3 replies to this topic

[Jenergy]

Hi,

I'm trying to make a temperature profile along condensing tubes containing a little noncondensing gas, and I'd like to get your assistance to make it.

I think steam without air may be ideal, real steam contains more or less air.
Therefore condensing temperature of the steam under constant pressure cannot be a saturation point, but a range of dew points below pure saturation temperature. (Condensing of binary vapor mixture)

Suppose steam with a little air is condensing in tube side, and water is boiling outside tube(shell side), each 1-pass stream.
Although tube inlet temperature may close to pure steam saturation temperature, however, condensing temperature decreases along tubes with decreasing partial vapor pressure of steam. And, If tube length is long enough, tube outlet condensing temperature will arrive at the minum approach to boil shell side water.

Condidering above process description, I think fully long tube length to arrive at min. outlet approach temperature could be uneconomical because most of all the heat exchange occurs around pure saturation temperature(tube inlet part). I should decide tube length with tube outlet temperature under economical point of view.

Can anyone recommend documents or books presenting clear solution to this subject ?

[chemsac2]

Phenomenon of effect of air on steam is described in following link:

http://www.spiraxsar...ting-theory.asp

Exchanger design for condensing in presence of non-condensibles is covered in chapter 13 of Process Heat Transfer by Kern, D.Q. An iterative solution for sample steam-CO2 system is also given.

In HTRI there is an option to indicate if inert gas is present in condensing stream (options tab menu). However, I am not sure if it takes into account both effect on heat transfer coefficient and LMTD. You can try that feature.

Regards,

Sachin

[srfish]

Process Heat Transfer by Hewitt,etal has a section on condensation curves. The Hand Book of Heat Exchanger Design has a section on "Single vapor with noncondesable gas.

[Jenergy]

Dear chemsac2 , Dear srfish

Thanks very much for your help with such valuable informations,

I'm now studying them in spare times, and after completion of review, I'll try to present the solutions.

Regards.
.