Numerical analysis of transient heat and mass transfer for a water heat pipe under non-uniform heating conditions

•A transient CFD model of annular wicked water heat pipes is established.•The mass, momentum, and energy source terms are applied to simulate the phase change at the liquid–vapor interface.•The model predictions agree very well with experimental data in the literature.•The thermal-fluid characteristic under different adiabatic lengths, heating powers and heat distributions are analyzed. Non-uniform loads are widely present in heat pipe applications and have significant effects on their performance. In this work, a transient 3D CFD model is developed to investigate the liquid–vapor flow and heat transfer for a water heat pipe under various non-uniform loads. The source terms are added to the governing equations using the User-Defined Function (UDF) to simulate the evaporation and condensation process. The model is verified using the experimental and simulated data under uniform and non-uniform loads in the literature. The effects of key parameters including adiabatic length, heating power, and heat distribution on the thermal performance of heat pipes are analyzed. The results show that the non-uniform conditions would shift the maximum axial velocity of vapor to the unheated side and induce a significant circumferential flow in the wick region, especially in the evaporator section. The short adiabatic length and high heating power could reduce the elapsed time of reaching the steady state. The heat distribution in the evaporator section exhibits little effect on the elapsed time reaching the steady-state and the average steady-state vapor temperature