A heat exchanger process datasheet is the primary technical document by which a buyer communicates the thermal and mechanical requirements to the manufacturer. It is not a standard purchase order form — it is an engineering document. Manufacturers use the datasheet to run thermal design software (HTRI, Aspen EDR), size the exchanger, select materials, and prepare the mechanical drawing. An incomplete or ambiguous datasheet does not result in a cheaper quote — it results in a delayed quote, over-designed equipment (to cover unknown conditions), and often expensive design changes after the purchase order is placed.
The Six Data Blocks Every Datasheet Must Cover
- Block 1 — Service Identification: Unit name (e.g., Reactor Feed Preheater), plant name, equipment tag number, applicable codes (ASME Section VIII, TEMA class), and any plant-specific standards.
- Block 2 — Fluid Properties: Fluid name for both shell-side and tube-side. Phase (liquid, vapour, or two-phase). For two-phase — inlet quality (vapour fraction). For multi-component streams — composition by mass or mole fraction, or at minimum a physical property table at design conditions.
- Block 3 — Process Conditions: Flow rate (mass or volumetric, with basis), inlet temperature, outlet temperature (or duty in kW/MW if outlet temp is variable), operating pressure, and allowable pressure drop for each side. State which conditions are fixed and which are outcomes (e.g., 'outlet temperature of hot side is fixed at 80°C; cold side outlet temperature is a result').
- Block 4 — Physical Properties: Density, dynamic viscosity, specific heat, and thermal conductivity at design conditions for each stream. If the manufacturer has access to the fluid names and conditions, they can look these up — but providing them avoids ambiguity for unusual or proprietary fluids.
- Block 5 — Fouling and Corrosion Data: Fouling resistance (m²·K/W) for each side. If you do not know the fouling resistance, reference the TEMA table values for your service. Corrosion rate and corrosion allowance. The material of construction specified or preferred.
- Block 6 — Mechanical and Installation Requirements: Number of shells in series/parallel. Orientation (horizontal or vertical). Tube OD and gauge preference (if any). TEMA type if pre-selected. Any space constraints. Utility connections (e.g., flanged, welded). Insulation requirements.
The Most Commonly Missing Data — and What Happens When It Is Absent
| Missing Data | What the Manufacturer Assumes | Risk to You |
|---|---|---|
| Fouling resistance | TEMA normal values for the service — often conservative | Oversized exchanger, higher cost |
| Allowable pressure drop | Assumes a conservative low value | Oversized exchanger; more shells than necessary |
| Fluid viscosity vs temperature | Uses published data for similar fluids | Wrong sizing for high-viscosity or non-Newtonian fluids |
| Phase change details (flash fraction, dew/bubble point) | Assumes no phase change or uses average phase | Completely wrong thermal design; unit will not perform |
| Future capacity or turndown | Designs for stated conditions only | Unit performs poorly at reduced rates; may have flow instability |
| Preferred tube length | Selects shortest length that fits thermal duty | May not fit available space or plant layout |
| Number of passes | Optimises internally, may select 4 or 6-pass | Tube-side pressure drop higher than expected |
| Nozzle sizes and ratings | Selects optimum for velocity limits | May not match existing piping; flange rating mismatch |
How to State Fouling Resistance Correctly
Fouling resistance (Rf) is specified in units of m²·K/W (SI) or ft²·°F·hr/BTU (US customary). It represents the thermal resistance added by the fouling deposit layer on the heat transfer surface.
TEMA provides standard fouling resistance values by service type. Commonly used values:
TEMA fouling resistances are conservative starting points, not absolutes. For clean services with good water treatment, actual fouling may be 30–50% less than TEMA values. For heavy fouling services (crude oil, slurries), actual fouling may exceed TEMA values. If you have operating data from a similar existing unit, use that instead.
| Fluid / Service | TEMA Fouling Resistance (m²·K/W) |
|---|---|
| River water (treated) | 0.000176 |
| Sea water (velocity > 0.9 m/s) | 0.000088 |
| Cooling tower water (treated) | 0.000176 |
| Boiler feedwater (treated) | 0.000088 |
| Steam (oil-free) | 0.000088 |
| Organic solvents (clean) | 0.000176 |
| Crude oil above 50°C | 0.000528–0.000881 |
| Fuel oil | 0.000881 |
| Refrigerant vapour (clean) | 0.000176 |
| Chemical process streams (light) | 0.000176–0.000352 |
Specifying Design Margins: The Right Way
Many procurement specifications request a design margin of '10% on heat transfer area' or '10% excess area'. This practice, while common, can lead to significant oversizing when combined with conservative fouling resistances and conservative physical property assumptions.
A better approach: specify the expected fouling resistance, ask for a clean overall heat transfer coefficient (Uc) and dirty overall coefficient (Ud), and ensure Ud meets the thermal duty. The overdesign factor (ODF = Uc/Ud) then tells you how much extra capacity the unit has when clean — typically 1.1 to 1.3 is appropriate. Asking for 10% excess area on top of already conservative fouling resistances results in units that are 40–60% oversized — wasting capital and causing operational problems (flow maldistribution, vibration at part-load).
The One Question That Saves the Most Time
Before sending any datasheet, answer this: 'Is this exchanger replacing an existing unit?' If yes, provide the existing unit's dimensions, tube count, baffle spacing, and current performance data. This information allows the manufacturer to identify why the existing unit is failing or underperforming, and ensure the replacement addresses the root cause — not just replicate the same design.
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