Electronic components are mounted on the inner surface of a horizontal cylindrical duct whose inner diameter is 0.2m. 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 25oC, 1 bar and a velocity of 0.3 m/s and exits at 40oC with negligible changes in kinetic energy and pressure. Convective cooling occurs on the outer surface to the surroundings, which are at 25oC, in accord with hA = 3.4 W/K, where h is the heat transfer coefficient and A is the surface area (the rate of cooling by convection is given by Q = hA(Ts-Tsurr)) . The electronic components require 0.2 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, Ts, in oC
c. The rate of entropy generation, in W/K
Assume the ideal gas model for air.
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