Glossary

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).

This is 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.

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 or in all three phases. Most liquids form vapors when heated. A low vapor pressure minimizes the possibility of boiling and pump cavitation.

This result 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 HTFs have low vapor pressures and a lower tendency for bubble formation.

Lowest temperature at which vapors of the material will ignite, when given an ignition source.

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

Temperature at which a fluid becomes semisolid and loses its flowing characteristics. Most centrifugal pumps are unable to transfer fluids at a viscosity over 400 CSt

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

Lowest temperature at which the vapors from a fluid will continue to burn for at least 5 seconds after ignition by an open flame.

Measure of fluid resistance to shear stress. The lower the viscosity, the higher the heat transfer efficiency. The higher the viscosity, the better the thermal stability of a fluid.

The initial boiling point at a given pressure is defined as the temperature at which 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.

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.

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.

This is the maximum recommended heating temperature to which a fluid can be subjected. Heating a beyond this point will result in thermal degradation or “cracking.” This is characterized by low boilers (or “light ends”) coming off, lowering of flashpoint, increased vapor pressure and carbon build up.

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

This is an additive added to a mineral oil base stock to mitigate fluid oxidation.

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 (boiler).

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.

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

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