shaped heat pipes can be used to reduce energy consumption in the humidity control system of clean workshops.In this paper,by setting up a U-shaped heat pipe heat exchanger experimental platform in the enthalpy difference laboratory,the heat transfer performance of U-shaped heat pipe heat exchanger is experimentally studied.The parameters such as filling rate of the working fluid,type of working fluid,and temperature and humidity of the inlet air are changed to determine the influence of different factors on the heat transfer performance of U-shaped heat pipes and the optimal area of heat transfer performance.With the experimental data as boundary conditions,numerical simulation studies of single-elbow U-shaped heat pipes and double-elbow U-shaped heat pipes were carried out.The diameter of the U-shaped heat pipe used in the experiment is 15.88 mm,the length between evaporation section and condensation section is 1000 mm,and the length of the adiabatic section is 838 mm.When the commonly used inlet air temperature of the clean room is 25℃ with R410 A as the working fluid,the filling rate is within the range of8%-48%,the heat exchange amount first increases and then decreases with the increase of the filling rate,and the best liquid filling rate is 25%.Comparative studies using R410 A and R134 a as working fluids were carried out.The heat transfer coefficient of R410 A as working fluid in the evaporation section of the U-shaped heat pipe is 3.28% larger than that of R134 a on average.The heat transfer coefficient of R410 A is 4.70% larger than that of R134 a on average.When the optimal liquid filling rate is 25% with the inlet air temperature being changed within 21.2℃-33.7℃ and the inlet water temperature of the surface cooler being7℃,the heat transfer coefficients in the heat exchanger tube all increase with the increase of the inlet air temperature under two different working conditions.The heat transfer coefficient of R410 A in the evaporation section of the U-shaped heat pipe is 12.54% larger than the one of R134 a on average,and the heat transfer coefficient of R410 A in the condensation section is 15.82% larger than the one of R134 a on average..According to the experimental results,a calculation correlation formula suitable for the heat transfer coefficient in the heat exchanger tube of this study is fitted,and the error between experimental value and calculated value is within 5%,proving the applicability of the formula.CFD software is applied to carry out numerical simulation study of heat transfer in single elbow U-shaped heat pipe and double elbow U-shaped heat pipe.The numerical simulation selects VOF and CSF models.By loading the user-defined function UDF of gas-liquid transformation,it is realized that the simulation of the internal flow and heat transfer process in the evaporation section of the U-shaped heat pipe has obtained the changing laws of temperature and velocity of the evaporation section in the tube,and the movement of bubbles in the tube.The calculated correlation formula of the heat transfer coefficient in the U-shaped heat pipe and the results obtained from the numerical simulation obtained by the fitting in this paper can provide a reference for researchers when studying the U-shaped heat pipe.The research methods,content and results of this article can provide guidance for the engineering application of U-shaped heat pipes.