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The Heat Transfer and Pressure Drop Behavior of a Zeotropic Refrigerant Mixture in a Microfinned Tube

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The Heat Transfer and Pressure Drop Behavior of a Zeotropic Refrigerant Mixture in a Microfinned Tube The Heat Transfer and Pressure Drop Behavior of a Zeotropic Refrigerant Mixture in a Microfinned Tube K. A. Sweeney and J. C. Chato ACRC TR-95 May 1996 For additional information: Air Conditioning and Refrigeration Center University of Illinois Mechanical & Industrial Engineering Dept. 1206 West Green Street Prepared as part ofACRC Project 37 Urbana, IL 61801 Effect of Geometric Variables and R-22 Alternatives on Refrigerant-Side Evaporation and Condensation (217) 333-3115 J. C. Chato, Principal Investigator The Air Conditioning and Refrigeration Center was founded in 1988 with a grant from the estate of Richard W. Kritzer, the founder of Peerless of America Inc. A State of Illinois Technology Challenge Grant helped build the laboratory facilities. The ACRC receives continuing support from the Richard W. Kritzer Endowment and the National Science Foundation. The following organizations have also become sponsors of the Center. Amana Refrigeration, mc. Brazeway, mc. Carrier Corporation Caterpillar, mc. Dayton Thennal Products Delphi Harrison Thennal Systems Eaton Corporation Electric Power Research Institute Ford Motor Company Frigidaire Company General Electric Company Lennox mternational, mc. Modine Manufacturing Co. Peerless of America, mc. Redwood Microsystems, mc. U. S. Anny CERL U. S. Environmental Protection Agency Whirlpool Corporation For additional information: Air Conditioning & Refrigeration Center Mechanical & Industrial Engineering Dept. University ofIllinois 1206 West Green Street Urbana IL 61801 2173333115 TABLE OF CONTENTS PAGE LIST OF TABLES . ........... ........ ..... ... ........ ... ............. ........ ... .................. vii LIST OF FIGURES Vlll NOMENCLATURE ................................................................................. xi CHAPTER 1 INTRODUCTION ........... '" ............................................................. 1 2 LITERATURE REVIEW ........................................................................... 2 2.1 In-Tube Condensation ......................................................... 2 2.1.1 Flow Regimes in Two Phase Flow .............................. 2 2.1.2 Heat Transfer in Smooth Tubes .............................. 3 2.1.3 Pressure Drop in Smooth Tubes .................................. 6 2.1.3.1 Frictional Pressure Drop ..................... 7 . 2.1. 3.2 Acceleration Pressure Drop ..................... 8 2.2 Refrigerant Mixtures .................................................................. 8 2.2.1 Refrigerant Mixtures in Smooth Tubes ..................... 9 2.3 Internally Enhanced Tube Geometries ..................................... 11 2.3. 1 Microfinned Tubes .............................................. 11 2.3.2 Refrigerant Mixtures in Enhanced Tubes ................... 13 3 ZEOTROPIC REFRIGERANT MIXTURES .............................................. 16 3.1 Two Phase Phenomena' ....................................................... 16 3.2 Temperature Glide ................................................................ 17 3.3 Property Variations ................................................................ 18 4 EXPERIMENTAL APPARATUS AND DATA ANALYSIS ............................ 25 4.1 Experimental Apparatus ....................................................... 25 4.1.1 Refrigerant Side .............................................. 25 4.1.2 Water Side ....................................................... 27 4. 1.3 Data Acquisition System ..................................... 27 4.2 Data Collection Procedures ....................................................... 28 4.3 Data Reduction Procedures ....................................................... 28 4.3.1 Heat Transfer Analysis ..................................... 28 4.3.2 Enhancement and Penalty Factors ............................ 30 4.3.3 Experimental Uncertainty ..................................... 3 2 5 RESULTS AND DISCUSSION ................................................................ 37 5. 1 Heat Transfer Results ................................................................ 37 5.1.1 Heat Transfer Behavior in the Microfinned Tube .......... 37 5.1.2 Heat Transfer Behavior in a Smooth Tube ................... 38 5.1.3 Comparison Between the Smooth and Microfinned Tube ..................................... 39 5.1.4 Development of a Correlation for a Zeotropic Mixture .................................... .40 5.1.5 Discussion of the Enhancement Factor .................. .41 5.2 Pressure Drop Results ....................................................... 43 5.2.1 Pressure Drop in a Smooth Tube ........................... .43 5.2.2 Penalty Factors for a Zeotropic Refrigerant .................. .43 5.3 Comparing the Behavior of a Zeotropic Refrigerant ............................ 44 5.3.1 Relating the Enhancement and Penalty Factors .......... 44 5.3.2 Comparison of a Zeotropic Mixture to Other Refrigerants .................................... .4 5 6 CONCLUSIONS AND RECOMMENDATIONS ..................................... 66 6. 1 Conclusions ......................................................................... 66 6.1.1 Smooth Tube Correlation ..................................... 66 6. 1.2 Heat Transfer in the Enhanced Tube ............................ 67 6.1.3 Pressure Drop Penalties in an Enhanced Tube .......... 68 6.2 Recommendations for Further Research ..................................... 68 ACKNOWLEDGMENTS ......................................................................... 69 REFERENCES .................................................................................. 69 APPENDICES A: PRESSURE DROP CORRELl\. TIONS ....................................................... 73 B: EXPERIMENTAL DATA ................................................................ 81 C: REFRIGERANT PROPERTY INFORMATION .............................................. 83 D: SMOOTHTUBEEXPERIMENTALDATA .............................................. 86 II LIST OF TABLES TABLE PAGE 3.1 Composition Variations During Condensation at 35°C (95°F) ................... 23 3.2 Percent Differences in Properties Due to Composition Variation at 35°C (95°F) ......................................................................... 24 4.1 Test Conditions ......................................................................... 36 A.1 Pressure Drop Prediction using Souza [1992] Correlation ............................ 74 A.2 Test Conditions for Pressure Drop Data .............................................. 77 A.3 Pressure Drop Prediction using Souza [1995] Correlation ............................ 78 B.1 Experimental Data for the Enhanced Tube .............................................. 82 C.1 Property Curve Fits as a Function of Pressure ..................................... 84 C.2 Property Curve Fits as a Function of Pressure and Quality ............................ 84 C.3 Relationship Between Temperature and Pressure as a Function of Quality .......... 85 D.1 Modified Smooth Tube Data ................................................................ 87 ill LIST OF FIGURES FIGURE PAGE 2.1 Flow Regime Characteristics ................................................................ 15 3.1 Simple Temperature Composition Diagram .............................................. 21 3.2 Condensation Process on a Temperature Composition Diagram ................... 21 3.3 Temperature Composition Diagram for an Azeotropic Refrigerant Blend .......... 22 3.4 Temperature Changes for a Counterflow Condenser using a Pure or Azeotropic Refrigerant ....................................................... 22 3.5 Temperature Changes for a Counterflow Condenser with a Zeotropic Refrigerant ......................................................................... 23 4.1 Experimental Apparatus ................................................................ 33 4.2 Preheater Configuration ................................................................ 34 4.3 Test Section Diagram ......................................................................... 34 4.4 Cross Section of the Microfinned Test Section ..................................... 35 5.1 Effect of Quality and Mass Flux on Nusselt Number .................................... .46 5.2 Effect of Quality on Nusselt Number for the Low Mass Flux Cases ................... 46 5.3 Effect of Quality on Nusselt Number or the High Mass Flux Cases ................... 47 5.4 Nusselt Number Vs Quality for G=75 kg/m2-s (55 klbm/ft2-hr) ................ 47 5.5 Nusselt Number Vs Quality for G=150 kg/m2-s (110 klbm/ft2-hr) ................... 48 5.6 Nusselt Number Vs Quality for G=225 kg/m2-s (165 klbm/ft2-hr) .................. .48 5.7 Nusselt Number Vs Quality for G=300 kg/m2-s (220 klbm/ft2-hr) .................. .49 5.8 Nusselt Number Vs Quality for G=400 kg/m2-s (295 klbm/ft2-hr) ................... 49 5.9 Nusselt Number Vs Quality for G=450 kg/m2-s (330 klbm/ft2-hr) ................... 50 5. 10 Nusselt Number V s Quality for Original and Modified Smooth Tube Data .......... 50 5.11 Nusselt Number Vs Quality for the Smooth and Microfinned Tubes G=75 kg/m2-s (55 klbm/ft2-hr) .............................................. 51 5.12 Nusselt Number Vs Quality for the Smooth and Microfinned Tubes G=150 kg/m2-s (110 klbm/ft2-hr) .............................................. 51 5.13 Nusselt Number V s Quality for the Smooth and Microfinned Tubes G=300 kg/m2-s (220 klbm/ft2-hr) .............................................. 52 5.14 Comparison Between Smooth Tube Data and Dobson Prediction
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