a) The heat transfer rate without insulation. b) The thickness of the insulation if the material of the layer is polyurethane foam (k = 0.025 W⁄m ∙ °C) c) The thickness of the insulation if the material of the layer is fiber glass (k = 0.036 W⁄m ∙ °C)
Consider a wall of 6-m x 2.8-m constructed by the following three
layers: plaster with a thickness of 1 cm (k = 0.36 W⁄m ∙ °C),
brick with a thickness of 20 cm (k = 0.72 W⁄m ∙ °C) and wall
covering with a thickness of 2 cm (k = 1.4 W⁄m ∙ °C). Disregard
the effect of convection in the inner surface of the wall and consider
the inner temperature of the wall to be 23 °C. Consider the
temperature of the surroundings to be 8 °C. The heat transfer rate
in this wall must be reduced by 90% by the installation of a layer
of insulation. If heat transfer between the outer surface of the wall
and the surroundings is by natural convection (12 W m2 ⁄ ∙ °C)
and radiation, and considering the outer wall to be black with a
temperature of 9 °C, determine:
a) The heat transfer rate without insulation.
b) The thickness of the insulation if the material of the layer is polyurethane foam (k =
0.025 W⁄m ∙ °C)
c) The thickness of the insulation if the material of the layer is fiber glass (k = 0.036 W⁄m ∙ °C)
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