ROTARY HEAT REGENERATOR USING PARALLEL PLATE MEDIA

BACKGROUND

Regenerator heat exchange devices or regenerators are known for effecting the transfer of heat and moisture between two counter-flowing air streams. Such heat exchange devices are used, for example, in heating, ventilation and cooling (HVAC) systems to conserve energy within buildings. One type of regenerator is the rotary air-to-air heat exchanger, which is typically in the form of a rotary heat exchange wheel including a matrix of heat exchange material. When rotated through counter-flowing air streams, the rotating wheel matrix is heated by the air stream with the higher temperature and, in turn, heats the lower temperature air stream. In addition, the rotating wheel may transfer moisture between the counter-flowing air streams. To promote moisture transfer, the wheel heat exchange matrix can be made from, or coated with, a moisture adsorbent desiccant material. Examples of such prior art rotary regenerator wheels are shown in FIGS. 1-2.

FIG. 1 represents a cross sectional view of a rotary wheel heat exchanger assembly within an enclosure having two flow chambers separated by a divider. The first airflow being directed through the top chamber and through the top half of the rotary wheel, the second airflow being directed though the bottom chamber and through the bottom half of the wheel in a counter direction to the first airflow. FIG. 2 represents a face on view of the rotary heat exchange assembly showing 100 the top rotary wheel media exposed to the first airflow, and the bottom rotary wheel media exposed to the second airflow in a counter direction to the first airflow. The wheel is shown sealed circumferentially around it's perimeter to the wheel casing, and horizontally to the divider across the diameter of the wheel.

As the supply airflow and exhaust airflow (fluids) pass through a typical heat exchange substrate media, two types of fluid flow can be created, turbulent flow or laminar flow. If the velocity of the fluid is fast enough, and the passage geometry large enough, turbulent flow could be created. If the fluid velocity is low enough, and the passage geometry is small enough, laminar flow could be created. Turbulence or turbulent flow is a flow regime in fluid dynamics characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow regime, which occurs when a fluid flows in parallel layers, with no disruption between those layers.

Laminar flow means that along the boundary layer or wall of each layer of heat transfer material, the fluid velocity is non-turbulent. Therefore, this boundary layer fluid does not mix with the fluid flowing away from the boundary layer, and heat transfer from the heat transfer media surface through the fluid is decreased. Turbulent flow means that the velocity of the fluid along boundary layer is high enough for the specific passageway geometry that the boundary layer fluid is mixed with the fluid away from the boundary layer, and heat transfer from the heat transfer media surface through the fluid is increased. Most air-to-air sensible, or enthalpic, rotary wheel regenerators operate in region of laminar flow as described by the parameter (dimensionless number) the Reynolds Number (Re), which is typically expressed as ρVD/μ, where ρ (rho) is the density, μ (mu) is the absolute viscosity, V is the characteristic velocity of the flow, and D is the characteristic length for the flow. Typically these heat exchangers operate at Re numbers of between 200-1000, indicating laminar flow characteristics. Since laminar flow is not as effective as transferring heat as turbulent flow, other parameters of the heat exchanger design become more important, such as heat transfer media passageway geometry.

A matrix of a rotary heat exchange wheel can include strips of thin film material wound about an axis of the wheel so as to provide a plurality of layers. In such a design, the layers must have spacing means to create gas passageways extending through the wheel parallel with the axis. The layers are uniformly spaced apart so that the gas passageways are of uniform height throughout their length for greatest efficiency. Transverse elongated embossments have been provided in a plastic strip to form the gas passageways between the layers of the regenerator matrix. Numerous closely spaced transverse embossments are needed to maintain parallelism between layers if used alone to form the passageways. While such elongated embossments may maintain parallelism and prevent circumferential gas leakage, they replace parallel matrix surface area thereby reducing the heat exchange effectiveness of the regenerator.

Typical rotary wheel regenerators—whether made from plastic, metallic or paper media—are produced using heat transfer media substrate surfaces formed using a corrugated arrangement where every other layer is flat, and every other layer is corrugated. FIG. 3-6 depicts examples of prior art configurations of heat exchange media used for regenerators. An example of a prior parallel layer media arrangement having continually corrugated layers positioned between flat layers creating essentially triangular shaped passageways (fluted) is shown in FIG. 7.

For optimum heat and moisture transfer and from a manufacturing standpoint, it may be easiest to merely provide dimples in the strip to form the gas passageways between the layers of the regenerator matrix. While dimples can provide a desirable high aspect ratio between layers, they unfortunately allow appreciable circumferential gas leakage in those situations where there is a high pressure differential between the counter-flowing air streams, thereby reducing the heat exchange effectiveness of the regenerator. Additionally, such dimples are not practically applicable to certain materials such as thin-gauge aluminum or other metallic materials due to, for example, stress concentrations and other structural problems.

SUMMARY

An aspect of the present disclosure includes a parallel-plate rotary wheel regenerator including: a plurality of plates that are parallel, wherein the plurality of plates includes at least one central plate having a plurality of embossments that touch and physically separate the central plate from two other adjacent plates.

The central plate can be made of aluminum;

One or both of the adjacent plates can be made of aluminum.

The aluminum can have a thickness of, e.g., about 1 to about 5 mils.

The aluminum can include 1100 series aluminum alloy.

The plurality of embossments can include a compressed sine wave shape.

The compressed sign wave shape includes features joined at an angle in the range of approximately 5 degrees to approximately 15 degrees.

These, as well as other components, steps, features, objects, benefits, and advantages, will now become clear from a review of the following detailed description of illustrative embodiments, the accompanying drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

The drawings are of illustrative embodiments. They do not illustrate all embodiments. Other embodiments may be used in addition or instead. Details that may be apparent or unnecessary may be omitted to save space or for more effective illustration. Some embodiments may be practiced with additional components or steps and/or without all of the components or steps that are illustrated. When the same numeral appears in different drawings, it refers to the same or like components or steps.

FIG. 1 depicts a side view of an example of a prior art air-to-air heat exchanger including a rotary heat exchange wheel having a regenerator matrix.

FIG. 2 depicts an end elevation view of the prior art heat exchanger of FIG. 1 as viewed from cutting plane 2-2.

FIG. 3 depicts a perspective view of an embossed strip and an un-embossed strip being wound to form the regenerator matrix of FIG. 1.

FIG. 4 depicts an enlarged view of a portion of the embossed strip of the prior art regenerator matrix of FIG. 1.

FIG. 5 depicts an enlarged plan view of a portion of the embossed strip of the prior art regenerator matrix of FIG. 1.

FIG. 6 depicts a sectional view of the embossed strip of FIG. 5 taken along cutting plane 6-6.

FIG. 7 depicts an example of a prior art layered media arrangement having continually corrugated layers positioned between flat layers creating essentially triangular-shaped fluted passageways.

FIG. 8 depicts an example of a parallel-plate arrangement according to the present disclosure.

FIGS. 9A-9D depict further example of a parallel-plate arrangements according to the present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Illustrative embodiments are now described. Other embodiments may be used in addition or instead. Details that may be apparent or unnecessary may be omitted to save space or for a more effective presentation. Some embodiments may be practiced with additional components or steps and/or without all of the components or steps that are described.

The present disclosure provides improvements to and advantages for parallel-plate heat transfer media geometry utilized for rotary wheel regenerators, within the fluid velocity ranges where rotary wheel regenerators are typically applied (laminar flow), and can provide optimal performance tradeoff between heat transfer performance and friction loss. Although parallel-plate heat transfer media regenerators have been designed and produced using plastic heat transfer media, an aspect of the present disclosure provides parallel-plate regenerators of aluminum or other metallic or non-metallic media using periodic embossed standoffs. This parallel-plate geometry can also provide for media less prone to clogging due to contaminants in the air, and more easily cleaned if clogging does occur. Embodiments of the present disclosure can also provide for manufacturing less media length per wheel to produce a lighter and more cost effective media

An aspect of the present disclosure provides a rotary wheel regenerator using polymer, paper, metallic (e.g., aluminum, etc.) or other substrate having a parallel-plate heat transfer surface configuration. The substrate media can be either non-desiccant-coated “sensible” substrate, or “enthalpic” desiccant coated substrate. In exemplary embodiments, spirally wound substrate media strips are arranged in a parallel-plate manner using an embossed formation periodically to hold the strips in a parallel-plate configuration. The strip layers may be arranged so that every other layer has embossments and each alternating layer may be flat without embossments. The embossed standoffs—or embossments—are not intended to be aligned with one another periodically, and a parallel-plate arrangement is achieved, rather than a typical triangular shaped arrangement. The benefits of a parallel-plate geometry media over other typically used geometries include higher thermal performance resulting in increased energy savings, lower pressure drop to reduce fan power energy required and reduce structural load on the wheel frame, less clogging due to contaminates resulting in better long term savings, longer life, and less frequent cleaning, less material required to manufacture for lower cost and weight.

FIG. 8 depicts an example of a parallel-plate substrate media configuration 800 according to the present disclosure. As shown, a rotary wheel, shown as 801, can include rotary wheel media 802, which can include a number of layers of a parallel-plate configuration. Four such plates 804(1)-804(4) are shown, but any practical number may be used. The parallel plates 804(1)-804(4) are spaced apart creating parallel flow passageways 805(1)-805(3) to allow airflow through the rotary wheel in the direction of wheel depth. Of most importance is that the resultant parallel plates (shown as curved in this application) are uniformly spaced apart, and that the resultant parallel-plate passageways are not divided into small triangular, square, or round finite small passageways. While curved (circular) parallel plates are shown, other geometries can of course be realized within the scope of the present disclosure, e.g., “spiral” polygon shapes, concentric polygon shapes, straight parallel plates, etc. Moreover, while some embodiments may be wound, e.g., like tape on a spool, other embodiments may have concentric shapes, sized appropriately to next together such as shown in FIG. 9A-9B.

FIGS. 9A-9D depict further examples of a parallel-plate plate substrate media configurations 900A-900D according to the present disclosure. FIG. 9A depicts a section 900A of a concentric circular rotary wheel media having parallel and concentric plates that are not wound per se but assembled adjacent to one another in a nested circular fashion as shown. FIG. 9B depicts a section 900B of a concentric square rotary wheel media (fitting within the shape of a rotary wheel) having parallel and concentric plates that are not wound per se but assembled adjacent to one another in a nested arrangement of squares (or rhomboids or rectangles) as shown. FIG. 9C depicts a section 900C of a wheel media having parallel plates that are in a stacked flat and parallel arrangement as shown. FIG. 9D represents a section 900D of a spirally wound rotary wheel media showing three layers or plates of a parallel-plate configuration with embossments. The section 900D includes a central layer 902 and two adjacent layers 904(1)-904(2). The adjacent layers or plates 904(1)-904(2) are shown to be flat layers, while the middle or central layer or plate 902 is show to have periodically spaced standoffs, or embossments, 910(1)-910(3) to create the parallel-plate configuration. The embossments 910(1)-910(3) touch and physically separate the central plate 902 from two other adjacent plates 904(1)-904(2). The periodic spacing of the standoff embossments (such a 910A-910C) is not critical to the increased performance of parallel-plate designs described herein, as long as it is frequent enough to keep the layers from deforming or sagging thereby losing parallel configuration, and not too frequent to essentially create a square finite flute configuration rather than a parallel-plate configuration. The spacing between the embossments, thus, may be dependent upon the material(s) used for the layers or plates and the thickness of the layers or plates, and/or the desired height of the embossments. The embossments are preferably the full width of the matrix for leakage mitigation purposes, whatever the width is (e.g., 1″ to 12″). The embossments can be uniform across their length, e.g., with the profile as shown in FIG. 9D.

As shown, the crimped embossment can have a compressed sign-wave-like shape, in exemplary embodiments. Such a shape offers the advantages of centering the middle formed layer between flat layers uniformly and creating a structural support between the surface of one flat layer though the middle formed layer to the surface of the next flat layer. This sign wave shaped embossment helps to keep the wheel media from collapsing as it is spirally wound from a small diameter to large diameter while maintaining a uniform parallel-plate media configuration. Such an embossment can be made by any suitable method or technique. In exemplary embodiments, such embossments may be made by crimping or stamping or forming the media as required. One method of creating the sine wave formation would be to create a stamping die of the profile desired (e.g., a machined die set), and stamp that formation into a media layer at the desired frequency or spacing by drawing the layer strip through the die, and actuating the die at a rate coincidental to the rate of the strip to create the formations at the desired periodic spacing. Such embossments may, in exemplary embodiments, have features joined at an angle in the range of approximately 5 degrees to approximately 15 degrees. In exemplary embodiments, the layers or plates are made of 1100 series alumni having a uniform thickness in the range of between about 1 mil (0.001 inch) and about 5 mil (0.005 inch), e.g., 1 mil, 2 mil, 3 mil, 4 mil, or 5 mil. Of course, other types of aluminum alloy can be used. By employing embossments with such a configuration, a number of advantages are afforded. These advantages include, but are not limited to, the ability to use thin gauge metal for the matrix media, e.g., aluminum, aluminum alloys, stainless steel alloys (e.g., 300 series including 304 and 310), titanium, titanium alloys, and the like. These advantages also include the doing away of any need to use secondary embossments, such as single-sided embossments as used in the prior art, which reduces friction loss (lowering the pressure drop), which in turn reduces power requirements for one or more fans pushing air through the system. By doing away with a need to use secondary embossments, embodiments of the present disclosure can provide a much lower recovery efficiency ratio (RER) compared with prior art design. The RER, a well-known parameter in the HVAC energy recovery field, is defined as energy recovered over the energy expended in the recovery. Embodiments of the present disclosure can improve either or both of the numerator and denominator of the RER. Moreover, doing away with the need for using secondary embossments also removes the requirement of aligning the heights of the two different types of embossments, which task is normally labor, time, and energy intensive.

The challenge in designing heat transfer media passageway geometry is the tradeoff between having more heat transfer media surface area for better thermal performance and less heat transfer media surface area for lower friction, i.e. pressure drop through the regenerator. The laminar flow ratio (f/j) is a parameter that describes the friction to heat transfer media geometry for various passageway configurations. The letter f stands for the friction coefficient, and the letter j for the Coburn heat transfer factor. It has been shown that as the f/j ratio becomes smaller, the tradeoff between friction loss and heat transfer capability is optimized. Within typical heat transfer media spacing ranges used, f/j ratios have been calculated to support the idea that parallel-plate heat transfer media geometry has a higher performing configuration than round ducts, square ducts, triangular ducts, or random packed ducts. In the laminar flow region typically applied to energy recovery regenerators, the f/j factors can be calculated for various media geometries using the following formula:

$\begin{matrix} \frac{f}{j} = \Pr^{\frac{1}{3}} * \frac{f * Re}{Nu} . & [EQ . 1] \end{matrix}$

In Equation 1, Pr designates the Prandtl number for gas (0.7 for most gasses). (f*Re) is the resultant of multiplying the friction factor (f) of the geometry and the Reynolds number (Re). Nu is the Nusselt number resulting from the given geometry. Using Nu and f*Re values (e.g., from Kays and London Compact Heat Exchangers—third edition 1984, p. 120), f/j factors can be calculated for specific media geometries, giving f/j factors of 4.79 for triangular passageways, 4.23 for square ducts, 3.88 for round ducts, and 2.8 for parallel-plate ducts. This reveals that the parallel-plate geometry under laminar flow conditions exhibits superior performance (tradeoff between pressure loss and thermal transfer) per unit of media face area.

Having a regenerator media geometry that provides lower friction and higher thermal transfer per unit face area results in several performance advantages. Higher thermal transfer results in higher energy savings over time. Lower friction loss translates into lower pressure drop through the regenerator resulting in less fan power (energy) required to pass airflow through the device, which translates into better overall energy savings over time. Lower pressure drop also translates into less load on the wheel frame structure resulting in longer life of the device.

In some applications, VOCs or ‘sticky’ contaminants (such as cigarette smoke or airborne cooking oils) that may be present in the ventilated space will be passed through the wheel and can potentially stick to the media surface and eventually restrict the passageways. In addition, any dust or dirt particles in the space caught in the HVAC system will pass through the wheel, further dirtying and restricting the passageways. Once the wheel media passageways become restricted due to clogging, thermal performance is degraded and pressure drop through the wheel is increased resulting in lower energy savings, increased operational costs, higher structural loads to the wheel frame, and potentially decreased supply of ventilation air through the wheel.

Long, thin “flute” or straw-like triangular passageways resultant of a typical prior-art corrugated matrix geometry 700, such as shown in FIG. 7, can become restricted as the non-air particles build up, and block the passageway. Because the corrugated matrix design results in finite triangular shaped straw-like ‘fluted’ passageways, the velocity profile is not constant across the cross section of each passageway. The flow has a lower velocity in the corners of the triangles, as eddies and roll-ups from the corners' boundary layers block the incoming flow. These low velocity corners are perfectly suitable for dust and other contaminants to build up in, as the flow is too slow to force them out the long passageway. As the passageways in the wheel become restricted by built up contaminants, the pressure drop through the wheel will increase drastically as blockages in the incoming flow develop. As each finite fluted passageways become more and more clogged over time, less thermal performance and higher pressure drops are realized, and the passageway can eventually become completely blocked. These straw-like passageways are difficult to clean due to their small cross section and long flow length. In addition, the fluted design inherently results in a very stiff media assembly. Between the flow length of the passageway (often between 6 inches up to a foot), the rigidity of the media, and the triangular shape with tight, difficult to clean corners, the corrugated design can be difficult to clean of built up clogging.

The shape of the parallel plate geometry does not necessarily have tight corners to collect dust and dirt, and the length of the passageway is typically shorter, e.g., between 1 inches up to 6 inches depending on the design and size of the wheel. In addition, the parallel-plate media can flex since it lacks the high structural rigidity of the corrugated, triangular shape. This flexing can allow contaminants to more readily pass through the media rather than collect within a rigid finite passageway.

During use, the velocity profile across the wheel and within each parallel passageway is more uniform than the corrugated triangular fluted media at each diameter (due to the lack of tight passageways and increased area for open flow per diameter), helping prevent lower flow velocities that would allow a build-up of contaminants and thus flow blockages. The flexible matrix geometry allows slight motion during operation which will also help in keeping potentially clogging particles moving through the short passageway.

Cleaning of any substances attached to the media is more effective with the parallel-plate design, as there are no finite small flutes and fewer tight corners to flush out, and the media may be flexed to allow any particles to dislodge and exit the short flow length. The parallel-plate design also helps to prevent clogging during use, necessitating less frequent cleaning.

Because the parallel-plate design prevents the amount of blockage inherent to a corrugated design, the pressure drop is not expected to rise during use as it would in its corrugated counterpart. Thus, the parallel plate not only decreases the potential for clogging of the media and improves the clean-ability of the wheel, but also reduces the overall pressure drop through the wheel over time. Due to the potential of contaminants and other non-air substances flowing through the passageways of the wheel, the parallel-plate design is better suited than the fluted or corrugated design to applications with any possibility of contaminants that may foul the wheel.

Exemplary Embodiments

A rotary wheel regenerator with parallel plate media geometry design according to the present disclosure can provide one or more of the following advantages:

Having lower friction loss through the media passageways resulting in lower pressure loss profile through the regenerator therefore resulting in less energy (blower power) required to pass air through either side of the device (fresh air side and exhaust air side), resulting in better energy savings over time.

Having lower pressure drop due to better geometrical flow profile resulting in less load and stress on the structure of the heat wheel resulting in longer life of the wheel.

Having higher overall transfer of heat and/or moisture as desired from one side of the regenerator to the other resulting in higher energy savings.

Using less spirally wound length of material to manufacture the geometry than typical corrugated triangular flute media resulting in lower media cost and lighter weight of the finished device.

Having geometrical passageways that are less prone to collecting dirt and dust due to the passageway shape (parallel plate—long rectangular shape), and therefore are less apt to restrict and clog over time.

Having geometrical passageways that are slightly flexible to aid in allowing dirt and dust to pass through the media more readily.

Having passageways that are more readily cleaned due to shape and flexibility, resulting in better energy savings over time and consistent supply of fresh air for IAQ.

Having resultant transfer media that will maintain higher energy transfer over time and lower pressure losses over time due to being less prone to clogging, and due to better flow profiles through the cross section and more easily cleanable due to cross section shape and flexibility.

Having better energy savings over time due to less degradation due to clogging and ease of cleaning.

The components, steps, features, objects, benefits, and advantages that have been discussed are merely illustrative. None of them, nor the discussions relating to them, are intended to limit the scope of protection in any way. Numerous other embodiments are also contemplated. These include embodiments that have fewer, additional, and/or different components, steps, features, objects, benefits, and/or advantages. These also include embodiments in which the components and/or steps are arranged and/or ordered differently.

For example, as shown in FIG. 9, one method of creating parallel plate rotary wheel media is to create an intermediate layer, between two flat layers, having embossed formations sufficiently periodically spaced intended to stand the layers apart thus creating parallel plates. Variations to this method could include a variety of other methods of spacing the layers apart including inserting periodically small pins into a layer or layers, perpendicular to the face of the layers, to hold the layers uniformly apart, applying a spot of glue or polymer material of the appropriate thickness periodically to hold the layers uniformly apart, fastening thin spacers periodically extending across the wheel width from wheel face to wheel face to hold the layers uniformly apart, piercing small formations (e.g., like so-called “chads” on ballot cards) into the surface of each flat layer to create standoffs to hold the layers uniformly apart. Another method of holding the parallel plates apart could be to install a series of thin rods or wires from the outer diameter of the wheel rim, through all of the layers, and into the hub of the wheel, perpendicular to the wheel axis. Each layer (in this case all flat layers) would be pierced by the rods and held in their appropriate positions to create uniform spacings and passageways between the flat layers.

Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. They are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain.

All articles, patents, patent applications, and other publications that have been cited in this disclosure are incorporated herein by reference.

The phrase “means for” when used in a claim is intended to and should be interpreted to embrace the corresponding structures and materials that have been described and their equivalents. Similarly, the phrase “step for” when used in a claim is intended to and should be interpreted to embrace the corresponding acts that have been described and their equivalents. The absence of these phrases from a claim means that the claim is not intended to and should not be interpreted to be limited to these corresponding structures, materials, or acts, or to their equivalents.

The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows, except where specific meanings have been set forth, and to encompass all structural and functional equivalents.

Relational terms such as “first” and “second” and the like may be used solely to distinguish one entity or action from another, without necessarily requiring or implying any actual relationship or order between them. The terms “comprises,” “comprising,” and any other variation thereof when used in connection with a list of elements in the specification or claims are intended to indicate that the list is not exclusive and that other elements may be included. Similarly, an element proceeded by an “a” or an “an” does not, without further constraints, preclude the existence of additional elements of the identical type.

None of the claims are intended to embrace subject matter that fails to satisfy the requirement of Sections 101, 102, or 103 of the Patent Act, nor should they be interpreted in such a way. Any unintended coverage of such subject matter is hereby disclaimed. Except as just stated in this paragraph, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims.

The abstract is provided to help the reader quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, various features in the foregoing detailed description are grouped together in various embodiments to streamline the disclosure. This method of disclosure should not be interpreted as requiring claimed embodiments to require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description, with each claim standing on its own as separately claimed subject matter.

ROTARY HEAT REGENERATOR USING PARALLEL PLATE MEDIA

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