The present work investigates, the performance of a nonlinear longitudinal pin fin with all temperature-dependent linear/nonlinear parameters. The solution of the problem is evaluated with tip ...conditions ranging from unchallenging ones such as constant temperature, insulated tip, etc. to realistic ones such as convective and radiative tip. The non-linear governing equations are solved using Pdepe solver. The numerical results are validated with literature and found to be well in agreement. The experiments are performed and it is found that the results from experimental and numerical process are following the same trends. The uncertainty analysis is also done for the input parameters of experimental setup. The study investigates the effect of conduction-convection and conduction-radiation parameters on temperature profile and efficiency. Furthermore, the effect of non-linear temperature-dependent parameters i.e., n,β and γ on the temperature distribution and efficiency is too investigated. It is found that the effect of β and γ are insignificant on both temperature and efficiency. The effect of tip parameters i.e., Nbr and Bi are also investigated. The opposite effect of Biot number is observed on temperature profile on the tip as compared to surface convection. The experimental results are also presented after the numerical analysis for the sake of realization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Finned metal foam heat sinks are well-known because of their excellent performance in cooling of powered electronics. In this study, three-dimensional transient numerical simulations of finned ...aluminum foam heat sinks in a forced convection of air were carried out using commercial COMSOL. The geometry under consideration consists of an array of finned aluminum foam heat sinks mounted on heater blocks and placed on a plate in a horizontal channel. Heat sink aluminum foam regions were considered as porous media with a local non-equilibrium thermal model to evaluate thermal characteristics, while the Forchheimer-Brinkman extended Darcy model is considered for the flow analysis. Our main concern in the present study is to evaluate the transient thermal–hydraulic behavior and the cooling performance under constant flux heat sources while varying the Reynolds number and variable morphological parameters of the aluminum foam, i.e., porosity (ε) varied from 0.85 to 0.95. The thermal performance ratio and the average Nusselt number of the finned aluminum foam heat sinks are 23.14% and 30%, respectively, larger than the finned aluminum heat sinks. As the Reynolds number increases, the thermal characteristics are enhanced, and the pressure drop is increased. An increase in porosity causes a reduction in heat transfer rate and an elevation of pressure drop.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Loop heat pipe with a pouring porous wick for low-cost manufacturing was designed and tested.•LHP could start up from 5 W to 80 W with the evaporator surface temperature below 100 °C.•The maximum ...heat flux of the LHP was in the horizontal orientation 11.33 W/cm2.
The cost of manufacturing loop heat pipes (LHP) makes it difficult for engineering applications to be popularized on the ground. As for LHP components, the wick fabrication is the most difficult, important and expensive process. In this paper, we adopted a new way of the pouring porous wick. The morphology of the pouring porous wick was observed with the aid of scanning electronic micro-scope (SEM). Surface morphology analysis revealed that pore distribution was relatively uniform, and the pore size roughly distributed between 3 μm and 10 μm. At high resolution, Micro-structure of the pouring porous wick was similar to that of sintered biporous wick that distributed large pores and small pores. The selected samples’ porosity was tested by means of Archimedes drainage method, and ranged from 0.35 to 0.45. Meanwhile, the LHP with a pouring porous wick was constituted, and its transient performance was investigated at different heat sink temperatures. The experimental results demonstrated that this LHP system could start up at a heat load range from 5 W to 80 W with the evaporator surface temperature below 100 °C in the horizontal orientation. The LHP heat transfer characteristics were analyzed based on continuous operation with variable heat load.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The melting of NePCM is numerically addressed.•The FVM with enthalpy-porosity technique are used.•Nanoparticles of copper (Cu) with different volume fractions and shapes are inserted to enhance the ...heat transfer.•The effect of NePCM quantity and shape is analysed.•New correlations are developed for operating time and temperature.
In this paper, a numerical study is carried out to investigate the melting process of a nano-enhanced phase change material (NePCM) in a latent heat thermal energy storage unit (LHTESU) with insertion of Cu nanoparticles. The use of such a strategy provides passive cooling of a protruding electronic component attached to a substrate. The governing equations of heat transfer are solved using the enthalpy-porosity technique and the finite volume method based using a personal FORTRAN code. An investigation of the effect of the PCM quantity is carried out taking into account three different values of the characteristic length lo (0.06 m, 0.08 m and 0.10 m) which represents the PCM quantity. The effect of nanoparticle characteristics, including volume fraction and shape factor on melting rate, are also discussed. The results showed that the maximum operating temperature of the electronic component decreases by 2.9 °C with an insertion of a nanoparticles fraction of 0.04 and a characteristic length of 0.08 m. For the same characteristic length, the melting time is 8630 s, 8460 s and 8290 s with nanoparticles fraction of 0.00, 0.02 and 0.04, respectively. With the nanoparticles fraction of 0.04, the amount of sensible heat stored within the PCM increases by 1.3% and the latent heat decreases by 1.1%. In addition, the insertion of nanoparticles with a shape factor of 16.1 reduces the maximum operating temperature of the electronic component by 2.5 °C. Correlations, giving the electronic component maximum working time and the plateau temperature, were developed using the asymptotic computational fluid dynamics technique (ACFD).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•We present a monolithic methodology for the CFD simulation of cooling electronics.•The IBM was extended to include the radiation exchange between surfaces.•The implementation was verified by several ...simulations of benchmark cases.•The thermal behavior of a car component was studied simulating some configurations.
Considering that the most common reason for electronic component failure is the excessive temperature level, an efficient thermal management design can prolong the operating life of the equipment, while also increasing its performance. Computational Fluid Dynamics and Heat Transfer (CFD&HT) have proved valuable in the study of these problems, since they can produce reliable fields of fluid flow, temperature and heat fluxes. Moreover, thanks to the recent advances in high-performance computers, CFD&HT numerical simulations are becoming viable tools to study real problems. The conventional approach, which consists of employing body-conformal meshes to the solids and fluids regions, often results costly and ineffective in applications with very complex geometries and large deformation. For these cases, an alternative approach, the Immersed Boundary Method (IBM), which employs a non-body conformal mesh and discretizes the entire domain using a special treatment in the vicinity of the solid-fluid interfaces, has proven more effective. In this work, an IBM was extended to simulate problems with conjugate heat transfer (CHT) boundary conditions taking into account the radiative exchange between surfaces. It was designed to work with any type of mesh (domain discretization) and to handle any body geometry. The implementation was validated and verified by several simulations of benchmark cases. Moreover, the IBM was applied in an industrial application which consists of the simulation of a Smart Antenna Module (SAM). All in all, the carried out studies resulted in a monolithic methodology for the simulation of realistic situations, where all three heat transfer mechanisms can be considered in complex geometries.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
As part of the research in the field of thermal control of electronic components, a phase change material is confined in a liquid and is heated vertically on one side by a hot plate. The presence of ...the liquid around the phase change material prevents the formation of air bubbles produced in case of direct contact between the hotplate and the phase change material (extends the lifetime of the phase change material by reducing overheating zones). It improves heat transfer by increasing the thermal conductivity around the phase change material (raising the thermal exchange surface) and by accelerating the convective transfer. This work examines experimentally and numerically the effect of the water on the phase change material and on the heating plate. The water is used around the phase change material and a comparative study of the comportment of some important parameters like the melt front form, melting time, flow direction, temperature, and operating time is realized. It is found that the presences of the liquid around the phase change material seems to be more interesting for a thermal protection role than the standard case of the phase change material directly heated by the hotplate.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This experimental study deals with cooling electronics contained in a hemispherical cavity whose cupola is maintained isothermal, being its base inclined at an angle varying from 0° (horizontal disc ...with the cupola oriented upwards) to 135°. The active component is a dome centered on this base. The space between the differentially heated elements of the assembly is filled with a porous medium of high porosity saturated by a water-copper nanofluid whose volume fraction varies between 0% (pure water) and 7%. The Rayleigh number based on the radius of the cupola reaches high values up to 7.29 × 10
10
given the important surface heat flux generated by the device during operation. The ratio between the thermal conductivity of the solid matrix and that of the base fluid ranges between 0 (interstitial volume without porous medium) and 41.4 corresponding to the intended applications. This experimental study done with an industrial prototype at scale 1 quantifies the natural convective heat transfer via the Nusselt number determined for many configurations obtained by varying the solid-fluid thermal conductivity ratio, the inclination angle, the Rayleigh number, and the volume fraction. The study clearly shows that the cooling performance of the Cu-H
2
O nanofluid degrades with its age and the number of times it has been used. Analysis of the results reproducibility also proves the irreversibility of the performance. The measured values were compared with those obtained in a recent numerical study based on the volume control method. The observed deviations taking into account the experimental uncertainty margins validate the mathematical model implemented in the numerical approach.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A new configuration of a hybrid system for cooling electronics using a Vortex Tube is presented. The optimization of the geometry and functional parameters is based on the assumption that the thermal ...interaction between the moist air stream and the heat-generating electronic board, and the phase change of liquid water vaporization occurs simultaneously. The first step of this analysis is focused on the optimal geometry of the system, while the second step identifies the Vortex Tube regime that maximizes its coefficient of performance. The cooling below the adiabatic air saturation temperature and the increase of moisture transport explain the high performance of the new device. Our results shed some light on the practical procedure for the optimal configuration of the new system.
Two-phase liquid vapor cooling is a promising technology option to achieve enhanced heat removal from integrated circuit components, which can drastically outpace its single-phase counterparts by ...leveraging the latent heat of the fluid. However, its application has been limited due to its inherent system complexity and relative system instability. The two-phase cooling control loop that provides the ability to sustainably utilize much less expensive working fluids such as water with far superior heat-transfer coefficients compared to traditional single-phase approaches has been revisited as a solution option for addressing the ever-increasing thermal demand placed on electronic components. Also, since typical integrated circuit components require the die temperature to remain below junction temperature, usually at or below 100°C, the system pressure should be maintained below atmosphere such that the saturation temperature of water can be reduced well below 100°C.The current study evaluates the pressure drops and heat transfer characteristics of water coolant flow at sub-atmospheric pressures for two different cooling configurations: 1) bare-die under jet impingement flow showcasing effective heat transfer coefficient well over 10 W/cm 2 -°C and 2) microchannel cold plate with thermal resistances less than half that of single-phase cooling with similar flow conditions. It has been demonstrated under variable flowrate and heat-flux conditions leveraging a sub-ambient pressure environment coupled with specific fluid preheating and pressurizing differential conditions, very capable and sustainable thermal cooling performance can be achieved for both configurations.
Les travaux de cette thèse portent sur le refroidissement descomposants électroniques de puissance par métal liquide. Les efforts se sontconcentrés plus particulièrement autour de deux fonctions : la ...pompeélectromagnétique servant à mettre le fluide en mouvement et le refroidisseur àminicanaux situé sous la source de dissipation.Le mémoire de thèse se structure en quatre chapitres équivalents. Dans lepremier, l’apport des métaux liquides pour le refroidissement des composantsactifs de puissance est démontré. Dans un deuxième temps, l’étude théorique etexpérimentale d’une pompe électromagnétique à conduction est effectuée. Lesystème de refroidissement est plus particulièrement abordé dans le troisièmechapitre. Enfin, des réflexions sur la mise en oeuvre des refroidisseurs à métauxliquides en électronique de puissance sont discutées dans la dernière partie.Grâce à elles, nous voyons que le champ d’application de ces travaux favorisel'émergence de solutions innovantes pour la gestion thermique des composantsélectronique de puissance.
The work presented in this Phd manuscript deals with cooling powerelectronics devices using an electrical conductive fluid. Two important functionshave been considered: the study and the realization of the electromagnetic pumpwhich circulated the fluid in the cooling loop. The second function was study andrealization of the cooler which evacuated the heat from the electronics device.This document has four chapters: introduction to power electronics coolingsystem with liquid metal, electromagnetic pump study, cooler study, and at lastreflections on realizing liquid metal cooler for power electronics devices. Theresults of this work concern a wide range of applications, especially towards newthermal management solutions of power electronics devices.
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