Investigation of the performance of pulsating heat pipe subject to uniform/alternating tube diameters

The present study examines the performance of closed-loop pulsating heat pipes (CLPHPs) with an ID of 2.4 mm. The effect of uniform and alternating tube diameter on the performance is investigated. The working fluids include distilled water, methanol and HFE-7100. Tests are performed with both horizontal and vertical arrangement. For the horizontal arrangement, when compared to uniform design, the alternating channel design can be started at a rather low heat input with a much smaller thermal resistance. Normally the thermal resistance is decreased with the rise of heat input, and reveals a minimum value at a certain heat input followed by shows a marginal rise when the heat input is increased further. Both uniform and alternating design reveals the similar trend. For the vertical arrangement, the thermal resistance is much lower than that in horizontal arrangement. Different from that in horizontal arrangement, the thermal resistance shows a continuous decline against heat input for all the working fluids. For a low input power, CLPHP with HFE-7100 shows the least thermal resistance. By contrast, CLPHP with distilled water shows the smallest thermal resistance when the input power is increased over 60 W.