FME 422 – HEAT TRANSFER 1 Assignment 1 1. The wall of a drying oven is constructed by sandwiching an insulation material of thermal conductivity 0.05W/m°C between thin metal sheets. The oven air is at 300°C, and the corresponding convection heat transfer coefficient is 30W/m2 °C. The inner wall surface absorbs a radiant heat flux of 100W/m2 from the hot objects within the oven. The room air temperature is 25°C, and the overall coefficient for convection and radiation from the outer surface is 10W/m2°C. (a) Draw the thermal circuit for the wall and label all temperatures, heat rates, and thermal resistances. (b) What insulation thickness is required to maintain the outer wall surface at a safe-to-touch temperature of 40°C? (Hint: Neglect the thermal resistance of the thin metal sheets) 2. A steel pipe carries steam at 110°C. The pipe has an inner diameter of 100mm and outer diameter of 120mm. The pipe is located in a room where the ambient air temperature is 30°C, and the convective heat transfer coefficient between the pipe and air is 15W/m2 °C. Determine the heat transfer rate per unit length of the pipe. To reduce the heat loss from the pipe, it is covered with a 50mm thick layer of insulation of thermal conductivity 0.2W/m°C. Determine the heat transfer rate per unit length of the insulated pipe. Assume that the convective resistance of steam is negligible. 3. A long stainless bar of 20mm by 20mm square cross-section is perfectly insulated on three surfaces and is maintained at a temperature of 400°C on the remaining side. Determine the maximum temperature in the bar when it is conducting a current of 1000 amperes. The thermal and electrical conductivities of stainless steel are 16W/m°C and 1.5×104 (Ω-m)-1, respectively. The heat flow at the ends of the bar may be neglected. 4. Derive an equation giving the temperature at the centre of a circular rod conducting an electric current in terms of current-density (Amps/m2), the wall temperature, and the material properties. What is the centre temperature of a 20mm diameter stainless steel with similar properties as in Question 3 and outer surface temperature of 400°C when conducting a current of 1000A?