A furnace wall is of thickness 0.25 m (L.) and it is exposed to gas at its inner surface and to air at its outer surface. The gas and air are maintained at 400°C (T) and 50°C (T). The heat transfer coeffi- cients of hot gas (h ) and cold air (h) sides are 60 and 10 W/m'K respectively. If the surface area (A) of the wall is 3 m', find (1) the overall heat transfer coefficient; (ii) the heat transfer rate 'Q' and (iii) the surface temperature of the wall (T and T). Assume that the thermal conductivity (K) of the wall material is 1.5 W/mK.

The upper surface of a 50-cm-thick solid brass plate (k=109 W/mK) is being cooled by water with temperature of 10°C. The upper and lower surfaces of the solid plate maintained at constant temperatures of 60°C and 190°C, respectively. Determine the water convection heat transfer coefficient and the water temperature gradient at the upper plate surface. Water Ts.l · Ts.,2

The thermal conductivity of a solid material can be determined using asetup similar to the one shown in the accompanying figure. The thermocouples are placed at 2.5 cm intervals in the known material (copper alloy, k - 52 w/m.k) and the unknown sample, as shown. The known material is heated on the top by a heating element, and the bottom surface of the sample is cooled by running water through the heat sink shown. Determine the thermal conductivity of the unknown sample for the set of data given in the accompanying table. Assume no heat loss to the surroundings and perfect thermal contact at the common interface of the sample and the copper.