Numerical Simulation Study On Start-up And Stable Operation Of Pulsating Heat Pipe With Single And Mixed Working Fluid

Pulsating heat pipe has been regarded as an effective heat transfer way to electronic components cooling due to its advantages of simple structure,high heat transfer efficiency,high adaptability,low cost,etc.Until now,the gas-liquid two-phase flow,heat and mass transfer phenomenon has not yet been fully revealed in the working process of the pulsating heat pipe,and pulsating heat pipe working fluids are focused on pure substance.This paper set up some mathematical and physical models with quality,energy and momentum conservation equations by using the VOF model,CSF model and turbulent model to simulate and analyze the pulsating heat pipe of 2mm diameters and 5 bends based on its characteristics during start-up and stable operation stage return bends.In terms of choosing working fluids to stimulate the gas-liquid twophase flow,heat and mass transfer process and temperature variation characteristics of different working fluids(ethanol,methanol and acetone)during start-up,stable operation and heat transfer limit stages,The heat transfer characteristics of ethanolbased binary mixture pulsating heat pipe were studied.The working fluids were methanol mixed with ethanol and acetone mixed with ethanol separately.Mixed ratio of volume was 1: 1,3: 1 and 7: 1 under different working conditions of heat power(20 W,30 W,40 W,50 W and 60 W)and filling ratios(40%,50% and 60%).The results indicate that: In the operation process of the pulsating heat pipe,a stable circulation flow in one direction can be formed.With the increase of heating power,pulsating heat pipe will dry out locally when the heating power increases to a certain degree.The heating power for drying out onset of pulsating heat pipe using ethanol and methanol is obviously higher than that of the pulsating heat pipe using acetone.For the mixed working fluids under liquid filling rate of 40%,both methanol and acetone with different volume ratios' mixture of ethanol can effectively prevent or delay the emergence of pulsating heat pipe local dry-out phenomenon.And under larger heating power,the mixed working fluid heat pipe is much better than in heat transfer characteristics.Under medium filling rate of 50%,the mixture of acetone with different ratios of ethanol can also obviously restrain local dry-out.The heat transfer performance of pulsing heat pipe has been improved using the mixture of ethanol and acetone under higher heating power.When the filling rate reaches 60%,all 5 kinds of working fluids won't dry up locally.Compared to the single fluid,the mixed working fluid pulsating heat pipe did not show obvious advantages.