Method and device for enhancing a process involving a solid object and
a gas
FIELD OF THE INVENTION
The invention relates to a sonic device for enhancing a process involving a
solid object and a gas by reducing a laminar sub-layer. The invention further
relates to a method of enhancing a process involving a solid object and a gas
by reducing a laminar sub-layer.
BACKGROUND OF THE INVENTION
No heat flow is possible without temperature difference. Thus, the heat flux
between air/a gas and a surface of an object will be in direct proportion with
the temperature difference between the gas and the surface and with the
surface conductance, i.e.
where J denotes the heat flux, h the surface conductance, ts the temperature
of the surface and ta the temperature of the surrounding gas. Surface
conductance is measured in W/m2K.
Heat energy tends to migrate in the direction of decreasing temperature. The
heat transfer can take place by the processes of conduction, convection or
radiation. Heat is the energy associated with the perpetual movement of the
molecules and temperature is a measure of the vigor of this movement.
When materials at different temperatures are in contact the more vigorous
molecules transfer some of their thermal energy to less vigorous ones by
collisions. This is the process of heat conduction. It is the only way in which
heat can flow through an opaque solid.
Thermal energy can be transported through a gas by conduction and also by
the movement of the gas from one region to another. This process of heat
transfer associated with gas movement is called convection. When the gas
motion is caused only by buoyancy forces set up by temperature differences,
then the process is referred to as natural or free convection; but if the gas
motion is caused by some other mechanism, such as a fan or the like, it is
called forced convection.
For nearly all practically occurring gas flows, the flow regime will be turbulent
in the entirety of the streaming volume, except for a layer covering all
surfaces wherein the flow regime is laminar (see e.g. 203 in Figure 2a). This
layer is often called the laminar sub-layer. The thickness of this layer is a
decreasing function of the Reynolds number of the flow, so that at high flow
velocities, the thickness of the laminar sub-layer will decrease.
Heat transport across the laminar sub-layer will be by conduction or radiation,
due to the nature of laminar flow.
Concerning radiation all physical objects continuously lose energy by
emission of electromagnetic radiation and gain energy by absorbing some of
the radiation from other objects that is incident on them. This process of heat
transfer by radiation can take place without the presence of any material in
the space between the radiating objects.
Concerning conduction the mass transport across the laminar sub-layer will
be solely by diffusion. In the technology relating to heat exchangers, it is well
known that the principal impediment to the transfer or transmission of heat
from a gas to a solid surface is the boundary layer of the gas, which adheres
to the solid surface. Even when the motion of the gas is fully turbulent, there
exists a laminar sub-layer that obstructs the transmission of heat. While
various methods and types of apparatus have been suggested for
overcoming the problem such as by means of driving the gas with sonic
waves and vibrating the partition with external vibration generators, these
methods while being effective to some extend, are inherently limited in their
ability to generate an effective minimization of the laminar sub-layer and at
the same time covering an area large enough to make the method efficient
Likewise, the speed of a catalytic process involving a gas reacting with a
catalytic surface is, among many things, limited by the interaction between
the gas molecules and the catalytic surface, i.e. by the supply of reactants to
and the transport of reaction products away from the catalytic surface. The
mass transport through the laminar sub-layer covering the catalytic surface
can therefore only be done by diffusion of the reactants and reaction
products.
Similarly, when one kind of gas or mixture of gases is actively changed to
another composition of gases the time needed to flush the inner surface of
the container is limited to the time it takes to change the gases in the laminar
sub-layer. This change can only be done by diffusion.
Patent specification US 4.501.319 relates to increased heat transfer between
two fluids (i.e. not between an object and gas/air) and provides the increased
heat transfer by minimizing the thickness of the laminar sub-layer by
establishing a standing wave pattern. However, the use of a standing wave
pattern to minimize the laminar sub-layer does not give as very efficient or
large reduction of the laminar sub-layer (and thereby increase in heat
transfer), since the definition of a standing wave pattern includes a stationary
and repeatable location of nodes over the surface. At these nodes there will
be no displacement or velocity of the gas molecules.
Patent specification US 4,835,958 describes a process for producing work
onto rotatable blades of a gas turbine. The described process involves steam
as cooling media and a disruption of laminar steam film on the surfaces of a
nozzle thereby ensuring increased heat transfer. This is done by establishing
a sonic shock wave to disrupt the laminar sub-layer. Since the surface area
covered by the Shockwave has to be compared to the surface area used to
generate the shock wave, the proposed method does not give a reduction of
the laminar sub-layer (and thereby increase in heat transfer) over as large an
area as the present invention do, since ultrasound disperses over a larger
part of the object in question than the shock wave.
Patent specification US 6,629,412 relates to a turbine generator producing
both heat and electricity. The description includes a heat exchanger which
uses acoustical resonators (formed by cavities in the surface of the heat
exchanger) to prevent formation of a laminar boundary layer. The resonators
generate acoustic vortices as the gas flows over the surface of the heat
exchanger and thereby creating turbulence in the gas over the surface. The
generated turbulence will decrease the size of the laminar layer (see figure
2a) but the generated acoustic energy is not sufficiently high and therefore
not sufficiently efficient at minimizing the sub-layer.
Patent specification JP 07112119 relates to enhancing a catalytic process by
applying ultrasound and thereby disturbing a fluid border film over the porous
solid catalyst. The arrangement gives an inefficient coupling of the ultrasound
from a source/oscillator via the diaphragm and thereafter to the gas. This is
related to the large difference in acoustical impedance, which will apply for
any solid - gas transition.
Patent specification US 4,347,983 relates to a device for generating ultrasound.
It discloses that ultrasound may be useful for enhancing a heat transfer
by disruption of a liquid or gas layer. It is further mentioned that catalytic
effects can be improved due to molecular breakdown, production of free ions,
mixing and other effects. However, this arrangement does not address the
disruption of a laminar sub-layer. Further, this arrangement is not very suitable
for generating an acoustic pressure at sufficiently high levels needed for
effectively disrupting a laminar sub-layer. In addition the causes for improvement
of catalytic effects, i.e. molecular breakdown and production of free
ions, are effects that only take place under these circumstances in a liquid
medium and not in a gaseous medium.
Patent specification JP 2000 325903 discloses a method for removing dirt
from a fiber by spraying an ultrasonic gas flow where the boundary layer of
the gas generated around the optical fibers is broken by the ultrasonic waves
so that soil in the boundary layer can be removed. Creating such a turbulent
layer using ultrasound will have an enhancing effect for removing dirt. However,
it does not disclose a very efficient way of reducing the disadvantages
of the boundary layer if used for other processes as a sound intensity sufficient
to remove or eliminate the laminar sub-layer is not given.
Patent specification JP 07031974 discloses an adsorption method for ion in
water using an ion exchange resin in which water flows. An ultrasonic wave
generating device irradiates the water and the ion exchange resin so the
boundary layer of flow is broken and diffusion action is accelerated.
The boundary layer discussed in this application is not a laminar sub-layer.
Only the use of water is disclosed. Sound pressures in water and gas are not
directly comparable. The acoustic pressure in gaseous and not too viscous
flow media is the product of the mass density, the speed of sound, and the
vibrational speed of molecules (atoms). The speed of sound in water, for example,
is about 4 times higher than the one in the air, and the density of water
is approximately 3 orders of magnitude larger than that in the air. Therefore,
even the same speed of vibration of particles results in 3000-5000 times
higher amplitudes of the acoustic pressure in water than in gas. This very
large quantitative difference leads to a set of qualitative differences between
the processes of acoustic waves generation and propagation in gases and
liquids. Therefore, a simple replacement of the water with gas would involve
a dramatic decrease in efficiency and the solution of this disclosure is therefore
not suitable for enhancing a process involving a solid surface and a gas
surrounding.
Patent specification US 6,360,763 discloses a device and process wherein a
boundary layer of air on a solid surface is separated by use of an acoustic jet.
The disclosed boundary layer is not a laminar sub-layer. Furthermore, the
acoustic jet is driven by a plurality of frequencies where one or more of which
are sub-harmonics of them and having different phases and a loudspeaker is
used to obtain an oscillatory, zero-mass flux fluid flow into and out of the
main flow driven by wires by a signal. The forcing signal applied to the loudspeaker
has a frequency of 60 Hz. Generally, a use of an electro-acoustic
transducer as a gas pressure oscillation generator (i.e. the loudspeaker) and
other examples of gas pressure oscillation generators such as piezo flaps,
solenoid valves is given.
Such gas pressure oscillation generators work by vibrating, using sound, a
solid being in contact with a gas and thus transfers the vibrations to the gas.
Due to the tremendous difference in acoustic impedance for a solid and a
gas (the ratio of impedances is about 30000 to 50000 times), the most of
generated acoustic energy is reflected back into the solid at the solid-gas
interface, so that it is not possible in this way to generate sound or ultrasound
in the gas with an intensity that would be sufficiently high to remove or reduce
the laminar sub-layer. For example, 99.9895% of the total acoustic energy
is reflected back into the solid on the aluminum/air interface. For an
acoustic wave to overcome this solid/gas barrier and still having conserved a
140 dB (46 W/m2) intensity level it should have an initial intensity of about
440000 W/m2.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a device (and corresponding
method) for reducing a laminar sub-layer that solves (among other things) the
above-mentioned shortcomings of prior art.
Since diffusion is a slow process it is very useful to decrease the thickness of
the laminar sub-layer as much as possible in order to increase the efficiency
of any heat or mass transport, i.e. also for a catalytic process or change of
gases near a solid surface.
More specifically, it is an object to minimize the limitation of the above described
laminar sub-layer and the associated diffusion process(es).
It is a further object to provide an effective minimization of the laminar sublayer
in such a way that larger surface areas can be covered efficiently.
It is an additional object of the present invention to provide a practical implementation
by which the minimizing of the laminar sub-layer will significantly
increase the efficiency of heat transfer.
It is an additional object of the present invention to provide a practical implementation
by which the minimizing of the laminar sub-layer will significantly
increase the efficiency of a catalytic process where the catalyst has a solid
surface and the reactants are gases.
It is a further object of the present invention to provide a practical implementation
by which the minimizing of the laminar sub-layer will significantly increase
the efficiency of flushing a volume to change the composition of
gases.
These objects, among others, are achieved by a sonic device (and corresponding
method) for enhancing a process involving a solid object and a gas,
where the gas surrounds the object or at least is in contact with a surface of
the object, the device comprising sonic means for applying a high intensity
sound or ultrasound to at least the surface of the object, wherein the high
intensity sound or ultrasound, during.use of the sonic device, is applied directly
in the gas that is also the medium through which the high intensity
sound or ultrasound propagates to the surface of the object, whereby a laminar
sub-layer at the surface of the object is reduced and/or minimized, where
the high intensity sound or ultrasound has an intensity that is 140 dB or larger.
In this way, minimization or reduction of the laminar sub-layer on the surface
of an object is provided. Further, the laminar sub-layer is minimized over a
large area or the entire area of the surface of the object.
Further, greater efficiency with respect to minimization of the laminar sublayer
is provided, due to the larger intensity of the high intensity sound or ultrasound,
e.g. compared to other types of sonic waves.
Additionally, since the high intensity sound or ultrasound is generated directly
in the air/gas surrounding the object (or at least the air/gas surrounding the
relevant surface of the object) (instead of generating the ultrasound in the
catalyst or the object to transfer heat from or from any solid transmitter) a
greater efficiency of the relevant process is obtained. In this way, less dampening
of the intensity is achieved, as there will be substantially no loss from
the transition between a solid transmitter of the high intensitysound/
ultrasound to the air/gas. This loss will occur whenever there is a large
difference in acoustical impedance, which on the other hand will apply for any
solid - gas transition.
High intensity sound or ultrasound in gases leads to very high velocities and
displacements of the gas molecules. For example, 160 dB corresponds to a
particle velocity of 4,5 m/s and a displacement of 33 ^m at 22.000 Hz. In
other words, the kinetic energy of the molecules has been increased significantly.
In one embodiment, the sound intensity of the high intensity sound or ultrasound
is selected from the range of approximately 140 - 160 dB. Alternatively
it is above 160 dB.
In a preferred embodiment, the sonic means comprise: an outer part and an
inner part defining a passage, an opening, and a cavity provided in the inner
part, where said sonic means is adapted to receive a pressurized gas and
pass the pressurized gas to said opening, from which the pressurized gas is
discharged in a jet towards the cavity.
In one embodiment, the temperature of said surface is greater than the temperature
of said gas, and said process is a heat exchange process, whereby
said reduction and/or minimization of the laminar sub-layer causes an increased
heat exchange from said object to said gas.
In this way, a forced heat flow from the surface to surrounding gas/air is provided
by increasing the conduction by minimizing the laminar sub-layer. The
high intensity sound or ultrasound will increase the interaction between gas
molecules and the surface and thus the heat conduction that thereafter can
be followed by passive or active convection at the surface, i.e. increased heat
transfer efficiency is provided, due to reduction of laminar sub-layer.
This is e.g. desirable when the heat transfer is insufficient/too small from a
surface of an object to the surrounding air/gas, when cooling of the object
and/or heating of the gas is wanted. This will be the case when a too large
laminar sub-layer is causing Insufficient/reduced heat transfer or if there is a
wish to use a smaller heat exchanger. In this way, a maximization of a
minimization of the sub-layer is provided thereby increasing the heat flow
from a surface into air.
In an alternative embodiment, the temperature of said surface is smaller than
the temperature of said gas, and said process is a heat exchange process,
whereby said reduction and/or minimization of the laminar sub-layer causes
an increased heat exchange from said gas to said object.
In this way, a forced heat flow from the surrounding gas/air to the surface is
provided by increasing the conduction by minimizing the laminar sub-layer.
This is e.g. desirable when the heat transfer is insufficient/too small from the
surrounding air/gas to a surface of an object, when cooling of the air/gas
and/or heating of the object is wanted.
In one embodiment, the surface of said object is a catalyst and that said gas
comprise at least one reactant of the catalyst, and said process is a catalytic
process, whereby said reduction of the laminar sub-layer causes an
increased speed of said catalytic process.
In this way, a decrease of the reaction time of a catalytic process (i.e.
increase of the speed the catalytic process) in air/gas on the catalyst surface
is provided by applying high intensity sound or ultrasound to the surface.
Hereby, a forced interaction between gas molecules and the surface of the
catalyst is established. The high intensity sound or ultrasound increases the
interaction between gas molecules and the surface by minimizing the laminar
sub-layer and thus increasing the speed of the catalytic process.
Please note, that this process is not equivalent to ultrasound assisted
catalytic processes in fluids, which already are well known and described in
the prior art. The actual sound pressure in a gas will for instance be much
less than those used in fluids for an ultrasound assisted catalytic process.
Similarly there will be no possible cavitations processes in a gas.
This is e.g. desirable when the speed of catalytic process is to insufficient/too
small or there is a wish to use a smaller catalyst.
In one embodiment, said surface is an inner surface of a given volume, and
said process is a change of gas composition between said gas and a
previous gas composition at said inner surface, whereby said reduction of the
laminar sub-layer causes an increased gas exchange by increasing the
interaction between gas molecules of said gas and said previous gas
composition at said inner surface.
In this way, a decrease of the necessary flushing time during a gas exchange
in a volume is provided by decreasing the time needed for diffusion over the
laminar sub-layer of the surface by applying high intensity sound or
ultrasound to the surface. Hereby, a forced interaction between gas
molecules and the previous gas composition at the inner surface of the given
volume is established. The high intensity sound or ultrasound increases the
interaction between gas molecules and the previous gas composition at the
surface, i.e. provide increased gas exchange, by minimizing the laminar sublayer
and thus increasing the speed of establishing the new equilibrium.
This is e.g. desirable when the time of flushing (involving a solid surface) with
a new gas mixture is insufficient or too slow compared to when the new
equilibrium will be established. This is e.g. relevant for the use of protection
gases during welding or filling of protective/inactive gasses in food packing,
etc, e.g. by removing oxygen or the like.
The present invention also relates to a method of enhancing a process
involving a solid object and a gas, where the gas surrounds the object or at
least is in contact with a surface of the object, the method comprising the
steps of: applying a high intensity sound or ultrasound to at least the surface
of the object by sonic means, where the high intensity sound or ultrasound is
applied directly in the gas that is also the medium through which the high
intensity sound or ultrasound propagates to the surface of the object,
whereby a laminar sub-layer at the surface of the object is reduced and/or
minimized.
The method and embodiments thereof correspond to the device and
embodiments thereof and have the same advantages for the same reasons.
Advantageous embodiments of the method according to the present
invention are defined in the sub-claims and described in detail in the
following.
The present invention also relates to a nozzle comprising cooling channels
wherein said cooling channels is in connection with a sonic device generating
ultrasound during use that is distributed in said channels.
The present invention also relates to a printed circuit board comprising at
least one sink and at least one fan both arranged to cool at least a part of
said printed circuit board or components thereon during use, wherein said
printed circuit board further comprises a sonic device generating ultrasound
during use that is directed to at least a part of said at least one sink.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects of the invention will be apparent from and
elucidated with reference to the illustrative embodiments shown in the
drawings, in which:
Figure 1a schematically illustrates an object having a given heat transfer to
the surrounding or contacting air/gas or having a given catalytic process
reaction time or having a given flushing time according to prior art;
Figure 1b schematically illustrates the heat transfer, the catalytic process
reaction time and/or the flushing time in relation to the object of Figure 1a
when the present invention is applied;
Figure 2a schematically illustrates a (turbulent) flow over a surface of an
object according to prior art;
Figure 2b schematically shows a flow over a surface of an object, where the
effect of applying high intensity sound or ultrasound to/in air/gas surrounding
or contacting a surface of an object according to the present invention is
illustrated;
Figure 3a schematically illustrates a preferred embodiment of a device for
generating high intensity sound or ultrasound;
Figure 3b shows an embodiment of an ultrasound device in form of a discshaped
disc jet;
Figure 3c is a sectional view along the diameter of the ultrasound device
(301) in Figure 3b illustrating the shape of the opening (302), the gas
passage (303) and the cavity (304) more clearly;
Figure 3d illustrates an alternative embodiment of an ultrasound device,
which is shaped as an elongated body;
Figure 3e shows an ultrasound device of the same type as in Figure 3d but
shaped as a closed curve;
Figure 3f shows an ultrasound device of the same type as in Figure, 3d but
shaped as an open curve; •
Figure 4a illustrates an exploded view of a nozzle illustrating cooling
channels and manifolds for cooling gas; and
Figure 4b illustrates one example of a placement of an ultrasound generator
in a manifold according to one embodiment of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1a schematically illustrates an object having a given heat transfer to
the surrounding or contacting air/gas or having a given catalytic process
reaction time or having a given flushing time according to prior art.
Shown is an object (100) having a surface having a temperature of TL A
surrounding gas or a gas (500), illustrated by a broken box, contacting a
relevant surface of the object (100) has a temperature of TO, where T-i > TOAccording
to a first aspect of the present invention, heat energy tends to
migrate in the direction of decreasing temperature. The heat transfer can
take place by the processes of conduction, convection or radiation. Heat is
the energy associated with the perpetual movement of the molecules and
temperature is a measure of the vigor of this movement. When materials at
different temperatures are in contact the more vigorous molecules transfer
some of their thermal energy to less vigorous ones by collisions. This is the
process of heat conduction. It is the only way in which heat can flow through
an opaque solid.
Former methods have suggested different methods to decrease this laminar
sub-layer for instance by establishing a standing wave pattern over the
surface. However, the use of a standing wave pattern to minimize the laminar
sub-layer does not give a very efficient or large reduction of the laminar sublayer,
since the definition of a standing wave pattern includes a stationary
and repeatable location of nodes over the surface. At these nodes there will
be no displacement or velocity of the gas molecules. Another method
suggests the use of Shockwaves, which again has the drawback of covering
a small part of the surface. Finally it has been suggested to generate
acoustic turbulence at the surface or transfer acoustic energy from a solid,
either from the surface itself or from a transmitter. All of them not resulting in
those very high levels of intensity that gives the efficiency of decreasing the
laminar sub-layer. The condition of Figure 1a results, for the first aspect, in a
given heat transfer'1'.
According to a second aspect of the present invention, Figure 1a
schematically illustrates an object (100) being a catalyst. The reactants are
the surrounding or contacting gas(ses) (500) and the catalyzing product (100)
has to migrate through the laminar sub-layer by diffusion. The catalyst has
the temperature Ti and the reactant(s) in gas form (500) has the temperature
To.
Former methods have suggested a method to transfer acoustic energy (high
frequency vibration) from a solid transducer, via a solid bar and through a
diaphragm. The acoustic energy is emitted into the gas (500) and thereby
disturbing the fluid border film on the outer surface of the porous solid
catalyst. However, the arrangement gives an inefficient coupling of the
ultrasound from the diaphragm to the gas (500). This is related to the large
difference in acoustical impedance, which will apply for any solid - gas
transition. The condition of Figure 1a results, for the second aspect, in a
given catalytic process reaction time(1).
According to a third aspect of the present invention, Figure 1a schematically
illustrates an object (100) being the inner wall of a volume, where the
composition of the gases (500) is going to be changed. The new gas (not
specifically shown) and the previous gas (500) have to migrate through the
laminar sub-layer by diffusion. The inner wall of the volume has the
temperature T-i and the previous gas (500) has the temperature TQ.
The condition of Figure 1 a, according to the third aspect, results in a given
flushing time(1> before the new equilibrium is established.
Please note, the three mentioned aspects are not exclusive as some of the
processes may happen at the same time.
Figure 1b schematically illustrates the heat transfer, the catalytic process
reaction time and/or the flushing time in relation to the object of Figure 1a
when the present invention is applied. Shown is the object (100) of Figure 1a,
but in a situation where the present invention is applied. The object (100) has
the same temperature T-i as in Figure 1 a and the surrounding or contacting
gas (500) has also the same temperature T0 as in Figure 1a.
According to the first aspect, the object (100) (or a surface of the object) is
according to the present invention submitted to high intensive sound or
ultrasound in the contacting or surrounding gas(es). This leads to very high
velocities and displacements of the gas molecules. In other words, the kinetic
energy of the molecules is increased significantly by being subjected to
ultrasound or high intensive sound. Figure 1 b illustrates that the high intensity
sound or ultrasound will increase the interaction between gas molecules and
the surface and thus the heat conduction that thereafter can be followed by
passive or active convection at the surface, as will be explained in greater
detail in connections with Figures 2a and 2b. The application of the invention
results in a given heat transfer'2' that is greater than heat transfer(1) of Figure
Since the limitations of heat transfer are equivalent to the same limitations of
an effective catalytic process, the present invention also provides a way to
decrease the reaction time of a catalytic process in air/gas on the surface of
a catalyst surface by means of applying high intensity sound or ultrasound to
the surface of an object. According to the second aspect of the present
invention, a forced interaction between gas molecules and the surface of the
catalyst is established, because the high intensity ultrasound will minimize
the laminar sub-layer, as will, be explained in greater detail in connections
with Figures 2a and 2b. As a result the diffusion time will decrease and thus
increasing the speed of the catalytic process. Applying the invention results
in a given catalytic process reaction time(2) that is smaller/shorter than the
catalytic process reaction time(1) of Figure 1 a.
Please note, that this process is not equivalent to ultrasound assisted
catalytic processes in fluids, which already are well known and described in
the prior art. The actual sound pressure in a gas will for instance be much
less than those used in fluids for an ultrasound assisted catalytic process.
Similarly there will be no possible cavitations processes in a gas.
Since the limitations of heat transfer are equivalent to the same limitations of
an effective diffusion through the sub-layer, the present invention also
provides a way to decrease the time to establish a new equilibrium when the
gas composition in a volume is changed, by means of applying high intensity
sound or ultrasound to the surface of an object. According to the third aspect
of the present invention a forced interaction between gas molecules and a
previous gas at the surface of the volume is established, because the high
intensity ultrasound will minimize the laminar sub-layer, as will be explained
in greater detail in connections with Figures 2a and 2b. As a result the
diffusion time will decrease and thus increasing the speed of establishing the
new equilibrium. Applying the invention results in a given flushing time(2) that
is smaller/shorter than the flushing time(1* of Figure 1a.
The gas may e.g. be air, steam, or any other kind of gas.
Figure 2a schematically illustrates a (turbulent) flow over a surface of an
object according to prior art. Shown is a surface (204) of an object with a gas
(500) surrounding or contacting the surface (204). As mentioned, thermal
energy can be transported through gas by conduction and also by the
movement of the gas from one region to another. This process of heat
transfer associated with gas movement is called convection. When the gas
motion is caused only by buoyancy forces set up by temperature differences,
the process is normally referred to as natural or free convection; but if the
gas motion is caused by some other mechanism, such as a fan or the like, it
is called forced convection. With a condition of forced convection there will be
a laminar boundary layer (201) near to the surface (204). The thickness of
this layer is a decreasing function of the Reynolds number of the flow, so that
at high flow velocities, the thickness of the laminar boundary layer (201) will
decrease. When the flow becomes turbulent the layer are divided into a
turbulent boundary layer (202) and a laminar sub-layer (203). For nearly all
practically occurring gas flows, the flow regime will be turbulent in the entirety
of the streaming volume, except for the laminar sub-layer (203) covering the
surface (204) wherein the flow regime is laminar. Considering a gas molecule
or a particle (205) in the laminar sub-layer (203), the velocity (206) will be
substantially parallel to the surface (204) and equal to the velocity of the
laminar sub-layer (203). Heat transport across the laminar sub-layer will be
by conduction or radiation, due to the nature of laminar flow. Mass transport
across the laminar sub-layer will be solely by diffusion. The presence of the
laminar sub-layer (203) does not provide optimal or efficient heat transfer or
increased mass transport. Any mass transport across the sub-layer has to be
by diffusion, and therefore often be the final limiting factor in an overall mass
transport.
Figure 2b schematically shows a flow over a surface of an object, where the
effect of applying high intensity sound or ultrasound to/in air/gas (500)
surrounding or contacting a surface of an object according to the present
invention is illustrated. More specifically, Figure 2b illustrates the conditions
when the surface (204) is applied with high intensity sound or ultrasound.
Again consider a gas molecule/particle (205) in the laminar layer; the velocity
(206) will be substantially parallel to the surface (204) and equal to the
velocity of the laminar layer prior applying ultrasound. In the direction of the
emitted sound field to the surface (204) in Figure 2b, the oscillating velocity of
the molecule (205) has been increased significantly as indicated by arrows
(207). As an example, a maximum velocity of v= 4.5 m/sec and a
displacement of +/- 32 ^m will be achieved where the ultrasound frequency
f=22 kHz and the sound intensity = 160 dB. The corresponding (vertical)
displacement in Figure 2b is substantially 0 since the molecule follows the
laminar air stream along the surface. In result, the ultrasound will establish a
forced heat flow from the surface to surrounding gas/air (500) by increasing
the conduction by minimizing the laminar sub-layer. The sound intensity is in
one embodiment 100 dB or larger. In another embodiment, the sound
intensity is 140 dB or larger. Preferably, the sound intensity is selected from
the range of approximately 140 - 160 dB. The sound intensity may be above
160dB.
The minimized sub-laminar layer has the effect that heat transfer from the
surface (204) to the surrounding or contacting gas (500) is increased (if the
temperature of the surface is greater than the temperature of the surrounding
or contacting gas). Further, the minimization will have the effect that the
catalytic process reaction time is reduced if the surface/object is a catalyst
and the surrounding gas comprises a reactant. Additionally, the minimization
will have the effect that the flushing time is reduced
In one embodiment, the invention is used to speed up the process of
generating hydrogen from natural gas and steam. In this embodiment, the
natural gas and the steam is directed at a surface of a catalyst enhancing the
speed of the process as generally known. Further, the natural gas or the
steam (or both) may be the medium through which the ultrasound is
propagating as explained in the following. The efficiency is increased by the
influence of the ultrasound as explained above and elsewhere.
Figure 3a schematically illustrates a preferred embodiment of a device (301)
for generating high intensity sound or ultrasound. Pressurized gas is passed
from a tube or chamber (309) through a passage (303) defined by the outer
part (305) and the inner part (306) to an opening (302), from which the gas is
discharged in a jet towards a cavity (304) provided in the inner part (306). If
the gas pressure is sufficiently high then oscillations are generated in the gas
fed to the cavity (304) at a frequency defined by the dimensions of the cavity
(304) and the opening (302). An ultrasound device of the type shown in figure
3a is able to generate .ultrasonic acoustic pressure of up to 160 dBSPL at a
gas pressure of about 4 atmospheres. The ultrasound device may e.g. be
made from brass, aluminum or stainless steel or in any other sufficiently hard
material to withstand the acoustic pressure and temperature to which the
device is subjected during use. The method of operation is also shown in fig
3a, in which the generated ultrasound (307) is directed towards a surface
(204) of an object (100) i.e. a heat exchanger or a catalyst or the inside of a
volume.
Please note, that the pressurized gas can be different than the gas that
contact or surround the object.
Figure 3b shows an embodiment of an ultrasound device in form of a discshaped
disc jet. Shown is a preferred embodiment of an ultrasound device
(301), i.e. a so-called disc jet. The device (301) comprises an annular outer
part (305) and a cylindrical Inner part (306), in which an annular cavity (304)
is recessed. Through an annular gas passage (303) gases may be diffused
to the annular opening (302) from which it may be conveyed to the cavity
(304). The outer part (305) may be adjustable in relation to the inner part
(306), eg. by providing a thread or another adjusting device (not shown) in
the bottom of the outer part (305), which further may comprise fastening
means (not shown) for locking the outer part (305) in relation to the inner part
(306), when the desired interval there between has been obtained. Such an
ultrasound device may generate a frequency of about 22 kHz at a gas
pressure of 4 atmospheres, the molecules of the gas are thus able to
migrate up to 36 |im about 22,000 times per second at a maximum velocity of
4.5 m/s. These values are merely included to give an idea of the size and
proportions of the ultrasound device and by no means limit of the shown
embodiment.
Figure 3c is a sectional view along the diameter of the ultrasound device
(301) in Figure 3b illustrating the shape of the opening (302), the gas
passage (303) and the cavity (304) more clearly. It is further apparent that
the opening (302) is annular. The gas passage (303) and the opening (302)
are defined by the substantially annular outer part (305) and the cylindrical
inner part (306) arranged therein. The gas jet discharged from the opening
(302) hits the substantially circumferential cavity (304) formed in the inner
part (306), and then exits the ultrasound device (301). As previously
mentioned the outer part (305) defines the exterior of the gas passage (303)
and is further bevelled at an angle of about 30° along the outer surface of its
inner circumference forming the opening of the ultrasound device, wherefrom
the gas jet may expand when diffused. Jointly with a corresponding bevelling
of about 60° on the inner surface of the inner circumference, the above
bevelling forms an acute-angled circumferential edge defining the opening
(302) externally. The inner part (306) has a bevelling of about 45° in its outer
circumference facing the opening and internally defining the opening (302).
The outer part (305) may be adjusted in relation to the inner part (306),
whereby the pressure of the gas jet hitting the cavity (304) may be adjusted.
The top of the inner part (306), in which the cavity (304) is recessed, is also
bevelled at an angle of about 45° to allow the oscillating gas jet to expand at
the opening of the ultrasound device.
Figure 3d illustrates an alternative embodiment of an ultrasound device,
which is shaped as an elongated body. Shown is an ultrasound device
comprising an elongated substantially rail-shaped body (301), where the
body is functionally equivalent with the embodiments shown in Figures 3a
and 3b, respectively. In this embodiment the outer part comprises two
separate rail-shaped portions (305a) and (305b), which jointly with the railshaped
inner part (306) form an ultrasound device (301). Two gas passages
(303a) and (303b) are provided between the two portions (305a) and (305b)
of the outer part (305) and the inner part (306). Each of said gas passages
has an opening (302a), (302b), respectively, conveying emitted gas from the
gas passages (303a) and (303b) to two cavities (304a), (304b) provided in
the inner part (306). One advantage of this embodiment is that a rail-shaped
body is able to coat a far larger surface area than a circular body. Another
advantage of this embodiment is that the ultrasound device may be made in
an extruding process, whereby the cost of materials is reduced.
Figure 3e shows an ultrasound device of the same type as in Figure 3d but
shaped as a closed curve. The embodiment of the gas device shown in
Figure 3d does not have to be rectilinear. Figure 3e shows a rail-shaped
body (301) shaped as three circular, separate rings. The outer ring defines
an outermost part (305a), the middle ring defines the inner part (306) and the
inner ring defines an innermost outer part (305b). The three parts of the
ultrasound device jointly form a cross section as shown in the embodiment in
Figure 3d, wherein two cavities (304a) and (304b) are provided in the inner
part, an wherein the space between the outermost outer part (305a) and the
inner part (306) defines an outer gas passage (303a) and an outer opening
(302a), respectively, and the space between the inner part (306) and the
innermost outer part (305b) defines an inner gas passage (304b) and an
inner opening (302b), respectively. This embodiment of an ultrasound device
is able to coat a very large area at a time and thus treat the surface of large
objects.
Figure 3f shows an ultrasound device of the same type as in Figure 3d but
shaped as an open curve. As shown it is also possible to form an ultrasound
device of this type as an open curve. In this embodiment the functional parts
correspond to those shown in Figure 3d and other details appear from this
portion of the description for which reason reference is made thereto.
Likewise it is also possible to form an ultrasound device with only one
opening as described in Figure 3b. An ultrasound device shaped as an open
curve is applicable where the surfaces of the treated object have unusually
shapes. A system is envisaged in which a plurality of ultrasound devices
shaped as different open curves are arranged in an apparatus according to
the invention.
Figure 4a illustrates an exploded view of a nozzle illustrating cooling
channels and manifolds for cooling gas. Shown is a nozzle (600) comprising
cooling channels (601) and manifolds (602).
Construction of nozzles, e.g. for use in rockets, is in many ways limited by
the aspect of establishing an efficient cooling of the inner wall of the nozzle
(600).
Having the walls to thin gives a too weak construction, which cannot fulfil the
necessary requirements during use. On the other hand, a too thick wall will
not be able to be cooled efficiently and the surface temperature of the inner
wall will be too high.
The cooling of the inner wall is often established by having a hollow wall
structure with a number of cooling channels (601), where an appropriate
cooling gas is forced through.
The efficiency of the cooling is among other things, limited by the following:
- The efficiency of heat transport from the warm inner wall of the
channel (601) to the cooling gas. That part of the heat, which is
transferred by convection, will be limited by the thickness of the
laminar sub-layer above the surface of the walls, as described
previously. In the sub-layer, the heat transport time will be limited to
diffusion time and
- The cooling is also limited due to a change of density of the cooling
gas when the gas temperature increases. The cold gas, having a high
density, is forced against the outer wall of the nozzle because of gas
velocity and nozzle geometry. This effect is amplified as the gas near
the inner surface gets warmer thereby having less density. The overall
heat distribution in the gas is therefore limited by the insufficient
mixing of warm and cold gas.
Figure 4b illustrates one example of a placement of an ultrasound generator
in a manifold according to one embodiment of the present invention.
Shown is a manifold (602), e.g. corresponding to the one of Figure 4a,
comprising an aerodynamic ultrasonic generator (301), e.g. a disk-jet or the
like. Preferably, the ultrasonic generator (301) is located at the inlet of the
cooling gas or likewise. The ultrasound generator (301) may e.g. be powered
by an approx. 4 bar pressure drop of the gas. The generated ultrasound will
be distributed in the channels (601) e.g. via the manifolds (602).
Primarily, the high-energy ultrasound will disrupt the laminar sub-layer, as
described earlier, giving an up to two times higher energy transport from the
walls to the gas.
Additionally, the high-energy ultrasound will mix the warm and cold parts of
the cooling gas, due to the very high particle movements in the gas
increasing cooling even further.
In the claims, any reference signs placed between parentheses shall not be
constructed as limiting the claim. The word "comprising" does not exclude the
presence of elements or steps other than those listed in a claim. The word
"a" or "an" preceding an element does not exclude the presence of a plurality
of such elements.

Patent Claims (Amended):
1. A sonic device for enhancing a process involving a solid object (100) and a
gas (500), where the gas (500) surrounds the object (100) or at least is in
contact with a surface (204) of the object (100), the device comprising
• sonic means (301) for applying a high intensity sound or ultrasound to
at least the surface (204) of the object (100),
wherein the high intensity sound or ultrasound, during use of the sonic
device, is applied directly in the gas (500) that is also the medium through
which the high intensity sound or ultrasound propagates to the surface (204)
of the object (100), whereby a laminar sub-layer (203) at the surface (204) of
the object (100) is reduced and/or minimized, where the high intensity sound
or ultrasound has an intensity that is 140 dB or larger.
2. A device according to claim 1 , c h a r a c t e r i z e d in that the sound
intensity of the high intensity sound or ultrasound is selected from the range
of approximately 140 - 160 dB or is above 160dB.
3. A device according to claims 1-2, c h a r a c t e r i z e d in that said sonic
means (301) comprises:
• an outer part (305) and an inner part (306) defining a passage (303),
• an opening (302), and
• a cavity (304) provided in the inner part (306)
where said sonic means (301) is adapted to receive a pressurized gas and
pass the pressurized gas to said opening (302), from which the pressurized
gas is discharged in a jet towards the cavity (304).
4. A device according to claims 1-3, c h a r a c t e r i z e d in that
• the temperature (Ti) of said surface (204) is greater than the
temperature (To) of said gas (500), and
• said process is a heat exchange process, whereby said reduction
and/or minimization of the laminar sub-layer (203) causes an
increased heat exchange from said object (100) to said gas (500).
5. A device according to claims 1-3, c h a r a c t e r i z e d in that
• the temperature (Ti) of said surface (204) is smaller than the
temperature (T0) of said gas (500), and
• said process is a heat exchange process, whereby said reduction
and/or minimization of the laminar sub-layer (203) causes an
increased heat exchange from said gas (500) to said object (100).
6. A device according to claims 1-5, c h a r a c t e r i z e d in that
• the surface (204) of said object (100) is a catalyst and that said gas
(500) comprise at least one reactant of the catalyst, and
• said process is a catalytic process, whereby said reduction of the
laminar sub-layer (203) causes an increased speed of said catalytic
process.
7. A device according to claims 1-6, c h a r a c t e r i z e d in that
• said surface (204) is an inner surface of a given volume, and
• said process is a change of gas composition between said gas (500)
and a previous gas composition at said inner surface, whereby said
reduction of the laminar sub-layer (203) causes an increased gas
exchange by increasing the interaction between gas molecules of said
gas (500) and and said previous gas composition at said inner
surface.
8. A method of enhancing a process involving a solid object (100) and a gas
(500), where the gas (500) surrounds the object (100) or at least is in contact
with a surface (204) of the.object (100), the method comprising the steps of:
• applying a high intensity sound or ultrasound to at least the surface
(204) of the object (100) by sonic means (301),
where the high intensity sound or ultrasound is applied directly in the gas
(500) that is also the medium through which the high intensity sound or
ultrasound propagates to the surface (204) of the object (100), whereby a
laminar sub-layer (203) at the surface (204) of the object (100) is reduced
and/or minimized, where the high intensity sound or ultrasound has an
intensity that is 140 dB or larger.
9. The method according to claim 8, c h a r a c t e r i z e d in the sound
intensity of the high intensity sound or ultrasound is selected from the range
of approximately 140 - 160 dB or is above 160 dB.
10. A method according to claims 8-9, c h a r a c t e r i z e d in that said
sonic means (301) comprises:
• an outer part (305) and an inner part (306) defining a passage (303),
• an opening (302), and
• a cavity (304) provided in the inner part (306),
and wherein said method further comprises the step of:
• receiving a pressurized gas in said said sonic means (301),
• passing the pressurized gas to said opening (302),
• discharging the pressurized gas in a jet towards the cavity (304) from
said opening (302).
11. A method according to claims 8-10, c h a r a c t e r i z e d in that
• the temperature (Ti) of said surface (204) is greater than the
temperature (T0) of said gas (500), and
• said process is a heat exchange process, whereby said reduction
and/or minimization of the laminar sub-layer (203) causes an
increased heat exchange from said object (100) to said gas (500).
12. A method according to claims 8-10, c h a r a c t e r i z e d in that
• the temperature (Ti) of said surface (204) is smaller than the
temperature (To) of said gas (500), and
• said process is a heat exchange process, whereby said reduction
and/or minimization of the laminar sub-layer (203) causes an
increased heat exchange from said gas (500) to said object (100).
13. A method according to claims 8-12, c h a r a c t e r i z e d in that
• the surface (204) of said object (100) is a catalyst and that said gas
(500) comprise at least one reactant of the catalyst, and
• said process is a catalytic process, whereby said reduction of the
laminar sub-layer (203) causes an increased speed of said catalytic
process.
14. A method according to claims 8 - 13. c h a r a c t e r i z e d in that
• said surface (204) is an inner surface of a given volume, and
• said process is a change of gas composition between said gas (500)
and a previous gas composition at said inner surface, whereby said
reduction of the laminar sub-layer (203) causes an increased gas
exchange by increasing the interaction between gas molecules of said
gas (500) and said previous gas composition at said inner surface.
15. Use of a device according to claims 1 - 7 or a method according to
claims 8 - 14 to generate hydrogen, wherein natural gas and steam is used
to generate the hydrogen.