Effects of vibration conditions on thermo-hydrodynamic performances of oscillating heat pipes with various diameters

This paper investigates the thermo-hydrodynamic performance of oscillating heat pipes (OHPs) with different inner diameters (1.5 mm similar to 3.0 mm) under vibration conditions. The effects of vibration frequency (25 Hz, 50 Hz, and 100 Hz) and amplitude (0.4 mm, 0.8 mm, and 1.2 mm) on the startup and quasi-steady heat transfer of OHPs were analyzed. Results indicate that increasing vibration frequency promote fluid flow in OHPs, while increasing vibration amplitude has the opposite effect. The impact of vibration frequency and amplitude on hydrodynamic characteristics is more pronounced in OHPs with larger diameters due to additional forces induced by vibrations. The startup performance is firstly weakened and then gradually improved with the increasing vibration fre-quency, indicating the flow resistance is increased under low-frequency vibration condition. The initial fluid movement in the OHPs starts more easily under low-amplitude vibration condition, and thus the startup per-formance is optimum when the vibration amplitude is 0.4 mm. In addition, the startup performance of OHP with the inner diameter of 1.5 mm is affected mostly due to the finite fluid volume. The heat transfer performance, for the OHP with 3 mm inner diameter, will not be improved until the vibration frequency is higher than 100 Hz, and it is reduced most under the vibration amplitude of 0.8 mm.