Investigation and prediction of optimum meandering turn number of vertical and horizontal closed-loop pulsating heat pipes

Abstract

The objectives of this study are to experimentally investigate the effect of mean-dering turn numbers on thermal performance and to predict the optimum mean-dering turn number of vertical and horizontal closed-loop pulsating heat pipes. The closed-loop pulsating heat pipes were made from a Cu capillary tube with in-ternal diameter of 2.0 mm. The closed-loop pulsating heat pipes were bent into undulating tubes with various meandering turn numbers, such as 5, 7, 10, 16, and 30. Each set of the closed-loop pulsating heat pipes had different evaporator sec-tion lengths of 50 mm and 150 mm. Heat input was supplied to the closed-loop pulsating heat pipe by allowing the flow of distilled water as the heating medium through the evaporator section. The adiabatic section temperature was constant-ly controlled at 50 °C. It could be concluded that the optimum meandering turn number of vertical closed-loop pulsating heat pipes with an evaporator section length of 50 mm is 10 for both R123 and water, and the optimum meandering turn numbers of vertical closed-loop pulsating heat pipes with an evaporator sec-tion length of 150 mm are 5 and 10, respectively, for R123 and water. However, the optimum meandering turn number of the horizontal closed-loop pulsating heat pipes could not be found since the heat flux directly varies with the turn number. In addition, the correlation to predict the optimum meandering turn number of the vertical closed-loop pulsating heat pipes was successfully estab-lished.