[L1] 1 Overview [L2] 1) Definition of Refrigerant [L4] - A substance that transfers heat when cooling. [L2] 2) Function of Refrigerant [L4] - Generally, a medium that circulates within a refrigeration cycle, absorbing heat from the surroundings by evaporating in the low-temperature section and releasing heat by condensing in the high-temperature section. [L4] - A refrigerant that undergoes phase transition (gas to liquid, etc.) while circulating the cooling cycle is called a [Primary Refrigerant]. [L4] - A refrigerant that exchanges heat between low-temperature and high-temperature sections in a single-phase state without phase change is called a [Secondary Refrigerant]. [L1] 2 Types of Refrigerants [L2] 1) Evolution of Refrigerants [L3] ① 1st Generation: Ammonia [L4] - Excellent thermodynamic properties and high efficiency, but declined due to toxicity to humans. [L3] ② 2nd Generation: Chlorofluorocarbons (CFC Freon Gas) [L4] - Stable and harmless to humans, but banned since 2010 as they were known to cause ozone layer depletion. [L3] ③ 3rd Generation: Hydrofluorocarbons (HFC) [L4] - Developed as substances not containing Cl (Chlorine) in the CFC structure. [L4] - Banned as carbon dioxide was known to have a high greenhouse gas effect. [L3] ④ 4th Generation: Hydrofluoroolefins (HFO) [L4] - Recommended for use as they do not deplete the ozone layer and generate low greenhouse gases. [L2] 2) Types of Refrigerants [L4] - Ammonia [L4] - Liquid Helium, Liquid Hydrogen, Liquid Nitrogen [L4] - Hydrofluoroolefins (HFO) [L5] * Characterized by carbon double bonds (implies weak flammability). [L5] * Patents monopolized by DuPont and Honeywell. [L5] * Includes HFO-1234yf, HFO-1234ze, HFO-1336mzz, etc. [L1] 3 Requirements for Refrigerants [L2] 1) State [L4] - Evaporation pressure at low temperature should be higher than atmospheric pressure, and condensation pressure at room temperature should be low. [L4] - Must be non-flammable, non-explosive, harmless to humans, and non-irritating. [L4] - Must be chemically stable, and refrigerant vapor must not decompose due to heat of compression. [L4] - Must be inert, not causing chemical reactions with metals, etc., and not deteriorating lubricating oil. [L4] - Must have high electrical resistance and not cause dielectric breakdown. [L2] 2) Function [L4] - The maximum temperature at which liquefaction is possible (critical temperature) should be high, and the freezing temperature should be low. [L4] - For the same refrigeration capacity, required power should be low and the volume of refrigerant gas should be small. [L4] - Latent heat of evaporation should be large, and specific heat in liquid phase should be small. [L4] - Viscosity in liquid and gas phases should be low, and thermal conductivity should be high. [L4] - Price should be low, and transport and purchase should be easy. [L2] 3) GWP (Global Warming Potential) [L4] - A judgment criterion for conditions that do not affect ozone layer depletion and global warming. [L4] - GWP Index: The amount of solar energy absorbed by greenhouse gases, measured assuming the value of solar energy absorbed by 1kg of carbon dioxide is 1. [L4] - Quantifies greenhouse gas emissions and serves as a regulatory standard. [L5] * In Europe, F-Gas Regulations are enforced to gradually restrict the use of refrigerants with a GWP of 150 or higher. [L5] * From 2020, refrigerants with a GWP of 150 or higher cannot be used even for household air conditioners.