Oscillating Heat Pipe Heat Transfer Mechanism And Oscillating Behavior Investigation Under Pulse Heating

In this paper, a pulsed direct current regulated power supply instead of normal continuous power supply was applied to heat the oscillating heat pipe through transparent electrical heating film which was evenly coated on the evaporation section. Simultaneous visualization and temperature measurement experiments were performed to investigate the impact of pulse heating on the temperature difference between evaporation section and condensation section, temperature fluctuation, flow pattern change and flow behaviors of oscillating heat pipe.The experimental results indicated that the temperature difference between the evaporation section and the condensation section under pulse heating mode is highly dependent on the pulse duration and heating power. Furthermore, it was found that the pulse duration and pulse interval play an important role on the oscillating period of the temperature.Compare with continuous heating under the same heating power, the fluid flow inside OHP under pulse heating shows three advantages. Firstly, the thickness of liquid film of vapor columns under pulse heating is thinner than those under continuous heating; Secondly, under pulse heating with small pulse durations, the power corresponding to dry out dry-out of OHP is larger than one under continuous heating, indicating that the regions for safe operations of OHP can be enlarged by employing the pulse heating mode; Thirdly, two types of annular flow (local motion and global motion respectively) under pulse heating have been identified.Under pulse heating, instantaneous formed large amplitude oscillation is observed due to a phenomenon termed as’injection-contraction’phenomenon, which simultaneously reinforces both the sensible heat transfer and latent heat transfer. When heating power equals to or is larger than 90 W, pulse heating accelerates the liquid reflux to evaporation section as the heating is stopped during pulse interval. Under pulse heating mode, the regions corresponding to the safe operations of oscillation heat pipe can be also extended.The analysis of the motions of vapor bubbles and columns reveal that there exist strong interactions between motions of different vapor bubbles or columns and phase changes at evaporation or condensation section also play an important role on the fluid flow inside OHP.