Heat transfer in polytropic process

1. The problem statement, all variables and given/known data



A piston/Cylinder arrangement of initial volume 0.025 m³ contains saturated water vapor at 180 degree Celsius. The steam now expand in a Polytropic process with exponent n=1 to a final pressure of 200 kpa while it does work against the piston. Determine the heat transfer for this process.







2. Relevant equations

PVⁿ=constant





3. The attempt at a solution



I try solving this problem by using enthalpy.



Since state 1 is a saturated vapor, h₁= h_g=2778.16 kJ/kg



For state 2, its state is superheated vapor. By interpollating the value of h between 150 degree Celcius and 200 degree Celcius. I got the value of enthalpy equal 2829.79. Then i go for the heat transfer by using the formula, Q=m(h₂-h₁)



However, my answer is totally different from the answer key in the book. This problem is from Fundamental of Thermodynamic, Sontag and Borgnake, 8th edition, chapter 3, number 123.



The correct answer is 40.5 kJ .

1. The problem statement, all variables and given/known data







2. Relevant equations







3. The attempt at a solution