An industrial exchanger enquiry that lists only “water/glycol” leaves room for different assumptions about the fluid, concentration and operating conditions. Two quotations can appear comparable while using different property data and predicting different duties or pressure drops.
Specify glycol concentration together with the ethylene glycol (EG) or propylene glycol (PG) formulation, whether the percentage refers to glycol or commercial fluid, and its mass or volume basis. Provide applicable properties across the operating temperature range, then require a coordinated check of both-side heat duty, flow, temperatures and allowable pressure drop. Confirm the low-temperature protection requirement separately, and reassess the rating whenever the approved fluid or concentration changes.
This procurement framework applies to complete industrial shell-and-tube exchangers. The concentration itself must be selected for the actual fluid and project requirements; there is no single percentage or performance correction that can replace those inputs.
Identify the Glycol and the Actual Fluid Formulation
Specify the fluid by its chemical base and commercial identity. “Water/glycol” leaves the exchanger supplier without a defined liquid to rate.
Ethylene glycol (EG) and propylene glycol (PG) are separate fluid bases. Dow’s FLUIDFILE calculator treats them separately and provides product-specific selections. Do not substitute one for the other in a quotation while retaining the original property data.
Also distinguish the glycol itself from the formulated heat transfer fluid. An inhibited product includes a corrosion-control formulation; its product name identifies more than the base glycol. Use the selected product at its specified final composition as the enquiry basis, whether supplied as a premix or diluted from concentrate.
Request three identifiers:
- Product identity: Manufacturer, complete product designation and whether the supplied product is a concentrate or a premix.
- Document identity: Applicable technical data sheet, safety data sheet and the fluid-property data source, including their revisions or dates.
- Condition being rated: The proposed in-service composition, with any permitted variation identified for review.
If the product has not yet been selected, label the options as separate design cases. Ask bidders to identify which case they have used and which assumptions remain open. A quotation based on an unnamed “equivalent glycol” should be clarified before its thermal results are compared with another offer.
This is a fluid-definition requirement for purchasing a complete industrial exchanger. It does not establish that a particular commercial coolant is compatible with the project or endorse a coolant brand.
State Exactly What the Concentration Means
A percentage needs both a measurement basis and a named constituent. State whether it means glycol by mass, glycol by volume, or a specified commercial fluid diluted in water.
Dow’s calculator input fields distinguish weight and volume bases, and some product selections distinguish glycol content from formulated-fluid content. These labels should remain attached to the value throughout the RFQ, property file and rating report.
| Concentration field | What to state | Ambiguity it resolves |
|---|---|---|
| Constituent | Pure EG or PG content, or the named formulated product | Whether the percentage describes glycol itself or the commercial concentrate |
| Measurement basis | Mass fraction or the supplier-defined volume basis | Whether a bidder may treat the number as weight percent or volume percent |
| Reference conditions | Reference temperature and the supplier’s definition or conversion data for a volume-based specification | How the volume statement and corresponding property data are interpreted |
| Required range | Nominal concentration and any permitted variation, using the same basis | Which composition cases the supplier must evaluate |
Do not convert mass percent to volume percent by changing the label. Request the fluid supplier’s applicable conversion information. Likewise, do not assume that a percentage of inhibited concentrate equals the same percentage of pure glycol. Dow’s historical engineering guide illustrates the distinction with separate columns for glycol and formulated-fluid concentration. DOWFROST engineering guide, Table 3
Illustrative specification wording: “Rate the exchanger for the named inhibited fluid at the stated mass fraction of propylene glycol in the final solution, using the referenced property dataset. Evaluate the separately listed concentration limits as additional cases.”
That wording shows the required relationships; the project must supply the actual product, concentration and limits. For a volume-based requirement, replace the mass-fraction wording with the supplier’s defined volume basis and reference conditions. This is specification wording, not a mixing procedure.
Provide Properties Across the Operating Temperature Range
Provide a temperature-dependent property dataset for the selected formulation and concentration. A single room-temperature value cannot describe a duty that includes substantially different operating or startup conditions.
The main fluid inputs have distinct purposes:
| Property | Suggested SI unit | Use in the exchanger review |
|---|---|---|
| Density | kg/m³ | Relates mass flow to actual volumetric flow and supports hydraulic calculations |
| Dynamic viscosity | mPa·s | Helps establish flow behavior and the resistance to circulation |
| Specific heat capacity | kJ/(kg·K) | Relates sensible heat duty to mass flow and temperature change |
| Thermal conductivity | W/(m·K) | Contributes to the calculation of heat transfer through the fluid near the surface |
These are property categories, not assumed values. Dow’s fluid calculator reports these properties against temperature and concentration. If a source supplies kinematic viscosity instead of dynamic viscosity, identify that explicitly and have the rating engineer make any required conversion using consistent density data.
Ask for data covering each specified operating case, including the lowest temperature at which circulation is required. The rating engineer should also identify any additional properties or local-temperature data needed by the selected calculation method. Do not extend a correlation beyond its stated range without a justified basis.
Record the dataset’s product designation, concentration basis, units, temperature range and revision. If two bidders use different datasets, resolve that difference before attributing the difference in predicted performance to their exchanger designs.
Fluid properties are only part of the rating. Spirax Sarco’s heat transfer explanation identifies fluid properties, flow rates and surface geometry as influences on heat transfer coefficients. That is why a viscosity value alone cannot establish the required exchanger area.
For broader procurement issues involving viscous process streams, see the high-viscosity chemical heat exchanger guide. Here, the immediate task is to provide a consistent glycol property basis for the complete equipment rating.
Check Heat Duty and Pressure Drop Together
Require a thermal and hydraulic rating for the specified glycol cases, with acceptance criteria for both heat duty and pressure drop. A proposal that satisfies only one of these requirements remains incomplete.
The overall heat transfer coefficient includes resistance on both fluid sides and through the separating wall, with fouling included where applicable. Changing the glycol side therefore does not translate directly into an identical percentage change in whole-exchanger performance. Spirax Sarco: Heat Transfer
Use a coordinated review:
- Agree the conditions being held fixed. Identify the required duty, inlet conditions, outlet targets and the flow available on each side. State whether the specified flow is a mass flow or an actual volumetric flow at a defined condition. Mark calculated outputs separately from imposed requirements so incompatible inputs can be resolved.
- Request the thermal and hydraulic results for each case. Ask the exchanger supplier to state the fluid dataset used, predicted duty or outlet temperatures, and calculated pressure drop on both sides. Define the pressure-drop boundary, including whether exchanger nozzles are included. Compare each result with the same acceptance limits and fouling basis.
- Confirm that the surrounding system can provide the rated flow. Have the responsible system engineer review the circulation requirement against the available pumping arrangement. Do not assume that retaining the same pump guarantees the flow used in a revised exchanger calculation. Assign responsibility for resolving any mismatch.
Review cold startup and normal operation as separate cases when their conditions differ. The limiting hydraulic case need not be the case with the greatest heat duty; the calculation should identify the controlling conditions rather than assuming a single worst case covers everything.
Calculator boundary: A fluid-property tool can support the review, but a pressure-drop result expressed per unit length of pipe or tube is not a shell-and-tube exchanger rating. The equipment calculation must represent the proposed geometry, flow arrangement and agreed boundaries. Dow’s FLUIDFILE results table makes that distinction visible through its pipe-length pressure-drop units.
Separate Freeze Protection from Operating Performance
Define the low-temperature protection objective before choosing the concentration, then check that the resulting fluid meets the operating requirements. A freeze-protection statement alone does not confirm the exchanger’s thermal capacity or the circulation available during startup.
Dow’s engineering guide distinguishes freeze protection from burst protection. Burst protection may allow ice or slush in an inactive system with provision for expansion; it is not evidence that the fluid can circulate as required. The guide also identifies inhibitor concentration as a consideration. These are useful distinctions, but its historical product limits should not replace current supplier instructions. DOWFROST engineering guide, concentration selection
Give the fluid supplier and project engineer a clear set of conditions:
- The lowest expected fluid temperature during operation, shutdown and storage, as applicable.
- Whether the system must circulate or restart under those conditions.
- Whether ice formation is prohibited and what protection requirement the project specifies.
- The concentration range proposed for both protection assessment and exchanger rating.
Do not select extra glycol simply as an unspecified safety margin. Equally, do not reduce concentration to pursue thermal performance without checking the fluid’s protection requirements. Ask for a justified concentration range that can be evaluated against both objectives.
Water quality and compatibility belong in the same approval package. Dow’s guide explains that dilution-water impurities can affect corrosion protection and deposits, and that material suitability depends on the application. Obtain current requirements for the actual formulation and review the exchanger’s wetted materials and seals accordingly. DOWFROST engineering guide, dilution water and materials
The procurement deliverable is an agreed fluid specification and its supporting review. It is not a generic dilution recipe or a declaration that every inhibited glycol is suitable for every exchanger material.
Make the RFQ and Any Fluid Change Traceable
Issue one controlled set of inputs to all bidders, and require each offer to identify its departures. This makes a comparison of glycol concentration and heat exchanger performance meaningful: the equipment results must refer to the same fluid and duty basis.
Organize the RFQ into three linked documents:
- Fluid specification and property attachment: The approved product identity, concentration definition, applicable property data and compatibility requirements. Identify the owner of any unresolved fluid selection.
- Two-sided exchanger datasheet: Operating cases, fluid allocation or a request for the supplier’s proposed allocation, flow definitions, inlet conditions, outlet targets, heat duty and allowable pressure drop. Include operating and design conditions as separate fields, together with the project’s material, fouling and equipment requirements.
- Bidder response and deviation schedule: The calculation basis, results for each requested case, outstanding assumptions and any proposed change to the specified fluid or duty. Require alternatives to be shown separately from the compliant base offer.
If a formulation or concentration changes after quotation, send a revision to the parties responsible for fluid selection, exchanger rating and system integration. Request confirmation of which calculations and documents must change before accepting the substitution. The contract should identify who performs the reassessment and who approves it.
Illustrative change: A buyer substitutes a different inhibited PG product while leaving the glycol percentage unchanged. The appropriate next step is to obtain the new product’s concentration definition and applicable data, then have the responsible engineer determine whether the approved rating remains valid. Similar wording on two product labels is not a documented equivalence assessment.
At handover, retain the accepted fluid specification and rating basis with the equipment records. Later operating changes can then be compared with a known baseline instead of an isolated percentage in an old email.
Frequently Asked Questions
Can a water-rated exchanger be accepted unchanged for glycol duty?
Only after a documented reassessment confirms suitability for the specified glycol duty. Approval of the original water service is not approval of a different fluid. The review may conclude that the existing equipment is adequate, but it must address the revised thermal and hydraulic conditions as well as relevant material and operating limits. Mechanical design approval and thermal performance acceptance answer different questions.
Is a safety data sheet enough for the thermal rating?
Not by itself unless it contains all the required, applicable engineering data. Request the selected formulation’s property dataset over the specified concentration and temperature range. A document title or a single physical-property value does not demonstrate that the rating inputs are complete. Keep the safety data sheet in the fluid documentation package, alongside the technical information used for calculation.
Can a concentration instrument reading be copied directly into the RFQ?
Only when the reading’s scale and conversion basis match the specification. A result reported on a different scale needs the appropriate fluid-specific interpretation. Dow’s historical Table 3, for example, lists refractive index and Brix separately from glycol and product percentages. Ask the fluid supplier to identify the applicable measurement interpretation and report the concentration on the agreed basis. DOWFROST engineering guide, Table 3
Submit a Complete Shell-and-Tube Exchanger Enquiry
A useful glycol specification connects a named fluid, an unambiguous concentration and applicable property data to the required exchanger duty. It also records who must reassess the design when those inputs change.
For an industrial shell-and-tube heat exchanger, submit the fluid specification, both-side operating data, allowable pressure drops and equipment requirements together. Mark unresolved inputs clearly and use the project contact page to request a quotation against that defined scope.
References
- Dow. Heat Transfer Fluids Calculators / FLUIDFILE. Undated; accessed 16 October 2026. Calculator input definitions and output categories were reviewed; no project calculation was performed for this article.
- The Dow Chemical Company. Engineering and Operating Guide for DOWFROST and DOWFROST HD Inhibited Propylene Glycol-based Heat Transfer Fluids. September 2001, Form No. 180-01286-0901 AMS. Manufacturer publication hosted by Ingredi; accessed 16 October 2026. Used for concentration definitions and general protection, water-quality and compatibility principles. Obtain current product-specific instructions for design limits and application decisions.
- Spirax Sarco. Heat Transfer. Undated; accessed 16 October 2026. General heat transfer principles, particularly the effects of fluid properties, flow and thermal resistance. Steam-specific examples have not been applied as liquid-to-liquid rating assumptions.
