- #1
Acnhduy
- 31
- 1
Hi all,
I'm having some trouble figuring out why entropy is used instead of enthalpy for an open system.
From what I understand, an open system uses entropy to calculate internal energy. Since the control volume is constant (i.e. Δv = 0), wouldn't using : h = u + PΔv effectively be h = u? So in this case, wouldn't you use enthalpy instead of entropy since volume isn't changing?Just to confirm, in an open system like a turbine or something, with the assumption of no heat transfer and negligible potential energy, the energy balance becomes:
W = ΔU
W = m2(h2 + ke2 +pe2) - m1(h1 + ke1 + pe1)
... and with steady flow ...
w = (h2 + ke2) - (h1 + ke1)
Please let me know if I am misunderstanding something, thanks!
I'm having some trouble figuring out why entropy is used instead of enthalpy for an open system.
From what I understand, an open system uses entropy to calculate internal energy. Since the control volume is constant (i.e. Δv = 0), wouldn't using : h = u + PΔv effectively be h = u? So in this case, wouldn't you use enthalpy instead of entropy since volume isn't changing?Just to confirm, in an open system like a turbine or something, with the assumption of no heat transfer and negligible potential energy, the energy balance becomes:
W = ΔU
W = m2(h2 + ke2 +
... and with steady flow ...
w = (h2 + ke2) - (h1 + ke1)
Please let me know if I am misunderstanding something, thanks!
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