Bubbles and steam
electricity
T.V. Prevenslik
11F, Greenburg Court
Discovery Bay, Hong Kong
Abstract
In 1840, Lord Armstrong was the first to study the electrical charge
produced as steam escaped from boilers, the phenomenon called steam
electricity. In 1969, interest in steam electricity was renewed because
of explosions caused by the ignition of chemical vapors during the washing
of ship tanks with steam jets. Steam electricity is proposed explained
by the bubbles nucleated in the boiling of water droplets, the bubbles
behaving like resonant quantum electrodynamic (QED) cavities. During
bubble growth as the bubble cavity resonance coincides with vacuum ultraviolet
frequencies, the water molecules on the bubble walls dissociate by cavity
QED into hydronium H3O+ and hydroxyl OH- ions. After recombination,
only about 20% of the ions are available for electrification, the ions
called available ions to be distinguished from the hydronium and hydroxyl
ions in the bubble walls described by the pH and pOH of water, called
background ions. Boiler water having an acid pH is the result of acid-base
equilibrium between dissolved carbon dioxide and carbonic acid, the
concentration of background hydronium ions controlled by the buffering
action by carbonate and bicarbonate ions. The chemistry may be described
by the pH of the boiler water, and if acidic the bubble surface is charged
positive by the abundance of background hydronium ions. Available hydronium
ions are repulsed from the positive charged bubble surface and tend
to the center of the bubble forming a positive charged vapor; whereas,
the available hydroxyl ions are attracted to the bubble surface. Bursting
of the bubbles at the surface of the droplet produces positive charge
steam and negative charged droplets. Conversely, bubbles in boiling
water having a basic pH produce a negative charged vapor and positive
charged liquid droplets.
Keywords: bubbles, steam electricity, Leidenfrost,
lightning, atmospheric electricity
1. Introduction
In the 1840's, steam boilers were commonplace in England.
At Seghill, Newcastle on Tyne, steam happened to leak through a cement
seal around the safety valve on a boiler. When a workman placed his
hand in the steam while his other hand was on the lever of the valve,
a spark discharge occurred and the workman received a electrical shock,
the so called Seghill incident gaining much publicity. Lord William
G. Armstrong [1] in a letter to Faraday reported the phenomenon of steam
electricity. Faraday responded to Armstrong by letter [1] stating he
investigated the Seghill incident and using an electrometer found the
steam to be positive charged. Faraday determined the mine water used
in the boiler was acidic because of the sulfate of lime deposit found
on the inside surfaces of the boiler. But the steam was found not charged
at another boiler using rainwater. Faraday at that time thought the
steam electricity was caused by the nature of the water from which the
steam was produced.
The Sedghill incident reported by Armstrong and Faraday was confirmed
[2] by Pattinson. The review by Schafhaeutl [2] suggested the source
of steam electricity was connected with the deposits on the boilerplates.
Based on Faraday's suggestion that the nature of the water was somehow
connected to the steam electricity, Armstrong [3] tested other boilers
using the same mine water and found the same results. Shortly thereafter,
Pattinson [4] found the length of sparks from the discharge of electrified
steam to be proportional to boiler gage pressure.
In 1843, the notion of contact electrification by frictional charging
was introduced to explain steam electricity. Armstrong [5] was of the
belief that the source of electricity takes place at the point where
the steam was subjected to friction but had great difficulty with the
supposition that friction was the exclusive cause of the electricity.
Faraday [6] was satisfied that steam electricity was not due to evaporation,
or condensation, or a change of state based on the observation that
the charge of the steam could be changed by changing the material of
the nozzle while the evaporation remained the same. About this time,
Faraday changed his belief that the source of steam electricity was
the nature of the water in favor of contact electrification - the contact
electrification produced as particles of liquid water carried by the
steam rub against the solid walls of the nozzle.
Faraday confirmed Armstrong's findings [6] that steam alone produced
no electricity, but liquid water distilled from the boiler and added
to the steam produced positive charged steam and a negative charged
boiler. Positive charged steam ceased by adding small amounts of alkali
to the distilled water. Replacing the distilled water with common London
waters removed the steam charge. Ammonia added to distilled water produced
charged steam, the steam able to redden turmeric paper, but the charge
ceased after adding small amounts of sulfuric acid. Except for the latter,
pH measurements of the steam were not reported in the Faraday experiments.
Negative charged steam was found by adding olive oil, and oils of laurel
and turpentine to the distilled liquid water, but the charged steam
ceased when the oils alone were present without the distilled water.
If an alkali was added to the distilled water having olive oil, the
steam lost charge, but not if added to distilled water having the oil
of turpentine. Positive charged steam was found if sulfuric and camphor
powder were added to distilled water. Faraday interpreted the pure distilled
water droplets, the water globules coated with olive oil and oils of
laurel and turpentine, and the powders of sulfuric and camphor as the
rubbing agent and the nozzle as the rubbed surface, the sign of the
steam charge sign depending on the tribo-electric series.
Faraday's hypothesis is tenable for oils and powders that are physically
different from globules of water and suggest different frictional levels
and attendant tribo-electrical charging. But small amounts of acids
and alkalis soluble in water could not be expected to alter the contact
potential from that of distilled water and produce different tribo-electrical
charging. Contrarily, acids and alkalis were found to indeed alter the
steam electrification, a finding supportive of Armstrong's contention
that friction was not the exclusive cause of the steam electrification.
Faraday sought to eliminate steam altogether by working with compressed
air. A container was pressurized with air from a syringe, the container
providing a means to remove condensed moisture air before opening a
valve to send the air against different materials. However, the procedure
required extreme care to avoid oil contamination from the syringe. Both
dry and common air were tested, the dry air obtained by leaving the
compressed air in the container in contact with potassa fusa, a strong
alkali for 10 - 15 minutes. Common air having moisture condensation
was found to produce positive charge similar to steam; whereas, dry
air failed to be electrified. Contrary to the contact electrification
hypothesis, sulphur and silica powders in the compressed air experiments
rubbing against wood and metal nozzles were found charged in opposition
to their tribo-electrical order. Faraday expressed disappointment in
not being able to explain why the tribo-electrical order was not found
in the compressed air experiments
2. Scope, mechanisms, and purpose
2.1 Scope
In 1969, three large crude carriers were sunk or severely
damaged by explosions that were thought to be caused by sparks from
charge mist produced while their tanks were being washed with jets of
hot and cold liquid water or steam (see e.g. Jones and Bond, [7] ).
Since Armstrong [1], steam has been known to be electrified, but because
of the explosions during ship washing, wet steam was reaffirmed
(see e.g. Finke [8] ) as a source of highly charged mists. Hot and cold
liquid water jets also produce an electrified mist, but compared to
wet steam do not pose a sparking hazard. On this basis, the scope of
this paper is limited to electrification by wet steam.
2.2 Mechanisms
The interest of this paper is the mechanism by which the
charge is produced in steam electrification, more commonly called spray
charging. In 1972, Moore [9] discussed the prominent spray charging
theories of Lenard [10] and Natanson [11].
In 1892, Lenard proposed the double layer theory as the explanation
of waterfall electricity. The double layer is formed as the dipoles
of water molecules orient on the surface of bubbles with the negative
end pointing outward and the positive ends pointing inward. The positive
inward dipole ends attracting negative ions in the liquid. If the water
breaks up into a spray, the double layer and the attached negative ions
form particles in the fine spray are likely to carry a negative charge,
the positive charge remaining with the larger particles. In this way,
Lenard explained how negative charged vapor was found away from a waterfall
and a positive charge vapor remaining in liquid water particles near
the splash.
In 1950, Natanson proposed the theory of ion fluctuations to explain
spray charging. The liquid was considered to be composed of a large
number of positive and negative charges. Breakup of the liquid into
drops was assumed to produce drops having an excess of positive or negative
charge that form in the volume of the drop because of ion fluctuations.
In effect, Natanson related droplet charge to the ion density in the
liquid. But the ions of interest were the cations and anions of soluble
salts and not hydronium and hydroxyl ions. Small concentrations of salts
in distilled water were found to increase the symmetrical ionization
and decrease net charge; whereas, larger concentrations were required
to reverse the sign of the net charge. In the ion fluctuation theory,
charge separation is statistical and does not require any cause-effect
charge separation mechanism.
Both double layer and ion fluctuation spray charging theories provide
plausible explanations of how water dipoles and ionic charges in the
liquid are related to spray formation, but conservation of charge and
mechanisms by which charge is separated during spray formation are not
identified. Consistent with this view, Moore [9] makes the point that
charges transferred from the liquid are to be conserved with the charges
leaving with the spray. Neither double layer or ion fluctuation theory
explicitly conserve the charge lost in the liquid with charge gained
by the spray.
Loeb [12] discusses static electrification by electrolytic processes
whereby small quantities of acids and bases may drastically change the
pH of the water and the concentration of hydronium and hydroxyl ions,
but pH as a parameter is absent both double layer and ion fluctuation
theories. Consistent with Armstrong, the opinion here is that electrolytic
processes underlying the nature of the water in steam electricity are
important in spray charging.
2.3 Purpose
The purpose of this paper is to propose a theory for wet
steam electrification based on the dissociation of water molecules in
bubbles nucleated in water droplets by boiling.
3. Theory
In the steam electricity phenomenon, the boiling of water
droplets produces pressurized steam in the boiler as shown in Fig. 1.
Steam leaves the boiler through the nozzle, the liquid water droplets
breaking up as the jet exhausts the nozzle into the lower pressure surroundings.
Bubbles are nucleated in the liquid droplets by boiling, but bubbles
cannot be nucleated in a pure steam vapor. Hence, steam without liquid
fraction can not be electrified by the present theory.
Water molecules on the bubble walls are proposed to dissociate into
hydronium and hydroxyl ions by cavity QED as the resonant frequency
of the bubble coincides with the dissociation frequency of the water
molecule. After recombination, only about 20% of the ions are available
for electrification, called available ions, in order to be distinguished
from the hydronium and hydroxyl ions present in the boiler water, called
background ions. The ionization of water is,
(1)
(2)
(3)
The kinetics of carbonic acid formation from carbon dioxide
is relatively slow, on the order of seconds. Subsequent buffering action
is fast, but nonetheless limited by the formation of carbon dioxide.
Excess hydronium ions are converted to carbon dioxide through carbonic
acid by buffering with carbonate 
and
bicarbonate
ions.
(4)
In general, the boiler water may contain limestone, or
calcium carbonate 
as found
by Faraday [1]. Carbon dioxide dissolves limestone to form calcium and
bicarbonate ions, the calcium carbonate competing with the formation
of carbonic acid. Moreover, small amounts of NaCl in the boiler water
can combine with the hydroxyl ions to form sodium hydroxide NaOH, a
strong base. To avoid complicated acid-base chemistry, the charge separation
mechanism is simplified in terms of the pH of the boiler water as shown
in Fig. 2.
Charge separation in acidic boiler water having pH < 7 presumes the
available ions created on the bubble surface by cavity QED having already
undergone recombination do not undergo further recombination with background
ions. However, the hydronium and hydroxyl ions are not in equilibrium,
(5)
To satisfy Eqn. 5, the background 
ions
may be reduced to compensate for the available 
and
ions by buffering with
bicarbonate ions to produce carbon dioxide. But the carbon dioxide formation
time is long compared to the time for a bubble after nucleation to burst
at the droplet surface. Hence, local equilibrium of hydronium
and hydroxyl ions cannot be satisfied in the liquid phase, and therefore
to satisfy equilibrium both 
and
ions already on the bubble
surface move to the vapor phase of the bubble. Since acid pH carries
an abundance of background hydronium ions compared to hydroxyl ions,
the local bubble surface is charged positive. Available ions
separate in the vapor phase; the 
ions
are repulsed from the bubble surface and move to the center of the bubble,
while theions are attracted
and attach to the bubble surface. Thus, bubble bursting at the droplet
surface carries positive charge steam of hydronium
ions leaving behind the droplet charged negative with hydroxyl ions.
Chemistry for basic boiler water having pH > 7 again presumes the
available ions already having undergone recombination do not recombine
further with background ions. But to satisfy equilibrium in the liquid
state, 
ions still have
to be reduced to accommodate the available and
ions. Basic pH differs
from acid pH only by buffering with carbonate instead of bicarbonate
ions, but the formation time of carbon dioxide is still long compared
to the time for a bubble to burst in droplets. Local equilibrium on
the bubble surface is satisfied only by both availableand
ions moving to the vapor
phase of the bubble. Since basic pH carries an abundance of background
hydroxyl ions compared to hydronium ions, the bubble surface is charged
negative. Available ions separate in the vapor phase; the ions
are attracted and attach to the bubble surface, while the
ions are repulsed from the bubble surface and move to the center of
the bubble. Thus, bubble burst at the droplet surface carries a negative
charge steam of hydroxyl ions
leaving behind positive charged droplets of hydronium ions.
The average charge carried by the steam in the bubbles depends on the
charge of the bubble wall given by the background concentrations of
hydronium and hydroxyl ions in the droplet. The probability 
of
the bubble wall being positive or negative is,
and 
(6)
A normal statistical distribution of charged particles
about the mean or net charge is suggested based on data on the distribution
of charged droplets by Pounder [13,14].
3.1 Background
Steam electrification caused by the separation of hydronium
and hydroxyl ions in bubbles is common to many historical applications
in atmospheric electricity including lightning and thundercloud electrification,
and the Leidenfrost phenomenon.
Lightning based on thundercloud electrification [15] may be described
by the hydronium and hydroxyl ions produced from the dissociation of
the water molecules as moisture carried to high altitudes condenses
and supercools to form graupel, a liquid-ice mixture. Bubbles nucleate
in the supercooled water because of the large volume expansion that
accompanies freezing. Initial freezing of the graupel skin places the
graupel interior into compression, the compression tending to force
the bubble vapors through the skin into the surroundings. Charge separation
occurs within the bubbles as water molecules on the bubble walls dissociate
by cavity QED into hydronium and hydroxyl ions as shown for steam electrification.
Typically, the moisture in the updraft has an acid pH, and therefore
the liquid wall of the bubbles in the graupel carries a positive charge
because of the abundance of hydronium ions in the moisture. The available
hydronium ions leave the graupel as positive charged vapor, the companion
hydroxyl ions remaining to give the graupel a negative charge. Ice crystal
particles are formed by the vapor deposition of hydronium ions from
the bubble, the clouds of particles forming positive charged ice crystal
clouds. Cloud-to-cloud lightning in the upper atmosphere occurs between
graupel and ice crystal clouds, while cloud-to-ground lightning takes
place as graupel clouds that escaped discharge as cloud-to-cloud lightning
fall to the lower atmosphere and discharge with the positive charge
earth's surface.
The Leidenfrost phenomenon [16] describes the electrification of a drop
of boiling water supported from a hot surface by a film of its own vapor
and is quite similar to that of steam electrification. The temperature
of the hot surface is above 400 °C and heats the underside of the
drop to the 100 °C boiling point of water. After cavity QED dissociation
of water molecules, the available ions are separated in the bubble as
for steam electrification. If the drop has an acid pH, bubbles nucleated
in boiling leave the drop from its underside as a positive charged steam
of hydronium ions, the drop charged negative by hydroxyl ions. Conversely,
if the pH of the drop is basic, the steam vapor is charged negative
and the drop positive.
3.2 Sonoluminescence and the dissociation of water
molecules
How steam electrification is related to the dissociation
of the water molecule in bubbles finds basis in the phenomenon of sonoluminescence
(SL). SL was first observed [17] by Frenzel and Schultz in 1934 and
is usually described as the production of visible light during the cavitation
of water, but is also known [18] to produce hydroxyl ions. Many SL theories
have been proposed [19].
The Planck theory of SL [20] differs from other SL theories because
the source for producing SL photons is the Planck energy of the stimulated
emission from the bubble wall molecules as the bubble resonant frequency
during bubble collapse coincides with the dissociation frequency of
the water molecules. The bubble resonant frequency continuously increases
during bubble collapse, the significance of which is that the discrete
dissociation frequencies of the water molecule can always stimulated,
i.e., the bubble acts as a continuously variable vacuum ultraviolet
to soft X-ray laser. The Planck energy E is,
(7)
where, h is Planck's constant,
is
the bubble resonant frequency, c is the speed of light, and 
is
the wavelength of the bubble resonance. In a spherical bubble of radius
R, the bubble resonance may be considered as a wave of wavelength
and frequency 
, where
c is the velocity of light.
Liquid water is highly absorptive over the frequency range from the
vacuum ultraviolet to soft X-rays. Provided the bubble geometry collapses
to dimensions corresponding to this frequency range, QED resonance always
produces hydronium and hydroxyl ions. The bubbles at the time the water
molecules dissociate are not visible because vacuum ultraviolet frequencies
have wavelengths less than 160 nm, the corresponding bubble radius less
than 40 nm.
Charge separation is not of importance in bubble collapse because the
bubble wall collide. Excited OH* hydroxyl radicals are also produced,
the excited radicals combining with Ar atoms in the air dissolved in
the water bubble walls under the high stagnation pressures developed
as the bubble walls collide. The high pressures produce Ar*OH excimers,
the visible photons produced as the excimers decompose in the pressure
relief of the rarefaction shock.
Of interest here is the dissociation of the water molecule during bubble
nucleation and growth, rather than visible photons during bubble collapse.
Nucleation is collapse in reverse. Bubbles are nucleated at dimensions
on the order of the spacing between water molecules, the bubble dimensions
corresponding to soft X-ray frequencies, the water molecules dissociating
as the bubble grows to dimensions corresponding to frequencies in the
vacuum ultraviolet. SL photons are not produced as bubbles nucleate
and grow because the bubble walls do not collide to form the Ar*OH excimers,
but water molecules dissociate in both bubble growth and collapse.
The Planck theory of SL based on the emission produced as the bubble
resonance coincides with the dissociation frequency of the bubble wall
water molecules is consistent with the zero-point energy field. An arbitrary
cavity may be considered to contain zero point energy having field modes
with frequencies quantized by its dimensions, the lowest of which is
the bubble resonant frequency of cavity QED. Zero point energy considers
the cavity to contain a continuum of frequencies greater than resonance
that has been interpreted to imply a cavity contains an infinite source
of Planck energy. In this regard, the Planck theory of SL differs in
that only cavity field modes having frequencies greater than resonance
and which are contained in the absorption ( and emission ) spectrum
of the cavity wall are allowable, thereby limiting the Planck energy
in the cavity to be finite.
In the Planck theory of SL, the emission is not in equilibrium with
the temperature of the bubble wall. Stimulation of bubble wall water
molecules at vacuum ultraviolet frequencies may be considered caused
by zero point energy even though the bubble wall is at ambient temperature.
This means zero point energy 
is
always available to stimulate any bubble wall water molecule providing
the absorption ( and emission ) spectrum exists at that frequency. For
a Planckian photon produced by a pair of diametrically opposite bubble
wall molecules in resonance with the bubble cavity, the Planck energy
is the sum of the zero
point energy of the respective water molecules. Hence, the Planck theory
of SL is consistent with the general form of Planck's blackbody spectrum
in which the spectrum density
includes the zero point energy,
(8)
where, k is Boltzmann's constant, and T
is absolute temperature.
The general form of Planck's blackbody spectrum is consistent with that
of random electrodynamics proposed [21] by Boyer in 1969. However, both
Planck and Boyer formulations differ [22] from that by Einstein who
excluded the zero point energy. In this regard, Planck [23] commented
that the zero point energy provided an explanation of atomic vibrations
that are independent of temperature, e.g., electrons liberated by the
photoelectric effect that are independent of the temperature of the
metal and the intensity of the exciting radiation. This is consistent
with the Planck theory of SL that asserts the water molecules dissociate
on the bubble walls at ambient temperature by cavity QED resonance in
the same way they would dissociate if irradiated by an external laser.
In contrast, the Einstein formulation [22] of black body radiation would
require for the dissociation of the water molecules at a Planck energy
in the vacuum ultraviolet, say 10 eV, to have an unrealistic temperature
of about 100,000 K.
The Planck theory of SL was formulated to explain the SL in collapsing
bubbles, but is consistent with the dissociation of water molecules
during the nucleation of bubbles as applied to waterfall electricity
in the Lenard effect. Indeed, Prevenslik [24] reported a maximum of
about
water molecules
dissociate in every bubble nucleated in a waterfall splash, the number
consistent with the number of SL photons from a collapsing air bubble
in water, called the standard unit of SL, the number determined [25]
experimentally. A maximum 80 % recombination leaves from 
hydronium
and hydroxyl ions in each bubble for electrification.
4. Discussion
4.1 Historical review
Lenard's explanation [10] of negative charged vapor away
from waterfalls and a positive charge remaining in the splash is consistent
with the proposed theory for water having a basic pH common to limestone
riverbeds in mountains, 
.
Faraday's investigation of the Seghill incident [1] showing the steam
to be charged positive is consistent with an acid pH common to mine
water and the sulfate of lime residue found in the boiler, .
Rainwater dissolves carbon dioxide from the air and produces carbonic
acid having a pH ~ 5.8, but in a boiler the carbon dioxide is removed
to produce a neutral pH ~ 7. Hence the report the boiler using rainwater
did not produce charge is consistent with water having balanced positive
and negative charge, or a net neutral charge, .
Faraday's finding [6] that positive charged steam ceased by adding small
amounts of alkali to the distilled water may be explained by the distilled
water already acidic by dissolved carbon dioxide, being neutralized
by the alkali, . Loss
of positive charge found by replacing the distilled water with common
London waters is a similar in that dissolved carbon dioxide in the alkaline
water from River Thames is known to produce neutral pH. The reddening
of turmeric paper, today known as curcumin, in negative charged steam
produced by adding ammonia to distilled water means the boiler water
was basic having a pH > 8.6, .
After adding small amounts of sulfuric acid, the steam charge was reduced
to neutrality, .
With regard to contact friction, the opinion here is consistent with
that of Armstrong who had difficulty with the supposition that contact
friction was the exclusive cause of steam electrification. In 1840,
the nature of the water was thought to be the cause of electrification,
the nature of the water known today by electrolytic processes. Later
in 1843, Faraday instead proposed contact friction to explain steam
electrification. But Faraday's inability to explain the compressed air
experiments by contact charging only underscores the importance of electrolytic
processes.
Lack of pH measurements of the steam makes it difficult to fully compare
Faraday's results with the present theory that is based on pH. Certainly,
the contact friction hypothesis is tenable for oils and powders that
are physically different from globules of water, but Faraday's experiments
show contact friction may be overwhelmed by electrolytic processes requiring
small quantities of acids and alkalis, or the oils and powders themselves.
4.2 Spray electrification and charge conservation
Spray electrification as explained by the double layer
[10] and ion fluctuation [11] theories lacks explicit conservation of
charge between liquid and vapor. In contrast, the proposed theory requires
changes in the concentration of hydronium and hydroxyl ions obey ionic
equilibrium as spray leaving the liquid is electrified.
In spray charging, a continuous supply of water is available so that
the loss of capacity to produce charge is not noticed. But to illustrate
the importance of charge conservation, consider the spray charge produced
as bubbles are continuously being nucleated in a flask of boiling water
and burst at the liquid surface. Unlike the jet, the volume of water
in the flask is finite. Assume the water is distilled and has been boiled
to remove dissolved carbon dioxide and carbonic acid leaving a neutral
pH. Because of the orientation of water molecules on the bubble surface,
the bubble vapor in the double layer theory carries away negative ions
to the surroundings leaving the liquid with an excess of positive charge
and eventually producing an acidic water solution. In the distilled
water, ion fluctuations of dissolved salts are insignificant so as to
negate the applicability of the ion fluctuation theory altogether. Neither
theory answers the question how boiling is related to subsequent loss
of charge to the surroundings.
In contrast, the proposed theory does not produce an acid or a base,
but always produces water of neutral pH. Boiling of pure distilled water
instantly produces a neutral steam, but if the neutrality is perturbed
to be acidic by some reason, the bubble spray is first charged positive
by hydronium ions, the hydroxyl ions increasing the pH of the water.
Boiling next produces a negative charged spray leaving the water with
a reduced pH. Upon continued boiling, the pH converges to neutrality.
4.3 Steam electrification
In 1840, Pattinson [4] found the length 
of
the spark discharge from steam electrification to be proportional to
the pressure P of the steam, 
.
In the proposed theory, the steam is electrified as bubbles nucleate
in boiling drops, every bubble producing at least 
hydronium
and hydroxyl ions to electrify the steam. Hence, it may be argued that
the spark length is proportional
to the number N of bubbles nucleated in the droplets, 
.
The number N of bubbles is not known, but should vary inversely
with the heat of vaporization 
,
where 
and 
are
the enthalpy of the vapor and the fluid. The inverse relation is expected
because for the same amount of heat supplied to the boiler, a lower
heat of vaporization enables more bubbles to be nucleated to electrify
the steam, 
. Hence, 
.
Indeed, the liquid-vapor phase region of water is characterized by the
lowering of the heat of vaporization 
as
the pressure P is raised. Fig. 3 shows Pattinson's spark length
data to be proportional
to 
confirming the proportionality
of electrification by the number of bubbles produced in boiling.
In 1989, Finke [8] repeated the Faraday experiment [6] on steam electricity.
Like Faraday, Finke measured the current 
from
the nozzle to ground. Similar to the length of
spark, the current is expected
to vary inversely with the heat of vaporization, i.e., 
.
But Finke's data ( Fig. 2 of Ref. [8] ) shows sporadic charge reversals
at the nozzle. Fig. 3 shows the current that
excludes the sporadic charge reversal to be consistent with the number
of bubbles carrying charge. The charge reversals observed at the nozzle
were likely caused by chemical contamination, as there is no reason
to believe steam electrification would be sporadic.
5. Conclusion
Steam electrification is proposed to find origin in the
nucleation of bubbles in boiling, the electrification occurring as water
molecules on the bubble walls dissociate by cavity QED into hydronium
and hydroxyl ions. Separation of ionic charges takes place by the repulsion
and attraction to the bubble wall, the wall charge depending on the
pH of the boiling water.
The present theory for steam electrification may also be applied to
electrified mist from hot and cold liquid jets. Before liquid water
breaks up into spray droplets, bubbles nucleate in the liquid by the
rapid decompression in leaving the nozzle. But the number of bubbles
would be small compared to the far greater number if the water were
to boil. Hence, the mist from hot and cold liquid jets is electrified,
but far less than for wet steam.
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Fig. 1. Steam electricity - pH < 7
Fig. 2. Charge separation
Fig. 3 Steam electricity
Inverse proportionality of spark length and ground current to heat of
vaporization
