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 with the 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
Nucleate Boiling
Free Conv.
Bubble Initiation

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