HEAT-TRANSFER UNDER MULTIPLE SLOT JETS IMPINGING ON A PERMEABLE MOVING SURFACE

Local and average heat transfer were measured for a system of multiple jets impinging on a moving permeable surface at which there may be throughflow. Multiple jets were confined by a hood, as is required industrially for thermal efficiency. Exhaust ports located symmetrically between the jet nozzles eliminated crossflow, otherwise a strongly detrimental effect. Impingement surface motion decreases average heat transfer, by 17% at industrially relevant values of the surface motion parameter, Mvs. Enhancement of impingement heat flux by throughflow is linearly additive. Expressed as ΔSt, this enhancement depends only on the throughflow parameter, Mus, with ΔSt/Mus = 0.17. For typical operating conditions, withdrawal as throughflow of only 10% of the jet flow increases mean Nusselt number by over 50%. Industrial design modeling for the potential process of combined impingement and throughflow drying of wet webs such as paper is demonstrated. Copyright © 1990 American Institute of Chemical Engineers