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
Positive Displacement Carbon Dioxide Expansion Machines - Changes and Limitations -
Over the past years carbon dioxide has experienced a revival after it had been re-introduced by Lorentzen. In contrast to conventional refrigeration cycles the expansion of CO2 in refrigeration machines is a potential source of energy efficiency improvement, when the expansion energy can be put to practical use. Various efforts to realize expanders for CO2 have been reported at Purdue and IIR conferences. At FKW a simple reciprocating CO2 expansion machine without special valve- or slot-control has been studied as previously designed by Doll and Eder for cryogenic helium expansion /7/. This simple kind of charge and discharge control works without any additional control components except the piston and allows also dead volume capacity control. With a flexible simulation program for expansion machines thermodynamic calculations were done. The results of these calculations and the design of the machine will be described and discussed in the presentation as well as experimental investigations concerning the gained work both in transcritical two-phase operation and in the superheated single-phase region at comparable pressures. From these results conclusions will be drawn concerning the chances and limitations of the application of positive displacement expansion machines of the reciprocating and rotating types.
The Aesthetics of Mimesis: Ancient Texts and Modern Problems
Preface vii Acknowledgments xi Note to the Reader xiii INTRODUCTION: Mimesis and the History of Aesthetics 1 PART I CHAPTER ONE Representation and Reality: Plato and Mimesis 37 CHAPTER TWO Romantic Puritanism: Plato and the Psychology of Mimesis 72 CHAPTER THREE Mimesis and the Best Life: Plato's Repudiation of the Tragic 98 CHAPTER FOUR More Than Meets the Eye: Looking into Plato's Mirror 118 PART II CHAPTER FIVE Inside and Outside the Work of Art: Aristotelian Mimesis Reevaluated 151 CHAPTER SIX The Rewards of Mimesis: Pleasure, Understanding, and Emotion in Aristotle's Aesthetics 177 CHAPTER SEVEN Tragic Pity: Aristotle and Beyond 207 CHAPTER EIGHT Music and the Limits of Mimesis: Aristotle versus Philodemus 234 PART III CHAPTER NINE Truth or Delusion?The Mimeticist Legacy in Hellenistic Philosophy 263 CHAPTER TEN Images of Life: Mimesis and Literary Criticism after Aristotle 287 CHAPTER ELEVEN Renewal and Transformation: Neoplatonism and Mimesis 313 CHAPTER TWELVE An Inheritance Contested: Renaissance to Modernity 344 Bibliography 383 Index 419