Showing papers on "Electronics cooling published in 2018"

Role of inter-nanowire distance in metal nanowires on pool boiling heat transfer characteristics.

Abstract: Energy management in data centres is crucial where a maximum portion of energy is spent on thermal management and electronics cooling systems. It becomes very crucial when it comes to immersion cooling technique s (pool boiling mechanism) using dielectric fluids. Role of metal nanowires (Cu and Ag) with different inter-nanowire distance values were analysed for their pool boiling performance. Templates with different inter-pore distances (260 ± 20 nm, 320 ± 20 nm and 360 ± 20 nm) and diameter of 200 nm were used to deposit copper nanowires (CuNW) and silver nanowires (AgNW) over the copper substrate using electrodeposition technique. Electrodeposition conditions like voltage and time were optimised to obtain nanowires of near constant height and different surface density coverage. To investigate the role of these metal nanowires on pool boiling characteristics, a dedicated pool boiling experimental facility was fabricated and experiments were carried out using FC-72 as working fluid. As a result of experimental investigation, boiling incipience superheat was observed to reduce which is very important for electronics systems. Also, both the critical heat flux (CHF) and heat transfer coefficient (h) were found to be increased as compared to the bare copper surface. Increasing the distance between nanowires, decreases the number of nanowires per unit area and thus the surface density coverage. This increases the cavity density and cavity size of micron-scale cavities in favour of pool boiling enhancement. This also decreases the resistance to fluid flow at high heat flux values which delays the surface dryout and critical heat flux.

Towards Thermal-Acoustic Co-Design of Noise-Reducing Heat Sinks

Abstract: Several thermal management applications involve fan-mounted heat sinks that result in fan-generated noise as an undesired by-product. These applications require noise reduction and attempt to reduce noise using separate muffler devices. However, space for separate heat-sinking and noise-reducing functionalities may be challenging in high-performance applications such as electronics cooling, data centers, automotive, aviation, and various others. A first-principles-based approach for combined heat sinking and noise reduction in the same functional volume is discussed in this paper. This paper reports on thermal-acoustic co-design of 3-D periodic porous foam structures. In order to enable a design strategy, an analytical framework that characterizes the governing performance indicators of both acoustic and thermo-fluid design on a unifying platform is laid out. A combination of analytical and phenomenological models is used to predict the absorption coefficient, transmission loss (TL), and other acoustic performance indicators. For thermal predictions, an experimentally validated semiempirical model is presented to estimate thermal resistance and static pressure drop of foam heat sink as a function of geometrical parameters as well as flow rates. Octave-band weighted values of acoustic indicators are then compared against thermal indicators to investigate thermal-acoustic co-design aspects. As hydraulic pore radius of porous foam decreases, the acoustic absorption coefficient increases reaching local maxima. Concomitantly, the pore radius decrease not only increases the absorption coefficient while dissipating heat, but also increases the heat sink pressure drop. For a chosen sound absorption region of interest, there exists a particular static pressure drop that maximizes heat sink dissipation for a given radius. The paper concludes by reporting TL and heat sink thermal performance for a generic electronics cooling configuration while elucidating the nuances of the proposed heat sink design using a thermal-acoustic index.

Challenges and opportunities in Gen3 embedded cooling with high-quality microgap flow

Abstract: Gen3, Embedded Cooling, promises to revolutionize thermal management of advanced microelectronic systems by eliminating the sequential conductive and interfacial thermal resistances which dominate the present “remote cooling” paradigm. Single-phase interchip microfluidic flow with high thermal conductivity chips and substrates has been used successfully to cool single transistors dissipating more than 40kW/cm2, but efficient heat removal from transistor arrays, larger chips, and chip stacks operating at these prodigious heat fluxes would require the use of high vapor fraction (quality), two-phase cooling in intra- and inter-chip microgap channels. The motivation, as well as the challenges and opportunities associated with evaporative embedded cooling in realistic form factors, is the focus of this paper. The paper will begin with a brief review of the history of thermal packaging, reflecting the 70-year “inward migration” of cooling technology from the computer-room, to the rack, and then to the single chip and multichip module with — and liquid-cooled coldplates. Discussion of the limitations of this approach and recent results from single-phase embedded cooling will follow. This will set the stage for discussion of the development challenges associated with application of this Gen3 thermal management paradigm to commercial semiconductor hardware, including dealing with the effects of channel length, orientation, and manifold-driven centrifugal acceleration on the governing behavior.

Material Selection for Microchannel Heatsink: Conjugate Heat Transfer Simulation

Abstract: Heat dissipation during the operation of electronic devices causes rise in temperature, which demands an effective thermal management for their performance, life and reliability. Single phase liquid cooling in microchannels is an effective and proven technology for electronics cooling. However, due to the ongoing trends of miniaturization and developments in the microelectronics technology, the future needs of heat flux dissipation rate are expected to rise to 1 kW/cm2. Air cooled systems are unable to meet this demand. Hence, liquid cooled heatsinks are preferred. This paper presents conjugate heat transfer simulation of single phase flow in microchannels with application to electronic cooling. The numerical model is simulated for different materials: copper, aluminium and silicon as solid and water as liquid coolant. The performances of microchannel heatsink are analysed for mass flow rate range of 20-40 ml/min. The investigation has been carried out on same size of electronic chip and heat flux in order to have comparative study of different materials. This paper is divided into two sections: fabrication techniques and numerical simulation for different materials. In the first part, a brief discussion of fabrication techniques of microchannel heatsink have been presented. The second section presents conjugate heat transfer simulation and parametric investigation for different material microchannel heatsink. The presented study and findings are useful for selection of materials for microchannel heatsink.

An experimental study on the heat transfer and pressure drop characteristics of electronics cooling heat sinks with FC-72 flow boiling

Abstract: An experimental study was performed to measure FC-72(C6F14) flow boiling heat transfer and pressure drop in heat sinks for electronics cooling. The heat sink had cooling cross section area of 38.0 × 37.0 mm with rectangular fins. The height, length and thickness of a fin was 5.0, 24.0 and 1.0 mm, respectively. The width of fluid channels between the fins was 1.0 mm. The heat sink consisted of a heating and cooling section, and a cover. Two types of heat sinks were used in this study. The two heat sinks were different only in the cover, and the machined depth of the cover was 5.0 and 8.0 mm, respectively. Electric heating from 100 to 300 W was supplied by cartridge heaters and it was equivalent to the heat flux from 71.12 to 213.4 kW/m2 based on the cross section area of the cooled surface. The saturation temperatures of the FC-72 were from 59.8 °C to 71.5 °C during the experiment and the mass fluxes were from 24.2 to 230.0 kg/m2s. The trend of heat transfer and pressure drop variation with the change of vapor quality was similar to that of flow boiling in tubes such as the increase of heat transfer and pressure drop with the increase of vapor quality before dryout. Similar heat transfer coefficients and pressure drop values were measured under the same mass flow conditions for both types of heat sinks. In this study, the cooling performance with liquid water was also measured at the same heat sinks. The comparison of experimental data presented that the cooling capacity with FC-72 flow boiling was up to 330 % higher than that with liquid water. However, the FC-72 pressure drop was also significantly higher than water.

Performance Evaluation of Bent Heat Pipes

Abstract: Heat pipes are used in electronics cooling applications to transfer heat generated by devices to locations where it can efficiently be dissipated. Heat pipes have been studied since the early 1950s and are commercially available in a variety of forms. They are usually bent and flattened in order to fit within the specific geometrical restrictions of the intended application. Straight heat pipes have been studied and successfully demonstrated in past studies. The objective of the present work is to investigate the performance of heat pipes at various bend angles by means of investigating the effect of temperature drop between bend angles, the temperature difference across source and sink blocks and change in thermal resistance across the heat pipes. Copper heat pipes with meshed screen wick type having de-ionized water as the fluid with bent pipes varying from zero degree (straight pipe) to 180° (U - shaped pipe) in-steps of 45° were studied at various input power levels. Results show that the temperature drop is maximum for U-shaped heat pipe at 180° bend. Furthermore, it was observed that the heat pipe with temperature differential was higher for all bends at higher input power. Lastly, the thermal resistance calculated analytically was validated via experimental measurements.

Validating a Reduced-Order Model for Synthetic Jet Actuators Using CFD and Experimental Data

Abstract: Synthetic jet actuators (SJA) are emerging in various engineering applications, from flow separation and noise control in aviation to thermal management of electronics. A SJA oscillates a flexible membrane inside a cavity connected to a nozzle producing vortices. A complex interaction between the cavity pressure field and the driving electronics can make it difficult to predict performance. A reduced-order model (ROM) has been developed to predict the performance of SJAs. This paper applies this model to a canonical configuration with applications in flow control and electronics cooling, consisting of a single SJA with a rectangular orifice, emanating perpendicular to the surface. The practical implementation of the ROM to estimate the relationship between cavity pressure and jet velocity, jet velocity and diaphragm deflection and applied driving voltage is explained in detail. Unsteady Reynolds-averaged Navier Stokes computational fluid dynamics (CFD) simulations are used to assess the reliability of the reduced-order model. The CFD model itself has been validated with experimental measurements. The effect of orifice aspect ratio on the ROM parameters has been discussed. Findings indicate that the ROM is capable of predicting the SJA performance for a wide range of operating conditions (in terms of frequency and amplitude).

Enhancement of confined air jet impingement heat transfer using perforated pin-fin heat sinks

Abstract: The development of semiconductor fabrication process and electronic packaging technology causes the size and weight of electronic components to decrease consistently. Along with the increasing operating power, the heat generation rate of the electronic products apparently get higher. Efficient removal of heat from the electronic products in a limited space becomes a major task in electronics cooling. Air impingement cooling with a heat sink is an attractive option for electronic cooling, because it is inexpensive, robust and localized. Rapid heat transfer from heated surfaces and reducing material weight is also becoming a major task for design of heat exchanger equipment for electronic cooling. Rectangular plate fins as extended surfaces are good heat transfer equipment which are widely used for various industrial applications. Heat transfer rate can be improved by introducing perforations, porosity or slots. Moreover, due to restrictions in setup space and economic reasons, heat transfer equipment have been required to be much more compact in size and lighter in weight. Studies on three dimensional plate and pin fin heat sinks are extensive. But no focus has been yet given on air jet impingement heat transfer with perforated pin fin heat sink. Thermal-fluid characteristics of solid and perforated pin fin heat sinks cooled by confined air jet impingement are investigated numerically in this study. The SST k-ω turbulence model is used to predict the turbulence flow parameters. The numerical model is verified with previously published experimental data. Flow and heat transfer characteristics are presented for the impinging Reynolds number, Re= 5000 to 25000 having constant impingement distance (Y/D = 8), fin width (W/L = 0.1) and height (H/L =0.5). The main objective of this study is to examine the effects of fin perforations on the thermal performance of pin fin heat sinks. Results show that thermal resistance decreases and fin efficiency increases with the increase of Reynolds number due to perforation. Thus, this kind of heat sink equipment reduce cooling power consumption rate.

Thermal Expansion Investigation of Liquid Cold Plate with Varying Ambient Temperature at Storage

Abstract: Depending on the heat flux increment in recent two decades, liquid cooling techniques in thermal management became one of the most preferred choices for electronics cooling technique, especially in military applications. As the complexity and numbers of cold plate increase, it necessitates examining the design of cold plate in details to prevent catastrophic failures both during operation and storage. In liquid cooling applications, there are many precautions taken to prevent mechanical failures caused by liquid thermal expansion. It is well known that liquids cannot be compressed or very small compression can take place due to their nature. In thermal expansion problems, there is an interaction between stagnant fluid and solid. They expand together because of increase in temperature. As a result, hydrostatic pressure increases due to thermal expansion of trapped liquid even at small temperature increment. Therefore, in liquid cooling applications, one of the easiest measures is the usage of relief valves to release excess pressure to protect the system or design from overpressure. In this study, one cold plate has been selected as a case study to investigate the behavior of cold plate in terms of hydrostatic pressure and stress variation depending on the alternating ambient temperature. In addition, before performing tests, FEM structural analysis has been carried out to design the experiment. Finally, hydrostatic pressure values exerted by trapped liquid have been measured at different locations depending on the temperature.

High Potential of Magnet on the Performance of Dual Piezoelectric Fans in Electronics Cooling System

Abstract: Recently, piezoelectric fan has gained attention as potential active cooling method for electronics devices. Even though the piezoelectric requires high voltage, there are findings to overcome the shortcomings. Adding on a magnet at the tip of the piezoelectric fan to activate other magnetic passive fans is one of the methods to increase the total amplitude generated by the fans. This paper will discuss on the performance of integrated piezoelectric fan with passive fans (later refer to magnetic fans) to enhance the heat transfer in cooling system. A repulsive force produced by the magnets will cause the magnetic blades to oscillate together with the piezoelectric fan. The paper will focus on the optimization parameters of the magnets for selected dimension of piezoelectric fan. The parameters under investigation are the position of the magnet on the piezoelectric fan, number of magnets on each blades and orientation of blades with respect to adjacent blade. Results show that the magnet at middle location of extensive blade with double magnets generate the largest amplitude, 80% better than fan without magnet and for dual integrated piezoelectric fan with magnetic fan, radial orientation gives better result by 25%. By increasing the total amplitude using magnetic force, power consumption can be reduced while the heat transfer performance can be enhanced. it shows a good agreement for positive heat transfer and thermal resistance improvement compared to natural convection.

Conjugate heat transfer analysis of a thin liquid cooling heat sink using free software

Abstract: Because of the increase of heat generation density and high-density packaging, the limits of air cooling are being reached and demand for liquid cooling systems for electronics is increasing. Utilization of CFD simulation for the optimized design of flow passages in various configurations is needed. In this study, for optimization of mini channel structure in liquid cooling, OpenFOAM is employed. OpenFOAM is an open-source CFD toolbox with various functions and high parallel computation efficiency. By using OpenFOAM, details of heat transfer and fluid transport in the mini channel are evaluated, and strategy of optimization of mini channel structure is discussed. We aim to validate a numerical model using this tool and experimental data, to investigate other configurations.

Experimental Validation of Thermal Performance of a Plate Heat Exchanger (PHX) with Phase Change Materials (PCM) for Thermal Energy Storage (TES)

Abstract: Thermal energy storage (TES) platforms can help to improve the energy efficiency of various types of thermal management systems by actively modulating the transient response of these integrated thermal systems. A novel strategy for TES platforms involve the integration of Phase Change Materials (PCM) into various types of heat exchangers (HX). High performance, compact, and low cost HX platforms for TES involving PCM are often desired for applications such as power plants, edifice thermal management, transportation technologies (e.g., aerospace and automotive vehicles), and high heat flux electronics cooling. These applications are often constrained by requirements for minimizing pressure loss, miniaturizing the form factors, and the need for easy scalability to large systems. This imposes steep challenges for design, fabrication, and operation of these HX platforms. This also severely restricts the available options and material choices for PCM. In this experimental study, the transient performance of a Plate Heat Exchanger (PHX) integrated with PCM were analyzed for realizing a Latent Heat Storage Unit (LHSU). This study enabled a detailed experimental characterization of the efficacy of the LHSU realized in a PHX (model: SWEP B5T). The inner volume of the PHX was filled up with PCM. The PCM considered was PureTemp 29 with a phase transition temperature of 29 °C. The temperature of the Heat Transfer Fluid (HTF) was varied from 32°C - 38°C for melting and 20°C - 26°C for solidification. The HTF used in this study was water. The volumetric flow-rate ranged from 5, 7.5 and 10 GPH. Experimental validation for the transient response of the LHSU (i.e. the charging and discharging time periods) were performed by parametrically varying the design and operational conditions, which include: flow rate, fluid inlet and exit temperatures, and the energy storage capacity.

Experimental and Numerical Study Effect of Using Nanofluids in Perforated Plate Fin Heat Sink for Electronics Cooling

Abstract: An experimental and numerical investigation of the effect of using two types of nanofluids with suspending of (Al2O3 and CuO) nanoparticles in deionized water with a volume fraction of (0.1% vol.), in addition to use three types of fin plate configurations of (smooth, perforated, and dimple plate) to study the heat transfer enhancement characteristics of commercial fin plate heat sink for cooling computer processing unit. All experimental tests under simulated conditions by using heat flux heater element with input power range of (5, 16, 35, 70, and 100 W). The experimental parameters calculated are such as water and nanofluid as coolant with Reynolds number of (7000, 8000, 9400 and 11300); the air is blown in the inlet duct across the heat sink with Reynolds number of (10500, 12300, 14200 and 16000). The distance fin-to-fin is kept constant at (2.00 mm), and the channel employed in this work has a square cross-section of (7 cm) inside. It was observed that the average effectiveness and Nusselt number of the nanofluids are higher compared with those of using conventional liquid cooling systems. However, the perforated fin plate showed higher air heat dissipation than the other configuration plate fin employed in this study. The experimental results were supported by numerical results which gave a good indication to heat transfer enhancement in studied ranges.

Experimental Study on Thermal Performance of Loop Heat Pipe with Flat-Rectangular Evaporator Under Gravity Assisted Condition

Abstract: In company with extreme developments of electronic devices, there are some unavoidable challenges to the conventional cooling methods such as high heat dissipation, limitation of cooling space, reliable operation as well as saving energy consumption. Therefore, the necessity of studying on new or how to improve the existing technologies is undoubted. Among various methodologies, the loop heat pipe (LHP) whose operation principle base on phase changing process, can be considered as one of the potential solutions of modern electronics cooling. This paper introduces the experimental investigation on the thermal performance of a flat-rectangular evaporator LHP with sintered stainless-steel wick when functioning under gravity assisted condition. Working fluid of this LHP was water. The present LHP could maintain stable operation in the range of heating power from 50 W to 520 W and keep the temperature on the heater’s top surface at 85oC, commonly recommended as the limitation temperature of electronics, when heating power reaches value 350 W (129.6 kW/m2). Besides, when turning the heater off, it took about 15 minutes for the LHP to cool the heating block from 102oC to 37oC. In addition, an assumption of the boiling heat transfer is introduced in this paper to explain the performance of evaporator at different heat flux conditions of the experiment.