Operational characteristics of oscillating heat pipes under micro-gravity condition

A mathematical model to investigate the oscillating motion characteristics of liquid slugs and vapor plugs/bubbles in oscillating heat pipes (OHPs) was developed considering the contact angle hysteresis (CAH) and interconnected-tube induced pressure fluctuations. Results show that a short period less than 1 s is available to attain the steady state after startup and then the oscillation amplitudes and frequencies for both of slug/bubble displacement and velocity are kept fixed. The slug/bubble displacement and velocity display quasi-sine oscillating waves with small pressure fluctuations induced by the interconnected-tube. However, small oscillation waves are superimposed on a main quasi-sine oscillation wave and cause a chaotic oscillating behavior of slug/bubble inside the OHP if the induced pressure fluctuation is large enough. Besides, the effects of filling ratio, tube length, inner diameter, temperature difference between the evaporator and condenser sections, and working fluid on the oscillating motion were numerically analyzed and discussed. The numerical model provides a physical insight to understand the operational mechanism of OHPs under the microgravity condition.