Maximum vapor velocity from a heat exchanger into a turbine

[BlakeH]

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?

 

[Nidum]

Have you looked at the DeLaval nozzle and the DeLaval steam turbine ?

 

[BlakeH]

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