
634 Principles of Sustainable Energy Systems
© 2008 Taylor & Francis Group, LLC
condenser operate at an effective temperature difference of ∆T of 4 K, with an overall
heat transfer coefcient U of 6000 W/m
2
K. Use the Carnot efciency for the power plant
as an approximation.
Solution
The rate of heat transfer to the working uid in the evaporator of area A is approximately
qU
in
The rate of enthalpy increase of the water is
qQcT TQcT TT TQcT
in hc wh wc wh wc
=−=−−+
=−−
ρρ ρ() ()()
∆∆ ∆2
where
ρ is the density (1.0 kg/m
3
)
c is the specic heat (4.2 × 10
3
J/kg K)
The Carnot efciency η
c
of the energy conversion process is
η
c
hc
wh wc
TT
TT T
=
−
=