Active Heat Sink Research Articles

Regulating metal-acid double site balance on mesoporous SiO2-Al2O3 composite oxide for supercritical n-decane cracking

The balance between metal and acid sites directly affects the preparation of high-performance cracking catalysts with high heat sink and low coking. Nevertheless, how to control acid-metal sites balance and its relationship with cracking performance are reported scarcely. In this work, a series of Pt/Al2O3-SiO2 dual sites catalysts with different metal to acid active sites ratio (CM/CSA) were constructed by ethanol-assisted impregnation method and the impact on n-decane cracking under supercritical conditions was systematically and deeply investigated. The results showed that the conversion and carbon deposition increased gradually with varied CM/CSA and reached the balance at CM/CSA of 0.13. The proper ratio CM/CSA (0.13) can balance the deep dehydrogenation coking over metal active sites and high heat sink of cracking over acid active sites, the chemical heat sink reaches amazing 1.75 MJ/kg and carbon deposition is only 22.03 mg/cm2 at 750 °C. Meanwhile, the few metal sites at low CM/CSA and the few strong acid sites at high CM/CSA are the main factors limiting the cracking activity. Low CM/CSA limit the activation of C–H bond and deep dehydrogenation of coking precursor, resulting in relative low cracking activity and carbon deposition, while high CM/CSA limit the activation of C–C bond and increase the deep dehydrogenation. In this contribution, design and construction of metal-acid dual sites can not only provide the technical solution for the preparation of high heat sink and low coking cracking catalyst, but also deepen the understanding of the cracking path of hydrocarbon fuel.

Vertically Polarized, Electromagnetic Interference Suppressed Millimeter-Wave Active Heatsink Antenna Based on Gap Waveguide Technology

Vertically Polarized, Electromagnetic Interference Suppressed Millimeter-Wave Active Heatsink Antenna Based on Gap Waveguide Technology

Active Peltier Effect Heat Sink for Power Semiconductor Device Thermal Stability Enhancement

Active Peltier Effect Heat Sink for Power Semiconductor Device Thermal Stability Enhancement

Transient temperature control performance evaluation of a novel hybrid PCM-based active heat sink

In this study, a novel hybrid PCM-based active heat sink is proposed for temperature control management of transient high heat flux shock electronic devices. The temperature control features of the novel hybrid PCM-based active heat sink are numerically studied under the periodic heat flux condition. Impacts of parameters, including phase-change temperatures, heat transfer coefficient, heat sink parameters, and porosity of the porous metal structure embedded in PCM, are numerically investigated. Then the thermal control performance ratio is evaluated. Results reveal that the innovative hybrid PCM-based active heat sink achieves an outstanding temperature management performance when compared to a heat sink without PCM. And the temperature is reduced by more than 10 K. Increasing the height and width of the heat sink can make the temperature distribution more consistent, but an excessive increase seems unnecessary. Compared with pure PCM, When the porosity of porous metal structure decreases from 0.96 to 0.76, the initial melting time of PCM is delayed by 38.7%, and the solidification time is accelerated by 30.2%.

The influence exerted by active cooling on the permanent connection formed as a result of electric arc welding

The problem of temperature stresses is solved in the work. The process of electric arc welding with guaranteed penetration of steel plates of various thicknesses is simulated. The possibility of reducing residual stresses formed as a result of welding by applying heat removal from the surface of the near-weld region of a steel plate is being investigated. The temperature distribution is determined by solving a non-linear heat equation, in which the specific heat and thermal conductivity depend on temperature. The heat source is modeled using the double ellipsoid method proposed by John A. Goldak. The horseshoe-shaped heat sink follows immediately after the anode spot and is set by the heat flux in such a way that the main temperature of the plate does not decrease below its initial temperature. This limitation reduces the level of the temperature gradient, thereby reducing the stresses in the metal plate. To illustrate the effect of active heat sink, the temperature distribution in the top layer at the moment of termination of welding is compared with and without active heat sink. The material is assumed to be elastoviscoplastic, the deformations are small and consist of reversible and irreversible ones. Reversible deformations are related to stresses by the Duhamel - Neumann law. Irreversible strains increase when the von Mises plastic flow condition is satisfied, in which there is a plastic strain rate component responsible for the plastic flow viscosity. The elastic moduli (Young's modulus, Poisson's ratio) and the yield strength are assumed to be temperature dependent. The solution of the mechanical part of the problem is found by the method of simple iterations. For plates with different thicknesses, diagrams of residual stresses are given, located in the center of the plate from the seam to the periphery. As a result of the work, according to the obtained distributions of residual stresses in the plate material, it is concluded that the use of an active horseshoe-shaped heat sink from the near-weld zone when welding thin steel plates reduces residual stresses, therefore it is recommended to use in the welding process. The use of an active heat sink on the reverse side of the plate leads to an increase in the stress level, therefore it is not recommended for use.

Thermal Effect of Cylindrical Heat Sink on Heat Management in LED Applications

Light Emitting Diode (LED) applications are increasingly used in various microelectronic devices due to their efficient light generation. The miniaturisation of the LED and its integration into compact devices within the weight limit have resulted in excessive heat generation, and inefficient management of this heat could lead to the failure of the entire system. Passive and/or active heat sinks are used for dissipating heat from the system to the environment to improve performance. An ANSYS design modeller and transient thermal conditions were utilised in this study to design and simulate the LED system. The modeller performs its function by utilising the Finite Element Method (FEM) technique. The LED system considered in this work consists of a chip, thermal interface material, and a cylindrical heat sink. The thickness of the Cylindrical Heat Sink (CHS) fins used in the investigation is between 2 mm and 6 mm, whilst ensuring the mass of heat sinks is not more than 100 g. The input power of the LED chip is between 4.55 W and 25.75 W, as required by some original equipment manufacturers (OEMs). A mesh dependency study was carried out to ensure the results were synonymous with what can be obtained practically. The simulation results suggest that the power ratings did not affect the thermal resistance of the CHS. In addition, the thermal resistance increased with the increased thickness of the CHS fin. The efficiencies of the heat sink were found to increase with an increased thickness of the cylindrical fin and the accuracy between the calculated and simulated thermal efficiency ranges from 84.33% to 98.80%. Evidently, the CHS fin of 6 mm thickness is more efficient than the other CHS fins, as depicted in this study.

Cost-efficient copper-nickel alloy for active cooling applications

It is recently proposed that active (Peltier) and passive (conductive) cooling could be combined to design highly-efficient thermal conductors as active heat sinks. We study the potential of low-cost copper-nickel alloys for active cooling applications. We show that for this application, copper-nickel alloys prepared using industrial-grade powders to lower the manufacturing cost, are as good as copper-nickel alloys made out of high purity metals. Furthermore, directed energy deposition, a type of additive manufacturing, can produce copper-nickel alloys which have about 10 percent lower thermoelectric power factor compared to mechanical-alloying methods but have larger thermal conductivity values, hence, possessing similar effective thermal conductivity values, reaching 403 Wm−1K−1at 390K. Much larger values are expected at higher temperatures. The usage of additive manufacturing enables complex geometries and large-scale production.

Cooling chip on PCB by embedded active microchannel heat sink

The use of chips is inseparable from printed circuit board (PCB), therefore, it is an effective way to realize microchannel heat sink (MCHS) on PCB to actively cool chip. For improving the integration and cooling efficiency, and reducing the size, energy consumption and coolant consumption of cooling system for thermal management of chips on PCB, the principle and structure of cooling chip on PCB by embedded active microchannel heat sink (EAMCHS) are proposed. EAMCHS is formed by simultaneously integrating MCHS, diffuser/nozzle piezoelectric micropump (PMP) and piezoelectric microvalves with annular boundary on PCB. Chip to be cooled is mounted directly on MCHS. PMP and piezoelectric microvalves enable EAMCHS to drive and control coolant, respectively. The finite element simulation model and theoretical model of cooling chip on PCB by EAMCHS are established to simulate and analyze its heat transfer characteristics and flow characteristics. The manufacturing and assembly based on PCB process are studied and EAMCHS is manufactured. The size and weight of the assembled EAMCHS are small (about 6.5 cm3) and light (about 18.2 g), respectively. Utilizing high temperature co-fired ceramic (HTCC) to simulate chip heating, the working performances of cooling chip on PCB by EAMCHS are experimentally tested and analyzed on the constructed experimental setup. Research results show that EAMCHS can control the temperature of HTCC at 64.0 °C with heat flux of 50 W/cm2 through the flow rate of 30.11 mL/min of coolant. The established theoretical model can describe heat transfer characteristics and flow characteristics of cooling chip by EAMCHS, which will be conducive to its structural design and optimization. The proposed EAMCHS has low energy consumption, small size and light weight, and provides a novel principle, novel method and novel structure for thermal management of chips highly integrated on PCB.

Investigation on heat transfer performance of a novel active method heat sink to maximize the efficiency of thermal energy storage systems

In this work, a novel electric-body-force-equipped heat sink was investigated to determine the effect of the electric field on the heat sink performance. To introduce the optimal composition of the heat sink and electric field, different fin lengths of the heat sink with various arrangements of electrodes were investigated. Increasing the length of fins improves the transferred heat to a certain extent, but the results of this study show that using the electric field has decreased the limitation of this range. Using an electric field on the fins with several applied voltage levels and heat flux rates demonstrated that increasing the applied voltage had an improving effect on heat transfer until 20 kV, and the maximum efficiency occurred on heat flux of 800(W·m−2). The composition of high voltage and ground electrodes in two sides of fins was the best configuration for heat transfer enhancement in the heat sink. Employing this arrangement could transfer the trapped heat farther from fins by maximum creation of fluid flow near the surface of them. This modern heat sink can be used as an active method in accompany with the passive method advantages to maximize the efficiency of sensible heat energy storage systems.

Experimental investigation on active heat sink with heat pipe assistance for high-power automotive LED headlights

Compared with traditional halogen headlights, LED has obvious advantages in energy consumption, photoelectric efficiency, luminous flux, and life span. However, the thermal management of LEDs is usually limited by space. This paper proposes a novel design of a heat pipes assisted compact heat sink (HPACHS) for LEDs to reduce the LED junction temperature. The thickness of the double-sided LED can be reduced to 1.5 mm since there is no multilayer structure, and the double-sided LED headlight can emit more concentrated light. The results show that HPACHS can cool the 34 W LED substrate to 100.32 °C at an ambient temperature of 26 °C, with a cooling fan power of only 0.267 W and a thermal resistance from the LED base to the environment of 2.17 °C/W. The minimum thermal resistance of HPACHS is 1.86 °C/W, with a heat load of 18 W. The heat sink is 71 mm long and the maximum outer diameter is 38 mm. Therefore, as an efficient and high-power LED cooling device, this compact active radiator has sufficient application prospects and can be applied to the thermal management of automobile headlights.

Temperature Difference Sensor to Monitor the Temperature Difference in Processor Active Heat Sink Based on Thermopile

The monitoring of processor temperature is crucial to increase its efficiency. One of the novel approaches is use the information not only about the CPU (Central Processing Unit) thermal state, but also about changing environmental conditions. The additional temperature difference sensor to monitor thermal changes in the processor environment is necessary. The sensor dedicated for active heat sink, often used inside laptops, was designed, fabricated and investigated. To fulfill the requirements and to match to the specific shape of the active heat sink, the hybrid sensor was proposed. It was composed of six thermocouples and fabricated using thick-film and LTCC (Low Temperature Cofired Ceramic) technology combined with wire thermocouples. Thick-film/LTCC flat substrates with thermoelectric paths ensured good thermal contact between the sensor and the monitored surface. The thermoelectric wires allowed adjusting the sensor to the complicated shape of the active heatsink. Three different versions of the sensor were realized and compared. All of them seem to be suitable for measuring the temperature difference in the given application and they can be used in further works.

Experimental study on thermo-chemical behavior of PHWR fuel channel under slumped fuel pin condition

The safe operation of the reactor is compromised under postulated accident events. The events may originate from single or multiple failures. LOCA, along with the unavailability of ECCS, is one such multiple failure event. Phenomena like fuel heat up, fuel slumping, clad oxidation, hydrogen generation and fission product release are about to take place. However, moderator cooling to the external surface of fuel channels limits the fuel heat up. The steam starvation in the channel limits hydrogen generation. The purpose of this study is to analyze the thermo-chemical behavior of a fuel channel of PHWR, assuming that the 37 fuel elements of a bundle are collapsed and collected in a tightly packed stack at the bottom of the pressure tube of the fuel channel. The temperature distribution is obtained under a pseudo-steady-state for the various components of the simulated fuel channel exposed to an oxidative environment. Experimental results have indicated that a significant temperature gradient gets established in radial, circumferential and axial directions in the fuel channel due to slumped fuel bundle configuration as well as hydrogen generation. Estimation from the heat balance studies shows that moderator functions as an active heat sink.

Effect of multiple-failure events on accident management strategy for CANDU-6 reactors

Lessons learned from the Fukushima Daiichi nuclear power plant accident directed that multiple failures should be considered more seriously rather than single failure in the licensing bases and safety cases because attempts to take accident management measures could be unsuccessful under the high radiation environment aggravated by multiple failures, such as complete loss of electric power, uncontrollable loss of coolant inventory, failure of essential safety function recovery. In the case of the complete loss of electric power called station blackout (SBO), if there is no mitigation action for recovering safety functions, the reactor core would be overheated, and severe fuel damage could be anticipated due to the failure of the active heat sink. In such a transient condition at CANDU-6 plants, the seal failure of the primary heat transport (PHT) pumps can facilitate a consequent increase in the fuel sheath temperature and eventually lead to degradation of the fuel integrity. Therefore, it is necessary to specify the regulatory guidelines for multiple failures on a licensing basis so that licensees should prepare the accident management measures to prevent or mitigate accident conditions. In order to explore the efficiency of implementing accident management strategies for CANDU-6 plants, this study proposed a realistic accident analysis approach on the SBO transient with multiple-failure sequences such as seal failure of PHT pumps without operator's recovery actions. In this regard, a comparative study for two PHT pump seal failure modes with and without coolant seal leakage was conducted using a best-estimate code to precisely investigate the behaviors of thermal-hydraulic parameters during transient conditions. Moreover, a sensitivity analysis for different PHT pump seal leakage rates was also carried out to examine the effect of leakage rate on the system responses. This study is expected to provide the technical bases to the accident management strategy for unmitigated transient conditions with multiple failures.

Study of Active Plate Heat Sink using Different Slope Angles

In recent years, cost-effective compact size devices with high processing speed are made for a sharp rise in the electronics market. To compensate for the high heat fluxes produced in the device, heat sinks are extensively used. In this research, study of active plate heat sink using different slope angle without changing surface area and mass is carried out with the help of CFD tool. The methodology used in this study is the 3D CAD modeling using SOLIDWORKS software and CFD simulation using STAR-CCM+ software. Navier-Stocks equations are solved by using the conjugate heat transfer method. To establish a validation case, the numerical result obtained from this study is compared with the experimental results of the previous research paper. From the results, maximum temperature and thermal resistance performance of 7.5° slope geometry is increased by 1.57% and 16.87% respectively and pressure drop performance of 10° slope geometry is increased by 65.37%. Another considerable factor is the temperature profile at the bottom of the sloped heat sink geometries, which is more uniformly centered in case of 7.5° and 10° slope. The conclusion stated that the angular sloped geometries provides better result than the traditional plate heat sink geometry.

Diode Lasers with Near-Surface Active Region

Edge-emitting diode lasers with shallow location of a quantum-well active region at a depth of 0.92 μm were developed and their thermal resistance was evaluated from the analysis of true spontaneous emission spectra through the top contact window. Owing to a close spacing between the active region and laser heatsink, effective heat removal is achieved under continuous wave operation that is characterized by a low value of specific thermal resistance of 6 × 10–3 K/(W cm2).

Active Thermal Sensor for Improved Distributed Temperature Sensing in Haptic Arrays

The efficacy of integrating temperature sensors into compliant pressure sensing technologies, such as haptic sensing arrays, is limited by thermal losses into the substrate. A solution is proposed here whereby an active heat sink is incorporated into the sensor to mitigate these losses, while still permitting the use of common VLSI manufacturing methods and materials to be used in sensor fabrication. This active sink is capable of responding to unknown fluctuations in external temperature, that is, the temperature that is to be measured, and directly compensates in real time for the thermal power loss into the substrate by supplying an equivalent amount of power back into the thermal sensor. In this paper, the thermoelectric effects of the active heat sink/thermal sensor system are described and used to reduce the complexity of the system to a simple one-dimensional numerical model. This model is incorporated into a feedback system used to control the active heat sink and monitor the sensor output. A fabrication strategy is also described to show how such a technology can be incorporated into a common bonded silicon-on-insulator- (BSOI-) based capacitive pressure sensor array such as that used in some haptic sensing systems.

Active heat sink with piezoelectric translational agitators, piezoelectric synthetic jets, and micro pin fin arrays

Air-cooled heat sinks are widely used for electronics cooling. Active and passive cooling components can be added to enhance the performance of the air-cooled heat sinks. In this paper, piezoelectric translational agitators and synthetic jets are integrated as active cooling components while micro pin fins are adopted as a passive cooling scheme. The heat transfer performance of the active heat sink system that combines these active and passive cooling components along with a suction fan is experimentally investigated. The piezoelectric translational agitators installed within cooling channels are operating at 222 Hz ∼ 820 Hz with a peak-to-peak displacement of 1.0 mm ∼ 1.4 mm, depending on the attached carbon fiber blade type. The piezoelectric synthetic jet array provides impingement flow into the cooling channels with an inclined configuration, that has been successfully integrated into the system without interference with other components by using a wedge platform. The jet operates at 720 Hz with the jet velocity of up to 39 m/s. Micro pin fins are fabricated onto both surfaces of each heat sink channel walls by a double-sided microfabrication technique. They have diameter, height, and spacing of 500 μm, 250 μm, and 1500 μm, respectively. The experimental results indicate that the micro pin fins are most efficient among the employed active and passive cooling components, reducing thermal resistance up to 38%, compared to plain heat sink performance. The piezoelectric translational agitator reduces system thermal resistance by 22%, compared to the non-agitated condition, at the same through-flow rate. The synthetic jet shows weaker cooling capability in the setting tested, compared to enhancement by the agitator plates or pin fins. The active heat sink with the micro pin fins, agitators, and jets provides a thermal resistance of 0.064 °C/W at 70 CFM (33 L/sec) through-flow of air, about a 48% reduction from that of the non-agitated, plain heat sink under the same operating conditions. The results demonstrate how more effective the active heat sink system is compared to traditional air-cooled heat sinks.

A Rapid Nondestructive Inspection Method Applied to EAST Lower Divertor by Infrared Thermography

Lower divertor, as the most critical part of experimental advanced superconducting tokamak (EAST), has functions of protecting the vacuum vessel, particles exhausting, and heat load handling. Doped graphite with SiC coating is adopted as plasma-facing material, which is bolted to active water-cooling heat sink by an M8 screw with a soft graphite sheet inserted between graphite tile and heat sink to improve the capacity of heat transmission currently. In order to guarantee excellent performance of lower divertor, every striking target, which contains 27th graphite tiles, must be inspected for its assembly quality before being installed in EAST device. This paper introduces a rapid nondestructive inspection method for EAST lower divertor by infrared (IR) thermography. The poor assembly quality, such as unevenness of contact surface of graphite tile or heat sink, overlap of the soft graphite sheet, and unqualified values of torque, can be detected qualitatively by comparison of the surface temperature evolution of graphite tiles in symmetric positions of the same divertor target when water flowing in the tube welded into heat sink is changed from hot to cold. The 3-D thermal finite-element analyses are performed to simulate the case of target with excellent assembly quality and defect-free tiles and as a reference for the experimental observations obtained by IR thermography eventually.

Effects of piezoelectric fan on overall performance of air-based micro pin-fin heat sink

Due to the lack of studies on the thermal and hydraulic performances of roughed surfaces subjected to the piezoelectric fan in the presence of forced channel flow, an experimental investigation is performed for a micro pin-finned heat sink integrated with a specific piezoelectric fan in the current study. Some influence factors, such as characteristic Reynolds number of vibrating fan, fan tip-to-heated surface clearance and channel flow Reynolds number, are taken into considerations for two specific micro pin-fin configurations having the same pin-fin height. Particular attention is focused on evaluating the role of piezoelectric fan in the design of an active heat sink. It is confirmed that the micro pin-fin surface with a larger pin diameter (H250D400) provides a stronger heat transfer enhancement but greater additional flow losses than H250D250. The integration of piezoelectric fan into micro pin-fin heat sink is a highly efficient means for improving thermal performance. Its role on heat transfer enhancement behaves more significantly under a higher characteristic Reynolds number of vibrating fan and smaller fan tip-to-surface distance. With the presence of piezoelectric fan, the overall thermal performance parameter is generally bigger than the corresponding one without the piezoelectric fan except for the micro pin-fin type H250D400 under high channel flow Reynolds numbers. The linear relationships of heat transfer coefficient and overall thermal performance parameter are derived with respect to the total Reynolds number combining the channel flow and piezoelectric fan. It is demonstrated that the influence weighting of piezoelectric fan on the overall thermal performance parameter is weaker than that on the pure thermal performance of micro pin-fin heat sink.

Thin large area vertical Schottky barrier diamond diodes with low on-resistance made by ion-beam assisted lift-off technique

We designed and made 15μm large area vertical Schottky barrier diamond diodes with resulting substrate thickness of about 1μm. The ion-beam assisted lift-off technique was successfully used to separate 5×5mm2 active two-layered structure from ballast HPHT diamond substrate. The fabricated diodes had <6mΩ∗cm2 (0.03Ω) on-resistance at room temperature and 3mΩ∗cm2 (0.015Ω) at 200°C fixed temperature of the diode case. A removal of large ballast substrate resistance results in a significant drop of on-state voltage, power losses and, therefore, increasing of diode efficiency. An additional technology step of sacrificial layer formation by ion implantation did not cause a considerable degradation of diode reverse characteristics. As a result, the room-temperature Baliga's figure of merit of the fabricated thin diodes is more than ten times higher comparing to earlier made thick diodes with a drift layer of the same thickness and boron content. 20A maximum forward DC current and <2V voltage drop were measured at fixed case temperatures in the range from 0°C to 200°C using an active heat sink.