Microscale Oscillating Heat Pipe Model for Prediction of Start-Up, Oscillation Dynamics, and Dryout

Abstract Microscale oscillating heat pipes (OHPs) are a promising technology for thermal management of electronic devices, offering high effective thermal conductance and scalability for compact integration. Predictive modeling of OHPs at the microscale remains difficult due to extreme aspect ratios, complex two-phase transport, and transitions across multiple operating regimes. In this study, an efficient one-dimensional (1D) homogeneous model is developed to simulate unsteady two-phase flow dynamics of closed-loop microchannel OHPs, governed by conservation of mass, momentum, and energy. The homogeneous assumption treats liquid and vapor phases as uniform mixtures, enabling use of common variables?temperature, pressure, and velocity?to describe the flow. Thermophysical properties are expressed as functions of internal pressure and temperature, thereby capturing the thermomechanical cycles of vapor compression and expansion that drive OHP operation. The model is applied to multi-turn microchannel OHPs subjected to varying evaporator-to-condenser temperature differences. Simulations capture three operating regimes?pre-startup, oscillation, and dryout?and reproduce the strong dependence of thermal performance on regime. In particular, heat transfer enhancement is observed with the onset of oscillatory flow, consistent with prior experimental findings. The model further demonstrates robustness in predicting oscillations driven solely by internal thermomechanical instabilities, without requiring gravity, capillarity, or other external driving forces. Overall, the proposed framework provides a computationally efficient and reliable tool for investigating coupled thermal-fluid dynamics of microscale OHPs. These findings underscore the utility of homogeneous modeling approaches for guiding design optimization and advancing applications in next-generation thermal management systems.