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Our industry uses a lot of technical terms. Understanding them does not have to be complicated. Below is a helpful heat transfer fluid glossary. 

Have Questions?  Contact UsOur knowledgeable engineers and technical support team are available to provide expert product support and consultation. 

FAQ Answers

1 - Additive

A chemical added to a base fluid in order to improve specific properties of the lubricant such as fluid life, lubricity, wear protection, rust protection, etc.

2 - Anti-Oxidant

This is an additive added to a mineral oil base stock to mitigate fluid oxidation in order to prolong its service life. 

3 - Autoignition Temperature

Lowest temperature at which a fluid spontaneously ignites in normal atmosphere without an external source of ignition, such as a flame or spark.

4 - Base Oil

Base stock used as an inert ingredient in the manufacturing of heat transfer fluids.

5 - Cleveland Open Cup (COC) Test

This is a flash point test that is conducted in a vessel where the fluid is exposed to atmosphere. The temperature of the substance is gradually raised and an ignition source is passed over the top of it until the fluid reaches a point at which it “flashes” and ignites. 

6 - Closed Cup Test

This is a flash point test conducted inside a closed vessel. The fluid is not exposed to the outside atmosphere. The lid is sealed and the ignition source is introduced into the vessel itself, allowing for a closer approximation to conditions such as those found inside a fuel tank.

7 - Expansion Tank

A vessel designed to account for the expansion of heat transfer fluid as it is heated. It accommodates fluid expansion and helps to avoid overflow into the operating facility or over pressurization of system devices and associated equipment.

8 - Fire Point

Lowest temperature at which a combustible fluid will burst into flame in the presence of an extraneous ignition source. Fluid must continue to burn for at least 5 seconds after ignition by an open flame.

9 - Flash Point

Lowest temperature at which vapors of the fluid will “flash” in the presence of an ignition source.

10 - Fluid Oxidation

This is a fluid degradation phenomenon that occurs when it is exposed to oxygen. This leads to an increase in viscosity and TAN as well as the eventual formation of insoluble solids.

11 - Fouling

Accumulation of unwanted deposits on heat transfer surfaces. This creates an additional barrier for heat transport, reduces heat transfer efficiency and necessitates an increase in the temperature of the heat source. 

12 - Hazard Analysis Critical Control Point (HACCP)

A systematic approach to identify, evaluate and control food-safety hazards. It addresses physical, chemical and biological hazards with the goal of preventing hazards before products enter the food supply. From a fluid standpoint, an HACCP plan generally involves conducting a lubrication/fluid survey, which is a thorough examination of potential fluid-related food-contamination risks in a facility.

13 - Heat Capacity

The heat capacity of a fluid is the amount of heat (usually expressed in calories, kilocalories, or joules) needed to raise the fluid's temperature by one degree (usually expressed in Celsius or Kelvin).

14 - Heat Exchanger

This is a device that indirectly transfers heat energy between hot and cold streams. There are different types and configurations. For example: shell & tube, plate and frame, and spiral.

15 - Initial Boiling Point

The initial boiling point at a given pressure is defined as the temperature value when the first bubble of vapor is formed from the liquid mixture. For a multicomponent liquid mixture like thermal fluids, there is no single boiling point to vaporize the complete mixture. The boiling for such mixtures occurs over a range of temperature which depends on the components involved, pressure of the system and also the affinity they have for each other.  

16 - ISO Viscosity Grades

A grading system approved by the International Standards Organization (ISO) to evaluate the viscosity of a lubricant or fluid.

17 - Lubrication and Fluid Survey

An examination of potential lubrication- and fluid-related food-contamination risks in a facility, generally conducted as part of an HACCP (hazard analysis and critical control point) plan.

18 - Maximum Bulk Temperature

This is the maximum recommended heating temperature to which a fluid can be subjected. Heating a beyond this point will result in thermal degradation of the fluid and a reduced operating life.

19 - Maximum Film Temperature

This is the temperature at the conductive heat transfer boundary layer – pipe walls, heating elements. This is usually higher than the maximum bulk temperature.

20 - Pour Point

Temperature at which a fluid becomes semisolid and loses its flowing characteristics.

21 - Pump Cavitation

This results from the formation of bubbles or cavities in areas of relatively low pressure around a pump impeller. The imploding or collapsing of these bubbles trigger intense shockwaves inside the pump, causing significant damage to the impeller and/or the pump housing. In contrast with synthetic fluids, mineral oil-based heat transfer fluids have low vapor pressures and a lower tendency for bubble formation.

22 - RPVOT

Stands for ‘Rotary Pressure Vessel Oxidation Test’. This is a test that measures a thermal fluid’s resistance to oxidation. Viscosity and TAN increase are key indicators of fluid oxidation.

23 - Rust Inhibitor

A lubricant additive for protecting ferrous (iron and steel) components from rusting caused by water contamination or other harmful materials from oil degradation. Some rust inhibitors operate similarly to corrosion inhibitors by forming inert films on metal surfaces. Other rust inhibitors absorb water by incorporating it into a water-in-oil emulsion so that only oil touches the metal surfaces.

24 - Specific Heat

The amount of heat needed to increase the temperature of one pound of a fluid by 1°F.

25 - Thermal Cracking

This is a fluid degradation phenomenon that occurs when a fluid is heated above its maximum bulk temperature. Consequently, the fluid’s viscosity, flash point, fire point and auto-ignition temperature reduce significantly.

26 - Thermal Stability

The ability of a fluid to resist degradation under high-temperature operating conditions.

27 - Total Acid Number (TAN)

Measure of fluid acidity and indication of fluid oxidation. It is determined by the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of fluid.

28 - Vapor Pressure

This is the pressure exerted by a vapor when it is in equilibrium with the liquid or solid form (or both) of the same substance — i.e. When conditions are such that the substance can exist in both phases. Most liquids form vapors when heated. A low vapor pressure minimizes the possibility of boiling and pump cavitation.

29 - Viscosity

Measure of a fluid’s resistance to flow. This is typically measured as the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid. Viscosity varies inversely with temperature. The lower the viscosity, the higher the heat transfer efficiency. The higher the viscosity, the better the thermal stability of a fluid.

30 - Viscosity Index

The measure of the rate of change of viscosity with temperature. Heating tends to make fluids thinner; cooling makes them thicker. The higher the viscosity index is on a particular fluid, the less of a change in viscosity there will be over a given temperature range. 

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