Plume-Rise Effect on Natural Convection Heat Transfer in Staggered Arrays of Circular Heating Elements

The interactive effect of warm wakes induced by lower positioned heating elements on the natural convection of upper heating elements has been experimentally studied using a Mach-Zehnder interferometer. The heating elements consisting of circular horizontal tubes are arrayed in a staggered configuration. It is found that the qualitative behavior of heat transfer around each heating element is to some degree invariant with the tube spacing ratio and tube elevation in the tested range. Based on typical characteristic length, which includes tube diameter, tube spacing, and type of tube bundle arrangement, generalized correlating equations for average Nussell numbers on all tubes are presented in the modified Grashof number range of 1 x 10(5) to 2 x 10(8). The staggered arrangement of heating elements has always had a better heat-transfer performance than the in-line arrangement when other experimental conditions are maintained the same. However, the degree of enhancement depends on the tube spacing ratio.