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  1. A brick wall (k = 0.9 W/mK) of thickness 0.18 m separates the warm air in a room from the cold ambient air. On a particular Winter day, the outside air temperature is - 5°C and the room needs to be maintained at 27°C. The heat transfer coefficient associated with outside air is 20 W/m2K. Neglecting the convective resistance of the air inside the room, the heat loss, in (W/m2), is
    1. 88
    2. 110
    3. 128
    4. 160
Correct Option: C


Total thermal resistance

1
=
1
Rth
1
+
1
hk

1
=
1
= 4 w/m2K
Rth
1
+
0.18
200.9

Q =
∆T
[27 - (-5)] × 4 = 128 W/m2
Rth



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