Glossary of Terms
Are you new to heat transfer fluids and not quite sure what they are all about or what some of the industry lingo means?
Click on a term to skip down to the definition:
- Anti-Foam Additive
- Anti-Oxidant
- Anti-Rust
- ASTM
- Autoignition
- Catalyst
- Cavitation
- Centipoise and Centistoke
- Corrosion Inhibitor
- Anti-Foam Additive
- Causes air bubbles to break on the surface, prevents build up of foam. Can also help prevent oxidation, they cannot prevent air entrainment, but function as an aid to quicker release of entrained air.
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- Anti-Oxidant (oxidation inhibitor)
- An additive to retard oxidation.
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- Anti-Rust or Anti-Corrosion Additive
- Helps prevent oxidation of metal by displacing water from metal surfaces. It plates to metal with a polarized effect to give an internal "umbrella", helping to resist iron-oxide formation.
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- ASTM
- American Society for Testing and Materials; an agency that standardizes testing petroleum products.
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- Autoignition
- Minimum temperature which a substance must be heated without application of flame or spark to cause substance to ignite.
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- Catalyst
- A material which promotes some chemical action without itself entering into the reaction.
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- Cavitation
- In a heat transfer system, failure of the material to flow to the suction of the system pump for any reason.
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- Centipoise and Centistoke
- A centipoise is 1/100th of the unit of absolute viscosity (the poise), e.g., the viscosity of water at 20oC is approximately one centipoise. The centipoise is derived from one kinematic unit of viscosity (the centistoke), by multiplying the latter by the density of the liquid, i.e., 1 centipoise = 1 centistoke x the density of the liquid. These units are part of the metric system, commonly used in Europe and becoming adopted in the U.S. and Canada.
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- Corrosion Inhibitor
- An additive used to retard the corrosion process.
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- Deposits
- Oil-insoluble materials that result from oxidation of the oil and contamination from external sources and settle out in system components as sludge and varnish.
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- Fire Point
- The temperature at which the fluid will sustain a fire if ignited by an outside ignition source. It is quite common for heat transfer systems to be operated at temperatures above the fire point of the fluid as ignition sources should always be far removed from any heat transfer system.
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- Flash Point
- The temperature at which the vapors produced from a fluid will ignite (flash off) with the presence of an ignition source (the fluid will not burn at this point). The flash point is important from the viewpoint of safety; however it is quite common for heat transfer systems to be operated at temperatures above the flash point of the fluid.
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- Hydrocarbons
- Compounds containing only carbon and hydrogen. Petroleum fluids consist chiefly of hydrocarbons.
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- Hydrophilic
- Having an affinity for water; capable of uniting with or dissolving in water.
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- Hydrophobic
- Having antagonism for water; not capable of uniting or mixing with water.
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- Inhibitor
- A substance that slows or prevents chemical reactions, such as oxidation or corrosion.
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- Oxidation
- The process of combining with oxygen. All petroleum products are subject to oxidation to some degree. The reaction increases with rise in temperature. Oxidation produces oil-insoluble oxidized materials, which result in viscosity increase and deposits.
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- Oxidative Degradation
- Oxidative degradation is the reaction of oxygen (in air) with the fluid by a free radical mechanism to form larger molecules which end up as polymers or solids. These thicken the fluid and increase its viscosity. A more viscous fluid will be more difficult to pump, have poorer heat transfer characteristics as well as an increased chance of coke formation. Oxidation is also accompanied by an increase in the acidity (TAN) of the fluid.
- As with all chemical reactions, oxidation occurs more rapidly as the temperature is increased. At room temperature, the reaction rate is hardly measurable. However, it can become a factor in the life of the fluid in certain styles of heat transfer systems. At temperatures encountered in systems in use in the plastics extrusion and die casting industries, as an example, oxidation is the main cause of fluid degradation.
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- Oxidation Inhibitor
- A chemical additive that minimizes the formation of harmful acids and varnish forming compounds that form when a fluid is subjected to air at elevated temperatures.
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- Oxidation Stability
- The resistance of lubricants to chemically react with oxygen. The absorption and reaction of oxygen may lead to deterioration of lubricants.
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- Pour Point
- The lowest temperature at which a liquid will pour under specified conditions.
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- Pour-Point Suppressants
- Prevent insoluble wax molecules in oil from building a honeycomb (lattice-like structure) at colder temperatures. Particularly useful for paraffinic oils. Gives useful ability to pour at lower temperatures.
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- TAN ( Total Acid Number )
- Acids are formed when a fluid comes in contact with oxygen, TAN levels are a means to show the extent of which a fluid has been oxidized.
- New fluids typically have a TAN less than 0.05, most fluids should be changed at and have a condemning limit of a TAN of 1.0.
- The rate of oxidation is minimal under 200F however as the temperature climbs the effects of oxidation are exponential. It is an industry accepted standard to assume the rate of oxidation doubles for each 15 degree increase above 200F.
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- Thermal Degradation
- Thermal degradation or thermal cracking is the breaking of carbon - carbon bonds in the fluid molecules by heat to form smaller fragments which are free radicals. The reaction may either stop at that point, in which case smaller molecules than previously existed are formed, or, the fragments may react with each other to form polymeric molecules larger than previously existed in the fluid. In heat transfer terminology, the two types of degradation products are known as "low boilers" and "high boilers".
- If thermal degradation occurs at extreme temperatures greater than 400°C (752°F), the effect is not only to break carbon - carbon bonds but to separate hydrogen atoms from carbon atoms and form coke. In this case, fouling of the heat transfer surfaces is very rapid and the system will soon cease to operate.
- The effect of the low boilers is to decrease the flash point and viscosity of the fluid as well as to increase its vapor pressure. The effect of the high boilers is to increase the viscosity of the fluid as long as they remain in solution. However, once their solubility limit is exceeded, they begin to form solids which can foul the heat transfer surfaces.
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- Corrosion Inhibitor
- An additive used to retard the corrosion process.
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- Viscosity
- A measure of a fluids resistance to flow. A higher viscosity is essentially a thicker fluid. It is desirable for most high temperature heat transfer fluids to have viscosity in the range of 20cst to 40cst at 104F.
- Another aspect of a fluids viscosity is its VI (Viscosity Index) or how a fluids viscosity is affected by temperature. It’s a measure of the rate of change of viscosity with temperature. In lubricants a high VI is desirable to maintain a relatively consistent viscosity throughout the useable temperature range. In heat transfer fluids a lower VI is more desirable in order to allow the fluid to thin out ( reduce viscosity ) with temperature increases. This allows for more efficient thermal transfer properties.
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