Electronics Cooling

In the present work three dimensional numerical simulations were performed on
two microchannels, which contained a flow-restricting orifice. Either microchannel had
the same internal dimensions with an orifice aspect ratio of 2.89:1, an expansion ratio of
10:1, step size of 90µm, a rectangular aspect ratio of 1.3, and an effective expansion ratio
of 6.087. Model1 was a thin walled model, which neglected any conduction through a
substrate material prior to heat transfer into the channel. Model2 was theoretically
embedded in a silicon substrate and simulated flow through a multi-channel system of
microchannels. Model1 was investigated under uniform wall heat flux boundary condition on three sides while the top was considered to be adiabatic. Model2 was investigated under uniform wall heat flux boundary condition, which was only on the bottom of the silicon substrate. Heating in both channels did not occur until the end of the micro￾orifice. Both Channels where simulated using Water and R-123 as the working fluids. Tests were done using several different Reynolds numbers in the laminar regime from Reynolds number 10 to 1100. The models were built and meshed using Gambit software and simulations were performed using Fluent software. The presence of a micro-orifice changes the flow by significantly increasing the hydrodynamic and thermal entry lengths. The flow effects on low Reynolds number flows past a symmetric micro-orifice in a microchannel were also investigated. The laminar flow through the micro-orifice underwent a symmetry-breaking bifurcation at a critical Reynolds number. The critical Reynolds number evaluated from the simulations was compared to other values reported in the literature. Based on the temperature and heat flux distributions obtained, both the local and average Nusselt numbers are presented graphically along with center plane visualizations of the flow after the micro-orifice. The results of this numerical analysis are then compared with experimental results and show very good agreement.
Keywords: Microchannel, thermally developing; Electronics cooling; liquid cooling;
Heat Sink, bifurcation, channel flow, critical Reynolds number, effective expansion ratio,
sudden expansion, micro-orifice.

This paper describes the development of embedded droplet impingement for integrated cooling of electronics (EDIFICE), which seeks to develop an integrated droplet impingement cooling device for removing chip heat fluxes over 100W/cm2, employing latent heat of vaporization of dielectric fluids. Micromanufacturing and microelectromechanical systems are used as enabling technologies for developing innovative cooling schemes. Microspray nozzles are fabricated to produce 50–100 μm droplets coupled with surface texturing on the backside of the chip to promote droplet spreading and effective evaporation. This paper examines jet impingement cooling of EDIFICE with a dielectric coolant and the influence of fluid properties, microspray characteristics, and surface evaporation. The development of micronozzles and microstructured surface texturing is discussed. Results of a prototype testing of swiss-roll swirl nozzles with dielectric fluid HFE-7200 on a notebook PC are presented. This paper al...

Efficient thermal management is critical in high-power-density systems found in electronics, electric vehicles, renewable energy devices, aerospace platforms, and data centres. This study aims to enhance thermal performance through the development of nature-inspired heat sink geometries integrated with advanced nanofluids. Two novel biomimetic configurations, Inline Arranged Airfoil Integrated Curvilinear Pin-Fin (IACPF) and Inline Arranged Airfoil Integrated Corrugated Curvilinear Pin-Fin (AICCPF) were experimentally evaluated across heating powers of 75-300 W and flow rates ranging from 200 to 450 mL/min. These heat sinks were tested using mono and hybrid nanofluids formulated with silver (Ag), silicon carbide (SiC), and beryllium oxide (BeO) nanoparticles, chosen for their high thermal conductivity, dispersion stability, and economic viability. The experimental methodology focused on assessing thermal and hydraulic performance through key parameters including Nusselt number, thermal resistance, wall temperature, and pressure drop. Comparative study showed that, using water as the working fluid at 75 W, the AICCPF heat sink delivered a 10.23% improvement in Nusselt number over the IACPF. When benchmarked against a conventional straight-channel heat sink, the AICCPF design at 150 W demonstrated a 103% enhancement in Nusselt number, confirming its geometric effectiveness. Among nanofluids, the highest convective enhancement was achieved using Ag/SiC hybrid nanofluid, yielding a peak improvement of 22.29% in the AICCPF configuration. Pressure drops remained within manageable limits, with a maximum increase of 15.86%. These findings demonstrate that combining biomimetic heat sink architectures with thermally optimised nanofluids achieves high thermal performance while maintaining acceptable hydraulic penalties. The proposed approach offers scalable, energy-efficient solutions for next-generation cooling applications.

A fin heat sink (FHS) is a thermal heat transfer device employed to dissipate heat from a high temperature heat source to a lower temperature surrounding. A typical FHS consists of a flat metal base with an array of cooling fins on top. A problem normally encountered in thermal management of electronic packages is thermal heat spreading resistance which occurs as heat flows by conduction from a high temperature heat source to a low temperature heat sink with different cross-sectional areas. As high powered semiconductor chips are made more compact and requiring greater heat dissipation, more effective cooling systems have to be devised. There are various methods employed to minimize this heat spreading resistance. These include increasing the thickness of the base of the FHS or height of the fins. Another method is to use more expensive highly conductive materials like aluminum, copper and diamond which would increase cost. A more economical alternative would be to combine a flat he...

The efficient dissipation of localized heat flux by convection is a key request in several engineering applications, especially electronic ones. The recent advancements in manufacturing processes are unlocking the design and industrialization of heat exchangers with unprecedented geometric characteristics and, thus, performance. In this work, laser etching manufacturing technique is employed to develop metal surfaces with designed microstructured surface patterns. Such precise control of the solid-air interface (artificial roughness) allows to manufacture metal heat sinks with enhanced thermal transmittance with respect to traditional flat surfaces. Here, the thermal performance of these laser-etched devices is experimentally assessed by means of a wind tunnel in a fully turbulent regime. At the highest Reynolds number tested in the experiments ( R e L ≈ 16 , 500 ), elliptic scale-roughened surfaces show thermal transmittances improved by up to 81% with respect to heat sinks with fl...

The growing demand for efficient thermal management in compact electronic systems has intensified research into advanced heat sink designs. This experimental study investigates the thermal and hydraulic performance of staggered circular pin-fin heat sinks with various perforation patterns-longitudinal (L), longitudinal/transverse (LT), and longitudinal/transverse/vertical (LTV)-under forced convection and constant heat flux conditions. Using a Peltier module as the heat source and Armfield convection equipment, the study examines heat transfer enhancement across Reynolds numbers ranging from 2x10 3 to 12x10 3. The primary objective is to identify the optimal perforation configuration that maximizes heat dissipation while minimizing pressure drop and weight. The results showed that perforated pins significantly raise Nusselt number (Nu) over solid pins: 7% for L, 30% for LT, and 64% for LTV perforations. Pressure drops are reduced by 10% for L, 17% for LT, and 25% for LTV perforations relative to solid pins. At lower Reynolds numbers, the overall enhancement ratio peaks, notable for reaching a 40% rise with LTV-perforated pin fins. Additionally, fin effectiveness improves significantly: 14%, 34%, and 57% higher for L, LT, and LTV perforated pin fin arrays, respectively. These findings demonstrate the significant potential of multi-perforated pin-fin arrays in improving the thermal performance of heat sinks for electronic cooling applications.

Loop heat pipes (LHP) are heat transfer devices which use evaporation and condensation of working fluid to transfer heat and use capillary forces to provide fluid circulation in a closed loop. One of the main applications of LHP is cooling of electronic components. Further development of this field is associated with miniaturization. Thus, there are strict limits imposed upon size of elements of heat transfer devices in electronics cooling. One of such elements is an evaporator of the LHP, its main element. This paper deals with the LHP evaporator and is aimed at showing dependence of wick conductivity, thickness, and vapor flow geometry on overall heat transfer performance. An open loop experimental setup was created. Experiments were carried out with various configurations. The evaporator consisted of a microchannel (MC) plate, with groove widths of 100 and 300 μm, wick (metal and nonmetal porous materials were used) and a compensation chamber (CC). Heat load varied from 20 to 140...

Miniaturization and utilization of low-dimensional structures of recent electronic devices have witnessed some new micro cooling methods which can fulfil the cooling demand for the electronic devices. Microchannel heat sink (MCHS) is one of the micro cooling method which appears as a promising method that can provide high heat transfer rate due to small hydraulic diameter. Furthermore, microchannel heat sink is easy to be fabricated compare to other micro cooling device. Due to fast development in electronic industry, hybrid microchannel heat sink with optimal design has received a great deal of attention in order to provide sustainable cooling solutions. However, most of the studies of hybrid microchannel heat sink only provided the numerical analysis without any validation of the proposed design experimentally. This is very important since it also will determine whether the proposed hybrid microchannel heat sink can be fabricated or not. Therefore, the aim of this article is to validate the numerical model of hybrid microchannel heat sink (TC-RR-SC MCHS) experimentally. The validation result showed that the maximum discrepancy between both simulation and experimental analyses for Nusselt number and friction factor were 15.8% and 17.4%, respectively, which is less than 20%.

Miniaturization and utilization of low-dimensional structures of recent electronic devices have witnessed some new micro cooling methods which can fulfil the cooling demand for the electronic devices. Microchannel heat sink (MCHS) is one of the micro cooling method which appears as a promising method that can provide high heat transfer rate due to small hydraulic diameter. Furthermore, microchannel heat sink is easy to be fabricated compare to other micro cooling device. Due to fast development in electronic industry, hybrid microchannel heat sink with optimal design has received a great deal of attention in order to provide sustainable cooling solutions. However, most of the studies of hybrid microchannel heat sink only provided the numerical analysis without any validation of the proposed design experimentally. This is very important since it also will determine whether the proposed hybrid microchannel heat sink can be fabricated or not. Therefore, the aim of this article is to va...

Thermal ground planes (TGPs) are considered to be one the most promising thermal management devices for cooling the high heat flux miniaturized power electronic devices. This article presents an overview of the latest advancement in the design and operation of TGPs and its applications to various fields. It also summarizes the recent experimental, numerical investigations on internally grooved, mesh wick, sintered wick, hybrid wick, electro hydro dynamic effect, micro pillared and metal foam embedded TGPs. The heat transfer characteristics and mechanisms involved when using different working fluids, wick structures and materials for enhancing the heat transfer performance and operating range of TGPs are discussed. This review also provides future scope and insight of using TGPs to increase the efficiency and reliability of modern power electronic devices in renewable resource sector and other related applications.

The concept of thermal management in micro- electronic components is changing, and so is the potential for solid-state cooling to solve emerging problems. There is a qualitative change that differentiates the past from the future. We discuss past practices and future trends in the electronic cooling markets, setting the stage for an outline of designs and processes that provide new and enabling options. We briefly review the science that is empowering these changes, and conclude with some thoughts on the future direction of thermal management of microelectronics.

Heat dissipation has become a major hurdle for the electronics industry, especially as higher performance integrated circuits are being developed for the power industry. Two of the primary hurdles in dissipating this heat are:The thermal contact resistance between the IC and the cooling device.The ability to effectively spread the heat, such that traditional cooling technologies can be effective.By selecting ceramic materials that are thermo-mechanically matched (CTE) to IC materials, the proposed heat plate can be directly bonded by typical solder or braze techniques to the back-side of the IC. This eliminates thermal resistances due to contact and thermal interface materials. Within these heat plates, a three dimensional network of gas channels and fluid wicks spread the high-flux heat loads from localized hot spots to the surrounding regions via phase change fluids and mass transport. Like traditional heat pipes, these heat plates operate at nearly uniform temperature due to the ...

Increasing performance of electronic components is resulting in higher heat flux dissipation. Two-phase passive devices are proven solutions for modern microelectronics thermal management. In this context, heat pipe research is being continuously pursued evolving newer solutions to suit present requirements. Pulsating heat pipes (PHPs), a relatively new and emerging technology is one such field of investigation. The operating mechanism of PHP is not well understood and the present state of the art cannot predict required design parameters for a given task. The aim of research work presented in this paper is to better understand these mechanisms through experimental investigations. Experiments were conducted on a PHP made of copper capillary tube of 2-mm inner diameter. Three different working fluids viz. water, ethanol and R-123 were employed. The PHP was tested in vertical (bottom heat mode) and horizontal orientation. The results strongly demonstrate the effect of input heat flux and volumetric filling ratio of the working fluid on the thermal performance of the device. Important insight into the operational regimes of the device has been gained.

In this paper, laminar natural convection of copper/water nanofluid in an open-ended L-shaped cavity is investigated by Lattice Boltzmann Model (LBM). The results are compared by previous studies, that are in good agreement. Influences of Rayleigh number (Ra=〖10〗^3,〖10〗^4,〖10〗^5,〖10〗^6), cavity aspect ratio (AR=0.2, 0.4, 0.6) and volume concentration of Cu nanoparticles (0≤φ≤0.1) on the momentum, thermal fields and heat transfer in the enclosure are studied. Also, the effect of changing the boundary conditions, on the heat transfer rate has been investigated. It is observed that maximum heat transfer enhancement by adding the nanoparticles for Ra=〖10〗^6 with AR=0.4 (32.76%) occurs. Results illustrate that increasing the cavity aspect ratio decreases heat transfer rate for Ra=〖10〗^3 and Ra=〖10〗^4. The least and most heat transfer rate for Ra=〖10〗^5 occurs in enclosures by aspect ratios of 0.2 and 0.4 respectively, while it was observed at Ra=〖10〗^6 for minimum and maximum rate of heat...

With the availability of advanced manufacturing techniques, non-conventional shapes and bio-inspired/biomorphic designs have shown to provide more efficient heat transfer. Consequently, this research investigates the heat transfer performance and fluid flow characteristics of novel biomorphic scutoid pin fins with varying volumes and top geometries. Numerical simulations were conducted using four hybrid designs for Reynolds Number 5500–13500. The impact of pin fin 'top' geometrical features on the heat transfer coefficient (HTC) was evaluated by combining computational fluid dynamics (CFD), experimental data, and machine learning. The results highlighted that the new pin fins saved 6.3 % to 14.3 % volume/material usage but produced around 1.5 to 1.7 times more heat transfer than conventional square/rectangular fins. Also, manipulating pin fins via the top geometrical properties can lead to more uniform velocity and temperature distributions while demonstrating the potential for increased thermal efficiency with reduced thermal resistance. Furthermore, six machine learning models accurately predict HTC using volume and surface area as key variables, achieving less than 5 % mean absolute percentage error (MAPE). Overall, this research introduces innovative biomorphic designs with unconventional geometries, emphasising resource optimisation and efficient HTC prediction using machine learning. It simplifies design processes, supports agile product development, calls for re-evaluation of conventional heat sink geometries, and provides promising directions for future research.

A number of thermal management devices are used to actuate concentrated electronic appliances in an efficient way. A liquid cooling plate acts as a heat sink enclosed by materialized walls. This work aims to carry out design of liquid cooling plates such that the heat diffused by the electronic equipment is removed while their temperatures levels remain within safe limits. The liquid cooling plates expose ?cold surfaces? to electronic appliances. The performance of a cooling plate is estimated depending upon heat carrying capacity, associated heat transfer rates and concentrated thermal regions on the plate surface. For this study, the design of liquid cooling plate was done with SOLIDWORKS. Pure water was used as a working fluid in test channels. A comparative analysis of flow distribution, temperature contours, pressure drop, and pumping power for different channel configurations was carried out with ANSYS. It was observed that a channel configuration is of key importance in liqui...

The objective is to analyze the thermal and hydraulic performance in a Micro Channel Straight Printed Circuit Heat Exchanger. Counterflow and parallel flow configurations were analyzed for water cooling using ethylene glycol-based fluid and platelet-shaped nonspherical Boehmite alumina nanoparticles. The work presents results from applying a dimensionless theory that uses the concepts of thermal efficiency of heat exchangers and quantities associated with the second law of thermodynamics. Thermal efficiency, thermal effectiveness, thermal and viscous irreversibilities, thermodynamic Bejan number, and outlet water temperatures are presented in graph form. The data obtained allow us to conclude that the heat exchanger can work in a range of water and refrigerant flow rates below the design parameters. With the inclusion of nanoparticles with a volume fraction equal to 5.0%, the flow rates of the refrigerant fluid can be significantly reduced. The analysis performed shows that the use of nanoparticles improves the operational cost-benefit of the heat exchanger with a significant reduction in the hot water outlet temperature.

For cooling electronic systems new techniques are invented. Cold plate is liquid cooling system used in electronic components. In present work, the modification is done in design of cold plate to reduce its cost and also to increase the heat dissipation rate. Water at various flow rates is supplied for given power inputs and heat removing capacity of each flow rate at that particular heat load is calculated. It is found that water is best working fluid for all flow rates. Methanol and acetone are best suited for high mass flow rates. The cold plate is used to provide a "cold wall" to which individual electronic components are mounted. The design and performance evaluation of a cold plate follows a prescribed procedure that depends on the heat loading and whether the heat loading is on one or two sides of the cold plate. Due to transmission of applied current and voltage sometimes the temperature of the circuit plate goes increasing. This temperature limits the electronic operation. Thus it is necessary to control such temperature, in order to maintain speed of electronic devices.

A review, study, and quick reference guide to heat transfer. Included are fundamental equations, concepts, and definitions for conduction, convection, and thermal radiation heat transfer. Included are commonly used dimensionless ratios and information on supportive engineering physics topics.

Efficient thermal management is a critical challenge in various industries, particularly in electronics cooling, battery thermal management, and renewable energy systems. Phase Change Materials (PCMs) have emerged as an effective passive cooling solution due to their ability to absorb and store heat through latent heat energy. This project aims to evaluate the thermal performance of PCM-based heat sinks with and without fins using Computational Fluid Dynamics (CFD) simulations in ANSYS Fluent. The study compares rectangular and triangular fins to determine their impact on heat dissipation and PCM melting behaviour. The results demonstrate that the inclusion of fins significantly enhances the heat transfer efficiency of the system, with triangular fins exhibiting the best performance due to their increased surface area and improved conduction paths.

Two-phase flow boiling in microchannels is one of the most promising cooling technologies able to cope with high heat fluxes generated by the next generation of central processor units (CPU). If flow boiling is to be used as a thermal management method for high heat flux electronics it is necessary to understand the behaviour of a non-uniform heat distribution, which is typically the case observed in a real operating CPU. The work presented is an experimental study of two-phase boiling in a multi-channel silicon heat sink with nonuniform heating, using water as a cooling liquid. Thin nickel film sensors, integrated on the back side of the heat sinks were used in order to gain insight related to temperature fluctuations caused by two-phase flow instabilities under non-uniform heating. The effect of various hotspot locations on the temperature profile and pressure drop has been investigated, with hotspots located in different positions along the heat sink. It was observed that boiling inside microchannels with nonuniform heating led to high temperature non-uniformity in transverse direction.

This paper presents experimental investigation for the effects of a phase change material (PCM) and a nano/ phase change material (nano-PCM) on the thermal performance of an electronic chipset. A thermal storage system using Paraffin wax as a PCM is integrated with a heat sink. Additionally, the PCM is modified as nano-PCM by mixing it with multiwall carbon nanotubes (MWCNTs). The effects of various quantities of the PCM, concentrations of the MWCNTs in the PCM, and different power levels on three different modules of heat sinks (without PCM, filled with PCM, and filled with nano-PCM) are studied in passive and active operating modes. Experiments are also performed when the heat flux is applied intermittently, which commonly encountered in the thermal management of portable electronic devices. The phase front propagation is captured and analyzed by an image processing technique. It is found that the PCM can significantly increase the usage time of the system and the nano-PCM as compared to the PCM can extend this time under passive cooling condition. Under active cooling condition, the usage of PCM and nano-PCM may increase the steady-state temperature; however, it reduces the operating temperature of the chipset at the beginning period of the operating time. The nano-PCM module can enhance thermal management of the system by reducing the cooling time up to 6% as compared to the PCM. Under intermittent heating, using more on-and-off cycles lead to decreasing the chipset peak temperature. Using PCM and nano-PCM increases the operating time and reduces the peak temperature of the chipset under intermittent use.

Flying microrobots have garnered growing research interest owing to their technological intricacies and suitability for various applications leveraging miniaturized size. Electrohydrodynamic (EHD) thrust offers advantages by generating propulsion without moving parts, but real-world use is limited by insufficient thrust generation, manufacturing challenges, fragility, and cost. This work presents the design and development of an optimized ion-propelled flying microrobot that excels in low weight, high thrust-to-weight ratio, and cost efficiency. Regarding design, multiphysics simulations guided structural optimization to increase thrust while decreasing weight. For materials, metal-coated polyethylene terephthalate (PET) film was selected to leverage the combined merits of metal conductivity and polymer flexibility, light weight, and low cost, enabling further weight reduction, easy assembly, robustness, and cost-effectiveness. Various experiments, including voltagecurrent measurements, ionic wind speed, thrust quantification, and airflow visualization, directed design refinements and validated performance. Through structural optimization, the maximum wind speed attained 2.25 m/s. Flight demonstrations with payloads evidenced the microrobot can stably fly at an inherent 16 mg weight while carrying an additional 72 mg load, achieving a record 5.5 thrust-to-weight ratio. These results open possibilities to incorporate microelectronics, enabling autonomous flight functionality.

The increasing complexity of modern integrated circuits and need for high-heat flux removal with low junction temperatures motivates research in a wide variety of cooling and refrigeration technologies. Two-phase liquid cooling is especially attractive due to high efficiency and low thermal resistances. While two-phase microfluidic cooling offers important benefits in required flow rate and pump size, there are substantial challenges related to flow stability and effective superheating. This work investigates the use of hydrophobic membrane to locally vent the vapor phase in microfluidic heat exchangers. Previous work has demonstrated selective venting of gas in microstructures and we extend this concept to two-phase heat exchangers. This paper details the design, fabrication and preliminary testing of the novel heat exchanger. Proof-of-concept of the device, carried out using an isothermal air-water mixture, found the air-mass venting efficiency exceeding 95%. Two-phase, thermal op...

Doktore tesi honetan mikroemariak kontrolatzeko elementuak diseinatu eta garatuko dira, mikrobalbula eta mikrosentsore bat zehazki. Ondoren, gailu horiek batera integratuko dira likido emari kontrolatzaile bat sortzeko asmotan. Helburu nagusia gailuen fabrikazio arkitektura modular bat frogatzea da, non Lab-on-a-Chip prototipoak garatzeko beharrezko fase guztiak harmonizatuz, Cyclic-Olefin-Polymer termoplastikozko mikrogailu merkeak pausu gutxi batzuetan garatuko diren, hauen kalitate industriala bermatuz. Ildo horretan, mikrogailuak prototipotik produkturako trantsizio azkar, erraz, errentagarri eta arriskurik gabeen bidez lortu daitezkeenetz frogatuko da.

We here present an approach to cooling of electronics requiring dissipation of extreme heat fluxes exceeding 1 kW/cm 2 over ~1 cm 2 areas. The approach applies a combination of heat spreading using laser micromachined diamond heat sinks; evaporation/boiling in fine featured (5 μm) conformal porous copper coatings; microfluidic liquid routing for uniform coolant supply over the surface of the heat sink; and phase separation to control distribution of liquid and vapor phases. We characterize the performance of these technologies independently and integrated into functional devices. We report two-phase heat transfer performance of diamond/porous copper heat sinks with microfluidic manifolding at full device scales (0.7 cm 2) with heat fluxes exceeding 1300 W/cm 2 using water working fluid. We further show application of hydrophobic phase separation membranes for phase management with heat dissipation exceeding 450 W/cm 2 at the scale of a single extended surface (~300 µm).

The objective of this paper is to present the results of a numerical investigation of the effect of flow pulsations on local, time-averaged Nusselt number of an impinging air jet. The problem was considered to provide inputs to augmenting heat transfer from electronic components. The solution is sought through the FLUENT (Version 6.0) platform. The standard-model for turbulence equations and two-layer zonal model in wall function are used in the problem. Pressure-velocity coupling is handled using the SIMPLEC algorithm. The model is first validated against some experimental results available in the literature. A parametric study is carried out to quantify the effect of the pulsating jets. The parameters considered are 1) average jet Reynolds number (5130 8560), 2) sine and square wave pulsations, 3) frequencies of pulsations (25 400 Hz), and 4) height of impingement to jet diameter ratios (5 9). In the case of sine wave pulsations, the ratio of root mean square value of the amplitude to the average value () was varied from 18% to 53%. The studies are restricted to a constant wall heat flux condition. Parametric conditions for which enhancement in the time-averaged heat transfer from the surface can be expected are identified.

This work is dedicated to the improvement of effusion cooling efficiency on combustion liners, by using an innovative multiperforation made of shaped holes of elliptical crosssection. Low-temperature experiments provided a spatial characterization of cooling efficiency in a suction-type wind tunnel, whereas discrete measurements were performed in the engine-like conditions of THALIE facility. A RANS computational study was also performed to give a detailed insight on the aerothermodynamics of the complex flow created by effusion holes. Experimental and numerical data confirm the enhancement of effusion cooling by shaped holes, thanks to a better coverage of the first rows of the plate, and a better individual efficiency of each hole.

A brake is a friction device for converting the power of momentum or kinetic energy of a moving vehicle into heat energy by means of friction, thereby decelerating the motion of the vehicle. The heat energy is to be dissipated rapidly in order to control brake fade and brake failure. This can be subdue on brake drums, by providing cooling fins (extended surface) on the outer surface of the brake drums. This paper presents the development and analysis of a modified brake drum model having extended surface (fins) along its circumference. The fins or extended surface are designed to improve the heat dissipation rate from the surface of the brake drums which are convectively cooled by the streams of air flowing on its outer surface. One-fourth of the overall height thickness of the original brake drum model was converted into fins. The simulation carried out on the original and the modified models, shows that the modified brake drum model has a higher circumferential strength and better heat dissipation than the original brake drum model.

This study experimentally investigates heat transfer enhancement of an impinging free liquid jet on a hot surface of copper plate with different shapes, by replacing the base fluid, distilled water with Al 2 O 3 nanofluid (10 nm), different shapes of heated surface of copper plate (Flat, Concave, Convex Wavedand Corrugated), different impingement Reynolds numbers ranging from (7,565 to nearly 18,460), five nanoparticles mass concentrations (0%, 0.2%, 0.5%, 1% and 2%) were studied using distilled water and AL 2 O 3 nanofluid jet impingement.The results of the current experiments show that increasing the volume flow rate of the cooling fluid improves the heat transfer between the free liquid jet and the hot copper plate.Moreover, using nanofluid jet enhances the heat transfer.Additionally, increasing the surface area enhances the heat transfer between the cooling fluid and the hot plate and decreases the cooling time.Finally, it was noted that surface shape, impingement Reynolds number and nanofluid concentration affect the heat transfer enhancement processsignificantly.The accumulative effect of using nanafluid jet 2% with corrugated surface with higher flow rate on Nusselt number can reach 185%. On the other hand, using a dispersant for the nanofluid as polyethylene glycol keeps the nanofluid suspension and prevents agglomeration, but reduces its heat transfer enhancement effect.

Continuous miniaturization and high-end demand for digital devices and appliances have contributed to a dramatic rise in heat flux generation. As a result, traditional coolants and cooling methods are increasingly falling short of meeting the ever-increasing cooling requirements and challenges of these electronic devices that produce high heat. In this article, the recent studies performed on the use of channels in microelectronic devices, electronic devices, and refrigeration cooling applications are reviewed. Another intention behind this review is to explain the challenges of different design for channels for electronic cooling. Many researchers have reported on micro/mini channel heat sinks for cooling electronics for the past 5 years. Furthermore, the prospects for future study and the issues emerging in this field are introduced and explored. Keyword: Microelectronics, Electronics, Refrigration.

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, 0.3), inlet velocity (Vin = 0.015, 0.030, 0.045 m/s), and bottom wall temperature (Twall = 299.15, 303.15, 315.15, 350.15 K) are 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 NEPCM slurry as an advanced coolant. The maximum Nusselt number when NEPCM slurry (C = 0.3) with Vin = 0.015, 0.030, 0.045 (m/s) is employed, are 2.27, 1.81, 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 PCM particles due to partial melting of nanoparticles in this range. While, the latter phenomena is due 1 Corresponding Author. 2 to the lower capability of NEPCM particles and consequently coolant in absorbing heat at coolant temperatures higher than the temperature correspond to fully melted NEPCM. It was observed that NEPCM slurry has a drastic effect on Euler number, and with increasing volume fraction and decreasing inlet velocity, the Euler number increases accordingly.

In situ tests are suitable to confirm the real thermal performance of building
components, and several significant on-site measurement techniques have been studied in literature. However, among them the Thermometric (THM) method has been poorly examined by the scientific community, thus having opportunities for improvement, being a quite a new and non-standardized technique. The theory behind this technique is the Newton’s law of cooling
and the main issue is associated to the heat transfer coefficient for which there is no agreement about the value to use. Here, a simple experimental apparatus characterized by a vertical heated sample, suitably thermally insulated was realized. Sensors were installed and direct heat flux
measurements through a heat flux plate were performed and compared with (i) the heat flows obtained through the THM method (test conducted using the internal heat transfer coefficient recommended by the ISO 6946) and (ii) the heat fluxes obtained through the proposal of an enhanced THM method based on dimensionless groups analysis, thus requiring data processing based on convective and radiative components.

The present study focused on carrying out the creep analysis in an isotropic thick-walled composite cylindrical pressure vessel composed of aluminum matrix reinforced with silicon-carbide in particulate form. The creep behavior of the composite material has been described by the threshold stress based creep law. The values of stress exponent appearing in the creep law were selected as 3, 5 and 8. The constitutive equations were developed using well known von-Mises yield criteria. Models were developed to find out the distributions of creep stress and strain rate in thick-walled composite cylindrical pressure vessels under internal pressure. In order to obtain the stress distributions in the cylinder, the equilibrium equation of the continuum mechanics and the constitutive equations are solved together. It was observed that the radial stress, tangential stress and axial stress increases along with the radial distance. The cross-over was also obtained almost at the middle region of cylindrical vessel for tangential and axial stress for different values of stress exponent. The strain rates were also decreasing in nature along the entire radius.

One ef cient method of cooling electronics is to use a closed-loop two-phase thermosyphon system. The setup tested here utilizes three small evaporator s connected in parallel, each made from a small block of copper in which ve vertical channels with diameter 1.5 mm and length 15 mm were drilled. The article presents the experimental results in terms of heat transfer coef cients of smooth surfaces as well as for threaded surfaces. Tests were done at different heat uxes while maintaining constant system pressure. Tests were performed with heat loads of 30-450 W dissipated through the system. Two different refrigerants, R134a and R600a, were tested. The experimental two-phase ow heat transfer coef cients were compared to correlations from the literature.

Most electronic components whose duties are attracted to maximum power efficiency required of a system to dissipate internal heat out of such components. MOSFETs, CMOS and special Processors, whose applications geared towards high voltages must have a system to effectively dissipate heat for maximum performance. Components with embedded heat sink have advantage and function effectively, the fact remain that the heat sink material is that which can dissipates heat during conduction of heat from the component. This paper considered various heat sink materials for proper heat transfer, radiation and dissipation. Aluminum, Copper, tungsten and Zinc were evaluated having various thermal conductivity and dissipation, and briefly heat-sink materials characteristics: weight, conductivity and quick thermal dissipation of heat from the heatsink materials were discussed. And was observed that Aluminum heat sink material was more preferable during our evaluation and it was observed that the material is best for our modern day's high thermal components. Aluminum heat sink materials have a nomenclature of quick heat transfer, lighter in weight, Aluminum material is stability since thermal condition increases during high performance of the equipment, though some materials from the analysis have high conductivity but their weight and their radiation efficiency can affect the components which is firmly attached to it, considering new innovation in technology is revolving toward miniaturization of component sizes.

This work qualifies and quantifies the nanofluidic natural convective phenomena occurring in a hemispherical enclosure used for electronics applications. This cavity consists of a disk thermally insulated on its rear face, an active cube centered on the disk which generates a constant heat flux and an isothermal dome. The disc of the cavity remains horizontal while its dome is oriented either upwards or downwards. The considered nanofluid is a mixture of water with metallic ZnO nanoparticles. In order to examine the influence of these nanoparticles on the natural convective heat transfer, three values of the volume fraction considered: 0% (pure water), 1% and 5%. The dimensionless governing system of the problem under consideration is solved by means of the control volume method in combination with the SIMPLE algorithm. The structured mesh is composed of triangular surfacic elements and tetrahedral in the volumic domain. Temperature and velocity distributions are presented for some ...

This study represents a numerical investigation of the compatibleness of minichannel heat sink with high heat dissipation rate and the fluid flow patterns inside minichannels for integrating secondary channel (or interconnector). A novel shape, rectangular fin with rounded ends, mini-channel heat sink was proposed to compare with the thermal performance of rectangular finned and oblique finned mini-channel heat sink. In this study, hydrodynamic characteristics of water as coolant was considered in the single-phase regime, and the flow was considered under laminar flow conditions at Reynolds numbers range of 150 to 1050 with a constant heat flux of 200 KW/m2 at the bottom surface of the minichannel heat sink. Thereafter, a Performance Evaluating Criteria (PEC) was implemented for all cases to compare with the conventional mini-channel heat sink. The results showed that the overall Nu number for newly proposed rectangular fin with rounded ends shape minichannel heat sink increases slightly with Re number when compared with the conventional mini-channel heat sink. The slight increment of Nu number was recorded at Re = 1050 for the newly proposed mini-channel heat sink up to 8% as compared to the conventional parallel flow mini-channel heat sink.

This research aims to study the effect of inclination angle on the heat transfer performance of a Closed-Loop Oscillating Heat-Pipe with Check Valve (CLOHP/CV) with fi ns on the tube wall. The heat pipe was made from a copper pipe, and the capillary tube had a 5.0 mm inside diameter. There were 24 meandering turns with two check valves. The lengths of the evaporator section and condenser section were 200 mm and the adiabatic section was 100 mm. The working fl uid used was water with a fi lling ratio of 50% of the total volume of the tube. The temperatures for the evaporator section were 60, 70 and 80 o C. Inclination angles were 0, 20, 40, 45, 60, 80 and 90 degrees from the horizontal axis were established. It was found that when the variable temperature increased from 60, 70 to 80 o C heat fl ux and thermal effi ciency increased. In addition, when the inclination angle increased from 0, 20, 40, 45, 60, 80 and 90 degrees heat fl ux and thermal effi ciency increased. Therefore, this research concluded, from the experiment that the heat pipe was a CLOHP/CV. The maximum specifi c heat fl ux equaled 1,926.97 W/m 2 and the maximum thermal effectiveness equaled 0.44, the operating temperature was 80 °C and an angle of inclination to the horizontal axis was 90 o

There is an increasing demand for efficient cooling techniques in computer industry to dissipate the associated heat from the newly designed and developed computer processors to accommodate for their enhanced processing power and faster operations. Such a demand necessitates researchers to explore efficient approaches for central processing unit (CPU) cooling. Consequently, heat pipes can be a viable and promising solution for this challenge. In this chapter, a CPU thermal design power (TDP), cooling methods of electronic equipments, heat pipe theory and operation, heat pipes components, such as the wall material, the wick structure, and the working fluid, are presented. Moreover, we review experimentally, analytically and numerically the types of heat pipes with their applications for electronic cooling in general and the computer cooling in particular. Summary tables that compare the content, methodology, and types of heat pipes are presented. Due to the numerous advantages of the heat pipe in electronic cooling, this chapter definitely leads to further research in computer cooling applications.

Lightweight designs and demanding safety requirements in automotive industry are increasingly promoting the use of Advanced High Strength Steel (AHSS) sheets. Such steels present higher strength (above 800 MPa) but lower ductility than conventional steels. Their great properties allow the reduction of the thickness of automobile structural components without compromising the safety, but also introduce new challenges to parts manufacturers. The fabrication of most cold formed components starts from shear cut blanks and, due to the lower ductility of AHSS, edge cracking problems can appear during forming operations, forcing the stop of the production and slowing down the industrial process. Forming Limit Diagrams (FLD) and FEM simulations are very useful tools to predict fracture problems in zones with high localized strain, but they are not able to predict edge cracking. It has been observed that the fracture toughness, measured through the Essential Work of Fracture (EWF) methodology, is a good indicator of the stretch flangeability in AHSS and can help to foresee this type of fractures. In this work, a serial production automotive component has been studied. The component showed cracks in some flanged edges when using a dual phase steel. It is shown that the conventional approach to explain formability, based on tensile tests and FLD, fails in the prediction of edge cracking. A new approach, based on fracture mechanics, help to solve the problem by selecting steel grades with higher fracture toughness, measured by means of EWF. Results confirmed that fracture toughness, in terms of EWF, can be readily used as a material parameter to rationalize cracking related problems and select AHSS with improved edge cracking resistance.

IGBT power modules have been equipped with temperature/humidity sensors and integrated into a power converter system from the wind-power application. While exposed to climatic cycles, the power converter has been tested power-in-theloop in a climate chamber. The test profile is a sequence of actual stress conditions recorded in a wind turbine converter operating in the field.
During the tests, the internal conditions of the power modules and the power cabinet have been monitored. The resulting microclimates are
examined when varying electrical loads coincide with climatic cycles.