CONDUCTION

1. A furnace wall is made up of three layers of thicknesses 25cm, 10cm and 15 cm with thermal conductivities of 1.65,K and 9.2 W/mK respectively. The inside is exposed to gases at 1250oC with a convection coefficient of 25W/m2oC and the inside surface is at 1100oC,the outside surface is exposed to air at 25oC with convection coefficient of 12 W/m2K.Determine (i) The unknown thermal conductivity (ii) The overall heat transfer coefficient (iii) All the surface temperatures. 2. A cylinder 1m long and 5cm in diameter is placed in an atmosphere at 45oC. It is provided with 10 longitudinal straight fins of material having k=120W/mk. The height of 0.76mm thick fin is 1.27cm from the cylinder surface. The heat transfer coefficient between cylinder and atmosphere air is 17 W/m2K.Calculate the rate of heat transfer and the temperature at the end of fins if surface temperature of cylinder is 150oC. 3. Find out the amount of heat transferred through an iron fin of length 50mm width100mm and thickness 5mm.Assume k=210kJ/mhoC and h= 42kJ/m2hoC for the material of the fin and the temperature at the base of the fin as 80oC.Also determine the temperature at tip of the fin, If the atmospheric temperature is 20 oC. 4. Air at 25oC flows over 1m x 3m (3m long) horizontal plate maintained at 200oC at 10 m/s. Calculate the average heat transfer coefficient for both laminar and turbulent regions. Take Re (critical)= 3.5x105