Thermodynamic and thermal perspectives of failure in oscillating heat pipe

Oscillating heat pipes (OHPs) have garnered significant attention for thermal management applications due to their high heat transfer efficiency, ease of miniaturization, and adaptable form factor. However, their operation can be prone to failure under unpredictable heat input conditions, potentially leading to device malfunction. The mechanisms driving such failures remain poorly understood, thereby complicating efforts to reliably predict OHP performance limits. In this study, the operational limit at which OHP failure occurs is experimentally identified, and two predictive criteria—thermal convergence and the thermodynamic saturation limit—are introduced to explain and predict the onset of such failure. A 14-tube OHP is fabricated, with the evaporator and condenser sections constructed from copper tubing, and the adiabatic section made of non-conductive, transparent glass tubing. Temperature and pressure measurements are obtained from a selected tube for three working fluids: water, methanol, and ethanol. OHP failure is directly observed during experiments conducted with water as the working fluid. The predictive capability of the two criteria is validated using the experimental results for water, and subsequently applied to methanol and ethanol, enabling failure prediction without operating the OHP to the point of failure.