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
Revival of carbon dioxide as a refrigerant
In the present situation it seems appropriate to avoid as far as possible the use in large quantities of substances that are foreign to nature and will unavoidably be lost into the biosphere. A much safer philosophy must be to revert to ‘natural’ refrigerants: substances that are already present in our environment and which are known to be harmless. One such possibility is carbon dioxide (CO2), which comes very close to being the ideal working medium, provided that a process to give competitive energy performance can be designed. The paper presents some examples of how this can be done.
Physical Principles of Wind Energy Conversion
The primary component of a wind turbine is the energy converter which transforms the kinetic energy contained in the moving air, into mechanical energy. For the initial discussions of principles, the exact nature of the energy converter is irrelevant. The extraction of mechanical energy from a stream of moving air with the help of a diskshaped, rotating wind energy converter follows its own basic rules.