Numerical Simulation And Analysis Of Variable Tube Diameter Pulsating Heat Pipe

The pulsating heat pipe has the advantages of small size,simple structure and high efficiency of heat transfer.Because of its unique structure,it can meet the heat dissipation and installation requirements of electronic equipment.Therefore,it has become a new type of high efficiency element used in the field of electronic component cooling and space control.In this paper,a new type of single loop pulsating heat pipe with variable pipe diameter is proposed on the basis of the study of ordinary tube diameter pulsating heat pipe.The unsteady state model of gas-liquid two phase flow and heat transfer is established by VOF method.The numerical simulation of the ordinary equal diameter pulsating heat pipe and variable tube diameter single loop pulsating heat pipe is carried out.The gas-liquid two phase behavior and its flow characteristics in two kinds of pulsating heat pipes are analyzed by using the gas volume distribution image of the working fluid.The influence of the variable tube diameter structure on the starting temperature and the oscillation of the pulsating heat pipe is analyzed according to the temperature oscillation curve of the evaporation section of the two kinds of pulsating heat pipes.The start-up time and thermal resistance of two kinds of pulsating heat pipes were obtained,and the start-up time and thermal resistance of the two pulsating heat pipes were compared and analyzed.The simulation results show that the working fluid of the variable diameter tube pulsating heat pipe will form stable circulating flow during operation.It is also known from the temperature oscillation curve that the variable tube diameter structure increases the oscillation frequency of the working fluid evaporation section and reduces the oscillation amplitude of the temperature.With the increase of the diameter ratio,the starting time of the variable tube diameter pulsating heat pipe will increase.With the increase of the heating power,the difference between the starting time of the variable pipe diameter increases gradually.Under the same working conditions,the start-up time of the variable diameter pulsating heat pipe with methanol as the working medium is the shortest.With the increase of the diameter ratio of the variable pipe diameter,the thermal resistance of the pulsating heat pipe decreases first and then tends to be stable.At different filling rates,the optimal diameter ratio of the tube with variable pipe diameter is the best.When the filling rate is 40%,the influence of the variable pipe diameter on the pulsating heat pipe is stronger.At this time,the difference between the variable tube diameter pulsating heat pipe and the ordinary tube diameter pulsating heat pipe is the greatest.In the same working condition,the decrease degree of the heat resistance of the pulsating heat pipe with water,methanol and ethanol as the working medium is different,and the decreasing degree of the pulsating heat pipe with the methanol as the working medium is the most obvious.