The total heat transfer rate and average heat flux through the walls of each of

Question

The total heat transfer rate and average heat flux through the walls of each of two rooms, is to be determined. Ambient air on the outside of the building approaches parallel to the wall, with freestream velocity and temperature of uinfinity = 7 m/s and Tinfinity,2 = -20 degreeC. Both walls have the same inside air temperature (Tinfinity,1 = 20 degreeC) and heat transfer coefficient (h1 = 5 W/m2.K) and the same wall thickness and material (L=0.25 m and k = 1 W/m.K). Room A has a larger wall area (13m wide times 3.5 m high) and is a comer room of the building. Room B has wall area (7m wide times 3.5 m high), as shown in the figure. For each room wall, find the total heat transfer rate, as well as the average heat flux for the room wall. Does the wall for Room A or Room B have the higher heat flux value? Should we have expected this one to be higher -justify your answer.

Explanation / Answer

Total heat transfer rate for room 1= ? T/R

                                = 20-(-20)/1/h1+L/k*A

                                = 40/.2+5.49 x10-3

                                =195.12W

Hence flux = 195.12/35.5= 4.2W/m2

For room 2 since area= 7*3.5=24.5 m2

Total heat transfer rate for room 2=40/.2+(.25/1*24.5)

                                                                =190.29 W

Heat flux=190.29/24.5=7.76 W/m2

Wall for Room B have higher flux value

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