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FTFS Chap09 P146 - Chapter 9 Gas Mixtures and...

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Chapter 9 Gas Mixtures and Psychrometrics Adiabatic Mixing of Airstreams 9-146C This will occur when the straight line connecting the states of the two streams on the psychometric chart crosses the saturation line. 9-147C Yes. 9-148 Two airstreams are mixed steadily. The specific humidity, the relative humidity, the dry-bulb temperature, and the volume flow rate of the mixture are to be determined. Assumptions 1 Steady operating conditions exist 2 Dry air and water vapor are ideal gases. 3 The kinetic and potential energy changes are negligible. 4 The mixing section is adiabatic. Properties Properties of each inlet stream are determined from the psychometric chart (Figure A-33) to be air dry /kg m 882 . 0 air dry O/kg H kg 0119 . 0 air dry kJ/kg 7 . 62 3 1 2 1 1 v h and air dry /kg m 819 . 0 air dry O/kg H kg 0079 . 0 air dry kJ/kg 9 . 31 3 2 2 2 2 v h Analysis The mass flow rate of dry air in each stream is kg/min 5 . 30 air dry kg / m 819 . 0 min / m 25 kg/min 7 . 22 air dry kg / m 882 . 0 min / m 20 3 3 2 2 2 3 3 1 1 1 v V m v V m a a From the conservation of mass, ( . . ) . m m m a a a 3 1 2 22 7 305 532 kg / min kg / min Specific humidity and the enthalpy of the mixture can be determined from Eqs. 9-24, which are obtained by combining the conservation of mass and energy equations for the adiabatic mixing of two streams: 7 . 62 9 . 31 0119 . 0 0079 . 0 5 . 30 7 . 22 3 3 3 3 1 3 3 2 1 3 3 2 2 1 h h h h h h m m a a which yields, 3 3 kJ / kg dry air 0.0096 kg H O / kg dry air 2 h 450 . These two properties fix the state of the mixture. Other properties of the mixture are determined from the psychometric chart: air dry /kg m 845 . 0 3 3 3 3 v T 63.4% C 20.6 Finally, the volume flow rate of the mixture is determined from /min m 45.0 3 kg) / m .845 kg/min)(0 2 . 53 ( 3 3 3 3 v m V a 9-149 Two airstreams are mixed steadily. The specific humidity, the relative humidity, the dry-bulb temperature, and the volume flow rate of the mixture are to be determined. Assumptions 1 Steady operating conditions exist 2 Dry air and water vapor are ideal gases. 3 The kinetic and potential energy changes are negligible. 4 The mixing section is adiabatic. 9-88 P = 1 atm AIR 1 2 3 25 m 3 /min 12 C 90% 32 C 40% 20 m 3 /min 3 3 T 3
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P = 95 kPa AIR 1 2 3 25 m 3 /min 12 C 90% 32 C 40% 20 m 3 /min 3 3 T 3 Chapter 9 Gas Mixtures and Psychrometrics Analysis The properties of each inlet stream are determined to be air dry kJ/kg 9 . 64 kJ/kg) 559.9 (0.0128)(2 + C) C)(32 kJ/kg 005 . 1 ( air dry O/kg H kg 0.0128 kPa ) 92 . 1 (95 kPa) 92 . 1 ( 622 . 0 622 . 0 air dry kg / m 940 . 0 kPa 08 . 93 K) K)(305 kg / m kPa 287 . 0 ( kPa 08 . 93 92 . 1 95 kPa 92 . 1 kPa) 800 . 4 )( 40 . 0 ( 1 1 1 1 2 1 1 1 1 3 3 1 1 1 1 1 1 C 32 @ sat 1 1 1 1 g p v v a a v a g v h T C h P P P P T R v P P P P P P and air dry kJ/kg 5 . 33 kJ/kg) 523.4 (0.0085)(2 + C) C)(12 kJ/kg 005 . 1 ( air dry O/kg H kg 0.0085 kPa ) 277 . 1 (95 kPa) 277 . 1 ( 622 . 0
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