A Constrained Vapor Bubble (CVB) with a relatively large Bond number formed by partially underfilling liquid in an evacuated cavity is capable of high thermal conductance. It operates on the principle of closed loop phase-change along with capillarity to circulate the working fluid. Analytical investigations were conducted to compare with existing experimental data. A steady-state fluid flow model combined with a two-dimensional heat transfer model was developed and solved to yield key operating parameters (i.e., temperature and liquid meniscus curvature) of the CVB. The modeling results of the outside wall temperature in the evaporator were found to agree well with the measured experimental data. An area average heat transfer coefficient was used to characterize the heat transfer on the inside wall of the evaporator, The value of this heat transfer coefficient was found to increase with the heat flow rate. The fluid flow model with the heat transfer model in the evaporator to provide the energy balance was used successfully to fit the experimental curvature data. The mass flow rate in the bottom corners of the CVB was found to be higher than that in the top corners due to the gravitational body force.