POLYMER FILM HEAT EXCHANGER WITH INTEGRAL FLUID DISTRIBUTION MANIFOLDS AND METHOD
A polymer film heat exchanger with integral fluid distribution manifolds. Methods of making polymer film heat exchangers.
This invention was made with government support under Energy Cooperative Agreement No. DE-AR0000309 awarded by the U.S. Department of Energy Advanced Research Project Agency. The government has certain rights in the invention.
BACKGROUNDPolymer-based heat exchangers offer unique benefits to end users including low-cost material of construction, resistance to fouling due to smooth surfaces, and generally excellent corrosion resistance. However, polymers have relatively poor thermal conductivity, and it is not practical to construct a polymer heat exchanger based on conventional metal heat exchanger design principles. In order for the polymers to have sufficient mechanical strength for conventional metal heat exchanger designs, the wall thicknesses would be so thick as to hinder effective heat transfer.
Several designs have been proposed that adapt to the strength limitations of thin polymer interfaces, but none have resulted in a design simplicity that is required to dramatically lower costs. As a result, polymer-based heat exchangers are today limited to relatively high value applications that require the inertness that polymers can provide, e.g., pharmaceutical processing, healthcare products, and corrosive fluid processing.
U.S. Pat. No. 4,411,310 and U.S. Pat. No. 4,744,414 both refer to the use of polymer films to separate flow channels and serve as an effective heat exchanger surface. However, each of these examples also requires additional non-film components to complete the fluid circuits. U.S. Pat. No. 4,411,310 refers to a separate molded manifold to which the polymer film flow channels are bonded in order to distribute the heat-transfer fluids to the appropriate flow channels. Similarly, U.S. Pat. No. 4,744,414 refers to molded spacers between the polymer layers to form the flow channels and provide the fluid distribution function.
SUMMARY OF THE INVENTIONA polymer film heat exchanger with integral fluid distribution manifolds.
In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
A heat exchanger operates to transfer heat from one fluid to another. The fluid can be liquid, vapor, or gas or a combination of the matter states. Hygroscopic fluids can be extremely useful in certain heat exchanger applications to limit water use. Hygroscopic fluids can be extremely corrosive and polymers can provide excellent resistance to corrosive fluids.
There is a need for a polymer heat exchanger that is low cost in construction and less complicated than previous heat exchangers. Described herein is a heat exchanger that includes a stack of film layers (film stack). The film stack can include alternating fluid passages that are separate from each other. Each fluid passage can include an input port and an output port and the input ports and output ports can be arranged so that the heat exchanger operates on a counter flow basis; fluid A flows in one direction and fluid B flows in the opposite direction.
The entire fluid circuit for both heat-transfer fluids, including the fluid distribution manifolds, can be formed using only a flexible polymer film. Forming integral manifolds out of the polymer film itself eliminates the need for additional pieces to be added to the heat exchanger.
The heat exchanger described herein formed from a stack of flexible polymer film sheets forms a parallel plate heat exchanger having alternating layers of flow channels. Fluid distribution can be accomplished by selectively bonding together film layers around flow channel apertures in an alternating manner so that a single fluid connection port can be only in fluid communication with alternating flow channels associated with only one of the heat exchange fluids. Dimensions of the flow channels can be regulated by regulating fluid pressures applied to one or more of the heat exchanger fluids. The entire assembly can be restrained from overexpansion by external rigid plates that sandwich the polymer film stack.
To further illustrate the heat exchanger and method disclosed herein, a non-limiting list of examples is provided here:
In Example 1, a device can comprise: a plurality of polymer films including a first film adjacent a second film and including a third film adjacent the second film, the plurality of polymer films in stacked alignment and having a stack axis normal to a plane of the plurality of polymer films, wherein the first film is bonded to the second film with a first bond having a first pattern configured to form a first channel between the first film and the second film, and further wherein the second film is bonded to the third film with a second bond having a second pattern configured to form a second channel between the second film and the third film, and further including a first pair of ports fluidly coupled to the first channel and including a second pair of ports fluidly coupled to the second channel, wherein the first pair of ports and the second pair of ports have port axes aligned substantially parallel with the stack axis.
In Example 2, the device of Example 1 can optionally be configured such that the third film is bonded to a fourth film with a third bond, the third bond having the first pattern and wherein the first channel is fluidly coupled to a region bound by the third film and the fourth film.
In Example 3, the device of Example 2 can optionally be configured such that the fourth film is bonded to a fifth film with a fourth bond, the fourth bond having the second pattern and wherein the second channel is fluidly coupled to a region bound by the fourth film and the fifth film.
In Example 4, the device of any one or any combination of Examples 1-3 can optionally be configured such that the first channel is bound by the first bond and wherein the second channel is bound by the second bond.
In Example 5, the device of any one or any combination of Examples 1-4 can optionally be configured such that the first pair of ports and the second pair of ports are on a common side of the plurality of polymer films.
In Example 6, the device of any one or any combination of Examples 1-5 can optionally be configured such that the polymer films of the plurality of polymer films have a substantially rectangular profile and wherein the first pair of ports includes a first input port and includes a first output port and wherein the first input port and the first output port are aligned on a common diagonal determined by the profile.
In Example 7, the device of any one or any combination of Examples 1-6 can optionally be configured such that at least one of the first bond and the second bond includes at least one of a thermal joint, a weld joint, and an adhesive joint.
In Example 8, the device of any one or any combination of Examples 1-7 can optionally be configured such that the first channel is fluidly isolated from the second channel.
In Example 9, the device of any one or any combination of Examples 1-8 can optionally be configured to further include a first reinforcement plate coupled to a first selected polymer film of the plurality of polymer films.
In Example 10, the device of Example 9 can optionally be configured to further include a second reinforcement plate coupled to a second selected polymer film of the plurality of polymer films.
In Example 11, the device of Example 10 can optionally be configured to further include at least one spacer coupled to the first reinforcement plate and coupled to the second reinforcement plate, wherein the at least one spacer is configured to retain the first reinforcement plate and the second reinforcement plate in fixed alignment and at a predetermined distance apart.
In Example 12, the device of any one or any combination of Examples 1-11 can optionally be configured such that the first film and the second film have a dimension in common.
In Example 13, the device of any one or any combination of Examples 1-12 can optionally be configured such that the first film, the second film, and the third film have an aperture in common.
In Example 14, a method can comprise forming a first bond coupling a first film and a second film, the first bond having a first bond pattern, the first film and the second film in stacked alignment and having a first channel therebetween; forming a second bond coupling the second film and a third film, the second bond having a second bond pattern, the second film and the third film in stacked alignment and having a second channel therebetween, the second channel fluidly independent of the first channel; forming a first pair of ports in the first film, the first pair of ports in fluid communication with the first channel; and forming a second pair of ports in the third film, the second pair of ports in fluid communication with the second channel.
In Example 15, the method of Example 14 can optionally be configured to further include forming a third bond coupling the third film and a fourth film, the third bond having the first bond pattern, the third film and the fourth film in stacked alignment and wherein the first channel is fluidly coupled to a region bound by the third film and the fourth film.
In Example 16, the method of Example 15 can optionally be configured to further include forming a fourth bond coupling the fourth film and a fifth film, the fourth bond having the second bond pattern, the fourth film and the fifth film in stacked alignment and wherein the second channel is fluidly coupled to a region bound by the fourth film and the fifth film.
In Example 17, the method of any one or any combination of Examples 14-16 can optionally be configured such that forming the first pair of ports and forming the second pair of ports includes forming on a common side of the films.
In Example 18, the method of any one or any combination of Examples 14-17 can optionally be configured such that the first film, the second film, and the third film have a substantially rectangular profile and wherein forming the first pair of ports includes forming a first input port and includes forming a first output port and wherein the first input port and the first output port are aligned on a common diagonal determined by the profile.
In Example 19, the method of any one or any combination of Examples 14-18 can optionally be configured such that at least one of forming the first bond and forming the second bond includes forming at least one of a thermal joint, a weld joint, and an adhesive joint.
In Example 20, the method of any one or any combination of Examples 14-19 can optionally be configured to further include affixing a first reinforcement plate to the first film.
In Example 21, the method of Example 20 can optionally be configured to further include affixing a second reinforcement plate coupled to a film.
In Example 22, the method of Example 21 can optionally be configured to further include providing at least one spacer coupled to the first reinforcement plate and coupled to the second reinforcement plate, wherein the at least one spacer is configured to retain the first reinforcement plate and the second reinforcement plate in fixed alignment and at a predetermined distance apart.
In Example 23, the device and method of any one or any combination of Examples 1-22 can optionally be configured such that all elements, operations, or other options recited are available to use or select from.
The heat exchanger assembly 15 is illustrated as having the input and output ports extending through one reinforcement plate (see
An outer perimeter 41 of the film stack 1 is shown as located inwardly from the spacers 4. The spacers 4 can include a bore 13 and be positioned between corresponding holes 17 in the reinforcement plates 16, 18. A fastener 42 (such as a threaded bolt or threadless rivet) can extend through the bore 13 and holes 17 and secure the first reinforcement plate 16 to the second reinforcement plate 18. The spacers 4 and fasteners 42 can retain the reinforcement plates in fixed alignment and a predetermined distance apart. In another example, one or more spacers 4 can be integral with the first reinforcement plate 16, the second reinforcement plate 18, or both plates.
In an example, second film 62B is bonded on its bottom surface 56A with the first bond pattern 10 to the first film 62A. The second film 62B is bonded on its upper surface 57 with the second bond pattern 9 to the bottom surface 56B third film 62C. For example, when a film layer 20 is bonded to an adjacent film layer 20, one set of input/output apertures can have a fluid tight bond between the layers, while the other set of input/output apertures can remain unbonded between the two layers. In conjunction with the first pattern bond perimeter 40A or the second pattern bond perimeter 40B, such bonding at the apertures can create a flow channel 58 for either Fluid A or Fluid B, depending on whether the first bonding pattern 10 or the second bonding pattern 9 is used between the two layers. When the bonding pattern around a fluid aperture is bonded, and two adjacent film layers are bonded together at the fluid aperture, then no fluid at that fluid aperture can get between those two film layers. Conversely, when the bond pattern is such that two adjacent film layers are not bonded together at a fluid aperture, then fluid from the fluid aperture can enter between the two film layers and form a flow channel 58.
By alternating the first bonding pattern 10 and the second bonding pattern 9, the bonding patterns can be reversed, meaning that the first bonding pattern 10 can be bonded to a layer above, and the second bonding pattern 9 can be bonded to the layer below. This alternating pattern can be repeated until a desired number of flow channels 58 are reached. Each film layer 20 can be identical in dimensions and hole placements; the orientation of the bonding patterns can change from layer to layer, in other words the first bonding pattern 10 can be between one set of adjacent layers, the second bonding pattern 9 can be between the next set of adjacent layers and so on.
A third film 62C can be located over the second film 62B. The second film 62B can be bonded to the third film 62C by a second bond 66B having a second bonding pattern 9. The second bond 66B having the second bonding pattern 9 does not include any bonding between the second film 62B and the third film 62C in the region of the Fluid A input apertures 46 of the second and third films 62B, 62C. A second channel 70B can be formed between the second film 62B and the third film 62C. The second channel 70B can be fluidly connected to the Fluid A flow passage 22. The second bond 66B bonds the Fluid B output aperture 52 of the second film 62B to the Fluid B output aperture 52 of the third film 62C so Fluid A and Fluid B cannot mix at the Fluid B output aperture 52.
A fourth film 62D can be located over the third film 62C. A third bond 66C having the first bonding pattern 10 can bond the third film 62C to the fourth film 62D. The third bond 66C having the first bonding pattern 10 does not include any bonding between the third film 62C and the fourth film 62D in the region of the Fluid B output aperture 52 of the third film 62C and the fourth film 62D. A third channel 70C can be formed between the third film 62C and the fourth film 62D. The third channel 70C can be fluidly connected to the Fluid B flow passage 24. The third bond 66C bonds the Fluid A input aperture 46 of the third film 62C to the fourth film 62D so Fluid A and Fluid B cannot mix at the Fluid A input aperture 46. There is a fluid passage 84 between the first pattern bond perimeter 40A of the third bond 66C and the Fluid A input aperture 46. This fluid passage 84 is a portion of the third channel 70C and can also be seen from the top view of
A fifth film 62E can be located over the fourth film 62D. The fifth film 62E can be bonded to the fourth film 62D by a fourth bond 66D having the second bonding pattern 9. The fourth bond 66D having the second bonding pattern 9 does not include any bonding between the fourth film 62D and the fifth film 62E in the region of the Fluid A input aperture 46 of the fourth and fifth films 62D, 62E. A fourth channel 70D can be formed between the fourth film 62D and the fifth film 62E. The fourth channel 70D can be fluidly connected to the Fluid A flow passage 22. The fourth bond 66D bonds the Fluid B output aperture 52 of the fourth film 62D to the Fluid B output aperture 52 of the fifth film 62E so Fluid A and Fluid B cannot mix at the Fluid B output aperture 52.
The alternating bonding of the first bonding pattern 10 and the second bonding pattern 9 to additional film layers 20 can also create a fifth channel 70E, a sixth channel 70F, a seventh channel 70G, an eighth channel 70H and a ninth channel 70J. The fifth, seventh and ninth channels 70E, 70G, 70J can be fluidly connected to the Fluid B flow passage 24. The sixth and eighth channels 70F, 70H can be fluidly connected to the Fluid A flow passage 22.
The film layers 20 of the film stack 1 can be stacked in a direction that is substantially normal to the plane of each film layer 20. The connection of the channels to a fluid flow passage, such as the connection of the first, third, fifth, seventh and ninth channels 70A, 70C, 70E, 70G, 70J to the Fluid B flow passage 24 can form a Fluid B port manifold 25 at both the Fluid B input port 7 (see also
The film layer 20 can have a flattened sheet-like form. When containing a fluid, such as a pressurized fluid, the flow channels, such as channels 70A-H and 70J can expand the film layer 20 into a three dimensional form as shown. In an example, the film layer 20 can be formed of a semi-rigid material or pre-creased material that can maintain a three dimensional shape in a single layer or a non-pressurized channel. Additional bonds not needed for fluid channel sealing can be included between adjacent film layers to encourage uniform expansion of film layer 20 into a three dimensional form.
A third film 62C can be located over the second film 62B. The second film 62B can be bonded to the third film 62C by a second bond 66B having a second bonding pattern 9. The second bond 66B having the second bonding pattern 9 does not include any bonding between the second film 62B and the third film 62C in the region of the Fluid A input aperture 46 of the second and third films 62B, 62C. A second channel 70B can be formed between the second film 62B and the third film 62C. The second channel 70B can be fluidly connected to the Fluid A flow passage 22. The second bond 66B bonds the Fluid B output aperture 52 of the second film 62B to the Fluid B output aperture 52 of the third film 62C so Fluid A and Fluid B cannot mix at the Fluid B output aperture 52.
A fourth film 62D can be located over the third film 62C. A third bond 66C having the first bonding pattern 10 can bond the third film 62C to the fourth film 62D. The third bond 66C having the first bonding pattern 10 does not include any bonding between the third film 62C and the fourth film 62D in the region of the Fluid B output aperture 52 of the third film 62C and the fourth film 62D. A third channel 70C can be formed between the third film 62C and the fourth film 62D. The third channel 70C can be fluidly connected to the Fluid B flow passage 24. The third bond 66C bonds the Fluid A input aperture 46 of the third film 62C to the fourth film 62D so Fluid A and Fluid B cannot mix at the Fluid A input aperture 46. The fluid passage 84 described previously is shown on channels having the first bonding pattern 10. In
A fifth film 62E can be located over the fourth film 62D. The fifth film 62E can be bonded to the fourth film 62D by a fourth bond 66D having the second bonding pattern 9. The fourth bond 66D having the second bonding pattern 9 does not include any bonding between the fourth film 62D and the fifth film 62E in the region of the Fluid A input aperture 46 of the fourth and fifth films 62D, 62E. A fourth channel 70D can be formed between the fourth film 62D and the fifth film 62E. The fourth channel 70D can be fluidly connected to the Fluid A flow passage 22. The fourth bond 66D bonds the Fluid B output aperture 52 of the fourth film 62D to the Fluid B output aperture 52 of the fifth film 62E so Fluid A and Fluid B cannot mix at the Fluid B output aperture 52.
The alternating of the first bonding pattern 10 and the second bonding pattern 9 can also create a fifth channel 70E which can be fluidly connected to the Fluid B flow passage 24. Fluid connections 30 are shown bonded to the outer surface 102 of a sixth film 62F. The fluid connections 30 can extend through the second reinforcement plate 18. The fluid connections 30 can form fluid connections using any device common to the industry. These connections can include welded flanges or mechanical bulkhead fittings.
Although the film stacks 1 in
Method 900 includes at 920, bonding a second film and a third film. The third film can be located over the second film in stacked alignment. The second film and the third film can be bonded by a second bond. The second bond can include a second bonding pattern. The second bonding pattern can bond a perimeter between the second and third films. The second bond can form bonds around the respective pair of port apertures that are not bonded in the first bond and leave unbonded the respective pair of apertures that were bonded in the first bond. Such bonding can form a second channel between the second and third films. The second channel can be fluidly independent of the first channel. Although method 900 describes the first bond as having the first pattern, in another example, the first bond can have the second pattern. The first and second patterns are alternated, so if the first bond is the second pattern, the second bond will be the first pattern and so on.
Method 900 includes at 930, forming a first pair of ports. The first pair of ports can be in fluid communication with the first channel. Method 900 includes at 940 forming a second pair of ports. The second pair of ports can be in fluid communication with the second channel.
Method 900 can also include at 950, bonding a third film and a fourth film. The fourth film can be located over the third film in stacked alignment. The third film and the fourth film can be bonded by a third bond, having the first bonding pattern. The region bound by the third and fourth films can be fluidly coupled to the first channel. Method 900 can also include at 960, bonding a fourth film and a fifth film. The fifth film can be located over the fourth film in stacked alignment. The fourth film and the fifth film can be bonded by a fourth bond, having the second bonding pattern. The region bound by the fourth and fifth films can be fluidly coupled to the second channel.
Method 900 can also include at 970, forming both pairs of ports on a common side of the films. In an example, one pair of ports can be formed on one side of the films, while another pair of ports can be formed on the opposite side of the films. In an example, an input port for Fluid A and an input port for Fluid B can be formed on one side of the films, while an output port for Fluid A and an output port for Fluid B can be formed on the opposite side of the films. In an example, one port can be formed on one side of the films and three ports can be formed on the opposite side of the films. The additive sequence of 950 and 960 can be repeated for additional film layers to form the desired number of parallel flow channels.
Method 900 can also include at 975, films having a rectangular profile and having a pair of ports aligned on a common diagonal. The first film, the second film and the third film can have a substantially rectangular profile. Forming the first pair of ports can include forming a first input port and a first output port. The first input port and the first output port can be aligned on a common diagonal of the substantially rectangular profile. This diagonal port configuration encourages the counterflow interaction of Fluids A and B in during counterflow heat exchange.
Method 900 can also include at 980, bonding that includes at least one of a thermal joint, a weld joint or an adhesive joint. The bonding forms a fluid tight seal that separates fluids from intermixing and prevents leakages.
Method 900 can also include at 985, affixing a first reinforcement plate to a film. The reinforcement plate can be a rigid material made of polymer, rubber, plastic, metal, or combinations thereof. Method 900 can also include at 990, affixing a second reinforcement plate to a film. The first and second reinforcement plates can sandwich the film layers between them. The reinforcement plates can prevent the layers of films from over-expanding from pressurized fluids, provide structural protection for the films, and provide a rigid structure for attachment to another structure. Method 900 can also include at 995, providing at least one spacer coupled to the reinforcement plates that can retain the plates in fixed alignment and at a predetermined distance apart. The spacer length can be adjusted to change the number of film layers or the expandable dimensions of channels between films.
The films used in method 900 can be flexible. In an example, the films can be formed of a semi-rigid material or pre-creased material that can maintain a three dimensional shape in a single layer or a non-pressurized channel. Additional bonds not needed for fluid channel sealing can be included patterns between adjacent film layers to encourage uniform expansion of film layers into a three dimensional form.
The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments of the heat exchanger. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described.
The description herein is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
Claims
1. A device comprising:
- a plurality of polymer films including a first film adjacent a second film and including a third film adjacent the second film, the plurality of polymer films in stacked alignment and having a stack axis normal to a plane of the plurality of polymer films, wherein the first film is bonded to the second film with a first bond having a first pattern configured to form a first channel between the first film and the second film, and further wherein the second film is bonded to the third film with a second bond having a second pattern configured to form a second channel between the second film and the third film, and further including a first pair of ports fluidly coupled to the first channel and including a second pair of ports fluidly coupled to the second channel, wherein the first pair of ports and the second pair of ports have port axes aligned substantially parallel with the stack axis.
2. The device of claim 1 wherein the third film is bonded to a fourth film with a third bond, the third bond having the first pattern and wherein the first channel is fluidly coupled to a region bound by the third film and the fourth film.
3. The device of claim 2 wherein the fourth film is bonded to a fifth film with a fourth bond, the fourth bond having the second pattern and wherein the second channel is fluidly coupled to a region bound by the fourth film and the fifth film.
4. The device of claim 1 wherein the first channel is bound by the first bond and wherein the second channel is bound by the second bond.
5. The device of claim 1 wherein the first pair of ports and the second pair of ports are on a common side of the plurality of polymer films.
6. The device of claim 1 wherein the polymer films of the plurality of polymer films have a substantially rectangular profile and wherein the first pair of ports includes a first input port and includes a first output port and wherein the first input port and the first output port are aligned on a common diagonal determined by the profile.
7. The device of claim 1 wherein at least one of the first bond and the second bond includes at least one of a thermal joint, a weld joint, and an adhesive joint.
8. The device of claim 1 wherein the first channel is fluidly isolated from the second channel.
9. The device of claim 1 further including a first reinforcement plate coupled to a first selected polymer film of the plurality of polymer films.
10. The device of claim 9 further including a second reinforcement plate coupled to a second selected polymer film of the plurality of polymer films.
11. The device of claim 10 further including at least one spacer coupled to the first reinforcement plate and coupled to the second reinforcement plate, wherein the at least one spacer is configured to retain the first reinforcement plate and the second reinforcement plate in fixed alignment and at a predetermined distance apart.
12. The device of claim 1 wherein the first film and the second film have a dimension in common.
13. The device of claim 1 wherein the first film, the second film, and the third film have an aperture in common.
14. A method comprising:
- forming a first bond coupling a first film and a second film, the first bond having a first bond pattern, the first film and the second film in stacked alignment and having a first channel therebetween;
- forming a second bond coupling the second film and a third film, the second bond having a second bond pattern, the second film and the third film in stacked alignment and having a second channel therebetween, the second channel fluidly independent of the first channel;
- forming a first pair of ports in the first film, the first pair of ports in fluid communication with the first channel; and
- forming a second pair of ports in the third film, the second pair of ports in fluid communication with the second channel.
15. The method of claim 14 further including forming a third bond coupling the third film and a fourth film, the third bond having the first bond pattern, the third film and the fourth film in stacked alignment and wherein the first channel is fluidly coupled to a region bound by the third film and the fourth film.
16. The method of claim 15 further including forming a fourth bond coupling the fourth film and a fifth film, the fourth bond having the second bond pattern, the fourth film and the fifth film in stacked alignment and wherein the second channel is fluidly coupled to a region bound by the fourth film and the fifth film.
17. The method of claim 14 wherein forming the first pair of ports and forming the second pair of ports includes forming on a common side of the films.
18. The method of claim 14 wherein the first film, the second film, and the third film have a substantially rectangular profile and wherein forming the first pair of ports includes forming a first input port and includes forming a first output port and wherein the first input port and the first output port are aligned on a common diagonal determined by the profile.
19. The method of claim 14 wherein at least one of forming the first bond and forming the second bond includes forming at least one of a thermal joint, a weld joint, and an adhesive joint.
20. The method of claim 14 further including affixing a first reinforcement plate to the first film.
21. The method of claim 20 further including affixing a second reinforcement plate coupled to a film.
22. The method of claim 21 further including providing at least one spacer coupled to the first reinforcement plate and coupled to the second reinforcement plate, wherein the at least one spacer is configured to retain the first reinforcement plate and the second reinforcement plate in fixed alignment and at a predetermined distance apart.
Type: Application
Filed: Jan 20, 2015
Publication Date: Jul 21, 2016
Inventors: Christopher Lee Martin (Grand Forks, ND), Grant Edward Dunham (Grand Forks, ND)
Application Number: 14/600,927