Micropin-fin Heat Sink Research Articles

An artificial neural network model for predicting frictional pressure drop in micro-pin fin heat sink

Abstract This study is part of two studies conducted for developing artificial neural-network-based tools for predicting the thermal and hydraulic performance of micro-pin fin heat sinks used for high-heat-flux electronic devices. The thermal design of high-heat-flux electronics requires a strong understanding of both pressure drop and heat transfer coefficient. Increasing the pressure drop in a cooling system significantly increases the required pumping power and decreases the system energy efficiency, in addition to considerably increasing temperature nonuniformity and causing reliability issues. Micro-pin fin heat sinks can help in the thermal management of high-heat-flux electronic systems owing to their effective heat transfer characteristics, namely, a large surface area and passage flow turbulence generation, and the requirement of lower pumping power compared with the microchannel heat sink. Studies conducted over the past decade have revealed that the thermal and hydraulic performance of micro-pin fin heat sinks are highly dependent on their geometric and operational parameters. However, a universal approach to predicting the frictional pressure drop, which influences the amount of power required, in pin fin arrays for various operating conditions and geometric shapes has not been developed so far. In this study, a trained artificial neural network (ANN) was used to develop a universal model for predicting the friction factor of micro-pin fin arrays. The friction factor correlation was predicted from 1,651 experimentally determined friction factor data points obtained from 22 studies. The relationship between a wide range of geometric and operating conditions and the hydraulic performance was investigated for accurately training the ANN. Furthermore, the universal model was analyzed by comparing values predicted by it with values obtained in other experimental studies. The model was found to show superior performance compared with other regression-method-based correlations.

Computational modeling of thermal characteristics of hybrid nanofluid in micro-pin fin heat sink for electronic cooling

ABSTRACT Emerging technology in the electronic industry has led to miniaturization of electronic devices such as iPhones and laptops. Heat dissipation is required to maintain high performance and long-term reliability of these devices. Micro heat sinks and novel working fluids such as nanofluids are becoming popular. Until recent times the full potential of hybrid nanofluid in heat transfer has not yet been exploited. In order to address the lack of adequate modeling data in this field, the aim of this study is to systematically model and investigate computational heat transfer characteristics of Al2O3-Cu/water hybrid nanofluid in micro heat sink. Volume concentration in the range of 0.1%-0.5% was used for the working fluid. Hexagonal micro-pin fin heat sink with staggered arrangement was simulated in ANSYS Fluent. Reliable experimental result from literature was used to validate the accuracy of the results. The most obvious finding to emerge from this study is that the Nusselt number increases with increase in Reynolds number and this observation is consistently the same at different concentrations and pin spacing. Lower transverse pitch was observed to dominate the enhancement of Nusselt number. There was a 10% increase in heat transfer coefficient at 0.5% nanofluid concentration when compared to 0.1%. This phenomenon is highly influenced by the transition of the Re into turbulent situation which eventually enhances the heat transfer characteristics. Also, lower transverse pitch promotes swirling flow situation. At 0.5% hybrid nanofluid concentration, it was observed that the Nusselt number increased from 14.00 at transverse pitch of 3.81 mm to 17.00 at a transverse pitch of 1.81 mm and this corresponds to 16.05% enhancement of Nusselt number. The pressure drop penalty of the working fluid is a result of increase in viscous effect of the hybrid nanofluid, especially at high concentration.

Novel thermal design of micro-bream-fin heat sink using contour-extraction-based (CEB) method

This work proposes a novel method, namely contour-extraction-based (CEB) method, which extracts the wake flow contours in the channels as the geometry contours of the pin fin to enhance thermal and hydraulic performances of micro-pin-fin heat sink (MPFHS). By employing this method, a novel heat sink with bream-body-like fins, namely micro-bream-fin heat sink (MBFHS), is generated by improving the geometry of the micro-circular-fin heat sink (MCFHS). The fluid flow and heat transfer characteristics of the novel MBFHS are simulated using a conjugate 3D numerical model with RNG k-ε turbulence model which is analytically validated by the energy balance theory. The thermal and hydraulic performances of the novel MBFHS are evaluated in terms of the junction temperature, Nusselt number, friction factor, and overall performance indexes. It is found that MBFHS has a larger convection heat transfer surface area, a better fluid-solid interaction, a higher flow velocity, a better fluid mixing, and more solid materials compared to the conventional MCFHS, which all contribute to the enhancement in the heat transfer performance. And the promotion is more pronounced at high spacing ratios and Reynolds numbers. The pin convection performance of the novel bream fin could be up to 34% higher than that of the original circular fin, and the thermal resistance and bottom-wall temperature difference of MBFHS are lower by 26% and 38% than those of MCFHS, respectively.

Comment on the paper “Numerical analysis of the heat transfer and fluid flow characteristics of a nanofluid-cooled micropin-fin heat sink using the Eulerian-Lagrangian approach, Tehmina Ambreen, Arslan Saleem, Cheol Woo Park, Powder Technol., 345 (2019), 509–520”

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Enhanced Thermal Management of GaN Power Amplifier Electronics with Micro-Pin Fin Heat Sinks

This study introduces an enhanced thermal management strategy for efficient heat dissipation from GaN power amplifiers with high power densities. The advantages of applying an advanced liquid-looped silicon-based micro-pin fin heat sink (MPFHS) as the mounting plate for GaN devices are illustrated using both experimental and 3D finite element model thermal simulation methods, then compared against traditional mounting materials. An IR thermography system was equipped to obtain the temperature distribution of GaN mounted on three different plates. The influence of mass flow rate on a MPFHS was also investigated in the experiments. Simulation results showed that GaN device performance could be improved by increasing the thermal conductivity of mounting plates’ materials. The dissipated power density of the GaN power amplifier increased 17.5 times when the mounting plate was changed from LTCC (Low Temperature Co-fired Ceramics) (k = 2 Wm−1 K−1) to HTCC (High-Temperature Co-fired Ceramics) (k = 180 Wm−1 K−1). Experiment results indicate that the GaN device performance was significantly improved by applying liquid-looped MPFHS, with the maximum dissipated power density reaching 7250 W/cm2. A thermal resistance model for the whole system, replacing traditional plates (PCB (Printed Circuit Board), silicon wafer and LTCC/HTCC) with an MPFHS plate, could significantly reduce θjs (thermal resistance of junction to sink) to its theoretical limitation value.

Effect of Flow Normalization in Micro-Pin-Finned Heat Sink: Numerical Study

The micro-pin-fin heat sink (MPFHS) is widely employed for the heat transfer enhancement of microchannel heat sinks. In the current paper, the effect of flow normalization on the thermohydraulic performance of micro-pin-finned heat sinks is studied numerically. Two geometries of MPFHSs, the conventional design micro-pin-fin heat sink (CD-MPFHS) with a uniform-width micro pin fin and the proposed design micro-pin-fin heat sink (PD-MPFHS) with a nonuniform-width micro pin fin, are studied. Flow distribution analysis in the primary and secondary channels of MPFHSs is carried out. More flow resistance offered by wider central micro pin fins diverts more flow toward side channels; as a result of which, better flow distribution in primary channels and higher flow across secondary channels are noticed for the PD-MPFHS as compared to the CD-MPFHS. As a result of that, maximum and average base temperatures are reduced by 4.6 and 2.2 K as compared to the CD-MPFHS. The Nusselt number increased by 10.1%, and a better thermohydraulic performance index has been offered by the PD-MPFHS for the entire studied Reynolds number range.

Meta-Study on Integrated Cooling of Modern Integrated Circuits using Microfluidics

The substantial increase in the transistor density of integrated circuits (ICs) in recent times has allowed considerable improvements in computing power. With increasing transistor and power density, the heat produced by modern ICs has increased significantly. This in turn has negative effects on the performance, reliability, and power consumption of the ICs. A solution to the IC’s complications caused by overheating is integrated cooling, in which cooling fluid is delivered through microchannel heat sinks on the backside of an IC. This meta-study will investigate two microfluidic cooling technologies. First, implementing varied size microfluidic channels close to the silicone substrate of the IC. Additionally, a micro-pin fin heat sink is integrated into the ICs’ fluidic microchannels. Different sized pin fins were used, to achieve a wider understanding of the application of pin fins in microfluidic cooling and compare the thermal performances of each cooling method. Integrated cooling subverts the need for suboptimal thermal interfaces and bulky heat-sinks, as well as reducing the intensity of localised hotspots commonly present in high-power electronics. Further, by locating the main heat exchange medium closer to the die of an IC, we reduce the number of thermal interfaces. This meta-study suggests that cylindrical micro-pin fin arrays with pitch longitude and latitude of 60μm and 120μm, are more thermally efficient than plain microfluidic cooling channels.

Numerical analysis of micro-pin-fin heat sink cooling in the mainboard chip of a CPU

The cooling capability of heat sinks is important for a central processing unit (CPU). In this work, simulation has been done to investigate heat transfer (HT) in a heat sink (HS) mounted on the circular cylinder chip of a CPU that is studied and to explore the thermofluid behavior of the designed micro-pin-fin heat sink (MPFHS). Air cooling methods are used for heat extraction. This numerical work considers the effects of inlet turbulence intensity (TI) and fin diameter (D) of the micro-pin-fin on the performance of the HS. Turbulent SST model is used to explore turbulence regime in the system. The HT and pressure coefficient were obtained at different Reynolds number (Re) (i.e., different inlet velocities). As shown in this study, the Nusselt number (Nu) rises with the increase in air flow velocity which enhances the heat extraction from CPU.

New Approach of Triumphing Temperature Nonuniformity and Heat Transfer Performance Augmentation in Micro Pin Fin Heat Sinks

Abstract This study is the first part of the development of improved micro pin fin heat sink (MPFHS) for the thermal management of modern microprocessor chip cooling. In the current numerical study, a new fluid flow distribution scheme for MPFHS has been proposed for triumphing over surface temperature nonuniformity problem—one of the most critical issues interfering with the thermal management of modern microprocessors chip cooling. It is established that fluid, if supplied from the confronting sides (front/side directions) of the MPFHS, helps in mitigating temperature nonuniformity and intensifies heat transfer rate. Fluid starts enjoying following paybacks on account of proposed change: the benefits of the developing flow even in adverse temperature zones of the conventional design, enriched secondary channels fluid flow, and rigorous mixing of the cooling fluid between the primary and the secondary channels. Two front facing multi-inlet designs (MPFHSMI,F and MPFHSMI,FH) and one side facing multi-inlet design (MPFHSMI,SH) are conceptualized and compared with the conventional design MPFHSCD. Base surface temperature nonuniformity reduces 7.6 °C, 24 °C, and 7.4 °C by the MPFHSMI,F, MPFHSMI,FH, and MPFHSMI,SH designs, respectively. Average Nusselt number for the cases MPFHSMI,F, MPFHSMI,FH, and MPFHSMI,SH is found 26.7%, 52.3%, and 70.9% higher than the conventional design of MPFHS. Overall thermal performance factor of one design MPFHSMI,FH is found 1.66 at the applied heat flux of 125 W/cm2.

Thermal and hydraulic performance of micro pin fin heat sinks with different pin fin shapes

Efficient cooling of high heat flux devices has promoted the development of micro pin fin heat sinks. In this study, four micro pin fin heat sinks (MPFHSs) with different pin fin shapes, i.e., circular, square and diamond and streamline ones are fabricated by laser micromilling methods. Their single-phase heat transfer and fluid flow performance are explored to assess the pin fin shape effect. Convective flow tests are conducted at Reynolds number of 150-750 at two heat fluxes using deionized water as the coolants. It was found that the streamline MPFHS presented the best heat transfer performance. On the contrary, the diamond fin pin heat sink presented the worst heat transfer performance, whereas it featured the smallest pressure drop among the four MPFHSs. The diamond micro pin fins showed the smallest thermal resistance at a certain pressure drop, and should be selected as the optimum one for the MPFHS applications when the overall thermal and hydraulic performance is considered.

Numerical analysis of the heat transfer and fluid flow characteristics of a nanofluid-cooled micropin-fin heat sink using the Eulerian-Lagrangian approach

In the present study, the thermofluid characteristics of a water and nanofluid-cooled micropin-fin heat sink have been evaluated by implementing a two-phase Eulerian-Lagrangian model. The nanofluid consisted of an aqueous suspension of the spherical-shaped alumina nanoparticles with the particle volume fraction (φ) ranging from 0.25% to 1%. The analysis has been performed by considering a heat sink comprising the staggered arrangement of 72 micropin-fins of the circular cross-section without tip clearance. A constant heat flux of 300 kW/m2 was subjected at the base of the heat sink, whilst the utilised pressure drop (∆P) across the heat sink was limited to ∆P<3000Pa. Heat transfer and fluid flow parameters were evaluated in terms of the local heat transfer coefficient, the enhancement ratio of the average convective heat transfer coefficient, thermal resistance and volume flow rate through the heat sink. Additionally, the temperature contours and flow streamlines across the heat sink elaborated the temperature distribution and flow attributes. Results indicated that under identical ∆P conditions, replacing water coolants with nanofluids optimised the thermal performance of the heat sink with a perceptible margin at the higher particle loadings. At the optimal pressure drop and particle concentration, nanoparticle dispersion into the hosting fluid demonstrated a maximum of 16% enhancement in the average heat transfer coefficient.

Monolithic Integration of a Micropin-Fin Heat Sink in a 28-nm FPGA

Microfluidic cooling has been demonstrated as an effective means of cooling microelectronic circuits with a very low convective thermal resistance and potential for integration in close proximity to the area of heat generation. However, microfluidic cooling experiments to date have been limited to silicon with resistive heaters representing the heat generating circuitry. In this paper, a micropin-fin heat sink is etched into the back side of an Altera Stratix V field-programmable gate array (FPGA), built in a 28-nm CMOS process. Thermal and electrical measurements are made running a benchmark pulse compression algorithm on the FPGA. Deionized water is used as a coolant with flow rates ranging from 0.15 to 3.0 mL/s and inlet temperature ranging from 21 °C to 50 °C. An average junction-to-inlet thermal resistance of 0.07 °C/W is achieved.

Integrated Circuit Cooling Using Heterogeneous Micropin-Fin Arrays for Nonuniform Power Maps

As microelectronic system density continues to increase, cooling with conventional technologies continues to become more challenging and is often a limiter of performance and efficiency. The challenge arises due to both large heat fluxes generated across entire chips and packages, and localized hotspots with even higher heat flux. In this paper, nonuniform micropin-fin heat sinks are investigated for the cooling of integrated circuits with nonuniform power maps. Four heterogeneous micropin-fin samples were fabricated and tested in single-phase experiments with deionized water to investigate the effectiveness of local micropin-fin clustering for the cooling of hotspots. Cylindrical and hydrofoil micropin-fins were tested, as well as two types of heterogeneous arrays: those with pin-fins clustered directly over the hotspot and those with the high density cluster spanning the entire width of the channel to prevent flow bypass around the cluster. Samples were tested with a uniform nominal heat flux of 250 W/cm2 as well as a hotspot heat flux of 500 W/cm2. Local micropin-fin clustering was found to be an effective method of reducing local thermal resistance with a modest pressure drop penalty.

Experimental study and optimization of pin fin shapes in flow boiling of micro pin fin heat sinks

Micro pin fin heat sinks show their great merits of thermal management in high heat flux devices in microelectronic, energy, aerospace, and military areas. The design optimization of micro pin fin shapes is a critical issue for their applications, especially in two-phase flow boiling conditions. In this study, four types of staggered micro pin fins with different cross-section shapes, i.e., square, circular, diamond and streamline, were fabricated by a laser micromilling method, and constructed for heat sinks cooling systems. Flow boiling performance of the micro pin fin heat sinks (MPFHSs) was characterized using deionized water as coolant. The effect of cross-section shape on flow boiling characteristics of MPFHSs was examined. Test results showed that the square micro pin fins presented the best boiling heat transfer, followed by circular and streamline ones. The diamond micro pin fins performed worst in boiling heat transfer and suffered severe two-phase flow instabilities at moderate to high heat fluxes, whereas they introduced the smallest pressure drop. The streamline micro pin fins presented the largest two-phase pressure drop. The square and circular micro pin fins showed their superiority in the mitigation of two-phase flow instabilities. The square micro pin fins seem to be the optimum choice and should be selected for heat sink cooling systems. The results in this study provide critical information for the design optimization of micro pin fins heat sinks for the high heat-flux applications, and are of considerable practical importance.

Flow and Heat Transfer in Micro Pin Fin Heat Sinks With Nano-Encapsulated Phase Change Materials

In this paper, a 3D-conjugated heat transfer model for nano-encapsulated phase change materials (NEPCMs) cooled micro pin fin heat sink (MPFHS) is presented. The governing equations of flow and heat transfer are solved using a finite volume method based on collocated grid and the results are validated with the available data reported in the literature. The effect of nanoparticles volume fraction (C = 0.1, 0.2, and 0.3), inlet velocity (Vin = 0.015, 0.030, and 0.045 m/s), and bottom wall temperature (Twall = 299.15, 303.15, 315.15, and 350.15 K) is studied on Nusselt and Euler numbers as well as temperature contours in the system. The results indicate that significant heat transfer enhancement is achieved when using the NEPCM slurry as an advanced coolant. The maximum Nusselt number when NEPCM slurry (C = 0.3) with Vin = 0.015, 0.030, and 0.045 (m/s) is employed is 2.27, 1.81, and 1.56 times higher than the ones with base fluid, respectively. However, with increasing bottom wall temperature, the Nusselt number first increases then decreases. The former is due to higher heat transfer capability of coolant at temperatures over the melting range of phase change material (PCM) particles due to partial melting of nanoparticles in this range. However, the latter phenomenon is due to the lower capability of the NEPCM particles and consequently coolant in absorbing heat at coolant temperatures is higher than the temperature correspond to fully melted NEPCM. It was observed that the NEPCM slurry has a drastic effect on the Euler number, and with increasing volume fraction and decreasing inlet velocity, the Euler number increases accordingly.

Analysis of Signal Propagation Through TSVs Within Distilled Water for Liquid-Cooled Microsystems

This paper analyzes the impact of liquid cooling on the electrical characteristics of through-silicon vias (TSVs) using a microfluidic cooling testbed containing TSVs. The microfabrication of TSVs in a silicon micropin-fin heat sink is presented, and the high-frequency characterization of TSVs within a micropin-fin heat sink using distilled water is performed from 10 MHz to 20 GHz. TSV capacitance and conductance are extracted from measurements; TSVs within distilled water have larger capacitance and conductance than TSVs in silicon due to the lossy characteristics of distilled water at high frequencies. A coaxial-like TSV configuration, which consists of multiple ground TSVs surrounding a center signal TSV, is proposed and demonstrated to shield signal TSVs from the coolant.

A Review of Two-Phase Forced Cooling in Three-Dimensional Stacked Electronics: Technology Integration

Three-dimensional (3D) stacked electronics present significant advantages from an electrical design perspective, ranging from shorter interconnect lengths to enabling heterogeneous integration. However, multitier stacking exacerbates an already difficult thermal problem. Localized hotspots within individual tiers can provide an additional challenge when the high heat flux region is buried within the stack. Numerous investigations have been launched in the previous decade seeking to develop cooling solutions that can be integrated within the 3D stack, allowing the cooling to scale with the number of tiers in the system. Two-phase cooling is of particular interest, because the associated reduced flow rates may allow reduction in pumping power, and the saturated temperature condition of the coolant may offer enhanced device temperature uniformity. This paper presents a review of the advances in two-phase forced cooling in the past decade, with a focus on the challenges of integrating the technology in high heat flux 3D systems. A holistic approach is applied, considering not only the thermal performance of standalone cooling strategies but also coolant selection, fluidic routing, packaging, and system reliability. Finally, a cohesive approach to thermal design of an evaporative cooling based heat sink developed by the authors is presented, taking into account all of the integration considerations discussed previously. The thermal design seeks to achieve the dissipation of very large (in excess of 500 W/cm2) background heat fluxes over a large 1 cm × 1 cm chip area, as well as extreme (in excess of 2 kW/cm2) hotspot heat fluxes over small 200 μm × 200 μm areas, employing a hybrid design strategy that combines a micropin–fin heat sink for background cooling as well as localized, ultrathin microgaps for hotspot cooling.

Purpose, potential and realization of chip-attached micro-pin fin heat sinks

This work presents the design process of an actively cooled power semiconductor package that makes use of a structured chip contact that is preferably produced by Selective Laser Melting (SLM). The concept has a drastically reduced amount of material transitions within the cooling path and is designed for low thermo-mechanical stress. It is shown how to design and build the geometry of the integrated heat sink in such a way that plastic deformation of the applied materials is kept as low as possible. The comparison with state-of-the-art actively cooled power modules shows that a similar or even smaller thermal resistance can be achieved in a much smaller volume.

Silicon Micropin-Fin Heat Sink With Integrated TSVs for 3-D ICs: Tradeoff Analysis and Experimental Testing

Microfluidic cooling is proposed as a solution to reject heat from a 3-D IC stack of high power chips. However, the integration of interlayer microfluidic cooling in 3-D ICs inevitably increases wafer thickness and thus presents possible challenges for through-silicon via (TSV) integration. This paper discusses the thermal and electrical co-design of a microfluidic heat sink compatible with TSV technology. A TSV-compatible micropin-fin heat sink (MPFHS) with a height of 200 μm, a micropin-fin diameter of 150 μm, and a pitch of 225 μm is fabricated. The fabricated MPFHS is experimentally shown to maintain the chip junction temperature at a power density for a flow rate of 70 mL/min. The thermal results are benchmarked with an air-cooled heat sink and a chip junction temperature reduction of is observed. A 3 × 3 array of TSVs, each with a diameter of 10 μm and a height of 178 μm (18:1 aspect ratio), is integrated into each micropin-fin. This results in a TSV density of 17424 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> in the microfluidic heat sinks. Using four-point probing, the measured resistance of TSVs is 36.5±1.5 mΩ.

Computational analysis of nanofluid effects on convective heat transfer enhancement of micro-pin-fin heat sinks

Numerical investigation on the application of nanofluids in Micro-Pin-Fin Heat Sinks (MPFHSs) has been presented in this paper. To investigate flow and heat transfer behavior in MPFHS the three-dimensional steady Navier–Stokes and energy equations were discretized using a finite volume approach and have been solved iteratively, using the SIMPLE algorithm. DI-water is used as a base coolant fluid while the nanoparticles used in the present study are CuO nanoparticles with mean diameters of 28.6 and 29nm and Al2O3 nanoparticles with mean diameters of 38.4 and 47nm. The results show that (i) a significant enhancement of heat transfer in the MPFHS due to suspension of CuO orAl2O3 nanoparticles in the base fluid in comparison with pure water, (ii) enhancement of heat transfer is intensified with increasing volume fraction of nanoparticles and Reynolds number, (iii) increasing volume fraction of nanoparticles which is responsible for higher heat transfer performance leads to higher pressure drop or Euler number in MPFHS but the enhancements are small, especially for lower particle volume fractions, (iv) with decreasing particle diameters the Nusselt number increases for Al2O3–water nanofluid while the trend is reverse for CuO–water nanofluid.