Heat and Mass Transfer on Laminar Forced Film Condensation of Pure Vapour

Abstract

On the basis of Chaps. 9 and 10, heat and mass transfer investigation is done under the new similarity analysis system for laminar forced film condensation of pure vapour. The heat transfer analysis equations are provided where the wall dimensionless temperature gradient becomes only one no-given variable for prediction of condensate heat transfer. By means of the condensate mass transfer analysis, the condensate mass flow rate parameter is induced as the function of the dimensionless condensate liquid film thickness and the interfacial dimensionless condensate liquid velocity components. It is found that the condensate mass flow rate parameter is the only one no-given variable for prediction of condensate mass transfer. Take the laminar forced film condensation of water vapour on a horizontal flat plate as an example, the systems of key numerical solutions on the wall dimensionless temperature gradient and mass flow rate parameter is obtained, and further rigorously formulated by using curve-fitting approach. With the rigorously formulated equations on the wall dimensionless temperature gradient and mass flow rate parameter, the theoretical analysis equations on condensate heat and mass become available for simple and reliable prediction of heat and mass transfer on laminar forced film condensation of saturated and superheated water vapour. Thus, the effects of the wall subcooled grade and vapour superheated grads on the condensate heat and mass transfer are clarified. Although increasing the wall subcooled grade causes decreasing the wall temperature gradient, it will increase the condensate heat transfer. Increasing the wall subcooled grade causes increasing the condensate mass flow rate parameter, and further causes increasing the condensate mass flow rate. Increasing the vapour superheated grade causes decreasing the condensate mass flow rate parameter, and further causes decreasing the condensate mass flow rate. Compared with the effect of the wall subcooled grade on heat and mass transfer of the forced film condensation, the effect of the vapour subcooled grade is so slight that it can be ignored in the special range of the superheated grade. At last, a condensate mass–energy transformation equation is reported in this chapter under the new similarity analysis system for a better clarification of the internal relation of film condensate heat and mass transfer.