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Unformatted text preview: terms of fluid properties.
Taking the positive direction of work to be from the system (work output),
the energy balance for a steady-flow device undergoing an internally reversible process can be expressed in differential form as
dqrev dwrev dh dke dpe But
T ds T ds
dh υ dP (Eq. 6–16)
(Eq. 6–24) dqrev dh υ dP Substituting this into the relation above and canceling dh yield
dwrev υ dP dke dpe Integrating, we find
2 wrev 1 υ dP ke pe (kJ/kg) (7–51) When the changes in kinetic and potential energies are negligible, this equation reduces to
2 wrev 1 υ dP (kJ/kg) (7–52) Equations 7–51 and 7–52 are relations for the reversible work output associated with an internally reversible process in a steady-flow device. They will
give a negative result when work is done on the system. To avoid the negative cen54261_ch07.qxd 11/18/03 9:57 AM Page 305 305
CHAPTER 7 sign, Eq. 7–51 can be written for work input to steady-flow devices such as
compressors and pumps as
2 wrev, in 1 υ dP ke pe (7–53) The resemblance betwee...
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This document was uploaded on 11/28/2012.
- Spring '09