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Propylene glycol, 20 % by volume

A 20 % by volume propylene glycol solution, freeze protection to about −7 °C — the corrosion floor: any leaner and the inhibitors are too dilute to trust.

PhaseLiquid
Temperature range-5 to 100 °C
Freeze protectionabout -7.1 °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
-5°100°

Validated from -5 to 100 °C.

Density1,020.2 kg/m³
Dynamic viscosity2.02 mPa·s
Specific heat3.973 kJ/(kg·K)
Thermal conductivity0.483 W/(m·K)
Kinematic viscosity ν = µ/ρ1.98 mm²/s
Prandtl number Pr = cpµ/k16.62

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

Density kg/m³
Density from -5 to 100 °C, in kg/m³. Marked at 20 °C: 1,020 kg/m³-5 °C — 1,028 kg/m³0 °C — 1,027 kg/m³5 °C — 1,026 kg/m³10 °C — 1,024 kg/m³15 °C — 1,022 kg/m³20 °C — 1,020 kg/m³25 °C — 1,018 kg/m³30 °C — 1,016 kg/m³35 °C — 1,014 kg/m³40 °C — 1,011 kg/m³45 °C — 1,009 kg/m³50 °C — 1,006 kg/m³55 °C — 1,003 kg/m³60 °C — 1,000 kg/m³65 °C — 997.4 kg/m³70 °C — 994.2 kg/m³75 °C — 991 kg/m³80 °C — 987.5 kg/m³85 °C — 984 kg/m³90 °C — 980.4 kg/m³95 °C — 976.6 kg/m³100 °C — 972.7 kg/m³980990100010101020020406080100
Dynamic viscosity mPa·s
Dynamic viscosity from -5 to 100 °C, in mPa·s. Marked at 20 °C: 2.02 mPa·s-5 °C — 4.98 mPa·s0 °C — 4.05 mPa·s5 °C — 3.34 mPa·s10 °C — 2.79 mPa·s15 °C — 2.36 mPa·s20 °C — 2.02 mPa·s25 °C — 1.74 mPa·s30 °C — 1.52 mPa·s35 °C — 1.34 mPa·s40 °C — 1.18 mPa·s45 °C — 1.06 mPa·s50 °C — 0.95 mPa·s55 °C — 0.86 mPa·s60 °C — 0.78 mPa·s65 °C — 0.71 mPa·s70 °C — 0.66 mPa·s75 °C — 0.6 mPa·s80 °C — 0.56 mPa·s85 °C — 0.52 mPa·s90 °C — 0.49 mPa·s95 °C — 0.45 mPa·s100 °C — 0.43 mPa·s1234020406080100
Specific heat kJ/(kg·K)
Specific heat from -5 to 100 °C, in kJ/(kg·K). Marked at 20 °C: 3.973 kJ/(kg·K)-5 °C — 3.918 kJ/(kg·K)0 °C — 3.929 kJ/(kg·K)5 °C — 3.94 kJ/(kg·K)10 °C — 3.951 kJ/(kg·K)15 °C — 3.962 kJ/(kg·K)20 °C — 3.973 kJ/(kg·K)25 °C — 3.983 kJ/(kg·K)30 °C — 3.994 kJ/(kg·K)35 °C — 4.005 kJ/(kg·K)40 °C — 4.016 kJ/(kg·K)45 °C — 4.027 kJ/(kg·K)50 °C — 4.038 kJ/(kg·K)55 °C — 4.049 kJ/(kg·K)60 °C — 4.06 kJ/(kg·K)65 °C — 4.071 kJ/(kg·K)70 °C — 4.082 kJ/(kg·K)75 °C — 4.093 kJ/(kg·K)80 °C — 4.104 kJ/(kg·K)85 °C — 4.115 kJ/(kg·K)90 °C — 4.126 kJ/(kg·K)95 °C — 4.136 kJ/(kg·K)100 °C — 4.147 kJ/(kg·K)3.9544.054.1020406080100
Thermal conductivity W/(m·K)
Thermal conductivity from -5 to 100 °C, in W/(m·K). Marked at 20 °C: 0.483 W/(m·K)-5 °C — 0.449 W/(m·K)0 °C — 0.456 W/(m·K)5 °C — 0.463 W/(m·K)10 °C — 0.47 W/(m·K)15 °C — 0.477 W/(m·K)20 °C — 0.483 W/(m·K)25 °C — 0.489 W/(m·K)30 °C — 0.494 W/(m·K)35 °C — 0.5 W/(m·K)40 °C — 0.505 W/(m·K)45 °C — 0.509 W/(m·K)50 °C — 0.514 W/(m·K)55 °C — 0.518 W/(m·K)60 °C — 0.521 W/(m·K)65 °C — 0.525 W/(m·K)70 °C — 0.528 W/(m·K)75 °C — 0.531 W/(m·K)80 °C — 0.533 W/(m·K)85 °C — 0.535 W/(m·K)90 °C — 0.537 W/(m·K)95 °C — 0.538 W/(m·K)100 °C — 0.54 W/(m·K)0.460.480.50.520.54020406080100
Send PG 20 % 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 = 1020.2cₚ = 3.973

Reynolds Number

ρ = 1020.2μ = 2.02

Prandtl Number

μ = 2.02cₚ = 3.973k = 0.483

Learning zone

Twenty percent propylene glycol is the corrosion floor of the glycol range. The inhibitor package that keeps the fluid from eating steel and solder travels with the glycol, so a lean mixture carries a lean dose: at 20 % it still works, but with no margin — this is the concentration where annual inhibitor testing stops being good practice and becomes the thing keeping the loop alive. Below it the dose is too thin to maintain, the mixture turns corrosive within a few seasons, and no manufacturer will stand behind the charge.

What 20 % buys is burst protection more than freeze protection. Ice starts forming at about −7 °C, but in glycol it forms as a slush that expands far less than solid ice, so an idle coil survives a much colder night than the freeze point suggests — it just will not flow until it warms. That is a real duty: heat recovery and make-up air coils that can tolerate a no-flow morning but not a split tube are charged at exactly this strength.

The penalties are the mildest on the shelf. Specific heat at 20 °C is 3.97 kJ/(kg·K) against water's 4.18, down 5 %; thermal conductivity is 0.483 W/(m·K) against 0.598, down 19 %; viscosity is 2.02 mPa·s against 1.00 — double, which matters at the cold end (4.98 mPa·s at −5 °C) but is easily carried at operating temperature. Where 20 % is enough protection, the pump and the coils barely notice the glycol; the maintenance schedule is what notices.