HEAT TRANSFER FLUIDS - PROPERTIES

The role of a heat transfer fluid is to transport heat from a heat source to a heat sink, while complying with a certain number of constraints:

• technical constraints, such as reduced heat loss or low energy consumption for fluid transport. They are conditioned by thermodynamic and thermo-physical properties such as density, heat capacity or latent heat for phase-change fluids, dynamic viscosity... ;

• safety and environmental constraints (in particular, impact on the ozone layer and contribution to the greenhouse effect), which play a decisive role in the choice of fluids. They are conditioned by constantly evolving regulations that incorporate the traditional criteria of toxicity, flammability, safety for people and products, explosiveness, but also impact on the ozone layer and, above all, contribution to the greenhouse effect;

• economic constraints: the cost of the fluid itself, the structure and cost of the heat distribution network, and the size of pumping, compression or ventilation auxiliaries are directly determined by the thermodynamic properties of the fluids. The heat exchangers integrated into this network (in particular at heat sources and wells) are partly dimensioned by the "calovector" properties of the fluids, such as their conductivity.

Depending on their application, heat transfer fluids can be gases (nitrogen, helium, etc.), water, organic fluids, molten salts or liquid metals.

Current developments concern fluids, known as nanofluids, in which nanoparticles are introduced, offering the advantage of significantly increasing the fluid's thermal conductivity. These developments are still limited at the pre-industrial level, but could eventually represent a major step forward in thermal fluid technology.

This article is the second in a series dealing with heat- and heat-transfer fluids. It is supplemented by the article Heat transfer fluids – Properties [BE 9 572] concerning heat transfer fluids in particular.

For general definitions and selection criteria, please refer to the article Heat and cold transfer fluids – Definitions. Selection criteria