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Power Plant Components - h1012v1_106
Power Plant Components - h1012v1_108

Thermodynamics Heat Transfer and Fluid Flow Volume 1 of 3
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Thermodynamics SECOND LAW OF THERMODYNAMICS A pump is designed to move the working fluid by doing work on it.   In the application of the first law general energy equation to a simple pump under steady flow conditions, it is found that the increase in the enthalpy of the working fluid Hout  - Hin  equals the work done by the pump, Wp, on the working fluid. (1-28) Hout Hin Wp (1-29) m(hout hin) wp where: Hout = enthalpy of the working fluid leaving the pump (Btu) Hin = enthalpy of the working fluid entering the pump (Btu) Wp = work done by the pump on the working fluid (ft-lbf) = mass flow rate of the working fluid (lbm/hr) m hout = specific enthalpy of the working fluid leaving the pump (Btu/lbm) hin = specific enthalpy of the working fluid entering the pump (Btu/lbm) = power of pump (Btu/hr) wp These relationships apply when the kinetic and potential energy changes and the heat losses of the working fluid while in the pump are negligible.   For most practical applications, these are valid  assumptions.   It  is  also  assumed  that  the  working  fluid  is  incompressible.   For  the  ideal case,  it  can  be  shown  that  the  work  done  by  the  pump  Wp  is  equal  to  the  change  in  enthalpy across the ideal pump. W p ideal = (Hout - Hin)ideal (1-30) ideal= (hout - hin)ideal (1-31) wp m where: Wp = work done by the pump on the working fluid (ft-lbf) Hout = enthalpy of the working fluid leaving the pump (Btu) Hin = enthalpy of the working fluid entering the pump (Btu) = power of pump (Btu/hr) wp = mass flow rate of the working fluid (lbm/hr) m hout = specific enthalpy of the working fluid leaving the pump (Btu/lbm) hin = specific enthalpy of the working fluid entering the pump (Btu/lbm) The  reason  for  defining  an  ideal  pump  is  to  provide  a  basis  for  analyzing  the  performance  of actual pumps.   A pump requires more work because of unavoidable losses due to friction and fluid turbulence.   The work done by a pump Wp  is equal to the change in enthalpy across the actual pump. Rev. 0 Page 81 HT-01







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