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
The Study of Using Carbon Dioxide as the Alternative of R502 in Industrial Refrigeration Applications
This paper presents the simulation study and comparison of C02 and R502 as refrigerants. At first, as a single stage vapor compression refrigeration cycle's refrigerant, C02 can be used in subcritical and transcritical situations. The performances are studied completely. The results show that C02 has the same or better performance compared to R502's in certain temperature ranges. Finally C02 and R502's performances in a C02 liquefying system are discussed in detail. It is promising to use C02 as the alternative ofR502 in this case, either in performance or in economics. eq4! h Tamb T, T/e w t c p NOMENCLATURE exergy ofthe cooling capacity kJ/kg enthalpy kJ /kg ambient temperature K evaporating temperature K exergy efficiency work input for compressor kJ /kg condensing temperature 'C pressure MPa INTRODUCTION More than ten years ago, the Montreal Protocol, a real landmark decision to our global environmental protection was agreed by the main industrial nations. Since then, an extensive research work has been done in seeking the alternatives of CFCs and HCFCs. By now, substantial progress has been made in this field. The refrigerants RI34a, R407c, R404a, etc. were regarded as the main alternatives of RI2, R22 and R502 respectively. These new refrigerants have been produced commercially. However, these alternatives do not meet the demands of the long term alternatives. Almost every new alternative has a high greenhouse effect or some other defects. But the natural refrigerants such as C02, NH3, etc. are very excellent in environmental protection121•14l. Therefore using natural refrigerants is becoming more and more important once again. C02, as a refrigerant, can be obtained easily from the natural world. It has been used in many refrigeration machines in history. But the low critical temperature limited its applications, especially when freons were produced in 1930s. Because C02 has a high environmental protection performance, it has been noticed recently. More and more researches have been carried out by using C02 as the alternatives of freons131•151• It is proved that C02 supercritical heat rejection results in a large temperature glide and therefore can be used in heat recovery and heat pump applications. Many studies have investigated the benefits and disadvantages of using C02. Much has been written about the thennodynamic performance. And the applications are still very little. This paper will focus on the
Correlations for mass transfer between fluidized spheres and a liquid
Abstract Data on mass transfer between the solid particles and the liquid in a fluidized bed have been analyzed. After a convenient selection, various correlations have been derived. They show that for a given fluidized system, the Sherwood number is independent on the Reynolds number.