Low temperature heat transfer fluids. Properties

Interest in heat transfer fluids and the search for high-performance fluids for low-temperature applications is a recent phenomenon, due to environmental constraints which tend to limit refrigerant charges in refrigeration production systems. Traditionally, refrigeration engineers have relied on three categories of refrigerant fluids for common uses:

• gases, and especially air for a very large number of applications (deep-freeze tunnel...) and nitrogen gas when temperature levels (especially for temperatures below the triple point temperature of CO ₂ ) made it necessary;

• brines, which are aqueous solutions based on inorganic salts such as calcium chloride, potassium carbonate or, more rarely, sodium chloride for certain food uses;

• mixtures of water and antifreeze based on alcohols such as monoethylene glycol and propylene glycol, or, more rarely, mixtures of water and ammonia (ammonia water, also known as alkali).

The combined search for high energy performance in cold production/distribution systems and fluids with low environmental impact has prompted refrigeration engineers to turn their attention to "new" refrigerant fluids. New fluids have appeared on the market in addition to the previous ones:

• aqueous solutions with salts such as potassium acetate, potassium formate or mixtures of potassium acetate and potassium formate;

• water/alcohol mixtures such as ethanol, methanol, glycerol, or ethanol/glycerol-based mixtures;

• aqueous solutions based on betaine and d-propanediol;

• various organic fluids comparable to those described as heat transfer fluids [BE 9 571] : aromatic oils, silicone oils, hydrofluoroethers, citrus-based terpenes...

More recently, we have seen the emergence of "two-phase" refrigerant fluids of two distinct types:

• two-phase "liquid-steam" refrigerant carriers, of which carbon dioxide is the fluid whose use has been growing in recent years;

• two-phase "liquid-solid" refrigerant carriers, which also combine the "cold" distribution function between the production device and the end-user with a thermal storage function considered essential for better management...