1. During the winter, the inside of an average house is maintained at 20 °C, while the outside temperature is 0°C. Assuming that the only mechanism of hoat transfer is conduction, the walls are 10 cm thick and the heat conductivity of the walls is 0.5 W(K.m). ai Calculate the heat flux from the room to the surroundings i bi To reduce the heat loss through the walls, the material should be changed to an insulator material. The new overall conductivity will be 0.1 W/(K.m); the thickness of the walls is maintained. Calculate the reduction of the heat flux through the walls compared to the initial case.
1. During the winter, the inside of an average house is maintained at 20 °C, while the outside temperature is 0°C. Assuming that the only mechanism of hoat transfer is conduction, the walls are 10 cm thick and the heat conductivity of the walls is 0.5 W(K.m). ai Calculate the heat flux from the room to the surroundings i bi To reduce the heat loss through the walls, the material should be changed to an insulator material. The new overall conductivity will be 0.1 W/(K.m); the thickness of the walls is maintained. Calculate the reduction of the heat flux through the walls compared to the initial case.
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Transcribed Image Text:1. During the winter, the inside of an average house is maintained at 20 °C, while the outside temperature is 0 °C. Assuming that the only mechanism of
heat transfer is conduction, the walls are 10 em thick and the heat conductivity of the walls is 0.5 w/(K.m).
a) Caleulate the heat flux from the room to the surroundings in Wm.
bị To reduce the heat loss through the walls, the material should be changed to an insulator material. The new overall conductivity will be 0,1 W/(K.m); the
thickness of the walls is maintained. Calculate the reduction of the heat flux through the walls compared to the initial case.
2. A solar collector with an area of 1.5 m2 is installed on the rooftop of a heuse. Assume that the radiative energy amiving from the sun is 1000 Wm, The
collector reflects 10% of the energy arriving on its surface. Also, the collector is not perfectly insulated, and losses occur. The collector has a heat transfer
cocfficient h of 2 Wm2K!, The side arcas of the collector are assumed to be negligible. The ambient temperature is 20 °C and the collector is assumed to
be at a temperature of 50 °C. Consider thut this temperature is constunt throughout the whole collector. The collector is assamed to behave like a black
body.
u) What is the power output of the collector?
bị What percentage of the total losses is caused by radiation?
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