Patent Publication Number: US-9835893-B2

Title: Heat exchanger for back to back electronics displays

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/702,443 filed on May 1, 2015 which is now U.S. Pat. No. 9,173,325, which is a continuation of U.S. application Ser. No. 13/692,657 filed on Dec. 3, 2012 and now U.S. Pat. No. 9,030,641, which was a continuation U.S. application Ser. No. 12/753,298 filed on Apr. 2, 2010, now U.S. Pat. No. 8,351,014. U.S. application Ser. No. 12/753,298 is a non-provisional application of U.S. Provisional Application No. 61/252,295 filed Oct. 16, 2009. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/641,468 filed Dec. 18, 2009, now U.S. Pat. No. 8,654,302, which is a non-provisional application of U.S. Provisional Application No. 61/138,736 filed Dec. 18, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/411,925 filed Mar. 26, 2009, now U.S. Pat. No. 8,854,595, which is a non-provisional of U.S. Provisional Application No. 61/039,454 filed Mar. 26, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/556,029 filed Sep. 9, 2009, now U.S. Pat. No. 8,373,841, which is a non-provisional application of U.S. Provisional Application No. 61/095,615 filed Sep. 9, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/234,307 filed Sep. 19, 2008, now U.S. Pat. No. 8,767,165, which is a non-provisional application of U.S. Provisional Application No. 61/033,064 filed Mar. 3, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/234,360 filed Sep. 19, 2008, which is a non-provisional application of U.S. Provisional Application No. 61/053,713 filed May 16, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/237,365 filed Sep. 24, 2008, now U.S. Pat. No. 8,879,042, which is a non-provisional application of U.S. Provisional Application No. 61/057,599 filed May 30, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/235,200 filed Sep. 22, 2008, which is a non-provisional application of U.S. Provisional Application No. 61/076,126 filed Jun. 26, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/620,330 filed Nov. 17, 2009, now U.S. Pat. No. 8,274,622, which is a non-provisional application of U.S. Provisional Application No. 61/115,333 filed Nov. 17, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/556,209 filed Sep. 9, 2009, now U.S. Pat. No. 8,379,182, which is a non-provisional application of U.S. Provisional Application No. 61/095,616 filed Sep. 9, 2008. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/706,652 filed Feb. 16, 2010, now U.S. Pat. No. 8,358,397, which is a non-provisional application of U.S. Provisional Application No. 61/152,879 filed Feb. 16, 2009. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/630,469 filed Dec. 3, 2009, now U.S. Pat. No. 8,497,972. U.S. application Ser. No. 12/753,298 is also a continuation-in-part of U.S. application Ser. No. 12/234,182 filed Sep. 19, 2008, now U.S. Pat. No. 8,711,321, which is a non-provisional application of U.S. Provisional Application No. 61/033,064 filed Mar. 3, 2008. All aforementioned applications are hereby incorporated by reference in their entirety as if fully cited herein. 
    
    
     TECHNICAL FIELD 
     The exemplary embodiments generally relate to cooling systems and in particular to cooling systems for electronic displays. 
     BACKGROUND OF THE ART 
     Electronic displays are now being used in outdoor environments and other applications where they may be exposed to high ambient temperatures and/or direct sunlight. In many climates, radiative heat transfer from the sun through a display window becomes a major factor. In many applications and locations 200 Watts or more of power through such a display window is possible. Furthermore, the market is demanding larger screen sizes for displays. With increased electronic display screen size and corresponding display window size more heat will be generated and more heat will be transmitted into the displays. Also, when displays are used in outdoor environments the ambient air may contain contaminants (dust, dirt, pollen, water vapor, smoke, etc.) which, if ingested into the display for cooling the interior can cause damage to the interior components of the display. 
     A large fluctuation in temperature is common in the devices of the past. Such temperature fluctuation adversely affects the electronic components in these devices; both performance and lifetime may be severely affected. Thus, there exists a need for a cooling system for electronic displays which are placed within environments having high ambient temperatures, possibly contaminants present within the ambient air, and even placed in direct sunlight. 
     SUMMARY OF THE EXEMPLARY EMBODIMENTS 
     Exemplary embodiments may comprise two separate flow paths for gas through an electronic display. A first flow path may be a closed loop and a second flow path may be an open loop. The closed loop path forces circulating gas across the front surface of the image assembly, continues behind the image assembly where it may enter a heat exchanger, finally returning to the front surface of the image assembly. The open loop path may draw ambient gas (ex. ambient air) through the display (sometimes through a heat exchanger, behind an image assembly, or both) and then exhaust it out of the display housing. A heat exchanger may be used to transfer heat from the circulating gas to the ambient gas. In alternative embodiments, the ambient gas may also be forced behind the image assembly (sometimes a backlight), in order to cool the image assembly and/or backlight assembly (if a backlight is necessary for the particular type of display being used). A cross-flow heat exchanger may be used in an exemplary embodiment. 
     In an exemplary embodiment, two electronic displays are placed back-to-back and share a single heat exchanger. In this embodiment, two closed loop paths may travel though a single housing in order to cool the displays. 
     The foregoing and other features and advantages of the exemplary embodiments will be apparent from the following more detailed description of the particular embodiments of the invention, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of an exemplary embodiment will be obtained from a reading of the following detailed description and the accompanying drawings wherein identical reference characters refer to identical parts and in which: 
         FIG. 1  is an exploded view of an exemplary embodiment. 
         FIG. 2A  is a perspective view of one embodiment for the back-to-back displays showing cutting planes B-B and C-C. 
         FIG. 2B  is a section view along cutting plane B-B shown in  FIG. 2A . 
         FIG. 2C  is a section view along cutting plane C-C shown in  FIG. 2A . 
         FIG. 3A  is a perspective view of another embodiment for the back-to-back displays showing cutting planes B-B and C-C. 
         FIG. 3B  is a section view along cutting plane B-B shown in  FIG. 3A . 
         FIG. 3C  is a section view along cutting plane C-C shown in  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  provides an exploded view of an exemplary embodiment. In the exemplary embodiments, two electronic image assemblies are placed back to back in a substantially symmetrical manner. In this particular embodiment  10 , LED backlit LCD displays are used but the techniques taught herein could be applied to any electronic assembly for generating an image, including but not limited to: light emitting diode (LED), organic light emitting diode (OLED), field emitting displays (FED), light-emitting polymers (LEP), plasma displays, and any other flat/thin panel displays. As shown in  FIG. 1 , each LCD assembly  85  has a front portion  86  and rear portion  84  where the front portion  86  produces the image and the rear portion  84  faces the oppositely-facing LCD assembly  85 . A LED backlight  140  is placed adjacent to the rear portion  84  of the LCD assemblies  85 , as is known in the art. Edge-lit LED backlights or direct-lit LED backlights could be used with the various embodiments herein. For the particular embodiment shown in  FIG. 1 , a direct-lit LED backlight is preferable. 
     The exemplary embodiment shown in  FIG. 1  can cool various portions of the assembly shown, including but not limited to the rear surfaces of the LED backlights  140 . Ambient gas  40  may be drawn into the display housing  70  through the inlet apertures  179  and forced along the rear surface of the LED backlights  140 . The fan assembly  60  may be used to draw the ambient gas  40  into the display housing  70  and along the rear surface of the LED backlights  140 . Although shown at the bottom of the display housing  70 , the fan assembly  60  can be placed anywhere in the assembly. For example, fans could also be placed at the top of the housing  70  either instead of or in addition to the ones shown at the bottom in  FIG. 1 . Further, the fans may draw the ambient air from below the housing, above the housing, or from the sides. 
     In this embodiment, a heat exchanger  45  is placed between the two backlights  140 . A protective transparent plate  90  may be placed in front of the front portion of the LCD assembly  85 . The space between the protective transparent plate  90  and the LCD assembly defines a channel where circulating gas may travel in order to cool the front portion  86  of the LCD assembly  85 . The circulating gas then travels through a first pathway  44  of the heat exchanger  45  in order to be cooled by the ambient gas  145 . The circulating gas may be forced through the channel and the heat exchanger  45  by closed loop fan assembly  50 . Ambient gas  145  may be directed through a second pathway  46  of the heat exchanger  45 . The ambient gas  145  may be forced through the heat exchanger  45  by the fans  60  or may be forced using a separate fan  245 , controlled specifically for the heat exchanger  45 . The protective transparent plate  90  may be any rigid transparent material. Exemplary embodiments may use glass for the plate  90 . Further embodiments may combine anti-reflective layers and/or polarizers with the plate  90  to reduce the amount of reflected light. Ideally, these could be bonded to a plate of glass using pressure sensitive adhesive (PSA) and would preferably be index-matched. In some embodiments, the plate  90  may comprise two or more pieces of glass bonded together with index-matching optical adhesive. 
       FIG. 2A  provides a perspective view of an embodiment with the housing removed and showing the plates  90  installed in front of the LCD assemblies  85 . This figure shows the placement for cutting planes B-B and C-C which provide the section views in  FIGS. 2B and 2C  respectively. Cutting plane B-B passes vertically down the center of the assembly and through the heat exchanger  45 . Cutting plane C-C passes horizontally through the center of the assembly. 
     A second surface  226  may be placed behind the rear surface of each of the backlights  140 . The space between the rear surface of the backlight  140  and this second surface  226  may define an open loop channel  225  through which the ambient gas  40  may travel in order to cool the backlight  140  (or the electronic image assembly if no backlight is used). Exemplary embodiments of the LED backlights  140  would have a low level of thermal resistance between the front surface containing the LEDs and the rear surface which faces the second surface  226  and is in contact with the ambient gas  40 . A metallic PCB may be used as the mounting structure for this purpose. The rear surface of the backlight  140  may contain a thermally conductive material, such as a metal. Aluminum may be an exemplary material for the rear surface. 
       FIG. 2B  provides the section view from cutting plane B-B shown in  FIG. 2A . In this particular embodiment, ambient gas  145  travels through the heat exchanger  45  while ambient gas  40  travels through the open loop channels  225 . Thus, ambient gas  145  may be used to remove heat from the circulating gas and ambient gas  40  may be used to remove heat from the LED backlight  140 . As can be readily observed in this view, the LED backlight  140  and LCD assembly  85  could easily be substituted with any other electronic image assembly (such as those listed above or below). It should be noted that there is no requirement that ambient gas  145  and  40  be different in any way. For example, both ambient gas  145  and  40  may enter through the same inlet in the housing and even be exhausted out of the same exhaust aperture in the housing. Further, a single fan assembly can force both ambient gas  145  and  40 . They are simply shown with different numeral callouts so that one can see the separate passages for the ambient gas (i.e. one through the heat exchanger  45  and another through the optional open loop channels  225 ). As will be discussed further below, the open loop channels  225  are not required for all embodiments. This is especially true for electronic displays that do not require a backlight or displays which contain a backlight that does not produce relatively large amounts of heat. It is specifically contemplated that OLED displays could be used where only ambient gas  145  would be drawn into the display and through the heat exchanger  45  (although ambient gas could be used to cool other portions of the display, open loop channels  225  may not be required with OLED embodiments). 
       FIG. 2C  provides the section view from cutting plane C-C shown in  FIG. 2A . The circulating gas preferably travels in a closed loop where it is drawn through the first gas pathway  44  of the heat exchanger  45  and then directed into the entrances  110  of the channels  30 . As discussed above, the channels  30  may be defined by the space between the front surface of the LCD assembly  85  (or other electronic image assembly) and the transparent plate  90 . As mentioned above, sunlight (or high ambient surrounding temperatures) can cause a buildup of heat on the LCD assembly  85 . As the circulating gas travels through the channel  30 , it may remove heat from the front surface of the LCD assembly  85 . The circulating gas may then be directed out of the channel  30  through the exit  120 . The circulating gas may then be re-directed into the first gas pathway  44  of the heat exchanger  45  so that it may be cooled by the ambient gas  145  (which may be travelling through the second gas pathway  46  of the heat exchanger  45 ). 
     The closed loop fan assembly  50  may be placed so that the circulating gas will be forced through this closed loop. While the figure shows the placement of the fan assembly  50  after and away from the heat exchanger  45 , it should be noted that the fan assembly  50  could be placed anywhere in the system so that adequate velocity and flow of the circulating gas is achieved. Thus, some embodiments could even use two or more fan assemblies, placing them along two opposing edges (entrance and exit) of a heat exchanger  45 . The circulating gas could be ‘pulled’ across the front of the electronic image assembly and ‘pushed’ through the heat exchanger  45 . This is not required however; other embodiments may pull the isolated gas through the heat exchanger  45  and ‘push’ it through the channel  30 . Other embodiments may push the isolated gas only across the front of the electronic image assembly. Because the various fan assemblies described herein can be placed in multiple orientations, when referring to the placement of the various fan assemblies, the terms ‘push’, ‘pull’, ‘force’, and ‘draw’ will be used interchangeably and any orientation may be used with the various embodiments herein. 
     Various electronic components could be placed within the path of the circulating gas by placing them within cavity  41  which includes the heat exchanger  45 . The circulating gas may be used to extract heat from these devices as well. The electronic components may be any components or assemblies used to operate the display including, but not limited to: transformers, circuit boards, resistors, capacitors, batteries, power modules, motors, inductors, transformers, illumination devices, wiring and wiring harnesses, lights, thermo-electric devices, and switches. In some embodiments, the electrical components may also include heaters, if the display assembly is used in cold-weather environments. 
     In some embodiments, the ambient gas  145  and  40  may be air conditioned (or otherwise cooled) prior to being drawn through the heat exchanger  45 . This is not required however; as it has been found that proper design of the heat exchanger  45  and other various components can provide adequate cooling in most environments without additional air conditioning. 
     Although not required, it is preferable that the circulating gas and ambient gas  145  do not mix. This may prevent any contaminants and/or particulate that is present within the ambient gas  145  from harming the interior of the display. In a preferred embodiment, the heat exchanger  45  would be a cross-flow heat exchanger. However, many types of heat exchangers are known and can be used with any of the embodiments herein. The heat exchanger  45  may be a cross-flow, parallel flow, or counter-flow heat exchanger. In an exemplary embodiment, the heat exchanger  45  would be comprised of a plurality of stacked layers of thin plates. The plates may have a corrugated, honeycomb, or tubular design, where a plurality of channels/pathways/tubes travel down the plate length-wise. The plates may be stacked such that the directions of the pathways are alternated with each adjacent plate, so that each plate&#39;s pathways are substantially perpendicular to the pathways of the adjacent plates. Thus, ambient gas or circulating gas may enter an exemplary heat exchanger only through plates whose channels or pathways travel parallel to the path of the gas. Because the plates are alternated, the circulating gas and ambient gas may travel in plates which are adjacent to one another and heat may be transferred between the two gases without mixing the gases themselves (if the heat exchanger is adequately sealed, which is preferable but not required). 
     In an alternative design for a heat exchanger, an open channel may be placed in between a pair of corrugated, honeycomb, or tubular plates. The open channel may travel in a direction which is perpendicular to the pathways of the adjacent plates. This open channel may be created by running two strips of material or tape (esp. very high bond (VHB) tape) between two opposite edges of the plates in a direction that is perpendicular to the direction of the pathways in the adjacent plates. Thus, gas entering the heat exchanger in a first direction may travel through the open channel (parallel to the strips or tape). Gas which is entering in a second direction (substantially perpendicular to the first direction) would travel through the pathways of the adjacent plates). 
     Other types of cross-flow heat exchangers could include a plurality of tubes which contain the first gas and travel perpendicular to the path of the second gas. As the second gas flows over the tubes containing the first gas, heat is exchanged between the two gases. Obviously, there are many types of cross-flow heat exchangers and any type would work with the embodiments herein. 
     An exemplary heat exchanger may have plates where the sidewalls have a relatively low thermal resistance so that heat can easily be exchanged between the two gases. A number of materials can be used to create the heat exchanger. Preferably, the material used should be corrosion resistant, rot resistant, light weight, and inexpensive. Metals are typically used for heat exchangers because of their high thermal conductivity and would work with these embodiments. However, it has been discovered that plastics and composites can also satisfy the thermal conditions for electronic displays. An exemplary embodiment would utilize polypropylene as the material for constructing the plates for the heat exchanger. It has been found that although polypropylene may seem like a poor thermal conductor, the large amount of surface area relative to a small sidewall thickness, results in an overall thermal resistance that is very low. Thus, an exemplary heat exchanger would be made of plastic and would thus produce a display assembly that is thin and lightweight. Specifically, corrugated plastic may be used for each plate layer where they are stacked together in alternating fashion (i.e. each adjacent plate has channels which travel in a direction perpendicular to the surrounding plates). 
     The circulating gas and ambient gas can be any number of gaseous matters. In some embodiments, air may be used as the gas for both. Preferably, the circulating gas should be substantially clear, so that when it passes in front of the electronic image assembly it will not affect the appearance of the image to a viewer. The circulating gas would also preferably be substantially free of contaminants and/or particulate (ex. dust, dirt, pollen, water vapor, smoke, etc.) in order to prevent an adverse effect on the image quality and damage to the internal electronic components. It may sometimes be preferable to keep the ambient gas within the open loop from having contaminants as well. An optional filter may be used to ensure that the air (either in the closed or open loop) stays free of contaminants. However, in an exemplary embodiment the open loops (channels  225  and the second gas pathway  46  through the heat exchanger  45 ) may be designed so that contaminants could be present within the ambient gas  145  or  40  but this will not harm the display. In these embodiments, the heat exchanger  45  (and the optional channels  225 ) should be properly sealed so that any contaminants in the ambient gas  145  or  40  would not enter sensitive portions of the display. Thus, in these exemplary embodiments, ingesting ambient air for the ambient gas  145  or  40 , even if the ambient air contains contaminants, will not harm the display. This can be particularly beneficial when the display is used in outdoor environments or indoor environments where contaminants are present in the ambient air. 
       FIG. 3A  provides a perspective view of another embodiment where the housing has been removed. In this embodiment, the previously-shown open loop channels  225  behind the backlight  140  are not used. This figure shows the placement for cutting planes B-B and C-C which provide the section views in  FIGS. 3B and 3C  respectively. Cutting plane B-B passes vertically down the center of the assembly and through the heat exchanger  45 . Cutting plane C-C passes horizontally through the center of the assembly. 
       FIG. 3B  provides the section view from cutting plane B-B shown in  FIG. 3A . In this particular embodiment, ambient gas  145  only travels through the heat exchanger  45 . Thus, only ambient gas  145  may be used to remove heat from the circulating gas. As can be readily observed in this view, the LED backlight  140  and LCD assembly  85  could easily be substituted with any other electronic image assembly (such as those listed above or below). In some embodiments, the electronic image assembly could be placed in conductive thermal communication with the heat exchanger  45  so that the heat from the electronic image assembly could be distributed into the heat exchanger  45  and removed by ambient gas  145 . Thus, in some embodiments the backlight  140  could have thermal communication with the heat exchanger  45 . The thermal communication would preferably be conductive thermal communication. 
       FIG. 3C  provides the section view from cutting plane C-C shown in  FIG. 3A . The circulating gas preferably travels in a closed loop where it is drawn through the first gas pathway  44  of the heat exchanger  45  and then directed into the entrances  110  of the channels  30 . As discussed above, the channels  30  may be defined by the space between the front surface of the LCD assembly  85  (or other electronic image assembly) and the transparent plate  90 . As mentioned above, sunlight (or high ambient surrounding temperatures) can cause a buildup of heat on the LCD assembly  85 . As the circulating gas travels through the channel  30 , it may remove heat from the front surface of the LCD assembly  85 . The circulating gas may then be directed out of the channel  30  through the exit  120 . The circulating gas may then be re-directed into the first gas pathway  44  of the heat exchanger  45  so that it may be cooled by the ambient gas  145  (which is travelling through the second gas pathway  46  of the heat exchanger  45 ). 
     A pair of plates  300  (or surfaces) may be used to define the cavity  41  (or channel) which contains the heat exchanger  45  and the circulating gas as it travels behind the electronic image assemblies. In some embodiments, the rear portions of the electronic image assemblies (sometimes containing a backlight and sometimes not) may be placed in thermal communication with the plates  300  so that heat may be transferred from the image assemblies to the plates  300  and eventually to the circulating gas (where it can then be removed as it passes through the heat exchanger  45 ). The thermal communication between the electronic image assemblies and the plates  300  should preferably be conductive thermal communication. The plates  300  could also be placed in conductive thermal communication with the heat exchanger  45 . Thus, if using the LED backlights  140  these could be placed in conductive thermal communication with the plates  300 . The plates should preferably have a low thermal resistance. A metallic substance may provide a good material for the plates  300 . Aluminum would be an exemplary choice for plates  300 . 
     As mentioned above, various electronic components could be placed within the path of the circulating gas by placing them within cavity  41  (or channel) which includes the heat exchanger  45 . The circulating gas may be used to extract heat from these devices as well. The electronic components may be any components or assemblies used to operate the display including, but not limited to: transformers, circuit boards, resistors, capacitors, batteries, power modules, motors, inductors, transformers, illumination devices, wiring and wiring harnesses, lights, thermo-electric devices, and switches. In some embodiments, the electrical components may also include heaters, if the display assembly is used in cold-weather environments. 
     The embodiment shown in  FIGS. 3A-3C  may be used for a variety of applications. First, this embodiment may be preferable if the electronic image assembly being used does not require a backlight or does not produce a relatively large amount of heat from the rear side of the image assembly. Second, size or footprint may be an issue and this embodiment is thinner and possibly lighter than the embodiments that use the open channels  225 . Costs can also be reduced as the additional fans/power supplies/controllers for ingesting ambient air  40  are no longer required. Specifically, the embodiment shown in  FIGS. 3A-3C  may be preferable for OLED applications or edge-lit LED backlit LCD applications. However, even the direct-lit LED backlight LCD designs could use this embodiment if the application allows. One example would be if high-efficiency LEDs are used for the backlight. Further, this embodiment could be used if the display is only subjected to direct sunlight but relatively low ambient temperatures. 
     The cooling system described herein may run continuously. However, if desired, temperature sensing devices (not shown) may be incorporated within the electronic display to detect when temperatures have reached a predetermined threshold value. In such a case, the various cooling fans may be selectively engaged when the temperature in the display reaches a predetermined value. Predetermined thresholds may be selected and the system may be configured to advantageously keep the display within an acceptable temperature range. Typical thermostat assemblies can be used to accomplish this task. Thermocouples may be used as the temperature sensing devices. The speed of the various fan assemblies can also be varied depending on the temperature within the display. 
     It should be particularly noted that the spirit and scope of the disclosed embodiments provides for the cooling of any type of electronic display. By way of example and not by way of limitation, embodiments may be used in conjunction with any of the following: LCD (all types), light emitting diode (LED), organic light emitting diode (OLED), field emitting display (FED), light emitting polymer (LEP), organic electro luminescence (OEL), plasma displays, and any other type of thin/flat panel display. Furthermore, embodiments may be used with displays of other types including those not yet discovered. In particular, it is contemplated that the system may be well suited for use with large (40 inches or more) LED backlit, high definition (1080i or 1080p or greater) liquid crystal displays (LCD). While the embodiments described herein are well suited for outdoor environments, they may also be appropriate for indoor applications (e.g., factory/industrial environments, spas, locker rooms, kitchens, bathrooms) where thermal stability of the display may be at risk. 
     It should also be noted that the variety of open and closed cooling loops that are shown in the figures may be shown in a horizontal or vertical arrangement but it is clearly contemplated that this can be reversed or changed depending on the particular embodiment. Thus, the closed loop may run horizontally or vertically and in a clock-wise or counter-clockwise direction. Further, the open loop may also be horizontal or vertical and can run left to right, right to left, and top to bottom, or bottom to top. 
     It should also be noted that electronic image assemblies do not have to be used on both sides of the display. For example, one side may include an OLED display while the opposing side may be a static advertisement. Further, the same type of electronic image assembly does not have to be used on both sides of the display. For example, one side may contain an LED display while the second side contains an OLED display. 
     Having shown and described preferred embodiments, those skilled in the art will realize that many variations and modifications may be made to affect the described invention and still be within the scope of the claimed invention. Additionally, many of the elements indicated above may be altered or replaced by different elements which will provide the same result and fall within the spirit of the claimed invention. It is the intention, therefore, to limit the invention only as indicated by the scope of the claims.