Patent Application
20130168068
1. Field of the Invention
The present invention relates to cold plates that use a liquid coolant to remove heat from heat-generating devices, such as computer processors.
2. Background of the Related Art
Computer systems often rely on cold plates positioned on or near heat-generating electronic components, such as processors, to maintain performance of the component by removing heat and thereby maintaining a favorable operating temperature. Cold plates generally use a stream of a liquid coolant to remove the heat that is generated by the electronic component. Cold plate bodies typically have a plurality of liquid coolant channels there through to maximize heat transfer surface area. With increasing processor power densities, more heat is generated by processors that are disposed within the limited space of the computer chassis. It is important for the cold plate to have sufficient capacity to keep the processor cool so that the performance of the processor can be maintained. However, the cold plate must still fit within the available space and form factor of the chassis or server rack.
A cold plate body with a larger overall surface area for heat transfer is able to transfer more heat to a liquid coolant flowing through the liquid coolant channels through the cold plate body, but merely increasing the size and number of liquid coolant channels yields diminishing returns for the space consumed. Dense electronic configurations and increasing processor power densities demand greater heat transfer capability to maintain processor performance while controlling cold plate cost and weight. For this reason, some cold plates now include heat pipes or vapor chambers in the cold plate base.
One embodiment of the present invention provides a cold plate comprising a cold plate body having a base for thermally engaging a heat-generating device, a plurality of internal channels extending through the cold plate body for the passage of a liquid coolant, a first region between the base and the plurality of internal channels, and a second region between the plurality of internal channels and a top that is generally opposite the base from the plurality of internal channels. The cold plate body is made from a first thermally conductive material. The cold plate also comprises at least one thermally conductive member extending around the plurality of channels from the first region below the plurality of channels to the second region above the plurality of channels. The at least one thermally conductive member has a greater thermal conductivity than the first thermally conductive material to move heat from the first region to the second region.
Embodiments of the cold plate of the present invention comprise a cold plate body having a base for thermally engaging a heat-generating device, a plurality of internal channels extending through the cold plate body for the passage of a liquid coolant, a first region between the base and the plurality of internal channels, and a second region between the plurality of internal channels and a top that is generally opposite the base from the plurality of internal channels. The cold plate body is made from a first thermally conductive material. The cold plate also comprises at least one thermally conductive member extending around the plurality of channels from the first region below the plurality of channels to the second region above the plurality of channels. The at least one thermally conductive member has a greater effective thermal conductivity than the first thermally conductive material to move heat from the first region to the second region.
The thermally conductive members may extend from the first region of the cold plate body to the second region of the cold plate body along various paths or combinations of paths. In general, the thermally conductive members may follow any path that transfers heat from the first region, which is adjacent the heat generating device, to the second region, which is generally on the side of the plurality of internal channels that is opposite the first region. In this manner, the at least one thermally conductive member improves the distribution of heat throughout the cold plate body, thereby increasing the amount of heat that is transferred to the liquid coolant flowing through the upper portions of the internal channels. Accordingly, the cold plate is more effective in keeping the heat-generating component at a suitable operating temperature.
In one optional configuration of the cold plate, one or more of the thermally conductive members has a first end that extends around a first side of the plurality of channels and a second end that extends around a second side of the plurality of channels. Furthermore, in such a configuration, the first and second ends extend through the second region in order to transfer heat adjacent the upper portions of the internal channels.
In another optional configuration of the cold plate, one or more of the thermally conductive members form a loop that extends through the first region, around a first side of the plurality of channels, through the second region, and around a second side of the plurality of channels. Compared to discontinuous thermally conductive members (i.e., those having two ends), the use of such loops may provide greater heat transfer area in both the first and second regions.
In yet another optional configuration of the cold plate, there are a plurality of the thermally conductive members, each having a first end in the first region and second end in the second region. In a first option, a first thermally conductive member may extend around a first side of the cold plate body and a second thermally conductive member may extend around a second side of the cold plate, wherein the first and second sides are adjacent sides of a generally rectangular cold plate. In a second option, a first thermally conductive member has a first end that extends around a first side of the plurality of channels and a second end that extends around a second side of the plurality of channels, and a second thermally conductive member has a first end that extends around a third side of the plurality of channels and a second end that extends around a fourth side of the plurality of channels.
Regardless of the path that is traversed by the at least one thermally conductive members, the thermally conductive members may be secured to, or formed by, the cold plate body in various manners. For example, a thermally conductive member may be embedded into a surface of the cold plate body with an exposed surface that is flush with the cold plate surface. Where the thermally conductive member extends along the base through the first region, embedding the thermally conductive member in this manner places the member in direct thermal engagement with the heat-generating device. Accordingly, a thermally conductive member may be embedded in the cold plate body, such as along the base, by being received within an open groove formed in an exterior surface of the cold plate body. Preferably, the thermally conductive member is made to conform to the walls of the open groove for thermal engagement with the walls. Increasing the contact area between the thermally conductive member and the walls of the groove will increase the amount of heat transfer there between. It is also preferable that the exposed surface of the at least one thermally conductive member is flattened to provide a flat area for thermally engaging the heat-generating device, which presents a flat surface area for contacting the cold plate. As one alternative to an embedded member, a thermally conductive member may be secured to an exterior surface of the cold plate body for thermally engaging the cold plate body. Such a thermally conductive member is also preferably flattened to increase the contact area with the surface of the cold plate body.
In each of the foregoing embodiments that include a plurality of thermally conductive members, it is preferable that each of the plurality of thermally conductive members extend into an area of the base that thermally engages the heat generating device. For example, if the heat generating device is a computer processor, each of the thermally conductive members may pass into the first region adjacent the processor. Where the cold plate is centered over the processor, each thermally conductive member may extend along the base of the cold plate through a central area to thermally engage the processor. Conversely, each of the plurality of thermally conductive members is preferably spaced apart through the second region. Such a spaced apart configuration in the second region is beneficial to improve the distribution of heat throughout the second region.
The thermally conductive members may be any heat transfer device or material that serves to increase the transfer of heat from the first region to the second region. Non-limiting examples of such thermally conductive members include a heat pipe, a vapor chamber, a metal, graphite, and diamond. A heat pipe is a device or structure having a thermally conductive outer wall forming a sealed chamber containing a volatile fluid. A vapor chamber may be formed as a structure internal to the cold plate body without having its own discrete wall. In a specific embodiment, the first thermally conductive material is aluminum, and wherein the at least one thermally conductive member is made from copper. Such an embodiment is suitable, because copper has a greater thermal conductivity than aluminum.
The cold plate will also include a liquid coolant supply line and a liquid coolant return line that are fluidically coupled to the plurality of internal channels. It should be recognized that the liquid coolant supply line, the liquid coolant return line, or both may be fluidically coupled to the plurality of internal channels through a side of the cold plate body or through the top of the cold plate body. The supply line and return line may be located in order to avoid physical interference with a desired configuration of the thermally conductive members. It should be understood that in alternate installations the return line may be a drain line where the liquid coolant is not reused.
The liquid coolant channels may have a cross-section that is circular, oval, elongate, or any of a plurality of other shapes. The liquid coolant channels may also be parallel one to the others to increase the amount of surface area available for heat transfer from the cold plate body to the liquid coolant moving through the liquid coolant channels. The liquid coolant channels are preferably generally straight to minimize pressure drop within the liquid coolant flow path.
The embodiments of the present invention described herein are not limited to any actual or relative dimensions. However, for the sole purpose of providing an example, a cold plate might have a thickness of about 10 mm, a width of about 75 mm, and a length of about 75 mm.
A heat pipe is a thermally conductive member forming a sealed core containing a fluid to transfer heat from a hot location (i.e., the first region) to one or more cold locations (i.e., the second region) primarily through cyclic evaporation and condensation of the fluid sealed within the core, but to a lesser extent also by conduction through the solid outer portion. A wick member may be disposed within the core to promote movement of the fluid along the core of the heat pipe. The wick, which may, for example, comprise a few layers of a fine gauze, may be affixed to the inside surface of the core, such that capillary forces will move condensate condensed from vapor at the “condenser” portion(s) at the cold location(s) of the heat pipe through the wick to the “evaporator” portion(s) at the hot location(s) of the heat pipe. If the evaporator portions(s) of the heat bus are lower in elevation than the condenser portion(s), gravitational forces assist the capillary forces within the wick. A wickless heat pipe relies on gravitational forces alone to move condensed fluid within the core from the condenser portion(s) to the evaporator portion(s) of the heat pipe.
The improved distribution of heat from the base to the rest of the cold plate body improves the overall cooling performance of the cold plate. Accordingly, the cold plate may have less weight and require less space for a given heat transfer capacity.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components and/or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.
The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
