Ethylene glycol, 50 % by volume
A 50 % by volume ethylene glycol solution, freeze protection to about −37 °C — the standard chiller and automotive charge.
| Phase | Liquid |
| Temperature range | -30 to 100 °C |
| Freeze protection | about -37 °C |
| Source | ASHRAE Handbook—Fundamentals, Ch. 31 (Secondary Coolants), interpolated from published tables |
Validated from -30 to 100 °C.
| Density | 1,072 kg/m³ |
| Dynamic viscosity | 4.2 mPa·s |
| Specific heat | 3.29 kJ/(kg·K) |
| Thermal conductivity | 0.389 W/(m·K) |
| Kinematic viscosity ν = µ/ρ | 3.9179 mm²/s |
| Prandtl number Pr = cpµ/k | 35.52 |
Every fluid property in these opens already filled, all from the same state — so a density and a viscosity in one calculation always describe the same fluid at the same temperature.
Glycol Loop Heat Transfer (Capacity Derate)
ρ = 1,072c = 3.29
Reynolds Number
ρ = 1,072μ = 4.2
Prandtl Number
μ = 4.2cₚ = 3.29k = 0.389
Learning zone
Fifty-fifty ethylene glycol and water is the most-mixed heat transfer fluid in the world: it is what goes in car radiators and what charges most industrial chilled-water loops that see freezing. It protects to about −37 °C, and its burst protection extends well below that.
Against 50 % propylene glycol at 0 °C it is roughly half the viscosity — 9.5 mPa·s against 19.5 — and that difference is the entire argument for using it. Pump head, pressure drop and the laminar-transition risk all scale with viscosity, so the ethylene loop stays turbulent to lower temperatures and costs less to circulate.
The trade-off is specific heat: 3.29 kJ/(kg·K) at 20 °C against propylene's 3.54, so ethylene carries slightly LESS heat per kilogram despite transferring it better. Combined with a higher density the two nearly cancel on a volumetric basis. The choice between them is almost never thermal — it is whether the consequences of a leak into something people drink or touch are acceptable.