Heat transfer from flat plates to an air let

Abstract

Heat transfer from an electrically heated flat plate to an air jet at different angles of attack was investigated. Brass plates of diameters 1 in., 2 in., 4 in., 5 in., 6 in., and 8 in. were used in the study. The jet diameter at the nozzle exit was 6 inches. The surface temperature of the plate was varied from 100°F to 250°F, and the jet velocity at the nozzle exit was varied from 50 ft/sec to 170 ft/sec. The heat transfer data at = 90° and for different ratios of the distance of the centre of the plate from the nozzle exit to jet diameter, HD\frac{H}{D}DH , were correlated and are presented below.

(i) Heat transfer close to the stagnation point Shtot=0.007(Retot)0.86Sh_{\text{tot}} = 0.007 \left( Re_{\text{tot}} \right)^{0.86}Shtot =0.007(Retot )0.86 Valid for:

1<HD<51 < \frac{H}{D} < 51<DH <5 5.8×104<Retot<2×1055.8 \times 10^{4} < Re_{\text{tot}} < 2 \times 10^{5}5.8×104<Retot <2×105

(ii) Heat transfer from plates smaller than or equal to the size of the jet Shtot=0.045(Retot)0.70Sh_{\text{tot}} = 0.045 \left( Re_{\text{tot}} \right)^{0.70}Shtot =0.045(Retot )0.70 Valid for:

1<HD<51 < \frac{H}{D} < 51<DH <5 7×104<Retot<4.5×1057 \times 10^{4} < Re_{\text{tot}} < 4.5 \times 10^{5}7×104<Retot <4.5×105

(iii) Heat transfer from plates larger than the size of the jet (Sh, )=K Retotn(Sh, \, \theta) = K \, Re_{\text{tot}}^{n}(Sh, )=KRetotn Valid for:

1<HD<51 < \frac{H}{D} < 51<DH <5 1.2×105<Retot1.2 \times 10^{5} < Re_{\text{tot}}1.2×105<Retot

Heat transfer data at other angles of attack and for different HD\frac{H}{D}DH values have also been correlated and presented in the thesis. Heat transfer increased for all plates in the region 1<HD<51 < \frac{H}{D} < 51<DH <5. Investigation of the effect of angle of attack of the plate with respect to the jet showed that decreasing the angle of attack from 90° (normal flow) to 0° (parallel flow) increased the heat transfer.