Using Carbon Dioxide in a Transcritical Vapor Compression Refrigeration Cycle
For most of the last fifty years, refrigeration and heat pump systems have been based on cycles using a fluorocarbon as the working fluid. Hovvever, with the discovery that fluorocarbons may have a profoundly detrimental effect on the earth ·s atmosphere. it has become necessary to find a suitable replacement for a fluorocarbon based refrigeration cycle. Such a replacement must perform comparably t.o current refrigerants. be economically feasible. and significantly reduce the possibility of a negative environmental impact compared to current. refrigerants. A review of the literature on the first vapor compression refrigeration cycles indicat.e that carbon dioxide was used as the working fluid prior to and after the tum of the century. rvioreover, recent literature has suggested that carbon dioxide will work for certain air conditioning applications. Not only is carbon dioxide inexpensive and plentiful, but is a substance naturally occurring in large quantities in the earth's atmosphere. Furthermore, initial investigation of the heat transfer properties of carbon dioxide and subsequent modeling of a transcritical carbon dioxide vapor compression cycle suggest potential performance comparable to that of existing refrigeration systems. This paper will present a detailed literature re.-iew of carbon dioxide's role in refrigeration cycles, what has been investigated so far to find a suitable application for carbon dioxide as a. refrigerant. and what further research needs to be done to implement a feasible cycle. INTRODUCTION TO CARBON DIOXIDE Background Carbon dioxide's role in refrigeration stretches back well over 100 years and likely had the largest impact of any fluid on early food refrigeration and human occupied space air conditioning. Though the Evans-Perkins process upon which modern refrigerators and air conditioners are based, was developed in 1834 [Lorentzen 1994], it wasn't until 1866 when the American Thaddeus S.C. Lowe first harnessed carbon dioxide for ice production [Thevenot 1979]. Following a period of further development. the first documented carbon dioxide compressor was built by Windhausen in 1880 [Goosman 1927]. Other landmark uses of carbon dioxide refrigeration include the first marine installation a carbon dioxide plant by .} & E Hall in 1890 [Thevenot 1979] and the first continuous production of carbon dioxide refrigerating equipment in the United States by Kroeschell Bros. of Chicago in 1897 [Goosman 1927]. Not only were carbon dioxide based machines growing in popularity in the late 1800s, but improvements were continually being made on the basic cycle (almost from the incipience of initial development!). J & E Hall demonstrated that the efficiency of the vapor compression process could be improved through the use of two stage compression [Thevenot 1979]. In 190-5, Voorhees developed what is now known as the multiple effect cycle, which involves a separation of liquid and vapor at an intermediate stage in the expansion process. According to Voorhees, for heat absorption temperature of 0°F (-17.78°C) and a heat rejection temperature of 90°F (32.22°C) "the least possible gain in refrigeration will be 127% and a saving of 38% oft he power required per unit refrigeration will result" [Voorhees 1905]. The advent of refrigeration and air
A new, efficient and environmentally benign system for car air-conditioning
Abstract There is a widespread belief that the only viable refrigerants in most applications are new fluorocarbon chemicals. This trend will result in continued emissions of several hundred thousand tonnes of alien chemicals to the atmosphere each year, involving the potential risk of unforeseen environmental effects. A number of other options exist, or may be developed. By using substances that already have a natural role in the ecosystem, some uncertainty about the critical issue of our future environment can be avoided. By development and practical testing of a laboratory prototype it has been shown that carbon dioxide is an excellent refrigerant in car air-conditioners, solving completely all environmental problems associated with such systems. General use of carbon dioxide as a refrigerant may provide a number of advantages in the present situation, both from an environmental and practical point of view. It is the authors' considered opinion that the use of the old refrigerant carbon dioxide offers a key to the complete solution of the environmental problems in many areas of refrigeration usage.
Growth and Characterization of β-RDX Single-Crystal Particles
1,3,5-Trinitrohexahydro-s-triazine (RDX) single-crystal particles crystallized in the β phase have been successfully grown by sublimation–recrystallization. Synchrotron X-ray diffraction results confirm that the recrystallized products are β-RDX single crystals. Compared to the traditional solution deposition methods, the sublimation method used in this work breaks through the mass limitations during the growth of β-RDX. The distribution of α- and β-RDX on different substrates reveals that hydrophilic substrates are prone to grow β-RDX single crystals and that hydrophobic substrates prefer α-RDX single crystals. The sublimation rate dominates the growth of pure β-RDX. The mechanisms of the phase transition from β-RDX to α-RDX during the process of sublimation–recrystallization have been studied. The current results can promote the potential application of β-RDX in the propellant, explosives, and military fields.