Premium
Combined forced and free convection in a reverse osmosis system
Author(s) -
Chang C. Y.,
Guin J. A.
Publication year - 1978
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690240616
Subject(s) - rayleigh number , buoyancy , mechanics , sherwood number , schmidt number , convection , stream function , concentration polarization , natural convection , combined forced and natural convection , boundary layer , thermodynamics , chemistry , nusselt number , classical mechanics , physics , vorticity , reynolds number , vortex , turbulence , membrane , prandtl number , biochemistry
The influence of combined forced and free convection on the performance of a reverse osmosis system in a horizontal circular pipe is examined. The free convective motion, which is superimposed upon the main axial flow, is caused by buoyancy forces arising from the buildup of a dense solute boundary layer near the membrane surface. The three‐dimensional convective diffusion problem is solved by dividing it into a perturbation part accounting for the buoyancy effects present for Ra ≠ 0 and a nonperturbation part for the intrinsic convective flow pattern present even when Ra = 0. An approximate solution to the nonperturbation equations is obtained from the literature, and the perturbation equations are solved using a stream function‐vorticity scheme valid for high Schmidt numbers. The effects of rejection parameter, Rayleigh number, and pressure parameter on the Sherwood number and concentration polarization are studied. Correlations are developed for the asymptotic Sherwood number and the effective axial length at which free convection becomes significant. The numerical results are in reasonable agreement with limiting analytical solutions and with the experimental asymptotic Sherwood numbers measured by Derzansky and Gill (1974) and Hsieh et al. (1976).