Heat and mass transfer of countercurrent air-water flow in a vertical tube

The paper deals with the classification and the design features of direct contact heat exchangers used in various technological processes. It describes the existing two-phase flow regimes and the methods for heat and mass transfer prediction in heat exchangers with the direct contact of fluids in a vertical tube. The authors carried out the measurements of heat and mass transfer coefficients during the liquid film flow under the action of gravity towards the air flow in a vertical tube. The range of experimental variables is set to be the following: air mass flow rate is 1 center dot 10(-3)-4 center dot 10(-3) kg/s, air inlet temperature is 26-28 degrees C, air inlet humidity is 38-50 %, water mass flow rate is 1.5 center dot 10(-2) -4 center dot 10(-2) kg/s, and water inlet temperature is 55-58 degrees C. It is shown that an increase in the fluid flow rate leads to the heat and mass transfer intensification due to an increase of waves on the film surface. The authors obtained new empirical correlations for calculating convective heat and mass transfer coefficients. These equations consider the influence of the water flow rate for the film Reynolds number. The described methods are recommended to be used in the range of air Reynolds numbers from 2300 to 6700 and film Reynolds numbers from 600 to 1300.