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Flow electrification Flow electrification by cavity QEDby cavity QED
T. V. PrevenslikT. V. Prevenslik
11F, Greenburg Court11F, Greenburg Court
Discovery Bay, Hong KongDiscovery Bay, Hong Kong
T. V. PrevenslikT. V. Prevenslik
11F, Greenburg Court11F, Greenburg Court
Discovery Bay, Hong KongDiscovery Bay, Hong Kong
ContentsContents
Historical backgroundHistorical background
Contact electrification Contact electrification
PurposePurpose
QED Theory QED Theory
Flow analysisFlow analysis
ConclusionsConclusions
Historical Historical backgroundbackground
19501950 Streaming current Streaming current Zeta potential Zeta potential induced by induced by impurity ionsimpurity ions
19801980 Electrification Electrification density ionic charges as density ionic charges as double layer at the wall interfacedouble layer at the wall interface
20012001 Physiochemical corrosion-oxidation Physiochemical corrosion-oxidation
... No evidence of corrosion products... No evidence of corrosion products
… … Streaming currents Streaming currents shear stress shear stress
Source never identifiedSource never identified
Contact electrificationContact electrification
Contact and Balancing of Fermi levels Contact and Balancing of Fermi levels thermodynamic equilibrium thermodynamic equilibrium
Only one contact necessary for Only one contact necessary for equilibrium - independent of equilibrium - independent of materials.materials.
Experiment shows equilibrium is Experiment shows equilibrium is reached in a single contact only for reached in a single contact only for metals - many contacts are metals - many contacts are necessary to achieve equilibrium necessary to achieve equilibrium between metals and insulators.between metals and insulators.
Some mechanism - in addition to the Some mechanism - in addition to the balancing of Fermi levels - is at playbalancing of Fermi levels - is at play
Cavity QED Cavity QED induced photoelectric effectinduced photoelectric effect
Two-step model contact and Two-step model contact and separationseparation
Interface is a high frequency QED Interface is a high frequency QED cavity that inhibits low frequency IR cavity that inhibits low frequency IR radiation from thermal kT energy radiation from thermal kT energy inherent in atomic clusters. inherent in atomic clusters.
IR energy released concentrates to IR energy released concentrates to VUV levels in the surfaces of the VUV levels in the surfaces of the metal and insulatormetal and insulator
Electrons are produced by the Electrons are produced by the photoelectric effect.photoelectric effect.
Separation
Metal
Insulator_
+
e_
E
E
Contact
Metal
Insulator
PurposePurpose
Extend the cavity QED induced photoelectric effect Extend the cavity QED induced photoelectric effect in the Two-step model of contact in the Two-step model of contact
electrification to flow electrification. electrification to flow electrification.
Theoretical Theoretical backgroundbackground
Piping system and laminar flow Piping system and laminar flow
QED cavities in hydraulic oilsQED cavities in hydraulic oils
Comparison of contact and flow Comparison of contact and flow electrificationelectrification
Available EM energyAvailable EM energy
Photoelectric effectPhotoelectric effect
Piping system Piping system Hydraulic fluid is pumped Hydraulic fluid is pumped
in laminar flow through in laminar flow through small diameter - long pipe small diameter - long pipe
Loop is closed as the fluid Loop is closed as the fluid falls into an open falls into an open receiving tank and receiving tank and pumped back to the pumped back to the supply plenum.supply plenum.
Air enters the fluid in Air enters the fluid in falling into receiving tank falling into receiving tank - usually through the - usually through the pump .pump .
Pump
Receiving tank
Pipe
Air Air
Laminar flow Laminar flow relationsrelations
2
2
12R
rVV MxVelocityVelocity
R
V
dr
dV M 4Frictional stressFrictional stress
Re483
2
2 R
x
R
xVPP Matmx
PressurePressure
8
4R
x
PPAVQ atmx
MPoiseuille Eqn.Poiseuille Eqn.
Pipe w all
VM2R
L
PS Patm
x
PxA B
Laminar flow and QED Laminar flow and QED Cavities Cavities
Light and electron Light and electron emission occurs over emission occurs over dimensions from dimensions from walls less than 100 walls less than 100 mm
Light emission Light emission precedes electron precedes electron emission - similar to emission - similar to photoelectric effectphotoelectric effect
Depth 1.5 mm
30 mm
Flow 10 mm
Microscope studies show Microscope studies show cavities form in laminar flocavities form in laminar flow near surface of boundariw near surface of boundarieses
Washio et al, Proc Washio et al, Proc Instn Mech Engrs, Instn Mech Engrs, 215 Part J, (2001) 215 Part J, (2001)
373373
QED cavities in hydraulic QED cavities in hydraulic oilsoils
Air clusters in flowing hydrocarbon Air clusters in flowing hydrocarbon liquidsliquids
Tearing of oil during flowTearing of oil during flow
Tearing and QED electrificationTearing and QED electrification
Source of EM energySource of EM energy
Air clusters in hydraulic oilAir clusters in hydraulic oil
Oil Vapor bubbles POil Vapor bubbles Pxx < P < Pvapvap
Air bubbles PAir bubbles Pxx < P < Pair air
Air bubbles likely as PAir bubbles likely as Pair air >> P>> Pvapvap
Air enters the system through the open tankAir enters the system through the open tank
Solubility of air in hydraulic oils is significant Solubility of air in hydraulic oils is significant [Ostwald coefficient ~ 10 [Ostwald coefficient ~ 10 by volume] by volume]
Large air bubbles not likely by surface tension Large air bubbles not likely by surface tension
Air dissolved throughout oil as nano- clusters of air Air dissolved throughout oil as nano- clusters of air ( N( N22 and O and O22 molecules ) molecules )
Tearing of oil during flowTearing of oil during flow
Maximum tension theory Maximum tension theory [ Joseph, J Fluid Mech 366 (1998) 367] [ Joseph, J Fluid Mech 366 (1998) 367]
Cavitation in laminar flow is explained as viscous Cavitation in laminar flow is explained as viscous shear stress produces tensile stress at 45° to wall shear stress produces tensile stress at 45° to wall
Tearing of oil occurs if nominal tensile stress is Tearing of oil occurs if nominal tensile stress is raised above the rupture stress of oil because of the raised above the rupture stress of oil because of the
stress concentration of air clusters stress concentration of air clusters
Tearing separates oil from itself or boundary wall Tearing separates oil from itself or boundary wall leaving an evacuated space with oil clusters leaving an evacuated space with oil clusters
Tearing and QED Tearing and QED electrificationelectrification
Tearing produces vacuum spaces Tearing produces vacuum spaces with oil clusters with oil clusters
Spaces are a high frequency QED Spaces are a high frequency QED cavities that briefly suppress low cavities that briefly suppress low frequency IR radiation from oil frequency IR radiation from oil clusters. clusters.
Suppressed IR energy loss is Suppressed IR energy loss is conserved by a gain to VUV levels conserved by a gain to VUV levels in adjacent oil and wall surfacesin adjacent oil and wall surfaces
Electrons are produced by the Electrons are produced by the photoelectric effect.photoelectric effect. 1D cavity
Oil cluster
FlowFlow
Source of EM Source of EM energyenergy
Oil molecule has thermal kT energyOil molecule has thermal kT energy
Molecules are harmonic oscillatorsMolecules are harmonic oscillators
At ambient temperature, thermal kT At ambient temperature, thermal kT energy is equivalent to the molecule energy is equivalent to the molecule
emitting IR radiationemitting IR radiation
Oscillator and IR radiationOscillator and IR radiation
At T ~ 300 K, kT~0.025 At T ~ 300 K, kT~0.025 eVeV
Saturation at Saturation at ~ 100 ~ 100 m m
Most of IR energy in oil Most of IR energy in oil molecule occurs:molecule occurs:
> 20 > 20 m m
If QED cavity confines IR If QED cavity confines IR radiation to radiation to < 20 < 20 m, m, most of thermal kT most of thermal kT energy is suppressed energy is suppressed
At T ~ 300 K, kT~0.025 At T ~ 300 K, kT~0.025 eVeV
Saturation at Saturation at ~ 100 ~ 100 m m
Most of IR energy in oil Most of IR energy in oil molecule occurs:molecule occurs:
> 20 > 20 m m
If QED cavity confines IR If QED cavity confines IR radiation to radiation to < 20 < 20 m, m, most of thermal kT most of thermal kT energy is suppressed energy is suppressed
0.00001
0.0001
0.001
0.01
0.1
1 10 100 1000
Wavelength - microns
Pla
nck
ener
gy E
T -
eV kT
1exp
Tkhc
hc
ET
Oil cluster formation Oil cluster formation
Hydrostatic compression - IR uninhibited Hydrostatic compression - IR uninhibited
Hydrostatic tension - IR inhibitedHydrostatic tension - IR inhibited
Surface tensionSurface tension S S limits the radius limits the radius RR of the of the oil cluster that can be formed, oil cluster that can be formed, RR > R> R00
Heptane Heptane RR00 ~ 0.4 ~ 0.4 m m
IR
2R0
STP
SR
20
2R
IR energy in oil clusterIR energy in oil cluster
Spherical cluster energySpherical cluster energy
303
4RU IR
Energy densityEnergy density
3/2
1 kTNdof
dofN ~ Degrees of freedom
k ~ Boltzmann’s constant
VUV energy emitted by VUV energy emitted by clustercluster
Cavity QED Cavity QED momentarily momentarily suppresses IR suppresses IR
radiation from clusterradiation from cluster
Conservation of Conservation of energy requires the energy requires the prompt release of IR prompt release of IR
radiationradiation
Multi-IR photons Multi-IR photons combine to VUV combine to VUV
levels levels kT
R
R
RE
0
2
0 Electrons and VIS Electrons and VIS photons producedphotons produced
E
E
Ree--
D
Wall
--
Oil cluster
FlowFlow Air cluster
+ VISPhoton
R0
Photoelectric effectPhotoelectric effect
0.001
0.01
0.1
1
10
100
0 1 2 3 4 5
Cluster radius - microns
Ele
ctro
nic
ch
arg
e -
nC
Y = 1
Y = 0.1
NNdof dof = 6= 6
EEVUVVUV = 4.9 = 4.9 eVeV
VUVdof
VUV
IRVUV E
kTRN
E
UN
3
0
3
2
Number of VUV Number of VUV photonsphotons
pVUVe NN
Number of electronsNumber of electrons
eVEVUVp 10,1
Electron YieldElectron Yield
Flow electrificationFlow electrification Oil clusters and Oil clusters and
fragments in contact with fragments in contact with wall separate at entrance wall separate at entrance
IR radiation is IR radiation is suppressed and released suppressed and released as VUV as VUV
Electrons are freed from Electrons are freed from oiloil
Wall is charged negative Wall is charged negative and oil positiveand oil positive
FragmentFragment
ClusterCluster
1-D Resonance 1-D Resonance ~ 2 D~ 2 D
Suppression of IRSuppression of IR
D < 10 D < 10 mm
DD
FlowFlow
WallWall
dd
-
e-++
EE
SummarSummaryy
Flow electrification occurs as oil ruptures in a tearing actionFlow electrification occurs as oil ruptures in a tearing action
Rupture takes place if the tensile stress at a point exceeds the Rupture takes place if the tensile stress at a point exceeds the pressure at which the air dissolved in oil, usually atmospheric pressure at which the air dissolved in oil, usually atmospheric
pressurepressure
Air clusters uniformly distributed throughout the Air clusters uniformly distributed throughout the volumevolume of the of the oil act as local stress concentrators for ruptureoil act as local stress concentrators for rupture
Electron charge Electron charge Number of oil clusters Number of oil clusters volume volume
Electrical current is proportional to volume flow rate [ Current Electrical current is proportional to volume flow rate [ Current = Charge density x volume flow rate] = Charge density x volume flow rate]
Current not proportional to surface area of the wall Current not proportional to surface area of the wall
Flow Flow AnalysisAnalysis Streaming currentStreaming current
II Re Re x -x - flow experiment flow experiment
I I AA( ( PPxx -- PPatmatm ) - electrical analogy ) - electrical analogy
NNeeQQ replaces the flow replaces the flow QQ NNee is the electron density is the electron density
Since Since NNee NNOC OC PPxx-1-1
NNcc PPxx-1-1
222
1
R
Qx
PR
QxN
R
xQNI
xOCe
23
2
8Re4
R
Qxx
RPPAI atmx
- Poiseiulle - Poiseiulle
Volumetric current Volumetric current density density
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 500 1000 1500 2000
Reynold's number Re
Cur
rent
den
sity
I
/ Q
x
104
C/m
3
0.24 mm
0.58 mm
1.25 mm
Re 43
2
2
Rx
P
Rx
Q
I
atm
Chen et al, Ind Eng Chen et al, Ind Eng Chem Res. 35 (1996) Chem Res. 35 (1996)
3195 3195
Total current Total current
0
0.5
1
1.5
2
2.5
3
3.5
0 500 1000 1500 2000
Reynold's number Re
Cu
rre
nt
I x
1011
A
0.24 mm
0.58 mm
1.25 mmRe4
Re
3
2
Rx
P
Rx
I
atm
ConclusionConclusions s
Flow and contact electrification obey the same physics - Flow and contact electrification obey the same physics - Inhibited IR to VUV by cavity QED Inhibited IR to VUV by cavity QED
QED cavity is an evacuated space containing oil clusters that QED cavity is an evacuated space containing oil clusters that briefly forms as the oil ruptures and tears under tensile stressbriefly forms as the oil ruptures and tears under tensile stress
Tearing is governed by the tensile stress given by the Tearing is governed by the tensile stress given by the maximum tension theory maximum tension theory
Cavity QED converts thermal kT energy to VUV Cavity QED converts thermal kT energy to VUV
The analytical The analytical II and and II / / QQ relations derived are reasonable relations derived are reasonable approximations of flow electrification data for a approximations of flow electrification data for a volume volume chargecharge relation. An area charge relation does not correlate relation. An area charge relation does not correlate with the data with the data