To investigate the effects of pressure and air mass fraction on the condensation heat transfer in a vertical tube, experiments has been performed for steam-air mixture inlet pressures of 0.1, 0.2, and 0.4Mpa. Air mass fraction and mixture Reynolds number vary from 10% to 47% and from 4672 to 34310, respectively. Temperatures of the outer surface of the condenser tube, steam-air mixture bulk, and the coolant water are measured. The pressure of the upper plenum, the steam-air mixture flow rate, and the flow rate of the cooling water is measured, too. These data are reduced to give the local heat flux, heat transfer coefficient, condensate Reynolds number, air mass fraction, and Nusselt number. The local Nusselt number is correlated in terms of the local mixture Reynolds number, Jakob number, and air mass fraction.
It is found in this experiment that the condensation heat transfer coefficient increases as the air mass fraction of the steam-air mixture decreases and the system pressure increases. The condensation heat transfer increases with the increase of the diameter of the pipe connecting the steam generator and the test section. The increase of the venting from the lower plenum promote the condensation. When the steam-air mixture flows upward from the lower plenum, even at a low flowrate the countercurrent flow limitation phenomena is observed.