thermosyphone reboiler inlet/outlet pressure drop sizing and velocity

[delf]

Dear Professional eng-tips member

I have a project required to size the inlet/outlet pipe size of thermosyphone reboiler.
And, our deisgn guide is written that the liquid vleocty to the reboiler in the range of
2 to 7 ft/s. And, the pressure drop in the line to the reboiler is requried to be
in the 10 to 30% of the total system drop.
Any one can explain to me this is reasonable?

Also the maximum velocty of the vapor liquid from reboiler return to the column
is set to squart root of 4000 divided the denisty of mixture.
But, I wonder why there is not any
explian what is the prressure drop limit in the return line to the column.

Could anyone kindly give me any help?

Thank you.

 

[srfish]

The danger in using too low of velocity in the inlet piping is that it can create a back surge from above. Usually there is a valve placed in the inlet piping to better control the situation.

A rule of thumb for the outlet piping is for it to have the same flow area as the tubes. Restricting the vaporizer channel and outlet piping reduces the heat flux. There is an engineering tip on this on

http://www.gulleyassociates.com

under the heading " Choking a vertical thermosyphon".