Book contents
- Frontmatter
- Contents
- Preface
- Frequently Used Notation
- TWO-PHASE FLOW, BOILING AND CONDENSATION IN CONVENTIONAL AND MINIATURE SYSTEMS
- PART ONE TWO-PHASE FLOW
- PART TWO BOILING AND CONDENSATION
- 11 Pool Boiling
- 12 Flow Boiling
- 13 Critical Heat Flux and Post-CHF Heat Transfer in Flow Boiling
- 14 Flow Boiling and CHF in Small Passages
- 15 Fundamentals of Condensation
- 16 Internal-Flow Condensation and Condensation on Liquid Jets and Droplets
- 17 Choking in Two-Phase Flow
- APPENDIX A Thermodynamic Properties of Saturated Water and Steam
- APPENDIX B Transport Properties of Saturated Water and Steam
- APPENDIX C Thermodynamic Properties of Saturated Liquid and Vapor for Selected Refrigerants
- APPENDIX D Properties of Selected Ideal Gases at 1 Atmosphere
- APPENDIX E Binary Diffusion Coefficients of Selected Gases in Air at 1 Atmosphere
- APPENDIX F Henry's Constant of Dilute Aqueous Solutions of Selected Substances at Moderate Pressures
- APPENDIX G Diffusion Coefficients of Selected Substances in Water at Infinite Dilution at 25°C
- APPENDIX H Lennard–Jones Potential Model Constants for Selected Molecules
- APPENDIX I Collision Integrates for the Lennard–Jones Potential Model
- APPENDIX J Physical Constants
- APPENDIX K Unit Conversions
- References
- Index
12 - Flow Boiling
- Frontmatter
- Contents
- Preface
- Frequently Used Notation
- TWO-PHASE FLOW, BOILING AND CONDENSATION IN CONVENTIONAL AND MINIATURE SYSTEMS
- PART ONE TWO-PHASE FLOW
- PART TWO BOILING AND CONDENSATION
- 11 Pool Boiling
- 12 Flow Boiling
- 13 Critical Heat Flux and Post-CHF Heat Transfer in Flow Boiling
- 14 Flow Boiling and CHF in Small Passages
- 15 Fundamentals of Condensation
- 16 Internal-Flow Condensation and Condensation on Liquid Jets and Droplets
- 17 Choking in Two-Phase Flow
- APPENDIX A Thermodynamic Properties of Saturated Water and Steam
- APPENDIX B Transport Properties of Saturated Water and Steam
- APPENDIX C Thermodynamic Properties of Saturated Liquid and Vapor for Selected Refrigerants
- APPENDIX D Properties of Selected Ideal Gases at 1 Atmosphere
- APPENDIX E Binary Diffusion Coefficients of Selected Gases in Air at 1 Atmosphere
- APPENDIX F Henry's Constant of Dilute Aqueous Solutions of Selected Substances at Moderate Pressures
- APPENDIX G Diffusion Coefficients of Selected Substances in Water at Infinite Dilution at 25°C
- APPENDIX H Lennard–Jones Potential Model Constants for Selected Molecules
- APPENDIX I Collision Integrates for the Lennard–Jones Potential Model
- APPENDIX J Physical Constants
- APPENDIX K Unit Conversions
- References
- Index
Summary
Flow boiling is considerably more complicated than pool boiling, owing to the coupling between hydrodynamics and boiling heat transfer processes. A sequence of two-phase and boiling heat transfer regimes takes place along the heated channels during flow boiling, as a result of the increasing quality. The two-phase flow regimes in a boiling channel are therefore “developing” everywhere and are morphologically different than their namesakes in adiabatic two-phase flows.
Forced-Flow Boiling Regimes
The preferred configuration for boiling channels is vertical upflow. In this configuration buoyancy helps the mixture flow, and the slip velocity between the two phases that is caused by their density difference actually improves the heat transfer. However, flow boiling in horizontal and even vertical channels with downflow are also of interest. Horizontal boiling channels are not uncommon, and flow boiling in a vertical, downward configuration may occur under accident conditions in systems that have otherwise been designed to operate in liquid forced convection heat transfer conditions.
Figure 12.1 displays schematically the heat transfer, two-phase flow, and boiling regimes that take place in a vertical tube with upward flow that operates in steady state and is subject to a uniform and moderate heat flux. The mass flow rate is assumed constant. When the fluid at the inlet is a highly subcooled liquid, at a very low heat flux, the flow field in the entire channel remains subcooled liquid [Fig. 12.1(a)].
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- Two-Phase Flow, Boiling, and CondensationIn Conventional and Miniature Systems, pp. 321 - 370Publisher: Cambridge University PressPrint publication year: 2007
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