D.Bizzarri - PhD Thesis - 2008 iii

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D.Bizzarri - PhD Thesis - 2008 iii

ABSTRACT

A compact air separator demonstrator based on centrifugally enhanced distillation has been studied. The full size device is meant to be used on board of a Two Stage To Orbit vehicle launcher. The air separation system must be able to extract oxygen in highly concentrated liquid form (LEA, Liquid Enriched Air) from atmospheric air. The LEA is stored before being used in a subsequent rocket propulsion phase by the second stage of the launcher. Two reference vehicles are defined, one with a subsonic first stage and one with a supersonic first stage. In both cases, oxygen collection is performed during a cruise phase (M 0.7 and M 2.5 respectively). The aim of the project is to demonstrate the feasibility of the air separation system, investigate the separation cycle design, and assess that the separator design selected is suitable for the reference vehicles.

The project is described from original base ideas to design, construction, extended testing and analysis of experimental results. Preliminary computations for a realistic layout have been performed and the motivations for the choices made during the process are explained. Test rig design, separator design and technical discussion are provided for a subscale pilot unit. Mass transport parameters and flooding limits have been estimated and experimentally measured. Performance has been assessed and shown to be sufficient for the reference Two Stage To Orbit vehicles. The technology developed is found suitable without further optimization, although some volume and mass reduction would be desirable for the supersonic first stage concept. There are many ways of optimisation that can be further investigated. The aim of this program, however, is not to fully optimize the device, but to demonstrate that a device based on a simple, robust, low-risk design is already suitable for the launch vehicles. On top of that analysis, directions for improvements are suggested and their potentials estimated. A complete assessment of those improvements requires further maturation of the technological concept through further testing and practical implementations.

Directions for future work, general conclusions and a vehicle development roadmap

have also been provided.

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D.Bizzarri - PhD Thesis - 2008 iv

STRUCTURE OF THE DOCUMENT

The document is made of a main thesis text complemented by more detailed specific appendices. Not all appendices have been written using the same word processor for practical reasons, and the composite structure comes out of the fact that appendices given here are based on reports and notes that were part of a set of different, evolving documents that had to be maintained over time.

A detailed Table of Contents is given at the beginning of the main text and each Appendix with the exception of Appendix D.

LIST OF APPENDICES

APPENDIX A: TECHNICAL DESCRIPTION OF THE TEST CELL AND ITS SPINDLE

APPENDIX B: SEPARATOR AND CYCLE STUDIES AND ESTIMATIONS

APPENDIX C: PREVIOUS WORK PERFORMED RELATED TO THE PROJECT

APPENDIX D: THERMO-CHEMICAL PROPERTIES OF OXYGEN AND NITROGEN

APPENDIX E: FLOODING, PRESSURE DROP AND MASS EXCHANGE IN A CENTRIFUGAL DISTILLATION COLLUMN

D.Bizzarri - PhD Thesis - 2008 iii

D.Bizzarri - PhD Thesis - 2008 iii

ABSTRACT

Directions for future work, general conclusions and a vehicle development roadmap

have also been provided.

D.Bizzarri - PhD Thesis - 2008 iv

STRUCTURE OF THE DOCUMENT

A detailed Table of Contents is given at the beginning of the main text and each Appendix with the exception of Appendix D.

LIST OF APPENDICES

APPENDIX A: TECHNICAL DESCRIPTION OF THE TEST CELL AND ITS SPINDLE

APPENDIX B: SEPARATOR AND CYCLE STUDIES AND ESTIMATIONS

APPENDIX C: PREVIOUS WORK PERFORMED RELATED TO THE PROJECT

APPENDIX D: THERMO-CHEMICAL PROPERTIES OF OXYGEN AND NITROGEN

APPENDIX E: FLOODING, PRESSURE DROP AND MASS EXCHANGE IN A CENTRIFUGAL DISTILLATION COLLUMN

APPENDIX F: DESIGNING FOR OPERATION UNDER OXYGEN ENRICHED ATMOSPHERE

APPENDIX G: EXPERIMENTAL SET-UP APPENDIX G.1: INSTRUMENTATION

APPENDIX G.2: OXYGEN SEPARATION ANALYSIS

APPENDIX G.3: PRESSURE DROP ANALYSIS INSIDE THE SEPARATOR

D.Bizzarri - PhD Thesis - 2008 v

TABLE OF CONTENTS

1. INTRODUCTION ... 1

1.1. WHY COLLECTING OXYGEN DURING FLIGHT... 2

1.2. THE CONCEPTUAL AND EXPERIMENTAL STUDIES ... 4

1.3. INHERITAGE FROM PREVIOUS EUROPEAN RESEARCH AND THE VORTEX SEPARATOR... 6

1.4. THE REFERENCE CONCEPT AND THE REFERENCE VEHICLES... 8

1.5. THE NEED FOR DESIGN WORK AND EXPERIMENTAL RESULTS... 13

1.6. PROJECT RATIONALE... 14

2. OVERVIEW OF THE RDS DEVELOPMENT... 15

2.1. CHOICE OF THE SEPARATION PRINCIPLE... 15

2.2. FIRST SKETCH ... 16

2.3. THE DESIGN PROCESS IN EXPERIMENTAL WORK ... 18

2.4. DEEP COOLING FACILITY... 18

2.4.1. AVAILABLE FACILITY ... 19

2.4.2. ORIGINAL PROPOSAL... 19

2.4.3. FINAL SELECTED OPTION... 20

2.4.4. HEAT EXCHANGERS ... 20

2.5. FIRST ISSUE: SEPARATOR ARRANGEMENT... 21

2.5.1. MASS EXCHANGER CONCEPT: LIMITING LAYOUT COMPLEXITY, PROVIDING TESTING STRATEGY, ENHANCING MODULARITY ... 21

2.5.2. ACCOMMODATING AND FEEDING THE SEPARATION MEDIUM ... 23

2.5.3. RELATION TO A REAL SEPARATION SYSTEM ... 24

2.6. CORE SEPARATOR DESIGN ... 27

2.6.1. ARRANGING COUNTERFLOWS AND MASS TRANSPORT... 27

2.6.2. CORE MANUFACTURING... 36

2.6.3. SELECTED SEPARATION MEDIUM CHARACTERISTICS ... 40

2.6.4. REFERENCE CONDITIONS... 41

2.7. SKETCH OF THE SEPARATION UNIT... 43

3. THEORETICAL PROCESS STUDIES ... 45

3.1. A PREREQUISITE: COLLECTION OF THERMO-PHYSICAL DATA FOR THE WORKING FLUID... 45

3.2. ANALYSIS TOOLS AND MODELS: MASS EXCHANGE MODELS ... 48

3.2.1. EQUILIBRIUM STAGE APPROXIMATION (McCabe and Thiele Method, ETP model) ... 48

3.2.2. CONTINUOUS NTU MODEL... 51

3.2.3. TAKING FLOW SECTION VARIATION INTO ACCOUNT... 55

3.2.4. RELATING NTU and NETP ... 57

3.2.5. RELATION BETWEEN MASS EXCHANGER AND COMPLETE SEPARATION SYSTEM ... 58

3.3. STUDIES OF COMPLETE SEPARATION SYSTEMS... 58

3.3.1. PREVIOUS WORK: USE OF THE DOUBLE PRESSURE COLUMN LAYOUT58 3.3.2. THE HALF COLUMN LAYOUT, A RADICAL OPTION ... 62

3.3.3. IMPROVEMENTS OF THE COLLECTION RATIO... 66

3.3.4. THE COMPLETE COLUMN LAYOUT... 67

3.3.5. RESULTS OF DETAILED CYCLE STUDY... 69

3.3.6. PARAMETRIC STUDY, A SIMPLIFIED MODEL... 70

3.3.7. CONCLUSION ... 72

D.Bizzarri - PhD Thesis - 2008 vi 4. FLOODING, PRESSURE DROP AND MASS EXCHANGE IN A

CENTRIFUGAL DISTILLATION COLUMN: ESTIMATION OF

PARAMETERS ... 74

4.1. INTRODUCTION... 74

4.2. REFERENCE CONDITIONS USED FOR ESTIMATIONS ... 74

4.3. METAL FOAM CHARACTERIZATION... 74

4.4. SOME PREREQUISITE ... 75

4.4.1. Substitutes for the Specific Surface parameter ... 76

4.4.2. Gas Velocity in Porous Media... 76

4.5. F LOODING ... 77

4.5.1. Semi-empirical correlation from non-rotating systems ... 77

4.5.2. Data from rotating systems ... 81

4.5.3. Critical Assessment of Flooding Regressions for Random Packings ... 84

4.5.4. Comparison Chart (water-air system) ... 85

4.5.5. Flooding Prediction ... 87

4.6. P RESSURE D ROP ... 92

4.6.1. Viscous pressure drop ... 92

4.6.2. Centrifugal Pressure Drop... 95

4.6.3. Viscous Pressure Drop with Flooding... 95