The present invention is related to liquid cooling. Specifically, the present invention is related to providing liquid cooling for backlit displays.
Light emitting diode (LED) technology has been making significant advancement in recent years. The advancement of LED technology has produced numerous applications such as interior and exterior (outdoor) lighting, compact or portable lamps, automotive lights, and also light sources for backlit display systems. In the near future, LED lamps are expected to replace traditional incandescent, halogen, and/or fluorescent lamps (particularly mercury and/or cold cathode flourescent lamps) due to cost and energy savings. Additional advantages of modern LED technology include, for example, brighter colors, more compact lighting solutions, independent color control, and higher reliability. LED based backlit displays, in particular, have advantages in terms of brightness, white balance, and color control. More specifically, LED backlit displays are typically comprised of tri-chromatic LED arrays that are finely tunable for optimum white and color balance.
However, these LED applications generally suffer from high cost and high heat issues. In particular, the color performance of an LED display is a closely related function of junction temperature of the LED arrays. Higher power displays with high brightness capability necessitate the use of higher power LED sources. High power LEDs in turn present significant thermal challenges for traditional methods of cooling. For instance, traditional methods of cooling have difficulty coping with the high heat flux of modern LEDs. Traditional heat pipe designs in particular are bulky, which defeats the small and/or thin form factor advantages of many LED applications. Further, heat pipes are limited in the amount of heat they can move, and also in the distance they can move the heat from the heat source, which negatively impacts the display screen size. Thus, improved thermal design for LED cooling is critical to support the expansion of LED applications.
A cooling system for a backlit device includes a first heat collector, a first radiator, a first pump, an interconnect tubing, and a fluid. The first heat collector preferably has a micro structure such as micro channels or micro tubes, and is maintained in contact with the backlit device. The first radiator is for distributing heat and the first pump is for driving a fluid flow. The interconnect tubing is interposed between the first heat collector, the first radiator, and the first pump, to form a closed cooling loop. The fluid is for conducting heat and is sealed within the closed cooling loop.
In some embodiments, a method of cooling a backlit device disposes a heat collector in intimate contact with the backlit device. The heat collector has a fluid. The heat collector is used to collect heat from the backlit device and transfer the heat to a radiator using the fluid. The method rejects the heat from the radiator and recirculates the cooled fluid through the heat collector. The heat collector of some embodiments has a micro structure, and the fluid is pumped through the micro structure.
Preferably, the backlit device comprises an LED backlit flat panel display, and the flat panel display is typically an edge type LED backlit display that generates a high amount of heat per edge. Each edge includes one or more arrays of LEDs. The LEDs typically generate heat in the range of approximately 100 Watts to 1000 Watts. In a particular embodiment, the flat panel display has a thin form factor in the range of approximately 0.5 inches to approximately 4.0 inches in depth.
The first heat collector of some embodiments comprises an extruded multiport tubing in intimate contact with the backlit device. The micro tube of some of these embodiments has internal channels of approximately 0.5 to 5.0 millimeters in width by 0.5 to 5.0 millimeters in height and a wall thickness of approximately 0.5 to 1.0 millimeters. Preferably, the tubes are formed of extruded aluminum, or an alloy of aluminum. Other materials can be used. The first heat collector, in some embodiments, is a manifold that has a plurality of parallel flow vanes. The flow vanes are for directing fluid flow in parallel such that the temperature of the first heat collector is substantially distributed throughout the heat collector and transferred to the fluid in an approximately homogenous manner. In some exemplary implementations, the maximum pitch between the flow vanes is approximately 1.0 to 5.5 millimeters.
Preferably, the first heat collector is bonded to the backlit device by using a thermal interface material (TIM) layer. The TIM layer typically comprise at least one or more of Indium, a metallic coat, a thermal grease, a thermal pad, and/or a phase change material. In some embodiments, the first heat collector is also fastened to the backlit device by using a mechanical means. The mechanical means of these embodiments typically includes one or more of a screw, a bracket, and/or a clamp.
The cooling system of some embodiments further includes a reservoir and/or a fan. When implemented, the reservoir is for storing the fluid within the closed cooling loop, and further, preferably compensates for fluid loss over time. The fan is typically disposed in close proximity to the first radiator and is for rejecting heat from the first radiator.
The radiator of some embodiments has a thin form factor of approximately 15-50 millimeters. The fluid is typically selected from a set of cooling fluids comprising a glycol, an alcohol, a water based solution, and a dielectric solution. The cooling system of some embodiments includes a second heat collector, a plurality of radiators, and/or a plurality of pumps.
The novel features of the invention are set forth in the appended claims. However, for purpose of explanation, several embodiments of the invention are set forth in the following figures.
In the following description, numerous details are set forth for purpose of explanation. However, one of ordinary skill in the art will realize that the invention can be practiced without the use of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail.
Overview
Some embodiments of the invention provide a liquid cooling system for an LED backlit device, such as, for example, a flat panel display. These embodiments provide cooling to the LEDs of the display without significantly affecting the thin form factor of the device. The cooling system includes: one or more heat collectors; one or more radiator(s), fan(s), and/or fan radiators that have a small form factor; one or more mechanical pumps; tubing and interconnects to couple the elements of the cooling system together, and complete a closed cooling loop.
The heat collectors are typically made of an extruded multi port tubing which is in intimate contact with the device to collect heat from the device. For an LED backlit device, the LED arrays are traditionally a source of high heat. Accordingly, the heat collector is preferably disposed adjacent the LED arrays. The fluid, by the action of the pump(s), carries heated fluid from the heat collectors to the radiators, where the heat is rejected from the system. The cooled fluid is then (re)circulated by the pump(s) through the heat collectors to continuously draw more heat away from the hot LED array(s). Some embodiments further include a reservoir and/or a volume compensator to adjust the system for fluid loss over time.
Display
LED backlit displays are typically of the “direct” or the “edge” varieties. These categories generally refer to the location of the LEDs with respect to the view screen of the display. In typical LED backlit displays, the LEDs are organized into trichromatic (red, green, blue) arrays. With direct type LED displays, the LED arrays are generally uniformly distributed over the area of the display, such that the heat from the LED arrays is also generally distributed across the surface area of the display. For direct displays, macro or gross cooling solutions that blow cool air over the entire surface area of the distributed LED arrays is often sufficient.
In edge type displays, the LED arrays are grouped and concentrated at the top and bottom edges and/or the right and left edges (the rails) of the display. Optics direct the light from the rails through the remainder of the display. Due to the arrangement of the LED arrays, edge type displays often have cost savings and are advantageously very thin, in comparison to their direct type display counterparts. Some edge type displays, for example, are as thin as 0.50 inches deep, and use many fewer LEDs that are packaged in cost effective groups or arrays (rather than packaged discretely and more expensively as in direct displays). Costlier discretely packaged LEDs allow larger screen sizes for some direct displays, but further add to the thickness of a direct display's form factor. However, the main tradeoff for edge type displays is that the LED arrays must typically be very bright, and further, the heat from the LED arrays is concentrated within a smaller area of the display. Hence, the power consumed and also the heat generated by each concentrated rail of an edge type display is typically on the order of hundreds of Watts.
Cooling System and Fluid
From the first heat collector 220A, the tubing 210 then directs fluid to a first radiator 215A. In this embodiment, heat is collected by the first micro tube heat collector 220A from a first rail of hot LED array(s), and rejected at the first radiator 215A.
The tubing 210 then couples fluid from the first fan radiator 215A to a second micro tube heat collector 220B, which collects heat from a second rail of hot LEDs. The tubing 210 then couples fluid from the second heat collector 220B to a second radiator 215B, such that heated fluid is transported, by the action of the pump 205, from the second heat collector 220B to the second radiator 215B, where the heat is rejected from the system.
The tubing 210 then returns the fluid from the second radiator 215B to the pump 205. Also shown in
Regardless of the type of fluid employed, the cooling system 200 illustrated in
One of ordinary skill will recognize that
Pump and Radiator
The pump 205 typically delivers fluid pressure of approximately two to seven pounds per square inch (PSI), while moving a volume of approximately one to two liters per minute. Some embodiments employ a pump that has a low cost and small dimensions to maintain the small factor of the entire system 200. Quiet operation is an additional design consideration for the pump 205, and hence, the pressure and flow rate of the pump 205 are constrained by these considerations. As described below, the pump 205 is further constrained by the implementation details of the other components, and particularly the heat collector 220, of the system 200. These components of the system 200 of some embodiments are provided by Cooligy, Inc. of Mountain View, Calif. For instance, the pump 205 of some embodiments includes mechanical, electro-kinetic, and/or electro-osmotic pumps. U.S. Pat. No. 6,881,039 B2 entitled “Micro-Fabricated Electrokinetic Pump” and issued Apr. 19, 2005, which is hereby incorporated by reference, describes certain types of pumps in greater detail.
The radiator(s) of some embodiments are actually comprised of two or more radiator elements disposed in certain configurations, such as, a parallel configuration for example, within a single housing. The multiple radiator elements of these embodiments are advantageously implemented with separate fins and fluid pathways for receiving one or more fluid inputs and/or outputs. As shown in
In some embodiments, the radiators are fan radiators that advantageously combine a radiator with a fan in a single unit. To reject sufficient heat for a typical LED backlit display, the fans should move in the range of 5 to 30 cubic feet per minute (cfm). Where a single fan is used, the air flow may cause undesirable noise. Where multiple fans are used such as shown in
Typically, heated fluid flows along the fins of the radiator portion. Then, the heat is rejected from the fluid by the air flow generated around the fins by the fan. For instance, the radiators of some embodiments have a thickness of no more than about 15-50 millimeters. Radiators and heat rejection are described in further detail in United States Patent Application Serial No. [not yet assigned—COOL-01304] entitled “Cooling Systems Incorporating Microstructured Heat Exchangers,” filed Oct. 17, 2006, which is incorporated herein by reference.
As used herein, similar numerical identifiers represent similar features between figures. For instance,
As shown in
Heat Collector
As mentioned above, some embodiments employ a micro tube heat collector in close contact with the LED array of a display to collect and disperse the heat from the LED array.
Owing to the length of the arrays of LEDs, the heat collector of some embodiments could suffer from temperature gradients within the heat collector and undesirable fluid pressure drop. For example, the temperature and pressure in the region most adjacent to the inlet of the heat collector is different than the temperature and pressure of the region that is near the outlet of the heat collector. This has particularly undesirable effects for image display applications because the quality of the displayed image depends in some measure on temperature homogeneity of the LED arrays. Moreover, the temperature at each LED affects its individual performance and useful life.
Some embodiments of the present invention mitigate the temperature difference, from the region adjacent to the inlet to the region near the outlet of the heat collector, by increasing the pressure and/or flow rate at the pump. At sufficiently high flow rates and/or pressures, such as 2.0 liters per minute and/or about 7.0 psi of pressure, for example, the fluid moves quickly enough through the heat collector 920A such that a minimal temperature gradient occurs and any pressure drop does not affect the cooling efficacy of the system. However, as mentioned above, increasing the properties of the pump, such as flow rate and/or pressure, typically has undesirable tradeoffs such as an increase in the cost, noise, and/or the dimensions of the pump, or the other elements of the system, or constrains the type of pumping mechanism for the system. An alternative embodiment contemplates increasing a cross sectional volume of the micro tube to allow more fluid to flow at lower pressures.
Still other embodiments mitigate the temperature difference and pressure drop within the heat collector by using a parallel flow manifold.
As mentioned above, some embodiments optimize the heat transfer from the LEDs of a display to the heat collector of these embodiments.
Alternatively, the TIM layer 1180 of some embodiments bonds the heat collector 1120 directly to the substrate layer 1190, without the need for the metal layer 1185. Also shown in
As mentioned above, the heat collector 1120 is preferably coupled and/or bonded to the heat source in such a way as to optimize thermal transfer. Some embodiments also orient the flow of fluid through the heat collector 1120 in order to further maximize the conduction of heat via the travel of the fluid. For instance,
Method
At the step 1315, the heat is transferred to a radiator by using the fluid, and the process 1300 transitions to the step 1320. At the step 1320, the heat is dispersed or rejected from the radiator and then, at the step 1325, the cooled fluid is circulated and/or re-circulated through the system. After the step 1325, the process 1300 concludes. The (re)circulation of the fluid is typically performed by using a pump. Optionally, excess fluid is stored in a reservoir, which also preferably compensates for any loss of fluid over time.
While the invention has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention. Thus, one of ordinary skill in the art will understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.
This application claims priority under 35 U.S.C. section 119(e) of co-pending U.S. Provisional Patent Application No. 60/735,757, filed Nov. 9, 2005, and entitled “Liquid Cooling Systems for Backlit LED Display Products,” which is hereby incorporated by reference.
Number | Date | Country | |
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60735757 | Nov 2005 | US |