Natural convection in binary gases with simultaneous heat and mass transfer across a cavity

John Alan Weaver, Purdue University

Abstract

Natural convection in binary gases with simultaneous heat and mass transfer across a cavity was investigated experimentally and analytically considering both augmenting and opposing body forces. The physical phenomenon has various technological applications from crystal growth and vapor deposition to heat and mass transfer in buildings and containments of nuclear reactors. The steady-state conservation equations of mass, momentum, energy and species and the corresponding boundary conditions for natural convection due to horizontal temperature and concentration gradients was solved using a finite-difference algorithm. The effects of variable properties, interdiffusion of species, Soret mass flux and Dufour energy flux on the fluid flow and heat and mass transport processes were examined. Experiments involving natural convection in binary gases due to horizontal temperature and solutal gradients and due to horizontal temperature and vertical solutal gradients were performed. Measured temperature and concentration data obtained using thermocouple probes and Mach-Zehnder interferometry and smoke flow visualization were compared with predictions obtained from a mathematical model which utilized the Boussinesq approximation. The flow field is significantly changed when the solutal buoyancy force opposes the thermal buoyancy force. However, the solutal buoyancy force does not dominate the system for all values of the buoyancy parameter (N$\sp\*)$ less than zero for vertical concentration gradients. The flow field becomes unsteady for all values of N$\sp\*$ less than zero for natural convection due to horizontal temperature and concentration gradients. For natural convection due to horizontal temperature and vertical concentration gradients, the flow field is unsteady for N$\sp\*$ = $-$4.581 and $-8$.702. The comparison between flow visualization and predicted streamlines is typically good except when the flow is unsteady. In contrast, the comparison between predicted and measured temperature and concentration distributions due to horizontal temperature and vertical solutal gradients is typically poor. The agreement between measured and predicted temperature and concentration distributions due to horizontal temperature and solutal gradients is good at lower negative values of N$\sp\*$, but the discrepancy is greater at larger negative values of N$\sp\*$ due to the unsteady flow. Overall, the mathematical model utilized could not predict quantitatively the temperature and concentration fields.

Degree

Ph.D.

Advisors

Viskanta, Purdue University.

Subject Area

Mechanical engineering

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