IsenEff - act , out in & &-= To...

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1 ME 201 Thermodynamics Isentropic Efficiency Guide Real work control volume devices (pumps, compressors, fans, turbines, etc.) can be very effectively modeled by treating them first as ideal devices and then using the isentropic efficiency, sometimes called the adiabatic efficiency, to calculate actual work or power. The isentropic is defined differently depending on whether we have a work producing device (i.e., turbine) or a work consuming device (pump or compressor). Then by definition we have turbine a for W W ideal act s = η fan or , compressor pump, a for W W act ideal s = η A real pump, compressor, or turbine that is modeled by an isentropic efficiency is assumed to be adiabatic, so that the first law becomes ( 29 W - h h m 0 act
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Unformatted text preview: act , out in & &-= To perform a calculation for a real work control volume device with a specified isentropic efficiency, the following steps can be taken. 1. Perform an ideal device calculation, i.e. assuming s in = s out , to obtain W ideal . 2. Using the definition of s , calculate the actual work or power from turbine a for W W ideal s act & & = compressor or fan, pump, a for W W s ideal act & & = 3. The actual exit enthalpy can then be calculated form the first law, m W-h h act in act out, & & = 4. With the actual exit enthalpy and pressure known the actual exit state is fixed and the remaining properties can be obtained in the typical manner....
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