Thermodynamics
SECOND LAW OF THERMODYNAMICS
Pump efficiency,
, relates the work required by an ideal pump to the actual work required by
h p
the pump; it relates the minimum amount of work theoretically possible to the actual work
required by the pump. However, the work required by a pump is normally only an intermediate
form of energy. Normally a motor or turbine is used to run the pump. Pump efficiency does
not account for losses in this motor or turbine. An additional efficiency factor, motor efficiency
, is defined as the ratio of the actual work required by the pump to the electrical energy input
h m
to the pump motor, when both are expressed in the same units.
h m
W
p, actual
W
m, in
C
where:
= motor efficiency (no units)
h m
W
p, actual
= actual work required by the pump (ft-lbf)
W
m, in
= electrical energy input to the pump motor (kw-hr)
C
= conversion factor = 2.655 x 106 ft-lbf/kw-hr
Like pump efficiency
, motor efficiency
is always less than 1.0 or 100% for an actual
h p
h m
pump motor. The combination of pump efficiency
and motor efficiency
relates the ideal
h p
h m
pump to the electrical energy input to the pump motor.
(1-35)
h mh p
W
p, ideal
W
m, in
C
where:
= motor efficiency (no units)
h m
= pump efficiency (no units)
h p
W
p, ideal
= ideal work required by the pump (ft-lbf)
W
m, in
= electrical energy input to the pump motor (kw-hr)
C
= conversion factor = 2.655 x 106 ft-lbf/kw-hr
A heat exchanger is designed to transfer heat between two working fluids. There are several heat
exchangers used in power plant steam cycles. In the steam generator or boiler, the heat source
(e.g., reactor coolant) is used to heat and vaporize the feedwater. In the condenser, the steam
exhausting from the turbine is condensed before being returned to the steam generator. In
addition to these two major heat exchangers, numerous smaller heat exchangers are used
throughout the steam cycle. Two primary factors determine the rate of heat transfer and the
temperature difference between the two fluids passing through the heat exchanger.
Rev. 0
Page 83
HT-01
