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 generalized log-linear poisson-modeled correlation to predict the optimal heat rejection pressure of transcritical CO2 systems
In this study, a comprehensive literature survey of all the experimental data available in literature regarding optimal heat rejection pressure on transcritical carbon dioxide systems is carried out. Based on the phenomenological analysis and quantitative assessment of the data, a Poisson regression analysis is performed and a new dimensionless correlation to predict the optimal heat rejection pressure is developed. The influences of relevant parameters on heat rejection pressure, such as ambient temperature and temperature at the gas cooler are taken into account in the correlation development. The proposed correlation is tested against experimental measurements and is further validated by comparison to all existing experimental data collected from literature. Additionally, the predictive ability of the newly proposed correlation is discussed, tested against experimental data found in literature and compared with existing correlations. Upon comparison with existing correlations, the new generalized dimensionless correlation proposed in this study predicts the optimal heat rejection pressure with an average deviation of 1.31% and a standard deviation of 4.26 bar. Thus, becoming the most accurate correlation up to date, yet providing a much wider range of temperature applicability than the correlations currently available in literature.
Ammonia: An Excellent Alternative
Abstract Ammonia has been used as a refrigerant for more than 100 years in absorption as well as compression systems, so there is a tremendous amount of practical experience. Today it is applied largely in heavy industrial plant with reciprocating or screw compressors. It has a number of important advantages related to its low molecular weight and high evaporation enthalpy, some of which are not as yet fully exploited. The problems due to its toxicity and flammability are often overestimated and can be easily controlled by suitable design.