The effect of exit pressure and temperature on a turbine

In summary, the first scenario has the turbine adjacent to the final combustion chamber, and the pressure and temperature are the same. The second scenario has the pressure and temperature reversed.
  • #1
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I still struggle with the interchangeability of pressure and temperature and how they affect the performance of various bits of turbomachinery. Microscopically they're very interconnected, in that the measure of pressure is the result of the confinement of the measure of temperature, however macroscopically they are often treated as independent (albeit coupled) quantities.

I have been thinking about full flow staged combustion cycles in rocket engines and can't reconcile a couple of hypotheticals, so I was hoping for a bit of insight. These turbines can present a unique thermodynamic scenario, where fluid downstream of a turbine is at a lower pressure but much higher temperature than upstream fluid.

A typical staged combustion cycle might consist of some kind of pre-burner that burns some amount of fuel and oxidant before expanding the products over a turbine, which then flow into a combustion chamber and nozzle to produce thrust. There is some amount of piping between the turbine exit and the final combustion chamber, so immediately after the turbine, both the pressure and temperature of the fluid drops as you would expect.

What happens if you start to shorten that length of piping until your turbine is sitting adjacent to the final combustion chamber? In one extreme limit, fluid from the preburner expands directly into the main combustion chamber. The pressure upstream of the turbine is higher than the downstream pressure, however the temperature gradient is reversed due to the large amount of heat added in the main combustion chamber. Will the turbine still produce power?
 
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  • #2
I have a hard time imagining what you are asking about. At first, it sounded like a turbojet. Then a jet with the compressor stage replaced by a preburner, but then merging the stages. Is it a ramjet?

Maybe you can draw a diagram.
 
  • #3
Sorry. I should have made that more clear. It is a rocket engine which has a full flow turbine to drive a pump for propellants. I made a crude diagram of the two scenarios.

staged%20combustion%20diagram.png
 

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Related to The effect of exit pressure and temperature on a turbine

1. How does exit pressure affect a turbine's performance?

The exit pressure of a turbine is directly related to the amount of work that the turbine can produce. As the exit pressure increases, the amount of work that the turbine can produce decreases. This is because the turbine has to work harder to push the air out at a higher pressure, resulting in a decrease in efficiency.

2. What is the relationship between exit pressure and turbine efficiency?

The relationship between exit pressure and turbine efficiency is inverse. As the exit pressure increases, the turbine efficiency decreases. This is because the turbine has to work harder to maintain a higher pressure, resulting in a decrease in overall efficiency.

3. How does temperature affect the exit pressure of a turbine?

The temperature of the air entering a turbine affects the exit pressure in that it can cause changes in the density of the air. As the temperature increases, the air becomes less dense, resulting in a decrease in exit pressure. This can have an impact on the performance of the turbine.

4. What is the ideal exit pressure for a turbine?

The ideal exit pressure for a turbine is dependent on the specific design and purpose of the turbine. Generally, a lower exit pressure is preferred as it results in higher efficiency and less wear on the turbine. However, in certain applications, a higher exit pressure may be needed to achieve a desired level of work output.

5. How can the exit pressure and temperature be optimized for maximum turbine performance?

The exit pressure and temperature can be optimized for maximum turbine performance by carefully designing the turbine for the specific application, taking into account factors such as air flow rate, inlet temperature, and desired work output. Additionally, regular maintenance and adjustments can help ensure that the turbine is operating at its peak performance. Advanced control systems and technologies can also assist in optimizing the exit pressure and temperature for maximum turbine efficiency.

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