Elementary Principles 272

# Elementary Principles 272 - 7.49 (a) Pressure in cylinder =...

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7-27 7.49 (a) Pressure in cylinder =+ weight of piston area of piston atmospheric pressure P T sat = ⇒= ° 30.0 kg 9.807 N cm bar 400.0 cm kg 1 m 10 N m atm 1.013 bar atm C 22 5 2 100 10 1 108 1018 2 2 bg . . . Heat required to bring the water and block to the boiling point QU m U U m U T U ww l w l A lA l s a t A l == ° + ° = + = Δ ± . ± , ±± . .( . ) 20 839 0 94 1018 20 2630 bar, sat'd l 20 C C 7.0 kg 426.6 kJ kg 3.0 kg [ ]kJ kg kJ b g di b g 2630 kJ < 3310 kJ Sufficient heat for vaporization (b) TT fs a t ° 1018 . C . Table B.5 ± ., ± . ± , ± . VU ll vv 1046 426 6 1576 2508 6 Lkg k Jkg L kg kJ kg T 101.8°C P 1.08 bars 1576 L/kg, 2508.6 kJ/kg 1.046 L/kg, 426.6 kJ/kg Q (kJ) W (kJ) mv v (kg H O( )) 2 ml l (kg H O( )) 2 7.0 kg H O( ) 2 l ± . ± H = 4266 kJ / kg V = 1.046 L / kg (Since the Al block stays at the same temperature in this stage of the process, we can ignore it -i.e., UU in out = ) Water balance: 7 0 . mm lv (1) Work done by the piston: bar L 8.314 J / mol K 1 kJ 0.08314 liter - bar / mol K 10 J kJ piston atm atm 3 WF z w PAz w A PA z P V W m m vl + L N M O Q P =⇒ = + × ΔΔ b g b g b g 1576 1046 7 0 170 2 0113 0 7908 .. . . . Energy balance: Δ Δ UQW vL U Q W =− + =−− + ⇒+ = 2508 6
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