Heat-transfer enhancement using weakly ionized, atmospheric pressure plasma in metallurgical applications

Abstract

Experimental measurements and computational analysis of heat transfer in atmospheric pressure, midtemperature range (1200 to 1600 K) plasma flow over an aluminum cylinder have been carried out. A comparison of transient temperature measurements for the aluminum cylinder under convective unionized air flow and those with convective plasma flow shows significantly higher heat transfer from plasma flow compared to air flow under identical temperature and flow conditions. A heattransfer problem is computationally modeled by using available experimental measurements of temperature rise in the cylinder to determine the degree of ionization in the plasma flow. The continuity, momentum, and energy conservation equations, as well as conservation equations for electrons and ions, and the Poisson's equation for self-consistent electric field are solved in the plasma by a finite volume method. The conjugated transient heat transfer in the cylinder and in the plasma is obtained by simultaneous solution of the transient energy conservation equations. It is shown that the enhancement of heat transfer in plasma flow is due to the energy deposited by charged species during recombination reaction at the solid surface. An important finding is that even a small degree of ionization (<1 pct) provides significant enhancement in heat transfer. This enhancement in heat transfer can lead to a productivity increase in metallurgical applications.