CFD Analysis of Phase-Change Heat Transfer in Heat Pipes Using a Combined Boiling Model (CBM)

Predicting phase-change heat transfer in heat pipes represents a significant challenge owing to the complex interaction of boiling, condensation, and conjugate heat transfer mechanisms. This study presents a numerical investigation of a closed two-phase ther-mosyphon using the Combined Boiling Model (CBM) within a conjugate heat transfer (CHT) framework. The model combines wall boiling, film condensation, and bulk phase-change processes in an Euler–Euler multiphase formulation. Simulations were performed for heat loads ranging from 173 W to 376 W. The results were validated against experimental measurements and compared with predictions obtained using the VOF–Lee model. The CBM accurately reproduced key flow features, including vapour generation, vapour-pocket dynamics, and thin-film condensation, while reducing temperature de-viations typically below 3% in the evaporator and adiabatic sections and about 2 to 5% in the condenser. The results confirm that the CBM provides a physically consistent and computationally efficient approach for predicting evaporation–condensation phenomena in heat pipes.