4. A diffusion-convection system is shown to the right, in which liquid A is evaporating into gas B. The liquid level is kept constant at z = z1. At the liquid-gas interface, the gas phase mole fraction of A is XA1. A stream of gas mixture A-B of concentration XA2 flows slowly past the top of the tube, to maintain the mole fraction of A at XA2 at Z = Z2. The entire system is kept at constant temperature and pressure. Gases A and B are assumed to be ideal. This evaporating system is at steady state, and there is a net motion of A away from the interface and the species B is stationary. The rate of evaporation of A is as follows: NAz = CD AB InB2 Z2-Z1 XB1 Derive the above expression, starting with the following equation: Gas stream of A and B z=22 + Az NA + ↑ NA:\ z=2₁ Liquid A дха NAZ = XA(NAZ +1 +NBz)-CDAB dz Note that XA is not small and cannot be omitted. Derive the rate of evaporation of A without finding the concentration profile. Use a shell balance to determine in Naz is constant.

ISBN: 9781259696527

Author: J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart

Publisher: McGraw-Hill Education