Effect of aperture geometry on heat transfer in tilted partially open cavities

Free convection from a square, tilted partially open cavity was investigate d experimentally. The experiment was carried out to study the effect of the aperture geometry art the heat transfer between the cavity and the surroun ding air. Four different geometrical arrangements for the opening were inve stigated: (1) high wall slit, (2) low wall slit, (3) centered wall slit, an d (4) uniform wall slots. Each opening arrangement was studied at opening r atios (i.e., ratio of opening height to cavity height) of 0.25 0.5 and 0.75 . The average heat transfer coefficient between the cavity and the surround ing air was estimated for each geometrical arrangement for tilt angles rang ing from -90 deg to +90 deg with increments of 15 deg and at a constant hea t flux Grashof number of 5.5 x 10(8). The results sheaved that for tilt ang les between 90 and 75 deg, the heat transfer coefficient has a small value that is independent of the geometrical arrangement of the opening. The valu e of the heat transfer coefficient increases sharply with decreasing tilt a ngle until an angle value of zero degrees is reached The increase in the he at transfer coefficient continues in the negative range of tilt angle but n ot in the same rate as in the positive range of the tilt angle. The uniform slot arrangement gave in general higher heat transfer coefficient than the other three arrangements of the opening. Large differences in the heat tra nsfer coefficient were observed between the high and the lout wall slits wh ere the high wall slit is found to transfer more heat to the surroundings t han the low wall slit. Correlations were developed to predict the average N usselt number of the cavity in terms of the opening ratio and the cavity ti lt angle far cavities with high wall slit, low wall slit, centered wall sli t, and the uniform wall slots.