Meen 344- HW 11

# Meen 344- HW 11 - result Compute the stagnation pressures...

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MEEN 344: Section 502 HW Problem Set #11 1 . Air is expanded in a steady flow process through a turbine. Initial conditions are 1400 o C and 3.0 MPa (abs). Final conditions are 500 o C and atmospheric pressure. Show this process on a Ts diagram. Evaluate the changes in internal energy, enthalpy, and specific entropy for this process. 2. An aircraft passes overhead at 4 km altitude. The aircraft flies at M = 1.4; assume air temperature is constant at 20 o C. Find the air speed of the aircraft. A headwind blows at 30 m/s. How long after the aircraft passes directly overhead does its sound reach a point on the ground? 3. Air flows in an insulated duct. At point 1 the conditions are M 1 = 0.6, T 1 = 20 o C, and p 1 = 1.0 MPa (abs). Downstream, at point 2 , because of friction the conditions are M 2 = 0.7, T 2 = -5.62 o C, and p 2 = 136.5 kPa (abs). (Four significant figures are given to minimize roundoff errors.) Compare the stagnation temperatures at points 1 and 2 , and explain the
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Unformatted text preview: 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. 4. Consider steady, adiabatic flow of air through a long straight pipe with A = 0.05 m 2 . At the inlet (section 1 ) the air is at 200 kPa (abs), 60 o C, and 136 m/s. Downstream at section 2, the air is at 95.6 kPa (abs) and 280 m/s. Determine p o1 , p o2 , To1, T o2 and the entropy change for the flow. Show static and stagnation state points on a Ts diagram. 5. A CO 2 cartridge is used to propel a toy rocket. Gas in the cartridge is pressurized to 6 MPa (gage) and is at 25 o C. Calculate the critical conditions (temperature, pressure, and flow speed) that correspond to these stagnation conditions....
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