Mixed Forced and Natural Convection Mass Transfer

2 Mixed Forced and Natural Convection Mass Transfer 

The data correlations presented in the previous section include both forced convection and free convection processes. In nature as well as engineering applications, there are 

Additivity of Grashof numbers. For the combined mixed free-convection heat and mass transfer the procedure is to replace the Grj or GrA with Grj + GrA, the sum. For example. Equation 2.31 in Table 2.3 becomes 

The limitation on this procedure is Sca — Pr and this is frequently the case for transport processes in air. Since the thermal Grashoff number is normally much larger, neglecting the interaction would greatly underestimate the MTC. 

Free convection heat transfer as a source of forced convection mass transfer. It has been demonstrated on numerous occasions that the Chilton-Colburn analogy appearing in Table 2.3 is applicable for converting a forced-convection Nusselt number to a forced-convection Sherwood number as a means of converting the imbedded HTC into its equivalent MTC. In the present situation, the thermal buoyant forces provide the momentum source, which in effect provides the forced-convective flow that drives the mass transfer process. In addition, Grj Gta and Sc Pr. For this case the alternative equation is 

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