Simulation and Experimental Study on Vacuum Negative Pressure Infusion of Working Fluid for Micro Heat Pipes

Optimum filling ratio as an important parameter has a great effect on the heat performance of heat pipes. Especially for micro heat pipes with only hundreds of microliters of internal volume, their optimum filling ratios are hard to be obtained without the filling accuracy of an order of microliter magnitude. This paper simulated the filling process of water as the working fluid, and the change regularities of the pressure, the velocity and the volume fraction of liquid water were investigated. The simulation results show that the flow pattern of plug flow is the key to leading to the infusion error. The liquid-vapor slugs caused the pulsation of pressure and velocity, which would make the flow flux uncontrollable accurately. The maximum relative error in simulated filling ratios reached -1.8%, of which -1.6% was due to the slug flows as against only 0.1% due to phase change. To eliminate the influence of slug flows formed under negative pressure, a novel charging method with a buffer pipeline was proposed. Then a test of five groups of different charging quantities (20 mu L, 25 mu L, 30 mu L, 40 mu L, and 50 mu L) for two MHPs with about 100 mu L internal volume was carried out, and the results suggest that the mean absolute error is below 1 mu L.