Turbines, Compressors, Pumps, Nozzles, Valves Reference Page
Entropy Made Me Do It

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Intro to Turbines, Compressors, Pumps, Nozzles, and Valves

Many important engineering devices convert energy between different forms of mechanical and thermal energy.
Examples include turbines that generate power, compressors that increase gas pressure, pumps that move liquids, and nozzles that convert pressure into velocity.

The Second Law of Thermodynamics provides a way to measure how closely real equipment approaches ideal performance by comparing actual processes to isentropic reference processes.

Entropy Made Me Do It: Turbines, Compressors, and Other Second-Law Shenanigans

This video explains how the Second Law is used to evaluate turbines and compressors using isentropic efficiency.

Visuals

Entropy Made Me Do It: Pumps, Nozzles, and Other Second-Law Shenanigans

This video extends the same ideas to pumps, nozzles, and throttling devices.

Visuals

Examples and Definitions

Definitions

Isentropic or Ideal Work
The work required (for devices that consume work) or produced (for devices that generate work) if the process were isentropic.
Real or Actual Work
The work actually required or produced by a real device.
Actual work is compared with isentropic work to define device efficiencies.
Turbine or Expander
A mechanical device that produces work from an expanding fluid.

Turbine or Expander Efficiency

\[ \eta_\mathrm{turbine} = \frac{\dot W_\text{actual}} {\dot W_\text{isentropic}} \]

where the isentropic process has the same inlet state and outlet pressure as the real turbine.

Adiabatic Compressor
A device used to increase the pressure of a gas.
Its performance is often evaluated by comparing the actual compression process to an isentropic compression.

Isentropic Compressor Efficiency

\[ \eta_\mathrm{compressor} = \frac{\dot W_\text{isentropic}} {\dot W_\text{actual}} \]

Isothermal Compressor
A compressor designed to remove heat during compression so that the gas temperature remains approximately constant.

Isothermal Compressor Efficiency

\[ \eta_\mathrm{compressor} = \frac{\dot W_\text{isothermal}} {\dot W_\text{actual}} \]

Pump
A device used to move liquids and increase their pressure.

Pump Efficiency

\[ \eta_\mathrm{pump} = \frac{\dot W_\text{isentropic}} {\dot W_\text{actual}} \]

Nozzle
A device that increases the velocity of a fluid by converting pressure energy into kinetic energy.

Nozzle Efficiency

\[ \eta_\mathrm{nozzle} = \frac{u_\text{actual}^2}{u_\text{isentropic}^2} \]

Valve or Throttle
A device used to control or restrict fluid flow.
Throttling devices are usually modeled as isenthalpic processes

\[ \Delta H = 0 \]

so that

\[ H_\mathrm{out} = H_\mathrm{in} \]