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PROSPECTS OF USING R744 IN REFRIGERATION EQUIPMENT Bulov A.O. (Russian Federation) Email: Bulov462@scientifictext.ru
Bulov Artem Olegovich - graduate Student, DEPARTMENT OF REFRIGERATION CRYOGENIC ENGINEERING AND AIR CONDITIONING, INSTITUTE OF MECHANICAL ENGINEERING AND MECHATRONICS SIBERIAN STATE UNIVERSITY OF SCIENCE AND TECHNOLOGY NAMED AFTER M.F.
RESHETNEV, KRASNOYARSK
Abstract: this work considers the features of using natural refrigerant R744 (carbon dioxide) in the modern refrigeration equipment. The performance indicators of this refrigerant at low temperatures are given. The comparison of R744 with other refrigerants, as well as the output rating of a carbon dioxide screw compressor are demonstrated. Examples of successful use of carbon dioxide as a working fluid in steam vessels are given. Advantages and disadvantages are shown. Conclusions on the use of this refrigerant in the future are made.
Keywords: carbon dioxide, refrigerant, efficiency.
ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ R744 В ХОЛОДИЛЬНОМ
ОБОРУДОВАНИИ Булов А.О. (Российская Федерация)
Булов Артём Олегович - аспирант, кафедра холодильной криогенной техники и кондиционирования, институт машиноведения и мехатроники Сибирский государственный университет науки и технологий им. М.Ф. Решетнева,
г. Красноярск
Аннотация: в рамках данной работы рассмотрены особенности применения природного хладагента R744 (углекислый газ) в современной холодильной технике. Приведены показатели эффективности данного хладагента при низких температурах. Показано сравнение R744 с другими хладагентами, а также характеристики производительности винтового компрессора на углекислом газе. Приведены примеры успешного использования углекислого газа в качестве рабочего вещества на паровых судах. Показаны преимущества и недостатки. Сделаны выводы о применении данного хладагента в будущем.
Ключевые слова: хладагент, эффективность, экологическая безопасность.
Obtaining of artificial cold is possible only as long as simultaneous operation of the main parts of the refrigeration plant: compressor, condenser, evaporator and throttling device is ensured. Another conditional part of a refrigeration plant is the working fluid, i.e. refrigerant. Selection of optimum working media of refrigeration equipment is a topical task nowadays.
Today, freons are used as a working fluid in refrigerating machines. These refrigerants have a serious effect on the ecology of the whole planet. For example, freons contain fluorine compounds which escape into the atmosphere in case of leakage, and this entails destruction of the ozone layer of the earth [1].
The search for substances to replace refrigerants covered by the Montreal and Kyoto Protocols has had a fundamental impact on the refrigeration industry. Today, the refrigeration industry is increasingly interested in natural refrigerants. One of the best
known natural refrigerants is carbon dioxide (refrigerant R744). The use of carbon dioxide as a refrigerant has been known since the 1930s.
In Europe, about 14% of all large supermarkets use the R744 refrigeration equipment. Refrigeration equipment charged with carbon dioxide is becoming popular today not only in retail chains, but also in the industrial sector. This situation has become possible thanks to the emergence of a new type of refrigeration equipment, in which transcritical CO2 condensing units are involved, the parallel compression technology is used, efficient blowers are developed, and single or multiple ejectors are applied. Carbon dioxide refrigeration equipment has proven to be very productive even in places where it would have been hard to imagine — the countries such as India, Jordan, and Iran. We can state with confidence that carbon dioxide has replaced ammonia at many production sites. With the advent of higher capacity compressors on the market, the possibility of creating high efficiency transcritical or cascade carbon dioxide systems with ammonia has become a reality [2].
Carbon dioxide has low toxicity and is not combustible. The global warming potential of CO2, equal to 1, is considered a reference value for assessing the direct impact of refrigerants on global warming. Carbon dioxide used as a refrigerant is a byproduct of many technological processes [3].
The disadvantage is high pressure, which sets special demands on the technical components of the system, such as the compressor and heat exchangers. However, in this case it is possible to create more compact plants with smaller compressors and smaller pipe cross-sections. In the future, CO2 will be able to replace climate-damaging refrigerants both in refrigeration equipment and heat pumps [4].
Carbon dioxide has good performance indicators for low temperatures and very high specific refrigeration capacity, Figure 1 [5].
430
M -iO -O -W
evaporation temperature (C)
Fig. 1. Performance indicators of the Bitzer screw compressor with a volumetric capacity of220 m3/h
Carbon dioxide refrigeration plants are widely used in steam vessels. For example, one of the largest ferry operators, P&O Cruises, signed an agreement with the Swiss company GEA to build a carbon dioxide refrigeration system with several compressors made by GEA to improve system reliability for its cruise liners. By the way, carbon dioxide refrigeration machines are already in operation aboard the Arcadia, a P&O Cruises vessel with a capacity of 2,000 passengers [2].
Today carbon dioxide is the most promising alternative to traditional refrigerants. CO2 systems have already passed through several stages of evolution, and the industry has accumulated sufficient experience in the use of plants with this refrigerant. In Russia, carbon
dioxide refrigeration systems are not a novelty any more, and the process of their implementation in trade, warehousing and industry is spinning up.
Thus, as of today, the problem of assessing the prospects of using carbon dioxide as a working fluid in refrigeration equipment is becoming a topical area of research.
The refrigeration industry is a rapidly developing branch of the national economy. Refrigeration equipment is the basis for many enterprises. Volumes of refrigeration machinery grow year after year. Besides, the refrigeration branch is power-consuming, and this means that questions associated with the cost of energy resources, and requirements for the reduction of the harmful environmental impact are a hot topic of research. It is these factors that determine the need to find new solutions to improve the refrigeration technology, as well as the need to select the optimal working medium for refrigeration equipment.
Production of artificial cold is accompanied by an adverse environmental impact. The main reason for the ozone layer destruction is chlorine generation when Freon used in refrigeration units is decomposed [1].
Improving the environmental safety of refrigeration equipment is implementation of the provisions of the Montreal and Kyoto Protocols on withdrawal from circulation of refrigerants with a high potential of destruction of the ozone layer and global warming. The solution to this problem can be a reduction of the refrigerant charging of refrigeration systems [2].
Using natural refrigerants is an actual course of improving the environmental safety of refrigeration systems. The International Institute of Refrigeration considers the acceptable global warming potential max. 150 for such refrigerants. At the same time, high energy efficiency of refrigeration units should be provided. Respectively, researches on the synthesis of new refrigerants with high thermodynamic characteristics and low potential of the ozone layer destruction and global warming will continue. In this connection, it is very important to find universal analytical equations allowing for calculating refrigerant properties in a wide range of parameters with high reliability [3].
Another course is the use of thermal radiation in refrigeration systems. Using cooling systems operating due to thermal radiation allows for significant reduction of power consumption required for industrial refrigeration systems and air conditioning systems in residential buildings. In this case, emissions of ozone depleting substances and greenhouse gases, whose use is restricted by the Montreal Protocol to the Vienna Convention for the Protection of the Ozone Layer, which came into force on January 1, 1989, are also reduced.
Such units are mainly used abroad, in particular in the USA. In Russia, such systems are not widely used yet. To introduce such units, it is necessary to develop effective analysis and design methods allowing for determination of optimal parameters and the area of operability of such systems.
The peculiar feature of refrigeration systems using thermal radiation is that their operability depends to a large extent on climatic conditions of the region in which they are operated. Such systems do not use harmful, hazardous or ozone depleting substances, do not emit greenhouse gases, and are environmentally friendly systems [4].
One of the ways to solve the environmental problem in the refrigeration sphere is the use of gas refrigerating machines (GRMs) operating with the reverse Stirling cycle in the moderate temperature range [6]. High-volume output of household refrigerators using the Stirling cycle is already planned in South Korea in the near future. The research results show that moderate-cooling Stirling machines are 1.5 times more efficient than the best examples of steam-compression refrigeration machines, and their mass-size characteristics are 25-30% lower.
Thus, to achieve environmental safety of refrigeration units, it is forward-thinking to use environmentally safe refrigerants. Introduction of natural refrigerants into the refrigeration industry on a large scale is an actual area of modern research. It will positively influence the ecology of the planet.
Moreover, much attention is paid to systems operating due to thermal radiation, but such systems are used mainly in continental climate conditions.
To date, the study of Stirling refrigeration machines is also a sound area of development of the refrigeration technology. It is these machines that can solve environmental problems associated with the refrigeration industry, but they have a limited temperature range.
References / Список литературы
1. Bulov A.O., Ermakov M.A. Prospects for the development of vacuum refrigerating machines. Materials of the XXIII International Scientific. Practical conf., dedicated. in memory of the general designer of rocket and space systems Academician M.F. Reshetnev: at 2 o'clock / under the general editorship of Yu. Yu. Loginov. H 1. Krasnoyarsk, 2019. Pp. 210-212.
2. The future of cooling supply for carbon dioxide. [Electronic resource].URL: http://www.topclimat.ru/publications/184.html/ (date of access: 04.10.2021).
3. About natural refrigerants. [Electronic resource]. URL: http://www.ozoneprogram.ru/biblioteka/publikacii/o_hladagentah/ (date of access: 04.10.2021).
4. Prospects for the use of natural CO2 refrigerant in refrigeration. [Electronic resource]. URL: http://www.rusnauka.com/SND/Tecnic/5_fialkovskiy.doc.htm/ (date of access: 04.10.2021).
5. Gafurov Sh. Prospects for the use of carbon dioxide in refrigerating machines / Young scientist. 2017. № 7 (141). Pp. 46-48.
