Experimental Study of Mixed Convection from Horizontal Isothermal Elliptic Cylinders at Different Aspect Ratios

In this investigation, the mixed convective heat transfer from a horizontal isothermal elliptic cylinder has been experimentally studied. Three different elliptic test cylinders with the same perimeter and length (same surface area) are studied giving axis ratio (minor to major ratio) equal 1, 0.709 and 0.496. The buoyancy is due to the temperature difference between the test cylinder surface and incoming air. The corresponding Grashof number for the three test sections geometry are 9.8105, 1.5106, and 2.1106 respectively. In addition by varying the incoming air velocity, the Reynolds number varies from 111 to 1306. Consequently, the corresponding Richardson number was in the range of 1 to 102. The combined effect of natural and forced convection has been executed for angle of attack from 0° (assisting flow) to 180° (opposing flow) with an interval of 30°. The experimental results are presented in the form of average Nusselt number around the elliptic cylinder. It has been concluded that as the axis ratio decreases the average Nusselt number increases, in addition, increasing the angle of attack from 0° to 180° decreases the average Nusselt number considerably. New empirical correlation is obtained for the average Nusselt number as a function of the axis ratio, Richardson number and the attack angle. Keywords - Experimental; axis ratio; mixed convection; elliptic cylinder.