We numerically studied the thermal-hydraulic characteristics of a pump-driven two-phase (liquid–vapor) heat transport device. The volume of fluid (VOF) method was adopted to capture the liquid–vapor interface, and the temperature recovery method was used to estimate heat and mass transfer due to the phase change. First, we tested our model on two-dimensional film boiling and condensation problems. The numerical heat transfer coefficient results for the film boiling and condensation problems agreed well with Klimenko's and Nusselt's correlations, respectively, confirming the reliability of our model. Further, the effect of pressure difference in the flow channel on the heat transport performance of the device with phase change was investigated. In the case of a small pressure difference, the working fluid underwent a complete phase change and became superheated or subcooled. Conversely, increasing the pressure difference led to vapor plug thinning and liquid film thickening (around the vapor plug), which suppressed heat transfer via phase change.