Experimental investigation of heat recovery from R744 ... 418902/FULLTEXT01.pdf · PDF...

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Transcript of Experimental investigation of heat recovery from R744 ... 418902/FULLTEXT01.pdf · PDF...

  • Experimental investigation of heat recovery from R744 based

    refrigeration system

    ZAHID ANWAR

    Master of Science Thesis

    KTH School of Industrial Engineering and Management

    Energy Technology EGI-2011-02MSC

    Division of Applied thermodynamics & Refrigeration

    SE-100 44 STOCKHOLM

  • iii

    Experimental investigation of heat recovery

    from R744 based refrigeration system

    Zahid Anwar

    Master of Science Thesis Energy Technology 2011:02MSC

    KTH School of Industrial Engineering and Management

    Division of Applied Thermodynamic and Refrigeration

    SE-100 44 STOCKHOLM

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    Master of Science Thesis EGI 2011/ETT:02MSC

    Experimental investigation of heat recovery from

    R744 based refrigeration system

    Zahid Anwar

    Approved

    Date

    Examiner

    Professor Per Lundqvist

    Supervisor

    Yang Chen

    Commissioner

    Contact person

    Abstract

    With increasing energy price and concern on environmental impacts, more attention has been

    paid to refrigeration and heat pump systems. Several regulations have already been applied

    on the choice of refrigerants and the search for more energy efficient system solutions has

    been intensified. Due to these reasons, CO2 as an environmental benign natural refrigerant

    has attracted great interest since 1990s.

    Due to its low critical temperature (31.1 oC) and high critical pressure(73.8 bar), CO2

    refrigeration cycle works as a transcritical cycle, which means part of the cycle is located in

    supercritical region, where the temperature is independent of the pressure. Depending on the

    heat sink fluid temperature profile the temperature glide of CO2 in the supercritical region

    makes it possible for the CO2 refrigeration cycle to have less irreversibility in a heat recovery

    process than traditional refrigeration cycles.

    A new CO2 refrigeration/heat pump test rig is built at the division of Applied

    Thermodynamics and Refrigeration to investigate CO2 refrigeration/heat pump systems. With

    the newly built test rig following main tasks were performed in this thesis work,

    Overall system performance on various imposed operating conditions.

    Second law analysis of the system by exergy and entropy balance methods

    Basic components testing, namely the heat exchangers and the compressor.

    Uncertainty analysis.

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    Table of Contents

    Table of Contents ..................................................................................................................... vii

    List of Figures ........................................................................................................................... ix

    Nomenclature ............................................................................................................................ xi

    Chapter 1 .................................................................................................................................... 1

    1.1 Heat pump basics ................................................................................................................. 1

    1.1.1 Heat Pump ..................................................................................................................... 1

    1.1.2 Heat pump classification ............................................................................................... 1

    1.1.3 Why heat pump ............................................................................................................. 2

    1.2 Heat pump water heater (HPWH) ........................................................................................ 3

    Chapter 2 .................................................................................................................................... 5

    CO2 and the transcritical cycle ................................................................................................... 5

    2.1 Refrigerant progression history........................................................................................ 5

    2.1.1 Ozone Layer Depletion ............................................................................................. 5

    2.1.2 Global warming ........................................................................................................ 5

    2.2 CO2 as refrigerant ............................................................................................................ 6

    2.2.1 History of CO2 .......................................................................................................... 8

    2.3 CO2 Transcritical cycle .................................................................................................... 9

    2.4 CO2 heat pump water heater case studies ...................................................................... 11

    Chapter No 3 ............................................................................................................................ 15

    3.1 System performance Evaluation ........................................................................................ 15

    3.1.1 Coefficient of Performance (COP) ............................................................................. 15

    3.2 References for Transcritical cycle ................................................................................. 16

    3.2.1 The modified Lorenz cycle ..................................................................................... 16

    3.2.2 Ideal Lorentzen cycle .............................................................................................. 17

    3.2.3 Real Lorentzen cycle ............................................................................................... 17

    Chapter No 4 ............................................................................................................................ 19

    Heat Pump testing at KTH ....................................................................................................... 19

    4.1 CO2 heat pump at KTH (system layout) ........................................................................ 19

    4.1.1 System modifications .............................................................................................. 20

    4.2 Working principle .......................................................................................................... 20

    4.2.1 Methodology ........................................................................................................... 21

    4.2.2 Direct and Indirect mass flow measurement ........................................................... 21

    4.3 Results ............................................................................................................................ 23

    4.3.1 Overall system performance from meter reading ................................................... 23

    Case A .......................................................................................................................... 23

    Case B .......................................................................................................................... 26

    Case C Part 1 ................................................................................................................ 28

    Case C Part 2 ................................................................................................................ 30

    Case D .......................................................................................................................... 32

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    4.3.2 Results based on the compressor data ..................................................................... 34

    Case A .......................................................................................................................... 34

    Case B .......................................................................................................................... 35

    Case C Part 1 ................................................................................................................ 36

    Case C Part 2 ................................................................................................................ 36

    Case D .......................................................................................................................... 37

    4.3.3 Results for the components testing ......................................................................... 39

    4.3.3.1 Heat exchanger effectiveness ........................................................................... 39

    4.3.3.1.1 For the 1ST

    heat exchanger ........................................................................ 39

    4.3.3.1.2For the 3RD

    heat exchanger ........................................................................ 41

    4.4.4 Second law analysis of the transcritical cycle ......................................................... 44

    Chapter 5 .................................................................................................................................. 49

    Uncertainty Analysis ................................................................................................................ 49

    5.1 Uncertainty in the measurement of heating capacity ..................................................... 49

    5.1.1 Uncertainty in temperature measurement ...............................................................