Take
the TEMA
test
A brief guide to picking the right TEMA exchanger
Incorporated Engineer and
FUNKE Sales Manager UK
Specifying that workhorse of the process industries, the shell-and-tube heat exchanger, is usually a straightforward exercise in these days of computer-aided design packages, but you do need to ask the right questions. David Knightbridge offers a brief guide to that common one: ‘which type of TEMA exchanger?’
The advent of modern computer programmes has enabled many of us to thermally rate heat exchangers quickly and accurately. But how do we decide which design of heat exchanger for a given application will satisfy the operating conditions, all the mechanical/thermal criteria, and give a cost-effective solution?
Many customers have asked what forms the basis of a heat exchanger design for their particular enquiry. I well recall in my earlier years as a junior applications engineer, my mentor of the time showing me how to make a selection, saying that the enquiry we were looking at ‘was leading him by the nose’ to a certain type of heat exchanger design. His experience gained over the years enabled him to do this, but what was the thought process that went into selecting the right type of heat exchanger? In some cases there can be more than one solution.
Obviously it is not possible to cover all aspects of design or all available TEMA types of heat exchanger in just a few short lines, but the table and diagrams overleaf show some of the more commonly used types of TEMA heat exchangers [TEMA is the Tubular Exchanger Manufacturers Association — see table below].
All the types shown in the table can be designed in accordance with TEMA B, C and R codes. The table is intended as a general guide only and does not purport to cover all aspects of design. Full technical advice can be given by a heat exchanger applications engineer.
Another question that is often asked is ‘what is the difference between the three types of TEMA B, C and R codes?’ To answer that in detail would require a full review of TEMA standards, but the following guide lines may be useful:
TEMA B
generally for chemical process services, more stringent than TEMA C, but not as stringent as R
TEMA C
or generally moderate commercial and process application requirements. Probably the most commonly used in our industry
TEMA R
the highest integrity design.
The decision as to which class of TEMA to use does not lie with the heat exchanger manufacturer, but with the design authority responsible for that part of the project. The manufacturer must then consider all the thermal and mechanical requirements of the requested design code when making the selection.
Which type of TEMA Heat Exchanger?
| Typical TEMA type heat exchanger | Desxripzion of TEMA type heat exchanger | Removable tube bundle | Tubes can be leaned internally by rodding | Non-hazardous liquids & gases below 40barg | Non-hazardous liquids & gases above 40barg | Hazardous liquids & gases | No gaskets in contact with process side | Ability to resist thermal shock | |
| Below 190° C | Above 190° C | ||||||||
| AEW BEW |
Externally sealed Floating tube sheet |
Yes | Yes | Yes | No | No | No | No | No |
| AEP BEP |
Outside packed Floating head |
Yes | Yes | Yes | Yes | Yes² | No | No | No |
| AEL BEM |
Fixed tube sheet | No | Yes | Yes¹ | Yes¹ | Yes | Yes | Yes³ | No |
| NEN | Fixed tube sheet, channel integral with tubesheet | No | Yes | Yes¹ | Yes¹ | Yes | Yes | Yes³ | No |
| AEU BEU |
U tube | Yes | No | Yes | Yes | Yes | Yes | Yes⁴ | Yes |
| AET BET |
Pull through floating head | Yes | Yes | Yes | Yes | Yes | Yes | No | Yes |
| AES BET |
Floating head with backing device | Yes | Yes | Yes | Yes | Yes | Yes | No | Yes |
Notes:
1. Expansion bellows may be required. 2. Tube side only. 3. Shell side only. 4. Shell side only if tube bundle welded into shell and therefore not removable.
David Knightbridge IEng is UK sales manager for the German heat exchanger manufacturer Funke
Front end stationary head types
A - Channel and removable cover
B - Bonnet (integral cover)
B - Channel integral with
tube-sheet and removable cover
Shell types
E - One pass shell
The typical TEMA type heat exchangers listed in the table can be visualised from the diagrams shown here (right and left). From the three-letter coding for each type of exchanger (AEW, BEW, AEP and so on, as listed in the table) a picture can be built up of the final shell-and-tube assembly of front-end stationary head, shell type, and rear-end head
Rear end head types
L - Fixed tubesheet like “A” stationary head
M - Fixed tubesheet like “B” stationary head
N - Fixed tubesheet like “N” stationary head
P - Outside packed floating head
S - Floating head with backing device
T - Pull through floating head
U - U-tube bundle
W - Externally sealed floating tubesheet
