6 replies to this topic

[lafondejs]

Dear All,

I am new to Heat exchanger designing, and i would like to know some basic thumb rules of designing of finned tube heat exchangers, like air/gas coolers, economizers.

For example,

I would like to know regarding,

1. Optimum no of tube rows per bundle & Optimum tube length range (Tube bundle sizing)
2. How to select fin density & type of fins (L-fins, Extruded fines etc.)
3. No of bundle per unit and arrangement of bundles & Units (Parallel or serial)
4. Bare length of ends of a finned tube.
5. Deciding Header depth & Header type
6. How to avoid tube side fluid maldistribution & bypass through the pass partitions.

Thanks.

[Steve Hall]

My new book, Rules of Thumb for Chemical Engineers, Fifth Edition (Butterworth-Henemann, 2012) has several pages on air cooled heat exchangers. It includes thermal sizing and pressure drop calculations, as well as some rules of thumb which are attached here.

Attached Files

•  Air Coolers excerpt from Rules of Thumb for Chemical Engineers.pdf   25.71KB   26319 downloads

[breizh]

Consider this resource to support your query ( Chapter 4 ....)

http://www.wlv.com/p...ok/databook.pdf

Breizh

[srfish]

In the oil and gas industry most air coolers have 4 rows. There is an engineering tip in the air cooler section that is more definative on Art's spreadsheet download and my website www.gulleyassociates. The tip is named "Optimum number of tube rows".

Most services for air coolers can use L-fins (wrap-on), There is a tip on the above sources named "Maximum tube wall temperature for wrap-on fins. Above this temperature the fins should be embedded or extruded.

I am not familar in economizers for boilers but in waste heat systems where hot gas flows across fin tubes. The starting number of rows across in this trial and error solution .is 0.12 x sq root(flow) and flow is in lb/hr.

[Art Montemayor]

Lafondejs:

This is meant to complement both Steve Hall’s and Srfish’s constructive and valuable comments: do not make the mistake of believing that you can “optimize” a heat exchanger design employing only Rules of Thumb. Replacing required accurate calculations has never been the intention of employing Rules of Thumb.

Our engineering vernacular English as used in the USA sometimes gets misinterpreted outside the confines of our borders and this cause a lot of confusion. A Rule of Thumb is not a “rule” per se. It is an estimate that can quickly save time and effort in arriving at an acceptable answer – when used correctly and with engineering judgment. “Rules of Thumb” represent valuable, acquired engineering experience that has accumulated through the years. Most of it is not backed up by scientific experiment, theory, or documented engineering studies. It is valuable when used accordingly and judgment. You might use it to help you in reducing the amount of calculations and work involved, but I don’t believe you can use it as the sole justification for purchasing what you would define as an “optimized” heat exchanger.

[lafondejs]

Dear All, Thanks a lot for your valuable comments. All comments are really helpful to me.

[blcavender@gmail.com]

Hello,

 

I ran across this thread in researching the process to develop a practical quantitative solution for a 

 

finned heat exchanger.  The links were quite helpful, but I am still missing a key piece in how to take a 

 

given physical finned exchanger design to a practical numerical solution. Here is my physical situation:

 

Visualize a 24 x 24 x 3.5 inch exchanger built in 12 identical sections with a triple pass of 3/8ths inch 

 

copper tubing that carry 12 fins per inch. The manufacturer does not offer any thermal performance 

 

information...only a single point of performance:

 

200,000 BTU/Hr heat delivered at 

3300 CFM air flow and 

21 gallons per min H2O at 

180 degree inlet water with 

2.14 Inches of H2O air pressure drop across the exchanger.

 

Using that same exchanger and these inputs:

 

Air Flow equals 1300 CFM at 72 degrees F inlet

Coolant (water) Flow equals 6 gallons per minute

Inlet Water Temperature is 58 degrees F

 

I would like to compute:

 

BTU cooling

Outlet water temperature

Outlet air temperature

 

==================================

 

I found a very smart heat exchanger company, Exergy, that wisely puts the full computation of their 

 

Shell/Tube exchangers right on the Internet so a customer can quickly determine exactly how each of their 

 

products will perform at their specific conditions. More manufacturers should do this to move their products faster.

 

http://www.exergyllc.../calculator.php

 

==================================

 

My question:

 

Does anyone know of an Internet Heat Exchanger calculator that can compute these parameters for a triple 

 

pass unit like I described (or another way I can model this unit)? 

 

I am an electrical engineer, but am essentially totally inexperienced in this area. 

 

Any thoughts, links or suggestions would be greatly appreciated!

 

Bruce