Superheated Steam Heat Transfer 5

[Joesteam]

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.

 

[TD2K]

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.

 

[vpl]

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.

 

[Joesteam]

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

 

[Latexman]

Joesteam,

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


Good luck,
Latexman

 

[SBBlue]

Here's the solution:

1. Go to Archon Engineering web site:

http://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!!)

 

[rmw]

If you have time for snail mail, go to

http://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

 

[25362]

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:

390^oF 1128.6
395^oF 1130.8
400^oF 1133.0

 

[quark]

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.htm

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%.

 

[25362]

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:

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

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

 

[Joesteam]

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.

 

[XELR8]

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

 

[speco]

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

 

[XELR8]

Sepco,

Your correct. I misinterpreted the question.

Thanks,
Dracula