Onset and performance of a two layer oscillating heat pipe in a heat spreader

Experiments were performed to characterize a two-layer oscillating heat pipe in a heat spreading plate heated locally on one side and cooled throughout the other side. The 23-turn oscillating heat pipe with 2 mm hydraulic diameter square channels and interconnected between the layers was charged with a 70 percent fluid loading of degassed DI water. The effect of heating location, operating temperature and orientation were examined. The results showed that the thermal conductance (W/K) of the plate could be increased by more than 100 percent for a heater position near the edge of the plate but less for a central position where conduction through the plate was more effective. The change in the thermal conductance of the oscillating heat pipe path with the effective heat transfer through this path appeared independent of heater position but decreased modestly with operating temperature and for a horizontal plate orientation. The operation of the oscillating heat pipe was correlated using the heated wall superheat and the change in saturation pressure with temperature. The results suggest these were inversely correlated but the boundary delineating the onset of operation depended on orientation. Evidence of hysteresis effects and suppression of oscillation were observed.