Question

[6] A 20-cm thick wall of a house made of brick (k = 0.72W/m. C) is subjected to inside air at 22.C with a convection heat-transfer coefficient of 15 W/m2. C. The inner surface temperature of the wall is 18 C and the outside air temperature is -1 °C. Determine the outer surface temperature of the wall and the heat-transfer coefficient at the outer surface.

Answer 1

. Assuming steady state heat transfer condition The Limit' area of wall perpendicular to plane is considered Since heat transfer is steady stalo 야 = constant 2 TB=18 TC = ? q TA=22°C A h=155/20 TD= -1°C K= 0.72 WM- 11 hours qur (L2 k0.20m TA Тв Тр Тc WWW Riha A B Rother Rha 4 hoxlarea) Notein Area=1m2 h Area] KareArea) Considering convection between point A to pomt B TA-TB 60 Watt » q th 4) AA - q = 60 watt 22-18 a = Scanned with CamScanner

considering heat { transfer from poml A to pont c − q = T-TC hrank Area) 0.72/ I 22 - 1 T +0.2 + KxtAreas 15x4 60 = 22-TC 0.3444) 22-TC = 60 X0.3444 = 20:666 Tc = 20-20.666 Temperature at outer wall surtaro (TO =-0.666°C Considering heat this tranfer from ouder wall surface to air - (Tc - TD 와 hox Area >-0066-(-03-0666+/ 60 The ho hp ( 0.334) = 60 hp = 179.64 W/m2. C Heat transfer coefficient of outer surface Chall 179.64 W/m².c Scanned with CamScanner