Effect of non-condensable gas on the direct-contact condensation heat transfer of vapor in a convergent tube

The direct-contact condensation heat transfer of vapor in the presence of non-condensable gas (NCG) on the falling water column in a convergent tube was simulated with a two-phase boundary layer approach, and the variations of the condensation heat transfer parameters and the vapor condensation length were analyzed. Results show that the convergent angle has an important influence on the condensation heat transfer parameters. Both Nusselt and Stanton numbers rose as the convergent angle went up from 0(degrees) to 40(degrees). The increment in the convergent angle enhanced the condensation heat transfer coefficient from 1.06 to 4.8 times at the range of the vapor pressure from 1 atm to 3.6 atm. The increase in the inlet NCG mass fraction caused a reduction in the condensation heat transfer parameters. and its accumulation in the downstream where its mass fraction was over 90 %. The nozzle diameter and the inlet velocity and temperature of falling water column affected importantly the condensation heat transfer parameters. The vapor condensation length was increased with the rising inlet velocity. of falling water column, the vapor pressure and the nozzle diameter, while decreased with the ascending of the inlet NCG mass fraction and the convergent angle. The increment in the vapor pressure enhanced effectively the condensation heat transfer parameters, and weakened the adverse effect of NCG on the direct-contact condensation heat transfer.