Electronic components are mounted on the inner surface of

Chapter 6, Problem 6.93

(choose chapter or problem)

Electronic components are mounted on the inner surface of a horizontal cylindrical duct whose inner diameter is 0.2 m, as shown in Fig. P6.93. To prevent overheating of the electronics, the cylinder is cooled by a stream of air flowing through it and by convection from its outer surface. Air enters the duct at 25\(^{\circ}\)C, 1 bar and a velocity of 0.3 m/s and exits at 40\(^{\circ}\)C with negligible changes in kinetic energy and pressure. Convective cooling occurs on the outer surface to the surroundings, which are at 25\(^{\circ}\)C, in accord with hA 5 3.4 W/K, where h is the heat transfer coefficient and A is the surface area. The electronic components require 0.20 kW of electric power. For a control volume enclosing the cylinder, determine at steady state (a) the mass flow rate of the air, in kg/s, (b) the temperature on the outer surface of the duct,

in \(^{\circ}\)C, and (c) the rate of entropy production, in W/K. Assume the ideal gas model for air.