For the Aspen Plus simulated working fluid pump, why is the enthalpy increase in the results equal to the shaft power rather than the useful power?
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I used Aspen Plus v10 to simulate the pump, and found that the increase in enthalpy at the inlet and outlet is equal to the brake power, rather than the fluid power. Shaft power is the power that the pump receives from the motor; it represents the input power of the pump ； The useful power is the energy that the working fluid actually receives from the pump. The efficiency of the pump is equal to useful power divided by shaft power, that is, η = volume flow rate * head * density * g / shaft power. Therefore, the increase in enthalpy of the working fluid as it enters and leaves the pump, which represents the energy actually obtained by the pump, should be equal to the useful power, right? Could you please help explain where I went wrong? Thank you
This issue has been resolved through other means. The calculation of the pump is based on adiabatic principles; one part of the energy is used to increase the pressure of the fluid, which represents the useful power, while the other part, which is lost due to friction and similar factors, is converted into heat that is absorbed by the fluid, raising its temperature. Using the fluid as a reference, the energy supplied to the fluid from the outside is equal to the useful power plus heat; this sum represents the shaft power. When using the pump as a reference, the energy supplied to the pump is exactly the shaft power. The pump is considered in an adiabatic context, with no heat loss – all of the shaft power is absorbed by the fluid; it’s merely a difference in the form of energy. The testing of the pump’s characteristic curve involves only measuring the pressure difference between the inlet and outlet, that is, the effective power portion.
I’ve learned it.* The power delivered by the motor to the pump (excluding coupling efficiency) is called shaft power. The sum of the static pressure energy and kinetic energy that the pump imparts to the fluid is called the useful power. These are two concepts. There are three types of power in total: motor power, shaft power, and useful power.