Effects Of Channel Structure On Heat Transfer Performance Of Pulsating Heat Pipes

Pulsating heat pipe (PHP) is a new type of heat pipe with high efficience of heat transfer performance. The considerable interest in sucha heat pipe is due to its simple structure and high heat transfer performance. It has a promising future for dissipating high grade heat in high power LED field. The inner diameter is small egough so that there are many liquid slugs and vapor plugs in the tube. The temperature difference between the evaporation section and the condensation secetion is the driving force for the movement of the liquid slugs. The two-phase system which embodies multi-disciplinary physics is so complicated that the investigation on pulsating heatpipes is still ata primary stage. Forthis, many scholars made a number of studies in this field. The movement of liquid slug is very important for the heat transfer performance. We can change the movement condition to improve the efficiency of the pulsating heat pipe. Therefore, this dissertation aims to discover the effects of the structure of the pulsating heat pipes.Four kinds of different heat pipes were designed on the basis of an pipe with uniform rectangular channel structure. There were periodic expansion-constriction cross-sections in the channels, and experiments with different charging ratios were conducted. Besides, a new kind of pulsating heat pipe with two sides of channels were designed. The effects of inclination angles for the heat transfer performance and start-up were investigated. These studies can provide experimental support to improve the applicability of pulsating heat transfer performance and different installation environments and the feasibility of the application of high-power LED heat pipe cooling field.A series of experimental studies have shown that because of sharp corners, a rectangular cross-sectional structure of the pulsating heat pipe structure can promote and improve the movement of liquid slugs and the liquid backflow in evaporating section, so it has a better heat transfer propertie. In the periodic expansion-constriction cross-sections in the channels, the forces were different on the both sides. That causes asymmetric vapor-liquid interface and promotes the mixing effect of the liquid inside. Besides, the residual liquid in the evaporator section grooves will reduce dry wall area and promote liquid evaporations, helping improve the pulsating heat transfer performance. Compared with 1# heat pipe, the heat resistance of 3# heat pipe reduced 4%～32%,4%～25% and 6%～18%. However, when the hydraulic diameter is small, the liquid movement is hindered subject to greater resistance, leading to deterioration of the heat transfer performance.In the research for the double-sided rectangular channel heat pipe, the greater the angle, the greater of the gravity on the liquid, and the better the heat transfer performance. The larger heating power, the shorter the start-up time of the pilsating heat pipe and the higher the operating temperature when steady movement occurs.