Effects of Inclination Angle on Oscillating Heat Pipe Thermal Conductance and Dryout

Abstract

Predicting the operational limits of oscillating heat pipes (OHPs) under varying gravitational orientations remains a significant challenge for terrestrial and aerospace thermal management systems. The current paper extends and validates a previously reported two-dimensional conjugate heat transfer model to quantify the effect of inclination angles on the thermal performance and dryout behavior of an OHP filled with butane. The model couples a solid plate heat conduction module with a one-dimensional fluids module using the immersed boundary method. The gravity term has been added in the momentum equation to account for gravitational effects. Additionally, a novel computational method is used to simulate perfectly insulated edges on the plate and this updated approach accommodates complex OHP geometries in the future. The proposed model is quantitatively validated against terrestrial experiments across multiple inclination angles, demonstrating good agreement in predicting both steady-state thermal conductance and transient dryout thresholds. We characterize three representative cases: normal pseudo-steady operation, switching operation, and dryout. Finally, we observed that the dry fraction exhibits a strong correlation with the temperature difference and thus represents a key parameter controlling the thermal performance.