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.
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