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Electro-Hydro-Dynamics Enhancement of Multi-phase Heat Transfer

Electro-Hydro-Dynamics Enhancement of Multi-phase Heat Transfer. Thai Nguyen Faculty of Engineering (Mechanical) University of Technology, Sydney. What is EHD?. The application of Electric Fields to induce the fluid motion. Hence,

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Electro-Hydro-Dynamics Enhancement of Multi-phase Heat Transfer

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  1. Electro-Hydro-Dynamics Enhancement of Multi-phase Heat Transfer Thai Nguyen Faculty of Engineering (Mechanical) University of Technology, Sydney

  2. What is EHD? The application of Electric Fields to induce the fluid motion. Hence, • Enhance Heat Transfer caused by disruption of boundary layer near heat transfer surface • Pumping Action

  3. Why is EHD? • Controllable • Dielectric fluid • Simplified implementation • Localised cooling of complex curved passages • Applicable in zero gravity

  4. Applications • Air conditioning, refrigerant systems • Electronic cooling • Biomedical (alternative E, natural frequency) • Cryogenic processing system • Thermal control system

  5. Electric Fields in Pool Boiling Heat Transfer Enhancement by Heating Surface Treatment On Earth: 1D, constant g Gravitational Field No boiling In space: Absent • Electrode Design • High Voltage Complexity!? Electric Field Active Heat Transfer Enhancement Controllable

  6. Interactions among the fields in EHD Electric Field Dielectrophoretic force Temperature dependence on Electrical Conductivity, Permittivity and Mobility Electric Force Density fe Joule Heating Convection Current Forced Convection Flow Field Thermo Field Buoyancy Hydro-Dynamics

  7. Governing Equations of EHD Phenomena • Conservation Equations • Momentum Equation • Equation of Continuity • Energy Equation • Equation of State

  8. Governing Equations of EHD Phenomena • Maxwell Equations • Poisson’s Equation • Conservation of Electric Current • Definition of Electric Current • Definition of Electric Potential • Electric Force Density

  9. Governing Equations of EHD Phenomena • Charge Relaxation Equation where, charge relaxation time:

  10. Research Stages • Macroscopic Approach • EHD Bubble Dynamics

  11. Macroscopic Analysis • Quantitative Analysis - Modelling • q” = CDTanb • Variation of Heat transfer coefficient ratio: hehd/h0 withthe Parameters: • Heat Flux • Electrode Voltage • Electric field feature

  12. Experimental apparatus

  13. Test Rig Features • Specific design for EHD study • Computational and digital recording data (Labview) • Multi-temperature readings at diverse circumferential locations on the heating tube

  14. Effects of Nonuniformity of E on Heat Transfer Coefficient Ratio 8-wire electrode 16-wire electrode Nucleate Boiling NucleateBoiling Free Conv. Bubble Initiation

  15. Effects of Electrode Voltages on Heat Transfer Coefficient ratio 16-wire electrode 8-wire electrode

  16. Bubble Behaviour under EHD effects - 16 wire electrode 6kV 0kV 12kV 9kV Refrigerant R11, at atmospheric pressure Heat flux = 14.2kW/m2

  17. First Approach _ Conclusions • Qualitative Analysis • Bubbles behave differently at diverse locations of the heating tube: • Coalescing of bubbles underneath the heating tube • Suppression of nucleate sites on the sides • Quantitative Analysis • Heat transfer enhancement: large in natural convection region, decrease in nucleate region

  18. EHD Bubble Dynamics • Analysis of bubble behaviour under the influence of electric fields • Bubble parameters: • Frequency • Deformation • Number of nucleate site • Bubble diameter

  19. Experimental apparatus

  20. Electric field distribution -Kauss Analysis in Homogeneous media

  21. Images of Bubbles as at different Electrode Voltage - V(t) = mt Heat Flux = 30kW/m2, Fluid Temperature = 220C 0kV (No EHD) 2.0kV 4.5kV 8.0kV 6.0kV 6.6kV

  22. EHD effect on Bubble Deformation

  23. EHD effect on Bubble Diameter

  24. EHD effect on Nucleate Site Density

  25. EHD effect on Frequency of Bubble Departure

  26. EHD effect on Proportion of Latent heat to Total heat flux

  27. Second Approach - Conclusion • Bubble Behaviour • Time Dependency • Threshold Value • Contribution of latent heat on total heat transfer in pool boiling

  28. Future Investigation • Theoretical • Hysteresis effect • Time Dependency • Frequency dependency of dielectric properties • Mechanical oscillation of liquid-vapour interface • Line of zero force • Electrolysis (DC)

  29. Future Investigation • Experiment • Design and build of power supplier with frequency variable (pulse wave) • Measuring temperature of the wire • Development the test rig compatible with R123, aerospace fuel

  30. Time dependency in EHD Phenomena • Charge relaxation time In general, reduce of , increasing of heat transfer enhancement • Bubble frequency • Frequency of alternating field

  31. Time dependency in EHD Phenomena - Dielectric theory • Complex permitivity

  32. Heating Wire - Electrode arrangement

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