By Tabeel Jacob
Have you ever heard of a “refrigerant?” It almost sounds like “refrigerator,” right? Well, if you thought they might be related, you’d be right! In fact, a wide range of our daily appliances and machinery – such as air conditioners, refrigerators, and automobiles – contain refrigerants. The refrigerants in these systems undergo a cycle of condensation and evaporation to absorb heat from the one location and release it at a different location. Doing so, provides the cooling effect that we humans have become quite reliant upon in the 21st century.
Refrigerants currently being used can be classified as Hydrofluorocarbons (HFCs). HFCs have favorable heat transfer properties. However, as numerous studies have confirmed that HFC emissions contribute to global warming, these refrigerants have fallen under scrutiny given their environmental impacts. To combat this, majority of the developing and developed countries, through international agreements, have agreed to reduce their use of HFC refrigerants by more than 80% over the next 30 years. Finding a viable alternative to HFC refrigerants is crucial for these plans to succeed.
In order to mitigate the impact of HFC while still being able operate daily heating and cooling equipment, mixtures of hydrofluoroolefins (HFOs) and hydrofluorocarbons (HFCs) have been proposed as a potential alternative to pure HFCs. These HFC/HFO mixtures have significantly lower global warming potential (GWP), the measure of a gas’s contribution to the heating of the atmosphere. A higher GWP indicates an increased amount of heat trapped by the gas in atmosphere. For example, R404A is a widely used refrigerant with a GWP of 3922. It is set to be replaced by R448A, an HFC/HFO mixture with a GWP of 1273. That’s less than one-third of the GWP of R404A! Unfortunately, there is currently not enough experimental data available on the heat transfer capabilities, specifically condensation, of these newer refrigerants. This data is necessary to accurately design critical components in our daily appliances.
Previous studies on similar mixtures have reported decreased condensation performance as compared to their pure components at similar operating conditions. This occurs because theunderlying heat transfer mechanisms during condensation of mixtures differ significantly than those of pure refrigerants. Therefore, the appliances designed to use HFC/HFO mixtures may require different components than those developed for pure refrigerants. Motivated by the need to better understand the phase change process of HFC/HFO refrigerants and the need to reduce the impact on the environment, the focus of my doctoral research is to investigate the condensation heat transfer performance of low GWP refrigerant mixtures. An experimental facility designed specifically for this application will be used to test the performance of these new refrigerants. The experimental data will be used to introduce equations that can be used to design critical components for heating, cooling and refrigeration applications. The results of the study will be shared with industry and academics in order to further facilitate the adoption of low GWP refrigerants.