Showing papers on "Micro heat exchanger published in 1992"

Narrow channel finned heat sinking for cooling high power electronic components

Abstract: Dissipation of the heat produced by the operation of electronic circuitry may be improved by a heat sink which comprises a flat base from which a number of vertical fins extend. The fins are parallel to one another and define a number of parallel channels into which coolant flow is directed. The thermal resistance of the heat sink is optimized by setting fin thickness and channel width parameters to appropriate values. The heat sink may be attached in a heat conductive manner to a heat producing electronic component. One or more of these heat sinked components may be laid out in an in-line or staggered arrangement on a support in the form of a circuit pack. Cooling fluid is delivered to the circuit pack in a variety of ways to cool the heat sinked components. A method of determining the optimum fin thickness and channel width parameters involves determining a relationship between total thermal resistance of the heat sink and combinations of fin thickness and channel width parameters. A contour plot is produced in accordance with the relationship referred to above. The contour plot shows regions of optimum heat dissipation for heat sinks in accordance with the geometry identified here.

Design And Technology Of Heat Pipes For Cooling And Heat Exchange

Abstract: Introduction HEAT PIPE CHARACTERISTICS The Role of Capillarity in Heat Transport Pressure and Temperature Distributions Heat Transport Limits Heat Pipe Startup References HEAT PIPE TECHNOLOGY Heat Transport Fluids Containment and Wick Materials Wick Characteristics Heat Pipe Fabrication Environmental Influences on Heat Pipe Operation Heat Pipe Systems References FLUID FLOW IN A HEAT PIPE The Nature of the Flow Process General Pressure Drop Formulation Frictional Pressure Drop for Constant Surface Mass Flux Frictional Pressure Drop for Nonconstant Surface Mass Flux Hydraulic Diameter Frictional Pressure Drop in a Porous Flow Passage Frictional Pressure Drop for Convective Cooling References HEAT TRANSPORT LIMITS Capillary Pumping Limit Sonic Limit Entrainment Limit Boiling Limit Heat Pipe Operational Boundaries Comparison of Calculated and Experimental Heat Transport Limits References HEAT PIPE DESIGN: STEADY STATE Design Criteria and Constraints Heat Pipe Area-Temperature Relations Heat Pipe Internal Dimensions Structural Considerations Additional Design Topics Heat Pipe Exchangeers References HEAT PIPE DESIGN: TRANSIENT BEHAVIOR Heat Pipe Startup Features of the Transient Model Transient Equations Calculational Procedure Assessment of Heat Pipe Startup References DESIGN EXAMPLES Heat Pipe Space Radiator Transient Analysis of the Heat Pipe Space Radiator References Appendices

Electronics package with improved thermal management by thermoacoustic heat pumping

Abstract: Electronic chips are cooled to an efficient operating temperature by engaging their exposed planar surfaces with a heat sink assembly. The heat sink assembly is a part of the cold end heat sink of a thermoacoustic heat pump that utilizes either traveling wave or standing wave heat pumping to transport heat from the cold end heat exchanger to the warm end heat exchanger, utilizing a coaxial pulse tube refrigerator to pump or transport the heat from the electronic chips and the cold end heat exchanger.

Test Results of an Active Magnetic Regenerative Refrigerator

Abstract: The principle of the Active Magnetic Regenerator (AMR) is tested with an experimental refrigerator designed to operate within the temperature range of about 4 to 80 K. Applications, including helium and hydrogen liquefaction and hydrogen slush generation, are envisioned. The device uses a single moveable superconducting solenoidal magnet in persistent mode to alternately charge and discharge two in-line beds of magnetic material. Between magnet motions, a double-acting piston displacer moves heat transfer fluid in the form of helium gas through the beds, absorbing heat at the cold heat exchanger and rejecting heat at the hot heat exchanger.

Transient Natural Convection in Enclosures With Application to Solar Thermal Storage Tanks

Abstract: Many previously studied natural convection enclosure problems in the literature have the bounding walls of the enclosure responsible for driving the flow. A number of relevant applications contains sources within the enclosure which drive the fluid flow and heat transfer. The motivation for this work is found in solar thermal storage tanks with immersed coil heat exchangers. The heat exchangers provide a means to charge and discharge the thermal energy in the tank. The enclosure is cylindrical and well insulated. Initially the interior fluid is isothermal and quiescent. At time zero, a step change in the source temperature begins to influence the flow. The final condition is a quiescent isothermal fluid field at the source temperature. The governing time-dependent Navier-Stokes and energy equations for this configuration are solved by a finite element method. Solutions are obtained for 10[sup 3] [le] Ra[sub D] [le] 10[sup 6]. Scale analysis is used to obtain time duration estimates of three distinct heat transfer regimes. The transient heat transfer during these regimes are compared with limiting cases. In this paper correlations are presented for the three regimes.

Heat exchanger apparatus having fluid coupled primary heat exchanger unit and auxiliary heat exchanger unit

Abstract: A sturdy heat exchanger, having a variable configuration, is constructed by separately building a primary heat exchanger and an auxiliary heat exchanger, connecting the primary heat exchanger and the auxiliary heat exchanger via brackets mounted on the header pipes of the primary heat exchanger and on the auxiliary heat exchanger, and fluid connecting the header pipes via a connecting pipe. On the tops and bottoms of the primary heat exchanger and of the auxiliary heat exchanger, a pair of reinforcing side plates are mounted, and by engaging the opposing reinforcement plates to assemble the primary heat exchanger to the auxiliary heat exchanger, the heat exchanger's sturdiness is further reinforced, thereby preventing the header tanks from deforming the tubes.

Heat Transfer in Thin, Compact Heat Exchangers With Circular, Rectangular, or Pin-Fin Flow Passages

Abstract: Heat transfer and pressure drop have been measured of three thin, compact heat exchangers in helium gas at 3.5 MPa and higher, with Reynolds numbers of 450 to 36,000. The flow geometries for the three heat exchanger specimens were: circular tube, rectangular channel, and staggered pin fin with tapered pins. The specimens were heated radiatively at heat fluxes up to 77 W/sq cm. Correlations were developed for the isothermal friction factor as a function of Reynolds number, and for the Nusselt number as a function of Reynolds number and the ratio of wall temperature to fluid temperature. The specimen with the pin fin internal geometry had significantly better heat transfer than the other specimens, but it also had higher pressure drop. For certain conditions of helium flow and heating, the temperature more than doubled from the inlet to the outlet of the specimens, producing large changes in gas velocity, density, viscosity, and thermal conductivity. These changes in properties did not affect the correlations for friction factor and Nusselt number in turbulent flow.

Analysis of spray-cooled finned-tube heat exchangers

Abstract: A mathematical model has been developed for the analysis of spray-cooled finned-tube heat exchangers. An experimental study was conducted on a four-pass, finned-tube heat exchanger in a vertical air/water mist flow to validate the model, and the results compared well with the predicted performance. Significant performance enhancement (up to 3.5 times the dry performance) was found by spraying relatively small amounts of water onto the heat exchanger. The two-phase pressure drop across the heat exchanger was also measured, and the spray water mass flow rate was found to have a significant effect on the pressure drop across the tube bundle. This study helped to identify certain factors, such as the geometry of the finned tubes and the optimum air/spray water ratios, which have to be taken into consideration when designing spray-cooled heat exchangers.

Frictional pressure drop for gas/liquid two-phase flow in plate heat exchangers

Abstract: Two-phase flow occurs in plate heat exchangers used as evaporators or condensers. The frictional pressure drop for two-phase flow can be considerably higher than for single-phase flow, because of the interaction between the phases. In this article, measurements of air-water flow in two different plate-and-frame exchangers are presented. Correlations developed for tubular flow are compared with the experimental results. Recommendations for a calculation procedure are given.

Flow Distribution in Plate Heat Exchangers and Consequences on Thermal and Hydraulic Performances

Abstract: The misunderstanding of the consequences of a non-uniform flow distribution on thermal and hydraulic performances generally involves a poor design of the heat exchanger. Thus, a numerical model is developped to predict the flow distribution, and is validated by experiences. It appears that the overall pressure drop is closely related to the flow distribution, and that the thermal performances are less affected. But heterogeneity in temperature is observed at the outlet of the channels.

Heat Transfer Model of a Rotary Compressor

Abstract: Energy improvements for a rotary compressor can be achieved in several ways such as: reduction of various electrical and mechanical losses, reduction of gas leakage, better lubrication, better surface cooling, reduction of suction gas heating and by improving other parameters. To have a ' better understanding analytical/numerical analysis is needed. Although various mechanical models are presented to understand the mechanical losses, dynamics, thermodynamics etc.; little work has been done to understand the compressor from a heat uansfer stand point In this paper a lumped heat transfer model for the rotary compressor is described. Various heat sources and heat sinks are analyzed and the temperature profile of the compressor is generated. A good agreement is found between theoretical and experimental results. NOMENCLATURE D, inner diameter D. outer diameter Dmt upper bearing plate outer diameter .:lx conduction length Q rate of heat transfer S; heat generation within element i 1:!.£ change in internal energy D,.,., case inside diameter D,...., case outside diameter A,_; coeffients of the simultaneous equations [coefficients of the matrix] h, effective radiation heat transfer coefficient E emissivity h4 heat transfer coefficient between the case inside and the gas above the stator/rotor h_ heat transfer coefficient of the case and outside z, height of the case above the stator z, height of the stator B, _known parts of the system equations m mass flow rate of the gas W rate of work done r7 Stefan-Boltzmann constant

High performance microchannel heat exchanger for cooling high heat load x-ray optical elements

Abstract: Analysis has been carried out to demonstrate that a liquid nitrogen cooled microchannel heat exchanger can be designed to maximize the heat transfer from silicon to the working fluid. The results show that the performance of the liquid nitrogen cooled microchannel heat exchanger is significantly enhanced by approximately three times over flowing water through microchannels.

Indirect plate-type heat exchanger

Abstract: The plates (7) in this heat exchanger form a first assembly of passages (8A) serving to exchange heat and a second assembly of passages (8B) which are, for at least part of their extent, connected for exchange of heat with the first assembly of passages (8A) to a reduced extent or almost not at all. The second assembly is designed to fulfil an associated function with the heat exchanger, particularly a function of storage of liquid and/or recirculation of liquid and/or the separation of liquid and vapour. Application to cryogenic heat exchangers.

Temperature-stabilized heat exchanger

Abstract: A heat exchange module comprises a rotating-wheel type regenerative heat exchanger unit having a plurality of heat exchange elements mounted in baskets through the volume of the heat exchanger wheel. The heat exchanger wheel rotates about its axis so that the heat exchange elements are heated by a hot gas flow over a portion of the rotation, and transfer the heat to an air flow over another portion of the rotation. At least some of the heat exchange elements include phase change materials, such as salts, that absorb heat while maintaining a constant temperature. The phase change materials narrow the range of temperatures reached by the heat exchange elements located at various positions of the heat exchanger wheel. The phase change materials prevent excessively low temperatures that can result in condensation of corrosive acids on the surfaces of the heat exchange elements. They can also stabilize the heat exchange elements in particularly desirable temperature ranges for the operation of catalysts coated onto the heat exchange elements.

Study on Heat Transfer of Heat Exchangers in the Stirling Engine : Heat Transfer in a Heated Tube under the Periodically Reversing Flow Condition

Abstract: Heat-transfer characteristics in heated tubes under periodically reversing low conditions have been investigated experimentally using a test apparatus that simulates the heat exchangers for the actual Stirling engine. The experimental correlation considering the influence of the piston phase-angle difference for the heat-transfer coefficient has been induced by the use of the working gas velocity evaluated from the Schmidt cycle model which is one of the ideal Stirling cycles

Approximate Equations for the Design of Cross- Flow Heat Exchangers

Abstract: Cross-counterflow configurations with one fluid unmixed throughout are important flow arrangements for the design of air-coolers and extended surface exchangers. Approximate equations for the thermal calculation of these flow arrangements with arbitrary numbers of passes are proposed. Their accuracy and limitations are discussed. The accuracy of the given equations is more than sufficient for practical design.

Dispersion Model for Divided-Flow Heat Exchanger

Abstract: The axial dispersion model is used to analyse the thermal performance of divided-flow heat exchangers with N tube passes, arbitrary distribution of mass flow rate on the shellside, variable entrance location of the shellside flow and piecewise variation of heat transfer coefficient (or NTU), considering shellside maldistribution such as bypassing and leakage. Especially, the explicit formulas for calculating thermal effectivenesses as well as temperature profiles are derived for the 1-1 divided-flow heat exchanger. Measurements are carried out on a segmentally baffled 1-1 divided-flow heat exchanger with various clearances between segmental baffles and shell, in order to investigate the relationship between the dispersion factor and the flow pattern.

Incineration plant with heat exchanger

Abstract: An incineration plant includes a heat exchanger arranged in a flue gas flow following a reduction stage for nitrogen oxides and in front of a flue gas dust collector, and a heat transfer medium circuit for absorbing heat from the heat exchanger in the flue gas flow. The heat exchanger is connected to the heat transfer medium circuit such that the heat transfer medium conducted in the circuit is admitted to the heat exchanger. The heat transfer medium circuit has at least one additional heat exchanger for absorbing heat from the heat transfer medium. A feed water preheater is arranged in the heat transfer medium circuit.

Plastic Heat Exchangers

Abstract: Plastic properties may be used in the manufacturing of heat exchangers. Considering their advantages, their field of application is quite large: low temperature heat recovery, concentration of solutions. Three equipment are described: a liquid-liquid shell and tube exchanger, a gas-gas shell exchanger and a falling flow evaporator.

A study of start-up characteristics of a potassium heat pipe from the frozen state

Abstract: The start up characteristics of a potassium heat pipe were studied both analytically and experimentally. Using the radiation heat transfer mode the heat pipe was tested in a vacuum chamber. The transition temperature calculated for potassium was then compared with the experimental results of the heat pipe with various heat inputs. These results show that the heat pipe was inactive until it reached the transition temperature. In addition, during the start up period, the evaporator experienced dry-out with a heat input smaller than the capillary limit calculated at the steady state. However, when the working fluid at the condensor was completely melted, the evaporation was rewetted without external aid. The start up period was significantly reduced with a large heat input.

Heat storage type electrical hot air heater

Abstract: PURPOSE:To yield hot air with a higher amount of heat by disposing an adsorption heat type heat storage material in a hot air heater body as an auxiliary heat source, incorporating surrounding air containing moisture by suction means and supplying the same to the adsorption heat type heat storage material, and radiating stored heat, and further combining the foregoing heat with heat from an electrical heater. CONSTITUTION:Provided are an electrical hot air heater 2 in a hot air heater body l and an air fan 3 for blowing off hot air heated by the heater 2 from a suction inlet 7 to a blow-off outlet 4. The hot air heater 2 is used as a constant heat source and an auxiliary heat source device 40 is separately provided. Water is fed to the adsorption heat type heat storage material 41 of the auxiliary heat source device 40 as it is required, to take out adsorption heat in the adsorption heat type heat storage material 41. The adsorption heat is applied to the electrical heater 2 to yield hot air of a higher amount of heat. A heat radiation fin 57 is provided on a regeneration heater 45 for drying the adsorption heat type heat storage type material 41 in which time water is adsorbed so as to again produce heat, which fin 57 is in turn inserted into the heat storage material 41.