Answer Happy

Question 5 Based on Fourier Law of Heat Conduction, show that the overall heat transfer coefficient Uo through a plane wall with thickness Ax and conductivity k is given by 1 (a) (b) Vo = 1 Ax 1 + + k h₂ h₁ where h₁ and h₂ are the convective heat transfer coefficient for the internal and external surface of the wall respectively. A furnace wall is of three layers, first layer of insulation brick of 12 cm thickness of conductivity 0.6 W/mK. The face is exposed to gases at 870°C with a convection coefficient of 110 W/m²K. This layer is backed by a 10 cm layer of firebrick of conductivity 0.8 W/mK. There is a contact resistance between the first and second layers of 2.6×10¹4m² °C/W. The third layer is the plate backing of 10 mm thickness of conductivity 49 W/mK. The contact resistance between the second and third layers is 1.5x10-4 m² °C/W. The plate is exposed to air at 30°C with a convection coefficient of 15 W/m²K. Determine the heat flow, the surface temperatures and the overall heat transfer coefficient.