Systems and methods for providing heat transfer

There is provided a heat dissipating device. An exemplary heat dissipating device comprises a thermally conductive plate that is adapted to be disposed adjacent to at least one heat generating device. The thermally conductive plate has surface features configured to promote turbulent airflow over the thermally conductive plate, the thickness of the surface features being approximately equal to or less than the thickness of the plate.

BACKGROUND

Many of today's high-speed, high-power electronics generate significant amounts of heat. For example, as dual in-line memory modules (DIMMs) are designed to operate at faster operating speeds, they typically consume increasing levels of power and generate more heat. Removing heat from heat-generating devices such as DIMMs is a challenging problem.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The arrangement of DIMMs in linear banks may cause the air flow across the DIMMs to have laminar flow characteristics, for example, with the air near the surface of DIMM having a low velocity. This may lower the efficacy of cooling of the DIMMs. Exemplary embodiments of the present invention relate to systems and methods for improving heat transfer in electronic devices such as computer systems, blade servers, power supplies or the like.

One exemplary embodiment provides a memory module disposed between two heat spreaders. The heat spreaders contact the top surface of a heat-generating device or component such as memory module chips and dissipate heat away from the heat-generating device. Several memory modules of a memory bank may be disposed in parallel, forming airflow channels between the memory modules. A flow of cooling air may be provided through the airflow channels to draw heat away from the memory modules. The heat spreaders may include surface features, for example, slots, grooves, wires, and the like, that break up the airflow boundary layer attached to the surface of the heat spreaders and increase the turbulence of the air flowing between the memory modules. In this way, the surface features promote greater mixing of the cool air and warm air inside the channel and increase the velocity of the airflow in proximity to the heat spreaders, thus increasing the amount of heat transferred from the heat spreader to the cooling air. Furthermore, the surface features may be small enough to promote turbulence in the airflow channels without significantly reducing the rate of airflow through the channels.

FIG. 1is a perspective view of a memory bank with several dual in-line memory modules (DIMMs), in accordance with exemplary embodiments of the present invention. The memory bank100may be disposed on a circuit board102and may include one or more DIMM packages104installed in memory slots106. The memory bank100may be included in any suitable computer system, for example, a desktop computer, a blade server, and the like. Although, the memory bank100is described as including DIMMs, it will be appreciated that other exemplary embodiments of the present invention may include any suitable type of memory module, for example, single in-line memory modules (SIMMs), single in-line pin packages (SIPPs), and the like. Furthermore, embodiments of the present invention may also be employed to improve the cooling of other types of circuit devices other than memory modules. Exemplary circuit devices may include processors such as microprocessors, graphics processors, application specific integrated circuits (ASICS), and the like. Exemplary circuit devices may also include power semiconductor devices such as insulated gate bipolar transistors (IGBTs), power MOSFETs, and the like. Additional exemplary circuit devices may include power conditioning circuits such as capacitors, inductors, and the like.

Each DIMM package104may include a DIMM108, heat spreaders110, and clips112. The DIMM108may include one or more memory chips, which may include any suitable type of memory, for example, static random access memory (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), double-data-rate (DDR) SDRAM, and the like.

The heat spreaders110may include thermally conductive plates that are substantially flat, for example, about 1/16 inch to ¼ inch thick. The heat spreaders110may include any suitable thermally conductive material, for example aluminum, copper, thermally conductive polymer, and the like. The heat spreaders110may be disposed on both sides of the DIMM108and abut the top surface of the memory chips included in the DIMM108. Furthermore, a layer of thermal grease may be disposed between the heat spreader110and the memory chips of the DIMM108to increase the thermal conductivity between the DIMM108and the heat spreader110. The clips112may straddle the top edge of the DIMM package104and grip the sides of the heat spreaders110to hold the heat spreaders110in contact with the DIMM108. The clips112may be made of any suitable resilient material, for example, aluminum, plastic, and the like.

The parallel arrangement of the DIMM packages104provides air channels114between the dim packages104. In exemplary embodiments of the present invention, fans may provide a flow of cooling air116through the air channels114between the DIMM packages104. The cooling air116draws heat from the heat spreaders110and cools the DIMMs108. To increase the amount of heat transfer from the DIMMs108to the cooling air116, the heat spreaders110may also include surface features118. As will be described further below, the surface features118may include, for example, slots, holes, grooves, dimples, and the like. Additionally, the surface features118may be raised protrusions, for example, wires, buttons, and the like.

The thickness of the surface features118may be approximately equal to or less than the thickness of the heat spreaders110. For example, if the surface features118are cut into the heat spreaders110they may extend all the way through the head spreader110or only partly through the heat spreaders110, as discussed in further detail with respect toFIG. 3. Similar, if raised protrusions are used, the protrusions may extend out from the heat spreaders110by a distance that is less than the thickness of the heat spreaders110.

Without the surface features118, the cooling air116flowing through the air channels114may have laminar flow characteristics. In that case, a boundary layer may form over the surface of the heat spreaders110as the cooling air116passes through the air channel114. The boundary layer may cause warmer air at the surface of the heat spreaders110to stay in contact with the heat spreaders110while higher-velocity, cooler air near the center-line of the air channel114will tend to stay near the center-line and away from the heat spreaders110. Thus, the laminar airflow through the air channels114may decrease the amount of cooling air that contacts the heat spreaders110, which may tend to reduce the level of heat transfer from the DIMMs108to the cooling air116.

The surface features118increase the heat dissipation of the heat spreader110by disrupting the boundary layers and promoting turbulent airflow in the air channel114near the surface of the heat spreader110. In this way, the surface features118promote greater mixing of the cooler and warmer air within the air channel114and, thus, increase the level of heat transfer from the DIMMs108to the cooling air116.

In one exemplary embodiment of the present invention, the surface features118may include parallel slots120, which pass through the heat spreader110. The slots120may be oriented perpendicular to the flow of cooling air116, as shown, and the length122of the slots120may be any fraction of the height124of the heat spreader110, for example, 20, 40, 60, or 80 percent. In other exemplary embodiments, the slots120may be set at an angle relative to the flow of cooling air116. Furthermore, the heat spreader110may include any number of slots120, from 1 to about 10 or more. In some exemplary embodiments, the heat spreaders110may include four slots120disposed at about 10, 30, 70, and 90 percent of the length of the heat spreader110from the edge of the heat spreader110. The slots120may be formed in the heat spreaders110using any techniques suitable for the material. In an exemplary embodiment, the slots120may be cut into the heat spreader110using a cutting tool. In other embodiments, the slots120may be formed into the heat spreaders110, such as by an injection molding process used to form the heat spreaders110from a thermally-conductive plastic.

In addition to promoting turbulent flow, the slots120may also provide a flow of air through the heat spreader110. In this way, warm air that may otherwise tend to remain trapped between the DIMM108and the heat spreader110may be released into the air channel114.

FIG. 2is a perspective view of a heat spreader110with segmented slots120used for the surface features118, in accordance with exemplary embodiments of the present invention. As with the slots120discussed with respect toFIG. 1, the heat spreader110may include any number of segmented slots200, which may be oriented perpendicular to the flow of cooling air116, and the length of the segmented slots200may be any fraction of the height124of the heat spreader110. Furthermore, the segmented slots200may be divided into a plurality of segments202, for example, 2, 3, 4, 5 or more segments. As with the full slots120ofFIG. 1, the segmented slots200serve to break the boundary layer and promote turbulent airflow in the air channels114. Additionally, the material between the segments may conduct heat across the segmented slots200. Therefore, the segmented slots200may provide additional heat spreading along the length of the heat spreader110compared to a heat spreader110with full slots120. In some exemplary embodiments, the heat spreader110may include a combination of full slots120and segmented slots200.

FIG. 3is a perspective view of a heat spreader with grooves300used for the surface features118, in accordance with exemplary embodiments of the present invention. Unlike the slots120, the grooves300do not pass completely through the heat spreader110. The grooves300may be formed by cutting the groove300in the surface of the heat spreader110using, for example, a milling machine. In other exemplary embodiments, the grooves300may be formed as a half-shear, in which case the inside surface of the heat spreader110may be raised. In yet other exemplary embodiments, the grooves300may be molded into the plate, for example, in a thermoforming operation to form the heat spreader110from a conductive plastic. Accordingly, the grooves300may be positioned so that the raised surfaces are located between the memory chips of the DIMM108.

As with the full slots120ofFIG. 1and the segmented slots200ofFIG. 2, the grooves300serve to break the boundary layer and promote turbulent airflow in the air channels114. However, the grooves300may provide additional heat spreading along the length of the heat spreader110compared to a heat spreader110with either full slots120or segmented slots200. In some exemplary embodiments, the heat spreader110may include segmented grooves300, similar to the segmented slots ofFIG. 2.

FIG. 4is a perspective view of a heat spreader with raised surface features, in accordance with exemplary embodiments of the present invention. The surface features118may include raised surface features such as wires400. The wires400may include any suitable material, for example, plastic, metal, ceramic, and the like. In some exemplary embodiments, the wires may be thermally non-conductive. For purposes of the present description, a material may be considered thermally non-conductive if the thermal conductivity of the material is less than about 1 Watt/(meter·kelvin). The wires400may be welded to the heat spreader110or coupled to the heat spreader110with an adhesive. The wires400may be any suitable size, for example, 15 gauge to 40 gauge.

The wires400may be oriented perpendicular to the flow of cooling air116as shown, and the length122of the wires400may be any fraction of the height of the heat spreader110, for example, 20, 40, 60, 80, or 100 percent. In other exemplary embodiments, the wires400may be set at an angle with respect to the flow of cooling air116. Furthermore, the heat spreader110may include any number of wires400, from 1 to about 10 or more. In some exemplary embodiments, the heat spreaders110may include four wires400disposed at approximately 10, 30, 70, and 90 percent of the length of the heat spreader110from the edge of the heat spreader110.

As with the slots120discussed in reference toFIG. 1, the wires disrupt the boundary layer and promote turbulent flow in the air channels114. As a result, eddy currents may be formed near the surface of the heat spreader110, which promote the mixing of cooler and warmer air within the air channel114near the surface of the heat spreaders110. In this way, the cooling air116may tend to draw more heat from the heat spreader100compared to flat heat spreaders, and the thermal transfer from the DIMMs108to the cooling air116may be increased. Exemplary embodiments of the present invention may include heat spreaders110with any combination of surface features118.

FIGS. 5,6, and7show test results that demonstrate the effectiveness of heat spreaders110with wires400in accordance with present embodiments. To obtain the following test results, a simulated memory bank was modeled using simulated DIMMs that included 15 Watt electrical heaters to simulate the heat generated by the memory chips of the DIMM108. Heat spreaders110with were disposed on both sides of the simulated DIMM, and four thermocouples402,404,406,408were placed on the surface of the heat spreaders110to measure the temperature of the simulated DIMMs. The simulated memory bank was placed in an air duct and a flow of cooling air116was driven through the air channels114of the simulated memory bank. Furthermore, a baffle was placed over the simulated DIMMs so that the cooling air flowed only through the air channels116between the simulated DIMMs. Temperatures from thermocouples were then measured at various airflow speeds.

The approximate locations of the thermocouples402,404,406,408during the tests represented inFIGS. 5-7are shown inFIG. 4. The T1thermocouple402and the T3thermocouple404were placed just downstream from the upstream wire400on opposite sides of the simulated DIMM. The T2thermocouple406and T4thermocouple were placed just downstream from the downstream wire400on opposite sides of the simulated DIMM.

FIG. 5represents the baseline DIMM temperature measurements of a heat spreader110without surface features118.FIGS. 6 and 7represent the DIMM temperature measurements recorded using heat spreaders110with surface features118in accordance with embodiments of the present invention. Specifically, the heat spreaders110used in the tests represented byFIGS. 6 and 7included four thermally non-conductive wires disposed at approximately 10, 30, 70, and 90 percent of the length of the heat spreader110, as shown inFIG. 4.FIG. 6represents heat spreaders110with 30 gauge wires attached, andFIG. 7represents heat spreaders110with 28 gauge wires attached.

The columns labeled “10 CFM,” “15 CFM,” “20 CFM,” and “25 CFM” represent airflow speeds of 10, 15, 20, and 25 cubic feet per minute, respectively. The columns labeled “35° C. projected” represent the estimated temperature results for an ambient temperature of 35 degrees Celsius. The rows labeled “Ta” represent the measured air temperature of the ambient air before flowing through the simulated memory bank. The rows labeled “T1,” “T2,” “T3,” and “T4” represent temperature measurements from the four thermocouples402,404,406,408located on the outside of the simulated DIMM package.

The temperature measurements shown inFIGS. 5-7, demonstrate that the heat spreaders110with the wires400provided significantly greater cooling than the baseline heat spreaders without wires400. For example, at an air flow rate of 10 CFM the heat spreaders with 30 gauge wires provide approximately 2.5 to 3.5° C. greater cooling compared to the baseline and the heat spreaders with 28 gauge wires provide approximately 2 to 2.5° C. greater cooling compared to the baseline.

FIGS. 8,9and10show test results that demonstrate the effectiveness of heat spreaders110with slots120in accordance with present embodiments. To obtain the following test results, a simulated memory bank was modeled using simulated DIMMs that included electrical heaters to simulate the heat generated by the memory chips of the DIMM108. Heat spreaders110with were disposed on both sides of the simulated DIMM, and six thermocouples were placed on the surface of the heat spreaders110to measure the temperature of the simulated DIMMs. The simulated memory bank was placed in an air duct and a flow of cooling air116was driven through the air channels114of the simulated memory bank. Furthermore, a baffle was placed over the simulated DIMMs so that the cooling air flowed only through the air channels116between the simulated DIMMs. Temperatures from the six thermocouples were then measured at various airflow speeds and DIMM Wattage ratings.

FIG. 8represents another set of baseline DIMM temperature measurements of a heat spreader110without surface features118. By comparison,FIGS. 9 and 10represent the temperature measurements recorded using heat spreaders110with slots120accordance with embodiments of the present invention. Specifically, the heat spreaders110used in the tests represented byFIGS. 9 and 10included two slots120disposed at approximately 10 and 70 percent of the length of the heat spreader110.FIG. 9represents heat spreaders110with 1 mm wide slots120, andFIG. 10represents heat spreaders110with 2 mm wide slots120.

The columns labeled “13.3 CFM,” “9.8 CFM,” “7.4 CFM,” and “4.7 CFM” represent airflow speeds of 13.3, 9.8, 7.4, and 4.7 cubic feet per minute, respectively. Additionally, the wattage rating of the simulated DIMMs during each test is located below the “CFM” column heading. The columns labeled “35° C. projected” represent the estimated temperature results for an ambient temperature of 35 degrees Celsius. The rows labeled “Ta” represent the measured air temperature of the ambient air before flowing through the simulated memory bank. The rows labeled “T1,” “T2,” “T3,” “T4,” “T5,” and “T6” represent temperature measurements from the six thermocouples located on the outside of the simulated DIMM package.

The temperature measurements shown inFIGS. 8,9, and10, demonstrate that the heat spreaders110with the slots120provided significantly greater cooling than the baseline heat spreaders without slots120. For example, at an air flow rate of 13.3 CFM and DIMM power rating of 15 W, both of the slotted heat spreaders110provide approximately 2.5° C. greater cooling compared to the baseline.