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Effects of Varying Fan Speed on a Refrigerator/Freezer System

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Effects of Varying Fan Speed on a Refrigerator/Freezer System University of Illinois at Urbana-Champaign Air Conditioning and Refrigeration Center A National Science Foundation/University Cooperative Research Center Effects of Varying Fan Speed on a Refrigerator/Freezer System A. R. Cavallaro and C. W. Bullard ACRC TR-63 July 1994 For additional information: Air Conditioning and Refrigeration Center University of Illinois Mechanical & Industrial Engineering Dept. 1206 West Green Street Urbana, IL 61801 Prepared as part of ACRC Project 30 Cycling Performance of Refrigerator-Freezers (217) 333-3115 C. W. Bullard, 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. Acustar Division of Chrysler Allied Signal, Inc. Amana Refrigeration, Inc. Brazeway, Inc. Carrier Corporation Caterpillar, Inc. E. I. duPont Nemours & Co. Electric Power Research Institute Ford Motor Company Frigidaire Company General Electric Company Harrison Division of GM ICI Americas, Inc. Modine Manufacturing Company Peerless of America, Inc. Environmental Protection Agency U.S. Army CERL Whirlpool Corporation For additional information: Air Conditioning & Refrigeration Center Mechanical & Industrial Engineering Dept. University of Illinois 1206 West Green Street Urbana, IL 61801 217 333 3115 Abstract Air-side heat transfer correlations were developed to describe variable conductance models for the condenser and evaporator. Few experimentally estimated parameters described well the changes of refrigerant and air-side conditions over a wide range of steady-state operating conditions for the extensively instrumented test refrigerator. Existing empirical correlations that describe the difficult geometry of the heat exchangers were successful for the condenser, but not as successful for the evaporator. By relating dome and discharge temperature of the compressor with a linear fit, which could be accurately estimated if compressor manufacturers disclosed information for one more point other than the rating point and included the dome temperature, an experimentally estimated air-side heat transfer correlation described well the compressor for the same changes of refrigerant and air- side conditions. iii Table of Contents Page Abstract.........................................................................................................................................iii List of Figures ............................................................................................................................ vi List of Tables............................................................................................................................ viii Nomenclature............................................................................................................................. ix Chapter 1: Introduction ............................................................................................................ 1 Chapter 2: Evaporator and condenser variable conductance....................................... 2 2.1 Overall heat transfer coefficients...........................................................................................2 2.2 Refrigerant-side heat transfer correlations............................................................................2 2.3 Air-side heat transfer correlations .........................................................................................3 2.3.1 Empirical correlations for the evaporator..............................................................................................................3 2.3.2 Empirical and theoretical correlations for the condenser...................................................................................4 2.3.3 Experimental correlation for condenser and evaporator.....................................................................................5 2.4 Evaporator results..................................................................................................................5 2.5 Condenser results..................................................................................................................7 Chapter 3: Compressor convective heat transfer...........................................................10 3.1 Convective heat transfer correlation ................................................................................... 10 3.2 Use of rating point data ....................................................................................................... 10 3.4 Compressor simulation........................................................................................................ 11 Chapter 4: Summary and recommendations....................................................................14 Appendix A: Evaporator geometry and airflow rate measurement.............................15 Appendix B: Evaporator experimental air-side heat transfer coefficients................17 B.1 Governing equations........................................................................................................... 17 B.2 Parameter estimation ......................................................................................................... 18 B.3 Effect of superheat on estimating air-side heat transfer coefficient .................................... 20 Appendix C: Condenser calorimeter approach and airflow rate estimation............22 C.1 Purpose ............................................................................................................................... 22 C.2 Background......................................................................................................................... 22 C.3 Condenser cabinet configuration........................................................................................ 23 C.4 Calorimeter geometry......................................................................................................... 24 iv C.5 Airflow rate estimation........................................................................................................ 25 C.6 Varying motor speed and airflow rate ................................................................................ 25 Appendix D: Condenser experimental air-side heat transfer coefficient..................27 D.1 Governing equations........................................................................................................... 27 D.2 Variable air side heat transfer coefficients ......................................................................... 28 D.3 Factors contributing to uncertainty ..................................................................................... 30 D.3.1 Natural convection................................................................................................................................................31 D.3.2 Heat transfer through cabinet walls ...................................................................................................................31 D.3.3 Refrigerant mass flow rate....................................................................................................................................31 D.3.4 Refrigerant-side correlations ...............................................................................................................................31 D.3.5 Radiative losses.....................................................................................................................................................32 Appendix E: Refrigerant mass flow rate and compressor input power ....................33 E.1 Refrigerant mass flow rate .................................................................................................. 33 E.2 Compressor power.............................................................................................................. 34 Appendix F: Compressor heat transfer coefficients.......................................................36 F.1 Governing equations........................................................................................................... 36 F.2 Shell temperature ............................................................................................................... 36 F.3 Air-side heat transfer coefficients........................................................................................ 37 F.3 Relating compressor shell and discharge temperatures..................................................... 39 F.4 Estimating parameters from the rating point....................................................................... 40 F.5 Modeling of the compressor................................................................................................ 42 Appendix G: Compressor second law analysis...............................................................45 G.1 Parameter estimation ......................................................................................................... 45 G.2 Compressor model.............................................................................................................. 47 Appendix H: AC variable speed motor controller............................................................48 H.1 Variable motor
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