Refrigerants and air conditioning systems are critical to the survival of humans, especially in the contemporary world. However, with the increasing concerns of the negative effects of global warming and increased greenhouse gas emissions, the development of sustainable and energy-efficient refrigerants and air conditioning systems is inevitable and has attracted significant research attention in recent years. This requires the use of environmentally friendly compounds with extremely low global warming potential (GWP), such as hydrofluoroolefins. Unfortunately, most conventional refrigerants such as R-32 and R-410A do not meet the minimum GWP requirements. Therefore, the development of high-performance refrigerants with extremely low GWP is highly desirable.
Recently, AGC Inc, a Japanese-based company, developed HFO-1123 and HCFO-1224yd(Z) as alternatives for conventional R-32 and R-245fa refrigerants, respectively. Despite their remarkably low GWP and minimal ozone depletion potential (ODP), these new refrigerants exhibit few problems that limit their applications. To overcome these challenges, the company integrated their newly developed refrigerators with the conventional ones and reported good results. Most importantly, HCFO-1224yd(Z) demonstrated potential applications in organic Rankine cycle and high-temperature heat pump systems due to their low toxicity, non-flammability, and small GWP properties. These applications require a thorough understanding of the thermophysical properties of the refrigerants, such as speed of sound, heat capacity, relative permittivity, dipole moment, and density, that can also enable accurate estimation of their performance in practical thermal cycles.
To this note, Dr. Yuya Kano, together with Dr. Yohei Kayukawa and Dr. Yoshitaka Fujita from the National Institute of Advanced Industrial Science and Technology, studied the thermophysical properties evaluation from the relative dielectric permittivity and the speed of sound measurements for HFO-1123 and HCFO-1224yd(Z) refrigerants. The measurement data for the two refrigerants were obtained at different temperature and pressure ranges. Their research work is currently published in the International Journal of Refrigeration.
In brief, the authors commenced their experimental work by using a cylindrical acoustic-electromagnetic cavity resonator to simultaneously measure the sound speed and dielectric relative permittivity in the gas phase. For HFO-1123, the measurements were taken at a temperature and pressure range of 263 – 333K and 50 – 520 kPa respectively, and 303 – 353K and 20 – 200kPa for HCFO-1224yd(Z). Next, the dipole moment and density properties were derived from the relative permittivity data via dielectric virial equation, while the isobaric heat capacity was derived from the speed of the sound data through acoustic virial equation. Additionally, the standard uncertainties for the measured data were properly estimated and the temperature correlations for the ideal gas heat capacities were formulated and compared with those estimates by atomic group contribution methods.
The authors found out that the fractional standard uncertainties both for the speed of sound and the relative permittivity measurements were estimated to 0.02% less without taking into consideration the sample impurities. Other thermophysical properties such as density, dipole moment, and heat capacity were successfully derived from the relative permittivity and sound speed measurements. The dipole moment was reported to be 1.298D and 1.311D for HFO-1123 and HCFO-1224yd(Z), respectively. On the other hand, the obtained densities were in good agreement with the other reports. Moreover, the comparison results revealed that the estimated ideal gas heat capacity differed from the measured data by more than 2% for HFO-1123 and more than 5% for HCFO-1224yd(Z).
In summary, the authors reported the fundamental properties of HFO-1123 and HCFO-1124yd(Z) from the accurate measurements of relative dielectric permittivity and speed of sound. The acquired data revealed the discrepancy of the estimate values. Moreover, the thermophysical properties presented in the study enabled performance assessment of the HFO-1123 and HCFO-1224yd(Z) refrigerators. In a statement to Advances in Engineering, Dr. Yuya Kano, the lead author said their findings in this study will advance the development of sustainable and efficient refrigerants for practice use.
Kano, Y., Kayukawa, Y., & Fujita, Y. (2020). Dipole moment and heat capacity in the ideal gas state derived from relative permittivity and speed of sound measurements for HFO-1123 and HCFO-1224yd(Z). International Journal of Refrigeration, 118, 354-364.