Showing papers on "Heat sink published in 2009"

Thermal Conductivity of Diamond Composites

Abstract: A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices are aluminum and copper, with thermal conductivities of about 250 W/(m·K) and 400 W/(m·K), respectively. Significantly, the thermal expansion coefficient of metals differs markedly from those of the materials employed in semiconductor electronics (mostly silicon); one should add here the low electrical resistivity metals possess. By contrast, natural single-crystal diamond is known to feature the highest thermal conductivity of all the bulk materials studied thus far, as high as 2,200 W/(m·K). Needless to say, it cannot be applied in heat removal technology because of high cost. Recently, SiC- and AlN-based ceramics have started enjoying wide use as heat sink materials; the thermal conductivity of such composites, however, is inferior to that of metals by nearly a factor two. This prompts a challenging scientific problem to develop diamond-based composites with thermal characteristics superior to those of aluminum and copper, adjustable thermal expansion coefficient, low electrical conductivity and a moderate cost, below that of the natural single-crystal diamond. The present review addresses this problem and appraises the results reached by now in studying the possibility of developing composites in diamond-containing systems with a view of obtaining materials with a high thermal conductivity.

LED illuminating device and light engine thereof

Abstract: An LED illuminating device includes an optical section, an electrical section, and a heat dissipation section. The heat dissipation section is provided with a heat sink and at least one heat pipe therein. The heat sink includes a metal tube, a plurality of metal fins extending radially and outwardly from the metal tube, and a heat-absorbing plate attached to a bottom of the metal tube. A chamber is axially recessed from a top of the metal tube to the heat-absorbing plate. The heat pipe includes an evaporating section and a condensing section. The evaporating section of the heat pipe is attached to an inner surface of the heat-absorbing plate. The condensing section of the heat pipe is attached to an inner circumferential surface of the metal tube. The light source is attached to an outer surface of the heat-absorbing plate.

Heat sink for noninvasive medical sensor

Abstract: A noninvasive physiological sensor for measuring one or more physiological parameters of a medical patient can include a bump interposed between a light source and a photodetector. The bump can be placed in contact with body tissue of a patient and thereby reduce a thickness of the body tissue. As a result, an optical pathlength between the light source and the photodetector can be reduced. In addition, the sensor can include a heat sink that can direct heat away from the light source. Moreover, the sensor can include shielding in the optical path between the light source and the photodetector. The shielding can reduce noise received by the photodetector.

Electrocaloric devices based on thin-film heat switches

Abstract: We describe a new approach to refrigeration and electrical generation that exploits the attractive properties of thin films of electrocaloric materials. Layers of electrocaloric material coupled with thin-film heat switches can work as either refrigerators or electrical generators, depending on the phasing of the applied voltages and heat switching. With heat switches based on thin layers of liquid crystals, the efficiency of these thin-film heat engines can be at least as high as that of current thermoelectric devices. Advanced heat switches would enable thin-film heat engines to outperform conventional vaporcompression devices.

Heat dissipation device

Abstract: A heat dissipation device includes a primary heat sink ( 10 ) contacting a central processing unit and a secondary heat sink ( 20 ) attached on heat-generating electronic components adjacent the central processing unit. The primary heat sink includes a base ( 12 ) and a heat-dissipation portion ( 14 ) disposed on a middle of the base. The secondary heat sink includes a substrate ( 22 ) and a plurality of fin assemblies ( 24 ) arranged on the substrate. The base is laid on the substrate with the fin assemblies arranged around the heat-dissipation portion. The primary heat sink is partly superposed on the secondary heat sink with a compact structure. The heat-dissipation portion can simultaneously dissipate heat from the central processing unit and its adjacent heat-generating electronic components.

Heat Removal in Silicon-on-Insulator Integrated Circuits With Graphene Lateral Heat Spreaders

Abstract: Graphene was recently proposed as a material for heat removal owing to its extremely high thermal conductivity. We simulated heat propagation in silicon-on-insulator (SOI) circuits with and without graphene lateral heat spreaders. Numerical solutions of the heat-propagation equations were obtained using the finite-element method. The analysis was focused on the prototype SOI circuits with the metal-oxide-semiconductor field-effect transistors. It was found that the incorporation of graphene or few-layer graphene (FLG) layers with proper heat sinks can substantially lower the temperature of the localized hot spots. The maximum temperature in the transistor channels was studied as function of graphene's thermal conductivity and the thickness of FLG. The developed model and obtained results are important for the design of graphene heat spreaders and interconnects.

Method of forming led-based light and resulting led-based light

Abstract: A method of forming a LED-based light for replacing a conventional fluorescent bulb in a fluorescent light fixture includes shaping an elongate sheet of highly thermally conductive material to fashion a heat sink. Shaping the heat sink allows fashioning the heat sink to define cover and end cap attachment structures, surfaces for mounting LEDs at various angles, and a high surface area to width ratio for dissipating heat.

Low-Temperature Two-Phase Microchannel Cooling for High-Heat-Flux Thermal Management of Defense Electronics

Abstract: For a given heat sink thermal resistance and ambient temperature, the temperature of an electronic device rises fairly linearly with increasing device heat flux. This relationship is especially problematic for defense electronics, where heat dissipation is projected to exceed 1000 W/cm2 in the near future. Direct and indirect low-temperature refrigeration cooling facilitate appreciable reduction in the temperature of both coolant and device. This paper explores the benefits of cooling the device using direct and indirect refrigeration cooling systems. In the direct cooling system, a microchannel heat sink serves as an evaporator in a conventional vapor compression cycle using R134a as working fluid. In the indirect cooling system, HFE 7100 is used to cool the heat sink in a primary pumped liquid loop that rejects heat to a secondary refrigeration loop. Two drastically different flow behaviors are observed in these systems. Because of compressor performance constraints, mostly high void fraction two-phase patterns are encountered in the R134a system, dominated by saturated boiling. On the other hand, the indirect refrigeration cooling system facilitates highly subcooled boiling inside the heat sink. Both systems are shown to provide important cooling benefits, but the indirect cooling system is far more effective at dissipating high heat fluxes. Tests with this system yielded cooling heat fluxes as high as 840 W/cm2 without incurring critical heat flux (CHF). Results from both systems are combined to construct an overall map of performance trends relative to mass velocity, subcooling, pressure, and surface tension. Extreme conditions of near-saturated flow, low mass velocity, and low pressure produce ldquomicrordquo behavior, where macrochannel flow pattern maps simply fail to apply, instabilities are prominent, and CHF is quite low. One the other hand, systems with high mass velocity, high subcooling, and high pressure are far more stable and yield very high CHF values; two-phase flow in these systems follows the fluid flow and heat transfer behavior as well as the flow pattern maps of macrochannels.

Tubular blue LED lamp with remote phosphor

Abstract: A lamp (40) includes a linearly extending heat sink (12), blue-light-emitting LEDs (14) mounted on the heat sink (12), and a light emitting cover mounted on the heat sink (12) in line with the LEDs (14), a first portion (44) of the cover opposite the LEDs (14) including a phosphor (20) that is excited by the LEDs (14) to emit white light. The cover may be a tube (49) with the LEDs (14) outside the tube, a portion of the tube (41) nearest the LEDs (14) being transparent and receiving light from the LEDs (14). The tube (42) may include reflectors (48) that are attached to an exterior surface of the tube (42) to hold the tube on the heat sink (42). Alternatively, the cover may enclose the LEDs (14) on the heat sink (12), where a portion of the cover has an interior surface that reflects light from the LEDs (14) to the first portion. The lamp (40) may include electrical connections that allow for multiple lamps to be connected in series.

Omnidirectional led light bulb

Abstract: An LED light bulb has a hollow LED support/heat sink (222, 602, 702, 900, 802, 1002, 1102, 1216, 1404, 1502, 1606, 1906) with fins (234, 406, 604, 706, 804, 904, 906,1008, 1106, 1620) extending internally and openings at two ends (230, 232, 1522). Heat generated by the LEDs (238, 908, 1242, 1624, 2504) is conducted through the heat sink fins and is removed by a convectively driven air flow that flows through the LED support/ heat sink. LEDs are mounted on multiple external faces (236, 404, 910, 1524, 1622) of the LED support/heat sink thereby providing illumination in all directions. Lenses (1246, 2102, 2104) are provided for the LEDs to make the illumination highly uniform.

Thermal and hydrodynamic characteristics of constructal tree‐shaped minichannel heat sink

Abstract: A three-dimensional thermal and hydrodynamic model for constructal tree-shaped minichannel heat sink is developed. The heat and fluid flow in the constructal heat sink with an inlet hydraulic diameter of 4 mm are numerically analyzed, taking into consideration conjugate heat transfer in the channel walls. The pressure drop, temperature uniformity, and coefficient of performance (COP) of the constructal tree-shaped heat sink are evaluated and compared with those of the corresponding traditional serpentine flow pattern. The results indicate that the constructal tree-shaped minichannel heat sinks have considerable advantages over the traditional serpentine flow patterns in both heat transfer and pressure drop. The strong and weak heat flow can be effectively allocated in tree-shaped flow structures; hence, the inherent advantage of uniform temperature on the heating surface in the constructal tree-shaped heat sink is demonstrated. And in tree-shaped flow structures, the local pressure loss due to confluence flow is found to be larger than that due to diffluence flow. In addition, an aluminum constructal tree-shaped minichannel heat sink is fabricated to conduct the verification experiment. The experimentally measured temperature distribution and pressure drop are in agreement with the numerical simulation, which verifies that the present model is reasonable. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Thin film thermoelectric devices for hot-spot thermal management in microprocessors and other electronics

Abstract: A structure, system and method for controlling a temperature of a heat generating device in a solid medium, wherein heat is extracted from the medium into at least one heat extraction device, the heat extraction device dissipates heat into an environment apart from the medium by a heat sink thermally coupled to the heat extraction device; and heat from the medium is dissipated into the heat sink by a first thermal interface material thermally coupling the heat sink to the medium.

Effect of Wick Characteristics on the Thermal Performance of the Miniature Loop Heat Pipe

Abstract: Two phase heat transfer devices based on the miniature version of loop heat pipe (LHP) can provide very promising cooling solutions for the compact electronic devices due to their high heat flux management capability and long distance heat transfer with minimal temperature losses. This paper discusses the effect of the wick properties on the heat transfer characteristics of the miniature LHP. The miniature model of the LHP with disk-shaped evaporator, 10 mm thick and 30 mm disk diameter, was designed using copper containment vessel and water as the working fluid, which is the most acceptable combination in electronic cooling applications. In the investigation, wick structures with different physical properties including thermal conductivity, pore radius, porosity, and permeability and with different structural topology including monoporous or biporous evaporating face were used. It was experimentally observed that copper wicks are able to provide superior thermal performance than nickel wicks, particularly for low to moderate heat loads due to their low heat conducting resistance. With monoporous copper wick, maximum evaporator heat transfer coefficient (hev) of 26,270 W/m2 K and evaporator thermal resistance (Rev) of 0.06–0.10°C/W were achieved. For monoporous nickel wick, the corresponding values were 20,700 W/m2 K for hev and 0.08–0.21°C/W for Rev. Capillary structure with smaller pore size, high porosity, and high permeability showed better heat transfer characteristics due to sufficient capillary pumping capability, low heat leaks from evaporator to compensation chamber and larger surface area to volume ratio for heat exchange. In addition to this, biporous copper wick structure showed much higher heat transfer coefficient of 83,787 W/m2 K than monoporous copper wick due to improved evaporative heat transfer at wick wall interface and separated liquid and vapor flow pores. The present work was able to classify the importance of the wick properties in the improvement of the thermal characteristics for miniature loop heat pipes.