Maximum vapor velocity from a heat exchanger into a turbine

In summary, the designer is looking for a small impulse steam turbine that can run off of refrigerant vapor. The steam expands out of the heat exchanger at 10.5 m/s and through a 5 inch diameter pipe where a diverging nozzle is to be placed. After the turbine, the vapor will enter a condenser with sub atmospheric pressure. The pressure driving the flow is the difference between the 450 kpa steam at the turbine inlet and the sub atmospheric pressure at the turbine exit. The designer has looked at the DeLaval nozzle before, but hasn't read much into the use in steam turbines. If the design were to go subsonic, the designer would have to calculate the minimum nozzle diameter that
  • #1
BlakeH
2
0
Hi Everyone,

I am looking at designing a small impulse steam turbine that runs off of saturated refrigerant vapor delivered from a shell and tube heat exchanger. With the design of the turbine, I am looking to maximize the velocity that the steam can exit from a diverging nozzle in order to be directed at the turbine blades.

The refrigerant vaporizes at 450kpa and it expands out of the heat exchanger at 10.5 m/s and through a 5 inch diameter pipe where I would like to place a diverging nozzle right before the turbine. After the turbine, the vapor will enter a condenser with sub atmospheric pressure.

Where I am unclear with problem is that the expansion of the refrigerant should change its volume by about 20 times, however the pressure of the vapor remains the same due to the velocity increase of the vapor.

My question is how small of a nozzle can I make before there is noticeable pressure loss or reduced flow in the nozzle? Also, would the pressure driving the flow be the difference between the 450 kpa steam at the turbine inlet and the sub atmospheric pressure at the turbine exit?
 
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  • #2
Have you looked at the DeLaval nozzle and the DeLaval steam turbine ?
 
  • #3
I have looked studied the de laval nozzle before but haven't read much into the use in steam turbines. I will be sure to read into that.
I guess for my design I would have to ensure I have enough back pressure to reach supersonic speed exiting the nozzle.
If I decided to go subsonic with a converging nozzle, how would I calculate the minimum nozzle diameter I can push vapor through before I get reduced flow rate? Would the determining factor be the pressure difference between the inlet and the outlet of the nozzle?

Thanks
 

1. What is the purpose of a heat exchanger in a turbine system?

A heat exchanger is used to transfer thermal energy from one fluid to another without the fluids coming into direct contact. In a turbine system, the heat exchanger is used to heat the working fluid (usually water) to its boiling point, producing high-pressure steam that is then used to power the turbine.

2. How is maximum vapor velocity determined in a heat exchanger?

The maximum vapor velocity in a heat exchanger is determined by the design of the exchanger itself. Factors such as the flow rate, pressure, and temperature of the fluids, as well as the geometry of the exchanger, all play a role in determining the maximum vapor velocity. Computational fluid dynamics (CFD) simulations and experimental testing are commonly used to optimize the design and determine the maximum vapor velocity.

3. What are the potential consequences of exceeding the maximum vapor velocity in a heat exchanger?

If the maximum vapor velocity is exceeded in a heat exchanger, it can lead to fluid turbulence, pressure drops, and in extreme cases, structural damage to the exchanger. This can result in reduced efficiency and potential system failure, leading to costly repairs and downtime.

4. How can the maximum vapor velocity be increased in a heat exchanger?

The maximum vapor velocity in a heat exchanger can be increased by increasing the flow rate of the fluids, increasing the temperature difference between the hot and cold fluids, and optimizing the design of the exchanger. However, it is important to ensure that the velocity remains within safe limits to avoid potential consequences.

5. Are there any industry standards or guidelines for determining the maximum vapor velocity in a heat exchanger?

Yes, there are industry standards and guidelines, such as the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, which provide guidelines for the design and operation of heat exchangers. Specific standards may also exist for different types of heat exchangers, such as shell and tube or plate heat exchangers.

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