Experimental Study of a Novel Helix-Shaped Oscillating Heat Pipe and Design Parameters for Flow Stabilization

A novel helix-shaped oscillating heat pipe (OHP) designed for enhanced heat transfer in thermal management and heat recovery systems was studied experimentally. Two orientations were explored: side-heated, which is the intended orientation in which improved fluid circulation is predicted, and bottom-heated, a control resembling traditional bottom-heated OHPs. Results showed stronger circulation, reduced temperature differences, and lower startup thresholds in most cases. The side-heated orientation achieved higher maximum heat loads at a fill ratio of 0.5, although the maximum load decreased at a fill ratio of 0.7. Notably, the helix-shaped OHP attained effective thermal conductivity values over 9,000 $WmK$ in multiple test cases and a maximum heat transport of 676 W. Additional parameters were explored, including heat load, fill ratio, condenser temperature, and the presence of noncondensible gases (NCGs). The presence of NCGs increased not only the temperature drop as expected, but also increased the maximum heat transport, indicating potential benefits in certain applications. Elevated condenser temperatures not only decreased the temperature drop, but also reduced maximum heat transport. A previously developed OHP performance model was expanded to evaluate the novel helix-shaped OHP. The model predicted temperature drops during degassed experiments under moderate heat loads reasonably well. However, most data points fell outside the model's scope, emphasizing the need to extend it to handle condenser bubble collapse. The expanded analytical models for side-heated helix-shaped OHPs highlighted a different set of restrictions on circulation than traditional, bottom-heated OHPs, which likely explains the superior performance of the helix-shaped OHP in its intended orientation.