Condenser thermal performances, such as the back pressure and venting rate, are strongly affected by the tube arrangement. Condensers have three irreversible processes for the fluid flow, heat transfer and mass diffusion.The condenser venting rate is studied here based on an air mass entransy analysis. The air mass entransy increment rate for the steam and air mixture on the condenser shell side is expressed as a function of the distributed air mass fraction and the steam condensation rate to define the relationship between the condenser venting rate and the flow parameters. Condensers with three typical tube arrangements were analyzed numerically using the porous medium model. The results show that a bigger venting rate always corresponds to a smaller air mass entransy increment rate. The air mass entransy generally decreases in the air concentration region and increases in the air cooling region under the combined action of the air diffusion and steam condensation. The numerical results indicate that the air cooling region of a condenser should be carefully designed and the cooling tubes should be properly arranged to guide the steam flow so as to weaken air concentration,and consequently to decrease the venting rate. Condenser thermal performances, such as the back pressure and venting rate, are strongly affected by the tube arrangement. Condensers have three irreversible processes for the fluid flow, heat transfer and mass diffusion. Condenser charge rate is studied here based on an air mass entransy analysis. The air mass entransy increment rate for the steam and air mixture on the condenser shell side is expressed as a function of the distributed air mass fraction and the steam condensation rate to define the relationship between the condenser venting rate and the flow parameters. Condensers with three typical tube arrangements were analyzed numerically using the porous medium model. The results show that a larger venting rate always corresponds to a smaller air mass entransy increment rate. The air mass entransy generally decreases in the air concentration region and increases in the air cooling region under the combined action of the air diffusion and steam condensation. The numerical resu lts indicate that the air cooling region of a condenser should be carefully designed and the cooling tubes should be properly arranged to guide the steam flow so as to weaken air concentration, and compact to reduce the venting rate.