Experimental investigations of dynamic fluid flow in oscillating heat pipe under pulse heating

In this paper, dynamic fluid flow inside a closed loop oscillating heat pipe (OHP) is studied with the aid of high speed camera. The characteristics and the dynamic behavior of vapor columns or bubbles under pulse heating with different heating powers and pulse durations are shown and discussed. Comparing with continuous heating mode with 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 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. 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.