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Heat Transfer FluidFile Glossary


Density – Density is a material's ratio of mass to volume. English Units: lb/ft3., SI Units: kg/m3

Film Coefficient – Film coefficient is the heat transferred by convection per unit area per degree temperature difference between the surface such as a tube wall and the fluid. English Units: Btu/(hr) (ft2)(°F), SI Units: W/(m2)(K)

Kinematic Viscosity – is the ratio of absolute or dynamic viscosity to density - a quantity in which no force is involved. Kinematic viscosity at a given temperature can be obtained by dividing the absolute viscosity of a fluid with its mass density at that temperature.

Prandtl Number – A Prandtl number is a dimensionless number used in the study of diffusion in flowing systems, equal to the kinematic viscosity divided by the molecular diffusivity.

Pressure Drop – Pressure drop is the calculated decrease in fluid pressure due to friction for a length of pipe or tube. English Units: psi/100 ft of pipe, SI Units: kPa/100 m of pipe

Reynolds Number – A Reynolds number is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces and quantifies the relative importance of these two types of forces for given flow conditions.

Specific Heat – Specific heat (also called specific heat capacity) is the amount of heat required to change a unit mass (or unit quantity) of a substance by one degree in temperature. English Units: Btu/(lb · °F), SI Units: kJ/(kg)(K)

Thermal Conductivity – Thermal conductivity is a measure of the ability of a material to transfer heat. English Units: Btu/(hr · ft2)(°F/ft), SI Units: W/(m)(K)

Vapor Pressure – Vapor pressure is the pressure exerted by a vapor in equilibrium with its solid or liquid phase. English Units: psia, SI Units: Bar Abs

Viscosity – Or Absolute Viscosity of a fluid is the internal resistance to flow. English Units: cps, SI Units: mPa(s)


English Units – In FLUIDFILE, English Units refers to U.S. customary units.

SI Units – The International System of Units, which is a user option in FLUIDFILE™.


Bulk Temperature – The average temperature of all fluid in a specific part of a heat transfer system, such as the exit from a fired heater. Used by Dow as the basis for recommended fluid operating ranges.

Burst Protection – The lowest recommended temperature for a solution of glycol and water to be used for winterization of HVAC equipment. Some amount of freezing occurs but the glycol-ice mixture remains a flowable "slush" down to the burst protection temperature. System equipment must be capable of accommodating the volume expansion. (i.e. allow slush to flow to relieve the associated pressure build-up due to ice crystal formation). Burst protection is often called for when water-based systems are deliberately or accidentally idled during periods of freezing temperatures.

Film Temperature – The temperature of the heat transfer fluid in contact with the surface of heat transfer tubes or pipes. This is a calculated value. Film temperatures should remain within 50°F (28˚C) of the bulk temperature.

Freeze Protection – The lowest possible operating temperature for a solution of glycol and water (i.e. at no point will ice crystals form at temperatures above the freezing point). When designing a system, select a glycol concentration that provides freeze protection at least 3°C (5°F) lower than the lowest anticipated temperature.

Maximum Temperature – Set a maximum temperature within the recommended operating range for each fluid to avoid unacceptable fluid degradation. FLUIDFILE will indicate when properties have been calculated above a fluid's operating range.

Minimum Temperature – Set a minimum temperature within the recommended operating range for each fluid to ensure fluid pumpability. FLUIDFILE will indicate when properties have been calculated below a fluid's operating range. Heat tracing may enable fluids to be used below the minimum recommended temperatures.

Recommended Operating Temperature Ranges – Expressed as bulk fluid temperatures in the system. Typically these ranges describe the lowest temperature at which fluid is pumpable and the highest temperature at which the fluid can be operated without excessive thermal degradation and system fouling. Dow also recommends maximum film temperatures for its fluids. However, while fluids may withstand temporary temperature excursions above the recommended bulk temperature, prolonged operation can result in unacceptable fluid degradation.

Temperature Increments – Choose temperature in increments of 1° or higher.


Corrosion Protection – Dow glycol-based fluids contain proprietary corrosion inhibitor packages designed to prevent corrosion of system metals. A 25% to 30% fluid solution is typically required to maintain corrosion protection.

DOWFROST™ GEO 20 – This fluid is specially formulated with a fixed 20% (by volume) propylene glycol concentration and is intended only for use in geothermal heat pumps. FLUIDFILE does not permit comparison with other Dow glycol-based fluids, use of which is not recommended at concentrations below 25%. Contact Dow for Details.

Glycol Concentration Increment – Choose glycol concentrations in whole numbers in increments of 1% or higher.

Glycol Concentration – Dow glycol-based fluids are rarely used at concentrations higher than 50% to 55% in water. For optimum corrosion protection, a minimum of 25% to 30% glycol concentration is typically called for to ensure the system contains sufficient levels of corrosion inhibitors. FLUIDFILE allows users to compare plain water to Dow glycol-based fluids.

Pipe and Tube Diameter – For pipes and tubes, specify inner diameter. A friction factor is applied to account for the smoother surface of tubes.