EFFECT OF SHERWOOD NUMBER ON CRITICAL CONSTANTS OF DIFFUSION

Critical constants of mass diffusion through a membrane were related t o a critical time, t(c)', which designates the conversion between tran sient and steady-state conditions of the diffusion process. The critic al time t(c)', is precisely defined and analytically derived. In their dimensionless form, these critical constants depend solely on the She rwood number (Sh). Values of dimensionless critical constants were det ermined for the whole range of Sherwood numbers. The results are usefu l in cases where small amounts of diffused mass must be detectable. E. g.: in production from hazardous materials, in the design and evaluati on of diffusion experimental processes and devices. The effect of meas urement errors on the determination of the critical constants is also analyzed. The main results show that the evaluation of the critical co nstants is obtained a with minimum errors? when experiments are being performed under convective boundary conditions (Sh > 100). The results of this study are applicable to heat transfer problems as well. (C) 1 998 Elsevier Science Ltd. All rights reserved.