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Test_1_Sp04 - Test I Howell 1(33 a Ammonia is at a pressure...

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Test I: February 25, 2004, Howell 1 (33%) a): Ammonia is at a pressure of 200 kPa, and has a specific volume of 0.5000 m 3 /kg. What is the value of specific internal energy u of the refrigerant at this state (kJ/kg)? L LV L LV v v xv v v x v = + - = Using values from Table 18s, ( 29 3 3 0.5000 0.001507 ( / ) 0.8405 0.5931( / ) L LV m kg v v x v m kg - - = = = and 113.12 0.8405 1207.2 1127.8( / ) L LV u u xu kJ kg = + = + = b): Ammonia is at a temperature of 25 o F and pressure of 250 psia. What is the specific internal energy u of the ammonia at this state (Btu/lbm)? From Table 17e, find that at T=25 o F, P>P SAT (25 o F), so this state is a subcooled liquid. Therefore, u(T,P)=u L (T SAT =T=25 o F)=71.1 (Btu/lbm). c): What is the specific enthalpy of ammonia h (Btu/lbm) at the state given in part (b) above? For a subcooled liquid, [ ] [ ] 3 2 2 2 ( , ) ( ) ( ) ( ) 1 71.34( / ) 0.02488( / ) 250 53.8 ( / ) 144( / ) 778( / ) (71.34 0.90)( / ) 72.24( / ) L SAT L SAT SAT SAT h T P h T T v T T P P T T Btu lbm ft lbm lbf in in ft Btu ft lbf Btu lbm Btu lbm = = + = - = = + -•♠ - = + = Values again from Table 17e.
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2 (33%) A piston-cylinder system contains 5 lbm of refrigerant R-134a. The piston is originally 2 ft above the bottom of the cylinder. The piston has a face area of 1 ft
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