Analysis of A Screen Type Solar Air Collector Without Transparent Cover
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The performance of a screen type solar air collector of different uniform mesh sizes and without a glass cover is investigated theoretically. Formulation of simultaneous radiation and convection heat transfer for a semi-steady condition in an isotropic, absorbing set of wire screens is presented. Both colimated and diffuse radiant heat fluxes are incident on the screens, causing absorption, reflection (scattering), emission and heating, the screens, which in turn heat the circulated air flowing normal to their surfaces. In the analysis, the interspacing of screens is chosen such that natural convection currents are prohibited. A set of theoretical equations is developed and solved numerically to obtain the temperature of the air at each screen level, and that leaving the collector. The results indicate that the performance of this type of collector could be further improved if the screens are designed such that the porosity of the upper layers is higher than that of the lower ones.