Chapter 12, Problem 40P

Air flows in an insulated duct. At point ① the conditions are M₁ = 0.1, T₁ = − 20° C and p₁ = 1.0 MPa absolute. Downstream, at point ②, because of friction the conditions are M₂ = 0.7, T₂ = − 5.62°C, and p₂ = 136.5 kPa absolute. (Four significant figures are given to minimize round off errors.) Compare the stagnation temperatures at points ① and ②, and explain the result. Compute the stagnation pressures at points ① and ②. Can you explain how it can be that the velocity increases for this frictional flow? Should this process be isentropic or not? Justify your answer by computing the change in entropy between points ① and ②. Plot static and stagnation state points on a Ts diagram.