lecture 15 - Thermal and Fluids Engineering I Lecture 15...

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Thermal and Fluids Engineering I Lecture 15 Page 1 Lecture 15 – Steady Flow Devices Compressors and Pumps A compressor is the opposite of a turbine. In a compressor, work is done on a gas or vapor to raise it to a higher pressure. Axial Flow Compressor The first law for a compressor is the same as that for a turbine. From the first law for an open system 22 cv i e cv cv i i i e e e dE QW m h g z m h g z dt ⎛⎞ =−+ + + + + ⎜⎟ ⎝⎠ ∑∑ & & && VV In a compressor, kinetic and potential energy are generally negligible. The first law becomes cv cv cv i i e e dE m h m h dt & & Compressors operate with one inlet and one exit cv cv cv i e dE m h m h dt & &
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Thermal and Fluids Engineering I Lecture 15 Page 2 If the compressor is adiabatic and operating in steady state () 0 cv i e Wm h h =− + & & A pump is, in some ways, similar to a compressor. Compressors raise the pressure of gases; pumps raise the pressure of liquids. The first law for a pump in steady operation reduces to cv i e h h & & Designating the entrance as state 1 and the exit as state 2 12 cv h h & & compressor, pump The liquid traveling through a pump can usually be considered as incompressible and isothermal. In that case, the enthalpy change is 21 hhv PP −= pump Combining the last two equations produces cv v P P & & pump
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lecture 15 - Thermal and Fluids Engineering I Lecture 15...

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