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Propylene glycol, 40 % by volume

A 40 % by volume propylene glycol solution, freeze protection to about −21 °C — the middle charge — full winter protection at a manageable pumping penalty.

PhaseLiquid
Temperature range-20 to 100 °C
Freeze protectionabout -21.1 °C — full curve, 0 to 60 %
SourceDow, Engineering and Operating Guide for DOWFROST and DOWFROST HD, SI tables, by volume; typical values for inhibited product
Properties at temperature
°C
-20°100°

Validated from -20 to 100 °C.

Density1,037.4 kg/m³
Dynamic viscosity4.59 mPa·s
Specific heat3.702 kJ/(kg·K)
Thermal conductivity0.384 W/(m·K)
Kinematic viscosity ν = µ/ρ4.4245 mm²/s
Prandtl number Pr = cpµ/k44.25

Click on a chart to print it with your selected value marked.

Density kg/m³
Density from -20 to 100 °C, in kg/m³. Marked at 20 °C: 1,037 kg/m³-20 °C — 1,053 kg/m³-15 °C — 1,052 kg/m³-10 °C — 1,050 kg/m³-5 °C — 1,048 kg/m³0 °C — 1,046 kg/m³5 °C — 1,044 kg/m³10 °C — 1,042 kg/m³15 °C — 1,040 kg/m³20 °C — 1,037 kg/m³25 °C — 1,035 kg/m³30 °C — 1,032 kg/m³35 °C — 1,029 kg/m³40 °C — 1,026 kg/m³45 °C — 1,023 kg/m³50 °C — 1,020 kg/m³55 °C — 1,017 kg/m³60 °C — 1,013 kg/m³65 °C — 1,010 kg/m³70 °C — 1,006 kg/m³75 °C — 1,002 kg/m³80 °C — 998.4 kg/m³85 °C — 994.3 kg/m³90 °C — 990.1 kg/m³95 °C — 985.7 kg/m³100 °C — 981.2 kg/m³100010201040-20020406080100
Dynamic viscosity mPa·s (log scale)
Dynamic viscosity from -20 to 100 °C, in mPa·s (log scale). Marked at 20 °C: 4.59 mPa·s-20 °C — 48.9 mPa·s-15 °C — 33.07 mPa·s-10 °C — 23.11 mPa·s-5 °C — 16.63 mPa·s0 °C — 12.3 mPa·s5 °C — 9.32 mPa·s10 °C — 7.21 mPa·s15 °C — 5.7 mPa·s20 °C — 4.59 mPa·s25 °C — 3.75 mPa·s30 °C — 3.12 mPa·s35 °C — 2.62 mPa·s40 °C — 2.24 mPa·s45 °C — 1.93 mPa·s50 °C — 1.68 mPa·s55 °C — 1.48 mPa·s60 °C — 1.31 mPa·s65 °C — 1.18 mPa·s70 °C — 1.06 mPa·s75 °C — 0.96 mPa·s80 °C — 0.88 mPa·s85 °C — 0.81 mPa·s90 °C — 0.75 mPa·s95 °C — 0.69 mPa·s100 °C — 0.65 mPa·s110-20020406080100
Specific heat kJ/(kg·K)
Specific heat from -20 to 100 °C, in kJ/(kg·K). Marked at 20 °C: 3.702 kJ/(kg·K)-20 °C — 3.569 kJ/(kg·K)-15 °C — 3.586 kJ/(kg·K)-10 °C — 3.603 kJ/(kg·K)-5 °C — 3.619 kJ/(kg·K)0 °C — 3.636 kJ/(kg·K)5 °C — 3.652 kJ/(kg·K)10 °C — 3.669 kJ/(kg·K)15 °C — 3.685 kJ/(kg·K)20 °C — 3.702 kJ/(kg·K)25 °C — 3.718 kJ/(kg·K)30 °C — 3.735 kJ/(kg·K)35 °C — 3.751 kJ/(kg·K)40 °C — 3.768 kJ/(kg·K)45 °C — 3.784 kJ/(kg·K)50 °C — 3.801 kJ/(kg·K)55 °C — 3.817 kJ/(kg·K)60 °C — 3.834 kJ/(kg·K)65 °C — 3.85 kJ/(kg·K)70 °C — 3.867 kJ/(kg·K)75 °C — 3.883 kJ/(kg·K)80 °C — 3.9 kJ/(kg·K)85 °C — 3.916 kJ/(kg·K)90 °C — 3.933 kJ/(kg·K)95 °C — 3.949 kJ/(kg·K)100 °C — 3.966 kJ/(kg·K)3.63.73.83.9-20020406080100
Thermal conductivity W/(m·K)
Thermal conductivity from -20 to 100 °C, in W/(m·K). Marked at 20 °C: 0.384 W/(m·K)-20 °C — 0.346 W/(m·K)-15 °C — 0.351 W/(m·K)-10 °C — 0.356 W/(m·K)-5 °C — 0.361 W/(m·K)0 °C — 0.366 W/(m·K)5 °C — 0.371 W/(m·K)10 °C — 0.376 W/(m·K)15 °C — 0.38 W/(m·K)20 °C — 0.384 W/(m·K)25 °C — 0.388 W/(m·K)30 °C — 0.392 W/(m·K)35 °C — 0.396 W/(m·K)40 °C — 0.399 W/(m·K)45 °C — 0.402 W/(m·K)50 °C — 0.405 W/(m·K)55 °C — 0.408 W/(m·K)60 °C — 0.41 W/(m·K)65 °C — 0.413 W/(m·K)70 °C — 0.415 W/(m·K)75 °C — 0.416 W/(m·K)80 °C — 0.418 W/(m·K)85 °C — 0.419 W/(m·K)90 °C — 0.42 W/(m·K)95 °C — 0.421 W/(m·K)100 °C — 0.422 W/(m·K)0.360.380.40.42-20020406080100
Send PG 40 % at 20 °C into a solver

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 = 1037.4cₚ = 3.702

Reynolds Number

ρ = 1037.4μ = 4.59

Prandtl Number

μ = 4.59cₚ = 3.702k = 0.384

Learning zone

Forty percent propylene glycol protects to about −21 °C — real winter protection for most exposures, one step short of the −33 °C a 50 % charge buys. It is the sensible middle of the range: enough glycol that a rooftop coil or an exposed run can sit through a cold snap, not so much that the loop's hydraulics have to be redesigned around the fluid.

The penalties at 20 °C: specific heat 3.70 kJ/(kg·K) against water's 4.18, down 11 %; thermal conductivity 0.384 W/(m·K) against 0.598, down 36 %; density up 4 % to 1037 kg/m³; and viscosity 4.59 mPa·s against 1.00. As always with glycol, the number to design against is the cold-end one: at 0 °C the fluid is 12.3 mPa·s and at −20 °C it is 48.9 — the same coil that runs turbulent in September can be laminar in January at the same pump setting.

These are the manufacturer's typical values for the inhibited product, tabulated by volume percent, which is how glycol is actually sold and refractometer-checked. They run slightly denser and a little different in detail from the generic ASHRAE tables behind the 30 % and 50 % entries — the inhibitor package and the manufacturer's own measurements both move the numbers — which is a useful reminder that the data sheet for the fluid actually in the loop beats any library table, this one included.