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Published byTomas Dobkins Modified over 2 years ago

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

Thai Nguyen Faculty of Engineering (Mechanical) University of Technology, Sydney

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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

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**Why is EHD? Controllable Dielectric fluid Simplified implementation**

Localised cooling of complex curved passages Applicable in zero gravity

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**Applications Air conditioning, refrigerant systems Electronic cooling**

Biomedical (alternative E, natural frequency) Cryogenic processing system Thermal control system

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**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

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**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

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**Governing Equations of EHD Phenomena**

Conservation Equations Momentum Equation Equation of Continuity Energy Equation Equation of State

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**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

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**Governing Equations of EHD Phenomena**

Charge Relaxation Equation where, charge relaxation time:

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Research Stages Macroscopic Approach EHD Bubble Dynamics

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**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

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**Experimental apparatus**

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**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

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**Effects of Nonuniformity of E on Heat Transfer Coefficient Ratio**

8-wire electrode 16-wire electrode Nucleate Boiling Nucleate Boiling Free Conv. Bubble Initiation

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**Effects of Electrode Voltages on Heat Transfer Coefficient ratio**

8-wire electrode 16-wire electrode

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**Bubble Behaviour under EHD effects - 16 wire electrode**

6kV 0kV 12kV 9kV Refrigerant R11, at atmospheric pressure Heat flux = 14.2kW/m2

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**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

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

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**Experimental apparatus**

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**Electric field distribution -Kauss Analysis in Homogeneous media**

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**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

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**EHD effect on Bubble Deformation**

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**EHD effect on Bubble Diameter**

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**EHD effect on Nucleate Site Density**

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**EHD effect on Frequency of Bubble Departure**

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**EHD effect on Proportion of Latent heat to Total heat flux**

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**Second Approach - Conclusion**

Bubble Behaviour Time Dependency Threshold Value Contribution of latent heat on total heat transfer in pool boiling

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**Future Investigation Theoretical Hysteresis effect Time Dependency**

Frequency dependency of dielectric properties Mechanical oscillation of liquid-vapour interface Line of zero force Electrolysis (DC)

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**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

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**Time dependency in EHD Phenomena**

Charge relaxation time In general, reduce of , increasing of heat transfer enhancement Bubble frequency Frequency of alternating field

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**Time dependency in EHD Phenomena - Dielectric theory**

Complex permitivity

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**Heating Wire - Electrode arrangement**

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