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MAE204_F11_HW6_Scan

MAE204_F11_HW6_Scan - 5—7 Air enters a nozzle steadily at...

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Unformatted text preview: 5—7 Air enters a nozzle steadily at 2.21 kg/m3 and 40 m/s and leaves at 0.762 kg/m3 and 180 m/s. If the inlet area of the nozzle is 90 cm2, determine (a) the mass flow rate through the nozzle, and (b) the exit area of the nozzle. Answers: (a) 0.796 kg/s, (b) 58 cm2 5—34 Steam enters a nozzle at 400°C 'and 800 kPa W velocity of 10 m/s, and leaves at 300°C and 200 kPa W II losing heat at a rate of 25 kW. For an inlet area of 800 determine the velocity and the volume flow rate of the st L" at the nozzle exit. Answers: 606 m/s, 2.74 m3/s 400°C 800 kPa 10 m/s 300°C 200 kPa (2 FIGURE P5—34 5—48 Refrigerant-134a enters a compressor at 180 kPa as a saturated vapor with a flow rate of 0.35 m3/min and leaves at 700 kPa. The power supplied to the refrigerant during compression process is 2.35 kW. What is the tem- perature of R-134a at the exit of the compressor? Answer: 488°C 5—67 Saturated liquid-vapor mixture of water, called wet steam, in a steam line at 2000 kPa is throttled to 100 kPa and 120°C. What is the quality in the steam line? Answer: 0.957 Throttling valve - 100 kPa 120°C FIGURE P5-67 5—76 A hot-water stream at 80°C enters a mixing chamber with a mass flow rate of 0.5 kg/s where it is mixed with a stream of cold water at 20°C. If it is desired that the mixture leave the chamber at 42°C, determine the mass flow rate of the cold-water stream. Assume all the streams are at a pres— sure of 250 kPa. Answer: 0.865 kg/s FIGURE P5—76 5—84 A thin-walled double-pipe counter-flow heat is used to cool oil (cp— — 2. 20 kJ/kg- °C) from 150 to , . rate of 2 kg/s by water (cp = 4.18 kJ/kg °C) that enters at a rate of 1.5 kg/s. Determine the rate of heat tranSfe heat exchanger and the exit temperature of water. Hot oil 2 kglsi150°C FIGURE P5—84 5-98 A llO—volt electrical heater 1s used to warm 0. 3: of air at 100 kPa and 15°C to 100 kPa and 30°C. How current in amperes must be supplied to this heater? An insulated 0.15-m3 tank contains helium at 3 MPa 30°C. A valve is now opened, allowing some helium to . The valve is closed when one-half of the initial mass 'c’aped. Determine the final temperature and pressure in tank- Answers: 257 K, 956 kPa ...
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