STEAM FLOW

[dkm0038]

I have a question about steam flow...

I have recieved specs from a steam turbine generator that the steam leaving it is at 4000 lb/hr. To find the velocity I simply divide by its density and the cross sectional area.

This steam is then going to be condensed to water. It seems that the mass flow rate should be constant and we will have 4000 lb/hr of water. And to find the velocity we do the same as above. but since water is some much more dense than steam there is a big difference in velocities in the pipe.

for example if i had 4000 lb/hr of steam at 100 psig, 0.25 lbm/ft3 going through a 1 ft diameter pipe the velocity is 5.6588 ft/s. When it condenses to liquid with 60.271 lbm/ft3 the calculated velocity is 0.023 ft/s.

Is this correct? is the mass flow rate of steam the same for water? what other factors are at work?

Thank you for any advice or references anyone can refer me to.

 

[rmw]

I would refer you back to your thermo book.

rmw

 

[dougarthur42]

I agree refer to thermo book. Also remember that when the steam get to condenser will most likely not be @ 100psi.
Doug

 

[rmw]

It could well be a back pressure turbine exhausting into a heater acting as a condenser for the steam at 100 psig.

DKM, give us a little more description of your process, please. It might help us to better be able to offer meaningful advice. I still stand by my initial reply, however. Given your question, that is where I would start (or with a good set of steam tables.)

rmw

 

[quark]

What you calculated is correct. That is the reason why condensate lines are much smaller than steam lines. 1ft dia pipe for 4000 lb/hr steam flowrate is gigantic. 2" line would have been much better unless you have a strong reason.

 

[dkm0038]

thanks quark and rmw.

I assure you though the first places i looked was literature. I have 4 books on thermo and two on fluid and after looking through them the above is what i concluded. This forum was my last effort to get a proffesional opinion of what i have concluded.

The actual application is for a condenser and I am trying to get an idea of the flow of the steam and water in the tubes, constant diameter.

 

[racookpe1978]

No. A condensor (almost always for the little turbine generator you stated at the beginning) has the cooling water in the tubes, the condensing gas (your 4000 lbm steam) around outside of the tubes.

you will not ever see "steam and water" flowing in the "constant diameter" tubes - that's where the cooling water stays as a fluid.

For your problem, you're mixing up the inlet flow conditions (4000 lbm/hr steam at 100 psig in an unknown pipe diameter) with the outlet of the turbine conditions (12" dia pipe - AFTER the "work" of the turbine has been extracted by removing enthalpy at an unknown pressure and temperature for saturated water of unknown quality) with the condensate water conditions (still at 4000 lbm/hr water at some unknown pressure and temperature in an unknown diameter pipe) with the COOLING water conditions (an unknown nbr of tubes at an unknown diameter of unknown wall thickness pipe conducting an unknown mass of cooling water at an unknown pressure and temperature (unknown Reynolds nbr and unknown roughness factor further fouling up your problem.)

 

[dkm0038]

racookpe1978,

The condenser that we use is air cooled. the steam is distributed into the tubes and condenses and leaves the tubes as water. the steam/water is condensed inside the tubes and air cooles them on the outside.

 

[racookpe1978]

Thank you! I've never seen that arangemment.

 

[rmw]

Look in the steam property tables in one of the thermo books or a set of steam tables at the specific volume for the steam at the condensing pressure for the vapor state and the liquid state for that same temperature and pressure. In a condenser you have a change of state from a vapor (gigantic specific volume) to a liquid (much smaller specific volume.) The change in specific volume is what creates the vacuum that makes the condenser work. There will be air (non condensables) removal equipment and it will be called vacuum pumps or vacuum jets and people (who don't know any better) think that the vacuum pumps or jets create the vacuum. THEY DONT (yes, a hogger vacuum pump or jet will initially bring the condenser to a near deep vacuum so that the condensing can start but that is all it does) The air removal equipment merely removes the air so that the condenser can condense the steam. The change of state where the steam changes from the vacuum specific volume to the liquid state specific volume creates the vacuum.

The water that condenses naturally flows by gravity to the lower parts of the condenser (in the tubes with the steam that is entering and condensing all the while) where it is collected and pumped out. And yes, those lines are much smaller than the steam lines by several orders of magnitude.

Sorry for my initial response but your OP was pretty rough and I didn't want to waste time trying to explain engineering stuff to a non engineering professional. This site has lots of those. If you have 4 thermo books, you are ahead of me. Go to the head of the class. If you hadn't known what a thermo book was, I wouldn't have posted this.

rmw