What distinguishes turbines from expanders? I've observed that numerous cogeneration cycles incorporate expanders, but I lack knowledge about their specific characteristics.
According to wikidiff.com. en.wikipedia.org. files.chartindustries.com. and ajstacksolutions.com, turbines, and expanders, while similar, have distinct differences:
- A turbine is a type of rotary machine that uses the kinetic energy of a continuous stream of fluid (a liquid or a gas) to turn a shaft. The name comes from the Latin ‘turbo,’ meaning vortex, and thus, the defining property of a turbine is that a fluid or gas turns the blades of a rotor, which is attached to a shaft that can perform useful work.
- An expander, a turboexpander, or an expansion turbine is a centrifugal or axial-flow turbine through which a high-pressure gas is expanded to produce work often used to drive a compressor or generator. Because work is extracted from the expanding high-pressure gas, the expansion is approximated by an isentropic process (i.e., a constant-entropy process), and the low-pressure exhaust gas from the turbine is at a very low temperature. Turbo expanders are widely used as sources of refrigeration in industrial processes.
In essence, the main distinction of a turboexpander is that it expands the gas stream for its own sake, and mechanical work is generated as a byproduct.
- In cooling cycles, we need to reduce the temperature of fluid after condenser. This is mostly done by expansion valve or throttle. Expander do the same with less entropy generation. So, the pressure and temperature reduction happens a bit more gradually.
- Now, think about how much potential power we are losing by these expanders. Especially in bigger fassilities. Here, we can use "turbo expander" to generate power as a byproduct while our main purpose is still cooling the fluid by pressure reduction.
- Many times you can see "expander" is used instead of "turbo expander". It's not completely correct because "expander" doesn't refer to power production, and not completely wrong as it is still an expander.
- "Turbine" is a general term referring to converting a fluid's enthalpy to work. The most important differences are: (1) in turbines our only purpose is power generation but turbo-expanders aim to reduce the pressure and secondly generate power, (2) while turbo-expanders are mostly pressure reduction based, turbines are pressure/temperature or velocity reduction based (e.g. wind turbines).
- You might see turbo-expanders in non-cooling systems. For example, we use them in gas pipelines to reduce the gas pressure close to a big delivery point (e.g. a city or a large consuming industry) instead of throttling it. Then we can make power as a byproduct.
*** Despite all the explanations, I personally don't think if you use these two terms in other's place, it is wrong. In fact, turbine is kinda an expander. It's more about how different industries call an equipment. For example, while many people uses "gas turbine", some people or some countries prefer to use "combustion turbine".
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