Temperature of Steam After it goes through a PRV 1

[dabigoj]

I am trying to determine the temperature of the steam after it goes through a pressure reducing valve (prv).

The upstream pressure is 600 psig @ saturation temperature. The down stream pressure is 400 psig.

From my understanding going through a prv the enthalpy of the system should stay the same.

Therefore, I usually look up the enthalpy at the higher pressure then look up the properties of the steam with the lower pressure and same enthalpy. Thus I get the down stream temperature. For the case above the enthaply at saturation temperature are listed below.

Enthalpy of saturated 600 psig steam is 1203.50 btu/lb

Enthalpy of saturated 400 psig steam is 1205.16 btu/lb

Therefor my method does not work to get the temperature or any properties of the lower pressure steam. Is there a more accurate way to calculate the down pressure steam?

 

[DRWeig]

Go here:

http://www.spiraxsarco.com/esc/SS_Properties.aspx?lang_id=ENG&country_id=US

Best to you,

Goober Dave

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[MisterDonut]

The enthalpy of the system (in theory) stays the same. Some of the steam will condense.

 

[dabigoj]

Goober Dave,

Thanks for the link, but that is what I use to get my properties. The problem is if I put in 400 psig with 1203.5 BTU i get an error.

 

[dabigoj]

MisterDonut,

Thanks, so if i understand correctly the 400 psig steam will just be at saturation temperature?

OJ

 

[MisterDonut]

The steam will be at 400 psig but it will be "wet," meaning a mixture of saturated steam and saturated liquid.

 

[dougarthur42]

If the 600# steam is at saturation is is about 488*f. When you reduce the pressure you are not reducing the temperature so the 400# steam should be slightly superheated still around 488*f. Unless you desuperheat it it will remain hotter than saturation. Another point to ponder if enthalpy is btu/lb than the more the lbs or psi the more the btu's??

 

[dabigoj]

Here is a link of the mollier chart showing that when you go through the PRV and enthalpy stays the same you move into the "wet steam region". Just as MisterDonut said it would.

 

[Latexman]

dabigoj - correct. There is an inflection point at about 460 psia.

Good luck,
Latexman

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[Thermoiler]

If you reduced the pressure while keeping enthalpy constant, you will get superheated steam. So you have to look up the temperture on the superheated steam tables.

http://www.spiraxsarco.com/resource...iples-and-heat-transfer/superheated-steam.asp

Scroll down to "The effects of reducing steam pressure"

 

[Thermoiler]

Forget what I just said. Damn I wish I could delete my post. Should have thought it through before posting. Right out of uni. My bad.

 

[EnergyMix]

Thermo, red flag your post (or posts) and tell the system administrators why you want to delete or edit them.

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