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Laughing gas as an alternativ refrigerant for R-23
Federal Ministry of Economics and Technology
04/2016 – 09/2018
Dr. Joachim Germanus
Natural non-flammable low-temperature refrigerant
The target of the project is the qualification of the high pressure refrigerant R-744A (N2O) for cooling applications. Up to now, there are only a few experimental results available. Most considerations are just of theoretically. R‑744A is considered a potential alternative to the non-flammable refrigerant R-23 (global warming potential: 14,800). Under ambient conditions, laughing gas is a stable compound with advantageous thermodynamic properties for refrigeration engineering application. As a natural and non-flammable refrigerant it has a 50 times lower GWP in comparison to R-23. Disadvantages are the oxidation effect and the chemical instability of R-744A. At higher temperatures and pressures, it decomposes spontaneously into nitrogen and oxygen under release of energy. Therefore, it should be investigated experimentally which concentration of a suitable added desensitizing agent need to be added to prevent decomposition under conditions of a compression refrigeration cycle. Due to the high oxidation power of the refrigerant none of the usual lubricants like PAG, POE or mineral oils can be used. Instead, only per-fluorinated compounds with the required chemical stability can be used and must be qualified for the special cooling application. As a part of the research project, a cooling cascade is to be designed and assembled as a functional model. In the low-temperature cooling stage, N2O mixed with another component should be used as refrigerant. The vapour pressure of laughing gas is slightly lower than the vapour pressure of carbon dioxide. However, the significantly lower triple point of N2O in comparison to carbon dioxide is advantageous. Therefore, lower evaporation temperatures are possible without a phase change from liquid to solid. Evaporation temperature down to -85 °C seems to be possible. Figure 1 shows the vapour pressure curves of different low temperature refrigerants. The commercial availability of suitable components like compressors, heat exchanger and injection systems for high pressure conditions like R-744 applications are the principle basis for the possibility to use such components for R-744A applications, too. There is a huge range of applications at temperatures below -50 °C. Examples are applications in the fields of environmental simulation, medicine and pharmaceutical technology, cryopreservation, lyophilisation, and food technology. After a successful completion of the research project, a qualification of a new environmental friendly refrigerant is achieved to replace R-23 in its current main applications.
Fig. 1: Vapor pressure curves of different low temperature refrigerants
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