Expanding a gas through a valve or through a turbine

In summary, when expanding gas through a turbine, some potential energy is converted into kinetic energy in the turbine, resulting in less random kinetic energy in the gas molecules and a lower temperature. This is due to the First Law of Thermodynamics, where dQ is the change in heat energy, dU is the change in internal energy, and dW is the change in energy due to work.
  • #1
charlie95
32
0
Can somebody explain to me why the temperature gets colder when expanding through a turbine versus expanding through a valve.

Please explain with equations.
 
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  • #2
somebody must know this...
 
  • #3
charlie95 said:
Can somebody explain to me why the temperature gets colder when expanding through a turbine versus expanding through a valve.

Hot gas under pressure stores some potential energy, rather like a compressed spring. This energy is released when the gas expands. If you let the gas out through a valve, almost all of the potential energy goes to speeding up the escaping stream of gas, and this ends up as random kinetic energy of the gas molecules as they bounce around. If the gas expands through a turbine, some of the potential energy ends up as kinetic energy in the rotating turbine, so less ends up as random kinetic energy in the gas molecules.

Less random kinetic energy in the same (after expansion) volume of gas means a lower temperature.
 
  • #4
thank u Nugatory:)
But I think somebody once explained to me somethng about dQ=dU+dW.
And that when we expand throgh a turbine, work(dW) is done and therefore we get a much colder gas instead of just expand through a valve.
Is this just ********? :):)
If there is some logic in this, can someone please explain to me what dQ,dU and dW means??
 
  • #5
dQ is the change in heat energy or enthalpy of a substance
dU is the change in internal energy of a substance
dW is the change in energy due to the work of a substance.

It's not BS. It's the First Law of Thermodynamics.
 

What is the purpose of expanding a gas through a valve or through a turbine?

The purpose of expanding a gas through a valve or through a turbine is to convert the energy stored in the gas into mechanical or electrical energy. This can be used to power machines or generate electricity.

What is the difference between expanding a gas through a valve and through a turbine?

The main difference between expanding a gas through a valve and through a turbine is the method in which the energy is extracted from the gas. In a valve, the gas expands and does work against the resistance of the valve itself, while in a turbine, the gas expands and does work against a rotor, which is connected to a generator to produce electricity.

How does expanding a gas through a valve or through a turbine affect the temperature and pressure of the gas?

Expanding a gas through a valve or through a turbine results in a decrease in both temperature and pressure. This is due to the gas expanding and doing work, which results in a decrease in the internal energy of the gas.

What factors affect the efficiency of expanding a gas through a valve or through a turbine?

The efficiency of expanding a gas through a valve or through a turbine is affected by several factors, including the type and design of the valve or turbine, the properties of the gas being expanded, and the operating conditions. Additionally, the efficiency can be improved by minimizing losses due to friction and turbulence.

What are some real-world applications of expanding a gas through a valve or through a turbine?

Expanding a gas through a valve or through a turbine has a wide range of real-world applications, including power generation in gas turbines, refrigeration in air conditioning systems, and propulsion in jet engines. It is also used in industrial processes such as chemical production and oil refining.

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