The perforated nature of nets makes it impossible to measure the thermal radiative properties (emittance, , transmittance, , and reflectance, ) correctly by using any measuring device under natural conditions. In this study, a theoretical model was developed and validated to predict , , and precisely by solving the model equations simultaneously. The net was tacked onto a wooden frame; thermal radiation balance was applied below and above the net surfaces and above a black substrate underneath the frame. The downward and upward thermal radiation fluxes were measured below and above the net to be used as input parameters to the simulation. Nets with different porosities () and colors were used for the study. The results showed that the estimated ranged from 0.41 to 0.82 and ranged from 0.16 to 0.55 for the nets tested, whereas the reflectances were very low (). The color and porosity together affect the properties of the net. Even though under equilibrium conditions of a net with the surrounding environment, the emittance of the net is equal to its absorptance. However, the absorbed thermal radiation by the net dose not equal to the emitted radiation and the difference is a convected heat.
Estimating the Thermal Radiative Properties of Shading Nets Under Natural Outdoor Conditions
Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 10, 2014; final manuscript received December 6, 2014; published online June 1, 2016. Assoc. Editor: Ziad Saghir.
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Abdel-Ghany, A. M., Al-Helal, I. M., and Shady, M. R. (June 1, 2016). "Estimating the Thermal Radiative Properties of Shading Nets Under Natural Outdoor Conditions." ASME. J. Heat Transfer. September 2016; 138(9): 091004. https://doi.org/10.1115/1.4032953
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