Chapter_9 - Chapter 9 9-4C The cold air standard...

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Unformatted text preview: Chapter 9 9-4C The cold air standard assumptions involves the additional assumption that air can be treated as an ideal gas with constant specific heats at room temperature. 9-10C Yes. 9-13C Stroke is the distance between the TDC and the BDC, bore is the diameter of the cylinder, TDC is the position of the piston when it forms the smallest volume in the cylinder, and clearance volume is the minimum volume formed in the cylinder. 9-15 The four processes of an air-standard cycle are described. The cycle is to be shown on P- v and T-s diagrams, and the net work output and the thermal efficiency are to be determined. Assumptions 1 The air-standard assumptions are applicable. 2 Kinetic and potential energy changes are negligible. 3 Air is an ideal gas with variable specific heats. Properties The properties of air are given in Table A-17. Analysis ( b ) The properties of air at various states are kJ/kg 828.1 49.10 1310 kPa 2668 kPa 100 kPa 2668 kPa 800 K 539.8 K 1800 1310 kJ/kg 1487.2 K 1800 K 539.8 kJ/kg 389.22 088 . 11 1.386 kPa 100 kPa 800 386 . 1 kJ/kg 300.19 K 300 4 3 4 2 2 3 3 2 2 2 3 3 3 3 3 2 2 1 2 1 1 3 4 3 1 2 1 h P P P P P T T P T P T P P u T T u P P P P P h T r r r r r r v v From energy balances, kJ/kg 570.1 9 . 527 . 1098 kJ/kg 527.9 19 . 300 1 . 828 kJ/kg 1098.0 2 . 389 2 . 1487 out in out net, 1 4 out 2 3 in q q w h h q u u q ( c ) Then the thermal efficiency becomes 51.9% kJ/kg 1098.0 kJ/kg 570.1 in out net, th q w 9-23 A Carnot cycle with the specified temperature limits is considered. The net work output per cycle is to be determined. Assumptions Air is an ideal gas with constant specific heats. Properties The properties of air at room temperature are c p = 1.005 kJ/kg.K, c v = 0.718 kJ/kgK, R = 0.287 kJ/kg.K, and k = 1.4 (Table A-2). q q q Analysis The minimum pressure in the cycle is P 3 and the maximum pressure is P 1 . Then, or kPa 3 . 935 K 300 K 900 kPa 20 1.4/0.4 1 / 3 2 3 2 / 1 3 2 3 2 k k k k T T P P P P T T The heat input is determined from Then, kJ 0.393 kJ 0.5889 0.667 .7% 66 K 900 K 300 1 1 kJ 0.5889 K kJ/kg 0.2181 K 900 kg 0.003 K kJ/kg 0.2181 kPa 2000 kPa 935.3 ln K kJ/kg 0.287 ln ln in th out net, th 1 2 in 1 2 1 2 1 2 Q W T T s s mT Q P P R T T c s s H L H p 9-40E An ideal Otto cycle with air as the working fluid has a compression ratio of 8. The amount of heat transferred to the air during the heat addition process, the thermal efficiency, and the thermal efficiency of a Carnot cycle operating between the same temperature limits are to be determined. efficiency of a Carnot cycle operating between the same temperature limits are to be determined....
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Chapter_9 - Chapter 9 9-4C The cold air standard...

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