Blends are a combination of two or more other single component refrigerants. These blends have different chemical and interactive properties. Refrigerants are substances that are mixtures and undergo constant phase transitions from liquid to gas and vice versa. They may also be classified as azeotropic or zeotropic
An ideal refrigerant blend will be noncorrosive to mechanical parts and be safe. It will not be flammable and register low in toxicity to humans. Further, the present creators of refrigerant blends want to make a chemical that does not cause a depletion of the ozone and does not contribute to climate change.
Acceptable refrigerants must meet certain thermodynamic property expectations. The boiling point needs to be below the target temperature and it must have a moderate density in liquid form. It must have a high density in gaseous form and a high critical temperature. Further, it must have a high heat of vaporization.
Blends may also have up to four different components. They may also be a blend of HCFC, HFC, and HC. The blend will be given a name from its creator and color and safety codes will accompany its presentation to the world.
Each component of a blend has its own particular relationship between pressure and temperature. They also have precise physical properties. These properties of density, heat of vaporization and heat transfer coefficient must be appropriately matched between blend components.
Blends are further classified into being either an Azeotrope or Zeotrope chemical interaction. The type of system being used and the required volume of air to be conditioned will determine the type of blend necessary.
Azeotrope-This is a mixture of two or more refrigerants that then act as a single fluid. The components will not separate under normal conditions. They also have very similar boiling points.
In the field of chemistry, an azeotrope is a mixture of liquids that have a constant boiling point due to the fact that the vapor has the same composition as the liquid mixture. At certain pressures an azeotropic mixture will act like a pure refrigerant.
An azeotropic mixture contains refrigerants that have certain levels of attraction and interaction with molecules which gives it unique properties.
Blends that function zeotropically are mixtures made up of two or more components with different boiling points. Zeotropic mixtures experience temperature glide and should be charged as a liquid.
Because zeotropes have different properties than pure fluids, they have applications in distillation, cleaning, and refrigeration. If they are being used in refrigeration they are given numbers in the 400s.
The goal is to phase out harmful halogenated substances to remain in line with standards placed on the HVAC industry by the demands of the Montreal Protocol and the Kyoto Protocol.
Zeotropic refrigerants experience temperature glide and are therefore subject to leaks. This is due to boiling points being different. This temperature glide must be matched when using various and multiple refrigerants to charge a system.