HEAT EXCHANGERS

Abstract

Provided herein are air-to-air heat exchangers. In some embodiments, the air-to-air heat exchanger comprises at least one first air passageway extending between a first air inlet and a first air outlet; at least one second air passageway extending between a second air inlet and a second air outlet; at least one heat-conductive wall separating the at least one first air passageway from the at least one second air passageway; and at least one electrohydrodynamic device disposed in at least one of the first and second air passageways for enhancing airflow therein. Also provided herein is a method of using electrohydrodynamic devices to enhance airflow and efficiency of air-to-air heat exchangers.

Description

BACKGROUND OF THE DISCLOSURE

There is a need for energy-efficient air-to-air heat exchangers and methods that provides efficient heat exchange between airflows divided by one or more separation walls.

SUMMARY OF THE DISCLOSURE

Provided herein are air-to-air heat exchangers that are electrohydrodynamically enhanced. In some embodiments, the air to air heat exchanger comprises at least one first air passageway extending between a first air inlet and a first air outlet; at least one second air passageway extending between a second air inlet and a second air outlet; at least one heat-conductive wall separating the at least one first air passageway from the at least one second air passageway; and at least one electrohydrodynamic device disposed in at least one of the first and second air passageways for enhancing airflow therein.

In some embodiments, the at least one heat conductive wall comprises at least one essentially planar wall. In some embodiments, the at least one heat conductive wall comprises a plurality of essentially planar walls that are essentially parallel to one another. In some embodiments, the plurality of heat conductive walls are essentially equidistantly arranged.

In some embodiments, airflow in the first air passageway and airflow in the second air passageway are essentially in opposite direction.

In some embodiments, each electrohydrodynamic device comprises one or more emitter electrodes, one or more enhancer electrodes positioned downstream of the one or more emitter electrodes, and one or more collector electrodes positioned downstream of the one or more enhancer electrode. In some embodiments, the one or more emitter electrodes, the one or more enhancer electrodes, and the one or more collector electrodes extend essentially parallel to the heat conductive walls and essentially orthogonal to the airflow.

In some embodiments, the one or more emitter electrodes have a higher electric potential than the one or more enhancer electrodes, and the one or more enhancer electrodes have a higher electric potential that the one or more enhancer electrodes. In some embodiments, the one or more enhancer electrodes are grounded.

In some embodiments, the one or more enhancer electrodes are positioned closer to the one or more emitter electrode than to the one or more collector electrodes.

In some embodiments, the one or more emitter electrodes are separated from the closest heat conductive wall by an emitter-wall distance.

In some embodiments, the one or more enhancer electrodes and the one or more collector electrodes are attached to the heat conductive wall, and the heat conductive wall is dielectric. In some embodiments, the one or more enhancer electrodes and the one or more collector electrodes are made of heat conductive material.

In some embodiments, the heat conductive wall is electrically conductive and grounded, the one or more enhancer electrodes are separated from the closest heat conductive wall by an enhancer-wall distance, and wherein the one or more collector electrodes are separated from the closest heat conductive wall by a collector-wall distance.

In some embodiments, the collector-wall distance is smaller than the enhancer-wall distance. In some embodiments, the collector-wall distance and the enhancer-wall distance are both smaller than the emitter-wall distance.

In some embodiments, each electrohydrodynamic device further comprises one or more arrays of convection promoter electrodes positioned downstream of the one or more collector electrodes. In some embodiments, the one or more arrays of convection promoter electrodes extend essentially parallel to the heat conductive walls and essentially orthogonal to the airflow.

In some embodiments, the convection promoter electrodes are separated from the closest heat conductive wall by a promoter-wall distance of (h) that is smaller than any of the emitter-wall distance, enhancer-wall distance, and collector-wall distance. In some embodiments, the convection promoter electrodes within each array are separated from one another by a promoter-promoter distance (s) that is greater than the promoter-wall distance (h).

In some embodiments, each electrohydrodynamic device comprises two array of the convection promoter electrodes positioned between two adjacent heat conductive walls, wherein both arrays and have same electrical potential.

In some embodiments, one array of convection promoter electrodes of a first electrohydrodynamic device and one array of convection promoter electrodes of a second electrohydrodynamic device are disposed on opposite side of a heat conductive wall with an offset distance (u), and have opposite electric potentials.

In some embodiments, the promoter-promoter distance (s) is no less than 2h+u, and wherein the promoter-promoter distance (s) is no greater than X(2h+u), wherein X ranges between 1.5 and 2.0.

In some embodiments, the at least one first air passageway, the at least one second air passageway, the at least one heat-conductive wall, and the at least one electrohydrodynamic device are enclosed in a housing. In some embodiments, the housing comprises the first air inlet, the first air outlet, the second air inlet, and the second air outlet.

In some embodiments, the first air inlet is configured to receive air from atmosphere, and the first air outlet is connected to a desiccator of a ventilation system. In some embodiments, the second air inlet is configured to receive exhaust air from the ventilation system, and wherein the second air outlet is configured to release air into atmosphere. In some embodiments, a temperature of air entering into the first air inlet is higher than a temperature of air exiting the second air outlet.

Also provided herein is a method of electrohydrodynamically enhancing in air-to-air heat exchangers. In some embodiments, the method comprises activating at least one electrohydrodynamic device disposed in air passageways of the air-to-air heat exchanger. Each electrohydrodynamic device comprises one or more emitter electrodes, one or more enhancer electrodes positioned downstream of the one or more emitter electrodes, and one or more collector electrodes positioned downstream of the one or more enhancer electrodes. The activation comprises creating gradient electric potential differential from the emitter electrodes to the enhancer electrodes and to the collector electrodes.

In some embodiments, the activation comprises coupling the emitter electrodes with a source of positive electric potential, coupling the collector electrode with a source of negative electric potential, and grounding the enhancer electrodes.

Other features and technical effects of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments, are given by way of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the disclosed air-to-air heat exchangers and method of electrohydrodynamically enhancing in air-to-air heat exchangers are set forth with particularity in the appended claims. A better understanding of the features of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the present disclosure are utilized, and the accompanying drawings of which:

FIG. 1A-1C graphically illustrate configurations of heat exchangers suitable for use in the present disclosure: pipe-based (1A), cell-based (1B), and plate-based (1C);

FIG. 2A-2B graphically illustrate general concept of an ionic wind generator (2A) and a cross-sectional view of a two-stage EHD device (2B), with the schematic diagram in 2A illustrating gas velocity profiles before and after electrohydrodynamic enhancement;

FIG. 3 graphically illustrates configuration of an ionic wind generator with the enhancer electrode;

FIG. 4A-4B schematically illustrate ionic wind generators with enhancer electrodes embedded into dielectric rectangular duct with one (4A) and two (4B) emitter electrode of corona discharge in the form of elongated members. Thin lines denote electrical couplings. The case of positive corona is illustrated as a non-limiting example;

FIG. 5 schematically illustrates configuration of ionic wind generator embedded in a pipe-based heat exchanger. Thin lines denote electrical couplings;

FIG. 6 schematically illustrates the arrangement of a plurality of ionic wind generators of the preferred configuration embedded into plate-based heat exchanger with electrically non-conductive plates. Electrical couplings are not shown. The case of positive corona sign is provided as a non-limiting example;

FIG. 7A-7B schematically illustrate configurations of ionic generators of bulk air wind embedded between the neighboring conductive plates of plate-based heat exchanger in the cross-section view with one emitter electrode (7A) and two emitter electrodes (7B) of the assisted corona discharge. Emitter electrodes are in the form of elongated members, enhancer and collector electrodes are in the form of elongated members as a non-limiting example;

FIG. 8 schematically illustrates the arrangement of a plurality of short-range ionic wind generators of the preferred configuration embedded into plate-based heat exchanger with electrically conductive plates. Electrical couplings are not shown; and

FIG. 9 schematically illustrate the arrangement of a plurality of ionic generators of bulk air flow with alternating signs of corona discharge and a plurality of series of short-range ion wind generators embedded into plate-based heat exchanger with electrically conductive plates. Ionic wind generators of bulk air flow which configurations are given in FIG. 9 are simply denoted with the sign of (emitter electrode) of corona discharge. Electrical couplings are not shown.

It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed device or method which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure is described in greater detail below. This description is not intended to be a detailed catalog of all the different ways in which the present disclosure may be implemented, or all the features that may be added to the present disclosure. For example, features illustrated with respect to one embodiment may be incorporated into other embodiments, and features illustrated with respect to a particular embodiment may be deleted from that embodiment. In addition, numerous variations and additions to the various embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure, which do not depart from the present disclosure. Hence, the following specification is intended to illustrate some particular embodiments of the present disclosure, and not to exhaustively specify all permutations, combinations and variations thereof.

CERTAIN TERMINOLOGY

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which the claimed subject matter belongs. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of any subject matter claimed.

In the present disclosure, the use of the singular includes the plural unless specifically stated otherwise. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. In the present disclosure, the term “or” means “and/or” unless stated otherwise. Furthermore, use of the term “including” as well as other forms, such as “include”, “includes,” and “included,” is not limiting.

As used in the present disclosure, ranges and amounts are sometimes expressed as “about” a particular value or range. About also includes the exact amount. Hence “about 2.0” means “about 2.0” and also “2.0”. Generally, the term “about” includes an amount that would be expected to be within experimental error. For example, the term “about” in some embodiments refers variation of ±1%, ±2%, ±3%, ±4%, ±5%, ±6%, ±7%, ±8%, ±9%, or ±10%. In some embodiments, the term “about” refers to variation of ±5%. In some embodiments, the term “about” refers to variation of ±10%.

As used in the present disclosure, positional relationship in some embodiments is refers to as “essentially” a particular geometric definition. “Essentially” also includes the exact geometric definition. Hence “essentially planar” includes “planar”, “essentially parallel” includes “parallel”, “essentially orthogonal” includes “orthogonal”, and “essentially equidistant” includes “equidistant”. Generally, the term “essentially” includes an amount that would be expected to be within acceptable variation.

For example, the term “essentially planar” in some embodiments refers to a surface that is at least 99% planar, at least 98% planar, at least 97% planar, at least 96% planar, at least 95% planar, at least 94% planar, at least 93% planar, at least 92% planar, at least 91% planar, at least 90% planar, at least 85% planar, or at least 80% planar, In some embodiments, the term “essentially planar” refers to a surface that is at least 95% planar. In some embodiments, the term “essentially planar” refers to a surface that is at least 90% planar. In some embodiments, the term “essentially planar” refers to a surface that is at least 85% planar. In some embodiments, the term “essentially planar” refers to a surface that is at least 80% planar.

Further, the term “essentially parallel” and/or the term “essentially orthogonal” refers to a variation of within 1°, within 2°, within 3°, within 4°, within 5°, within 6°, within 7°, within 8°, within 9°, within 10°, within 11°, within 12°, within 13°, within 14°, within 15°, within 20°, within 25°, or within 30°. In some embodiments, term “essentially parallel” and/or the term “essentially orthogonal” refers to a variation of within 5°. In some embodiments, term “essentially parallel” and/or the term “essentially orthogonal” refers to a variation of within 10°. In some embodiments, term “essentially parallel” and/or the term “essentially orthogonal” refers to a variation of within 15°. In some embodiments, term “essentially parallel” and/or the term “essentially orthogonal” refers to a variation of within 20°. In some embodiments, term “essentially parallel” and/or the term “essentially orthogonal” refers to a variation of within 25°. In some embodiments, term “essentially parallel” and/or the term “essentially orthogonal” refers to a variation of within 30°.

Still further, the term “essentially equidistant” refers to a variation of an equidistant configuration that would be expected to be within acceptable range. For example, the term “essentially equidistant” in some embodiments refers an equidistant configuration having variation of ±1%, ±2%, ±3%, ±4%, ±5%, ±6%, ±7%, ±8%, ±9%, ±10%, ±15%, ±20%, or ±25%. In some embodiments, the term “about” refers to variation of ±5%. In some embodiments, the term “about” refers to variation of ±10%. In some embodiments, the term “about” refers to variation of ±15%. In some embodiments, the term “about” refers to variation of ±20%. In some embodiments, the term “about” refers to variation of ±25%.

As used in the present disclosure, the term “conventional air pump” refers to a device or system that produces airflow without electrohydrodynamic enhancement or ionic wind generation. Examples of conventional air pumps include, but are not limited to, traditional electric fans, mechanical blowers, sources of vacuum, sources of compressed air/gas, etc.

As used in the present disclosure, the term “upstream” and “downstream” refer to positional relationships according to bulk airflow within a passageway, in which upstream is closer to the inlet of the airflow/passageway, and downstream is closer to the outlet of the airflow/passageway.

Air-to-Air Heat Exchangers

Heat exchangers are apparatuses built to provide efficient heat transfer from one medium to another. Heat transfer generally occurs from a region of high temperature to another region of lower temperature. In a typical air-to-air heat exchanger, two gas streams with different temperatures are separated by a solid wall to prevent their mixing. In operation of air-to-air heat exchangers, heat transfer from the first gas stream (high temperature) to the second gas stream (low temperature) occurs in three stages: (1) heat is transferred from the first gas stream to the adjacent (first) surface of the wall, (2) heat is transferred from the first surface to the second surface of the wall adjacent to the second gas stream, and (3) heat is transferred from the second surface to the second gas stream.

During the second stage of this process, heat is generally transferred via the solid wall by conduction, sometimes referred as heat diffusion. To achieve a high heat transfer rate, the wall material for heat exchangers is highly heat conductive (e.g. a metal) and its thickness is generally not significantly greater than the minimal value required for the mechanical strength and integrity of the apparatus. As gases are generally poor heat conductors, heat transfer between wall surfaces and gas by conduction in stages (1) and (3) is small compared to that by forced convection, such as gas flows generated by conventional air pumps. However, the lower part of a thin gas boundary layer adjacent to the wall surface, where the gas velocity approaches zero at the wall surface.

One common application of air-to-air heat exchangers is in heat recovery ventilation systems, or climate chambers/air treatment chambers, such as those associated with various enclosed spaces in a building or green house. To increase the energy efficiency of heating and cooling, builders have used better construction techniques and materials to greatly reduce air leaks into and out of a building. In some buildings, this natural air infiltration now replaces inside air every 4 to 10 hours, compared to every 30 minutes decades ago.

While some air tight buildings or greenhouses reduce the costs of heating and cooling, a reduction in the outside airflow entering the building sometimes lead to problems with inside air quality. Some of the most common quality issues are excess humidity, carbon dioxide, and pollutants that are produced by human habitation (cooking, cleaning, breathing, combustion, etc.), as well as the chemicals that off-gas from building materials. In some hermetic greenhouses with low air changes per hour (ACH), the evapotranspiration by plants increases the relative humidity (RH) of air to values not favorable for plant growth. Moreover, in such low ventilated greenhouses operating in warm climates and thus requiring the cooling, solar radiation incoming to the greenhouse enclosure sometimes leads to a temperature increase above values optimal for plant growth even if an infra-red radiation protective glass or film is used.

In a classic heat recovery ventilation system, both the exhaust air from a compartment air-conditioned by some means and the incoming fresh air are delivered to an air-to-air heat exchanger driven by conventional air pumps, where the temperature of the warmer air decreases and the temperature of the cooler air increases. As a result, the incoming air is pre-conditioned by the exhaust air, which leads to a reduction in the cooling or heating load on the air conditioning system and thus in energy consumption, rather than just discharging air conditioned air out to the atmosphere. In practice, achieving higher values of temperature transfer efficiency requires higher values of the heat transfer area of the wall and the velocity of bulk air flow.

Configurations of heat exchangers disclosed herein include: (1) pipe-based, (2) cell-based, and (3) plate-based, which are schematically illustrated in FIGS. 1A-1C. Referring first to FIG. 1A, a pipe-based air-to-air heat exchanger (10) includes at least one first air passageway (12) extending between a first air inlet (14) and a first air outlet (16), at least one second air passageway (18) extending between a second air inlet (20) and a second air outlet (22), and at least one heat-conductive wall (24) separating the at least one first air passageway (12) from the at least one second air passageway (18). In the non-limiting embodiment shown in FIG. 1A, airflow in the at least one first air passageway (12) is essentially orthogonal to airflow in the at least one second air passageway (18). However, in other embodiments of the present disclosure (not shown), airflow in the at least one first air passageway (12) is opposite to airflow in the at least one second air passageway (18). The heat conductive walls (24) in the pipe-based air-to-air heat exchanger (10) are tubular walls. In the non-limiting embodiment shown in FIG. 1A, the tubular walls have an oval cross-sectional profile. In other embodiments, the tubular walls have circular, rectangular, or square cross-sectional profile.

Turning now to FIG. 1B, a cell-based air-to-air heat exchanger (10) includes at least one first air passageway/cell (12) extending between a first air inlet (14) and a first air outlet (16), at least one second air passageway/cell (18) extending between a second air inlet (20) and a second air outlet (22), and at least one heat-conductive wall (24) separating the at least one first air passageway (12) from the at least one second air passageway (18). In the non-limiting embodiment shown in FIG. 1A, airflow in the at least one first air passageway/cell (12) is essentially orthogonal to airflow in the at least one second air passageway/cell (18). However, in other embodiments of the present disclosure (not shown), airflow in the at least one first air passageway (12) is opposite to airflow in the at least one second air passageway (18). The heat conductive walls (24) in the cell-based air-to-air heat exchanger (10) are essentially planar, and essentially parallel walls. In the non-limiting embodiment shown in FIG. 1A, the heat conductive walls (24) are essentially equidistantly arranged. In other embodiment, the essentially planar walls have varying wall-to-wall distances. In the embodiment shown in FIG. 1B, the air passageways/cells have a triangular cross-sectional profile. In other embodiments, the air passageways/cells have rectangular or square cross-sectional profile.

Referring now to FIG. 1C, a plate-based air-to-air heat exchanger (10) includes at least one first air passageway (12) extending between a first air inlet (14) and a first air outlet (16), at least one second air passageway (18) extending between a second air inlet (20) and a second air outlet (22), and at least one heat-conductive wall (24) separating the at least one first air passageway (12) from the at least one second air passageway (18). In the non-limiting embodiment shown in FIG. 1A, airflow in the at least one first air passageway (12) is essentially orthogonal to airflow in the at least one second air passageway (18). However, in other embodiments of the present disclosure (not shown), airflow in the at least one first air passageway (12) is opposite to airflow in the at least one second air passageway (18). The heat conductive walls (24) in the cell-based air-to-air heat exchanger (10) are essentially planar, and essentially parallel walls. In the non-limiting embodiment shown in FIG. 1A, the heat conductive walls (24) are essentially equidistantly arranged. In other embodiment, the heat conductive walls (24) have varying wall-to-wall distances.

Electrohydrodynamic Device

Ionic wind, also known as ion wind, corona wind, coronal wind, electric wind and electrohydrodynamic (EHD) wind, is the localized air flow induced by electrostatic forces linked to corona discharge arising at the external surface of an electrode with relatively “sharp” surface features, i.e. surface areas of relatively low radius of curvatures on which corona discharge occurs, which is generally referred to as the emitter electrode in the present disclosure. The relatively “sharp” surface features include, but are not limited to, needles, wedges, tips, edges, threads, spiks, barbs, blades, etc. In some embodiments, the radium curvature of the relatively “sharp” surface features on the emitter electrode approaches zero, such as for example needles and blades.

In use, the emitter electrode is at a high voltage relative to another electrode with relatively “blunt” surface features, i.e. surface areas of relatively high radius of curvatures on which corona discharge does not occur, which is generally referred to as the enhancer electrode and collector electrode in the present disclosure. The relatively “blunt” surface features include, but are not limited to, flat surfaces, smooth cylindrical surfaces or sections thereof, smooth spherical surfaces or sections thereof, etc. In some embodiments, the radium curvature of the relatively “blunt” surface features on the emitter electrode approaches infinity, such as for example flat surfaces.

Referring now to FIG. 2, a basic EHD device 40 is illustrated as having one or more emitter electrodes (42) and one or more collector electrodes (46) positioned downstream of the one or more emitter electrodes (42). In the pipe-based embodiment shown in FIG. 2A, the one or more emitter electrodes (42) and the one or more collector electrodes (46) extend in a direction essentially orthogonal to the airflow. An electric potential differential is created between the emitter electrodes (42) and the collector electrodes (46). In the non-limiting embodiment shown in FIG. 2A, the emitter electrodes (42) are connected to a source of positive electric potential and the collector electrodes (46) are grounded. In other embodiments (not shown), the emitter electrodes (42) are connected to a source of positive electric potential and the collector electrodes (46) are connected to a source of negative electric potential.

Electric charges on electrodes generally reside on their external surfaces, which results in high strengths of electric field in the vicinity of their external surfaces. If this electric field strength exceeds a threshold value, known as the gradient of corona discharge inception potential, some air molecules are ionized through electron attachment or detachment in an area around the external surface of emitter electrodes (42). This area is referred to as the ionization zone (43).

Most of ionized air molecules produced by corona discharge have the same electric sign as that of the emitter electrodes (42). Within milliseconds after its ionization, i.e. loosing or gaining the electron, an air molecule attracts electrically polar air molecules (i.e. possessing the own electrical dipole moment) of water and some trace gases, which leads to the formation of a small charged molecular cluster that is called air ion. Air ions are repulsed from the like-charged emitter electrode (42), leave the ionization zone (43), and then drift towards the collector electrode (46), driven by the electric force in the electric field between the emitter electrodes and the collector electrodes, and the electric field of the air ion space charge. As illustrated in FIG. 2A, ionic wind is produced by the momentum transfer from the moving air ions to air molecules that collide with air ions, which enhances airflow within the air passageways.

In the electrohydrodynamic (EHD) device, the electric energy is directly converted to the energy of bulk air motion. This is in contrast to the process in a conventional air pump, such as for example an electric fan, in which electric energy is first converted to the kinetic energy of the fan and then to the energy of bulk air motion. The ion-driven air propulsion is achieved without moving mechanical parts. In some embodiments, the ion-driven air propulsion is controlled by the voltage of corona discharge. The present disclosure recognizes that a well-designed EHD device is more energy efficient and/or has better performance than electric fans and other conventional air pumps.

Generally, the operating voltage range for corona discharge lies between the corona onset voltage and breakdown voltage of air gap between emitter and collector electrodes. In practice, the highest acceptable voltage is in some cases smaller and determined by ozone production constraints. Ion wind is produced with positive, negative, or even alternate electrical polarity of emitter electrodes. Due to a slightly lower electrical mobility of positive air ions compared to that of negative ones, a higher ion wind velocity is sometimes achieved by positive corona discharge. The present disclosure recognizes that performance of EHD devices in air-to-air heat exchangers depends on factors including, but not limited to, the electric potential of the electrodes, position and configuration of the electrodes, device geometry, etc.

In addition, the present disclosure recognizes that the short-range nature of ionic wind is sometimes improved by using a plurality of EHD devices operating in sequence. Referring to FIG. 2B, two EHD devices (40, 40′) are illustrated as operating in sequence. The upstream EHD device 40 is illustrated as having one or more emitter electrodes (42) and one or more collector electrodes (46) positioned downstream of the one or more emitter electrodes (42). The downstream EHD device (40′) is illustrated as having one or more emitter electrodes (42′) positioned downstream of the one or more collector electrodes (46) of the upstream EHD device, and one or more collector electrodes (46′) positioned downstream of the one or more emitter electrodes (42′).

In the embodiment shown in FIG. 2B, the one or more emitter electrodes (42, 42′) and the one or more collector electrodes (46, 46′) extend in a direction essentially orthogonal to the airflow. An electric potential differential is created between the emitter electrodes (42) and the collector electrodes (46), and between the emitter electrodes (42′) and the collector electrodes (46′). In the non-limiting embodiment shown in FIG. 2B, the emitter electrodes (42, 42′) are connected to a source of positive electric potential and the collector electrodes (46, 46′) are grounded.

Enhancer Electrode

In some embodiments, the efficiency of EHD devices is increased by utilizing an enhancer electrode to refine the electric field and thus further enhance the range/velocity of the ionic wind. The enhancer electrode has an electric potential between the electric potential of the emitter electrode and the electric potential of the collector electrode, and as such serves to partially de-couple ionization and ion drift. Referring now to FIG. 3, a three-electrode EHD device (40) is illustrated as having one or more emitter electrode (42), one or more enhancer electrodes (44), and one or more collector electrodes (46). The one or more emitter electrodes (42), the one or more enhancer electrode (44), and the one or more collector electrodes (46) extend in a direction essentially orthogonal to the airflow. The enhancer electrode (44) is positioned downstream of the emitter electrodes (42) and upstream of the collector electrode (46). In the non-limiting embodiment shown in FIG. 3, the enhancer electrode (44) is closer in proximity to the emitter electrode (42) than the collector electrode (46).

In operation, ions created in the vicinity of the emitter electrode (42) drift towards the enhancer electrode (44); but instead of all ions being collected there, some ions continue to drift towards the collector electrode (46) due to a potential difference between the enhancer electrode (44) and the collector electrode (46). As a result, the distance traveled by the ions is increased without significant effect on the corona characteristics. In such a configuration, the overall ionic current from the discharge and the achieved air flow rate is significantly increased without altering the standard corona discharge to the primary collecting electrode.

Still referring to FIG. 3, in some embodiments where the ionic wind flows essentially parallel to the heat conductive dielectric wall (24), the enhancer electrode (44) is covered by an optional insulating dielectric barrier (45). It is contemplated that the insulating dielectric barrier (45) reduces the ion loss on the enhancer electrode (44). In some embodiments, the voltage of the enhancer electrode has a duty cycle, in which this voltage periodically matches the voltage of the emitter electrode (42). At the latter condition, the charge accumulated on the surface of dielectric barrier will be driven off and accelerated towards the collector electrode (46). Such intermittent discharges reduce the maximum charge accumulated on the barrier insulating dielectric barrier (45). The present disclosure recognizes that uncontrolled increase in this charge would result in either electrical breakdown of the dielectric barrier (45) or a decrease in the potential between the emitter electrode (42) and the enhancer electrode (44), which ultimately leads to termination of corona discharge.

In the embodiment shown in FIG. 3, the emitter electrode (42) is electrically coupled to the positive electrode of the first high voltage direct current (HVDC) source, the second electrode of which is grounded. The enhancer electrode (44) is grounded. The collector electrode (46) is electrically coupled to the negative electrode of the second HVDC source, the second electrode of which is grounded.

The present disclosure recognizes that the efficiency of ion acceleration on the second stage is higher, sometimes much higher, than that efficiency on the first stage, and as a result the overall efficiency of the EHD device having emitter-enhancer-collector electrodes (i.e. emitter-enhancer-collector EHD device) is higher compared to that of a reference EHD device having emitter-collector electrodes without the enhancer electrode (i.e. emitter-collector EHD device). In some embodiments, the energy consumption of the emitter-enhancer-collector EHD device is lower than that of the emitter-collector EHD device for the same exit flow velocity. In some embodiments, the thrust achieved by the emitter-enhancer-collector EHD device is higher than that of the emitter-collector EHD device for the same energy consumption. In some optimized setup, the emitter-enhancer-collector EHD device achieves both lower energy consumption and higher thrust compared to the emitter-collector EHD device.

The present disclosure recognizes the importance of efficient ionization, i.e. reducing ion loss, in particular on the enhancer electrode, for further enhancing airflow velocity and energy efficiency. In addition to the introduction of dielectric barriers to enhancer electrodes with variable potential as previously discussed, another feature contemplated in the present disclosure is the production of pulsed corona discharges repetitively to allow air ions produced during the pulse of voltage on the emitter electrode to be diverted to the collector electrode before reaching the enhancer electrode on which they recombine.

Pipe-Based Heat Exchangers Using Emitter-Enhancer-Collector EHD Enhancement

In some embodiments, the EHD devices disclosed herein, such as those using annular electrodes (e.g. shown in FIG. 2A), is incorporated into the pipe-based air-to-air heat exchanger, provided that the dielectric material of pipes or square ducts has high heat conductivity. Such materials, that are typically plastics with the inclusion of multi-sized particles of alumina (Al2O3) or a number of other suitable substances, are available in mass production. The bulk air propulsion achieved in the EHD devices is due to ionic wind jets produced in the vicinity of the internal surface of pipe or square duct. Additionally, those jets cause a significant increase in the coefficient of air-to-wall (convective) heat transfer. The latter increase is due to a significantly higher disturbance of boundary layer of air near the internal surface of pipe or duct in the enhanced air velocity profile (i.e. that after passing the ionic air propulsion generator) compared to that disturbance by the bulk air flow. The visual comparison of velocity profiles of bulk and enhanced air flows, i.e. those before and after the said generator is illustrated in the top diagram of FIG. 2A.

In the EHD enhanced pipe-based or duct-based air-to-air heat exchanger, the bulk air flow produced by EHD devices operating in sequence reduces, if not eliminates, the need for a conventional air pump, such as a traditional electric fan. Additionally, the heat transfer exchange between that air flow and the wall separating two air flows is sometimes significantly enhanced due to an increase in the coefficient of air-to-wall heat transfer, which ultimately leads to an increase in temperature transfer efficiency of the heat exchanger.

Referring now to FIG. 4A, a duct-based air-to-air heat exchanger (10) includes a dielectric heat conductive wall (24) having a square or rectangular cross-sectional profile, one or more emitter electrode (42), one or more enhancer electrode (44), and one or more collector electrode (46). Both the enhancer electrodes (44) and the collector electrodes (46) are in the shape of flat strips and with smooth edges to prevent parasitic corona discharge, arranged essentially orthogonal to the air flow direction and attached to internal surfaces of the duct walls (24). In some embodiments, the length of the enhancer electrodes (44) and the collector electrodes (46) are the same as the width of the wall surfaces to which the electrodes attach. The enhancer electrodes (44) and the collector electrodes (46) are mechanically secure to the heat conductive wall (24), and thermally coupled to the heat conductive wall (24), e.g. providing a layer of a highly heat conductive medium between electrodes and walls.

Turning to FIG. 4B, the second configuration of the duct-based air-to-air heat exchanger (10) differs from the first configuration illustrated in FIG. 4A by deploying two electrically coupled emitter electrodes (42). The feature of this modified configuration is a lower corona onset voltage. It is contemplated that the lower onset voltage is attributable to the symmetrical (relative to each of two emitter electrode of corona discharge) presence of the electric charge, the emitter electrode and space charge produced (in this case the intermediate enhancer electrode is responsible for corona onset).

Referring now to FIG. 5, a pipe-based air-to-air heat exchanger (10) includes a dielectric heat conductive wall (24) having a circular or oval cross-sectional profile, one or more emitter electrode (42), one or more enhancer electrode (44), and one or more collector electrode (46). In this embodiment, the emitter electrode (42) is in the shape of needle located at the axis of the pipe (dielectric support is not shown) with its sharp tip pointing to a downstream direction. Both the enhancer electrodes (44) and the collector electrodes (46) are in the shape of loops of electrically conductive strips. The enhancer electrodes (44) and the collector electrodes (46) are mechanically secure and thermally coupled to the internal surface of pipe in the same way as previously discussed in connection with the embodiments shown in FIGS. 4A and 4B.

Plate-Based Heat Exchangers Using Emitter-Enhancer-Collector EHD Enhancement

In some embodiments of the plate-based heat exchangers according to the present disclosure, it is contemplated herein that possible vapor condensation on one surface of heat conductive walls separating airflows of different temperatures would make the wall surface electrically conductive. To operate in electrically conductive enclosure, some embodiments of plate-based heat exchangers use a plurality of emitter-enhancer-collector EHD devices operating in sequence.

One feature of the plate-based heat exchanger comprising a plurality of emitter-enhancer-collector EHD devices operating in sequence is the enhancement of the overall performance of the heat exchanger by the introduction of ion wind generators in the second airflow leading to the enhancement of heat transfer on the other surface of air flow separating wall. This would reduce, if not eliminate, the need for conventional air pumps and lead to an enhancement of convective heat transfer coefficient between the wall and the second airflow. This brings the feature of minimizing the electric field interference between the neighboring ionic wind generation engines that sometimes lead to their performance degradation. Therefore, in a preferred embodiment, the collection of corona electrodes of a particular ionic wind generator should be arranged at the maximum possible distance from the neighboring generators. This brings the feature that the directions of heat exchanging airflows in the proposed heat exchanger are opposite, which leads to the feature that ionic wind generator electrodes as whole in different airflow channels are essentially parallel to each other and shifted by a distance which is the half of the distance between them in the neighboring flow channel. Schematic configuration of this arrangement is presented in FIG. 6.

In the embodiment shown in FIG. 6, each emitter-enhancer-collector EHD device (40) includes one or more emitter electrodes (42) in the form of one or more elongated members, one or more enhancer electrodes (44) in the form of one or more elongated members, which are electrically coupled to electrically conductive and grounded heat exchanger plates, and one or more collector electrodes (46) in the form of one or more elongated members, or smooth-edged electrically conductive strips, which are at an electrical potential relative to the ground with the sign opposite to that of emitter electrode.

In some embodiments, the enhancer electrodes (44) of the EHD devices (40) are electrically coupled and grounded. The emitter electrodes (42) of the EHD devices (40) are electrically coupled to each other and to the positive (in this example) electrode of the first HVDC source, which negative electrode is earthed. The collector electrodes (46) of the EHD deices (40) are electrically coupled to each other and to the negative (in this example) electrode of the second HVDC source, which positive electrode is earthed. In some embodiments, direct current of a certain polarity supplied to the one or more emitter electrodes is provided in periodic pulses.

Plate-Based Heat Exchangers with Electrically Conductive Walls

Sometimes, atmosphere air entering a heat exchanger has high relative humidity, which leads to condensation walls of the heat exchanger. Designs of commercial heat exchangers typically include the means for collecting and discarding the condensed water. This includes the preferably vertical position of heat exchanger walls such as pipes, cells, or plates, a tray for collecting water drops descending from the walls, and an outlet that allow this water to leave the heat exchanger. As the water condensed on the surface of heat exchanger wall makes it electrically conductive, EHD devices of some embodiments of the present disclosure are configured to work under this condition regardless on which side of the wall the condensation occurred. In such embodiments, EHD devices are configured for heat exchanger walls that are made of thermally conductive and electrically conductive materials, such as certain metals as non-limiting examples.

Referring to FIG. 7A, the emitter-enhancer-collector EHD device (40) includes one or more emitter electrodes (42) in the form of one or more elongated members, one or more enhancer electrodes (44) in the form of one or more elongated members, which are electrically coupled to electrically conductive and grounded heat exchanger plates, and one or more collector electrodes (46) in the form of one or more elongated members, or smooth-edged electrically conductive strips, which are at an electrical potential relative to the ground with the sign opposite to that of emitter electrode.

The emitter electrode (42), the enhancer electrodes (44) and the collector electrodes (46) are separated from their closest heat conductive wall (24) by predetermined distances. For example, the emitter electrode (42) is separated from the closest wall (24) by an emitter-wall distance. The enhancer electrodes (44) are separated from the closest wall (24) by an enhancer-wall distance. The collector electrodes (46) are separated from the closest wall (24) by a collector-wall distance. In some embodiment, such as the embodiment shown in FIG. 7A, the collector-wall distance is less than the enhancer-wall distance. In some embodiments, the enhancer-wall distance is less than the emitter-wall distance. In some embodiments, the collector-wall distance is less than the enhancer-wall distance, which in turn is less than the emitter-wall distance. It is contemplated that such positional configurations contribute to the improvement of wind velocity near the wall. In addition, the present disclosure recognizes that the collector-wall distance should have a minimum threshold as positioning the collector electrode (46) too close to the heat conductive wall (24) sometimes decreases the performance and/or efficiency of the EHD devices, such as requiring a higher voltage to operate. It is contemplated in the present disclosure that a collector-wall distance too small would lead to the effective electric field of the collector electrode being close to a dipole of opposite charge lines, requiring a significantly higher voltage of the connected power source would be required.

In some embodiments, the enhancer electrodes (44) of the EHD devices (40) are electrically coupled and grounded. The emitter electrodes (42) of the EHD devices (40) are electrically coupled to each other and to the positive (in this example) electrode of the first HVDC source, which negative electrode is earthed. The collector electrodes (46) of the EHD deices (40) are electrically coupled to each other and to the negative (in this example) electrode of the second HVDC source, which positive electrode is earthed. In some embodiments, direct current of a certain polarity supplied to the one or more emitter electrodes is provided in periodic pulses.

Turning to FIG. 7B, the second configuration of the plate-based air-to-air heat exchanger (10) differs from the first configuration illustrated in FIG. 7A by deploying two electrically coupled emitter electrodes (42). The feature of this modified configuration is a lower corona onset voltage. It is contemplated that the lower onset voltage is attributable to the symmetrical (relative to each of two emitter electrode of corona discharge) presence of the electric charge, the emitter electrode and the space charge produced (in this case the intermediate enhancer electrode responsible for corona onset).

In addition, similar to the configuration of the EHD-enhanced plate-base exchanger shown in FIG. 6, where multiple EHD devices operate in sequence in both air passageways divided by non-conductive plates, multiple EHD devices shown in FIGS. 7A and 7B are also configured in sequence in one or both of first and second air passageways divided by electrically conductive plates in some embodiments of the present disclosure.

Convection Promoter Electrodes

In some embodiments, the EHD devices shown in FIGS. 7A and 7B having ionic wind velocity profile that is close to that of bulk air, i.e. the ionic wind velocity in the vicinity of wall is lower than that achieved in the bulk air. This is because the air acceleration by ion drag in the electric field of collector electrode continues only up to the collector electrode, a feature of EHD devices operating in an electrically conductive enclosure. A lower wind velocity in the vicinity of the wall leads to a lower coefficient of convective heat transfer. While using EHD devices operating in sequences between the electrically conductive plates of heat exchanger would result in a fully EHD-driven embodiment without conventional air pumps, the overall performance and efficiency of the heat exchangers in some embodiments are further enhanced through improvement of heat transfer feature.

In some embodiments, such improvement is achieved by introducing an array of electrodes in the vicinity of each surface of each wall to produce short-range ionic wind in the vicinity of the wall surface, which de-couples the EHD production of bulk airflow for the enhancement of the convective heat transfer coefficient. This feature allows control of the bulk airflow, which velocity is determined by a certain operational regime in a particular application, while enhancing the heat exchange efficiency with short-rage ionic wind independently. The arrangement and configuration of EHD devices that further incorporate convection promoter electrode to generate short-range ionic wind is shown in FIGS. 8 and 9.

In FIG. 8, an EHD device (40) is illustrated as having one or more emitter electrodes (42), one or more enhancer electrodes (44), one or more collector electrodes (46), and one or more arrays of convection promoter electrodes (50). In some embodiments, the enhancer electrodes (44) of the EHD devices (40) are electrically coupled to the wall (24) and grounded. The emitter electrodes (42) of the EHD devices (40) are electrically coupled to each other and to the positive (in this example) electrode of the first HVDC source, which negative electrode is earthed. The collector electrodes (46) of the EHD deices (40) are electrically coupled to each other and to the negative (in this example) electrode of the second HVDC source, which positive electrode is earthed. The convection promoter electrodes (50) are electrically coupled to the positive electrode of the first HVDC source, or the negative electrode of the second HVDC, or the positive or negative electrode of a separate third HVDC source. In some embodiments, direct current of a certain polarity supplied to the one or more emitter electrodes is provided in periodic pulses.

In some embodiments, the emitter electrode (42), the enhancer electrodes (44), the collector electrodes (46), and the convection promoter electrodes are separated from their closest wall (24) by predetermined distances. For example, the emitter electrode (42) is separated from the closest wall (24) by an emitter-wall distance. The enhancer electrodes (44) are separated from the closest wall (24) by an enhancer-wall distance. The collector electrodes (46) are separated from the closest wall (24) by a collector-wall distance. The convection promoter electrodes (50) are separated from the closest wall (24) by a promoter-wall distance (h). In some embodiment, such as the embodiment shown in FIG. 8, the promoter-wall distance (h) is less than any of the emitter-wall distance, the enhancer-wall distance, and the collector-wall distance. In some embodiments, such as the embodiment shown in FIG. 8, the array of convection promoter electrodes is essentially equidistantly arranged in the direction of airflow, with a separation distance between the neighboring emitter electrodes, hereinafter referred to as promoter-promoter distance (s).

In some embodiments, the promoter-promoter distance (s) is greater than the promoter-wall distance (h). In some embodiments, the promoter-promoter distance (s) is not less than two times the promoter-wall distance (h). In some embodiments, the promoter-promoter distance (s) is not less than three times the promoter-wall distance (h).

In some embodiments, such as the embodiment shown in FIG. 8, two arrays of convection promoter electrodes (50) are provided in the air passageway between two adjacent walls, and have the same electric potential, such as by coupling to the same positive or negative electrode of a HVDC source. In some embodiments, an array of convection promoter electrode (50) in a first air passageway and an array of convection promoter electrodes (50) in a second air passageway are positioned at opposite sides of the same wall (24) dividing the first and second air passageways. In some embodiments, the two arrays of convection promoter electrodes (50) separated by the wall (24) have electric potential of opposite polarities, such as by coupling one array of the convection promoter electrodes (50) to a position or negative electrode of a HVDC source and coupling the other array of convection promoter electrodes (50) to the other electrode of the HVDC source. In some embodiments, the two arrays of convection promoter electrodes (50) separated by the wall (24) have the same promoter-wall distance but are offset in a direction of airflow by an offset distance (u).

In some embodiments, the offset distance (u) between two arrays of convection promoter electrodes (50) at opposite sides of a particular wall (and therefore of opposite electric signs) is dependent on the direction of bulk air flow in a particular air passageway. It is contemplated that this feature ensures that the tangential (relative to the surface of wall) component of electrical force on the produced ions that tends to be directed to the closest convection promoter electrode of corona discharge of the opposite charge across the wall is in the same direction as the bulk airflow in each channel, and as such the additional airflow caused by the short-range ionic wind is in the same general direction as the bulk airflow. The normal (relative to the surface of wall) component of electrical force on the produced ions directed towards the wall ensures that the additional air flow produced by the described short-range ionic wind generators is kept in the vicinity of the wall surface. On the microscopic level, the additional effect of the said component of electric force is to drag the air from areas with different temperatures along the trajectory of an ion approaching the wall through the low-velocity boundary layer in the vicinity of the wall.

In some embodiments, the promoter-promoter distance (s) in each array is no less than a minimum distance that is two times the promoter-wall distance plus the offset distance (2h+u). In some embodiment, the promoter-promoter distance (s) in each array is no more than a maximum distance that is X times the minimum distance described above, i.e. X(2h+u). In some embodiment, the parameter X ranges between about 1.1 and about 5.0. In some embodiment, the parameter X ranges between about 1.1 and about 5.0. In some embodiment, the parameter X ranges between about 1.1 and about 4.0. In some embodiment, the parameter X ranges between about 1.1 and about 3.0. In some embodiment, the parameter X ranges between about 1.1 and about 2.0. In some embodiment, the parameter X ranges between about 1.5 and about 2.0. In some embodiment, the parameter X is about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.5, or about 3.0. It is contemplated that the combination of the electrical, positional and/or geometric configurations of the convection promoter electrodes (50), or with further combination with electrical, positional and/or geometric configurations of the emitter electrodes (42), the enhancer electrodes (44), and collector electrodes (46) contribute to improved bulk airflow and surface airflow, as well as overall improvement of performance and efficiency of the heat exchangers.

Referring now to FIG. 9, the present disclosure recognizes that further improvement to the heat exchangers incorporating both bulk and short-range ion wind generators in the plate-based heat exchanger comprising electrically conductive plates is achieved by the selection and configurations of the corona sign, e.g. the electrical sign of the emitter electrodes (42) and the convection promoter electrodes (50). A non-limiting example is provided in FIG. 9.

In FIG. 9, the air passageways separated by the heat conductive wall 24 are each configured with EHD devices (40) operating in sequence. The EHD devices (40) within each air passageway have the same corona sign, i.e. either positive corona or negative corona. The EHD devices (40) in two neighboring air passageways have opposite corona sign, i.e. the EHD devices (40) in one air passageway have positive corona sign and the EHD devices (40) in the neighboring air passageway have negative corona sign, or vice versa. The present disclosure recognizes that the alternate signs of emitter electrodes of corona discharge in some embodiments reduces or minimizes the corona inception voltage. In some applications, EHD devices (40) (e.g. bulk ionic wind generators) with positive corona are used in the passageway of exhaust airflow, and EHD devices (40) (e.g. bulk ionic wind generators) with negative corona are used in the passageway of incoming airflow. It is recognized that this configuration allows s some negative ions to be present in the airflow into the building (e.g a greenhouse or a residential or commercial building), which has beneficial effects (e.g. health effects) on plants, humans, and animals.

In some non-limiting embodiments, the EHD device (40) have convection promoter electrode (50) positioned both upstream and downstream of the EHD device (40). In some embodiments, the upstream convection promoter electrodes (50) have the same corona sign as the EHD device (40) while the downstream convection promoter electrode (50) have the opposite corona sign as the EHD device (40). In some embodiments, such as the embodiment shown in FIG. 9, two arrays of convection promoter electrodes (50) are provided in the air passageway between two adjacent walls, and have the same electric potential, such as by coupling to the same positive or negative electrode of a HVDC source. In some embodiments, an array of convection promoter electrode (50) in one air passageway and an array of convection promoter electrodes (50) in another neighboring air passageway are positioned at opposite sides of the same wall (24) dividing the first and second air passageways. In some embodiments, the two arrays of convection promoter electrodes (50) separated by the wall (24) have electric potential of opposite polarities, such as by coupling one array of the convection promoter electrodes (50) to a position or negative electrode of a HVDC source and coupling the other array of convection promoter electrodes (50) to the other electrode of the HVDC source. In some embodiments, the two arrays of convection promoter electrodes (50) separated by the wall (24) have the same promoter-wall distance but are offset in a direction of airflow by an offset distance (u), such as those describe in embodiments shown in FIG. 8.

Application and Usage

The present disclosure recognizes that the EHD enhanced air-to-air heat exchanger in some embodiments are suitable for use in essentially enclosed spaces, such as spaces that are generally enclosed except for necessary practical or operational purposes including, but not limited to, space entry, space exit, convenience and recreation, safety protocols and regulations, construction/manufacturing protocols and regulations, etc. For non-limiting examples, the essentially enclosed space includes, but is not limited to, space in: (1) residential buildings and school buildings, (2) commercial buildings (including for example shopping malls, hotels, restaurants, office buildings, hospitals, airports, data centers, arenas, stadiums, etc.); (3) industrial/manufacturing buildings (e.g. assembly line factories, power stations, etc.); (4) horticultural buildings or enclosures (e.g. greenhouses, etc.); (5) underground networks (e.g. underground mines, subways or underground metro systems, underground residential or office establishments etc.).

Generally, the practical limitation to the voltages of emitter electrodes of corona discharge is related to the concentration of corona-generated ozone in the conditioned air, which acceptable level depends on a particular application, such as in residential buildings or in commercial establishments including for example airports, data centers, arenas, stadiums, etc. The present disclosure recognizes that for using EHD air-to-air heat exchangers in greenhouses, this limitation is relaxed compared to because it was found that ozone at a certain level/amount is beneficial for plant growth.

In some embodiments, heat exchangers according to the present disclosure further include an insulating enclosure housing for the plates of heat exchanger and/or insulating supports for all electrodes. In some embodiments, the enclosure housing also includes collection tray and an outlet for the condensed water. As a non-limiting example, the condensed water harvested from an EHD air-to-air heat exchanger in an air cooling system for a greenhouse operating in a warm and humid environment significantly reduces the total water consumption from an external source, e.g. water desalination system in arid areas.

The foregoing is illustrative of the present disclosure, and is not to be construed as limiting thereof. While embodiments of the present disclosure have been indicated and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the present disclosure. It should be understood that various alternatives to the embodiments of the present disclosure are within the scope of the present disclosure.

Claims

1. An air-to-air heat exchanger, comprising:

at least one first air passageway extending between a first air inlet and a first air outlet;

at least one second air passageway extending between a second air inlet and a second air outlet;

at least one heat-conductive wall separating the at least one first air passageway from the at least one second air passageway; and at least one electrohydrodynamic device disposed in at least one of the first and second air passageways for enhancing airflow therein, wherein each electrohydrodynamic device comprises one or more emitter electrodes, one or more enhancer electrodes positioned downstream of the one or more emitter electrodes, and one or more collector electrodes positioned downstream of the one or more enhancer electrodes.

2. The heat exchanger of claim 1, wherein the at least one heat conductive wall comprises at least one essentially planar wall.

3. The heat exchanger of claim 1, wherein the at least one heat conductive wall comprises a plurality of essentially planar walls that are essentially parallel to one another.

4. The heat exchanger of claim 3, wherein the plurality of heat conductive walls are essentially equidistantly arranged.

5. The heat exchanger of claim 3, wherein airflow in the first air passageway and airflow in the second air passageway are essentially in opposite direction.

6. (canceled)

7. The heat exchanger of claim 1, wherein the one or more emitter electrodes, the one or more enhancer electrodes, and the one or more collector electrodes extend essentially parallel to heat conductive walls and essentially orthogonal to the airflow.

8. The heat exchanger of claim 7, wherein the one or more emitter electrodes have a higher electric potential than the one or more enhancer electrodes, and wherein the one or more enhancer electrodes have a higher electric potential that the one or more collector electrode.

9. The heat exchanger of claim 8, wherein the one or more enhancer electrodes are grounded.

10. The heat exchanger of claim 9, wherein the one or more enhancer electrodes are positioned closer to the one or more emitter electrode than to the one or more collector electrodes.

11. The heat exchanger of claim 10, wherein the one or more emitter electrodes are separated from the closest heat conductive wall by an emitter-wall distance.

12. The heat exchanger of claim 11, wherein the one or more enhancer electrodes and the one or more collector electrodes are attached to the heat conductive wall, and wherein the heat conductive wall is dielectric.

13. The heat exchanger of claim 12, wherein the one or more enhancer electrodes and the one or more collector electrodes are made of heat conductive material.

14. The heat exchanger of claim 11, wherein the heat conductive wall is electrically conductive and grounded, wherein the one or more enhancer electrodes are separated from the closest heat conductive wall by an enhancer-wall distance, and wherein the one or more collector electrodes are separated from the closest heat conductive wall by a collector-wall distance.

15. The heat exchanger of claim 14, wherein the collector-wall distance is smaller than the enhancer-wall distance.

16. The heat exchanger of claim 15, wherein the collector-wall distance and the enhancer-wall distance are both smaller than the emitter-wall distance.

17. The heat exchanger of claim 14, wherein each electrohydrodynamic device further comprises one or more arrays of convection promoter electrodes positioned downstream of the one or more collector electrodes.

18. The heat exchanger of claim 17, wherein one or more arrays of convection promoter electrodes extend essentially parallel to the heat conductive walls and essentially orthogonal to the airflow.

19. The heat exchanger of claim 18, wherein the convection promoter electrodes are separated from the closest heat conductive wall by a promoter-wall distance of (h) that is smaller than any of the emitter-wall distance, enhancer-wall distance, and collector-wall distance.

20. The heat exchanger of claim 19, wherein the convection promoter electrodes within each array are separated from one another by a promoter-promoter distance (s) that is greater than the promoter-wall distance (h).

21. The heat exchanger of claim 20, wherein each electrohydrodynamic device comprises two array of the convection promoter electrodes positioned between two adjacent heat conductive walls, wherein both arrays and have same electrical potential.

22. The heat exchanger of claim 21, wherein one array of convection promoter electrodes of a first electrohydrodynamic device and one array of convection promoter electrodes of a second electrohydrodynamic device are disposed on opposite side of a heat conductive wall with an offset distance (u), and have opposite electric potentials.

23. The heat exchanger of claim 22, wherein the promoter-promoter distance (s) is no less than 2h+u, and wherein the promoter-promoter distance (s) is no greater than X(2h+u), wherein X ranges between 1.5 and 2.0.

24. The heat exchanger of claim 1, wherein the at least one first air passageway, the at least one second air passageway, the at least one heat-conductive wall, and the at least one electrohydrodynamic device are enclosed in a housing.

25. The heat exchanger of claim 24, wherein the housing comprises the first air inlet, the first air outlet, the second air inlet, and the second air outlet.

26. A ventilation system comprising a desiccator and the heat exchanger of claim 25, wherein the first air inlet of the heat exchanger is configured to receive air from atmosphere, the first air outlet of the heat exchanger is connected to the desiccator.

27. The ventilation system of claim 26, wherein the second air inlet of the heat exchanger is configured to receive exhaust air from the ventilation system, and wherein the second air outlet of the heat exchanger is configured to release air into atmosphere.

28. The ventilation system of claim 26, wherein a temperature of air entering into the first air inlet of the heat exchanger is higher than a temperature of air exiting the second air outlet of the heat exchanger.

29. A method of enhancing air flow in an air-to-air heat exchanger, the method comprising:

activating at least one electrohydrodynamic device disposed in air passageways of the air-to-air heat exchanger, wherein each electrohydrodynamic device comprises one or more emitter electrodes, one or more enhancer electrodes positioned downstream of the one or more emitter electrodes, and one or more collector electrodes positioned downstream of the one or more enhancer electrodes,

wherein the activation comprises creating gradient electric potential differential from the emitter electrodes to the enhancer electrodes and to the collector electrodes.

30. The method of claim 1, wherein the activation comprises coupling the emitter electrodes with a source of positive electric potential, coupling the collector electrode with a source of negative electric potential, and grounding the enhancer electrodes.