Engineers are often faced with the task of determining the optimal choice of heat transfer fluids for a particular application. Beyond common parameters like bulk temperature, flash point, pour point, base chemistry, and others, you can take your evaluation one notch higher by considering two additional parameters – the Heat Transfer Factor (HTf) and the Pressure Drop Factor (Fρ).

Heat transfer efficiency can be predicted by considering these parameters in conjunction with other important factors. HTf and Fρ are functions of thermal fluid properties that are subject to change with temperature. A plot of HTf and Fρ vs. temperature can be used to compare several heat transfer fluids options.

Heat Transfer Factor :

Heat Transfer Factor (HTf) compares the capacity of a thermal fluid to add or remove heat under fully developed turbulent flow conditions (Re > 10,000) for a given geometry. The higher the HTf, the better the heat transfer efficiency. HTf can be calculated as follows:

HTf = 0.023 · k 0.67 · (r ·cp) 0.33 · n – 0.47


k = Thermal conductivity
r = Density
cp = Specific heat
n = Kinematic viscosity

Pressure Drop Factor :

When heat transfer fluid flows through a pipe , a pressure drop occurs as a result of resistance to flow. A lower Pressure Drop Factor (Fρ) relates to reduced frictional loss, given the same fluid velocity and tube geometry. A higher Fρ indicates that more pumping power is required. Fρ is computed as follows:

Fρ = 0.092 · ρ · ν 0.2


ρ = Density
ν = Kinematic viscosity

If you have any questions regarding the optimal heat transfer fluid choice for your application, the Thermal Fluid Engineers at Relatherm Heat Transfer Fluids are always ready to help. Give us a call anytime.