Please Answer: A particular house wall consists of three layers and has a surfac
ID: 1858242 • Letter: P
Question
Please Answer:
A particular house wall consists of three layers and has a surface area of 30 m2. The inside layer is 10 mm thick and made of plaster board with a thermal conductivity of k = 0.2 W/(m. degree C). The middle layer is made of fiberglass insulation with k = 0.04 W/(m middot degree C). The outside layer is 20 mm thick and made of wood siding with k = 0.1 W/(m middot degree C). The inside temperature is 20degreeC, and the convection coefficient for the inside wall surface is k, = 40 W/(m2 middot degree C). The convection coefficient for the outside wall surface is ho = 70 W/(m2.degreeC). How thick must the insulation layer be so that the heat loss is no greater than 400 W if the outside temperature is -20degreeC?Explanation / Answer
Req= R1+R2+R3+R4+R5=1/hiA+ L1/k1A+L2/k2A+L3/k3A+1/hoA Q=(Ti-To)/Req=400 Req= 0.1 L2/k2A= 0.1-(0.00083+0.0017+0.0067+0.00047)= 0.0903 L2= 0.10836 m=10.83cm