Question

HW3.3. A cylindrical steel pipe is used to carry water steam with an averaged heat transfer coefficient of h 150 W/m2-K at Ti- 100 °C. The steel pipe goes through the roof of a factory where the ambient temperature is 23°C (To), with a natural heat convection coefficient of 5 W/m2-K. The inner and outer diameters of the steel pipe are 2 cm and 2.2 cm, respectively, and thermal conductivity of the steep pipe is k, -20 W/m-K To prevent heat loss into the ambient, a layer of asbestos of thickness d (in cm) is now wrapped around the steel pipe. Thermal conductivity of asbestos is ka -0.2 W/m-K. (a) Derive and plot the rate of heat transfer per unit length, q/L as a function of d in the range of 0sds10 cm. (b) Determine the critical radius of the asbestos layer, der, and use der to interpret the plot you obtained in (a) ho T 0, Asbestos, ka h, T steel pipe, k T -To W/m; 2tk na Plot[qL, (d, 0,0.1)] 2 0.02 0.0 0.0 k, 0.2 ho 5 dr-4-1.1 cm -2.9 cm, which is the result of d shown in the plot

Answer 1