The composite 1-dimensional wall consists of three materials with thermal conduc

Question

The composite 1-dimensional wall consists of three materials with thermal conductivities, kA = 20 W/m*K, kB = 15 W/m*K, and Kc = 50 W/m*K and wall thickness, LA = .3 m, LB = .3 m and Lc = .2 m. Under Steady state operating conditions, measurements reveal an inner temperature of Ts, 1 = 1 600 degree C, hot air temperature of T infinity, 1 = 1 800 degree C and heat transfer convection coefficient of 25 W/m^2K. The outside temperature T infinity, 4 = 4 30 degree C and the convection heat transfer h4 is unknown. Find the heat flux, overall heat transfer coefficient, convection heat transfer for the cold side and temperature at surface two.

Explanation / Answer

A = surface area

b = wall thickness

Thermal resistance due to conduction = b/(kA)

Thermal resistance due to convection = 1/(hA)

Taking A to be 1 m^2 we have,

Thermal resistance due to conduction = b/k

Thermal resistance due to convection = 1/h

Total thermal resistance of composite wall

= 1/h1 + b1/k1 + b2/k2 + b3/k3 + 1 /h4

= 1/25 + 0.3/20 + 0.3/15 + 0.2/50 + 1/h4

= 0.079 + 1/h4

Heat flux q = h1*(T1

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