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superheated wet steam (avoid condensation in a nozzle)

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Old   August 12, 2009, 02:37
Default superheated wet steam (avoid condensation in a nozzle)
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Ralf Schmidt
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Hi!

I would like to simulate the steam flow in a flow nozzle for mass flow measurement (differential pressure method).

The aim is:

1.: to determine the minimum superheat of the steam, that condensation due to the pressure drop in the nozzle is avoided.

2.: To estimate the error in mass flow measurement, when superheat is to low and condensation in the nozzle occurs.

Has someone done something similar? Are there any experimental or numerical literature data to compare results?

The flow is NOT sonic and NOT transonic!!!

Thank You!
Ralf
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Old   August 12, 2009, 16:18
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Rich
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Ralf:

> 1.: to determine the minimum superheat of the steam, that >condensation due to the pressure drop in the nozzle is avoided.

If you know the inlet and outlet pressures, you can use the closed-form equations for quasi-one-dimensional nozzle flow. Using R and gamma for steam, you can start at the nozzle exit, using the temperature that will cause condensation at that pressure, and then work backwards to the inlet. I'd estimate that it's a half-page calculation.

>2.: To estimate the error in mass flow measurement, when superheat >is to low and condensation in the nozzle occurs.

That would probably require a multi-species simulation of quasi-one-dimensional flow using both steam and water. You would have one equation specifying the rate of evolution of water and disolution of steam. That equation would feed the two continuity equations, providing for loss of mass in the steam equation and gain of mass in the water equation. Since water will condense out and no longer be part of the flow, you could probably get away with not having a momentum equation for the water.


Regards,

Rich
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