1. Exercises for Q1

3. Insulated copper tube A thin walled 10 mm copper tube is used to transport a low-temperature refrigerant with a temperature that is less than that of the ambient air (convection coefficient of 5 W/m 2 -K). The temperature difference is about 200 K. What is the heat transfer rate, total thermal resistance if the tube is insulated with 0, 5 10, 15, 20 mm thick of cellular glass material (k = 0.05 W/m-K)? What is the overall heat transfer coefficient based on the outside surface area if the tube has 6-mm thick insulation?

4. Critical radius of insulation Derive the critical radius of insulation for an insulated steam pipe in terms of the thermal conductivity of the insulating material and the outside convective heat transfer coefficient.

5. Containment of radioactive waste Radioactive waste (k = 20 W/m-K) are stored in a 10 cm thick spherical stainless steel (k = 15 W/m-K) container of inner radius r i = 0.5 m. Heat is generated volumetrically within the waste at a uniform rate of 10 5 W/m 3, and the outer surface of the container is exposed to a water flow for which the bulk temperature is 25 o C and the convective heat transfer coefficient is 1000 W/m 2 -K. Determine the maximum temperature in the radioactive waste. Ans. 338 C