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Mass Flow Turbine Optimization

03/13/2017 4:04 PM

Generally speaking, any mass flow turbine benefits from improved compressibility of the working fluid. However, there can be a trade off between lowering the inlet plenum temperature by water evaporative cooling, and the total mass of the air plus moisture compared to relatively dry air at reference temperature (and preferably at sea level).

The point of discussion here:

Which fluid produces the most work (PV) assuming both start at the same temperature between air and steam? I say that since air is heavier than water vapor (steam), it should produce more mass flow in a mass flow turbine, and therefore produce more work. Thus, the higher the relative humidity, as the humidity approaches 100%, can there be an actual point of lessened returns before inlet saturation takes place?

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#1

Re: mass flow turbine optimization

03/13/2017 4:50 PM

The answer lies with the difference in enthalpy between start conditions and end conditions of the two fluids <...air...steam...> multiplied, in the case of each fluid, by the flowrate and the efficiency of the setup.

Given the temperatures, pressures and a set of tables for the thermodynamic properties of each fluid at those conditions, and the flowrates, the rest is simple arithmetic using either a pocket calculator, a slide rule, log tables or indeed, subtraction and multiplication by hand.

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#2

Re: Mass Flow Turbine Optimization

03/14/2017 9:27 AM

You are not looking at the change of enthalpy in a thermodynamic system.

Water is the superior working fluid

Did you miss those Thermo 101 classes at University??

https://en.wikipedia.org/wiki/Enthalpy%E2%80%93entropy_chart

https://en.wikipedia.org/wiki/Rankine_cycle

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#4
In reply to #2

Re: Mass Flow Turbine Optimization

03/14/2017 10:14 AM

However water is lighter than air, so how can that be better in a "mass flow" turbine? We are not talking steam turbine here, we are talking about Open cycle Brayton turbine.

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#3

Re: Mass Flow Turbine Optimization

03/14/2017 9:31 AM

you must check specific heat capacity of air and steam.

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#5
In reply to #3

Re: Mass Flow Turbine Optimization

03/14/2017 10:15 AM

I don't want to.

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#7
In reply to #5

Re: Mass Flow Turbine Optimization

03/14/2017 11:51 AM

I wonder what turbine that is handling 2 phase air and steam.

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Guru

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#6

Re: Mass Flow Turbine Optimization

03/14/2017 11:29 AM

Quiet day, huh?

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#8
In reply to #6

Re: Mass Flow Turbine Optimization

03/14/2017 12:28 PM

Yep. Mainly, this is about how far the evaporative cooling moisture loading can go before it starts to degrade, rather than enhance gas turbine output.

We normally run within one or two degrees F of the wet bulb temperature. Forget reaching dew point. I am looking at watering the grass with the blow-down from the intake cooler for the area surrounding the gas turbine to see if we get any additional cooling, but I expect the flow and evaporation rates are what they are, and we will not see anything other than green grass.

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