When reviewing a thermal oil circulation pump curve, the first question is not simply how much flow the pump can deliver. The key question is: under what liquid, temperature, viscosity, speed and impeller conditions was the curve established? A water-test curve, a manufacturer curve already corrected for the target fluid, and a curve for the same fluid at another temperature are not interchangeable just because the pump model is the same.
Water curves are commonly the starting point for centrifugal-pump assessment. The Hydraulic Institute notes that pumps are commonly tested with clear water and that viscous liquids may change flow, head, efficiency and input power. A water curve is therefore not automatically unusable, but its role as an input must be checked against the target-fluid properties and the applicable method.
Manufacturer-corrected curves may already reflect the target liquid and viscosity. They may be based on testing or calculation, which are different forms of evidence and should be identified. Applying a water-curve viscosity correction again to a curve that already includes the same effect can double count it.
Other-condition curves may be labelled “thermal oil” but relate to another temperature, viscosity, speed or impeller arrangement. They should not be used directly, nor automatically treated as water curves. The original conditions must be completed before an appropriate conversion path can be confirmed.
For centrifugal pumps, higher viscosity can change internal losses and performance. Public guidance can explain why further calculation may be needed, but an example factor from another pump or fluid must not be used as a product result. Keep dynamic and kinematic viscosity distinct, including units and temperature basis.
Viscosity correction also does not replace separate checks for materials, seals, allowable temperature, suction conditions and other equipment requirements.
Thermal oil may have different viscosity at different operating states. Each assessed state should be linked to a traceable property source. Pump documentation should identify the model, impeller configuration, speed, curve number and revision, test liquid, and whether the curve has already been corrected.
AFT Fathom 13 explains that its viscosity-correction feature needs water-curve best-efficiency-point head and flow, plus rated pump speed. This is a boundary for that software feature and its referenced method—not a universal instruction for every pump or every program. Missing efficiency or BEP data should remain visible as an information gap.
A pump curve describes pump performance under stated conditions. System head depends on piping, equipment, valves and boundary conditions. The pump-side curve and system-side resistance calculation must use a consistent operating case.
Viscosity effects inside the pump and viscosity effects in the piping are different calculation objects. “Double correction” normally means re-converting a pump curve that already includes the same pump-performance effect; it does not mean removing necessary fluid-property treatment from the piping model.
Use the sequence original curve → manufacturer treatment → software input → calculation output. Ask the manufacturer to confirm curve number, revision, pump configuration, speed, test liquid and whether viscosity effects are already included. If corrected, request the target fluid, temperature, viscosity and method or basis.
AFT’s public documentation states that its feature is for an entered water curve. If the manufacturer provides a curve for the intended working liquid at the required viscosity, enter that curve directly and keep the feature off to avoid double counting. A manufacturer curve for the same liquid at another viscosity is not automatically an appropriate input for this water-curve feature.
Confirm curve number, revision, pump configuration, impeller and speed.
State the test liquid and the source of the original performance data.
Confirm whether the curve already includes viscosity effects; if so, state liquid, temperature, viscosity and method.
Provide efficiency and BEP information, and identify whether the project case is within the stated applicability range.
Separate tested results, calculated results and open items; retain the original files, written confirmations and model version.
A water curve can have a valid role in a thermal oil project, but only after its identity and conditions are clear. Confirm the curve type first, then align temperature, viscosity and speed, and finally check whether the same pump-performance effect has been counted more than once.
Hydraulic Institute, How Viscosity Affects Pumping (7 Dec 2022). This article uses only its public discussion of possible performance changes with viscous liquids; diagram values are not used as product parameters.
AFT Fathom 13, Viscosity Correction. This article uses only the public notes on water-curve inputs, double counting and scope; it is not treated as product-selection approval.
