Solved Problems on the Thermodynamics - Assignment 6 | ME 201, Assignments of Thermodynamics

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Homework #6 Solutions

ME201 Homework #6 Solutions 4-57 A spring-loaded piston-cylinder device is filled with nitrogen. Nitrogen is now heated until its vo increases by 10%. The changes in the internal energy and enthalpy of the nitrogen are to be determinec Properties The gas constant of nitrogen is R = 0.2968 kPam*/kg-K. The specific heats of nitrogen at r temperature are c,= 0.743 kI/keg-K and c, = 1.039 kI/kg-K (Table A-22). Analysis The initial volume of nitrogen is 2H _ (0.010 ke 0.2968 kPa akg -K)Q7+273K) _ 0.00742 m! B 120 kPa The process experienced by this system is a linear P-uprocess. The equation for this line is P-B=cV-4) where P, is the system pressure when its specific volume is v;. The spring equation may be written as F,-F,3 ka k P-Ret Hs =“ mje U-Y 1 A 2 (ex) a U-) Constant c is hence = BOGEN) _ 6 511m x? (0.1m)* The final pressure is then Py =P ty -W)=F tell IW -Y)=F +0.1c4% =120kPa +0.1(16.211kN/m* )(0.00742 m?) =132.0kPa The final temperature is _ PV) (132.0 kPa)(1.10.00742 m3) T= = =363K 7 mR (0.010 kg)(0.2968 kPa m3 /kge-K) Using the specific heats, Au =, AT = (0.743 kW/kg- K)(363—300)K = 46.8 kJ/kg Ah =e, AT = (1.039 kI/kg -K)(363—300)K = 65.6 kJ/kg