Heat transfer characteristics of micro-grooved oscillating heat pipes

To data oscillating heat pipes (OHPs) are traditionally fabricated by wickless capillary tubes. In this work, microgroove (micro-fin) structure was introduced to OHPs to improve the heat transfer performance. The heat transfer characteristics of micro-grooved OHPs was experimentally investigated and compared with smooth-tube OHPs at vertical and horizontal orientations. All of these OHPs were made from copper tubes and deionized water was used as the working fluid at a volumetric filling ratio of 50%. The internal diameters (IDs) of three smooth-tube OHPs are 3.4, 4.0 and 4.8 mm, respectively, and the internal hydraulic diameters (IHDs) of two micro-grooved OHPs are about 2.0 and 2.8 mm. Experimental results show that the microgroove structure enable a profound improvement of OHP performance and reduce the startup power input or temperature. Besides, the average evaporator temperature could also be reduced significantly. The effective thermal conductivity of vertically tested micro-grooved OHP with 2.0 mm IHD is as high as about 86,262 W/(m·K). The mechanism responsible for these results is presented and discussed. In practice the micro-grooved OHPs could provide a promising option for prospective applications of high energy utilization and conversion efficiency.