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Two sets of silicon-based micro pulsating heat pipes(SMPHPs) with trapezoidal cross section having hydraulic diameters of 352 μm(#1) and 394 μm(#2) respectively were fabricated for the first time using MEMS technology.With FC-72 as the working fluid,the start-up,steady operation state,as well as flow patterns were investigated using a CCD camera.It was found that the start-up process of these two SMPHPs was rather rapid.At the start-up period,no nucleation was observed,and the vapor plugs at the evaporator U-bends were formed mainly due to the breakup of liquid slugs.At the steady operation state,self-sustained oscillation with large amplitudes dominated the flow behavior when the inclination angle varied from 10° to 90°,but the nucleate boiling and bulk circulation were observed only in SMPHP #2.While bubbly,slug/plug,annular/semi-annular,and wavy-annular flows were observed in both two SMPHPs,the injection flow only appeared in SMPHP #2.
Two sets of silicon-based micro pulsating heat pipes (SMPHPs) with trapezoidal cross section having hydraulic diameters of 352 μm (# 1) and 394 μm (# 2) respectively were fabricated for the first time using MEMS technology. the working fluid, the start-up, steady operation state, as well as flow patterns were investigated using a CCD camera. It was found that the start-up process of these two SMPHPs was rather rapid. At the start-up period, no nucleation was observed, and the vapor plugs at the evaporator U-bends were formed mainly due to the breakup of liquid slugs. At the steady operation state, self-sustained oscillation with large amplitudes dominated the flow behavior when the inclination angle varied from 10 ° to 90 °, but the nucleate boiling and bulk circulation were observed only in SMPHP # 2. Whilst bubbly, slug / plug, annular / semi-annular, and wavy-annular flows were observed in both two SMPHPs, the injection flow only occurred in SMPHP # 2.