Air-cooled Heat Sink Research Articles

Development of a multi-scale topology optimization method for thermal-fluid problems

In this presentation, we discuss how to optimize both microstructure and macrostructure in the topology optimization of 3D thermal fluid. First, the 3D thermal fluid model is approximated by a 2D thermal fluid field. Next, a proxy model of microstructural properties is constructed by learning the relationship between microstructure geometry, permeability, thermal conductivity, and heat transfer coefficient through off-line numerical analysis. The macrostructure optimization is then formulated as a microstructure selection problem from the surrogate model. Finally, a simple numerical example confirms the validity of the method. In this study, as a specific example, topology optimization is performed with two design variables on a two-dimensional model of a 3D forced air-cooled heat sink with prismatic fins. The properties of the 3D prismatic fins are analyzed individually in advance and learned offline using an RBF network so that they can be used in the two-dimensional topology optimization, which requires differentiation.

Statistical Analysis of the Thermal Performance and Reliability in the Heat Sink With Heat Pipes for the Power Electronics Module

Cooling devices are often used with power electronics systems to allow them to operate stably over long periods of time, they help guarantee not only thermal performance but also reliability. To understand the performance of these cooling devices it is important they are verified by various types of testing, also the test results themselves should be quantified and analyzed using recognized statistical methods. For this paper, we investigated an air-cooled heat sink with heat pipes by conducting heat load, high/low temperature storage limits, accelerated life, and transport vibration tests. The collected experimental data were analyzed by statistical methods such as the independent samples t-test, the paired samples t-test, correlation analysis, process capability analysis, and the tolerance interval analysis. A newly manufactured power conditioning system had one heat sink on which the two power electronics modules were attached while providing a heat load of up to 3.2 kW. It was found that there was no deterioration in the thermal performance of the heat sink due to vibrations while being transported from the Republic of Korea to the United States. If such a heat sink is used over 20 years, it is anticipated that there will be a performance degradation of 6.2% over those years with a 95% confidence level for a B10 life. Based on our accelerated life testing, the heat sink is capable of dealing with a heat load of up to 3.1 kW over the design lifetime of 20 years. Thermal engineers should eventually introduce design margins in consideration of the reduction in quality and reliability that can occur over the lifetime of a cooling device.

Investigation of boiling behaviors in vapor chambers in response to transient heat input profiles

Vapor chambers are being increasingly utilized as passive heat spreaders in various high-power density thermal management architectures. Particularly, in applications involving power electronics packaging, there is a need to understand and predict thermal performance of vapor chambers under different transient heat loads. It is known that boiling could occur in the wick structure of a vapor chamber at the location of heat input if sufficiently high heat fluxes are directly imposed on the chamber wall. Prior experimental studies that characterize the steady state thermal resistance of vapor chambers versus input power can only identify the behavior before and after the transition to boiling. However, because the initiation of boiling is a discrete event that occurs during the transient powering up, it is critical to understand how boiling behaviors will affect the performance of the vapor chamber in response to the transient heat input profile characteristics. Furthermore, currently available transient vapor chamber modeling efforts do not consider the occurrence of nucleate boiling, precluding their usage for applications where boiling is likely to occur. In this paper, we experimentally characterize the occurrence and effect of nucleate boiling in a vapor chamber coupled with an air-cooled heat sink, subject to various transient heat input profiles. The long-time step response behaviors are first studied for ten on–off cycles, at different on-powers, to illustrate the complete temperature response to a steady state in each cycle. For a range of intermediate powers, an interesting phenomenon is observed, where boiling occurs in every alternate cycle; we identify this range as the transition regime of boiling incipience in the vapor chamber. We further investigate the transient response to a pulsed heat input for various on-times ranging three orders of magnitude from 0.1 s to 400 s, and with two duty cycles (0.25 and 0.5), while keeping either the on-power or the average power constant. For a fixed on-power, lower on-times (0.1 s – 2 s) do not cause any boiling, but for longer on-times (≥ 20 s), cases with lower duty cycles led to occurrences of boiling incipience. Furthermore, for a fixed average power, a higher on-power at a lower duty cycle is more likely to cause boiling, which interestingly leads to an even lower mean steady temperature compared to cases with lower on-power and larger duty cycle. These studies provide insights into the nature of boiling incipience in vapor chambers for their usage under realistic transient input powers mimicking power electronics.

Forced air cooled heat sink with uniformly distributed temperature of power electronic modules

• Low-cost improvement of conventional heat sink for power electronic modules. • Redistribution of the airflow through the heat sink fins using V-cut guide plate. • Uniform distribution of the temperature across the power electronic modules. • Modelling and verification of the proposed power semiconductor cooling system. The paper discusses an approach to the design of the forced air-cooling heat sink for power electronic application to uniformly distribute the temperature of the semiconductor modules fixed on the top of the heat sink. The proposed approach suggests a minor modification of a conventional fin-based heat sink commonly manufactured for cooling of power electronic modules. Following the proposed modification, an air guide plate having a V-shaped cut is attached to the bottom of the heat sink to redistribute the airflow through the fins. To verify the proposed approach, the modified forced air-cooling system for a power electronic circuit comprising of three IGBT modules was modelled and numerically simulated using Ansys Fluent software under steady-state conditions. The numerical analysis was conducted for a range of power loss 50–100 W in each IGBT module and an airspeed of 5 m/s through the heat sink. The simulation results have shown a good uniform distribution of the temperature across the IGBT modules where the temperature difference does not exceed 0.21 °C.

Air Cooling of Power Electronics Through Vertically Enhanced Manifold Microchannel Systems (VEMMS)

Abstract To improve the reliability and efficiency of power electronics, their thermal management must be further enhanced. Next-generation electronics systems are predicted to dissipate more heat as die size shrinks and power levels increase. Traditional air-cooling approaches usually provide insufficient performance or require heavy and bulky heat sinks to achieve adequate thermal management. To address this problem, a novel air cooled vertically enhanced manifold microchannel system (VEMMS) was developed. While minimizing the footprint required on the printed circuit board, the system offers efficient thermal management in a conformal scheme that accommodates the associated power electronics and their electrical connections. This work describes the manufacturing process of the air-cooled VEMMS heat sink and its experimental characterization and thermo-fluidic performance. Good agreement was obtained between the test results and numerical predictions. Using air at ambient conditions, thermal resistance of 2.6 K/W was achieved with a single-sided cooling architecture with a <1.5 cm2 footprint and <2 cm3 total heat sink volume. A full-bridge electrical power density of ∼84 kWe/L and overall direct current (DC–DC) converter power density of ∼20 kWe/L were achieved at reasonable flow rates and pressure drops using commercially available miniature electric fans.

Modelling sound wave propagation through corrugated macro-geometry arrangement of porous material for combined heat sink and noise reduction applications

In convective air-cooled heat sink applications with space constraints, corrugated geometries can be used as in-duct sound absorbing structures offering lower duct-flow resistance than other geometries such as block-shape, wedge-shape geometries. Sound wave propagation through this geometry is presented using a simple 1-D acoustic model. Using the model, acoustic performance of corrugated sample is evaluated in terms of its transmission loss in dB. Thermal resistance and pressure drop values are also reported and compared with acoustic performance as function of number of corrugations and length of corrugated sample. A rectangular corrugated geometry has alternate inlet and outlet channels separated by porous walls. Sound propagation across this arrangement is modelled by extending prior model from literature with similar geometries. Prior model by Allam and Åbom (2005) is highly symmetric about the channels and porous walls are modelled by simple steady flow resistance equation. In current work, appropriate considerations are taken into account for the configuration of corrugated geometries suitable to general heat sink applications and sound wave propagation through porous walls is predicted by using Johnson-Champoux-Allard (jca) model. The porous walls at ends of the geometry are modelled as in acoustically series-parallel network combinations. Further, effect of heat sink temperature on sound wave propagation is also explored using the model.

Design and Simulation of Ethylene Cooled Microchannel Heat Exchanger for Micro Processors

In this study, a microchannel heat exchanger with operating with ethylene was proposed instead of air-cooled microprocessor heat sinks and flow and heat transfer simulations were made using Flo-EFD software. First, the temperature distribution of the air domain and the microprocessor in the computer case was obtained for air-cooled heat sink, and then the flow paths of the air coming from the outside with the help of the fan were observed. Afterwards, the system with the proposed micro channel heat exchanger was subjected to the same processes and the results were compared. As a result of the study, it was revealed that the micro channel heat exchanger reduced the processor temperature between 54-55°C and 18-19°C. It has also been observed that removing the heat sink allows the air drawn from the outside environment to circulate more efficiently around other heat generating elements in the computer case. Hence more homogeneous and lower temperature distribution within the computer case was obtained.

Experimental investigation on heat transfer enhancement of air-cooled heat sink using multiple synthetic jets

The heat transfer enhancement of air-cooled heat sink using multiple synthetic jets is investigated experimentally. A heat sink is located inside synthetic jet actuator cavity in order to reduce space occupied by the cooling device. It has been observed that heat sink located inside the synthetic jet actuator cavity dissipates heat in a manner similar to the heat sink cooled by impinging synthetic jet. The thermal resistance of the heat sink depends on the synthetic jet Reynolds number and dimensionless stroke length. The paper presents experimental results of synthetic jet Reynolds number, dimensionless stroke length as well as the heat sink thermal resistance and coefficient of performance. The value of the heat sink thermal resistance of 0.22 K/W was measured during operation of synthetic jest cooling while the thermal resistance of the heat sink without loudspeaker was found to be 1.4 K/W. A correlation of thermal resistance as a function of Reynolds number and dimensionless stroke length based on the experimental results is presented and discussed.

Air-Cooling System Optimization for IGBT Modules in MMC Using Embedded O-Shaped Heat Pipes

Insulated gate bipolar transistor (IGBT) modules are the most critical components of modular multilevel converters (MMCs). However, they are subjected to repetitive thermo-mechanical stress caused by thermal cycles on different materials, which can easily lead to failures in the solder layers. Moreover, when MMCs work at high power factor, the IGBT modules have severely uneven temperature distribution due to the inherent dc-bias in arm currents. Some chips are much hotter than others. These hot spots significantly reduce the lifetime of the whole module. This article proposes an optimized and low-cost air-cooling system dedicated to the application of MMC. Uniquely designed O-shaped heat pipes are embedded on the heatsink to add another thermal path without extra fans and fins. The unique shape and layout of heat pipes can minimize the hot spots temperature. The operating principle and power loss of MMC are analyzed first. Then, 3-D finite element (FE) simulation is performed in ANSYS 19.2. Nine modified air-cooling heatsinks with embedded heat pipes are proposed and compared. Finally, the optimal one and a conventional air-cooling heatsink are fabricated for experimental evaluation. The comparative experiment results show that the optimized cooling system is superior over the conventional one by 20% lower in the hot spot temperature.

Introducing a novel heat sink comprising PCM and air - Adapted to electronic device thermal management

With the introduction of PCM-based heat sinks, the cooling of the electronic components in transient applications has been developed. The PCM-based heat sink effectiveness is acceptable only within the melting time, so that in the post-melting stage, the electronic component temperature increases significantly. In this study, a novel hybrid heat sink filled with PCM and air was introduced. This heat sink uses the PCM and air potentials simultaneously to neutralize the effects of the incoming heat flux to keep low the electronic device temperature. Incorporation of air into the PCM-based heat sink leads to acceleration in the heat rejection to the ambient (positive effect) and reduces the PCM volume fraction (negative effect). Based on the results, the positive effect outweighed the negative one and consequently, the cooling ability of the novel heat sink was better than the PCM-based as well as air-cooled heat sinks. As the convective coefficient increases, the positive effect strengthened and hybrid heat sink effectiveness become more apparent. It was found that the novel heat sink (with 50 W.m−2.K−1) can compete with air-cooled heat sinks with much higher convective heat transfer coefficient (100 W.m−2.K−1).

The role of convective heat transfer coefficient in CuO nanoparticles-PCM cooling ability in heat sinks with insulated side walls: comparison with the air cooled one

In this study, the effectiveness of the heat sink with an insulated wall equipped with nano-PCM and air-cooled one was compared. Heat sink effectiveness was defined as the ability of the heat sink to keep lower the base temperature. It was found that for each heat sink, a critical heat transfer coefficient can be supposed. If the convective heat transfer coefficient is less than the critical value, the effectiveness of the nano-PCM filled heat sink is superior to that of the air-cooled one up to the end of the melting time. Otherwise, it is recommended to use the air-cooled heat sink. A novel correlation was proposed to estimate the critical value, and it was shown that the closer the melting temperature to the ambient, the higher the critical value which means the greater the ability of the PCM-HS to compete with air-cooled one.

Redox flow desalination based on the temperature difference as a driving force

How to effectively reduce the consumption of electrical energy is a key topic in many studies of electrochemical desalination. In this work, we use the temperature difference to drive a continuous process of dialysis desalination. The system consists of a thermoelectric unit and a desalination unit connected in series. The thermoelectric unit includes a thermoelectric generator (TEG), a heater as heat source and an air-cooled heat sink to generate electricity and for the desalination unit. The desalination unit contains two platinum-coated hydrophobic carbon cloths as current collectors, a mixture of [Fe(CN)6]3-/4- as anolyte and catholyte, concentrated and diluted salt streams with two cationic and one anionic exchange membranes separated configuration (CEM|AEM|CEM). During the charging process driven by temperature difference, chloride and sodium ions in the diluted salt stream move to the concentrated salt stream and cathodic reservoir, respectively. The results show that the concentration of brine drops significantly from 5,000 ppm to 344.3 ppm as the current decreases to 0.06 mA from the initial 1.30 mA when the temperature difference is maintained at 65 K. Concurrently, the average salt removal rate is up to 8.8 μg cm−2 min−1 and average heat consumption is 284.3 MJ mole-1. Moreover, the influences from the temperature difference, salt feeds content and electrolyte concentration are also investigated in detail. This research has the potential application for the freshwater obtainment via the utilization of waste heat, and will be significant in places with the shortage of the electrical energy such as ships, islands and oceans with the temperature differences.

An autonomous solar driven adsorption cooling system

Attempts to develop autonomous solar adsorption chillers without additional controls to regulate system operation have yielded low cooling capacity and poor coefficients of performance (COPs) due to the use of the sun’s diurnal cycle for control of system operation. A thermally driven, solar adsorption chiller with consistent cooling rates is investigated here. A model for a single-bed system is considered with activated-carbon/ammonia as the working pair. The modeled heat input corresponds to 1 m2 of collector area. Autonomous operation is achieved using novel thermally activated controls to regulate the heating and cooling of the adsorbent bed, rather than relying on the solar cycle. Heat from the collector is stored in a hot-side thermal mass during the adsorption phase, and cooling is delivered by an air-cooled heat sink. The system does not require pumping power or any auxiliary systems for operation. The simple design and elimination of expensive complex components make this system ideal for cooling applications in the developing world or in installations not connected to the grid.

Analysis of Thermal Performance Metrics—Application to CPU Cooling in HPC Servers

Optimization of heatsinks has a critical importance for the energy-efficient cooling of high-performance computing (HPC) servers to meet reliability, performance, and cost targets. This article provides a detailed application of the effectiveness as a performance metric to provide a qualitative comparison of the CPU heatsink solutions. First, the use of effectiveness as a metric to provide an absolute performance of heatsinks on a simple scale of 0–1 is highlighted. Then, the effectiveness and thermal resistances are compared to explore the limits of air cooling and the relative merits of liquid cooling. Second, a response surface method (RSM) for the heatsink optimization is presented. Furthermore, a response surface optimization (RSO) based on the design of experiments (DOE) is performed on the numerical models of the heatsink and cold plates using FloTHERM computational fluid dynamics (CFD) software. The simulation results obtained at 45 °C inlet are used to provide an objective comparison among the optimum heatsink and cold plates. The simulations show that heatsinks have the effectiveness of 0.65–0.75 and a cooling capability of 150–250 W. The cold plates have an effectiveness of 0.25–0.30 and a cooling capability of 325–425 W. Furthermore, the simulation results are compared with benchmark validation studies. Counterintuitively, the higher effectiveness obtained for the air-cooled heatsinks indicates limited scope for further improvement, whereas the cold plates (with lower effectiveness) provide great scope for further improvements to meet future cooling challenges.

Thermal Performance of a Phase Change Material-Based Heat Sink Subject to Constant and Power Surge Heat Loads: A Numerical Study

Abstract A power surge is a frequent phenomenon that occurs in electronics. Inadequate and improper cooling during power surges results in a rapid increase in operating temperatures that may lead to failure of the electronics. In the present investigation, the thermal characteristics of a phase change material (PCM)-based heat sinks, having different configurations and orientations of fins, subject to (i) constant heat load and (ii) heat load with a power surge, are studied numerically. Preliminary investigations showed that a heat sink with PCM gets heated at a much lower temperature than an air cooled heat sink. Following this, four finned heat sinks are considered for further investigations. The heat sink with PCM, sans fins, is used for baseline comparison. The orientation of fins in the other four heat sinks is either vertical or horizontal with square and rectangular cross sections. The heat sink and fins are made of aluminum, and the PCM used is n-eicosane (C20 H42). The enthalpy-porosity method is used to model the solid–liquid phase change in the PCM. All the transient three-dimensional numerical simulations are carried out using ansys fluent 15.0. For a constant heat load of 5 W and power surges of various magnitudes at different time instants, the heat sink with vertical square fins shows superior performance. However, the performance variation among the heat sinks with different fin configurations is insignificant for constant heat load. Even so, for power surges, the location and the configuration of fins have a significant effect on the heater temperature. Cases with high power surge and shorter duration of the surge were also considered to critically examine the effect of fins in controlling the maximum temperature in the heat sink. The numerical results of the best-performing heat sink, i.e., the heat sink with vertical square fins, are finally validated against in-house experiments.

Influence of secondary pass location on thermo-fluidic characteristic on the novel air-cooled branched wavy minichannel heat sink: A comprehensive numerical and experimental analysis

This paper presents a new fin pattern for air-cooled branched-wavy minichannel heat sink (BWMCHS) where three different secondary passes at a distance of 0.5λ, 1.0λ and 1.5λ have been considered (λ is the wavelength and equals to 20 mm). A comprehensive computational and experimental analysis is implemented to investigate the thermo-fluidic characteristics in detail. The RNG k-ε model with enhanced wall treatment with pressure and thermal effect has been used in the numerical analysis. Numerical investigations were validated with experiments. The numerical result is further examined to understand the phenomenological understanding of the air flow through these geometries. In the spanwise direction, BWMCHSs was observed to induce significant non-uniform distribution of air mass flow rate at the inlet and outlet. The pressure drop penalty exceeded the heat transfer enhancement due to flow migration. BWMCHS 0.5λ reported a higher pressure penalty among all the MCHSs. The BWMCHSs showed enhanced thermal performance over a straight minichannel heat sink (SMCHS). In conclusion, the overall performance of BWMCHS at 1.0λ secondary pass has been found superior over BWMCHS 0.5λ and BWMCHS 1.5λ in both numerical and experimental investigations.

Comparative numerical and experimental analysis of thermal and hydraulic performance of improved plate fin heat sinks

The benefits of multiple perforations and slots in a plate-fin heat sink are investigated using a conjugate heat transfer model and complementary experimentation. Heat transfer and pressure drop are analyzed across the two, novel plate-fin heat sinks (with perforations and slots). The experimental data validates the conjugate heat transfer CFD model for the air-cooled heat sink. The results from the CFD model show that novel plate-fin heat sinks tend to have a higher heat transfer coefficient than the plane fins without slots and perforations. Also, pressure drop of the novel plate-fin heat sinks is lower than the plane plate-fin heat sink, so less fan power is required for novel heat sinks. For a range of Re number 13,049 to 52195, on average novel plate-fin heat sink-1 (NPFHS-1) and novel plate-fin heat sink-2 (NPFHS-2) have 42.8% and 35.9% higher Nu number than that of the plane plate-fin heat sink (PPFHS). An additional advantage of the reduction in mass of heat sink is achieved because of slots and perforations.

A tapered inlet/outlet flow manifold for planar, air-cooled oblique-finned heat sink

Flow maldistribution compromises thermal and hydraulic performances of heat sinks. The oblique-finned heat sink is a multichannel heat sink comprising parallel (primary) and collinear oblique (secondary) channels and it was reported to suffer from a self-induced flow migration in liquid and air cooling. In this study, a novel tapered inlet/outlet flow manifold was proposed for the planar oblique-finned heat sink. Two heat sink configurations (oblique angles of 30° and 45°) and three flow manifold configurations (of 5%, 10%, and 20% wider flow domains) were investigated. Flow migration characteristics were studied via numerical simulations. Wind tunnel measurements, supported by infrared thermography, were performed to characterize thermal and hydraulic performances on a wide range of air flow rates. The flow manifold was observed to provide a favorable distribution of secondary flows in the spanwise direction of the heat sink. Up to 50% increase in Nusselt number with a negligible increase in pressure drop was observed with the 45° oblique-finned heat sink once the flow manifold was incorporated. 30° oblique angle −10% flow manifold combination provided the lowest heat sink temperature and the most uniform wall temperature. The novel tapered inlet/outlet flow manifold is the first effort reported in the literature to reduce the adverse effects of flow migration through the planar oblique-finned heat sinks.

Stepwise Design Methodology and Heterogeneous Integration Routine of Air-Cooled SiC Inverter for Electric Vehicle

Carrying on SiC devices, the air-cooled inverter of the electric vehicle (EV) can eliminate the traditional complicated liquid-cooling system in order to obtain a light and compact performance of the powertrain, which is considered as the trend of next-generation EV. However, the air-cooled SiC inverter lacks strategic design methodology and heterogeneous integration routine for critical components. In this article, a stepwise design methodology is proposed for the air-cooled SiC inverter in the power module, dc-link capacitor, and heat sink levels. In the power module level, an electrical–thermal–mechanical multiphysics model is proposed. The multidimension stress distribution principles in a six-in-one SiC power module are demonstrated. An improved power module is presented and confirmed by using the observed multiphysics design principles. In the dc-link capacitor level, ripple modeling of the inverter and capacitor are created. Considering the tradeoffs among ripple voltage, ripple current, and cost, optimal strategies to determine the material and minimize the capacitance of the dc-link capacitor are proposed. In the heat sink level, thermal resistance of air-cooled heat sink is modeled. Structure and material properties of the heat sink are optimally designed by using a comprehensive electro-thermal analysis. Based on the optimal design results, the prototypes of the customized SiC power module and heterogeneously integrated air-cooled inverter are fabricated. Experimental results are presented to demonstrate the feasibility of the designed and manufactured air-cooled SiC inverter.

Performance Enhancement of Air Cooled Heat Sink Used in Inverter Drives of Residential Air Conditioners

Inverter air conditioners are being widely used in the air conditioning sector for energy saving purposes. These air conditioners use an inverter or a variable frequency drive (VFD) to control the compressor operating speed based on cooling or heating load fluctuations. If the heat generated by the electronic components of the VFD is not dissipated properly, it can lead to failure of the VFD. In general, a heat sink is used for dissipating the heat generated by the electronic components of the VFD. The heat sink can be either air cooled or liquid cooled. Using computational fluid dynamics (CFD), this paper deals with optimization of the thermal performance of an air cooled plate-fin heat sink with rectangular fins used in a residential split inverter air conditioner. Commercially available CFD tool has been used for simulations. It has been observed that enhancing fluid flow around the heat sink and improving heat transfer area of the fins significantly improve the thermal performance of the heat sink. By using heat sink with rectangular fins having a stepped profile, it has been possible to improve the heat transfer from the baseline case by 27%. Whereas, by using hollow fins, heat transfer improvement of 20% has been achieved.