Novel Flat Plate Evaporator Of Loop Gravity Assisted Heat Pipe For High Heat Flux Electronic Cooling

With the rapid development in the electronic industry,electronic devices have been widely used in several areas and are developing toward miniaturization and high heat dissipation.Therefore,it is paramount to design cooling equipment with compact structure,reliable performance,flexible installation,and high heat transfer capacity.The two-phase loop gravityassisted heat pipe(LGHP)system,which is a type of phase-changed,passive,and indirect liquid cooling design,was proved to be applicable and reliable in cooling electronic devices with high heat fluxes.Compared with pump driven cooling system,the loop heat pipe does not require any pump or capillary action;thus,the system stability and reliability are greatly increasing and the maintenance costs become lower.However,a fundamental weakness of this system is the limited critical heat flux(CHF).Therefore,strengthening the heat transfer and flow performance to improve the CHF is extremely important for the LGHP.To solve the problem of heat dissipation in high heat flux electronic devices,a flat-type loop gravity-assisted heat pipe with upper and lower surfaces connected by a plurality of square columns is designed.An experiment was performed to study the heat transfer performance and CHF under different heating loads.The effect of evaporator placement and working fluid on heat transfer performance was also tested.To further explore the influence of different working fluids on the CHF,this study investigates both experimentally and theoretically the method to choose the working fluid for the loop gravity-assisted heat pipe.Based on CHF theory and fluid mechanics,a pressure drop model is established to yield a dimensionless number of X and self-circulating dynamic coefficient L,where the parameter L is only related with the properties of working fluid.We found that the CHF is positively correlated with the values of X and L.Consequently,the fluid property parameter L is proposed as a criterion to choose the working fluid for the LGHP system.