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Heat-transfer fluids

Freeze-Protection Concentration Selector

Finds the minimum coolant concentration whose committed freeze point meets a target protection temperature, by inverse interpolation on the committed freeze tables, and shows the two bracketing table rows.

A secondary-loop coolant must stay liquid down to the lowest temperature it will see. This calculator reads the minimum concentration whose committed freeze point meets a target protection temperature, by inverse interpolation on the committed freeze table of the selected fluid (ethylene glycol, methanol, ethanol, glycerol, potassium carbonate, lithium chloride or magnesium chloride), and shows the two bracketing table rows so the freeze line itself is visible. It also reads the density, viscosity and heat capacity at that concentration from the committed property grid — what the protection costs in pumping and heat transfer. Propylene glycol is absent: it has no committed freeze table.

TypeInteractive engineering calculator

Calculator

Target

Committed table reaches −51.2 °C at 60 wt%. °C primary; °F accepted.

Minimum concentration40.0 wt%

This is the freeze-point match from the committed Ethylene glycol table: the minimum concentration whose committed freeze point is at or below -23.8 °C.

Bracketing committed freeze-table rows
35 wt%
freezes at −18.8 °C
40 wt%
freezes at −23.8 °C
Trade-off at 40.0 wt%, 0 °C (coldest committed grid temperature at or above the target)
Density
1060.4 kg/m³
Dynamic viscosity
5.811 cP
Specific heat
3434 J/kg·K

A higher concentration raises viscosity and lowers heat capacity — what the freeze protection costs in pumping and heat transfer.

Industry practice applies a margin between the fluid's freeze point and the lowest expected operating temperature; margin selection is specified by the fluid supplier or the system designer.

Audit trail
  • Target -23.80 °C between committed rows 35 wt% (−18.8 °C) and 40 wt% (−23.8 °C)
  • Minimum concentration = 40.000 wt% (linear inverse interpolation on the committed Ethylene glycol freeze line)
  • Trade-off read at 40.0 wt%, 0 °C from the committed property grid
Copyable summary

On the committed ethylene-glycol freeze line, 40 wt% freezes at −23.8 °C and 50 wt% at −36 °C — exact freeze-table values, read straight from the dataset, not interpolations.

Minimum concentration whose committed freeze point meets the target, read by inverse interpolation on the committed freeze tables and cross-checked against the coolant property hubs. The freeze-point match only — not a margin recommendation.

Related: Superheat · Subcooling · Ethylene glycol properties

Formulas

Freeze-point match
minimum c such that T_freeze(c) ≤ T_target
Inverse interpolation
c interpolated linearly between the two bracketing committed freeze-table rows
Trade-off read-out
ρ, μ, c_p at (c, T_ref) from the committed property grid, T_ref the coldest committed grid temperature ≥ T_target

Diagram

wt%T_ffreeze linetargetmin wt%

Worked example

Ethylene glycol. Target protection temperature −23.8 °C. Find the minimum concentration and the trade-off properties.

  1. 01−23.8 °C falls exactly on the committed 40 wt% row of the ethylene-glycol freeze table
  2. 02Bracketing rows: 35 wt% freezes at −18.8 °C and 40 wt% at −23.8 °C
  3. 03Minimum concentration whose committed freeze point meets the target = 40.0 wt%
  4. 04Trade-off at 40 wt%, 0 °C (the coldest committed grid temperature at or above the target): density 1060.4 kg/m³, viscosity 5.811 cP, specific heat 3434 J/kg·K
Result

The minimum ethylene-glycol concentration is 40.0 wt% (freezing at −23.8 °C); at 40 wt% the coolant is denser and more viscous, with a lower heat capacity, than at a weaker mix.

FAQ

Is this the concentration I should use?
It is the freeze-point match from the committed table — the minimum concentration whose freeze point reaches the target. Industry practice applies a margin between the freeze point and the lowest expected operating temperature; that margin is specified by the fluid supplier or the system designer, not by this calculator.
Why does a colder target get refused?
Each freeze table ends at a floor — its coldest committed concentration and freeze point. Below that lies the eutectic region, where the freeze line is no longer monotonic and the committed table does not extend. The calculator refuses and names the floor rather than extrapolating.
Why is viscosity missing for some fluids?
A property is shown only where the committed grid tabulates it. Magnesium chloride, for example, has no committed viscosity grid, so its viscosity figure is honestly omitted. A property is also omitted where the cold-reference grid cell is null.
Where is propylene glycol?
Propylene glycol has no committed freeze table in the dataset, so it is deliberately absent — the calculator does not improvise a freeze line it cannot cite.

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