Thermodynamics closed system - first law

AI Thread Summary
The discussion revolves around a thermodynamics problem involving a closed system with 1 kg of water initially at 90 degrees Celsius and a quality of 10%. The first law of thermodynamics is applied, with the equation Q - W = ΔU guiding the calculations. The user attempts to determine the total work done during the heating process to 800 kPa and 250 degrees Celsius but finds their calculation of ΔU to be incorrect. Assistance is requested to clarify the correct application of the work equation, specifically W = m(h2 - h1), emphasizing that enthalpy includes internal energy. The conversation highlights the importance of accurately applying thermodynamic principles to solve such problems.
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Homework Statement



1kg of water that is initially at 90 degrees celsius with a quality of 10% occupies a spring loaded piston cylinder device. The device is now heated until the pressure rises to 800kPa and the temperature is 250 degrees c
Determine the total work done during this process, in KJ


Homework Equations



The first law for closed systems
Q - W = ΔU
(h2-h1 - u2 - u1) = ΔU

The Attempt at a Solution



State 1

Saturated mixture (90 degrees)
x = 0.1
H1 = 605.29 KJ/kg
U1 = 588.67 KJ/kg

State 2 - super heated vapour

h2 = 2950.4 KJ/kg
u2 = 2715.9 KJ/kg

therefore,

ΔU = (2950.4 - 605.29) - (2715.9 - 588.67) = 217.88 KJ

which is incorrect, can you assist me with this question?
 
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You would actually just need to apply

W = m(h2-h1)

remember that enthalpy h includes internal energy u.
 
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