Modélisation et simulation du refroidissement des éléments à base de composants électroniques par des nanofluides

Dans cette thèse, nous avons étudié et modélisé par une simulation numérique en régime laminaire et stationnaire, le refroidissement par les écoulements convectifs des composants électroniques en utilisant des nanofluides, dans le but d’amélioration des échanges thermiques et pour augmenter l'efficacité du refroidissement. Pour cette raison, nous avons réalisé plusieurs études sous forme des applications. La première application a examiné numériquement le transfert thermique dans trois géométries différentes des mini-canaux en utilisant nanofluide Cu–eau avec une concentration volumique de 0.05. Quant aux deuxième, quatrième et troisième applications consacrées à l'étude de l'effet du type de nanofluides et de leurs concentrations volumiques, ainsi que de l'effet des sections et formes des mini canaux sur l'échange thermique et sur le refroidissement du composant électronique dans ces études, nous avons utilisé trois types différents de nanofluides à différentes concentrations et ces études ont montré que les minicanaux du troisième et neuvième cas améliorent le transfert de chaleur par rapport aux autres cas ainsi que la valeur de la température maximale de jonction du composant électronique et que l'utilisation de nano-fluide diamant-eau donne des coefficients de transfert de chaleur significativement plus élevés que les nanofluides Ag-eau et Cu-eau. Et L'augmentation de la concentration de nanoparticules dans le fluide de base (eau) permet d'améliorer le coefficient de transfert de chaleur. La cinquième application vise à déterminer l'effet de la position de l'obstacle à l'intérieur d'un mini canal horizontal sur le refroidissement du composant électronique en utilisant de nano-fluides avec une fraction volumique de 0,05. Dans cette étude, nous avons constaté que la position de l'obstacle dans le douzième cas offre de bien meilleures performances thermiques que les autres cas. Dans la sixième application, nous avons étudié l'effet de l'ajout des ailettes en forme de trois quarts du cercle et des ailettes en parallélogramme dans les micro-canaux sur les performances thermiques en utilisant un nanofluide Diamant - eau avec une fraction volumique de 0,05. Dans cette étude, le flux thermique généré par les composants électroniques est égal à q = 100 W /cm2 . Le nombre de Reynolds (Re) a été pris entre 200 et 600. Les résultats ont montré que les micro-canax dans le dix-septième cas qui contiennent les ailettes en forme de parallélogramme ont donné une amélioration de transfert thermique

Two Phase Flow, Phase Change and Numerical Modeling

The heat transfer and analysis on laser beam, evaporator coils, shell-and-tube condenser, two phase flow, nanofluids, complex fluids, and on phase change are significant issues in a design of wide range of industrial processes and devices. This book includes 25 advanced and revised contributions, and it covers mainly (1) numerical modeling of heat transfer, (2) two phase flow, (3) nanofluids, and (4) phase change. The first section introduces numerical modeling of heat transfer on particles in binary gas-solid fluidization bed, solidification phenomena, thermal approaches to laser damage, and temperature and velocity distribution. The second section covers density wave instability phenomena, gas and spray-water quenching, spray cooling, wettability effect, liquid film thickness, and thermosyphon loop. The third section includes nanofluids for heat transfer, nanofluids in minichannels, potential and engineering strategies on nanofluids, and heat transfer at nanoscale. The forth section presents time-dependent melting and deformation processes of phase change material (PCM), thermal energy storage tanks using PCM, phase change in deep CO2 injector, and thermal storage device of solar hot water system. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society

Hydrothermal performance of aluminium oxide/water and cupper oxide/water nanofluids in divergent-convergent minichannel heatsink with dimples

The recent trend in technological advancements in electronic devices offers high-performance compact systems. However, highly concentrated heat flux restricted their efficiency and reduced the Mean time before failure (MTBF). Many researchers exploit different passive heat transfer techniques like geometry modification to alleviate high heat flux. Despite the potential of divergent-convergent minichannel in mixing flow and a higher proportion of surface area to volume than conventional channels, research on it is inadequate. The study aims to develop and examine the influence of combined multi passive heat transfer techniques in an electronic device minichannel heatsink towards further augmenting heat transfer with minimal pressure loss and thermal resistance. This study combines corrugated geometry with innovative high thermal conductive nanofluid as hybrid passive techniques. The experimental validation concerning measured and predicted pressure drop and Heat Transfer Coefficient data indicated a maximum deviation of 19.1% and 13.8%, respectively. The numerical analysis employed a commercial CFD code based on the finite volume method. The investigation of forced convective heat transfer and nanofluids’ flow achieved with single-phase and two-phase mixture models in a divergent-convergent minichannel heatsink (DCMH) having a hydraulic diameter of 1.42mm. The numerical investigation employed Al2O3/water and CuO/water nanofluids with 0 - 2.5 volume%, fluid velocity from 3 – 6 m/s (corresponding to Reynolds number (5000 – 10000), and the inlet temperature 303 K. The two-phase model exhibits better agreement with established correlation than the single-phase model. A numerical analysis of an enhanced geometry with dimples on the minichannel floor was developed to augment the hydrothermal performance. The results found that the effects of principal parameters on the chip heat flux demonstrated the heat transfer coefficient’s growth with a rise in volume fractions and fluid velocity. Both nanofluids indicated better performance enhancement than water. Al2O3/water and CuO/water nanofluids augment over water by about 6.44% and 8.33% for 2.5 vol.%. Also, pressure loss rises when the velocity increases. The pressure loss relative to water at 2.5 vol.% and 5.5 m/s yields 15.14% and 18.56 % for Al2O3/water and CuO/water. The highest pumping power is 0.057 W for all the cases, which indicates the pumping demand is much lower than 1.0 W. The introduction of dimples on DCMH has considerably advanced hydrothermal performance with a PEC of 1.214 over the smooth model. The overall results established that the combined effects of DCMH and nanofluids have significantly improved the heat sink’s hydrothermal performance and can provide the desired heat dissipation from the enclosed chips in compact electronic devices

Advances in Heat and Mass Transfer in Micro/Nano Systems

The miniaturization of components in mechanical and electronic equipment has been the driving force for the fast development of micro/nanosystems. Heat and mass transfer are crucial processes in such systems, and they have attracted great interest in recent years. Tremendous effort, in terms of theoretical analyses, experimental measurements, numerical simulation, and practical applications, has been devoted to improve our understanding of complex heat and mass transfer processes and behaviors in such micro/nanosystems. This Special Issue is dedicated to showcasing recent advances in heat and mass transfer in micro- and nanosystems, with particular focus on the development of new models and theories, the employment of new experimental techniques, the adoption of new computational methods, and the design of novel micro/nanodevices. Thirteen articles have been published after peer-review evaluations, and these articles cover a wide spectrum of active research in the frontiers of micro/nanosystems

Investigation of entropy generation and thermohydraulics of forced and mixed convection of Al₂O₃-Cu/water in a parabolic trough receiver tube

Heat transfer has long been a vital part of human life. Many sources have focused on increased heat transfer. Various industries, such as solar water heating systems, solar chemistry, solar desalination plants, and concentrating solar power plants, food processing plants, petrochemical plants, refrigeration systems and air conditioning equipment, and condensing central heating exchangers, etc., face the challenges of effective utilisation, conservation, and recovery of heat. In modern times, increasing the rate of heat transfer in concentrating solar collectors such as parabolic troughs by using various passive approaches have proven to be very effective. When passive approaches are used, more pumping power is needed to move the fluid through the receiver. Manufacturing of parabolic trough receiver tubes requires a significant financial commitment due to the high expenses of both capital and operation. Therefore, it is essential to develop parabolic trough receivers that are efficient. Several methods, such as heat transfer enhancement and minimisation of entropy generation, are used to do this. The current investigation makes use of tube insert technology and nanoparticle flow to achieve optimal thermohydraulic and thermodynamic designs. Previous research on fluid flow and heat transfer in a regular pipe (PT) and a pipe equipped with an elliptical-cut twisted tape insert (TECT) and a traditional twisted tape insert (TPT) has not been conducted, particularly emphasizing the utilization of hybrid nanofluid as the working medium. However, previous works on water and nanofluid do exist. In addition, the Bejan number and the generation of total entropy are not examined on tubes supplied with an elliptical-cut and classical twisted tape insert for different fluids. Hence, in this study, heat transfer and entropy generation in a turbulent flow of an Al₂O₃-Cu/water hybrid nanofluid in a plain tube with classical and elliptical-cut twisted tape inserts are investigated numerically. The current study focuses on the heat transmission augmentation and thermodynamic irreversibility of steady and unsteady turbulent flows through pipes with elliptical-cut and classical twisted tape introduced under uniform or non-uniform well heat flux for water, hybrid-nanofluids (Al₂O₃-Cu/water), and nanofluids (CuO/water). This work uses Star-CCM+ for numerical simulations. The realizable k-ℇ model is employed to simulate the turbulent flow computationally. The findings are utilised to determine which type of tube and fluid provides the highest performance by quantifying gains in steady state (friction factor, heat transfer, and thermal performance factor) and unsteady state (transient heat transfer). The total entropy generation has been examined in this PhD study to determine the type of tube and fluid that reduces entropy generation. The results indicate that the heat transfer augmentation and thermal performance factor provided by the tube fitted with elliptical-cut twisted tape are greater than those provided by the tube supplied with classical twisted tape and the ordinary tube. This is because the pipe supplied with elliptical-cut twisted tape mixes the fluids better than the tube supplied with traditional twisted tape and the ordinary tube. Also, when the number of nanoparticles increases, heat transmission and thermal performance factors increase. Furthermore, TECT, hybrid nanofluids, and mass concentrations of nanoparticles affect the rate of total entropy production. The mixed convection of Al₂O₃-Cu/water hybrid nanofluid is also investigated in a vertical pipe supplied with elliptical-cut twisted tape inserts. Further, the local and total entropy production as well as Bejan number of the system are calculated. The results clearly demonstrate the effect of mixed convection on heat transfer, thermal performance factor, and entropy production. Where the factor of thermal performance and the rate of heat transfer increase of pipe systems under mixed convection exceed those under forced convection. Moreover, mixed convection has a significant impact on the minimisation of the total entropy production