Electro-Hydro-Electro-Hydro-Dynamics Dynamics
Enhancement of Enhancement of Multi-phase Heat Multi-phase Heat
TransferTransferThai NguyenThai Nguyen
Faculty of Engineering Faculty of Engineering (Mechanical)(Mechanical)
University of Technology, University of Technology, SydneySydney
What is EHD?What is EHD?
The application of Electric Fields to The application of Electric Fields to induce the fluid motion. Hence,induce the fluid motion. Hence, Enhance Heat Transfer caused by Enhance Heat Transfer caused by
disruption of boundary layer near disruption of boundary layer near heat transfer surfaceheat transfer surface
Pumping ActionPumping Action
Why is EHD?Why is EHD?
ControllableControllable Dielectric fluidDielectric fluid Simplified implementationSimplified implementation Localised cooling of complex curved Localised cooling of complex curved
passagespassages Applicable in zero gravityApplicable in zero gravity
ApplicationsApplications
Air conditioning, refrigerant systemsAir conditioning, refrigerant systems Electronic coolingElectronic cooling Biomedical (alternative E, natural Biomedical (alternative E, natural
frequency)frequency) Cryogenic processing systemCryogenic processing system Thermal control systemThermal control system
Electric Fields in Pool Electric Fields in Pool BoilingBoiling
Gravitational Field
Electric Field
Controllable
On Earth: 1D, constant g
In space: Absent
Heat Transfer Enhancement by Heating Surface Treatment
No boiling
Active Heat Transfer Enhancement
Complexity!?•Electrode Design•High Voltage
Interactions among the Interactions among the fields in EHDfields in EHD
Electric Field
Flow Field Thermo Field
Joule Heating
Buoyancy
Forced Convection
Elec
tric
Forc
e D
ensi
ty f e
Temperature dependence on Electrical Conductivity, Permittivity and Mobility
Con
vect
ion
Cur
rent
Dielectrophoretic force
Hydro-Dynamics
Governing Equations of Governing Equations of EHD Phenomena EHD Phenomena
Conservation EquationsConservation Equations
Momentum EquationMomentum Equation
Equation of ContinuityEquation of Continuity
Energy EquationEnergy Equation
Equation of StateEquation of State
0. u
ufgpuut
ue
2)(
TkTuCt
TC pp
2).(
M
RTp
Governing Equations of Governing Equations of EHD PhenomenaEHD Phenomena
Maxwell EquationsMaxwell Equations
Poisson’s EquationPoisson’s Equation
Conservation of Electric CurrentConservation of Electric Current
Definition of Electric CurrentDefinition of Electric Current
Definition of Electric PotentialDefinition of Electric Potential
Electric Force DensityElectric Force Density
eE
.
0.
ite
Eui ee
E
22
2
1
2
1EEEf ee
Governing Equations of Governing Equations of EHD PhenomenaEHD Phenomena
Charge Relaxation EquationCharge Relaxation Equation
0
e
evt
where, charge relaxation time:
f
1
Research StagesResearch Stages
Macroscopic ApproachMacroscopic Approach EHD Bubble DynamicsEHD Bubble Dynamics
Macroscopic AnalysisMacroscopic Analysis
Quantitative Analysis - ModellingQuantitative Analysis - Modelling q” = Cq” = CTTaannbb
Variation of Heat transfer coefficient Variation of Heat transfer coefficient ratio: hratio: hehdehd/h/h0 0 withwith the Parameters: the Parameters: Heat FluxHeat Flux Electrode VoltageElectrode Voltage Electric field featureElectric field feature
Experimental apparatusExperimental apparatus
Test Rig FeaturesTest Rig Features
Specific design for EHD studySpecific design for EHD study Computational and digital recording Computational and digital recording
data (Labview)data (Labview) Multi-temperature readings at Multi-temperature readings at
diverse circumferential locations on diverse circumferential locations on the heating tubethe heating tube
Effects of Nonuniformity of E on Heat Effects of Nonuniformity of E on Heat Transfer Coefficient RatioTransfer Coefficient Ratio
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
0 10000 20000 30000 40000 50000 60000
Heat Flux (W/m2)
he/h
0
3kV
6kV
9kV
12kV
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
0 10000 20000 30000 40000 50000 60000Heat Flux (W/m
2)
he/h
0
3kV
6kV
9kV
12kV
8-wire electrode 16-wire electrode
Nucleate Boiling
Nucleate Boiling
Fre
e C
onv.
Bubble Initiation
Effects of Electrode Voltages on Heat Effects of Electrode Voltages on Heat Transfer Coefficient ratioTransfer Coefficient ratio
G = 0.0717Ve + 1
G = 0.0062Ve + 1
G = 0.0019Ve + 10.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
0 2 4 6 8 10 12 14
Electrode Voltage (kV)
he/h
0
Free Convection,
Isolated Boiling,
Jet Boiling,
0.6kW/m2
5.1kW/m2
27.9kW/m2
G = 0.1514Ve + 1
G = 0.0062Ve + 1
G = 0.0019Ve + 1
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
0 2 4 6 8 10 12 14
Electrode Voltage (kV)
he/
h0
Free Convection,
Isolated Boiling,
Jet Boiling, q" =
0.6kW/m2
5.1kW/m2
27.9kW/m2
8-wire electrode 16-wire electrode
Bubble Behaviour under EHD effects - Bubble Behaviour under EHD effects - 16 wire electrode16 wire electrode
Heater
Electrode wires
Bubbles
Bubble growth on electrode
Bubble coalescence
Bubble growth on wires
Bubbles
Electrode wires
Heater
0kV 6kV
9kV 12kV
Refrigerant R11, at atmospheric pressureHeat flux = 14.2kW/m2
First Approach _ First Approach _ ConclusionsConclusions
Qualitative AnalysisQualitative Analysis Bubbles behave differently at diverse Bubbles behave differently at diverse
locations of the heating tube:locations of the heating tube:* Coalescing of bubbles underneath the heating Coalescing of bubbles underneath the heating
tubetube
* Suppression of nucleate sites on the sidesSuppression of nucleate sites on the sides
Quantitative AnalysisQuantitative Analysis Heat transfer enhancement: large in Heat transfer enhancement: large in
natural convection region, decrease natural convection region, decrease in nucleate regionin nucleate region
EHD Bubble DynamicsEHD Bubble Dynamics
Analysis of bubble behaviour Analysis of bubble behaviour under the influence of electric under the influence of electric fieldsfields
Bubble parameters:Bubble parameters: FrequencyFrequency DeformationDeformation Number of nucleate siteNumber of nucleate site Bubble diameterBubble diameter
Experimental apparatusExperimental apparatus
Electric field distribution Electric field distribution -Kauss Analysis in -Kauss Analysis in
Homogeneous mediaHomogeneous media
Images of Bubbles as at different Images of Bubbles as at different Electrode Voltage - V(t) = mtElectrode Voltage - V(t) = mt
Heat Flux = 30kW/m2, Fluid Temperature = 220C
0kV (No EHD) 2.0kV 4.5kV
6.0kV 6.6kV 8.0kV
EHD effect on Bubble DeformationEHD effect on Bubble Deformation
, q" = 35.4kW/m2
q" = 30.0 kW/m2
1.00
1.05
1.10
1.15
1.20
1.25
1.30
0 200 400 600 800 1000 1200 1400 1600 1800
Electric Field Strength (kV/m)
dx/d
y
Time Dependend,
Time Independent,
EHD effect on Bubble DiameterEHD effect on Bubble Diameter
q" = 30kW/m2
q" = 35.4kW/m2
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0 200 400 600 800 1000 1200 1400 1600 1800
Electric Field Strength (kV/m)
Eq
uiv
ale
nt
Bu
bb
le D
iam
ete
r (m
m)
Time Dependent,
Time Independent,
EHD effect on Nucleate Site DensityEHD effect on Nucleate Site Density
q" = 40.0kW/m2
q" = 30.0kW/m2
q" = 35.4 kW/m2
0.0E+00
5.0E+04
1.0E+05
1.5E+05
2.0E+05
2.5E+05
3.0E+05
3.5E+05
4.0E+05
4.5E+05
0 200 400 600 800 1000 1200 1400 1600 1800
Electric Field Strength (kV/m)
Nu
cle
ate
Site
Den
sity
(1/
m2 )
Time Independent,
Time Independent,
Time Dependent,
EHD effect on Frequency of Bubble EHD effect on Frequency of Bubble DepartureDeparture
0
20
40
60
80
100
120
140
160
180
1200 1300 1400 1500 1600 1700 1800
Electric Field Strength (kV/m)
Fre
qu
ency
of B
ub
ble
Dep
artu
re (1
/sec
) Nucleate Site 1
Nucleate Site 2
Nucleate Site 3
Nucleate Site 4
EHD effect on Proportion of Latent heat EHD effect on Proportion of Latent heat to Total heat fluxto Total heat flux
q" = 35.4kW/m2
q" = 30.0 kW/m2
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
1200 1300 1400 1500 1600 1700 1800Electric Field Strength (kV/m)
Pro
po
rtio
n o
f L
ate
nt
He
at
to T
ota
l He
at (
%)
Time Dependent,
Time Independent,
Second Approach - Second Approach - ConclusionConclusion
Bubble BehaviourBubble Behaviour Time DependencyTime Dependency Threshold ValueThreshold Value Contribution of latent heat on total Contribution of latent heat on total
heat transfer in pool boilingheat transfer in pool boiling
Future InvestigationFuture Investigation
TheoreticalTheoretical• Hysteresis effectHysteresis effect• Time DependencyTime Dependency
• Frequency dependency of dielectric Frequency dependency of dielectric propertiesproperties
• Mechanical oscillation of liquid-vapour Mechanical oscillation of liquid-vapour interfaceinterface
• Line of zero forceLine of zero force• Electrolysis (DC)Electrolysis (DC)
Future InvestigationFuture Investigation
ExperimentExperiment• Design and build of power supplier Design and build of power supplier
with frequency variable (pulse with frequency variable (pulse wave)wave)
• Measuring temperature of the wireMeasuring temperature of the wire• Development the test rig Development the test rig
compatible with R123, aerospace compatible with R123, aerospace fuelfuel
constdfb
tieEE 0
f
1
Time dependency in Time dependency in EHD PhenomenaEHD Phenomena
Charge relaxation timeCharge relaxation time
In general, reduce of In general, reduce of , increasing of , increasing of heat transfer enhancementheat transfer enhancement
Bubble frequencyBubble frequency Frequency of alternating fieldFrequency of alternating field
j
Time dependency in Time dependency in EHD Phenomena - EHD Phenomena - Dielectric theoryDielectric theory
Complex permitivityComplex permitivity
Heating Wire - Electrode Heating Wire - Electrode arrangementarrangement