ch07 - CHAPTER SEVEN 0.80 L 35 10 4 kJ 0.30 kJ work . 1h 1...

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CHAPTER SEVEN 7.1 080 35 10 030 233 23 4 .. L kJ . kJ work 1 h 1 kW h L 1 kJ heat 3600 s 1 k J s kW kW × =⇒ 2 1 312 3 3 .33 kW 10 W 1.341 10 hp kW 1 W hp .1 hp 3 × . 7.2 All kinetic energy dissipated by friction (a) E mu k = = × ⋅⋅ = 2 2 2 22 4 2 5500 lb 5280 1 9 486 10 715 m 2 2 f 2 2 2 m 2 f 55 miles ft 1 h lb Btu 2 h 1 mile 3600 s 32.174 lb ft / s 0.7376 ft lb Btu . (b) 8 46 3 10 brakings 715 Btu 1 day 1 h 1 W 1 MW 2617 MW day braking 24 h 3600 s 9.486 10 Btu/s 10 W 3000 MW × = × 7.3 (a) Emissions: Paper 1000 sacks oz 1 lb sack 16 oz lb m m + = (. . ) . 00510 00516 641 Plastic 2000 sacks oz 1 lb sack 16 oz lb m m + = . ) . 00045 0 0146 239 Energy: Paper 1000 sacks Btu sack Btu + () . 724 905 163 6 Plastic 2000 sacks Btu sack Btu + . 185 464 130 6 (b) For paper (double for plastic) Raw Materials Acquisition and Production Sack Production and Use Disposal Materials for 400 sacks 1000 sacks 400 sacks 7- 1
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7.3 (cont’d) Emissions: Paper 400 sacks .0510 oz 1 lb sack 16 oz 1000 sacks .0516 oz 1 lb sack 16 oz lb reduction mm m ⇒+ 00 45 30% . = Plastic 800 sacks .0045 oz 1 lb sack 16 oz 2000 sacks .0146 oz 1 lb sack 16 oz lb reduction m 205 14% . = Energy: Paper 400 sacks Btu sack 1000 sacks Btu sack Btu; 27% reduction ⇒+ = × 724 905 119 10 6 . Plastic 800 sacks Btu sack 2000 sacks Btu sack Btu; 17% reduction × 185 464 108 10 6 . (c) . 3 10 persons 1 sack 1 day 1 h 649 Btu 1 J 1 MW person - day h 3600 s 1 sack 9.486 10 Btu J / s MW 8 -4 × × = 24 10 2375 6 , Savings for recycling: 017 2 375 . ( , MW) = 404 MW (d) Cost, toxicity, biodegradability, depletion of nonrenewable resources. 7.4 (a) Mass flow rate: gal 1 ft (0.792)(62.43) lb 1 min min 7.4805 gal 1 ft 60 s lb s 3 m 3 m ± . . m == 300 0330 Stream velocity: gal 1728 in 1 1 ft min min 7.4805 gal 0.5 in 12 in 60 s ft s 3 2 u 1 1225 2 . . Π bg Kinetic energy: .330 lb ft 1 1 lb s s 32.174 lb ft / s ft lb s ft lb s hp ft lb s m 2 f 2 m 2 f f f E mu k =× ⋅ × F H G I K J 2 2 3 3 3 5 2 01 2 2 5 2 770 10 1341 07376 140 10 . . ./ . . di (b) Heat losses in electrical circuits, friction in pump bearings. 7- 2
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7.5 (a) Mass flow rate: () 2 3 3 42.0 m 0.07 m 10 L 673 K 130 kPa 1 mol 29 g 127.9 g s s 4 1 m 273 K 101.3 kPa 22.4 L STP mol π == ± m ± ± . E mu k ⋅⋅ = 2 2 2 14 2 0 113 127.9 g kg m 1 N 1 J 2 s 1000 g s 1 kg m / s N m Js 2 2 2 (b) ( ) 3 3 22 127.9 g 1 mol 22.4 L STP 673 K 101.3 kPa 1 m 4 49.32 m s s 29 g 1 mol 273 K 130 kPa (0.07) m = ± ± . . ±± ) ± ) E mu EE E k kk k = 2 2 2 9 3 2 1558 127.9 g kg m 1 N 1 J 2 s 1000 g s 1 kg m / s N m J/s = (400 C - (300 C = (155.8 -113) J / s = 42.8 J / s 43 J / s 2 2 2 DD (c) Some of the heat added goes to raise T (and hence U ) of the air 7.6 (a) ∆∆ Em g z p =− 1 gal 1 ft 62.43 lb ft lb 7.4805 gal s 32.174 lb ft / s ft lb 3 m f 3 2 m 2 f 32174 10 1 834 . . (b) mu mg z u g z kp = = = F H G I K J L N M O Q P = 2 12 2 2 2 32174 10 254 bg b g .. ft s ft ft s 2 (c) False 7.7 (a) ± E positive k When the pressure decreases, the volumetric flow rate increases, and hence the velocity increases. ± E negative p The gas exits at a level below the entrance level. (b) ± . . m = = 5 m 1.5 cm 1 m 273 K 10 bars 1 kmol 16.0 kg CH s 10 cm 303 K bars 22.4 m STP 1 kmol kg s 23 4 42 3 2 101325 0 0225 2 out out out out in in 2 in in in out in out in out in out (m/s) A(m ) (m/s) A(m ) 10 bar 5 m s 5.555 m s 9 bar PV V u PP nRT nRT V P u P P uu P =⇒=⇒ = ⇒= = = ± ± 2 1 2 0.5(0.0225) kg (5.555 5.000 )m 1 N 1 W s s 1 kg m/s 1 N m/s 0.0659 W 0.0225 kg 9.8066 m -200 m 1 N 1 W s ko u t i n po u t i n g z z ∆= − = = ± ± ±
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ch07 - CHAPTER SEVEN 0.80 L 35 10 4 kJ 0.30 kJ work . 1h 1...

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