Koichi Mashiko

Use of heat pipe/heat sink for thermal management of high performance CPUs

This paper will describe various cooling solutions in notebook PC and desktop/server applications. In the notebook PC application, miniature heat pipes of diameter 3-6 mm, flatten to desire thickness, are commonly used to improve heat spreading and more efficient transfer heat generated from the CPU to a remote heat dissipation area. Examples of three typical thermal solutions in notebook PC are given in this paper. Whereas in the desktop server application, flat type rectangular heat pipes or so-called vapor chambers are used to attach under the base of the heat sink to help temperature uniformity across the heat sink base. This will reduce the spreading resistance in the heat sink base and therefore improve the heat sink performance. Experimental results showed that with a vapor chamber installed can achieved a 45% improvement in the heat sink performance for heat sink of length 110 mm, width 72.5 mm, height 50 mm and base thickness 7 mm.

The design and testing of the super fiber heat pipes for electronics cooling applications

Cooling of electronics is one of the major fields of application for heat pipes (3-9-mm outside diameter) with a worldwide demand exceeding one million per month. The high heat fluxes associated with electronics cooling require heat pipes with high maximum heat transfer at any inclination, and therefore improved wick structures are needed. In particular, the operation at top heat mode (vertical orientation) is required by most notebook manufacturers with a decrease of 30%-50% of the thermal resistance over conventional systems. A new wick structure has been developed so the capillary channels are increased with small effects on the heat pipe permeability. Using this new design criterion, (which balances the permeability and capillary needs), super fiber bundle heat pipes have been developed. The diameter of the wire used in the fabrication varied from 0.05 to 0.1 mm and the maximum input power was 16 W. It was found that the vapor space/liquid space ratio is an important parameter for this type of heat pipe. The test results show that the thermal resistance of the heat pipes is a strong function of the orientation. We have fabricated heat pipes with two to five times lower thermal resistance than previous conventional heat pipes (for the top heat mode operation). A comparison with other types of wick structures is also presented. Thermal resistances as low as 0.5/spl deg/C/W (top heat mode) and 0.2/spl deg/C/W (horizontal operation) have been observed. The application to electronics cooling it has been successful, especially in notebook computers and telecommunications applications.

Advanced cooling system using miniature heat pipes in mobile PC

This paper describes various cooling solutions using heat pipes for cooling of notebook PCs including: (1) a heat pipe with heat spreader plate; (2) a hybrid system, i.e. a heat pipe with heat sink and fan; and (3) a hinged heat pipe system. For heat input of less than 12 W, the thermal resistances measured between the CPU surface and ambient are: >8/spl deg/C/W for system (1) and 4-6/spl deg/C/W for systems (2) and (3). This means that the hybrid system and the hinged heat pipe systems are the most suitable candidates for cooling of the current CPU, which may require heat dissipation of more than 8 W at ambient of 40/spl deg/C and CPU maximum temperature of 95/spl deg/C. Experimental results of these three systems are included and discussed in this paper.

Data center energy conservation utilizing a heat pipe based ice storage system

Data centers constantly expand and upgrade their capacity due to the ever-increasing demand for remote file storage. It is estimated that around 50% of the total data center power consumption is for cooling. With this trend, a reduction in the cooling power consumption would result in a substantial reduction in overall power consumption, as well as C02 emission. With the focus going towards renewable and natural sources of energy, a heat pipe based ice storage system is being proposed. This system is being considered as one good solution to reduce the power consumption, as well as CO2 emission of data centers. This Ice storage system is aimed at utilizing the low temperature of cold areas to form ice and cold water. The freezing index, which is the combined duration and magnitude of below freezing temperatures at a given freezing season, would be the criteria for choosing the data center location. The data center will be constructed in cold regions wherein the freezing index is 400°C-days and above. The thermosiphon, which acts as a thermal diode, can effectively cool down the water until ice is formed. This ice storage system can be integrated with the existing cooling system and can be utilized as an alternate cooling system or a back-up cooling system. The existing cooling system may be utilized during the warmer periods of the year. The actual ice storage system container, which is made of concrete, is to be constructed under ground, and integrated in parallel with the existing cooling system.

Overview latest technologies using heat pipe and vapor chamber for cooling of high heat generation notebook computer

The trend of the processor performance and heat dissipation increased significant every year. In the year 2000, the clock speed of processor used in notebook is marginal 1GHz and heat dissipation marginal 20 W, but in the current year 2003 the processors clock speed is higher than 2 GHz and heat dissipation higher than 50 W and approaching 100 W by year 2004. Heat dissipation increased but in contrary the size of the processor reduced and thus the heat flux is critically high. The heat flux is about 10-15 W/cm/sup 2/ in the year 2000 and could reach over 100 W/cm/sup 2/ by year 2004. The purpose of this paper is to provide overview of various cooling solutions using heat pipe and vapor chamber for cooling high power processors in a confined space of the notebook.

Energy conservation approach for data center cooling using heat pipe based cold energy storage system

In the present paper, design and economics of the novel type of thermal control system for data center cooling using heat pipe based cold energy storage system has been proposed and discussed. Two types of cold energy storage system namely: Ice storage system and cold water storage system are explained and sized for datacenter with heat output capacity of 8800 KW. Basically, the cold energy storage will help to downsize the chiller and decrease its runtime that will save electricity related cost and decrease green house gas emissions from the electricity generation. The proposed cold energy storage system can be connected in the existing datacenter facilities without major design changes. Out of the two proposed systems, ice based cold energy storage system is mainly recommended for small to medium size datacenters which are located in very cold locations and offers long term seasonal storage facility. Water based cold energy storage system provides more compact size with short term storage (hours to days) and is potential for both small to large size datacenters with yearly average temperature below the cold storage water temperature (~ 25°C). The cold water storage system is sized on the basis of metrological conditions in Poughkeepsie, USA. As an outcome of the thermal and cost analysis, an optimum size of cold energy storage system should be designed to handle 60% of the yearly datacenter load. Preliminary results obtained from the experimental system design to test the ice formation potential of the heat pipe based cold energy storage system has shown good result and validated the proposed concept.

Micro Channel Vapor Chamber for high heat Spreading

The cooling technology that is most widely used for computers is air-cooling, because this is a mature technology with the least operation and maintenance cost. In order to push the limit of the air-cooling capability, enhancement of heat transfer from the processor to cooling medium is needed. Recently, the processor has multi-cores such as dual-cores, quad-cores. So, the heat dissipation from the processor surface is not uniform. For effective cooling, it is required least temperature gradient between the heat source and radiating componets. The well-known devices for effective heat transfer or heat spreading with the lowest thermal resistance are heat pipes and vapor chambers, which are two-phase heat transfer devices with excellent heat spreading ad heat transfer characteristics. In this paper, various designs using vapor chamber for CPU (Central Processor Unit) are presented with advanced technology of micro channel wick structure instead of traditional sintered powder wick.

Hot Spot Elimination by Thin and Smart Heat Spreader

Heat pipes are recognized as an excellent heat transport devices and extensively investigated for applications in electronic cooling. Different types of heat pipes have been developed such as micro/miniature heat pipes, loop heat pipes and so on, and these heat pipes have been widely applied in the field of electronics cooling such as notebook, desktop, data center; as well as aerospace, industrial cooling field. However, in recent years the application of heat pipe is widening to the filed of hand held mobile electronic devices such as smart phone, tablet pc, digital camera etc. With the development in technology these devices have different user friendly functions and capabilities, which requires the highest processor clock speed. In general, high clock speed of processor generates lot of heat which need to be spread or removed to eliminate the hot spot. It becomes a challenging task to cool such electronic devices as mentioned above with a very confined space and concentrated heat sources. Regarding to this challenge, ultra thin flat heat pipe is developed; this newly developed heat pipe consists of a special fiber wick structure which can ensure vapor spaces on the two sides of the wick structure.In this paper a novel thin spreader is proposed to eliminate the hot spot; generally the proposed heat spreader consists of 0.20mm thick metal plate and ultra thin heat pipe of 0.40mm thickness soldered in its body. Maximum thickness of this spreader is 0.63mm. Metal plate is 60mm × 110mm in size; and the ultra thin heat pipe can be fabricated from different original diameter ranges from 2.0mm to 3.0mm Cu tube. Theoretical and experimental analysis have been done to evaluate this thin spreader. In addition, some real application of this spreader will be introduced in this paper.Copyright

Direct impingement cooling of LED by Piezo fan

In this paper, an innovative heat management solution for the Light Emitting Diodes (LEDs) based on direct impingement cooling by Piezo fan has been proposed and evaluated. Round Piezo fans with 26 to 30 mm blade diameter, 1 to 5 mm fan thickness and narrow flow orifice (~ 3 to 7.5 mm) were developed which could provide very high velocity air jet (> 10 m/s) for impinging heat source footprint directly. These fans were driven at high operating frequency (300 to 550 Hz) and voltage (40 to 50 Vrms) to get high impact air jet at fan outlet. Different test cases have been studied to demonstrate and characterize the cooling capability of the Piezo fan based thermal solutions. Direct impingement cooling of the 5 × 5 mm2 heat source with Piezo fan (30 mm diameter, 1.1 mm thickness and 7.5 mm orifice width) inclined at 35° to horizontal was tested which was able to reduce source temperature by 3 to 4 times as compared to natural convection cooling. Similarly, incorporation of Piezo fan for cooling multiple chips (x5) LED package with 9 W output heat load reduced the source temperature by more than 42 °C. Automotive headlamp with two LED packages and single heat sink was impinge cooled by two dedicated Piezo fans which reduce the source temperature by 7.6 °C and enhance the heat sink heat dissipation capacity by 48% due to improvement in the enclosure heat transfer coefficient. Piezo based impingement cooling can therefore increase the heat removal from heat source as well as can reduce the size of the heat sink designed for natural convection cooling. Based on these results, impingement type Piezo fan can be classified as standalone as well as heat sink integrated cooling solution for LED packages.

Applications of Cold Plate Units With Micro-Channel for Cooling Electronics

Until recently, effective cooling solutions with high performance were required especially in data-centers and super computers because of the huge and ever-increasing power consumption in these applications. Water cooling systems have been considered for use in the cooling of large scale data-centers and super computers.For the cooling of super computer CPUs, a water cooling system using advanced cold plate technology is reconsidered. The thermal resistance of a cold plate for cooling the CPU is required to dissipate 80 to 100W of heat at 0.05 K/W. Also, in this application, the cold plate is required to be mechanically reliable in withstanding a cooling water pressure of 1MPa. We adopted a micro-channel structure as a heat transfer surface of this cold plate and developed a new brazing method so that the tips of the micro-channel fins are bonded to the inside of cover plate of the cold plate. In collaboration with a customer in charge of the design, we completed the water cooling unit consisting of cold plates, pipes and coupler manifold, assembled by brazing.Finally, the high volume products were manufactured with reliability inspection (pressure test and helium leakage test) and used to effectively cool the CPUs of an advanced super computer, which was awarded the fastest super computer record.Water cooling technology provides effective high capacity cooling in compact space limits, and has been widely used in applications like fiber laser machines and others. This paper describes the development of cold plate with micro-channels and its applications.Copyright