Power Plant Components

Thermodynamics Heat Transfer and Fluid Flow Volume 1 of 3
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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

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