Take the TEMA test
11 Apr 2005
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 br
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 below show some of the more commonly used types of TEMA heat exchangers [TEMA is the Tubular Exchanger Manufacturers Association.]
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 — for 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.
The standard-setting TEMA team
TEMA, the Tubular Exchanger Manufacturers Association, is a US trade association of leading manufacturers of shell-and-tube heat exchangers, which has pioneered the research and development of heat exchangers since its foundation in 1939.
TEMA standards and software are now accepted worldwide as the authoritative source on shell-and-tube mechanical design.
Eight editions of TEMA standards have been published over the years, each one updating the industry on the latest developments in technology. The standards have been developed with input from the likes of the API (American Petroleum Institute) and ASME (the American Society of Mechnical Engineers), both standard-setting organisations in their own right.
TEMA has also developed engineering software products which complement the TEMA standards in the areas of flexible shell elements (expansion joints) analysis, flow induced vibration analysis and fixed tubesheet design and analysis. The software programs feature a materials databank of 38 materials of construction.
David Knightbridge FInstSM is UK sales manager for the German heat exchanger manufacturer Funke.
