Showing papers on "Electronics cooling published in 2001"

An electrohydrodynamic polarization micropump for electronic cooling

Abstract: This paper presents the design, fabrication, and characterization of an innovative microcooling device for microelectronics applications. The device incorporates an active evaporative cooling surface, a polarization micropump, and temperature sensors into a single chip. The micropump provides the required pumping action to bring the working fluid to the evaporating surface, allowing the effective heat transfer coefficient through a thin-film evaporation/boiling process. The device is based on VLSI microfabrication technology, allowing the electrohydrodynamic (EHD) electrodes to be integrated directly onto the cooling surface. Since the EHD electrodes are fabricated using the same technology as the electronic systems themselves, the proposed microelectronic cooling system in the form of an integrated microchip is very suitable for mass production. The prototype devices demonstrated a maximum cooling capacity of 65 W/cm/sup 2/ with a corresponding pumping head of 250 Pa. The results of this investigation will assist in the development of future microcooling devices capable of operating at high power levels.

Local Heat Transfer Distributions in Confined Multiple Air Jet Impingement

Abstract: Heat transfer from a discrete heat source to multiple, normally impinging, confined air jets was experimentally investigated. The jets issued from short, square-edged orifices with still-developing velocity profiles on to a foil heat source which produced a constant heat flux. The orifice plate and the surface containing the heat source were mounted opposite each other in a parallel-plates arrangement to effect radial outflow of the spent fluid. The local surface temperature was measured in fine increments over the entire heat source. Experiments were conducted for different jet Reynolds numbers (5000ϽRe Ͻ20,000), orifice-to-target spacing ͑0.5ϽH/dϽ4͒, and multiple-orifice arrangements. The results are compared to those previously obtained for single air jets. A reduction in orifice-to-target spacing was found to increase the heat transfer coefficient in multiple jets, with this effect being stronger at the higher Reynolds numbers. With a nine-jet arrangement, the heat transfer to the central jet was higher than for a corresponding single jet. For a four-jet arrangement, however, each jet was found to have stagnation-region heat transfer coefficients that were comparable to the single-jet values. The effectiveness of single and multiple jets in removing heat from a given heat source is compared at a fixed total flow rate. Predictive correlations are proposed for single and multiple jet impingement heat transfer.

High performance heat sink for electronics cooling

Abstract: Heat sinks are provided that achieve very high convective heat transfer surface per unit volume. These heat sinks comprise a spreader plate having a recessed area on one surface and a flat area on another surface, at least two fins and porous reticulated foam blocks having intervening gaps that fill the width and at least a portion of the length between the fins. The foam block may be a continuous single block within the space between two adjacent fins along the length of the fins or may be an array of short-length blocks having intervening gaps along the length of the fins.

Parametric optimization of multichanneled heat sinks for VLSI chip cooling

Abstract: This paper presents an optimization study of multichannel heat sinks for electronic devices. Specifically, we present a method of determining optimum values of the channel diameter, flow rate and number of channels for minimum pumping power or minimum pressure drop. Optimized parameters are expressed in dimensionless form. The calculated results for both laminar and turbulent regimes present several important relationships among the parameters. A criterion for choice of the flow regime to be used is presented. For a current electronic cooling requirement, the optimized diameter of a channel lies in the micro-scale range when water is used as working fluid. Several advantages of an optimized heat sink and its' feasibility toward actual cooling problems are discussed.

Ultra high fin density heat sink for electronics cooling

Abstract: The present invention is directed to liquid-cooled or air-cooled metallic heat sinks formed as unibody structures that include a planar base and upright fins. The fins are located on one side of the heat sink and the ratio of fin spacing to fin height is low. In order to achieve low value of the ratio of fin spacing to fin height, a fin density of greater than about twelve fins per centimeter is employed. The length of the fins in the flow direction is restricted in order to yield high rate of heat dissipation from the finned surface. Furthermore, flow of the cooling fluid over the fins is maintained laminar in order to reduce the noise level and pumping power for the fluid.

An integrated micro cooling system for electronic circuits

Abstract: A fully FR4-compatible integrated cooling system has been developed. Cooling channels have been etched into a thick copper layer to form microchannels. The structure is reinforced by two prepreg layers toward the component and solder side. Several cooling channels can be independently run. The heat dissipation capability of the system is 20 W per channel (and heat source). Typical coolants are water or methoxynonafluorobutane. For an outlet to inlet temperature difference of 25/spl deg/C and a power dissipation of 30 W, a (water) flow rate of 20 ml/min is required. Pressure losses are below 300 mbar (for water).

Two-phase flow patterns, pressure drop and heat transfer during boiling in minichannel and microchannel flow passages of compact evaporators

Abstract: The small hydraulic diameters employed during flow boiling in compact evaporator passages are becoming more important as they are employed in diverse applications including electronics cooling and fuel cell evaporators. The high pressure drop characteristics of these passages are particularly important as they alter the flow and heat transfer, especially in parallel multi-channel configuration. The pressure drop oscillations often introduce dryout in some passages while their neighboring passages operate under singlephase mode. This paper presents a comprehensive review of literature on evaporation in small diameter passages along with some results obtained by the author for water evaporating in 1-mm hydraulic diameter multi-channel passages. Critical heat flux is not covered in this paper due to space constraint.

A pin fin microheat sink for cooling macroscale conformal surfaces under the influence of thrust and frictional forces

Abstract: Conventional microheat sink design primarily focuses on the use of continuous fin arrays to optimally dissipate thermal energy from electronic components. By contrast, this paper experimentally measures the thermal and structural performance of two micro pin fin heat sinks designed for use in load bearing applications such as mechanical seals and thrust bearings. One pin fin array is of low porosity, which is more optimal for load bearing capacity, and the other is of high porosity, which is more optimal for heat dissipation. By using these two extreme cases, the thermal-structural tradeoff found in load bearing microheat sinks is demonstrated. The heat sinks are constructed of nickel, electrodeposited onto a stainless steel thrust ring using a modified LIGA technique. Under forced air cooling, the thermal performance of each is compared to a simple model based on a combination of macroscale pin fin heat sink results and classical correlations for fins in cross flow. The low porosity design is also tested under the application of a 44.5 N thrust load at 2500 rpm and found to be structurally sound. Experimental temperature profiles demonstrate a substantial benefit of the microheat sink in cooling the load bearing surface.

Thermoelectric micro modules for spot cooling of high density heat sources

Abstract: The paper represents further progress in the development of short-legged thermoelectric (TE) micro modules for cooling high power density electronic components. Theoretical analysis and experimental study are conducted to define an available temperature lowering and maximum heat flux densities for short-legged coolers with different kinds of substrates. Temperature differences exceeding 70 K are obtained with TE leg lengths down to 0.2 mm. A new series of micro modules with TE legs 0.2 and 0.3 mm long is developed with an aluminum nitride ceramic.

Biporous heat pipes for high power electronic device cooling

Abstract: A biporous heat pipe is proposed to overcome heat transfer crises in the evaporator. The two levels of pore sizes of the biporous heat pipe result in high heat pipe performance. When vaporization phenomena occur in biporous wicks, bubbles formed in the near wall layer easily escape from the porous media and the possibility of vapor blanket layer formation on the heating surface decreases. Evaporation mostly occurs on the smaller surface pores. This not only increases the heat transfer performance by extended surface and smaller pore sizes, but also increases the capillary force which enables the liquid supply. The biporous structure improves the vapor and liquid distribution in the porous media when vaporization phenomena occur in it. Thermal analysis of a solid copper heat spreader and monoporous and biporous heat pipe modules are performed. Compression of the results shows the heat transfer performance of the monoporous and biporous heat pipes are better than the solid copper spreader and the biporous heat pipe has an advantage in the relatively high heat flux range. The biporous heat pipe is very attractive for high power electronic device cooling.

Characterization of laminar jet impingement cooling in portable computer application

Abstract: A thermal characterization study of laminar air jet impingement cooling of electronic components within a geometry representative of the CPU compartment of a typical portable computer is reported. A finite control volume technique was used to solve for the velocity and temperature fields. Convection, conduction and radiation effects were included in the simulations. The range of jet Reynolds numbers considered was 63 to 1500; the applied compartment heat load ranged from 5-15 W. Radiation effects were significant over the range of Reynolds numbers and heat loads considered, while the effect of natural convection was only noticeable for configurations when the ratio Gr/Re/sup 2/ exceeded 5. The predicted importance of Re rather than jet size was confirmed with test data. Proof of concept was demonstrated with a numerical model representative of a full laptop computer. Both simulations and laboratory tests showed that low flow rate JI cooling schemes can provide cooling comparable to a high volume flow rate configuration, while using only a fraction of the air flow. Furthermore, under the conservative assumption of steady state, fully powered components, a hybrid cooling scheme utilizing a heat pipe and laminar JI was capable of cooling the processor chip to within 11/spl deg/C of the vendor specified maximum temperature for a system with a total power dissipation of over 21 W.

Heat transfer coefficient for water cooled heat sink: application for standard power modules cooling at high temperature

Abstract: This study presents an overview of water cooling methods used in the power electronic field. The first one uses the classical method with separated power module and cooling device. The second one deals with high reduction of conductive thermal resistance and could predominately be the final cooling solution in the near future. The last one, foreseen for future applications, consists in designing the power module and the cooling device in the silicon material, improving even more the overall thermal resistance. Each alternative may require a good knowledge of the thermal exchange laws in the heat exchanger. The Nusselt number, as a characteristic thermal parameter proposed in the literature, is not always realistic for all kinds of cooling devices. The work focuses on that correlated value determination taking into account the channel geometry, the fluid flow rate and its temperature. Then, the obtained value is used to make a real optimisation of the cooling device.

Numerical heat transfer predictive accuracy for an in-line array of board-mounted pqfp components in forced convection

Abstract: Numerical predictive accuracy is assessed for componentPrinted Circuit Board (PCB) heat transfer in forced convection using a widely -used, Computational Fluid Dynamics (CFD) based software dedicated for the analysis of electronics cooling. This is achieved by comparing numerical predictions with experimental benchmark data for an in -line array of fifteen, equally spaced, PCB-mounted 160-lead Plastic Quad Flat Pack (PQFP) components. Test case complexity is incremented in controlled steps, from a single component, to components individually powered on the fully populated PCB, to a simultaneously powered configuration exhibiting a high degree of component thermal interaction. Benchmark criteria are based on component steady-state junction temperature and component-PCB surface temperature profiles, measured using thermal test chips and infra-red thermography respectively. These measurements were taken with the test vehicle mounted in a wind tunnel. Component numerical modeling is based on nominal package dimensions and material thermal properties. In the absence of a dominant length scale for describing the fluid flow regime in non -dimensional form, the fluid domain is solved using both laminar and turbulent flow models. Component junction temperature prediction accuracy for the fully powered, populated PCB is typically within ±1°C to ±10°C (up to 25%). The full complexity of component thermal interaction is shown not to be fully captured. Neither the laminar or turbulent flow model could resolve the complete flow field, suggesting the need for a turbulence model capable of modeling transition. Overall, component junction temperature prediction accuracy would not be sufficient for the predictions to be used as boundary conditions for subsequent reliability

Loop heat pipe technology for electronics cooling

Abstract: Loop heat pipes (LHPs) are passive heat transport devices with the capillary-driven circulation of the two-phase working fluid. LHPs currently used mainly in Aerospace applications due to their relatively high fabrication cost. LHPs outperform conventional heat pipes in terms of the maximum heat transport capability, operation in any orientation in the gravity field, and heat transport length. It can be advantageous to use loop heat pipes for transporting, spreading, and dissipating heat in modern electronics, where the heat dissipation per unit volume is rapidly increasing This paper describes some LHP design features and experimental results obtained for two low-cost LHPs.

Electronics cooling device

Abstract: PROBLEM TO BE SOLVED: To connect a package consisting of a porous material and a heat sink with each other at a low contact heat resistance in the case where there are large undurations on the contact surface of the package to the heat sink SOLUTION: A sheet formed by coating a compound 71 on a base material 70 having barrier properties to the component of oil is installed on the side of a package and a heat conductive grease is made to interpose between the sheet and the heat sink to connect the package with the heat sink

Capillary pumped loop heat spreader for electronics cooling

Abstract: As cooling requirements for electronic devices, e.g. computer processor units, power modules, etc. increase beyond the capabilities of air-cooling, interest has moved to several alternatives such as thermoelectric coolers, impinging jets and heat exchangers with phase change. Included among these, the capillary pumped loop is a very competitive cooling device, because of its performance reliability, no power requirements and low manufacturing cost. In this paper, a heat spreader employing capillary pumped loop principles was made of aluminum and copper and tested. The copper CPL heat spreader with heat sinks and fans on the condenser (86mm thick, 60mm wide, 181mm long) has demonstrated a cooling capacity of 640W at atmospheric pressure in the vertical orientation and maintains a difference between TIHE (temperature of the interface between heater and evaporator) and TAMB (ambient temperature) lower than 100°C.

A Natural Circulation Model of the Closed Loop, Two-Phase Thermosyphon for Electronics Cooling

Abstract: We present a model for the two-phase flow and heat transfer in the closed loop, two-phase thermosyphon (CLTPT) involving co-current natural circulation. The focus is on CLTPTs for electronics cooling that exhibit complex two-phase flow patterns due to the closed loop geometry and small tube size. The present model is based on mass, momentum, and energy balances in the evaporator, rising tube, condenser, and the falling tube. The homogeneous two-phase flow model is used to evaluate the friction pressure drop of the two-phase flow imposed by the available gravitational head through the loop. The saturation temperature dictates both the heat source (chip) temperature and the condenser heat rejection capacity. Thermodynamic constraints are applied to model the saturation temperature, which also depends upon the local heat transfer coefficient and the two-phase flow patterns inside the condenser. The boiling characteristics of the enhanced structure are used to predict the chip temperature. The model is compared with experimental data for dielectric working fluid PF-5060

Leak sealing inaccessible accelerator cooling systems

Abstract: Cooling water systems associated with experimental facilities often suffer from minor leakage in inaccessible areas. Such leaks can interfere with vacua, electronics or reduce cooling efficiency. Replacement of these defective pipes may cause extensive experimental programme downtime and associated financial costs. The paper describes a novel technique to permanently repair such leaks remotely by injecting a water based sealant into the pipe. The sealants used are fully compatible with pipework, valves and instrumentation. The internals of the pipe are not coated in any way; hence the heat transfer properties of the cooling system are unaffected. This technique has been perfected over the past 30 years in the nuclear power industry. The paper describes how this technology has now been successfully applied to cooling systems within experimental facilities, such as at ISIS, Rutherford Appleton Laboratories (Oxford, UK). A variety of components associated with the linac at the Los Alamos Neutron Science Centre (USA) were sealed during a demonstration of the technique.