Patent Application
20140158325
The claimed subject matter relates generally to cooling computer systems. More specifically, the claimed subject matter relates to a thin barrier bi-metal heat pipe.
Portable electronic devices such as laptops, tablets, smart phones, and the like, are growing in popularity due to a wide array of functionality, high performance, and convenience. Unfortunately, these conveniences are resource-intensive, which increases the load on the hardware. Accordingly, as more functions are integrated into these devices, the heat generated by these devices increases. The increase in heat becomes a drain on other resources, e.g., battery power. One additional drain on battery power comes from thermal management, i.e., hardware and software that regulate device temperatures.
One technique for thermal management includes using heat pipes. A heat pipe is a passive heat transfer device. The heat pipe has no moving parts, but effectively transfers heat away from heat sources in electronic devices. A working fluid inside the heat pipe cycles through vapor and liquid states, thereby removing heat from the heat source. There are on-going efforts to improve the efficiency of heat pipe cooling systems.
The same numbers are used throughout the disclosure and the figures to reference like components and features. Numbers in the 100 series refer to features originally found in
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding. However, it will be apparent to one skilled in the art that embodiments may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring embodiments.
Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
Typically, heat pipes are made from various metals based on their thermal conductivity. Thermal conductivity is an indicator of an object's ability to conduct heat. The efficiency of the heat pipe improves as thermal conductivity of the heat pipe material increases. Example metals include, but are not limited to copper and aluminum. Heat pipes made from copper or copper alloys may be used with a water phase change fluid, which may be less expensive and more efficient than other typical coolants. Aluminum heat pipes may also provide a cost advantage over copper heat pipes. However, water cannot be used as a coolant in aluminum heat pipes because hydrogen gas results from the interaction of water with the aluminum. Hydrogen gas is non-condensable gas, and as such, increases the pressure inside, thereby decreasing or blocking condensation of the H2O gas, which may render the heat pipe useless.
In one embodiment, an aluminum heat pipe uses a thin barrier metal and a water coolant. The thin barrier metal prevents the water coolant from interacting with the aluminum. Advantageously, such an embodiment has lower mass and cost than typical copper heat pipes in computing devices.
The computer system 100 may also include chipset 107 coupled to the bus 105. The chipset 107 may include a memory control hub (MCH) 110. The MCH 110 may include a memory controller 112 that is connected to a main memory 115. The main memory 115 may store data and sequences of instructions that are executed by the processor 102, or any other device included in the system 100. In one embodiment, the main memory 115 includes computer-readable media such as, volatile memory and nonvolatile memory. The nonvolatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically-programmable ROM (EPROM), electrically-erasable programmable ROM (EEPROM), flash memory, and so on.
Volatile memory may include random access memory (RAM), such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), DRAM (SLDRAM), direct RAM (RDRAM), direct dynamic RAM (DRDRAM), dynamic RAM (RDRAM).
The MCH 110 may also include a graphics interface 113 that is connected to a graphics accelerator 130. The graphics interface 113 may be connected to the graphics accelerator 130 via an accelerated graphics port (AGP). Additionally, a display (not shown) may be connected to the graphics interface 113. The MCH 110 may be connected to an input/output control hub (ICH) 140 via a hub interface. The ICH 140 provides an interface to input/output (I/O) devices within the computer system 100. The ICH 140 may be connected to a Peripheral Component Interconnect (PCI) bus. Thus, the ICH 140 may include a PCI bridge 146 that provides an interface to a PCI bus 142. The PCI bridge 146 may provide a data path between the CPU 102 and peripheral devices such as, for example, an audio device 150 and a disk drive 155. Although not shown, other devices may also be connected to the PCI bus 142 and the ICH 140.
The processor 102 and graphics accelerator 130 are examples of heat-generating devices. For proper functioning of the CPU 102 and other components in the computer system 100, the temperature of heat-generating devices is regulated by a cooling system 160.
The attach block 202 is coupled to a heat-generating device, e.g., processor 102 to extract heat from the device. The attach block 202 may be manufactured using copper, aluminum, or other metals based on their thermal conductivity. The attach block 202 may be coupled to the processor 102 through a thermal interface material.
The attach block 202 is coupled, or otherwise connected, with the heat pipes 204, 206. The heat pipes 204, 206 are sealed tubes made of an aluminum or aluminum alloy. The heat pipes 204, 206 may include water or water containing mixture as a coolant. The inside of the heat pipes 204, 206 are typically at a low pressure, in some cases, nearing a vacuum. The amount of water and pressure inside the heat pipes 204, 206 may be based on the operating temperature of the processor 102.
In the cooling system 200, heat from the processor 102, enters the heat pipes 204, 206 at an evaporation portion of the heat pipes 204, 206, such as the evaporation ends 208, causing the coolant inside to vaporize. The vapor flows along the heat pipes 204, 206 towards the condensation ends 210 due to a pressure gradient caused by the vaporization. At a condensation portion of the heat pipes 204, 206, such as the condensation end 210, the coolant condenses, giving up latent heat of the vaporization.
The heat exchanger 212 removes heat from the heat pipes, helping to cool the condensation ends 210. The heat exchanger 212 may include a fan 214 to provider higher airflow. It is noted that, in some embodiments, the heat exchanger 212 may not include the fan 214.
The heat exchanger 212 may be manufactured using aluminum, or aluminum alloys. Additionally, the heat exchanger 212 may be bonded with the heat pipes 204, 206. The bonding materials for such a connection may be an aluminum alloy with a lower melt temperature than the inner aluminum alloy of the heat pipe and the inner aluminum alloy of the heat exchanger fins. These elements of the system 200 may be bonded by placing them in an oven at a temperature above the melt temperature of the cladding material, but below that of the metals of the heat exchanger 212 and heat pipes 204, 206.
In one embodiment, the outer material of the heat pipes 204, 206 may be skived into fins that provide the heat exchanger function. Skiving is process whereby a thin layer of metal is peeled upward, resembling a fin of the heat exchanger 212. In such an embodiment, the system 200 may not include the heat exchanger 212 in addition to the skived heat pipes.
Depending on the service temperature, the thickness of the structural outers 302A, 302B, may develop and grow in thickness. As such, aluminum atoms may protrude through the copper barriers 304A, 304B, and come into contact with water. However, in one embodiment, the heat pipes 300A, 300B include a thin intermetallic compound barrier layer (not shown) that may be disposed between the structural outers 302A, 302B, and the copper barriers 304A, 304B. Alternatively the intermetallic compound barrier layer may be disposed between the copper barriers 304A, 304B, and the water.
The thin IMC barrier layer, for example, may be composed of a copper alloy containing a percentage of nickel that inhibits the growth or diffusion of aluminum atoms to the IMC. The thin IMC barrier layer is not limited to a copper alloy containing nickel. This layer may be composed of materials based on a predetermined level of IMC growth inhibition.
The heat pipe 300B includes a wicking mechanism, such as a screen mesh 308B and a sintered copper powder wick that may be made from a metal, such as copper. Other materials that may be used as the wick include fabrics, non-woven plastic fabrics, fiberglass, and the like. The wicking mechanism 308B exerts a capillary pressure on the liquid water, moving the water from the condensation ends 210 back to the evaporation ends 208. In the round heat pipe 300A, a wicking mechanism may be provided by micro-grooving a series of lines in the copper barrier 304A parallel with respect to the pipe axis. Such grooves exert capillary pressure on liquid coolant toward the evaporation ends 208. The heat pipes 300A, 300B may not use a wicking mechanism if another source of acceleration is provided to overcome the surface tension of the liquid coolant. For example, the condensation ends 210 may be tilted upwards, enabling the acceleration from gravity to move the liquid coolant back to the evaporation ends 208.
In diffusion bonding, the aluminum and the copper are bonded together by migrating atoms of copper across a joint with the aluminum, due to concentration gradients. The two metals are pressed together at an elevated temperature, less than the melting point of either. The pressure relieves the void that may occur due to the different topographies of the metal surfaces.
In electro-deposition, copper ions in a solution are moved by an electric field to coat the aluminum. An electrical current reduces cations of the copper from the solution and coat the aluminum with a thin layer, e.g., several atoms, of the copper.
In chemical vapor deposition, a vacuum deposition method may be used to deposit a thin film of copper on the aluminum. The film is deposited by the reaction of a vaporized copper compound, such as Cu(II) bis-hexafluoroactylactonate, among others, with the aluminum surfaces. A copper layer is deposited, and the resulting organic compounds are swept out with a feed gas.
Physical vapor deposition may also be used. Physical vapor deposition involves the high temperature vacuum evaporation of copper from a surface, for example, by electron or plasma bombardment, with subsequent condensation on the target aluminum surface.
In-air plasma deposition may also be used, where a plasma deposits Cu atoms on the surface of the aluminum in an air environment. The plasma reduces surface contaminants and oxidation, thereby preparing the surface of the aluminum for covalent bonding of the Cu, and deposits the Cu on the surface of the aluminum to produce the barrier layer.
At block 404, a wicking mechanism is configured for the heat pipe. For a round heat pipe, a micro grooving operation is applied to the aluminum to provide the wicking mechanism. The microgrooving is done before the copper deposition on to the aluminum. In this way, the microgrooving prevents loss of the thin copper layer from the surface. For a flat-thin heat pipe, a copper screen mesh may be positioned in relation to the bi-metal such that when formed, the heat pipe 204 encloses the screen mesh. In other embodiments, a fabric mesh may be placed inside the bimetal pipe.
At block 406, a heat pipe is configured from the bi-metal such that the copper lining is disposed within the heat pipe 204. The configured heat pipe 204 may be a round heat pipe, or a flat-thin heat pipe.
At block 408, the vapor pressure within the heat pipe 204 may be modified. In one embodiment, air from within the heat pipe 204 is evacuated until the pressure inside reaches a specified threshold.
At block 410, a water coolant is added to the inside of the heat pipe. At block 412, the heat pipe is sealed.
Advantageously, the heat pipe 204 has lower mass, and, accordingly, a lower cost than heat pipes made from heavier, more expensive metals, such as copper. Such a heat pipe enables thermal solution providers to create cooling systems at a cost savings over typical solutions.
It is to be understood that specifics in the aforementioned examples may be used anywhere in one or more embodiments. For instance, features of the computing device described above may alternatively be implemented with respect to either of the methods or the computer-readable medium described herein. Furthermore, although the Figures herein describe embodiments, embodiments of the claimed subject matter are not limited to those diagrams or corresponding descriptions. For example, flow need not move through each illustrated box of
Embodiments are not restricted to the particular details listed herein. Indeed, those skilled in the art having the benefit of this disclosure will appreciate that many other variations from the foregoing description and drawings may be made. Accordingly, it is the following claims, including any amendments thereto, that define the scope.
