Thermodynamics SECOND LAW OF THERMODYNAMICSCausesofInefficiencyIn the preceeding sections, cycle and component efficiencies have been discussed, but the actualcauses or reasons for the inefficiencies have not been explained. In this section we will comparesome of the types and causes for the inefficiencies of real components and cycles to that of their"ideal" counterparts.ComponentsIn real systems, a percentage of the overall cycle inefficiency is due to the losses by theindividual components. Turbines, pumps, and compressors all behave non-ideally due toheat losses, friction and windage losses. All of these losses contribute to the non-isentropic behavior of real equipment. As explained previously (Figures 24, 25) theselosses can be seen as an increase in the system’s entropy or amount of energy that isunavailable for use by the cycle.CyclesIn real systems, a second source of inefficiencies is from the compromises made due tocost and other factors in the design and operation of the cycle. Examples of these typesof losses are: In a large power generating station the condensers are designed to subcoolthe liquid by 8-10°F. This subcooling allows the condensate pumps to pump the waterforward without cavitation. But, each degree of subcooling is energy that must be putback by reheating the water, and this heat (energy) does no useful work and thereforeincreases the inefficiency of the cycle. Another example of a loss due to a system’sdesign is heat loss to the environment, i.e. thin or poor insulation. Again this is energylost to the system and therefore unavailable to do work. Friction is another real worldloss, both resistance to fluid flow and mechanical friction in machines. All of thesecontribute to the system’s inefficiency.Rev. 0 Page 95 HT-01
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