Alternative technologies for refrigeration and air conditioning applications

Transcription

1 Retrospetive Theses and Dissertations 1993 Alternative tehnologies for refrigeration and air onditioning appliations Don arlyle Gauger Iowa State University Follow this and additional works at: Part of the Mehanial Engineering ommons Reommended itation Gauger, Don arlyle, "Alternative tehnologies for refrigeration and air onditioning appliations " (1993). Retrospetive Theses and Dissertations This Dissertation is brought to you for free and open aess by Iowa State University Digital Repository. It has been aepted for inlusion in Retrospetive Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please ontat

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5 Order Number Alternative tehnologies for refrigeration and air onditioning appliations Ganger, Don arlyle, Ph.D. Iowa State University, 1993 UMI 300 N. ZeebRd. Ann Arbor, MI 48106

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7 Alternative tehnologies for refrigeration and air onditioning appliations by Don arlyle Ganger A Dissertation Submitted to the Graduate Faulty in Partial Fulfillment of the Requirements for the Degree of DOTOR OF PHILOSOPHY Department: Mehanial Engineering Major: Mehanial Engineering Approved: Signature was redated for privay. In harge of Major Work Signature was redated for privay. For the Major Department Signature was redated for privay. For the Graduate ollege Iowa State University Ames, Iowa 1993

8 ii TABLE OF ONTENTS AKOWLEDGEMENTS xviii HAPTER 1. PROJET OVERVIEW 1 Introdution 1 Projet Objetive 5 Projet Desription 5 HAPTER 2. IDENTIFIATION OF REFRIGERATION TEH NOLOGIES 7 Introdution 7 U.S. Patent Survey 8 Searh Method for Patents Granted Prior to Searh Method for Patents Issued from 1950 to Present 10 Survey Results 12 HAPTER 3. LASSIFIATION OF REFRIGERATION TEH NOLOGIES AND REFRIGERATION APPLIATIONS 14 Introdution 14 Refrigeration Tehnology lassifiation System 14 lassifying Refrigeration Appliations 17

9 iii HAPTER 4. OMPARING THE PERFORMANE OF REFRI GERATION SYSTEMS 20 Introdution 20 oeffiient of Performane 20 Ideal OP 24 Modeled OP 25 Atual OP 25 yle Effiieny 26 HAPTER 5. REVERSED BRAYTON REFRIGERATION Introdution 27 History 28 U.S. Patent Searh 29 Literature Review 30 Thermodynanni Model 31 Introdution 31 Non-Regenerative Reversed Brayton yle 31 Regenerative Reversed Brayton yle 35 Thermodynami Properties 37 Results 38 HAPTER 6. STIRLING REFRIGERATION 52 Introdution 52 History 52 U.S. Patent Searh 53 Literature Review 53

10 iv Stirling yle Models 56 Introdution 56 Idealized Stirling Refrigeration yle Model 56 Ideal Stirling Refrigeration Model with Harmoni Piston Motion Other Models 64 Results 66 HAPTER 7. PULSE TUBE AND THERMOAOUSTI RE FRIGERATION 71 Introdution 71 Pulse Tube 71 History 71 Theory of Operation 71 Theoretial Model 78 Thermoaousti Refrigerator 78 History 78 U.S. Patents 79 Thermoaousti Refrigerator Theory of Operation 79 Results 81 HAPTER 8. THERMOELETRI REFRIGERATION 85 Introdution 85 Literature Searh 86 Theory 86 Introdution 86 Joulean Power Loss 87

11 V Seebek Effet 87 Peltier Effet 88 Thomson Effet 89 Thermoeletri Refrigeration Model Development 89 oeffiient of Performane 93 Results 95 onlusions 96 HAPTER 9. MAGNETI REFRIGERATION 99 Introdution 99 Literature Review 99 Theory 100 Ideal Magneti Materials 100 Thermodynami Properties of Atual Magneti Materials 103 Magneti Stirling yle 105 Magneti Erisson yle 106 Numerial Model Thermodynami Properties Ill Ill ombined Magneti yle Numerial Model 112 Results 116 HAPTER 10. TEHNIAL ASSESSMENT OF ALTERNATIVE REFRIGERATION TEHNOLOGIES 119 Introdution 119 Environmental Aeptability onsiderations 119 ost Related Tehnology Assessment onsiderations 121

12 vi Rating Fators 123 Magneti Refrigeration 125 Environmental Aeptability of the Tehnology 125 State of the Art 126 omplexity 128 Maintenane 129 Useful Life 130 Size/Weight 131 Energy/Effiieny 131 losure 132 Pulse Tube and Thermoaousti Refrigeration 133 Environmental Aeptability of Pulse/Thermoaousti Systems State of the Art 134 omplexity 134 Size/Weight 135 Maintenane 136 Useful Life 136 Energy/Effiieny 137 losure 137 Thermoeletri Refrigeration 138 Environmental Aeptability of the Systems 138 State of the Art 139 omplexity 140 Size/Weight 141

13 vii Maintenane 142 Useful Life 143 Energy/Effiieny 143 losure 144 Reversed Stirling-Type Refrigeration 146 Environmental Aeptability of Reversed Stirling-Type Systems State of the Art 147 omplexity 149 Size/Weight 150 Maintenane 150 Useful Life 151 Energy/Effiieny 151 losure 153 Reversed Brayton Refrigeration 154 Environmental Aeptability of Reversed Brayton Systems 154 State of the Art 155 omplexity 156 Size/Weight 157 Maintenane 158 Useful Life 158 Energy/Effiieny 159 losure 159 Absorption Refrigeration 160 Introdution 160

14 Environmental Aeptability of Absorption Refrigeration Systems State of the Art 161 omplexity 163 Size/Weight 164 Maintenane 165 Useful Life 165 Energy/Effiieny 166 losure 168 Solid Sorption Refrigeration 169 Introdution 169 Environmental Aeptability of Solid Sorption Refrigeration Systems 171 State of the Art 172 omplexity 173 Size/Weight 174 Maintenane 175 Useful Life 176 Energy/Effiieny 176 losure 178 Tehnology Assessment for Vapor-ompression Refrigeration 178 Introdution 178 Environmental Aeptability of Vapor-ompression Systems 179 State of the Art 179 omplexity 180 Size/Weight 181

15 » ix Maintenane 182 Useful Life 183 Energy/Effiieny 184 losure 187 Ejetor Refrigeration 187 Introdution 187 losure 190 Tehnial Assessment Ratings of the Refrigeration Tehnologies 190 HAPTER 11. RESULTS OF TEHNOLOGY ASSESSMENT AND SUMMARY OF ONLUSIONS 192 Introdution 192 Tehnology Assessment riteria Weighting Fators 193 Results 193 onlusions 198 BIBLIOGRAPHY 200 APPENDIX A. TEHNOLOGIES IDENTIFIED DURING PATENT AND LITERATURE SURVEYS 210 APPENDIX B. ALTERNATIVE REFRIGERATION TEHNOL OGY MODELING PROGRAM 220 APPENDIX. SAMPLE DATA FROM ALTERNATIVE REFRI GERATION TEHNOLOGY YLE PROGRAM 270 APPENDIX D. ALTERNATIVE REFRIGERATION YLE TEH NIAL ASSESSMENT PROGRAM 273

16 X APPENDIX E. SAMPLE DATA FROM THE TEHNOLOGY ASSESSMENT PROGRAM 303

17 » xi LIST OF TABLES Table 2.1: U.S. patent lasses and sublasses surveyed 11 Table 3.1: Thermodynami yles used to aomplish refrigeration identified during the survey of tehnologies 16 Table 3.2: Thermal soure and sink temperatures for the five refrigeration appliation ategories 19 Table 5.1: Parameter values for the atual, best possible and ideal reversed Brayton and regenerative reversed Brayton model ase study 39 Table 6.1: Experimental results reported by Fabien [42] for prototype free-piston Stirling oolers intended for domesti refrigerators. 56 Table 8.1: Thermoeletri yle oeffiients of performane for different refrigeration and air onditioning appliations 98 Table 10.1: Linguisti interpretation of the numerial ratings for tehnology assessment riteria 124 Table 10.2: Numerial definition of the energy/effiieny rating sale in terms of yle effiieny (perent of the arnot OP) 124

18 » xii Table 10.3: Tehnology assessment for magneti refrigeration 133 Table 10.4: Tehnology assessment for pulse and thermoaousti refrigeration 138 Table 10.5: Tehnology assessment for thermoeletri refrigeration Table 10.6: Tehnology assessment for reversed Stirling-type refrigeration. 154 Table 10.7: OP of the theoretial reversed Brayton yle for three different isentropi ompressor and expander effiienies. Tsoure 4, = 35, Pressure ratio = Table 10.8: Tehnology assessment for reversed Brayton refrigeration Table 10.9: Tehnology assessment for absorption refrigeration 169 Table 10.10: Tehnology assessment for solid sorption refrigeration 178 Table 10.11: Tehnology assessment for vapor-ompression refrigeration Table 11.1: Tehnology assessment riteria weighting fators by appliation ategory 193 Table 11.2: Ranking of domesti air onditioning tehnologies 194 Table 11.3: Ranking of ommerial air onditioning tehnologies 195 Table 11.4; Ranking of mobile air onditioning tehnologies 196 Table 11.5: Ranking of domesti refrigeration tehnologies 197 Table 11.6: Ranking of ommerial refrigeration tehnologies 198

19 » xiii LIST OF FIGURES Figure 3.1: Refrigeration Tehnology lassifiation Diagram 15 Figure 4.1: Shemati of a refrigeration system driven by mehanial work. 22 Figure 4.2: Shemati of a refrigeration system driven by heat transfer.. 23 Figure 5.1: Shemati of a non-regenerative reversed Bray ton yle Figure 5.2: Temperature vs. entropy diagram for a non-regenerative reversed Brayton yle 33 Figure 5.3: Shemati of the regenerative reversed Brayton yle 35 Figure 5.4: Temperature vs. entropy diagram for the regenerative reversed Brayton yle 36 Figure 5.5: OP vs. soure temperature for an ideal reversed Brayton refrigeration system 40 Figure 5.6: yle effiieny vs. soure temperature for an ideal reversed Brayton refrigeration system 41 Figure 5.7: OP vs. soure temperature for a reversed Brayton refrigeration system operating with parameters given in the "best possible" ase 42

20 » xiv Figure 5.8: yle effiieny vs. soure temperature for a reversed Brayton refrigeration system operating with parameters given in the "best possible" ase 43 Figure 5.9: OP vs. soure temperature for a reversed Brayton refrigeration system operating with parameters given in the atual ase 44 Figure 5.10: yle effiieny vs. soure temperature for a reversed Brayton refrigeration system operating with parameters given in the atual ase 45 Figure 5.11: OP vs. soure temperature for an ideal regenerative reversed Brayton refrigeration system 46 Figure 5.12: yle effiieny vs. soure temperature for an ideal regenerative reversed Brayton refrigeration system 47 Figure 5.13: OP vs. soure temperature for a regenerative reversed Brayton refrigeration system operating with parameters given in the "best possible" ase 48 Figure 5.14: yle effiieny vs. soure temperature for a regenerative reversed Brayton refrigeration system operating with parameters given in the "best possible" ase 49 Figure 5.15: OP vs. soure temperature for a regenerative reversed Brayton refrigeration system operating with parameters given in the atual ase 50

21 » XV Figure 5.16: yle effiieny vs. soure temperature for a regenerative reversed Brayton refrigeration system operating with parameters given in the atual ase 51 Figure 6.1: Shemati of a Stirling refrigeration yle 57 Figure 6.2: Pressure vs. volume diagram for a Stirling refrigeration yle. 58 Figure 6.3: Temperature vs. entropy diagram for a Stirling refrigeration yle 59 Figure 6.4: Pressure vs. volume diagrams for a Stirling refrigerator with harmoni piston motion 64 Figure 6.5: OP vs. soure temperature for a Stirling refrigerator with irreversible heat exhange proesses 67 Figure 6.6: yle effiieny vs. soure temperature for a Stirling refrigerator with irreversible heat exhange proesses 68 Figure 6.7: OP vs. soure temperature for a Stirling-type refrigerator alulated using the Kelly model 69 Figure 6.8: yle effiieny vs. soure temperature for a Stirling-type refrigerator using the Kelly model 70 Figure 7.1 Figure 7.2 Figure 7.3 Figure 7.4 Figure 7.5 Two pulse tube refrigerator onepts 72 yle exeuted by a ontrol mass element in a pulse tube Step funtion pressure hange in an ideal pulse tube 75 T-S diagram for the pulse tube refrigeration yle 76 P-v diagram for the pulse tube refrigeration yle 77

22 xvi Figure 7.6: oeffiient of performane vs. soure temperature for the pulse tube yle using helium gas 82 Figure 7.7: yle effiieny vs. soure temperature for the pulse tube yle using helium gas 83 Figure 7.8: Measured oeffiient of performane for the STAR refrigerator [62] 84 Figure 8.1: Shemati of a thermoeletri refrigerator and its surroundings. 90 Figure 8.2: Shemati of a thermoeletri refrigeration iruit 91 Figure 8.3: OP vs. soure temperature for an ideal thermoeletri refrigerator 96 Figure 8.4: yle effiieny vs. soure temperature for an ideal thermoeletri refrigerator 97 Figure 9.1: Temperature versus speifi entropy diagram for an ideal ferromagneti material 102 Figure 9.2: Temperature versus entropy at onstant field strength diagram for a ferromagneti material 104 Figure 9.3: Temperature versus speifi entropy diagram for a magneti Stirling yle 106 Figure 9.4: Temperature versus speifi entropy diagram for a magneti Erisson yle 108 Figure 9.5: Temperature versus speifi entropy diagram for a yle involving a magneti polytropi proess 109

23 > xvii Figure 9.6: Temperature versus speifi entropy diagram for a ombined yle 110 Figure 9.7: Temperature versus speifi entropy diagram illustrating the determination of areas for the ombined yle 114 Figure 9.8: Temperature versus speifi entropy diagram illustrating the magneti work and heat aeptane areas for the ombined yle 115 Figure 9.9: OP versus soure temperature for an ideal ombined magneti refrigeration yle 117 Figure 9.10: yle effiieny versus soure temperature for an ideal ombined magneti refrigeration yle 118 Figure 10.1: Shemati diagram of a simple ejetor refrigeration system.. 188

24 xviii AKOWLEDGEMENTS I wish to express my gratitude to Dr. Howard Shapiro and Dr. Mihael Pate for their guidane and friendship throughout my graduate studies. I want to partiularly thank them for their onstant enouragement and support. It was a privilege to work with them. I also wish to thank the members of my graduate ommittee, Dr. Ron Nelson, Dr. Brue Munson, and Mr. James Patterson. Their suggestions on this work were very appreiated. I am thankful that Dr. Donald Young graiously agreed to serve on my ommittee after Dr. Munson left for a sabbatial Dr. Young, "Thank you." This researh projet was funded by the United States Environmental Protetion Ageny, Air and Energy Engineering Researh Laboratory. I wish to thank the AEERL staff for their suggestions and support. My life-long friend. Dr. William J. ook, has been a onstant soure of enouragement from the time I deided to beome an engineer. It's going to take a lot of hunting trips to repay you, get ready. I am grateful for the help I have reeived from Joe Huber, Frank Poduska, Joe Struss, and Sylvester Upah in solving omputer related problems. When I didn't think there was a rabbit in the hat, they helped me find one!

25 xix Finally, I wish to thank my wife, harlotte, and our hildren, Benjamin, Elizabeth, and Amelia, for their understanding, patiene, and loving support.

26 1 HAPTER 1. PROJET OVERVIEW Introdution Presently, the most widely used method of aomplishing ooling for for domesti, ommerial, and mobile refrigeration and air onditioning appliations is the vapor-ompression yle. Vapor- ompression refrigeration dates bak to 1834 when Jaob Perkins patented a losed yle ie mahine using ether as the refrigerant. The development of ommerial vapor ompression mahinery ontinued in Ameria, Europe and Australia between 1850 and 1870 with the prinipal appliation being ie making. In the 1890s, smaller ompressors were developed, bringing about refrigeration units suitable for household use. Refrigerants for early vapor ompression systems inluded ammonia, arbon dioxide, ethylamine, methylamine, ethyl hloride, methyl hloride, and sulphur dioxide. The industrial and heavy ommerial refrigeration industry used (and was satisfied with) ammonia. The light ommerial and domesti setor used sulphur dioxide, isobutane, methylamine, ethyl hloride, and methyl hloride. When leaked, even in small onentrations, sulphur dioxide reated a very irritating atmosphere apable of waking a person from a deep sleep. Isobutane was flammable though not very toxi. Ethyl and methyl hloride were toxi in onentrations as low as 2% by volume. In the late 1920s, Frigidaire orp., a division of General Motors, was the largest

27 I 2 manufaturer of light ommerial and household refrigerators. Frigidaire used sulphur dioxide as a refrigerant. The nuisane aused by the esape of sulphur dioxide prompted Frigidaire to ask the GM researh laboratory to develop a new refrigerant for them. In 1930, dihloromonofluoromethane (F-21) and dihlorodifluoromethane (F-12) were developed by a team led by Thomas Midgley, Jr. By the end of the deade the use of vapor-ompression systems with F-12 as the refrigerant was ommon [1]. Vapor-ompression tehnology has been developed to its present level of maturity beause of FG and HF refrigerants. These refrigerant ompounds have exellent thermodynami properties for ooling yles. They are inexpensive, stable, nontoxi; and until 1974, thought to be environmentally safe. In 1974, Rowland and Molina [2] published a paper hypothesizing the potential destrution of upper atmosphere ozone due to the release of hlorofluoromethanes. This naturally ourring ozone in the upper atmosphere serves to shield the earth's surfae from ultraviolet radiation emitted from the sun. Depletion of ozone would result in additional transmittane of ultraviolet (UV) band eletromagneti radiation to the environment. Overexposure to UV radiation has been linked to skin aner and other medial problems. In 1987, an international onferene, the "Montreal Protool for Substanes that Deplete the Ozone Layer," sponsored by the United Nations Environmental Programme (UNEP), was onvened to identify whih substanes were harmful to the ozone layer. The resulting agreement, referred to as the Montreal Protool, established a world wide time table for the redution of Fs, and an eventual ban on their prodution.

28 3 A subsequent UNEP sponsored onferene was onvened in London in Sientifi findings regarding ozone depletion were reassessed. Based upon these findings the phase-out for Fs was sheduled for the year In addition, the phaseout of hydrogenated hlorofluoroarbons (HFs) was disussed. To failitate the phase-out in the United States, federal legislation was enated. The lean Air At Amendment [3] was passed in November, The lean Air At Amendment alls for a total prodution phase-out of HFs by the year Based upon findings that the ozone layer was being depleted more rapidly than it was thought. President Bush announed an aelerated shedule for the redution of ozone-depleting ompounds in the United States, with the omplete phase-out of Fs by the year Refrigeration equipment utilizing the vapor-ompression yle is apable of ooling performane whih has been onsidered aeptable in areas where a ready supply of low-ost eletriity is available. Vapor-ompression mahinery also has the advantages of a low first ost and high reliability as ompared to other existing refrigeration methods. This is partly due to its high level of development. Reently, two global problems have aused the engineering ommunity to explore alternatives to vapor-ompression refrigeration: 1. Global environmental hanges brought about by ozone depletion in the upper atmosphere and global warming. 2. The ontinuing need and an inreased desire for refrigeration in parts of the world where eletriity is not readily available or eonomial.

29 I 4 Ozone depletion has brought about the phase-out of F (and eventually HF) refrigerants. New refrigerants suh as HF-134a are being developed as replaements. Global warming is aused by the release of greenhouse gases into the atmosphere. It has been estimated that one-half to two-thirds of the enhanement of the greenhouse effet is expeted to ome from inreasing onentrations of atmospheri 02- Sine the early 19th entury, there has been a 25% inrease in atmospheri O2 with 10% of the inrease ourring sine Three-fourths of the total O2 emissions ome from the ombustion of fossil fuels [4]. The release of HF and F refrigerants also ontributes to the greenhouse effet. These gases an have a long atmospheri lifetime and a muh higher global warming potential (GWP) than 02- Refrigeration systems an make two potential ontributions to the greenhouse effet: 1. The diret GWP ontribution results from the release of refrigerants with a high GWP into the atmosphere. The leakage an originate from shaft seals, pipe joints, and refrigerant hoses, or it an be aused by system failure, reharging, and intentional venting during repair and salvage operations. 2. The indiret GWP results from the reation of O2 during the ombustion of fossil fuels to produe work to drive mehanial systems or to onvert the fossil fuel energy to thermal energy to drive heat driven systems. This researh projet takes into onsideration both the diret and indiret GWP of a refrigeration system.

30 » 5 Projet Objetive The objetive of this projet was to identify, analyze, and assess tehnologies whih ould serve as alternatives to vapor-ompression for the purpose of aomplishing refrigeration. Projet Desription The projet was onduted in three phases: 1. Identifiation and lassifiation of refrigeration tehnologies. 2. Thermodynami analysis of some of the more promising yles. 3. Tehnial assessment of the alternative tehnologies. The U.S. patents and the tehnial literature were used as soures for identifying the different means for aomplishing refrigeration. One a representative group of refrigeration method onepts had been identified, a method of lassifying them for thermodynami analysis was developed. Some of the alternative refrigeration yles were analyzed in detail. A thermodynami model was developed for eah of these yles and omputer subroutines were written for eah model. In some ases, thermodynami property subroutines were also developed to approximate the properties of the working material used in the yle. An interative main program was written to allow the user to hoose whih yles they wished to onsider and to vary speifi parameters on a ase by ase basis. The program was used to provide an estimate of the both the oeffiient of performane (OP) and the Seond Law effiieny for the yles.

31 » 6 The final segment of this projet was a tehnology assessment of refrigeration onepts. riteria whih were ommon to all refrigeration systems were identified. These riteria were rated on a sale of 1 (low) to 5 (high) for eah tehnology and appliation ategory. A omputer program was written to rank the refrigeration tehnologies from best to worst for eah of the appliation areas.

32 7 HAPTER 2. IDENTIFIATION OF REFRIGERATION TEHNOLOGIES Introdution The first phase of this projet involved the identifiation of refrigeration tehnologies for the purposes of further analysis and tehnial assessment. A survey of U.S. Patents and the literature was onduted to disover what refrigeration methods were known to the tehnial ommunity. The starting date for the U.S. Patent survey was 1918 and ontinued through The 1918 date was hosen to predate the ommerial introdution of household refrigerators using the vapor ompression yle, F refrigerants («1930), and air onditioning. A literature survey was onduted in parallel with the patent survey. The purposes of this survey were to: Identify additional refrigeration methods whih may not have been found during the survey of U.S. patents. Provide additional information regarding the theory underlying a partiular refrigeration method found during the patent survey.

33 8 Provide additional information regarding hardware used to aomplish a refrigeration method found during the patent survey. Determine the environmental onsequenes related to the use of working materials ommonly found in eah refrigeration method found. Disover what alternative working materials were known for the refrigeration methods. Identify the potential appliations for whih the refrigeration method was intended. Identify the potential temperature lift for a single stage of a system using a partiular refrigeration method. Determine the atual OP range whih had been observed by experiment for a partiular tehnology. Identify the soure of major performane losses for a partiular refrigeration method and the manner in whih these losses ould be redued. Soures for the literature survey inluded tehnial journals, thermodynami texts, refrigeration trade publiations, and information supplied by the Environmental Protetion Ageny Air and Energy Engineering Researh Laboratory. U.S. Patent Survey Patents are assigned a number in the hronologial order in whih they are granted. An initial hallenge in loating patents for this projet was to determine whih patents (by number) would be possible andidates for review.

34 » 9 Patents are grouped into different tehnologial ategories through a system of lasses and sublasses. These lasses and sublasses an be found in the Index to the U.S. Patent lassifiation System. [5] This index is an alphabetial list of tehnology subjet headings, by indeia number, to the lassifiation system. The Manual of lassifiation [6] lists the numbers and brief desriptive titles (more than 100,000 in all) of the lasses and sublasses. If a more definitive desription of a lass or sublass is required, it an be found in the lassifiation Definitions. There are ontinual hanges in the lassifiation system. New lasses are established as a result of advanements in siene and tehnology. onversely, old lasses and sublasses are abolished when rendered obsolete by tehnologial advanement [5]. Searh Method for Patents Granted Prior to 1050 The initial searh for refrigeration patents was done manually at the Iowa State University Library. An orderly searh proedure similar to one reommended by Ardis [7] was developed. The proedure for manually loating refrigeration patents was as follows: 1. Determine the funtion or effet of the art or instrument to be investigated; in this ase, refrigerators, oolers, and air onditioning. 2. San the Index to the U.S. Patent lassifiation System or the Manual of lassifiation to determine the lasses whih appear to desribe the invention sought. 3. After determining the appliable lasses, review the subleisses in the Index or Manual of lassifiation to determine whih ones are appliable.

35 4. Loate the U.S Patent Index for the year being surveyed. Patents are listed by number within the lass and sublasses. Therefore, a list an be onstruted for all lasses and sublasses of interest for a partiular year. 5. Loate the volume of the Offiial Gazette of the United States Patent Offie. [8] whih ontains the abstrat of the patent being sought. 6. Review the patent abstrat to determine the nature of the patent. 7. Aept or rejet the patent based upon the information in the abstrat. If the patent was aepted, a opy was ordered from the ommissioner of Patents and Trademarks. If the patent was rejeted, no further ation was taken. Searh Method for Patents Issued from 1950 to Present Databases are available whih ontain a omplete listing of all U.S. patent titles and abstrats granted from 1950 to present. The patents relating to a partiular tehnology are loated in the database by supplying the omputer with a list of the appropriate lass and sublass numbers. lass and sublass numbers whih had been identified during the manual patent searh (for the time period from 1918 to 1950) were used as a starting point. Sine lasses and sublasses within the system hange with time, the 1991 Index to the U.S. Patent lassifiation System was used as a referene to determine if any additional lasses or sublasses whih might be appliable had been added to the system. Table 2 ontains a listing of the refrigeration and air onditioning lasses and sublasses used for the database searh. The proedure for the database survey was:

36 11 Table 2.1: U.S. patent lasses and sublasses surveyed. lass Name Sublass Name lass No. Sublass No. Automobile ooler ooler Air ooler Air onditioning D Equipment ooler ooling and Heating Apparatus ooler Liquid Refrigerators abinet struture, ombined Refrigerators ar Refrigerators ompositions to produe hemial Refrigerators ompositions to produe Proesses ombined Refrigerators ompositions to produe Proesses ombined, Sorption type Refrigerators ompositions to produe Refrigerants, Brines Refrigerators ompositions to produe, Refrigerants, Evaporative Refrigerators Design of mahine D15 81 Refrigerators Oupant type. Vehile

37 12 1. The database was queried using the list of patent lasses and sublasses. 2. A list of patent titles (but not patent numbers) was returned along with a number whih was proprietary to Dialog Database Servie. 3. These patent titles were reviewed to determine the probable nature of the patent. If the patent title impliated that the patent dealt exlusively with a hardware item or other feature whih was not appliable to this projet, it was disarded. 4. Abstrats were purhased from Dialog Database Servie for patent titles whih appeared to have merit with respet to the projet. 5. The abstrats were reviewed to determine the nature of the patent, as done in the "manual" searh. 6. The patent was aepted or rejeted based upon the information in the abstrat. If the patent was aepted, a opy was ordered from the ommissioner of Patents and Trademarks. If the patent was rejeted, no further ation was taken. Survey Results In all, approximately 2140 patent titles and abstrats were surveyed. Roughly, 800 of these were from the 1918 to 1950 time period, the remainder were taken from the post-1950 group. Many patents were rejeted sine they dealt with a minor hardware item, suh as the door lath on a refrigerator. Some were rejeted sine they were granted for

38 » 13 a tehnologies whih were no longer usable; ie boxes, for example. Several patents were abandon beause they dealt speifially with an unaeptable refrigerant suh as methyl hloride. Many of the refrigeration onepts set forth in the remaining patents were similar. Therefore, representative patents were seleted from the remaining group. Seventy eight patents were seleted as being representative of the refrigeration tehnologies found during the patent survey. Three additional refrigeration onepts were found during the literature searh. Appendix A ontains a list of the refrigeration onepts found during the patent and literature survey. One a representative sample of refrigeration tehnologies was found, a method of lassifying them into similar thermodynami yles was developed. The lassifiation proedure is presented in hapter 3.

39 14 HAPTER 3. LASSIFIATION OF REFRIGERATION TEHNOLOGIES AND REFRIGERATION APPLIATIONS Introdution Two lassifiation systems were developed for this projet: One to lassify refrigeration tehnologies whih had been identified during the U.S. Patent and literature searh; the seond to define the types of appliations in whih the refrigeration tehnologies would be used. Refrigeration Tehnology lassifiation System During the review of the U.S. patents found during the patent survey, it was determined that the tehnologies tended to fall into speifi groups. Within these groups the tehnologies had many ommon features. These ommon features were used to ategorize the refrigeration tehnologies for the thermodynami analysis and tehnial assessment phases of the projet. Figure 3.1 is a diagram illustrating the lassifiation method developed to ategorize the refrigeration tehnologies found during the patent and literature surveys. The number in parenthesis indiates the number of representative tehnologies whih were plaed in a partiular ategory. The first tier in Figure 3.1 represents the energy soure used to drive the re-

40 » 15 HEAT MEHANIAL WORK DIRET ELETRI MAGNETI PRIMARY WASTE OTHER PHASE HANGE PHASE HANGE OLLAPSING FIELD DISPLAED ORE EVAPORATIVE OMPRESSION (43) GAS DR VAPOR LIQUID Figure 3.1: Refrigeration Tehnology lassifiation Diagram. frigeration system. Heat, mehanial work, the diret onversion of eletriity into refrigeration, and the indiret onversion of eletriity into refrigeration (through eletromagneti fields) are the four soures of energy used to drive the systems. A hange in phase of the working fluid ourred in the thermodynami yles for all of the heat driven systems. Most of the tehnologies driven by mehanial work involved a phase hange proess during the yle. Phase hange during the yle is important beause the heat aeptane and rejetion from the system an approah an isothermal proess.

41 16 The mehanially driven refrigeration tehnologies whih did not have a phase hange proess used either a gas or liquid as the working material. The working materials used in all of the diret eletri onversion and magneti systems were solids whih did not undergo a phase transformation during the refrigeration yle. The thermodynami yle used to aomplish refrigeration was established during the review and seletion of representative patents. Table 3.1 summarizes the thermodynami yles used to aomplish refrigeration in eah tehnology ategory. Table 3.1: Thermodynami yles used to aomplish refrigeration identified during the survey of tehnologies. Ref. Tehnology ategory Heat Driven Mehanial Work, Phase hange Mehanial Work, No Phase hange Diret Eletri Magneti Thermodynami yle or Proess Absorption Adsorption Ejetor Vapor-ompression Evaporative Reversed Brayton Reversed Stirling Pulse Tube &: Thermoaousti Reversed M alone Thermoeletri Magneti

42 17 lassifying Refrigeration Appliations During the refrigeration tehnology identifiation and lassifiation phases, no onsideration had been given as to the appliation for whih the refrigeration system would be used. The next step was to define general appliation areas. These appliation areas were seleted: 1. Domesti air onditioning. 2. ommerial air onditioning. 3. Mobile air onditioning. 4. Domesti refrigeration. 5. ommerial refrigeration. The temperatures of the thermodynami soure (from whih heat is aepted) and sink (to whih heat is rejeted) were established for eah of the appliations. A searh of standards and other tehnial literature was onduted to determine a pratial set of soure and sink temperatures for eah appliation areas. Standards to determine the performane of domesti air onditioners and refrigerators have been promulgated by the Assoiation of Home Appliane Manufaturers (AHAM). These performane standards have been adopted by the Amerian National Standards Institute (ANSI) to help bring about uniformity in the domesti refrigeration industry. Guidelines for testing the performane of ommerial air onditioners and refrigerators are established by the Air-onditioning and Refrigeration Institute (ARI) and the Amerian Soiety of Heating, Refrigerating, and Air-onditioning

43 18 Engineers (ASHRAE). ASHRAE has also established a standard for the environmental onditions in buildings. As with the AHAM standards, ANSI has adopted the ASHRAE standards to bring about onformity in the refrigeration industry. Standards for establishing the performane of domesti and ommerial air onditioners [10, 11, 12] all speified the temperature to whih heat is rejeted (sink temperature) during performane tests to be, 35 (95 F). All three standards speified a room air temperature (soure temperature) of 26.7 (80 F) for performane testing. This temperature appeared to be too high for atual domesti and ommerial air onditioning appliations. Therefore, the ANSI/ASHRAE Standard for Thermal Environmental onditions for Human Oupany [13] was onsulted. The optimum temperature for people during light, primarily sedentary ativity at 50% relative humidity and mean air speed < 0.15 ^ was given as 24.5 (76 F) with an aeptable temperature range of ± 1.5. Multerer and Burton [14] established an interior temperature for automobiles as 24 for a study of alternative automotive air onditioning systems. For domesti refrigerators, AHAM lists three ambient temperatures for testing refrigerators, freezers, and refrigerator-freezers [15]: 21.1 (70 F) 32.2 (90 F) and 43.3 (110 F) AHAM also reommended an average freezer ompartment temperature of (OP).

44 19 ARI Standard 420 speifies an ambient temperature of 35 for performane tests. Four groups were established by the ARI for performane the testing of ommerial refrigerators. Eah group orresponds to a ooling spae temperature for different ommerial refrigeration appliations. These temperatures are given in Table 3.2. Based upon this survey a set of soure and sink temperatures has been established for eah of the five appliation ategories. Table 3.2 is a summary of the five refrigeration appliation ategories and the soure and sink temperatures to be used for omparing refrigeration tehnologies in eah ategory. Table 3.2: Thermal soure and sink temperatures for the five refrigeration appliation ategories. Ref. Appliation ategory Soure Temp. () Sink Temp. () Domesti Air onditioning ommerial Air onditioning Mobile Air onditioning Domesti Refrigeration ommerial Refrigeration ARI Group I ARI Group II ARI Group III ARI Group IV

45 20 HAPTER 4. OMPARING THE PERFORMANE OF REFRIGERATION SYSTEMS Introdution In this hapter, methods of omparing the performane of refrigeration systems will be disussed. The refrigeration tehnologies found during the survey use mehanial work, heat transfer, and eletriity to drive them. The yle effiieny was used to ompare the relative performane of the different tehnologies. The lausius statement of the seond law of thermodynamis is: " It is impossible to onstrut a devie that operates in a yle and produes no effet other than the transfer of heat from a older to a hotter body." For refrigeration systems, the lausius statement implies that a system that aomplishing the transfer of heat from a ooler soure to a hotter sink requires the input of additional work or energy to ause the temperature lift. oeffiient of Performane The performane of refrigeration and air onditioning systems is the ratio of the amount of heat aepted from the ooling spae to the amount of heat or work

46 21 required to drive the refrigeration system. This ratio is known as the oeffiient of performane (OP). Figure 4.1 illustrates a refrigeration system ommuniating with two thermal reservoirs: The soure, at temperature and the sink, at temperature Tjj. The refrigeration system is driven by mehanial work. The OP is defined as; OPw (4.1) where, OPw = The oeffiient of performane for a work driven system. Qj^ = The amount of heat aepted from the soure reservoir. Wiji = The amount of work input from an external system. Heat driven refrigeration systems an be onsidered as two systems: a refrigeration system driven by a heat engine. Figure 4.2 is a shemati of the two systems. Three thermal reservoirs at three different temperatures are required. The heat engine aepts heat from a high-temperature reservoir at temperature ^Gen rejets heat to the sink reservoir at temperature Tfj produing work. The refrigeration system aepts heat from the soure reservoir at temperature and rejets heat to the sink reservoir. The net work from the heat engine is used to drive the refrigeration system. The OP for the refrigeration system is given by Equation 4.1. The thermal effiieny of the heat engine an be defined as, W (4.2) where,

47 HEAT SINK TH QH REFRIGERATION SYSTEM HEAT SOURE Figure 4.1: Shemati of a refrigeration system driven by mehanial work. W = The net work output of the heat engine. QOen. ~ The heat transferred to the heat engine. The OP for heat driven systems is then, OPh = Vth-^OPw (4.3) - (4.4) Qen. Refrigeration systems with high OPs are desirable beause they are less expen-

48 23 HIGH-TEMP. HEAT SOURE T GEN, HEAT ENGINE HEAT SINK REFRIGERATION SYSTEM HEAT SOURE Figure 4.2: Shemati of a refrigeration system driven by heat transfer.

49 24 sive to operate, and they have a lower indiret GWP sine less fuel must be burned to operate them. Ideal OP An ideal refrigeration system would transfer heat reversibly between the soure and sink. The OP for a reversible refrigeration system would be the highest theoretially possible. Using the definition of the Kelvin temperature sale, it an be shown that the ideal OP for work driven refrigeration yles an be expressed as ratios of the absolute temperatures of the soure and sink reservoirs [17]. The ideal OP (OP^jju) for a work driven system is [18], OPi^ = ^ ^. (4.5) For heat driven systems, the ideal OP {OP^^) would be that of a reversible heat engine driving a reversible refrigerator. It an be expressed as ratios of the absolute temperatures of the high-temperature reservoir, sink, and soure. Using Equation 4.2 and the definition of the thermal effiieny for an ideal heat engine, an expression involving absolute temperatures an be written for the ideal heat driven refrigeration system: OP,.^ = ( ") (ïf^) While reversible operation (and thus the ideal OP) are not possible for atual refrigeration systems, it an be shown as a orollary to the seond law of thermodynamis that any two reversible refrigeration yles aepting and rejeting heat at two partiular temperature levels must have the same OP. Therefore, the ideal

50 25 OP an be used as a standard of omparison for the performane of modeled and atual refrigeration systems. Modeled OP The OP of refrigeration systems an be estimated through modeling of the thermodynami yle with whih the system operates. The models attempt to aount for some of the irreversibilities whih our in atual systems. There are different levels of sophistiation in thermodynami models, ranging from simply multiplying the ideal OP by an effiieny through multi-dimensional transient models in whih the energy, momentum, and ontinuity equations are simultaneously solved for elemental ontrol volumes or mass elements throughout the system. As the level of sophistiation of the model inreases, so does the amount of information whih must be known or assumed about the system. For this projet, models were onstruted in whih the thermodynami state was determined at the end of eah proess omposing the yle. Where possible, omponent effiienies were aounted for. The properties defining the thermodynami state were determined by using property routines. Atual OP The atual OP is that of an atual refrigeration system as is determined through experiments onduted using laboratory refrigeration systems or prodution systems. For work driven systems the OP is alulated using Equation 4.1, while for heat driven systems it is alulated using Equation 4.3.

51 > 26 yle Effiieny The yle effiieny, Vyle^ ^e used to examine the effiieny of a refrigeration tehnology operating at different soure temperatures and operating onditions. It will also be used to ompare the relative effiienies of different tehnologies at the same soure temperature. The yle effiieny is defined as, Iyle OP OPamot (4.7)

52 27 HAPTER 5. REVERSED BRAYTON REFRIGERATION Introdution Refrigeration an be aomplished by employing a gas yle rather than a vapor yle in whih the working fluid undergoes hanges from the liquid phase to the vapor phase and vie versa. Gas refrigeration yles inlude the reversed Brayton, Stirling, and pulse-type yles inluding the pulse tube developed by GifFord and Longsworth [50] and thermoaousti devies whih have been studied by Hoffler [57]. In this hapter the reversed Brayton yle, with and without a regenerator, will be examined. The refrigeration effet per unit mass of fluid irulated in a vapor-ompression yle is equivalent to a large fration of the enthalpy of vaporization. In ontrast, the refrigeration effet in a gas yle is the produt of the temperature rise of the gas passing through the low-temperature heat exhanger and the onstant-pressure speifi heat of the gas. Therefore, as ompared to the vapor-ompression yle, a larger mass flow rate is required in the gas yle to produe the same amount of heat removal from a spae. Gas-yle refrigeration an be designed and operated either as an open or losed system. In open systems the gas, ommonly air, is expanded into the spae to be ooled whih is at atmospheri pressure, and then exhausted or re-ompressed. Open

53 I 28 systems often require dehumidifiation of the air prior to expansion to prevent ie formation at the low-temperature points of the system. Open-yle air systems have beome a ommon method of spae onditioning in airraft. The prinipal advantages of the open-yle air system in airraft appliations are: 1. Pressurisation of the abin may be required. 2. Ventilation air is required in the airraft abin. 3. ompressed air is available and is a small fration of the air ompressed in the airraft engine ompressor setion. 4. ool ambient air is available for ooling the ompressed air. In losed-yle gas refrigeration systems, the refrigerant gas is ontained in the piping and omponent parts of the system at all times. Furthermore, the lowtemperature heat exhanger is maintained at pressures above atmospheri. Historially, the term "dense-air system" was derived from the higher pressures maintained in the losed system as ompared to the open system [19]. History Open- and losed-yle gas refrigeration systems using air as the refrigerant were some of the earliest mehanial refrigeration means dating bak to 1834 [23]. The first ommerial air yle mahine was an open-yle mahine introdued by Franz Windhausen in 1889 [20]. The primary appliation for the Windhausen system was old-storage and spae onditioning aboard ships. Air-yle refrigeration mahinery was favored by the shipping industry beause ammonia or arboni aid used in

54 other refrigeration yles of that era was unavailable in many ports of all. Airyle refrigeration was also used in other ommerial appliations as land-based oldstorage and theater ooling. Another advantage of the air system was a ompletely safe and inexpensive refrigerant [19]. The prinipal objetions to the Windhausen open-yle design were diretly related to moisture in the air whih reated the need for inreased maintenane of the mahinery and frost ontamination of the old-storage argo. The Allen dense-air system, inorporating a losed-air system operating at a low pressure of 60 to 70 psig and a pressure ratio of three or four, was adopted to solve the moisture-related problems. The introdution of F refrigerants removed the safety and refrigerant ost advantages of air-yle refrigeration mahines and vapor-ompression systems were favored due to their higher effiienies and ompatness. The vapor-ompression system was inherently more adaptable to different ooling appliations. U.S. Patent Searh A U.S. patent searh was onduted to disover different gas-yle tehnologies for refrigeration appliations. One patent was disovered for an air reversed-brayton yle mahine. U. S. Patent number 1,295,724 was issued February 25, 1919 to Julius Frankenberg for an "Air-Refrigerating Mahine" [21]. This mahine was a unitized ompressor, expander, and high-temperature system. It inorporated rotary ompressor and expander setions onneted by a ommon shaft. A water-ooled heat exhanger was mounted above the ompressor/expander unit to ool the air between the ompressor

55 30 and expander stages. No laim for a low-temperature heat exhanger or regenerator was made in the patent. Literature Review The tehnial literature was reviewed to determine what present researh has been onduted to develop reversed Brayton or modified reversed Brayton refrigeration yles. KaufFeld et al. [22] investigated the reversed Brayton yle as a replaement for vapor-ompression in refrigeration and air onditioning appliations. An analysis of fifteen variations of the reversed Brayton yle was onduted. The variations inluded: open yle, regeneration, and two-stage ompression with interooling. alulated oeffiients of performane from 0.6 to 1.16 were reported assuming an ambient temperature of 30, a room entry temperature of 5, and isentropi effiienies of the expansion and ompression devies of 80%. Open-yle test apparatus with single- and two-stage ompression were onstruted and evaluated. Measured OPs of up to 0.45 were reported. Problems with moisture removal, oil odor, and noise were also reported. Henatsh and Zeller [23] thermodynamially modeled the Joule (reversed Brayton) proess and a modified Joule-Erisson proess inluding the effets of regeneration. The model inluded adiabati two-stage ompression with interooling.

56 > 31 As part of the study, an earlier investigation omparing the isentropi effiienies to volumetri flow rates of ommerially available turbines, radial flow ompressors and dry-type srew ompressors by Henatsh was inorporated. Effiienies on the order of 88% were noted for large displaement turbines and radial flow ompressors and 80% for large radial flow ompressors. For a non-regenerative open yle, oeffiients of performane ranging from 0.61 to 0.77 were noted for mass flow rates of 0.10 and 0.35 ^ respetively, an ambient temperature of 42, and a temperature ratio of 1.1. Thermodynami Model Introdution Thermodynami models for the non-regenerative and regenerative reversed Brayton yles were onstruted and programmed in FORTRAN for analysis on an IBM ompatible personal omputer. A subroutine to alulate the thermodynami properties of the air was also developed. Non-Regenerative Reversed Brayton yle The ideal thermodynami model of the reversed Brayton yle inludes two isentropi and two isobari proesses [25]. Sine the atual ompression and expansion proesses are irreversible, provisions were made in the model to allow for and vary the degree of irreversibility using isentropi ompressor and expander effiienies. Figures 5.1 and 5.2 are the shemati and temperature vs. entropy diagrams for a non-regenerative reversed Brayton yle.