Numerical Simulation And Analysis Of Flat Pulsating Heat Pipe With Varying Section Diameter

Flat pulsating heat pipe not only has the advantages of small volume,simple structure and high effective heat transfer,but also can meet the demand of heat dissipation installation of electronic equipment because of its unique structure.Therefore,it has been regarded as an effective heat transfer component to undertake the field of electronic components cooling.Based on the study of flat pulsating heat pipe with ordinary channel diameter,a new kind of flat pulsating heat pipe with varying channel diameter is proposed according to the micro pump effect.A unsteady state model of vapor-liquid two phase flow and heat transfer is established by the volume of fluid method,and numerical simulation of flat pulsating heat pipe with ordinary channel diameter and flat pulsating heat pipe with varying channel diameter is carried out.The vapor-liquid phase behavior and the characteristics of the flow in two kinds of flat pulsating heat pipes are analyzed by using the vapor volume distribution cloud picture of the working fluid;The influence of the varying channel diameter on the start-up temperature and temperature fluctuation of flat pulsating heat pipe is analyzed based on the curve of temperature fluctuation in evaporator section;By changing the ratio of large / small cross section of flat pulsating heat pipe and operation conditions,the rule of start-up time and thermal resistance on two kinds of flat pulsating heat pipes are obtained and compared.The results and conclusions are summarized as follows:(1)Varying channel diameter has little effect on the behavior of vapor-liquid phase,but it increases the range of bubbly flow in the evaporator section of flat pulsating heat pipe,and it also improves the possibility of forming a unidirectional circulation in flat pulsating heat pipe;The curve of temperature fluctuation in evaporator section of flat pulsating heat pipe shows that the existence of varying channel diameter increases the temperature fluctuation frequency and reduces the amplitude of temperature fluctuation in the evaporator section of flat pulsating heat pipe.(2)With the increase of the ratio of the large / small cross section,the starting advantage of flat pulsating heat pipe varying channel diameter is becoming more and more obvious;When the filling ratio is 40%or 50%,the difference of start-up time between the two kinds of flat pulsating heat pipes is large,while when the filling ratio is over 50%,the difference of start-up time between the two kinds of flat pulsating heat pipes decreases;With the increase of the heating flux,the difference between the two kinds of flat pulsating heat pipes is large;The influence of varying channel diameter on two kinds of flat pulsating heat pipes with different medium is different.(3)With the increase of the ratio of large / small section,the thermal resistance of flat pulsating heat pipe decreases and then increases,and it reaches the best when the ratio of large / small section is 1.5:1;Under largerheat flux,the influence of varying channel diameter on flat pulsating heat pipe is enhanced,At this time,the difference of thermal resistance between the two kinds of flat pulsating heat pipes is obviously larger than that of the smaller heat flux;Under same working conditions,when the working medium is water,methanol or ethanol,the reduction of thermal resistance between two kinds of flat pulsating heat pipes is different,and the thermal resistance of the flat pulsating heat pipe with methanol is the best.