Showing papers on "Heat pipe published in 1996"

Attachment assembly for integrated circuits

Abstract: An integrated circuit package has a top die attach area and a bottom heat spreader thermally coupled to the die for conducting heat generated by the die through a thermal interface in the main circuit board to a heat sink or heat pipe mounted underneath the main circuit board. The preferred thermal interface is a thin, thermally conductive slug mounted through an opening formed in the main circuit board. The heat spreader spans the bottom surface of the integrated circuit package substantially parallel to the main circuit board and preferably extends substantially to the inner periphery of the pin arrangement which preferably, although not exclusively, is in a ball grid array. The opening formed in the main circuit board through which the thin, thermally conductive slug is fitted, is preferably substantially flush with the bottom surface of the main circuit board and juxtaposed against the heat spreader. A thermally conductive adhesive is preferably applied to the adjoining surfaces of the heat spreader and the slug.

Packaging system for thermally controlling the temperature of electronic equipment

Abstract: A passive method and packaging system for thermally controlling the temperature of electronic equipment within a housing are disclosed. The packaging system provides for two cooling steps, each of which uses a different passive cooling technology. Cooling by changing the phase of Phase Change Material, assists in controlling internal ambient temperatures by limiting the effects of short term localized thermal phenomena which would otherwise further increase internal temperatures. Cooling is also provided for by switching on a second passive cooling means, preferably a heat pipe, as the internal temperature of the housing increases above a predetermined temperature and to switch it off as the internal temperature drops below the predetermined temperature. Turning the second passive cooling means on and off provides respectively, a low or high thermal resistance path between the interior and exterior of the housing. The second passive cooling means allows for cooling of the housing above the predetermined temperature as well as heating of the housing below the predetermined temperature by preserving heat generated by the equipment. The two cooling steps in combination, co-operate to limit both maximum and minimum temperatures within the housing and of components. The combination of cooling steps also allows control over the temperature delta between the maximum and minimum temperatures during internal temperature swings.

Theoretical analysis of the maximum heat transport in triangular grooves : A study of idealized micro heat pipes

Abstract: A mathematical model for predicting the minimum meniscus radius and the maximum heat transport in triangular grooves is presented. In this model, a method for determining the theoretical minimum meniscus radius was developed and used to calculate the capillary heat transport limit based on the physical characteristics and geometry of the capillary grooves. A control volume technique was employed to determine the flow characteristics of the micro heat pipe, in an effort to incorporate the size and shape of the grooves and the effects of the frictional liquid-vapor interaction. In order to compare the heat transport and flow characteristics, a hydraulic diameter, which incorporated these effects, was defined and the resulting model was solved numerically. The results indicate that the heat transport capacity of micro heat pipes is strongly dependent on the apex channel angle of the liquid arteries, the contact angle of the liquid flow, the length of the heat pipe, the vapor flow velocity and characteristics, and the tilt angle. The analysis presented here provides a mechanism whereby the groove geometry can be optimized with respect to these parameters in order to obtain the maximum heat transport capacity for micro heat pipes utilizing axial grooves as the capillary structure.

Flat type heat pipe

Abstract: A flat type heat pipe for mounting a heating power element, which is capable of forming an optionally shaped heat transferring path with high accuracy, which is of a thin type and to which fins are easily attached. The flat type heat pipe includes at least two aluminum plates substantially in parallel with each other and brazed to each other so as to form a heat transferring path therebetween. The flat type heat pipe also includes an operating liquid which fills the heat transferring path. Because the heat transferring path 25 is formed by means of press molding, punching, laser beam machining, or cutting various shapes of heat transferring paths can be formed finely and with high accuracy. The flexible flat type heat pipe can be made thin, which allows for a variety of uses. Grooves and wicks can be disposed in the heat transferring path, thereby improving the heat conductivity. Because the surface is flat, the fins can be easily attached thereto, thereby a satisfactory radiation effect can be obtained.

Experimental Investigation of the Maximum Heat Transport in Triangular Grooves

Abstract: An experimental investigation was conducted and a test facility constructed to measure the capillary heat transport limit in small triangular grooves, similar to those used in micro heat pipes. Using methanol as the working fluid, the maximum heat transport and unit effective area heat transport were experimentally determined for ten grooved plates with varying groove widths, but identical apex angles. The experimental results indicate that there exists an optimum groove configuration, which maximizes the capillary pumping capacity while minimizing the combined effects of the capillary pumping pressure and the liquid viscous pressure losses. When compared with a previously developed analytical model, the experimental results indicate that the model can be used accurately to predict the heat transport capacity and maximum unit area heat transport when given the physical characteristics of the working fluid and the groove geometry, provided the proper heat flux distribution is known. The results of this investigation will assist in the development of micro heat pipes capable of operating at increased power levels with greater reliability.

Effective thermal conductivity of heat pipes

Abstract: Several heat pipes were designed and manufactured to study the effect of the working fluids, container materials, and the wick structures on the heat transfer mechanism of the heat pipes. Also, the effect of the number of wick layers on the effective thermal conductivity and the heat transfer characteristics of the heat pipes have been investigated. It was found that the flow behavior of the working fluid depends on the wicking structures and the number of wick layers. The heat transfer characteristics and the effective thermal conductivity are related directly to the flow behavior. Increasing the number of wick layers (up to 16 layers) increases the heat flux with smaller temperature differences. The flattening phenomena of the thermal resistance was observed after 16 wicks layers due to the entrainment limit.

Electrically insulated envelope heat pipe

Abstract: The disclosure is for a heat pipe in the form of a simple foil envelope and a method of constructing such a heat pipe. Two plastic coated metal foil sheets are sealed together on all four edges to enclose a semi-rigid channeled sheet of plastic foam, and the envelope is evacuated and loaded with a suitable quantity of liquid to act as a heat pipe. Despite the use of the essentially poor thermally conductive materials such as the plastic coating on the surface of the casing and the foam plastic for the wick, the apparatus operates well as a heat spreader for an integrated circuit chip placed in contact with the envelope surface. The heat is transferred across the thin plastic coating with only a small temperature differential, and the foam plastic wick with channels efficiently transports condensed liquid back to the heat input location for evaporation.

The Interline Heat Transfer of Evaporating Thin Films Along a Micro Grooved Surface

Abstract: An analytical investigation of the heat transfer characteristics for evaporating thin liquid films in V-shaped microgrooves with nonuniform input heat flux was conducted. This investigation assumed that the capillary pressure difference caused by the receding of the meniscus is responsible for the axial liquid flow along the groove, and that the disjoining pressure difference along the groove side wall provided the driving force for the flow up the groove wall. The combined heat transfer mechanisms of both liquid conduction and interfacial vaporization were used to describe the local interfacial mass flux in the interline region. Based on this approach, a local heat transfer coefficient was defined. The local and average heat transfer coefficients were both found to be sensitive to the characteristic thermal resistance ratio. In addition, when the film superheat was constant, the primary factor affecting the length of the evaporating interline region was found to be the heat flux supplied to the bottom plate, and for high heat flux conditions, the highest heat transfer coefficient did not necessarily exist at the axial dryout point. The expression developed for the evaporating film profile was shown to assume an exponential form if the heat flux distributed on the active interline region was assumed to be uniform.

Heat pipe and process for manufacturing the same

Abstract: A heat pipe (11,42,47) for transferring heat as the latent heat of evaporation to a radiating portion (12b,22b,25b,27b,28b,31b,33b,43,47b) at a lower temperature by heating a heating portion (12a,22a,25a,27a,28a,31a,33a) of a container to evaporate a working fluid (13) and by conveying the produced vapor to the radiating portion thereby to condense the vapor. The container (12,22,25,27,28) is formed into a flattened hollow shape by: a flat heating portion (12a,22a,25a,27a,28a,31a,33a) a radiating portion (12b,22b,25b,27b,28b,31b,33b,43,47) opposed at a distance to the heating portion and having a larger area than that of the heating portion; and side wall portions (12c,27c,27d) jointing the heating portion and the radiating portion to each other along the entire peripheral edge portions of the same.

Cooling unit for electronic equipment

Abstract: Heat generated at heat generating components is efficiently transported to a wall of a metal box serving as a heat dissipation section to cool the heat generating components even in an apparatus, in which box the heat generating components together with other components are mounted. The heat generating components and the heat dissipation section are connected to each other through a thermal transport device having a flexible structure. The heat generating components and the box are readily connected to each other irrespective of the arrangement of components, and heat is efficiently transported by driving the liquid. In the heat dissipation section, because the heat generating components and the wall of the metal box are thermally connected to each other, a high heat dissipation capacity is obtained as heat is diffused extensively into the wall due to a high thermal conductivity of the metal box.

Coupled, flux transformer heat pipes

Abstract: A heat pipe includes a heat input end including an evaporator an adiabatic section and an output end including a condenser, with the evaporator and the condenser joined by a hollow adiabatic section containing a wicking material and a coolant, a heat pipe including a plurality of heat pipe stages connected in cascade with the condenser of the preceding stage secured to the evaporator of the succeeding stage each of the stages having a larger internal cross-sectional area at the condenser than at the evaporator. The stages of heat pipes are interconnected to form an integral part of a unitary heat pipe, with the condenser and the evaporator screwed together, or individual heat pipes are interconnected by sleeves of variable lengths screwed one into the other. A heat pipe can be composed of flexible material, and more particularly the heat pipe is connected to the box containing the device as a heat sink. The heat pipes can increase in diameter in steps stage by stage; or the heat pipes increase in diameter linearly stage by stage and linearly within a stage.

Method and apparatus for transferring heat from transducer array of ultrasonic probe

Abstract: A device for improving thermal transfer inside an ultrasound probe and reducing heat build-up near the transducer face. The cable components (40) are used as heat pipes which conduct heat out of the probe handle (14). These heat pipes are coupled to an internal heat pipe (36) which is in heat conductive relationship with the transducer pallet (2). Thus, heat generated by the transducer array can be transferred, via the internal heat pipe plate and the cable heat pipes, away from the probe surface which contacts the patient. A heat conductive structure can be embedded in the overall shield braid of the cable (16). Suitable heat conductive structures include thread or wire made of material having a high coefficient of thermal conductivity, as well as narrow tubing filled with heat conductive fluid. Alternatively, inlet and return flow paths for cooling fluid are incorporated in the cable. The inlet and return flow paths inside the cable are respectively connected to the inlet and outlet of a flow path which is in heat conductive relationship with the heat pipe in the probe handle.

Heat dissipating lid hinge structure with laterally offset heat pipe end portions

Abstract: A notebook computer display housing is pivotally connected to its associated CPU housing by a heat dissipating hinge structure having telescoped, relatively rotatable first and second sections respectively anchored to the CPU and display housings. The heat absorbing evaporation end of a first thermosyphoning heat pipe is conductively connected to a heat generating electronic component within the CPU housing, with the heat rejecting condensing end of the heat pipe defining the first hinge structure section. During computer operation, heat from the electronic component is sequentially transferred through the heat pipe and the second hinge structure section, in which the first hinge section is journaled, to the display housing for dissipation therefrom to ambient. Heat transfer from the second hinge structure section to the display housing is representatively facilitated by a second thermosyphoning heat pipe having an evaporator end received in an opening in the second hinge structure section, and laterally offset from the condensing end of the first heat pipe, and a condensing end thermally communicated with the display housing.

Computer having a heat sink structure incorporated therein

Abstract: A computer having a heat sink structure incorporated therein provides efficient heat dissipation for heat generating components within the computer. In a preferred embodiment, a computer has a chassis, a circuit board with a heat generating device mounted thereon, and a structural member with a heat pipe disposed thereon. The heat pipe transfers heat from the heat generating device to a heat dissipating portion of the structural member. The structural member strengthens the chassis and provides convective transfer of the heat to the environment.

Heat radiating apparatus

Abstract: A heat radiating apparatus includes a metal pipe attached to at least one side of a metal plate, a heat pipe inserted into an internal hollow of the metal pipe, the hollow being filled with grease having high thermal conductivity, a sleeve seal provided at least one longitudinal end of the metal pipe for sealing the grease in such a way as to permit the heat pipe to freely rotate, and a heat receiving section through which a part of the heat pipe is in contact with a heating body.

NaX zeolite, carbon fibre and CaCl2 ammonia reactors for heat pumps and refrigerators

Abstract: The key elements of solid sorption machines are the chemical compressors-adsorbers. Two categories of the solid sorption system are analyzed: adsorbents NaX zeolite, carbon fibre “Busofit” with NH3, and complex combinations that undergo chemical reaction and physical adsorption (CaCl2 + carbon fibre “Busofit” with NH3). Two phase ammonia motion inside the adsorbent bed was checked. That accompanied NH3/CaCl2 solution redistribution between the cold and hot surfaces of the sorbent bed, resulting in a rich CaCl2 concentration at the boundaries. Solid sorption heat pump and refrigerator technology utilizing heat pipe heat recovery with a condensing/evaporating refrigerant holds considerable promise for bivariant (space and domestic) applications due to the variable temperature and variable load capabilities of such machines.

Electronic system having fluid-filled and gas-filled thermal cooling of its semiconductor devices

Abstract: An electronic system having improved thermal transfer from a semiconductor die in a semiconductor device assembly (package) by at least partially filling a cavity in the package with a thermally conductive fluid, immersing a heat collecting portion of a heat pipe assembly into the fluid, and sealing the cavity In order that the thermally conductive fluid does not chemically attack the die or its electrical connections, the die and connections can be completely covered with an encapsulating coating of an inorganic dielectric material, such as silicon dioxide, by any of a variety of techniques The heat pipe provides highly efficient heat transfer from within the package to an external heat sink by means of an evaporation-condensation cooling cycle The optional dielectric coating over the die permits selection of the thermally conductive fluid from a wider range of fluids by isolating the die and its electrical connections from direct contact with the fluid In another embodiment, an absorptive wick is disposed within the package to transport condensed coolant to close proximity with the die A heat pipe and wick may be employed in combination, and the heat pipe may have hollow fins, and the wick may extend into the fins (as well as into the package cavity) The use of a wick improves the thermal characteristics of the packaged device irrespective of its physical orientation

Cooling system for thin profile electronic and computer devices

Abstract: An apparatus and method for removing heat from a heat generating component located within a thin-profile consumer electronic or computer system enclosure is disclosed. In one embodiment the cooling system of the present invention includes an air duct comprising a thermally conductive housing having internal fins dispersed along the internal walls of the duct. An air flow generator produces an air flow that is directed from an inlet port located at or near the center of the air duct to first and second exit ports located at opposite ends of the duct. A low resistance thermal path, such as a heat pipe, transfers heat from the heat generating component to the air duct housing.

A pore-network study of bubble growth in porous media driven by heat transfer

Abstract: We present experimental and theoretical investigations of vapor phase growth in pore-network models of porous media. Visualization experiments of boiling of ethyl alcohol in horizontal etched-glass micromodels were conducted. The vapor phase was observed to grow into a disordered pattern foUowing a sequence of pressurization and pore-filling steps. At sufficiently small cluster sizes, growth occurred "one pore at a time," leading to invasion percolation patterns. Single-bubble (cluster) growth was next simulated with a pore-network simulator that includes heat transfer (convec- tion and conduction), and capillary and viscous forces, although not gravity. A boundary in the parameter space was delineated that separates patterns of growth dictated solely by capillarity (invasion percolation) from other patterns. The region of validity of invasion percolation was found to decrease as the supersaturation (heat flux), the capillary number, the thermal diffusivity, and the vapor cluster size increase. Implications to continuum models are discussed. Introduction Flows in porous media that involve liquid-to-gas phase change occur in many problems of interest. The phase change can be brought about by solute diffusion, where the supersatura- tion is supplied by pressure reduction (see Li and Yortsos, 1994, 1995a, b), or by heat conduction, where the phase growth is controlled by the rate of heat supply. The latter include problems in enhanced boiling heat transfer (Thome, 1990), flows in geo- thermal systems (Schubert and Straus, 1979; Straus and Schu- bert, 1981 ), heat pipes (Ogniewicz and Tien, 1979; Udell, 1983, 1985), and severe nuclear reactor accident scenarios (Dhir and Catton, 1977). In this paper we consider the second problem with particular emphasis on single-bubble growth. As with other porous media processes, this problem can be studied at three different levels: ( 1 ) the single-pore level, where the emphasis is on the mechanics of gas-phase nucleation, film and comer flows, wetting phenomena, and the distribution of phases within single pores; (2) the pore-network level, where the emphasis is on the integration of events in an interacting ensemble of pores, where pore network topology is predomi- nant; (3) the continuum level, where the emphasis is on the average behavior of the system in terms of variables such as heat fluxes, temperature, and saturation levels. Most of past efforts have addressed the continuum level, where the pore-space dynamics are lumped into relative perme- ability and capillary pressure functions imported from the iso- thermal, immiscible displacement literature (Bau and Torrance, 1982; Udell, 1985; Stubos et al., 1993; see also Epstein, 1994). This approach has certain shortcomings: ( 1 ) In enhanced boil- ing experiments, the porous layers might not be extensive enough for the volume-averaging implicit in the continuum ap- proach to be valid; (2) the relative permeability and capillary pressure functions are taken to be independent of the rates of heat transfer. This assumption may not be valid. Experimental investigations also focused on macroscale quantities (Sondergeld and Turcotte, 1977; Straus and Schubert,

Heat pipes inserted into first and second parallel holes in a block for transferring heat between hinged devices

Abstract: The apparatus is a device for transferring heat across the hinged joint between the two sections of the case of a laptop computer. Two simple heat pipe cylinders are inserted into parallel cylindrical holes in a heat conductive block. One cylinder is bonded within its hole, and the other cylinder is permitted to rotate within its hole. The axis of the rotatable cylinder is located in line with the axis of the mechanical hinges which permit the panels to pivot relative to each other. A heat producing device in one panel can be then attached to one heat pipe, and a heat sink on the other panel can be attached to the other heat pipe. The heat transfer between the heat source and the heat sink is essentially that of a heat pipe except for the very short heat conductive path through the solid block and the one rotating joint.

Fluid flow effects in evaporation from liquid-vapor meniscus

Abstract: A mathematical model of the evaporating liquid-vapor meniscus in a capillary slot has been developed. The model includes two-dimensional steady-state momentum conservation and energy equations for both the vapor and liquid phases, and incorporates the existing simplified one-dimensional model of the evaporating microfilm. The numerical results, obtained for water, demonstrate the importance of accounting for the fluid flow in calculating the effective evaporative heat transfer coefficient and the superheat of the vapor over the liquid-vapor meniscus due to the heat transfer from the heated wall. With higher heat fluxes, a recirculation zone appears in the vapor near the heated wall due to the extensive evaporation in the thin-film region of the liquid-vapor meniscus.

Heat pipe to baseplate attachment method

Abstract: An integrated circuit package which has a heat pipe that is incorporated into the body of the package. The package contains an integrated circuit which is mounted to a package substrate. The integrated circuit die is enclosed by a cover plate that is attached to the substrate. The heat pipe is attached to a nut that is screwed into the cover plate. The heat pipe has a bottom surface that is thermally coupled to the die to provide a direct thermal path between the integrated circuit and the heat pipe.

Wick-interrupt temperature controlling heat pipe

Abstract: The wick-interrupt temperature controlling heat pipe (WITCH) is a device for controlling the temperature of spacecraft temperature-sensitive, heat dispensing devices. A heat transporting working fluid is conveyed in saturated equilibrium with its vapor across a discontinuous internal capillary liquid wick, within a tubular cylindrical pressure vessel, from a condenser section to an evaporator section located on either side of the discontinuity. When the temperature within the WITCH rises to a predetermined level, a sliding wick located within the internal capillary liquid wick is inserted across the discontinuity by a temperature sensitive control rod, thereby allowing the heat transporting working fluid to circulate from the condenser section wick to the evaporator section wick. In this configuration, the WITCH operates identically to the "constant-conductance heat pipe" commonly used. When the component's or heat pipe's temperature drops to a predetermined level the control rod contracts relative to the heat pipe vessel wall and retracts the sliding wick, again creating a wick discontinuity between the evaporator and condenser sections and thereby interrupting the flow of the heat transporting working fluid and causing evaporator dry-out and curtailment of heat pipe operation. This "ON" and "OFF" heat pipe operation is the means whereby temperature is actively controlled to within a narrow range while heat transport varies over a wide range.

Serpentine heat pipe and dehumidification application in air conditioning systems.

Abstract: A heat pipe heat exchanger is provided in the form of a continuous closed-loop pipe (200) so that the heat exhanger can operate with or without the aid of gravitational effects. The continuous closed-loop pipe (200) has integral condenser (201) and evaporator (202) portions separated by a divider (207) to form a one-slab heat exchanger. The continuous closed-loop heat pipe heat exchanger (200) may be used to increase the dehumidification capacity of an air conditioner.

Honeycomb sandwich panel with built in heat pipes

Abstract: A sandwiched honeycomb panel with built in heat pipes includes a radiating fin which is integral with an envelope having a heat pipe formed therein. A heat block may be used in place of the radiating fin.