modeling refrigeration system with simulink frink 2007

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MODELING AND CONSTRUCTION OF A COMPUTER CONTROLLED AIR CONDITIONING SYSTEM by BRANDON S. FRINK B.S., Kansas State University, 2005 A THESIS submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE Department of Mechanical and Nuclear Engineering College of Engineering KANSAS STATE UNIVERSITY Manhattan, Kansas 2007 Approved by: Major Professor Warren N. White Abstract As energy efficient devices become more necessary, it is desired to increase the efficiency of air conditioning systems.Current systems use on/off control, where the unit primarily operates in the long lasting start up transients.A proposed solution is an air conditioning unit that runs continuously with active computer control implemented to maximize efficiency.The objective of this thesis is to develop a mathematical model for a specific air conditioning unit and to compare this model to measurements made on the specific unit.This model can then be used to develop a multi-input multi-output control law in the future. In this thesis, a linearized moving interface lumped parameter model is presented, and the derivation verified with great detail.The model predicts transient perturbations from a steady state operating point.The air conditioner tested in this work required several modifications including the addition of sensors and controllers.A description of the system is provided.Methods used to determine all of the parameters for the model are given with explanation.The model is simulated with computer software and compared with experimental data.Simulations predict the final value of superheat and pressures in the evaporator and condenser well for step changes in the compressor speed and expansion valve opening.iii Table of Contents List of Figures .................................................................................................................... vi List of Tables ................................................................................................................... viii Nomenclature for the Evaporator....................................................................................... ix Nomenclature for the Condenser ........................................................................................ x Acknowledgements............................................................................................................ xi CHAPTER 1 - Introduction ................................................................................................ 1 CHAPTER 2 - Lumped Parameter Modeling Equations.................................................... 3 Non-Linear Modeling Equations of the Evaporator ....................................................... 7 Non-Linear Modeling Equations of the Condenser ...................................................... 10 Linear Modeling Equations of the Refrigeration Loop ................................................ 13 CHAPTER 3 - Experimental Setup .................................................................................. 16 System Description of Components ............................................................................. 17 Modifications to Original Design ................................................................................. 18 Measurements and Controls.......................................................................................... 19 Electrical Wiring....................................................................................................... 21 Software .................................................................................................................... 22 Air Flow Rate Meters................................................................................................ 26 CHAPTER 4 - Determination of Modeling Parameters ................................................... 30 Mutual ........................................................................................................................... 30 Evaporator..................................................................................................................... 33 Condenser ..................................................................................................................... 37 CHAPTER 5 - Simulation Results and Comparison to Measured Data........................... 41 Modified Parameter Results.......................................................................................... 47 CHAPTER 6 - Conclusions .............................................................................................. 57 Critical Analysis of Model............................................................................................ 57 Possible Solutions for a Better Model .......................................................................... 59 References......................................................................................................................... 60 Appendix A - Derivation of Evaporator Equations .......................................................... 65 iv Two-Phase Region........................................................................................................ 65 Mass Balance on the refrigerant in Two-Phase Region of the Evaporator............... 65 Energy Balance on Refrigerant in Two-Phase Region of the Evaporator ................ 68 Energy Balance on the Tube Wall in Two-Phase Region of the Evaporator............ 73 Superheat Region.......................................................................................................... 75 Mass Balance on the Refrigerant in the Superheat Region of the Evaporator.......... 75 Energy Balance on the Refrigerant in the Superheat Region of the Evaporator....... 77 Energy Balance on the Tube Wall in the Superheat Region of the Evaporator........ 82 Overall Mass Balance of Evaporator ............................................................................ 84 Appendix B - Derivation of Condenser Equations ........................................................... 85 Superheat Region.......................................................................................................... 85 Mass Balance on Refrigerant in the Superheat Region of the Condenser ................ 85 Energy Balance on the Refrigerant in the Superheat Region of the Condenser ....... 87 Energy Balance on the Tube Wall in the Superheat Region of the Condenser ........ 91 Two-Phase Saturation Region ...................................................................................... 94 Mass Balance on Refrigerant in the Two-Phase Region of the Condenser .............. 94 Energy Balance on the Refrigerant in the Two-Phase Region of the Condenser ..... 96 Energy Balance on the Tube Wall in the Two-Phase Region of the Condenser .... 102 Subcool Region........................................................................................................... 104 Mass Balance on Refrigerant in the Subcool Region of the Condenser ................. 104 Energy Balance on the Refrigerant in the Subcool Region of the Condenser ........ 106 Energy Balance on the Tube Wall in the Subcool Region of the Condenser ......... 110 Overall Mass Balance of Condenser........................................................................... 112 Appendix C - Derivation of Linear Modeling Equations ............................................... 113 Evaporator Equations.................................................................................................. 113 Condenser Equations .................................................................................................. 116 Complete Model ......................................................................................................... 120 Evaporator Matrix Elements....................................................................................... 124 Condenser Matrix Elements........................................................................................ 125 Appendix D - Experimental Setup References ............................................................... 127 System Diagrams ........................................................................................................ 127 v Wiring Diagrams......................................................................................................... 130 LabVIEW Block Diagrams......................................................................................... 137 Parts Lists.................................................................................................................... 144 Air Flow Meter Calibration ........................................................................................ 146 Appendix E - Modeling Parameter Values ..................................................................... 147 vi List of Figures Figure 2-1 Refrigeration Loop Schematic .......................................................................... 6 Figure 2-2 Pressure-Enthalpy Plot ...................................................................................... 6 Figure 2-3 Evaporator Schematic ....................................................................................... 7 Figure 2-4 Condenser Schematic...................................................................................... 10 Figure 3-1 Picture of Setup............................................................................................... 16 Figure 3-2Front Panel of Virtual Instrument .................................................................. 23 Figure 3-3 Air Flow Meter Sketch.................................................................................... 27 Figure 3-4 Air Flow Meter Calibration Setup................................................................... 28 Figure 3-5 Calibration Plots....................................................

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