10 replies to this topic

[panoska]

Hello everyone,

I was reading somewhere about liquid hold up on the tube sheet of heat exchanger. But, I could not realize what it really means liquid hold up in a heat exchanger.

Could you please enlighten me?

[breizh]

Hi,

Are you talking about modulating the heat transfer area?

I would advise you to get a copy of Process heat transfer by D.Q. Kern, Mac Graw hill international edition, by far the bible in heat transfer.

 

Breizh 

[latexman]

Liquid hold-up is the accumulation of liquid.  Do you have a question about a specific kind of liquid accumulation in a heat exchanger?  There are several that come to mind.  Can you narrow the scope, please?  I don't want to write a tome.

[panoska]

Yeah it is a condenser, where at the top tube sheet of the condenser the liquid holdup should be minimized. Is it more clear now?

[panoska]

Thank you Breizh, I will try to find a copy of this book.

[latexman]

Yeah it is a condenser, where at the top tube sheet of the condenser the liquid holdup should be minimized. Is it more clear now?

 

So, don't extend the tubes far above the surface of the tubesheet.  Talk to the HX designer about your options to limit the liquid hold-up on the top tubesheet.  I assume this is a vertical, down draft condenser.

[panoska]

What I do not get is why there is liquid hold up there? Because of the vapor enters the condenser?

[latexman]

 Capture.JPG   14.23KB   1 downloads

 

Now do you get it?  I Googled Image "tube to tubesheet joint types"

 

The Protruding Tubes type would definately hold-up liquid that condensed onto the tubesheet.

[panoska]

Not yet, I will think a bit more and I will let you know if I figured it out.

[Pilesar]

In a vertical condenser, liquid travelling down the tubes must overcome tube pressure drop. If there is vapor moving up the same tubes the liquid is coming down, there will likely be a percolation of flow as the overall pressure drop must be equal for each tube since the inlet pressure is the same for all tubes and the outlet pressure is the same for all tubes. The liquid can be carried above the top tubesheet where it can build up until it finds a path down. There needs to be a clear path for the liquid to travel. Larger tubes than you would prefer may be needed in order to change the two-phase flow regime away from plugging. Or an alternate liquid drain path may be needed for the liquid.

[panoska]

Latexaman, thank you so much for the explanation with the screenshot. It was very useful.
Pilesar thanks for the further explanation.

Now, it is clear!!!