3 replies to this topic

[dilova2011]

Hi all,

 

 

In the design of a vacuum surface condenser (6 Torr), I'm supposing a horizontal disposal, with the condensation of vapors in the shell and  ethylenglicol/water circulating in the tubes. Well, my question is that is neccesary a minimum height (above ground or above hotwell), like barometric condensers, which incluye a barometric leg.

 

Or simply, my system with the vacuum surface condenser  requires that condensate should be removed by a condensate pump. And then, this condensate can be delivered to a hotwell or a heat exchanger for temperature increasing.

 

Finally, is calculated the pressure drop in the shell  like a condenser without vacuum pressure? or exists other methods from vacuum condensers?

 

The only information that I have found is provided by Coulson, that says:

 

"A common practice is to calculate the pressure drop using the methods for single-phase flow and apply a factor to allow for the change in vapour velocity. For total condensation, Frank (1978) suggests taking the pressure drop as 40 per cent of the value based on the inlet vapour conditions; Kern (1950) suggests a factor of 50 per cent"

Edited by dilova2011, 23 May 2013 - 07:22 PM.

[srfish]

As far as pressure drop is concerned in a vacuum condenser, it depends how accurate you are required to be in your project. Those two methods you mention are approximations only. Normally the pressure drop is very important in the design of a vacuum condenser. There is a very large change in the density of the flowing stream. There are two different systems for calculating two-phase pressure drop. There is the homogenous flow method or the separated flow method. In the case of a vacuum condenser I would use the separated flow system.

[dilova2011]

Thanks, Where I can find the basis of the methods that you quote?

 

 

As for my first question,  exists or is neccesary a minimum height (above condensate pump or above hotwell)?

I think it depends only on required NPSH from condensate pump that impulses the liquid condensate downstream, but I'm not sure.

[srfish]

If you can get ahold of the big Heat Exchanger Design Handbook it has information of both types of flow. Some publications have a two-phase shell-side flow pattern map by Grant (1975).