A heat exchanger is selected to deliver a defined duty without violating pressure drop, temperature approach, materials, and maintainability. Catalogue 'models' are the wrong starting point for process plant equipment. Send process data; the configuration follows.
1. Lock the process case
Write down both streams: identity, flow, inlet/outlet temperature, operating and design pressure, phase (liquid, condensing, boiling), and allowable pressure drop. If duty is known, include it. If not, the temperatures and flows must be complete enough to calculate duty. Missing one side is the most common reason an RFQ cannot be engineered.
2. Assign fluids to shell and tube
There is no universal rule, but these heuristics are used in industry:
- Put the high-pressure fluid in the tubes when it would force a thick shell.
- Put the fouling or corrosive fluid where it can be cleaned or where the cheaper metallurgy can be isolated.
- Put condensing steam often on the shell side for good distribution — unless the specification says otherwise.
- Put the stream that needs mechanical tube cleaning on the tube side of a straight-tube exchanger with a removable cover.
3. Choose the configuration Ohm manufactures
| Type | Choose when | Avoid when |
|---|---|---|
| Shell & tube (fixed tubesheet) | Clean shell side, modest ΔT, high integrity | Shell-side fouling that needs bundle pull without bellows/floating head |
| U-tube | Large differential expansion, removable bundle | Dirty tube-side fluid that must be rodded |
| Double-pipe / hairpin | Small area, high pressure, modular add-on | Large duties (usually uneconomic) |
| Kettle reboiler | Vaporising duty with disengagement space | Plot-limited thermosiphon-preferred services |
4. Materials and code
Name the materials (e.g. CS shell / SS 316L tubes) and the design code (TEMA class, ASME VIII-1, IS 2825). Do not ask the vendor to 'use the best material' without a process constraint. Ohm lists carbon steel and stainless steels as standard; duplex and other alloys when specified and procurable.
5. What to send with the RFQ
Use the technical RFQ form: equipment type, application, fluids, flows, temperatures, pressures, materials, quantity, delivery location, and drawing upload. That is enough to start engineering review.
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