A momentum integral model for prediction of steady operation and flooding in thermosyphons

An analytical momentum integral model is developed for the prediction of the steady operation of closed two-phase thermosyphons over a wide range of temperatures, pressures and heat inputs. Using a new proposed velocity distribution for the flow of the liquid film, differential equations for mass, momentum, and energy balances have been solved simultaneously to obtain the continuous solution for the thickness of the liquid film, mass flow rate, and heat transfer along the length of the condenser. The interfacial shear due to phase-change at the liquid–vapor interface, as well as acceleration of the condensate film in the momentum balance equation, has been taken into account. The current model uses minimal number of semi-empirical correlations for interfacial shear and heat transfer coefficient and utilizes self-consistent assumptions. The current model is able to accurately predict the essential performance parameters of the system including local and overall mass flow and heat transfer rates through the length of the condenser for a wide range of low to medium heat inputs, up to the flooding limit. Despite the simplicity of the model in comparison to previous studies, the predictions for local mass flow rates and heat fluxes are in excellent agreement with available experimental data.