The convective rates of heat transfer through inclined longitudinal slots is studied for the case where heat is transferred from a lower heated isothermal surface, through the slots, to an upper cooled isothermal surface. Experimental data are given for longitudinal slots having aspect ratios from 6–12, slot heights of 25–60 mm, inclinations from horizontal to vertical, and Ra < 107. Data are also given for a transverse slot of aspect ratio 6, for inclinations from horizontal to vertical, and Ra < 107. It is shown that convective heat transfer rates are essentially independent of slot orientation for inclinations up to 15 deg from the horizontal, but longitudinal slots are more effective in suppressing natural convection than transverse slots with the same aspect ratio, for inclinations from 24 to 75 deg from the horizontal. The difference in heat transfer rates for longitudinal and transverse slots inclined between 24 and 75 deg from the horizontal are shown to be due to different convective flows occurring in each slot. The heat flow measurements are supported by convective flow visualization experiments which demonstrate the modes of convective flow within slots.

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A new apparatus that incorporates an integrating sphere is described, which enables the solar transmittance of test samples to be measured as a function of both angle of incidence and azimuth angle. This apparatus was developed to perform measurements on both planar and nonplanar samples of larger dimensions than can be accommodated in a spectrophotometer. Solar transmittance measurements from this apparatus are compared with those from a Gier & Dunkle spectrophotometer for a range of sample materials, and excellent agreement has been found. Errors in solar transmittance measurement may arise from changes in the integrating sphere entrance port reflectance due to placement and then the removal of the test sample from the port. A correction procedure is derived to take account of these errors and is applicable to all single-beam integrating spheres.

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