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Superheated Steam Heat Transfer
5

Superheated Steam Heat Transfer

Superheated Steam Heat Transfer

(OP)
I need to figure out how much superheated steam is needed for my application.

I have 120 psig steam at 400 Deg. F.

I need to transfer 100,000 btu/hr with a maximum drop of 5 Deg. F of the steam.

I can't seem to find a BTU/LB for just the vapor phase of the superheated steam.  Any help would be appreciated.

RE: Superheated Steam Heat Transfer

The heat capacity of the steam will be about 0.55 BTU/lbF.

Find a copy of the steam tables.  Look up the enthalphy of your superheated steam at the pressure and temperature.  Then, look up the enthalphy of superheated steam at an adjacent temperature.  You can use those two values to work out the sensible heat.

RE: Superheated Steam Heat Transfer

Joe

Not sure if I'm missing something --- with superheated steam, it's all vapor, so you should be able to read the enthalpy value off of a steam table.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

RE: Superheated Steam Heat Transfer

(OP)
I cannot seem to find a superheated steam table that changes for every five degrees, I guess this is my problem.

RE: Superheated Steam Heat Transfer

Joesteam,

Have you ever heard of I-N-T-E-R-P-O-L-A-T-I-O-N?

Good luck,
Latexman

RE: Superheated Steam Heat Transfer

Here's the solution:

1. Go to Archon Engineering web site: www.archoneng.com
2. Order their Steam Program. It only costs $40, and if you're making a living designing steam systems it will pay for itself in about two or three hours. (It does all the i-n-t-e-r-p-o-l-a-t-i-o-n for you!!)

RE: Superheated Steam Heat Transfer

If you have time for snail mail, go to www.graham-mfg.com, ejectors page, software, and order a vacworks II, or better still call your local graham rep to bring you one.

It has a wonderful steam table built in, and is good up to 2700 PSI or so.  Great engineering tool.

RMW

RE: Superheated Steam Heat Transfer

2
The NIST WEBBOOK will give you all the info you need on water (and, of course steam).
For that pressure, enthalpies, Btu/lb, this source gives:

                            390oF     1128.6
                            395oF     1130.8
                            400oF     1133.0

RE: Superheated Steam Heat Transfer

You require 35606lb/hr of steam. The specific heat of steam at the above mentioned superheat condition is 0.561711 btu/lb deg.F.

Download steamtab from the link below. This will give you the desired values of saturated steam, superheated steam and water.

http://www.chemicalogic.com/steamtab/companion/default....

Regards,

Believe it or not : Though human body is made up of intricate and subtle mechanism, it is very poor in energy conversion. The maximum efficiency is 20% during cycling. During under water swimming it is just 4%.

RE: Superheated Steam Heat Transfer

Thanks to quark's message I discovered having misread NIST tables quoting internal energy values instead of enthalpies. The correct enthalpy values in Btu/lb are:

                   390oF               1217.4
                   395oF               1220.2
                   400oF               1223.1
                   405oF               1225.9

For a 5oF drop starting at 400oF the amount of steam would be 100,000/2.9=34,483 lb/h, which could be rounded up to 34,500 lb/h.                             

RE: Superheated Steam Heat Transfer

(OP)
Thank you quark and 25362 for doing my legwork and not making me purchase an elaborate steam table that I would use maybe once a year.  You have proved the worth of this board.

RE: Superheated Steam Heat Transfer

Hey Joe,

Your enthalpy is 1224.62 Btu/lbs and the mass flow rate should be about 81.66 lbs/hr of steam.

Any more questions?

Dracula

RE: Superheated Steam Heat Transfer

Dracula,

The problem is that Joesteam only wants to desuperheat the steam by 5 deg.  He is not condensing at all.  Therefore only a very small portion of the enthalpy is available to use.  This makes the required steam much higher to do the 100,000 BTU/hr duty.

Also, condensing or not, the total heat available per pound of steam would be the difference between the inlet and outlet enthapy.  To get the entire 1224.62 BTU per pound out of the steam, you would have to desuperheat it, condense it, and subcool it to 32 deg F, but not freeze it.

Regards,

Speco

RE: Superheated Steam Heat Transfer

Sepco,

Your correct. I misinterpreted the question.

Thanks,
Dracula

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