6 replies to this topic

[peclpassic]

Dear all members:

 

I was assigned a BEU type condenser rating work, but I found the HTRI result seems a little bit wired.

 

 

Parameters given by client are below:

 

 

This type of condenser is BEU type and Horizontal, and I have tried using HTRI rating mode to set Single-segmental baffles, 4 cross pass, tube length = 2440mm.

But, the pressure drop in shell side still always greater than allowable pressure drop (0.005 bar) in shell side, even if I increase the shell id to 1056 mm.

I also tried double-segmental baffles so that the pressure drop could be much smaller than that in shell wiht signle-segmental baffles, but unfortunately,

the pressure drop is still greater than allowable pressure drop. By the way, I tried use design mode in HTRI and there is a good convergence result in HTRI.

(The pressure drop in shell is in allowable range). But, our leader is not accepted this design mode result since the baffle cut ratio is optimizing automatically by HTRI.

 

I was wondering this BEU type given by client seems wrong, because TEMA J shells are most typically specified for this phase change duties where significantly reduce shell side pressure drop are required. They are commonly used with a single nozzle as inlet and two nozzle as outlet, for vapor and liquid separate better. Please justify and give any suggest about my deduction and calculation result.

 

Thank you so much.

 

Best regards,

 

 

[Art Montemayor]

Wow!  You are talking about only 0.005 bar of pressure drop (2 inches of water column).  That is a very, very, special case of shell side design.

 

I believe this is a topic for SRFish, our expert heat transfer member who I believe has already addressed something similar to this topic in:http://www.cheresour...ate/#entry77055

 

I have had this type of problem in the past and I resolved it by going to Graham Heat Exchangers, a firm specializing in special exchanger designs - especially this low of a shell-side pressure drop.  I hope SRFish reads this thread and responds with his expert advice.

[srfish]

You are correct when you post "BEU type given by client seems wrong". Because of such a low allowable pressure drop it will take some form of divided flow(type J) or NTIW. The one nozzle in and two nozzles out is normally used in vaporizing services. Using a single nozzle in causes more tubes to be removed for impingement protection and therefore causes a larger and more expensive shell.

[peclpassic]

Since my boss wouldn’t like to make such effort to change type of heat exchanger from BEU to BJU. Therefore, I choose the double segmental baffle in this BEU type exchanger

, and enlarge the shell side inlet and outlet nozzle.

 

Also, I noted that  this total pressure drop (only 0.005 bar) is made of sum of pressure drop of the nozzle, and baffle window, so enlarged the shell side inlet nozzle from 20" -> 24" and shell outlet nozzle for liquid from 3" -> 4".

 

The HTRI result of pressure drop in the shell side is limited in the allowable range.

 

Please share some light in my post if this is weird to use double segmental in the BEU type heat exchanger.

 

Thank you very much for all of your suggestion.

 

Best regards,

[srfish]

No, it is not weird to use double segmental baffles in a BEU type as long as they meet the allowable shell side pressure drop.

[peclpassic]

I am very appreciate for your time and your help. The warning message following may be too general for you to help.

 

 

1. The bundle entrance velocity is over critical velocity. Is any method to be adjust this error? (Bundle entrance velocity seems very complex problem about fluid in shell so Increasing shell id may not make the velocity less, and it is hard to find optimal by only adjusting the bundle-to-shell clearance to make the velocity less than critical )

 

2. The inlet unsupported span length exceeds the TEMA maximum unsupported span length? (Does user only solve this to give any tried-and-error number by increasing or decreasing the inlet spacing in HTRI baffle Geometry panel?)

 

Also, someone suggest me switch to Aspen EDR tool cause it is much better in dealing two phase question than HTRI, but I am not complain that I can't solve this

two phase case through HTRI.

 

 

Thank you for your help again.

 

Best regards,

 

 

 

[ask1590]

peclpassic,

 

email your HTRI model file with all the available information. I will fix it.

 

chem_ashraf@yahoo.com