Numerical Simulation On Flow And Heat Transfer Characteristics Of The Coaxial Radial Heat Pipe

Our country has been faced with pressure of environmental pollution and energy shortage in recent years,thus the use of heat pipe technology for heat recovery and energy saving in a vast range of engineering applications has been on the rise.Heat pipe have some characteristics of small pressure loss,high heat transfer efficiency,compact structure,superior performance and so on,which has become an important equipment in the industrial field.There is a large amount of corrosive waste heat smoke in the chemical or metallurgical industry,the heat pipe heat exchanger with radial heat pipe can effectively prevent dew point corrosion.The coaxial radial heat pipe is investigated in the dissertation.The main contributions are listed as follow:(1)This paper set up a radial heat pipe experimental apparatus,and heat transfer characteristics of heat pipe can be obtained under different operating conditions,operating conditions and structure conditions.What’s more,this paper selected the optimal experimental data to verify the results of the steady state numerical model and the CFD numerical model.The calculation difference between MIXTURE and VOF model is analyzed.The influence of surface tension and physical properties of gas and liquid is considered by this paper.And the evaporation,condensation and phase change processes in a radial heat pipe were dealt with by adding a user-defined function(UDF)to the FLUENT code.(2)The VOF and MIXTURE technique was used to model the interaction between these phase.By simulating evaporation and condensation model,observed the process of the formation,merger,and exfoliation of droplets.the CFD predicted temperature profile in the heat pipe was compared with experimental measurements and a good agreement was observed.Through grid independence test,both errors remain within 5%,which verifies the accuracy of CFD numerical simulation(3)This paper analysed the heat transfer process of radial heat pipe in detail,and the mass conservation of working fluid was considered into steady state of heat pipe,which indicates effect of working fluid filling ratio on performance of jacket radial heat pipe.Then this paper write the MATLAB program with stable operation of heat pipe,and make use of the computer to carry on imitating the calculation under different conditions.In addition,When the filling rate is up to 44.8%,the performance of heat pipe can reach the best heat transfer effect.(4)With the Nusselt condensation model,the liquid film thickness and the local heat transfer coefficient of the inner wall surface is calculated by MATLAB software.Research shows the liquid film thickness is thicker at input heating power increased gradually,but it has little influence on the local heat transfer of the condensing tube wall.(5)The non-steady-state startup model and condensation heat transfer model of horizontal pipe are developed.It is indicated that the coordination of temperature response is realized among average temperatures of vapor,evaporator and condenser section under different input power and cooling water velocity.Research shows that it has a certain guiding significance for the start and operation of the exhaust-heat boiler.