Showing papers on "Heat pipe published in 1995"

Heat Pipe Science And Technology

Abstract: Preface Nomenclature 1.Introduction 2.Solid-Liquid-Vapor Phenomena, Driving Forces and Interfacial Heat and Mass Transfer 3.Steady Hydrodynamic and Thermal Characteristics 4.Heat Transfer Limitations 5.Continuum Transient and Frozen Startup Behavior of Heat Pipes 6.Two-Phase Closed Thermosyphons 7.Rotating and Revolving Heat Pipes 8.Variable Conductance Heat Pipes 9.Capillary Pumped Loop and Loop Heat Pipe Systems 10.Micro/Miniature Heat Pipe Characteristics and Operating Limitations 11.Heat Pipe Heat Exchangers 12.Analysis of Nonconventional Heat Pipes 13.Special Effects on Heat Pipes 14.Heat Pipe Fabrication, Processing, and Testing Appendix A:Thermophysical Properties Appedix B:Experimental Heat Pipe Results Index

Heat pipe exchanger system for cooling a hinged computing device

Abstract: A heat pipe exchanger system for cooling a hinged computing device. The hinged computing device includes a first hinged member having a first edge and second hinged member having a second edge. The first and second hinged members are rotatably attached along the first and second edges. A heat exchange sheath is mounted substantially parallel to the first and second edges and defines a first opening and a second opening. A first heat pipe is thermally coupled to the integrated circuit and has a portion disposed within the first opening. A second heat pipe is coupled to the display housing and has a portion disposed within the second opening. Alternately, the first heat pipe is coupled to the first hinged member and has a first portion substantially parallel to the first edge and the second edge. In this case, the second heat pipe is coupled to the second hinged member and has a first portion substantially perpendicular to the first heat pipe as well as a second portion conformally engaging the first heat pipe.

Heat Transfer During Evaporation on Capillary-Grooved Structures of Heat Pipes

Abstract: A detailed mathematical model is developed that describes heat transfer through this liquid films in the evaporator of heat pipes with capillary grooves. The model accounts for the effects of interfacial thermal resistance, disjoining pressure, and surface roughness for a given meniscus contact angle. The free surface temperature of the liquid film is determined using the extended Kelvin equation and the expression for interfacial resistance given by the kinetic theory. The numerical results obtained are compared to existing experimental data. The importance of the surface roughness and interfacial thermal resistance in predicting the heat transfer coefficient in the grooved evaporator is demonstrated. 17 refs., 5 figs., 2 tabs.

Apparatus for cooling charge coupled device imaging systems

Abstract: Apparatus for cooling charge-coupled device (CCD) imaging systems. The apparatus comprises a thermoelectric cooler thermally coupled to the imaging system for transferring heat away from and cooling the imaging system portion of the imaging system. The thermoelectric cooler has a cold side and an opposing hot side, with the cold side thermally coupled to the imaging sensor to enable the transfer of heat from the sensor in response to a supply of power. A power supply is coupled to the cooler for supplying required power. The hot side of the cooler is thermally coupled to a heat pipe, which is composed of a heat-conducting material having a hollow portion containing a wicking material and a working fluid. A heat sink is thermally coupled to the heat pipe enabling heat dissipation. The working fluid cyclically evaporates into vapor and condenses into liquid to effect the heat transfer from the heat pipe to the heat sink.

Passive cooling of enclosures using heat pipes

Abstract: A cooling system for passively cooling an enclosure (18) incorporates at least one inclined heat pipe (24) having an evaporator side (22) extending within the enclosure (18) and a condenser side (28) extending outside the enclosure (18) in contact with the ambient environment (30). A thermal storage device (12) within the enclosure (18) has a first portion (14) extending outside and adjacent the evaporator side (22) of the heat pipe (24) and a second portion (20) extending within, and generally concentric with, the evaporator side (22) of the heat pipe (24). A solid-to-liquid phase change material (26) is sealed within this thermal storage device (12) such that this material (26) changes to a liquid upon the absorption of heat. To further enhance the transfer of heat from within the enclosure (18) to outside the enclosure (18), a series of fins (44) can be added to the first portion (14) of the thermal storage device (12) as well as to the condenser side (28) of the heat pipe (24). Additionally, a series of internal fins (46) can be mounted to the second portion (20) of the thermal storage device (12) which would preferably be submerged in the working fluid (32) contained within the evaporator side (22) of the heat pipe (24).

Capillary pumped loop body heat exchanger

Abstract: A capillary pumped loop for transferring heat from one body part to another body part, the capillary pumped loop comprising a capillary evaporator for vaporizing a liquid refrigerant by absorbing heat from a warm body part, a condenser for turning a vaporized refrigerant into a liquid by transferring heat from the vaporized liquid to a cool body part, a first tube section connecting an output port of the capillary evaporator to an input of the condenser, and a second tube section connecting an output of the condenser to an input port of the capillary evaporator. A wick may be provided within the condenser. A pump may be provided between the second tube section and the input port of the capillary evaporator. Additionally, an esternal heat source or heat sink may be utilized.

Two-phase cooling system for a laptop computer lid

Abstract: A two-phase cooling system for a portable computer, the system consisting of an evaporator and a condenser that are both included in either the lid or the base of the computer. The two-phase cooling system is positioned proximate to the computer's heat-producing circuitry, such that the system draws liquid coolant past the circuitry and heat is transferred from the circuitry to the coolant. A fan may also be included, to assist in heat rejection from the cooling system. In a preferred embodiment, the cooling system consists of a flattened heat pipe, with a first side operating as the evaporator and a second side operating as the condenser.

Rotable and slideble heat pipe apparatus for reducing heat build up in electronic devices

Abstract: A rotatable and slidable heat pipe apparatus for transferring heat away from a microprocessor chip more rapidly than by heat sink surface area dissipation to the surrounding air alone, comprising a heat sink with an integral cylindrical passageway adapted to receive a first end of a heat pipe shaped like a crankshaft, and a heat spreader formed from a metal plate with a first end rolled up to define a cylindrical opening adapted to receive a second end of the heat pipe. The heat spreader is attached to an underside of a keyboard. Since the heat pipe is able to rotate within the cylindrical passageway and the cylindrical opening, the keyboard can be raised to an open position and lowered to a closed position quickly and simply without the risk of breaking or bending the heat pipe, and manufacturing position tolerances between the heat pipe apparatus components are increased resulting in a simplified manufacturing process. The heat pipe can also be slid in to and out of the cylindrical passageway or the cylindrical opening, thereby enabling computer manufacturers to incorporate the heat pipe into portable battery powered notebook-type computer systems designed to allow a user to remove, replace, or swap internal components by simply flipping open or removing the keyboard, and further enabling a user to perform maintenance work or repairs on the computer system without concern for damage to the heat pipe.

Thermal Characteristics of Conventional and Flat Miniature Axially Grooved Heat Pipes

Abstract: A detailed mathematical model of low-temperature axially grooved heat pipes (AGHP) is developed in which the fluid circulation is considered along with the heat and mass transfer processes during evaporation and condensation. The results obtained are compared to existing experimental data. Both capillary and boiling limitations are found to be important for the flat miniature copper-water heat pipe, which is capable of withstanding heat fluxes on the order of 40 W/cm 2 applied to the evaporator wall in the vertical position. The influence of the geometry of the grooved surface on the maximum heat transfer capacity of the miniature AGHP is demonstrated.

Porous media heat exchangers for cooling of high-power optical components

Abstract: Technologies based on porous media can be used in several classes of heat exchangers that can be used to meet the cooling needs of high heat load optical components as well as other high heat flux applications. These include mechanically pumped single-phase and two-phase porous media heat exchangers, as well as capillary pumped (heat pipe) two-phase designs. A brief overview of each of these classes of heat exchangers is given, and several applications representative of the state of the art are described. Various specific technologies are discussed that have demonstrated the capability to dissipate heat fluxes greater than 1000 W/cm2 over areas of interest in optics applications. Finally, an assessment is given of the capabilities of each approach to meet the needs of specific applications.

Flexible thermal transfer apparatus for cooling electronic components

Abstract: A thermal transfer apparatus (10) adapted for thermal connection to a heat source (11) for conducting heat away from the heat source. The thermal transfer apparatus includes a container (12) which is substantially impermeable to fluid and forms an expandable compartment (16) that is substantially gas-free. A thermal transfer liquid (14) is positioned within the expandable compartment for thermal connection to the heat source. The thermal transfer liquid has a boiling point that is at or below an operating temperature of the heat source. When the heat source is in a non-operating state, the thermal transfer liquid is compressed and substantially fills the expandable compartment. When the heat source is in an operating state, the thermal transfer liquid conducts heat from the heat source. The liquid vaporizes and forms a vapor (13) within the expandable compartment which causes the expandable compartment to expand and create a vapor space above the liquid. A condenser (24) condenses the vapor into a condensate at a location remote from the heat source. The condensate then returns to the body of liquid for additional cooling of the heat source.

Flexible heat pipe for integrated circuit cooling apparatus

Abstract: A heat pipe (10) which is flexible and thus conformable to the space in which it is to be deployed consists of two or three layers, namely, a relatively thin, highly conductive plate (12) as a bottom layer, a plastic sheet (16) as a top layer and wicking (14) as an optional middle layer. The bottom plate (12) has a relatively high modulus of elasticity and it is stiff, yet ductile. It is preferably made of metal, such as aluminum, or a plastic sheet or plate. To manufacture the heat pipe (10), the bottom (12) and top layers (16) are aligned, with the wicking (14) between them, and sealed together around three edges. Liquid coolant is then added and the fourth edge is sealed. The sealing is preferably performed by heat sealing. The heat pipe (10) may include heat-dissipating fins (36) or ridges on the end of the pipe that operates as a condenser. The opposing end of the pipe, which acts as the evaporator, is positioned proximate to a heat-generating component. In an alternative embodiment, additional layers of plastic and optional wicking are attached to an otherwise exposed surface of the bottom plate. The heat pipe is narrow and can thus be installed in existing space proximate to a heat generating component, flexing and/or elastically deforming as necessary to facilitate installation. Further, the heat pipe can be bent, to conform to the shape of the component.

The Interfacial Thermodynamics of Micro Heat Pipes

Abstract: Successful analysis and modeling of micro heat pipes requires a complete understanding of the vapor-liquid interface. A thermodynamic model of the vapor-liquid interface in micro heat pipes has been formulated that includes axial pressure and temperature differences, changes in local interfacial curvature, Marangoni effects, and the disjoining pressure. Relationships were developed for the interfacial mass flux in an extended meniscus, the heat transfer rate in the intrinsic meniscus, the 'thermocapillary' heat-pipe limitation, as well as the nonevaporating superheated liquid film thickness that exists between adjacent menisci and occurs during liquid dry out in the evaporator. These relationships can be used to define quantitative restrictions and/or requirements necessary for proper operation of micro heat pipes. They also provide fundamental insight into the critical mechanisms required for proper heat pipe operation. 29 refs., 6 figs.

Fabrication of vapor-deposited micro heat pipe arrays as an integral part of semiconductor devices

Abstract: Vapor-deposited micro heat pipe arrays (VDMHP) were fabricated as an integral part of semiconductor devices to act as efficient heat spreaders by reducing the thermal path between the heat sources and heat sink. Fabrication of the VDMHP was accomplished by first establishing a series of grooves in a silicon wafer. Orientation dependent etching (ODE) using a KOH-1-propanol-H/sub 2/O solution on a (100) wafer with a (111) flat covered with an oxide mask, resulted in grooves 25 /spl mu/m wide and 25 /spl mu/m deep with sharp, perpendicular edges. The wafers were predeposited with a layer of chromium followed by a layer of gold to improve the adhesion characteristics. Dual electron beam vapor deposition, followed by planetary process using molybdenum crucibles, were used to deposit copper 31.5-33.0 /spl mu/m thick, and provide complete closure of the grooves. A glass cover slip was bonded on the top of the deposited layer. The grooves were finally charged and sealed. A computer model Simulation and Modeling of Evaporated Deposition Profiles (SAMPLE) was used to optimize the metal step coverage and successfully predict the cross-sectional profile of the VDMHP. >

Integrated circuit cooling apparatus

Abstract: The apparatus is a cooling device for an integrated circuit chip which includes a heat conductive pad for contact with the top surface of the chip and for attachment to a heat pipe to dispose of the heat. One surface of the pad is flat and contacts the circuit chip while the opposite surface of the pad is attached to a simple cylindrical heat pipe. The pad includes extensions from its sides to which a holding fixture applies force so that the pad is held tightly against the chip. The holding fixture is held on the mounting board by screws while the top of the pad which is attached to the heat pipe protrudes through a hole in the holding fixture. A finned heat exchanger is attached to an end of the heat pipe remote from the conductive pad.

Analysis of Asymmetric Disk-Shaped and Flat-Plate Heat Pipes

Abstract: An analytical investigation and conceptual design of a disk-shaped asymmetric heat pipe is presented in this work. Using the conservative formulations for the steady incompressible vapor and liquid flow for a disk-shaped heat pipe, an in-depth integral analysis is applied. Analytical results for the asymmetric vapor velocity profile, the vapor and liquid pressure distributions, and the vapor temperature distribution in the heat pipe are obtained and compared to those of rectangular flat-plate heat pipe. The analysis establishes the physics of the process and the intrawick interactions for the disk-shaped heat pipe. The effects of variations in the thicknesses of the vapor channel and the wick as well as the heat pipe on the performance of both disk-shaped and rectangular flat-plate heat pipes are analyzed in detail and compared with each other. The factors limiting heat pipe performance are discussed and the results show that the disk-shaped heat pipe, while utilizing a smaller surface area and being more adaptable to several application areas, significantly increases the heat transfer capability per unit surface area compared to rectangular flat-plate heat pipe.

Two-Dimensional Rotating Heat Pipe Analysis

Abstract: A detailed transient numerical simulation of rotating heat pipes is presented. This two-dimensional, axisymmetric formulation accounts for the thin liquid condensate film on the inner surface of the rotating pipe wall, the vapor flow in the vapor space, and the unsteady heat conduction in the pipe wall. The thin liquid film is coupled to the vapor velocity at the liquid-vapor interface, and the effects of the vapor pressure drop and the interfacial shear stress are included in the Nusselt-type condensation analysis. 12 refs., 7 figs.

Thermal solutions to Pentium processors in TCP in notebooks and sub-notebooks

Abstract: Less than one year after the introduction of the 90 MHz Pentium Processor in Pin Grid Array (PGA) package, 75 MHz Pentium Processor in Tape Carrier Package (TCP) has been introduced for applications in mobile products. Notebooks and sub-notebooks using the 75 MHz Pentium Processor in TCP are expected to be on the market early 1995. In this paper, we will review the various thermal enhancements from the component, board and system level for the use of the Pentium processor in TCP in notebooks and sub-notebooks. The thermal tests are conducted in one reference notebook and sub-notebook using test boards and thermal test die. Thermal characterizations of the TCP find that with 4 Watts of board power, the TCP can dissipate up to 3.55 Watts of CPU power in the reference notebook and 2.71 Watts in the reference sub-notebook. Various thermal enhancements such as heat sinks, metal plates, are evaluated in the reference notebook. For the design target of 6.5 Watts of CPU power, four solutions are proposed for the reference notebook: the heat sink and aluminum plate solution, heat pipe connected to the keyboard solution, heat pipe connected to the outside aluminum plate solution and fan/heat sink solution. Two solutions are proposed for the reference sub-notebook: the heat pipe connected to the keyboard solution and heat pipe on the bottom chassis solution. Although the study is conducted in the reference notebook and sub-notebook, the thermal design trade offs and relative cooling capabilities are applicable to the general notebook and sub-notebook thermal designs.

Charge optimization for a triangular-shaped etched micro heat pipe

Abstract: An analytical model considered to be the first analytical micro heat pipe model to predict the capillary limit of operation as well as the radius of curvature in the evaporator section and the optimal value of liquid charge was developed for a triangular-shaped, etched micro heat pipe This model predicted optimal liquid prime values between 16-25% for various power levels and also indicated an optimal charge value which would not exceed 25% Micro heat pipe arrays with liquid prime values ranging from 10 to 50% were used The model was validated by comparing the predicted values of maximum heat transport capacity with experimental data at various liquid fill ratios Although the model correctly predicted the trends associated with the variations in the fill ratio, significant differences were evident in the predicted and measured dryout level 8 refs

Refractory-composite/heat-pipe-cooled leading edge and method for fabrication

Abstract: A thermal protection system containing several innovative features has been developed with heat pipes embedded in a composite material. The techniques used in the fabrication of the heat pipes permit a smaller radius and a higher use temperature heat pipe than could be manufactured under pervious techniques. The techniques used to embed the heat pipes in a refractory composite material yield a light weight leading edge that is able to tolerate the thermal stresses generated by the difference in thermal expansion between the heat pipes and the composite material. The heat pipes for the leading edge have a "J-shape", and are placed so that the long leg of the heat pipe alternates between the upper and lower surfaces. A coating is placed on the heat pipes that protects the heat pipe from oxidation and reaction with the components of the composite material. A compliant layer is placed between the heat pipes and the composite material to reduce the effects of the thermal stresses that arise due to the mismatch of thermal expansion between the heat pipe and the composite material. A gap forming layer may also be placed between the heat pipe and the composite material so that after it is removed or shrunk, a small gap will be left that will reduce thermal stresses.

Three-dimensional heat pipe

Abstract: A heat pipe heat exchanger is provided in the form of a serpentine heat pipe that does not have the ends of the individual tubes manifolded to one another via a straight pipe or via any other common connector. Instead, it has been discovered that heat pipes connected via U-bends to form a continuous coil function adequately. The serpentine heat pipe may include integral condenser and evaporator portions separated by a divider to form a one-slab heat exchanger, or separate evaporator and condenser coils connected to one another by vapor and return lines to form a two-section heat pipe. The heat pipe heat exchanger may be formed in a continuous closed-loop pipe so that the heat exchanger can operate with or without the aid of gravitational effects. A method of producing a serpentine heat pipe includes providing a plurality of U-shaped tubes which are interconnected to form a single serpentine heat pipe, one of the tubes having an open end, and inserting sufficient refrigerant in the one tube to allow each of the tubes to function as a separate heat pipe. The serpentine heat pipe heat exchanger may be used to increase the dehumidification capacity of an air conditioner.

Air/liquid cooled metallic turn for high frequency high power charging transformers

Abstract: Heat exchanger that are also outer turns of secondary windings of a transformer for use in a charge port of battery charging apparatus. The outer turns may have any shape or thickness, may be air or liquid cooled, or may be vapor changers (heat pipes). Other turns of the secondary windings cannot be used in this manner because they cause excessive energy dissipation, due to proximity losses. When used to a liquid cooled turn, the present invention comprises porting liquid coolant from a cooling system including a pump, a compact heat exchanger, and a fan through the outer windings. Heat dissipation from the secondary windings of the transformer is efficiently removed by providing an internal coolant flow passage or passages formed or integrated at the center of the outer windings comprising the heat exchangers. The internal passages may be configured in several ways. One approach is to construct thin, flat, self-contained flexible coolant bladders made of metal, such as copper. When applied to an air cooled turn, the present invention directs air from the fan through finned heat exchangers. The of the inner turns secondary windings are bonded directly to the finned heat exchanger turn in order to provide good thermal contact and a large heat transfer area.

Spacecraft radiator cooling system

Abstract: A heat pipe network for a satellite or spacecraft is disclosed. The network is constructed from formed and straight heat pipes securely connected together with a highly conductive material, such as Grafoil, serving as an interface gasket. The heat pipe network is interconnected to the subnadir panel and auxiliary panels, and thermally couples the North and South radiator panels. High thermal dissipating units can be mounted to heat pipes on panels attached to the main spacecraft radiator panels. The heat pipes transfer the thermal energy to the radiator panels where it is radiated to space.

Micro heat pipe panels and method for producing same

Abstract: Flat or curved micro heat pipe panels are fabricated by arranging essentially parallel filaments in the shape of the desired panel. The configuration of the filaments corresponds to the desired configuration of the tubes that will constitute the heat pipes. A thermally conductive material is then deposited on and around the filaments to fill in the desired shape of the panel. The filaments are then removed, leaving tubular passageways of the desired configuration and surface texture in the material. The tubes are then filled with a working fluid and sealed. Composite micro heat pipe laminates are formed by layering individual micro heat pipe panels and bonding them to each other to form a single structure. The layering sequence of the micro heat pipe panels can be tailored to transport heat preferentially in specific directions as desired for a particular application.

Heat pipe device and method for attaching same to a computer keyboard

Abstract: A heat transfer system is provided for dissipating thermal energy within the personal computer. The transfer system is designed to move heat from a heat source, such as a central processing unit (CPU), to a heatsink arranged upon the portable computer keyboard. The heat transfer mechanism includes a heat slug thermally coupled to the CPU heat source and a heat pipe thermally coupled to a backside surface of a computer keyboard. The heat pipe is designed having minimal thermal gradient, and includes an evaporation/condensation cycle associated with its operation. The heat pipe is preferably orthogonally shaped having at least one flat surface arranged near the intersection of the orthogonal members. The flat section is in registry with a heat source. Movement of the flat section relative to the heat source effectuates abutment and thermal contact therebetween. The present thermal energy transfer system is designed for enhanced heat transfer within a portable computer system without undergoing the disadvantages of bulky finned heatsinks and/or fans.

Design, manufacture and testing of a closed cycle thermosyphon rankine engine

Abstract: The Thermosyphon Rankine Engine (TSR) is a recent concept for power generation using solar or other available low grade heat sources. The basis of the engine is the modification of a heat pipe, with its excellent heat and mass transfer characteristics, to incorporate a turbine, thereby making the system into a Rankine Cycle Engine. The TSR is directed towards power production from solar ponds, geothermal energy and heat produced by solar collectors, as well as for waste heat utilisation for electrical power generation. A theoretical formulation and results from experiments on prototype units are presented. Based on the results, it is concluded that the TSR engine may play an important role for conversion into electrical energy of thermal energy produced by conventional solar collectors, geothermal sources and waste heat.