Optimal slot height in the jet cooling of a circular cylinder

Experimental results are presented for heat transfer cooling of an electrically heated circular cylinder, of diameter D=10 mm, by a slot jet, of height S=2.5 mm, i.e. with D/S=4. Mean and local Nusselt numbers are presented versus the Reynolds numbers, the distance of the cylinder from the slot exit, H, and the angle from the impinging point. Mean Nusselt numbers, defined according to the cylinder diameter, D, are higher than the values in an infinite flow. The maximum mean Nusselt number is measured when the cylinder is set at a distance H, from the slot exit, such that H/S=8. The minimum local Nusselt number is measured at an angle of 180° from the impinging point, i.e. on the rear of the cylinder. Comparisons have been done among the mean Nusselt numbers of this work and previous experimental results of the same authors, carried out with diameter to slot height ratios equal to D/S=1 and 2. The conclusion is that the mean Nusselt number, defined as , is higher for D/S=4, versus the Reynolds number, defined as ReD=WD/ν. On the contrary, the mean Nusselt number, defined on the basis of the slot height, , has similar values, for the different slot heights, versus the Reynolds number, defined as ReS=WS/ν, with the trend of higher results for the slot with D/S=2.