Tien Nguyen

Formulation and analysis of the heat pipe turbine for production of power from renewable sources

Abstract The heat pipe turbine or thermosyphon Rankine engine is a new concept for power generation using solar, geothermal or other available low grade heat sources. The basis of the engine is the thermosyphon cycle, with its excellent heat and mass transfer characteristics, modified to incorporate a turbine in the adiabatic region. The basic configuration is a closed vertical cylinder functioning as an evaporator, an insulated section and a condenser. The turbine is placed in the upper end between the insulated section and condenser section, and a plate is installed to separate the high pressure region from the low pressure region in the condenser. Conversion of enthalpy to kinetic energy is achieved through the nozzles. The mechanical energy developed by the turbine can be converted to electrical energy by direct coupling to an electrical generator. This paper describes the development of the heat pipe turbine from concept to reality, a series of development steps taken to optimise the design and manufacture. Also in this paper, attempts have been made to provide relationships for the developed power in terms of the geometric and thermodynamic parameters and to discuss limitations on the efficiencies of these turbines.

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.

Revolution in Fan Heat Sink Cooling Technology to Extend and Maximize Air Cooling for High Performance Processors in Laptop / Desktop / Server Application

The trend of the processor performance and heat dissipation have been increased significantly every year. In the year 2000, the clock speed of processors used in Personal Computers (PC) was approximately 1GHz and heat dissipation approximately 20 W, but in the year 2004 the processor’s clock speed is higher than 3 GHz and the heat dissipation is approaching 100 W. Heat dissipation has increased but in contrast the size of die on the processor has reduced or remained the same size and thus the heat flux is critically high. The heat flux is about 10–15 W/cm2 in the year 2000 and could reach 100 W/cm2 in 2005. The purpose of this paper is to provide an overview of practical various cooling solutions including the use of heat pipes and vapor chambers for cooling high power processors in a confined space of PCs. This paper discusses how to extend the air cooling capability and maximize its performance. Included in this paper are the design, data, photos and discussion of various fan sink air cooling designs showing how the design changes can push the limit of the air cooling capability.Copyright

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.

Advanced Micro-Channel Vapor Chamber for Cooling High Power Processors

After the introduction of Pentium™ processor in 1993, the trend of the processor performance and power consumption have been increased significantly each year. Heat dissipation has been increased but in contrast the size of die on the processor has been reduced or remained the same size due to nano-size circuit technology and thus the heat flux is critically high. The heat flux was about 10–15 W/cm2 in the year 2000 and had reached 100 W/cm2 in 2006. The processor’s die surface where the heat is generated is usually small, approximately 1 cm2 . For effective cooling should required least temperature gradient between the heat source and radiating components. The best known devices for effective heat transfer or heat spreading with lowest thermal resistance is heat pipe and vapor chamber. Basically, heat pipe and vapor chamber are an evacuated and sealed container which contains a small quantity of working fluid which is water. When one side of the container is heated, causing the liquid to vaporize and the vapor to move to the cold side and condensed. Since the latent heat of evaporation is large, considerable quantities of heat can be transported with a very small temperature difference from end to end. The 2-phase heat transfer device has excellent heat spreading and heat transfer characteristics, is the key element in thermal management challenge of ever power-increasing processors. In this paper, authors presented case designs using vapor chamber for cooling computer processors. Proposed ideas of using micro-channel vapor chamber for heat spreading to replace the traditional metal plate heat spreader. Also included in the paper are ideas and data that showed performance improvement of heat spreading devices.Copyright

Thermal Characterization of a Copper Microchannel Heat Sink for Power Electronics Cooling

An investigative prototype of a single-phase cooling system based on the microchannel heat sink with water as the heat transfer medium was developed to study the fluid flow and forced-convection heat transfer characteristics for the cooling of electronics microprocessors with extremely high heat fluxes. The microchannel heat sink was made from copper with a high fin aspect ratio of 17.5. In the experiment, pressure losses through the heat sink and thermal characteristics of the cooling section under different heat fluxes (25 to 200W from 7 x 7 mm2 and 11 x 13 mm2 heat sources) and coolant flow rates (1.7 to 15 cm3=s) were studied. Under similar test conditions, minimum cold-plate thermal resistances Rcp of 0.11 and 0:33oC=W were achieved with 11 x 13 mm2 and 7 x 7 mm2 sources, respectively. Heat fluxes of up to 4:1 MW=m2 were effectively dissipated while maintaining a junction temperature below 100oC. With a 15 cm3=s (Re =150) coolant flow rate, maximum values of 5334 W=m2 · Kfor the convection heat transfer coefficient and 3.4 for the Nusselt number were achieved with a 3.3 kPa coolant pressure drop through the system. As an outcome of the present investigation, the copper water-based microchannel heat sink has proved to be a reliable cooling solution for high-end microprocessors.

Development of miniature loop heat pipes for the thermal control of laptops

Thermal management of laptops is becoming increasingly challenging task due to the high heat flux associated with the microprocessors and limited available space for the integration of the thermal control device inside the cabinet. In this paper, results from the investigation of two different designs of miniature Loop Heat Pipe (mLHP) for thermal control of compact electronic devices including notebooks have been discussed. Two prototypes of mLHP, one with a disk shaped evaporator of 30 mm in diameter and 10 mm thick, and the other with a rectangular shaped evaporator of 45×35 mm2 planar area and 5 mm thick, were designed to handle heat fluxes of up to 50 W/cm2. Total thermal resistance of these mLHPs lies in the range of 1 to 5 °C/W. In addition to this, two new designs of the mLHP pertaining to enhance the heat transfer inside the evaporation zone and to develop the loop evaporator with thickness as small as 3 mm are discussed. In conclusions, the designed mLHPs were able to satisfy the thermal and design requirements of the current laptop equipments and can be classified as potential candidates for cooling of the compact electronic devices with restricted space and high heat flux chipsets.

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