Inlet nozzles on shell and tube heat exchanger 6

[dipbit]

I was looking for insight into what dictates whether a fluid is fed from the top of the shell or the bottom. In particular, for a liquid cooling application. thanks.

 

[Christine74]

Generally fluids that are being heated will have their inlet at the bottom and outlet at the top of the exchanger while fluids that are being cooled will have their inlet at the top and outlet at the bottom of the exchanger.

While this is essential for two-phase flow (gravity is working for you pulling condensate down as vaporized fluids tend to rise), it is still typically done for single-phase fluids as well.

-Christine

 

[MJCronin]

dip..


In the USA, a manufacturer's organization called TEMA has standardixed a three letter code describing shell-and-tube heat exchanger "types".

It is this TEMA type that will dictate the inlet/outlet scheme.

http://www.tema.org/

http://www.engineeringpage.com/heat_exchangers/tema.html

Most STHEs are counterflow design.

My opinion only..

-MJC

 

[Montemayor]

dipbit:

What dictates how the fluids are fed to a TEMA shell & tube heat exchanger (& any other type as well) is common horse sense. This common horse sense is based strictly on the same parameters that enter into the basic heat transfer equations and assumptions used to calculate the size and type of heat transfer equipment: the heat transfer coefficients are calculated for a specific fluid phase - either liquid or vapor, but never both at the same time. Consequently, it behooves you to adhere strictly to the basis for the calculations.

If you are using cooling water, always introduce the cool, entering CW at the bottom nozzle of either the shell or the tube side. The calculations are based on 100% liquid flooded conditions to ensure a liquid film coefficient and to produce this effect, you should ensure that all gaseous, non-condensables are positively and naturaly kept out of the exchanger. To positively bring this about, the bottom entry is used to purge and positively sweep out all existing non-condensables. This is common sense.

The opposite also occurs when creating a phase change - such as a total condenser. You want to separate your liquid phase as quickly and efficiently as possible from your vapor phase in order to allow the latter to continue to condense. To stimulate and ensure that, you introduce the hot vapors at the top and facilitate the separation of the liquid internally as soon as it is forming by using gravity to precipitate the same liquid to the bottom of the unit (preferably the shell side) and drain off the saturated condensate as fast as it is formed, leaving the vapors to continue their path towards condensation and ultimate venting of non-condensables. The cooling media is introduced such that the LMTD is maximized and most effective - usually in a counter-flow manner. This also is common sense.

There are no fast-and-hard rules; the above forms the basics of what you are trying to do. Sometimes - such as is the case with TEMA BKU and some BEM or BEUs you may be forced to compromise on what seems to be common sense due to layout, corrosive fluids, piping requirements, fluid pressures, etc. These are usually exceptions that are applied due to specific needs and/or requirements. If you apply the exchanger in the manner that it was calculated and designed, it will work with success. Therefore, it is essential for an engineer to know and apply what the basic design equations have assumed.