FEATURES OF GRAVITATIONAL FLOW OF HEATED AIR IN AN EXHAUST SHAFT ABOVE A MULTIROW FINNED BANK

The authors have carried out investigations into the introduction of hot-air heating systems in buildings and structures, and also the applicability of mixed convection in calorifers of recirculating air heaters. The heat transfer of two- and four-row staggered air-heater banks consisting of bimetallic fi nned tubes in mixed convection has been studied. Experimental investigations into the characteristics of a gravitational fl ow of heated air in an exhaust shaft above a heat-exchange bank in a mixed-convection regime have been presented. An increase of 1.5–3 times in the heat transfer in the mixed-convection regime compared to the heat transfer under conditions of free convection of the air has been established. The dynamics of motion of a geyser fl ow of heated air in the exhaust shaft above the heatexchange bank under gravity has been described. A decline of 20–50% in the heat transfer of staggered two- and four-row banks because of the presence of geyser air fl ows has been established. A method to diminish the adverse impact of geyser air fl ows on the heat transfer of the bank has been proposed.
   
Author:  A. B. Sukhotskii and G. S. Marshalova
Keywords:  air heating, gravitational movement of air, bimetallic fi nned tube, exhaust shaft, mixed convection, heattransfer coeffi cient, Nusselt number, Grashof number, geyser air fl ow
Page:  596