Fridges are appliances with a range of utility, from personal use in homes to commercial use in laboratories. The key component within these machines is refrigerant, a fluid which uses properties of the ideal gas law to allow heat to dissipate away from stored contents (McLinden and Huber, 2020). Despite contributing immensely towards efficient storage, the development of fridges came with its fair share of environmental consequences, particularly affecting the atmosphere (McLinden, Seeton and Pearson, 2020).
Fridges often implement a vapour-compression system in use with refrigerants. This system has four stages: “compressor, condenser, expansion device, and evaporator” (McLinden and Huber, 2020). In accordance with the ideal gas law, PV=nRT where P∝T, the compressor increases the pressure of the refrigerant (Leafy, 2021) and consequently increases temperature (Process Solutions, 2020). The refrigerant then goes through condensation, expansion, and evaporation to cool down the temperature, as seen in Figure 1.
Figure 1: A diagram exhibiting the vapour-compression system. As the refrigerant cycles through the system, its physical state is changed. This allows the refrigerant to heat up, cool down, and absorb heat once again to lower temperatures (Process Solutions, 2020).
In the 1930s, early refrigerants could contain fluids like SO2. These fluids were favourable in terms of thermodynamic characteristics, but were also highly toxic (McLinden and Huber, 2020). Due to the flammable and harmful nature of these substances, they were replaced by halogenated compounds like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which are otherwise known as freons (McLinden, Seeton and Pearson, 2020). These refrigerants were seemingly ideal, as they were not flammable and were nontoxic, and thus were commercialized and in use until the 1990s (McLinden and Huber, 2020). However, they were extremely destructive to the atmosphere. As seen in Figure 2, the boom in use of CFCs and HCFCs led to an overwhelming depletion of ozone, leading to the creation of the Montreal Protocol, an international agreement to reduce the use of CFCs (UCAR, n.d).
After the Montreal Protocol was put in effect, it was evident that the reduction in CFCs facilitated the recovery of the ozone layer, as seen in Figure 2. To replace CFCs, refrigerants began to be produced using compounds such as hydrofluoroolefins (HFO), ammonia, CO2, and hydrocarbons (McLinden and Huber, 2020). However, each compound has its tradeoffs. HFOs can react in the atmosphere to form trifluoroacetic acid, a compound that is soluble in water and toxic to aquatic organisms (McLinden, Seeton and Pearson, 2020). Additionally, ammonia is toxic to humans, CO2-based systems have an increased cost of production, and hydrocarbons are flammable (McLinden, Seeton and Pearson, 2020).
Thus, the search for a refrigerant that is efficient, environmentally friendly, and safe is still on-going. It is likely that refrigerants will continue to evolve, along with the regulations surrounding their production (McLinden and Huber, 2020).
References
Goyal, K., Nanditta, R.V., Teja, P.D., Malarmannan, S. and Manikandaraja, G., 2021. Analysis of vapor compression refrigeration system employing tetrafluroethane and difluroethane as refrigerants. Journal of Physics: Conference Series, 2054, p.012054. https://doi.org/10.1088/1742-6596/2054/1/012054
Leafy, E., 2021. How does a refrigerator work? Understanding Your Walk-in. [online] Arcticwalkins. Available at: <https://arcticwalkins.com/how-does-a-refrigerator-work-understanding-your-walk-in/#:~:text=The%20compressor%20increases%20the%20pressure,out%20via%20the%20condensing%20line.> [Accessed 14 Sep. 2023].
McLinden, M.O. and Huber, M.L., 2020. (R)Evolution of Refrigerants. Journal of Chemical and Engineering Data, 65(9), pp.4176–4193. https://doi.org/10.1021%2Facs.jced.0c00338
McLinden, M.O., Seeton, C.J. and Pearson, A., 2020. New refrigerants and system configurations for vapor-compression refrigeration. Science, 370(6518), pp. 791–796. https://doi.org/10.1126/science.abe3692
NASA GSFC, 2023. [image online] Available at: <https://svs.gsfc.nasa.gov/30602> [Accessed 15 September 2023)
Process Solutions 2020. How does a compression refrigeration system work? [online] Process Solutions. Available at: <https://processsolutions.com/how-does-a-compression-refrigeration-system-work/> [Accessed 15 Sep. 2023].
UCAR 2023. Layers of the Atmosphere. [online] UCAR. Available at: <https://scied.ucar.edu/learning-zone/atmosphere/ozone-layer> [Accessed 15 Sep. 2023].