An air heater consists of a steel tube ( = 20 W/mK) with inner and out radii of and , and eight integrally machined longitudinal fins, each of thickness t=3 mm. The fins extend to a concentric tube, which is of radius and insulated on its outer surface. Water at a temperature flows through the inner tube while air at flows through the annular region formed by the larger concentric tube.
a. Sketch the equivalent thermal circuit of the heater and related each thermal resistance to appropriate system parameters.
b. If hi = 5000 W/m2K and ho= 200 W/m2K, what is the heat rate per unit length?
