U.S. patent application number 12/296224 was filed with the patent office on 2010-06-17 for electrohydrodynamic micropump and its use.
Invention is credited to Jan Gimsa, Moritz Holtappels, Marco Stubbe.
Application Number | 20100150738 12/296224 |
Document ID | / |
Family ID | 37983543 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100150738 |
Kind Code |
A1 |
Gimsa; Jan ; et al. |
June 17, 2010 |
Electrohydrodynamic Micropump and Its Use
Abstract
An electrohydrodynamic micropump having at least one pumping
passage for pumping a liquid, wherein there is at least one
electrode device for generating an electrical alternating field and
at least one device for producing a temperature gradient in the
liquid to be pumped, which is arranged in and/or on the at least
one pumping passage.
Inventors: |
Gimsa; Jan; (Rostock,
DE) ; Holtappels; Moritz; (Bremen, DE) ;
Stubbe; Marco; (Bad Doberan, DE) |
Correspondence
Address: |
LERNER GREENBERG STEMER LLP
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Family ID: |
37983543 |
Appl. No.: |
12/296224 |
Filed: |
February 26, 2007 |
PCT Filed: |
February 26, 2007 |
PCT NO: |
PCT/EP2007/001641 |
371 Date: |
February 16, 2010 |
Current U.S.
Class: |
417/48 |
Current CPC
Class: |
F04B 19/006
20130101 |
Class at
Publication: |
417/48 |
International
Class: |
F04B 19/00 20060101
F04B019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2006 |
DE |
10 2006 009 424.7 |
Claims
1-38. (canceled)
39. An electrohydrodynamic micropump comprising: at least one
pumping passage for pumping a liquid flowing medium; at least one
electrode device for generating an alternating electric field; and
at least one heating device for generating a temperature gradient
in the liquid to be pumped being arranged in and/or at said at
least one pumping passage.
40. The electrohydrodynamic micropump according to claim 39,
wherein said at least one electrode device and said at least one
device for generating the temperature gradient are coupled.
41. The electrohydrodynamic micropump according to claim 39,
wherein said at least one pumping passage is at least partly
linear.
42. The electrohydrodynamic micropump according to claim 39,
wherein said at least one pumping passage includes two or more
segments.
43. The electrohydrodynamic micropump according to claim 42,
wherein said segments are linear and disposed at an angle between
0.degree. and 180.degree..
44. The electrohydrodynamic micropump according to claim 42,
wherein said electrode device includes at least two electrodes, and
said segments and said electrodes are arranged such that the an
inflow of the liquid flowing medium is substantially vertical to
electric field lines generated by said electrode device.
45. The electrohydrodynamic micropump according to claim 44,
wherein the outflow of the liquid flowing medium is substantially
parallel to the electric field lines.
46. The electrohydrodynamic micropump according to claim 42,
wherein said at least two segments have a transition region
including at least one flow guiding member.
47. The electrohydrodynamic micropump according to claim 46,
wherein said at least one flow guiding member constricts a flow
cross-section for the liquid flowing medium.
48. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device includes at least one first electrode
and at least one second electrode, said first electrode and second
electrode are located opposite each other, and the liquid flowing
medium flows between said first and second electrodes.
49. The electrohydrodynamic micropump according to claim 39,
wherein said electrode devices includes a first and second
electrodes and the electric field is formed between said first and
second electrodes in said at least one pumping passage.
50. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device comprises at least two electrodes
extending flat on at least one of a the bottom, ceiling or side
wall of said at least one pumping passage.
51. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device includes at least one electrode which
is at least partly surrounded by the liquid flowing medium.
52. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device includes an electrode which is one of
a grating or one wire mesh and is traversed by the liquid flowing
medium.
53. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device comprises at least two metallic
electrodes with a high thermal conductivity.
54. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device comprises at least two metallic
electrodes with different thermal conductivity.
55. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device comprises at least two electrodes
with at least one of different dimensions or shapes.
56. The electrohydrodynamic micropump according to claim 39,
wherein said electrode device comprises at least first and second
electrodes, said first electrode has at least one of a greater
surface area, a greater thickness or a greater volume than said
second electrode.
57. The electrohydrodynamic micropump according to claim 39,
wherein said heating device comprises at least one heating element
disposed for generating an additional temperature gradient and
arranged in said at least one pumping passage.
58. The electrohydrodynamic micropump according to claim 57,
wherein said at least one heating element is arranged in said at
least one pumping passage in a flow direction one of before or
behind said electrode device.
59. The electrohydrodynamic micropump according to claim 57,
wherein said electrode device includes an electrode and said at
least one heating element (3) and said electrode (5) are at least
partly combined in one component.
60. The electrohydrodynamic micropump according to claim 57,
wherein said at least one heating element is a conducting
microstructure with an electrically insulated surface comprising at
least one of heating wires or thermal radiators.
61. The electrohydrodynamic micropump according to claim 39,
wherein the alternating electric field has one of a sinusoidal or
rectangular time pattern and is generated one of continuously or
pulsed.
62. The electrohydrodynamic micropump according to claim 39,
wherein the alternating electric field has a frequency which is an
electric resonance frequency of the micropump.
63. The electrohydrodynamic micropump according to claim 39,
wherein said micropump has an additional inductive resonance
system, in which the liquid flowing medium to be pumped is at least
part of a dielectric of a capacitive element.
64. The electrohydrodynamic micropump according to claim 39,
wherein said at least one pumping passage is arranged on a
microsystem comprising one of a .mu.TAS-chip or a Lab-on-Chip
system.
65. The electrohydrodynamic micropump according to claim 64,
wherein said at least one pumping passage is arranged in a chamber
which comprises a microreactor.
66. The electrohydrodynamic micropump according to claim 65,
wherein said microreactor includes at least one of a chemical or
biological reaction system.
67. The electrohydrodynamic micropump according to claim 39,
wherein said at least one pumping passage is coupled to a pumping
system comprising at least one pumping chamber and at least one
discharge chamber.
68. The electrohydrodynamic micropump according to claim 67,
wherein said at least one pumping chamber opens into said at least
one pumping passage on at least one discharge opening.
69. The electrohydrodynamic micropump according to claim 67,
wherein said at least one pumping passage opens into said discharge
chamber on at least one outlet opening.
70. The electrohydrodynamic micropump according to claim 67,
wherein said one discharge chamber is one of directly or indirectly
connected with at least one further passage.
71. The electrohydrodynamic micropump according to claim 70,
wherein said pumping chamber and said discharge chamber are
connected by said further passage.
72. The electrohydrodynamic micropump according to claim 70,
wherein said pumping chamber, said at least one pumping passage,
said discharge chamber and said further passage comprise a pumping
system which is closed at least for a time.
73. The electrohydrodynamic micropump according to claim 72,
wherein one of said pumping system or said chamber comprise a
microreactor, and said microreactor is filled or evacuated by a
microdosing system.
74. A method of pumping liquids, which comprises: providing an
electrohydrodynamic micropump for pumping liquids according to
claim 39, and pumping liquids with the micropump.
75. A method for pumping a liquid in an electrohydrodynamic
micropump, comprising the steps of: forming an alternating electric
field and a temperature gradient in a liquid being pumped between
electrodes in at least one pumping passage; and controlling a
pumping direction by a frequency of the alternating electric field
applied and the temperature gradient in the at least one pumping
passage.
76. The method according to claim 75, including the further step
of: forming an additional temperature gradient by using a heating
element, and causing the additional temperature gradient to extend
into a region of the alternating electric field between the
electrodes or overlap the field wholly or in part.
77. The electrohydrodynamic micropump according to claim 43,
wherein said at least two linear segments are disposed at an angle
of substantially 90.degree..
78. The electrohydrodynamic micropump according to claim 46,
wherein said at least two segments have a transition region, and at
least one non-dielectric flow guiding member device dispose din
said transition region.
79. The electrohydrodynamic micropump according to claim 47,
wherein said at least one flow guiding member has a wedge-shaped
cross-section.
80. The electrohydrodynamic micropump according to claim 42,
wherein said one flow guiding member is a non-dielectric
material.
81. The electrohydrodynamic micropump according to claim 47,
wherein said at least one flow guiding member has a wedge-shaped
cross-section.
Description
[0001] This invention relates to an electrohydrodynamic micropump
according to the generic part of claim 1, a use of the micropump
according to claim 36, and a method for pumping a liquid according
to claim 37.
[0002] Pumps or micropumps which produce a pumping effect on
liquids by applying electric fields are known. In particular,
pumping systems have been described, whose pumping power is
influenced by the cooperation of alternating electric fields and
dielectric elements.
[0003] U.S. Pat. No. 4,316,233, for instance, discloses an
apparatus for the transport of fluids or particles by means of an
applied electric field. The apparatus consists of a pumping chamber
with two electrodes, wherein a dielectric element with a sawtooth
structure is arranged on one electrode. The specific arrangement
results in the formation of a traveling electric field, whereby the
fluid to be pumped is polarized and a pumping force is generated in
the direction of the traveling field.
[0004] DE 103 29 979 A1 likewise describes a pump which includes a
pumping chamber with an electrode device for generating an
alternating electric field and a dielectric element. The dielectric
element influences the field lines of the alternating electric
field, wherein the pumping force necessary for pumping is generated
by the alternating electric field. The dielectric element is formed
such that the alternating electric field has a stationary and
time-independent field gradient inside the pumping chamber in
pumping direction. As a result, a stationary and time-independent
polarization gradient is produced in the liquid in pumping
direction.
[0005] With this configuration, forces are generated which act both
in pumping direction and against the pumping direction. The
transport of liquid is caused by an unsymmetric construction of the
dielectric element and of the entire pumping system. The
unsymmetric construction of the dielectric element leads to the
generated force prevailing in one direction, and there is a
transport of liquid in pumping direction, wherein the pumping
direction cannot be changed or reversed due to the specific
construction.
[0006] What is also disadvantageous in the described pumping system
is the increased flow resistance caused by the dielectric element,
since the dielectric elements necessarily constrict the flow
passage and thus increase the flow resistance
F.sub.r.about.1/r.sup.4 according to the Hagen-Pouseuille law.
[0007] Therefore, it is the problem underlying the invention to
provide a micropump with which the pumping direction is easier to
control, the pumping direction can be varied as desired, and with
which a higher flow velocity can be achieved.
[0008] In accordance with the invention, this object is solved by
an electrohydrodynamic micropump with the features of claim 1.
[0009] Accordingly, the electrohydrodynamic micropump includes at
least one pumping passage, wherein at least one electrode device
for generating an alternating electric field and a means for
generating a temperature gradient in the liquid are provided in
and/or at the at least one pumping passage.
[0010] In a simple, but efficient way, the micropump in accordance
with the invention provides for an improved control of the pumping
direction and of the pumping rate. In dependence on the alternating
electric field applied and on the kind of liquid used, the pumping
direction and the pumping rate can be influenced selectively.
[0011] For instance, ionic physiological salt solutions with
concentrations up to 200 mM, in particular between 15 and 150 mM,
have a defined pumping direction upon application of an alternating
electric field with a frequency below 20 and 200 MHz, respectively.
With an increase of the salt concentration to above 200 mM and the
resulting higher ionic strength, there will also be an increase of
the frequency above which there can be a change of the pumping
direction into the opposite direction.
[0012] If non-ionic liquids such as e.g. hydrocarbons with a chain
length of C.sub.10 to C.sub.19 are used, there can also be a
reversal of the pumping direction at the same frequency of the
alternating electric field applied.
[0013] Upon application of the alternating electric field, the
electrode device furthermore acts as a heating element. At least
one electrode of the electrode device acts as a heat sink, which
results in the formation of a temperature gradient in the liquid to
be transported, in particular in the vicinity of the electrode
device. The temperature gradient causes the formation of a gradient
of the conductivity and/or of the dielectric constant in the liquid
to be transported. In the alternating electric field generated, the
liquid experiences a resultant force in the direction of lower
conductivities or dielectric constants due to the gradient, which
results in a transport of liquid.
[0014] In addition, the flow resistance is reduced considerably due
to the absence of the dielectric element. The at least one pumping
passage can even be broadened as desired, in order to generate a
larger volume flow.
[0015] Furthermore, the pump in accordance with the invention does
not require a stationary, time-independent field gradient and hence
no dielectric element for influencing the electric field lines
between the electrodes.
[0016] Advantageous constructions can be achieved when the at least
one electrode device and the at least one means for generating the
temperature gradient are coupled. Such coupling can for instance be
effected in the form of an integration in one component.
[0017] A simple guidance of the flow is obtained when the at least
one pumping passage is at least partly formed linear. More complex
constructions can be realized when the at least one pumping passage
includes two or more segments. At least two linear segments can
include an angle between 0.degree. and 180.degree., in particular
90.degree..
[0018] Advantageously, the arrangement of the segments and the
electrodes is chosen such that the inflow of a liquid is effected
substantially vertical to the electric field lines. It is also
advantageous when the arrangement of the segments and electrodes is
chosen such that the outflow of a liquid is effected substantially
parallel to the electric field lines.
[0019] The flow can be influenced in a positive way, when in the
transition region of at least two segments at least one flow
guiding means, in particular of a dielectric material, is arranged.
The flow guiding means can prevent e.g. an otherwise occurring
circular flow. Advantageously, the at least one flow guiding means
constitutes a constriction of the flow cross-section for the
flowing medium, in particular has a wedge-shaped cross-section.
[0020] The electrode device of the pump in accordance with the
invention preferably includes at least one first and at least one
second electrode, which are located opposite each other, wherein
the electrodes are arranged as plates flat on the bottom, wall
and/or ceiling of the at least one pumping passage of the
micropump. The flat arrangement provides for an overflow of the
liquid to be transported, so that a further reduction of the flow
resistance is achieved.
[0021] The electrode device can include at least one electrode,
which is at least partly surrounded by the flowing medium. In such
an arrangement, the electrode device includes at least one grating
or at least one wire mesh as electrode, which is traversed by the
flowing medium.
[0022] In principle, all electrode materials can be used as
electrode material. Advantageously, however, the electrode device
comprises at least two electrodes, in particular metallic
electrodes with a high thermal conductivity. Particularly
advantageously, the electrode device comprises at least two
electrodes, in particular metallic electrodes, with different
thermal conductivity. Advantageously, at least one of the
electrodes has a high thermal conductivity. Preferred electrode
materials include gold, platinum, indium tin oxide or further
metals or metal oxides with a high thermal conductivity (e.g.
greater than 20 W/(m K)). In principle, polymers can also be used.
The very high thermal conductivity of a metallic electrode
contributes to an increase of the temperature gradient and thus
enhances the pumping power.
[0023] Advantageously, the first and second electrodes have
dimensions and/or shapes different from each other. Preferably, the
first electrode is characterized by a greater surface area, width
and/or greater volume than the second electrode. The different
dimensions lead to the formation of a stronger temperature
gradient, since the greater first electrode has a supporting effect
in its function as an additional heat sink in the system.
[0024] Advantageously, in at least one pumping passage at least one
heating element is provided for generating an additional
temperature gradient in the liquid, wherein the heating element
preferably is located, depending on the frequency of the field, in
flow direction before or behind the electrode device.
[0025] The additional temperature gradient generated by the heating
element reaches into the region of the alternating electric field
generated by the electrode device and supports the formation of a
gradient of the conductivity and of the dielectric constant in the
liquid to be transported.
[0026] The advantage of this arrangement consists in that the
specific arrangement of the heating element in flow direction
before or behind the alternating electric field generates pumping
forces in only one direction. This leads to a considerable increase
in efficiency.
[0027] In an advantageous embodiment, the at least one heating
element and the second electrode are at least partly combined in
the form of a common component.
[0028] The alternating electric field generated continuously and/or
in a pulsed manner advantageously has a sinusoidal or rectangular
time behavior. Preferably, the frequency of the alternating
electric field is adjusted to an electric resonance frequency of
the pump.
[0029] Each electrode of the pump inherently constitutes a
capacitive element. In a pump with two opposed electrodes, the
pumping medium can be interpreted as a dielectric of a conventional
capacitor. If the pumping medium is e.g. water, its relative
dielectric constant at room temperature is about 78. The supply
lines can be interpreted as inductances (coils). Since they are
electrically connected in series with the (electrode) capacitor,
this is a series resonant circuit (suction circuit), i.e. under
resonance conditions the voltage across the capacitor, i.e. on the
electrodes, is magnified, and the pumping effect is enhanced. This
enhancement also can occur very locally, in particular when the
resonance condition along the electrode inside the pumping
structure is satisfied only locally due to the inductance of the
electrode itself. In this connection, it should be noted that the
effective inductance of the electrode line surrounded by medium is
approximately increased by the factor of (root of relative
dielectric constant) (shortening factor). When using water, there
is an increase by the factor of about 9.
[0030] Due to the outer wiring of the pump, in particular an
additional inductance, the self-resonant frequency of the system
can be adjusted. The fact that there is a maximum pumping effect
under resonance conditions and that the dielectric constant in turn
depends on the medium itself and its temperature, can be utilized
for control effects. The resonance condition can for instance be
adjusted such that the pumping effect reaches a maximum, when an
undesired medium or object is present inside the pumping structure
in the case of media mixtures, emulsions or suspensions.
[0031] The heating element advantageously is provided in the form
of heating structures, heating wires and/or thermal radiators. The
heating elements or heating structures preferably are produced
together with the electrode device in one manufacturing
process.
[0032] Advantageously, the liquid to be transported by means of the
pump is characterized by a conductivity of 0.0001 S/m to 10 S/m and
a permittivity of 0.6 to 10000.
[0033] The at least one pumping passage of the micropump
advantageously is arranged on a microsystem, in particular a chip.
Examples for biological or chemical microsystems or chips are known
for instance under the names "factory on a chip", "Lab-on-Chip" or
"micro-total analysis system".
[0034] The chamber advantageously is filled with chemical and/or
biological reaction systems, such as nutrient solution, cell
cultures, physiological salt solutions, suspending agent and/or
chemical reaction solutions. The micropump provides for a transport
or movement of the reaction solutions inside the chamber and thus
substantially acts in the form of a microstirrer.
[0035] It is conceivable that in one embodiment chemical reactions
are performed or peptides are modified in the microreactor chamber.
It is also conceivable that cells are grown in such structure. An
encapsulation of substances or cells and the transport thereof in
this system also is possible when using long-chain hydrocarbons as
pumping liquid. In this case, the cells are enclosed in aqueous
droplets which are emulsified in the organic pumping liquid.
[0036] The microreactor chamber advantageously is filled or
evacuated by means of a microdosing system. The microdosing system
constitutes for instance a piezo element, piezo actuator with
corresponding valves.
[0037] The micropump--with or without said microreactor
chamber--can also be integrated in a pumping structure or pumping
system comprising at least one pumping chamber and at least one
discharge chamber,. Advantageously, the pumping chamber opens into
the at least one pumping passage on at least one discharge opening.
The at least one pumping passage, in which the electrode device and
possibly a heating element are arranged, in turn advantageously
opens into the discharge chamber on at least one outlet opening.
The discharge chamber likewise can be used for receiving biological
and/or chemical reaction solutions, e.g. for growing cells.
[0038] The discharge chamber advantageously is connected with at
least one further passage, whereby the micropump can be used e.g.
for spreading substances or materials in the microsystem of the
pumping structure. The pumping chamber and the discharge chamber
advantageously are also connected via the at least one pumping
passage and the further passage. The further passage preferably can
constitute a measurement channel, reaction channel and/or supply
channel.
[0039] In general, the pumping chamber, the at least one pumping
passage, the discharge chamber and the further passage
advantageously form a closed circulation system, wherein the at
least one pumping chamber and the discharge chamber each include at
least one inlet and/or outlet passage for filling and/or evacuating
the circulation system.
[0040] The object of the invention also is solved by a use of the
pump according to claim 36 and a method with the features of claim
37.
[0041] Accordingly, the micropump with the features according to
claims 1 to 35 is used for pumping liquids, in particular in closed
circulation systems.
[0042] The method of the invention for pumping a liquid in a
micropump according to at least one of claims 1 to 35 is
characterized by the formation of an alternating electric field and
a temperature gradient in the liquid to be pumped between at least
two electrodes, wherein the pumping direction is controlled by the
frequency of the alternating electric field applied and/or by the
temperature gradient in the at least one pumping passage.
[0043] The method of the invention advantageously is also
characterized by the formation of an additional temperature
gradient in the at least one pumping passage by a heating element,
wherein the temperature gradient reaches into the region of the
alternating electric field between the electrodes or wholly or
partly overlaps with the same.
[0044] The invention will be explained in detail below by means of
several embodiments with reference to the Figures, in which:
[0045] FIG. 1: shows a schematic representation of a first
embodiment of the micropump in accordance with the invention;
[0046] FIG. 2: shows a schematic representation of a second
embodiment of the micropump in accordance with the invention;
[0047] FIG. 3: shows a schematic representation of a third
embodiment of the micropump in accordance with the invention;
[0048] FIG. 4: shows a schematic representation of a closed
circulation system with the micropump in accordance with the
invention;
[0049] FIG. 5: shows a modelled representation of the temperature
profile (indicated in Kelvin) in a closed circulation system with
the micropump in accordance with the invention;
[0050] FIG. 6: shows a modelled representation of the course of the
force of flow (indicated in N/m.sup.3) in a closed circulation
system with the micropump in accordance with the invention;
[0051] FIG. 7: shows a modelled representation of the flow rate
(indicated in m/s) in a closed circulation system with the
micropump in accordance with the invention;
[0052] FIG. 8: shows a first diagram with the experimentally
obtained representation of the functional relation of applied
frequency and velocity in dependence on the conductivity of the
liquid to be pumped;
[0053] FIG. 9: shows a second diagram with the experimentally
obtained representation of the functional relation of applied
electrode voltage and velocity;
[0054] FIG. 10: shows a third diagram with the experimentally
obtained representation of the functional relation of heating power
and velocity;
[0055] FIG. 11A: shows a fourth embodiment with an angled pumping
passage;
[0056] FIG. 11B: shows a detailed view of the fourth embodiment of
the invention;
[0057] FIG. 12: shows a representation of a simulation result of
the fourth embodiment;
[0058] FIG. 13A: shows a fifth embodiment of the invention with an
angled pumping passage;
[0059] FIG. 13B: shows a detailed representation of the fifth
embodiment;
[0060] FIG. 14: shows a schematic representation of a sixth
embodiment;
[0061] FIG. 15: shows a representation of a simulation result
(temperature, field strength) of the sixth embodiment;
[0062] FIG. 16: shows a representation of a simulation result
(pressure distribution in the central region) of the sixth
embodiment;
[0063] FIG. 17: shows a schematic representation of a seventh
embodiment;
[0064] FIG. 18: shows a representation of a simulation result of
the seventh embodiment;
[0065] FIG. 19: shows a representation of a simulation result of
the seventh embodiment;
[0066] FIG. 20: shows a schematic representation of an eighth
embodiment;
[0067] FIG. 21: shows a simulation result of an embodiment without
a flow guiding means (wedge-shaped structure);
[0068] FIG. 22: shows an enlarged representation of a detail of
FIG. 21;
[0069] FIG. 23: shows a simulation result of an embodiment with a
flow guiding means;
[0070] FIG. 24: shows an enlarged representation of a detail of
FIG. 23.
[0071] FIG. 1 shows the schematic structure of a first embodiment
of the electrohydrodynamic micropump 1 of the invention, comprising
a pumping passage 2 and an electrode device 6. In the pump, the
electrode device 6 is arranged, which includes a first electrode 4
and a second electrode 5. The electrodes 4, 5 preferably are made
of materials with different thermal conductivities. The alternating
electric field generated and the temperature gradient generated
between the electrodes exert a force on the charge carriers and/or
dipoles of the liquid and thus generate a transport of liquid in or
against the illustrated flow direction 7.
[0072] In FIG. 1, only a linear pumping passage 2 is shown. In
principle, it is possible to provide a plurality of pumping
passages 2, which also can have more complex shapes. For reasons of
clarity, the passages illustrated in the Figures are shown in one
plane, and it is possible to spatially arrange the individual
components of the device. Thus, e.g. a plurality of pumping
passages 2 might be realized in a three-dimensional arrangement
with respect to each other.
[0073] In FIG. 1, the two electrodes 4, 5 are located opposite each
other on both sides of the pumping passage 2, with other
arrangements also being possible. In a further embodiment (see FIG.
11) it is shown that the electrodes can also be arranged in some
other way relative to the pumping passage 2 and relative to each
other. In the Figures, the electrodes 4, 5 also are shown only
schematically.
[0074] In a passage with two opposed, flat electrodes 4, 5 of the
same size and construction, a temperature maximum is obtained
exactly in the middle between the electrodes 4, 5 when current
flows between the electrodes 4, 5. The production of heat by the
electric current is in equilibrium with a discharge of heat via the
passage walls, via the electrodes 4, 5 themselves and via the
adjoining liquid in the passage, which lies outside the electric
field (see also FIGS. 12 and 15). This means that temperature
gradients are obtained in the vicinity of the passage walls and in
the surroundings of the electrodes.
[0075] The temperature gradients in the vicinity of the passage
wall are vertical to the electric field lines and therefore have no
effect (apart from the fact that a flow over the walls would not be
possible). The temperature gradients in the surroundings of both
electrodes extend parallel to the electric field and therefore
interact with the electric field. There is produced a flow pointing
away from the electrodes (at low frequencies).
[0076] In a symmetrical passage with two flat electrodes, a local
circular flow can be obtained above the electrodes, but no
resultant flow, as the forces in both directions should be equal.
For producing a resultant flow, e.g. two approaches can be used:
[0077] 1. the temperature field in the vicinity of an electrode is
influenced, e.g. by [0078] a. a heating element, so that the
temperature gradient is reduced or even inverted at this point (the
heat input of the heater then dominates the temperature field).
[0079] b. the electrodes themselves, which have a different size
and/or are made of a material with a different thermal
conductivity. [0080] 2. incorporation of an inlet in the passage
(see T-passage or angled pump), which is located between the two
electrodes and through which the medium can flow in both directions
over the electrodes. In the latter case, both temperature gradients
above the electrodes are equally used.
[0081] As shown in approach 2, it is for instance important for
generating a pumping force, how temperature gradient and electric
field lines are located relative to each other. Only if the same
extend substantially parallel, is a force exerted on the medium. In
a T-passage, no force therefore is obtained in the direction of the
inflow passage.
[0082] FIG. 2 schematically illustrates the structure of a second
embodiment of the electrohydrodynamic micropump 1 with a pumping
passage 2, a meander-shaped heating element 3 arranged in the
pumping passage, and an electrode device 6 with the electrodes 4
and 5. By generating an additional temperature gradient by means of
the heating element 3, the transport of liquid is supported.
[0083] A third embodiment of the pump in accordance with the
invention is shown in FIG. 3, in which the second electrode 5 is
combined with a portion of the heating element 3 to form a
component 8. Broadening the first electrode 4 leads to an improved
dissipation of heat and an increase of the temperature gradient and
hence a higher flow rate.
[0084] A further embodiment of the micropump in accordance with the
invention is incorporated in a circulation system 13 shown in FIG.
4. The circulation system 13 comprises the pumping chamber 9, the
pumping passage 2 with the heating element 3 and the electrode
device 6, the discharge chamber 10 and the further passage 11,
wherein the further passage 11 can contain a chemical or biological
system for practical applications. At the discharge opening 2a, the
pumping chamber 9 opens into the pumping passage 2 at right angle,
which pumping passage merges into the discharge chamber 10 at a
right angle at the outlet opening 2b. The passage 11 likewise is
arranged at right angles with respect to the pumping chamber 9 and
the discharge chamber 10.
[0085] FIG. 4 shows a substantially rectangular, planar system of
passages. In principle, it is also possible that the passages have
more complex shapes and are spatially arranged with respect to each
other.
[0086] In the embodiment shown here, the distance between the
pumping passage 2 and the passage 11 is 100 to 2000 .mu.m,
preferably 1100 .mu.m, and between the pumping chamber 9 and the
discharge chamber 10 it is 50 to 1500 .mu.m, preferably 900
.mu.m.
[0087] These values only are exemplary and can also differ in other
embodiments, corresponding to the object.
[0088] In the present embodiment, the circulation system 13 is
filled at the inlet passages 12 with an aqueous liquid with a
conductivity of 0.01 S/m and a relative permittivity of 80. Upon
filling, the passages 12 are closed, so that no further liquid
movement can occur in these directions. The pumping passage 2 has a
height between 20 and 100 .mu.m, preferably of 64 .mu.m.
[0089] As shown in FIG. 4, the heating element 3 constitutes a
meander-shaped heating coil. By applying a voltage (d.c.) of 1.5 V,
the liquid is heated to a temperature of more than 312 K, whereby a
temperature gradient is formed in the pumping passage 2 in
accordance with the model shown in FIG. 5.
[0090] The electrode device 6 includes two electrodes 4, 5
extending flat on the ground with a thickness of 10 to 1000 nm,
preferably 100 nm, whereby the liquid can flow over the electrodes
without an additional resistance. By applying an alternating
voltage (a.c.) of 30 Vrms with a frequency of 300 kHz, a strong
electric field is obtained between the electrodes. In accordance
with the model shown in FIG. 6, the liquid in the electric field
experiences a force up to 1169 N/m.sup.3 in the direction of a
lower conductivity or lower temperatures and thus is moved along
the pumping passage 2 in flow direction 7. A circular flow is
formed from the pumping passage 2 through the discharge chamber 10
into the passage 11 and the pumping chamber 9. In the pumping
passage 2 and in the passage 11, the flow rate exhibits the highest
values of up to 1.646e*10.sup.-4 m/s in accordance with the model
of FIG. 7.
[0091] FIG. 8 shows frequency spectra of liquids with different
conductivities at an applied electrode voltage of 40 V and a
heating power of 0.187 mW. As can be taken from the diagram, the
velocity is constant over a wide frequency range. With increasing
frequency, there will be a decrease in the pumping velocity and
finally, at a liquid-specific value of 0 .mu.m/s, a reversal of the
pumping direction.
[0092] In FIG. 9, the pumping power or velocity of two liquids with
different conductivities is graphically represented in dependence
on the applied electrode voltage. The measurements are made at a
heating power of 0.187 mW and a frequency dependent on the
conductivity of the liquid, wherein a frequency of 1 MHz is
employed for a first liquid with a conductivity of 1117 .mu.S/cm,
and a frequency of 3 MHz is employed for a second liquid with a
conductivity of 706 .mu.S/cm. The velocity of the liquid to be
pumped increases proportional to the applied electrode voltage.
[0093] FIG. 10 shows the influence of the heating power on the
velocity of the liquid to be pumped, with a proportional relation
being recognizable here as well. The velocity increases with
increasing heating power. The measurements are made at an electrode
voltage of 40 Vrms and at a frequency dependent on the conductivity
of the liquid, wherein here as well a frequency of 1 MHz is
employed for a first liquid with a conductivity of 1117 .mu.S/cm,
and a frequency of 3 MHz is employed for a second liquid with a
conductivity of 706 .mu.S/cm.
[0094] In FIGS. 11 to 24, further embodiments of the invention are
shown, in which the pumping passages 2 include a plurality of
segments 21, 22, 23.
[0095] Subsequently, in particular two variants of an angled,
electrohydrodynamic micropump (subsequently briefly referred to as
"angled micropump") will be described. FIG. 11A schematically shows
the structure of a first variant. There is used a T-passage, which
includes three linear segments 21, 22, 23. The inlet 21 (here also
referred to as measurement channel) merges into two outlets 22, 23,
which are shown on an enlarged scale in FIG. 11B. The point of
maximum force action is located directly at the bifurcation of the
T-passage. In this embodiment, the passage height is 60 .mu.m.
[0096] In FIG. 11A, a substantially T-shaped arrangement of three
segments 21, 22, 23 is shown, which also is referred to as angled
arrangement. By way of example, the linear segments 21, 22, 23
arranged in one plane are located at an angle of 90.degree. with
respect to each other, with other arrangements also being
conceivable. In particular, the segments 21, 22, 23 also can be
spatially arranged with respect to each other.
[0097] At the transition from the first segment 21 (measurement
channel) to the two other segments 22, 23, a wedge-shaped flow
guiding means 30 is arranged on both sides of the measurement
channel, which guides the flow from the measurement channel 21
still a bit further into the two segments 22, 23, which are
slightly constricted at the same time. In flow direction, the
channel then expands again behind the segment 22, 23.
[0098] Two electrodes 4, 5 are arranged flat on the wall of the
channel structure, substantially in the vicinity of the inlet
through the measurement channel 21 and the two outlets 22, 23. A
voltage (here e.g. an alternating voltage of 40 Vrms, 1 MHz)
between the electrodes generates an electric field, and a current
flows between the electrodes 4, 5. The flow of current heats the
conductive solution in the segments 21, 22, 23 of the pumping
passage between the electrodes and effects a temperature gradient
pointing from the electrodes to the middle of the inlet
passage.
[0099] In FIG. 12, the temperature gradients are illustrated as
simulation result of a similar geometrical configuration. In this
embodiment, the flow guiding means 30 differ from those of FIG.
11A. The temperature gradients are represented as arrows. The
conductivity is 500 mS/m, and the electrode voltage is 30 Vrms.
[0100] In combination with the electric field, a force is exerted
on the liquid, parallel to the electric field lines and against the
direction of the temperature gradients, i.e. in the direction of
the two outlet passages (see FIG. 11A, 11B).
[0101] The two wedge-shaped flow guiding means 30, which will be
discussed in detail below, constrict the transition to the segments
22, 23 of the outlet passages, in order to minimize a local
circular flow. By way of experiment, flow rates of about 25 .mu.m/s
can be measured in the measurement channel 21.
[0102] In FIG. 13A, a further embodiment is shown, whose flow
guidance substantially corresponds to the embodiment of FIG. 11A,
so that reference is made analogously to the corresponding
description.
[0103] In the embodiment of FIG. 13A, the electrodes 4, 5 are
arranged lying flat on the ground, wherein the electrodes 4, 5,
however, extend into the two segments 22, 23 of the outlet
passages. In the embodiment of FIG. 11A, on the other hand, the
electrodes 4, 5 were arranged in the wall. FIG. 13B shows an
enlarged representation of the T-shaped region. In such an
arrangement, a flow rate of about 100 .mu.m/s could be measured in
the measurement channel 21, i.e. a velocity higher by a multiple
than in the embodiment of FIG. 11A. The power supply to the
electrodes 4, 5 was effected like in the embodiment of FIG.
11A.
[0104] The measurement channel 21 of the angled micropump guides
the liquid to be pumped between the electrodes 4, 5 such that it
flows in rather vertical to the electric field lines (see FIGS. 12
and 15 to 21), while the orientation of the segments 21, 22 of the
outlet passage ensures an outflow rather parallel to the electric
field lines. The temperature gradient in the region of the electric
field should be rather steep and point from the outlet passage in
the direction of the middle of the inlet passage.
[0105] As shown in FIGS. 14 to 19, the passage geometries can be
varied, wherein at least one temperature gradient is obtained in
the vicinity of the electric field, which extends parallel to the
electric field and parallel to the outlet passage, and further
temperature gradients have no effect, because they are either
vertical to the electric field (e.g. inlet passage) or because the
passage wall prevents a flow (e.g. the passage angled by 90.degree.
in FIG. 17-19).
[0106] A further embodiment is shown in FIG. 14. The same includes
intersecting passages. The first segment 21 is represented
vertical, from which two segments extend at right angles. In the
representation of FIG. 14, the inflow is effected from above and
from below through the linear segment 21.
[0107] In this embodiment, the electrodes 4, 5 are located in the
vicinity of the points where the two segments 22, 23 open into the
first segment 21. The electrodes 4, 5 are arranged flat on the
wall, so that the medium can flow over the same. They lie flat on
the wall, in the bottom or on the ceiling of the outlet passages
22, 23, alone or in combination. It is also possible to form the
electrodes 4, 5 as a fine grating, which extends through the
cross-section of the outlet passages and can be traversed by the
medium.
[0108] In FIG. 15, the configuration of FIG. 14 is simulated. The
electrodes 4, 5 are only shown as lines. The inflow of the flowing
medium is effected vertical, the outflow parallel to the electric
field lines. The temperature gradients (arrows) point to the middle
of the segment 21 for the inlet passage.
[0109] In FIG. 16, the pressure field for this configuration is
shown in the central region of a pumping system. The pressure
gradient is greatest above the electrodes.
[0110] In order to move the liquid in the passages with a certain
velocity, the pump must pump against the flow resistance of the
passage walls. Before the point of the pumping effect, a negative
pressure is obtained, because the pump sucks in the medium
(liquid), and behind said point an excess pressure, because the
pump urges the medium further through the passage. What is
essential is the pressure difference. For the model calculation,
the marginal condition was assumed that the pressure at the passage
ends is 0. Hence, the inlet and outlet passages are at the same
pressure level and short-circuited, so to speak. FIG. 16 only is a
section of the model, which is why the values at the edges cannot
be seen. The calculated model is greater than in FIG. 16, i.e. the
passages are much longer. Thus, the medium can cover an appropriate
distance, and the pump hence must work against the corresponding
flow resistance. In this way, realistic flow velocities have been
calculated. For very short passages, the calculated velocity would
be distinctly higher.
[0111] On a representation of simulation results of the entire
model, details would not easily be visible. What is important in
FIG. 16 is the pressure difference above the electrodes 4, 5.
[0112] The number of the passages 21, 22, 23 can be reduced to one
segment 21 for the inlet and one segment for the outlet. In FIG.
17, such configuration is shown for an orthogonal arrangement. The
electrodes 4, 5 are arranged in the region of the second segment 22
and on the opposite wall of the first segment 21. The inflow is
effected vertical and the outflow parallel to the electric field
lines.
[0113] In FIG. 18, a simulation result of the configuration of FIG.
16 is shown. The electrodes are only represented as lines. The
inflow of the flowing medium is effected vertical, the outflow
parallel to the electric field lines. The temperature gradients
(arrows) point to the middle of the segment 21 for the inlet
passage.
[0114] In FIG. 19, the pressure field is shown for this
configuration. The highest pressures are present in the first
segment 21, so that there is a flow into the segments 22, 23 which
extend from the first segment 21.
[0115] As already explained above, the passages can also be
expanded spatially into the third dimension. In FIG. 20, a
rotationally symmetric body with the axis of rotation along the
outlet passage is illustrated with two segments 22, 23. The inlet
passage is formed by a disk-shaped segment. The inlet segment 21
can serve as reaction chamber and also include more than two
electrodes. The electrodes can be activated by different,
phase-shifted signals.
[0116] In the illustrated embodiments of the angled micropumps, the
arrangement of the segments of the pumping passages (inlet and
outlet passages) 21, 22, 23 is such that an inflow is effected
vertical and an outflow parallel to the electric field lines.
Depending on the constructional variant, inlet and outlet passages
therefore are connected as follows: In the case of one inlet and
one outlet passage each with an angle of about 90.degree. (FIG.
17). In the case of one inlet and two outlet passages (FIG. 11A) or
two inlet passages and one outlet passage with a T-shaped
bifurcation, and in the case of two inlet and outlet passages each
with a 90.degree. intersection. (FIG. 14, 17).
[0117] In the respective transition region from inlet to outlet
passage (angle, bifurcation, intersection), an electric field is
generated by two electrodes 4, 5, whose orientation satisfies the
above condition for the transport of liquid.
[0118] This embodiment does not require an asymmetric temperature
distribution between the electrodes 4, 5, which is generated by a
heating element or electrodes of different thermal
conductivity.
[0119] Subsequently, it will be described how the pumping effect
can be enhanced by an e.g. wedge-shaped flow guiding means for
shearing off a locally circulating flow (see FIG. 11A).
[0120] In particular on the inner edges of electrodes lying close
to each other, local circular flows can form (FIG. 21), which
always represent a loss of pumping power. FIG. 21 shows a
two-dimensional simulation model of an angled micropump without
wedge-shaped structure. The Figure shows the pressure (in Pa) and
the circular velocity field in the liquid. The velocity in the
measurement channel is 300 .mu.m/s. The conductivity is 236 mS/m,
and the electrode voltage is 30 Vrms.
[0121] Circular flows are obtained as soon as the forces acting in
the passage cross-section differ in amount or direction (FIG. 22).
FIG. 22 shows an enlarged view of the electrode edge. The acting
force varies greatly in the region above the electrode edge.
[0122] To prevent or restrict a circular flow, the passage has been
constricted at the point of the greatest force action (i.e. on the
inner edges of the electrodes) by a wedge-shaped structure such
that the return flow is largely sheared off (FIGS. 23 and 24). It
should be noted that the wedge-shaped structure, the flow guiding
means, is not a dielectric, but a hydrodynamic element.
[0123] FIG. 23 shows a two-dimensional model of an improved angled
micropump with a wedge-shaped structure as flow guiding means 30.
FIG. 23 shows the pressure (Pa) and the velocity field in the
liquid. The circular flows are largely prevented by protrusions in
the passage geometry. The velocity in the measurement channel was
quintupled to 1500 .mu.m/s. The conductivity is 500 mS/m, and the
electrode voltage is 30 Vrms.
[0124] Similar to FIG. 22, FIG. 24 shows an enlarged view of the
electrode edge of the model. The change of the acting forces is
smaller in the region above the electrode edge.
LIST OF REFERENCE NUMERALS
[0125] 1 electrohydrodynamic micropump [0126] 2 pumping passage
[0127] 2a discharge opening [0128] 2b outlet opening [0129] 3
heating element [0130] 4 first electrode [0131] 5 second electrode
[0132] 6 electrode device [0133] 7 flow direction [0134] 8
component of a combination of the second electrode 5 with portions
of the heating element 3 [0135] 9 pumping chamber [0136] 10
discharge chamber [0137] 11 further passage [0138] 12 inlet and/or
outlet passage [0139] 13 circulation system [0140] 21 first segment
of a pumping passage [0141] 22 second segment of a pumping passage
[0142] 23 third segment of a pumping passage [0143] 30 flow guiding
means
* * * * *