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1 – 10 of 197Ali Akbar Izadi and Hamed Rasam
Efficient thermal management of central processing unit (CPU) cooling systems is vital in the context of advancing information technology and the demand for enhanced data…
Abstract
Purpose
Efficient thermal management of central processing unit (CPU) cooling systems is vital in the context of advancing information technology and the demand for enhanced data processing speeds. This study aims to explore the thermal performance of a CPU cooling setup using a cylindrical porous metal foam heat sink.
Design/methodology/approach
Nanofluid flow through the metal foam is simulated using the Darcy–Brinkman–Forschheimer equation, accounting for magnetic field effects. The temperature distribution is modeled through the local thermal equilibrium equation, considering viscous dissipation. The problem’s governing partial differential equations are solved using the similarity method. The CPU’s hot surface serves as a solid wall, with nanofluid entering the heat sink as an impinging jet. Verification of the numerical results involves comparison with existing research, demonstrating strong agreement across numerical, analytical and experimental findings. Ansys Fluent® software is used to assess temperature, velocity and streamlines, yielding satisfactory results from an engineering standpoint.
Findings
Investigating critical parameters such as Darcy number (10−4 ≤ DaD ≤ 10−2), aspect ratio (0.5 ≤ H/D ≤ 1.5), Reynolds number (5 ≤ ReD,bf ≤ 3500), Eckert number (0 ≤ ECbf ≤ 0.1) , porosity (0.85 ≤ ε ≤ 0.95), Hartmann number (0 ≤ HaD,bf ≤ 300) and the volume fraction of nanofluid (0 ≤ φ ≤ 0.1) reveals their impact on fluid flow and heat sink performance. Notably, Nusselt number will reduce 45%, rise 19.2%, decrease 14.1%, and decrease 0.15% for Reynolds numbers of 600, with rising porosity from 0.85 to 0.95, Darcy numbers from 10−4 to 10−2, Eckert numbers from 0 to 0.1, and Hartman numbers from 0 to 300.
Originality/value
Despite notable progress in studying thermal management in CPU cooling systems using porous media and nanofluids, there are still significant gaps in the existing literature. First, few studies have considered the Darcy–Brinkman–Forchheimer equation, which accounts for non-Darcy effects and the flow and geometric interactions between coolant and porous medium. The influence of viscous dissipation on heat transfer in this specific geometry has also been largely overlooked. Additionally, while nanofluids and impinging jets have demonstrated potential in enhancing thermal performance, their utilization within porous media remains underexplored. Furthermore, the unique thermal and structural characteristics of porous media, along with the incorporation of a magnetic field, have not been fully investigated in this particular configuration. Consequently, this study aims to address these literature gaps and introduce novel advancements in analytical modeling, non-Darcy flow, viscous dissipation, nanofluid utilization, impinging jets, porous media characteristics and the impact of a magnetic field. These contributions hold promising prospects for improving CPU cooling system thermal management and have broader implications across various applications in the field.
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H.A. Kumara Swamy, Sankar Mani, N. Keerthi Reddy and Younghae Do
One of the major challenges in the design of thermal equipment is to minimize the entropy production and enhance the thermal dissipation rate for improving energy efficiency of…
Abstract
Purpose
One of the major challenges in the design of thermal equipment is to minimize the entropy production and enhance the thermal dissipation rate for improving energy efficiency of the devices. In several industrial applications, the structure of thermal device is cylindrical shape. In this regard, this paper aims to explore the impact of isothermal cylindrical solid block on nanofluid (Ag – H2O) convective flow and entropy generation in a cylindrical annular chamber subjected to different thermal conditions. Furthermore, the present study also addresses the structural impact of cylindrical solid block placed at the center of annular domain.
Design/methodology/approach
The alternating direction implicit and successive over relaxation techniques are used in the current investigation to solve the coupled partial differential equations. Furthermore, estimation of average Nusselt number and total entropy generation involves integration and is achieved by Simpson and Trapezoidal’s rules, respectively. Mesh independence checks have been carried out to ensure the accuracy of numerical results.
Findings
Computations have been performed to analyze the simultaneous multiple influences, such as different thermal conditions, size and aspect ratio of the hot obstacle, Rayleigh number and nanoparticle shape on buoyancy-driven nanoliquid movement, heat dissipation, irreversibility distribution, cup-mixing temperature and performance evaluation criteria in an annular chamber. The computational results reveal that the nanoparticle shape and obstacle size produce conducive situation for increasing system’s thermal efficiency. Furthermore, utilization of nonspherical shaped nanoparticles enhances the heat transfer rate with minimum entropy generation in the enclosure. Also, greater performance evaluation criteria has been noticed for larger obstacle for both uniform and nonuniform heating.
Research limitations/implications
The current numerical investigation can be extended to further explore the thermal performance with different positions of solid obstacle, inclination angles, by applying Lorentz force, internal heat generation and so on numerically or experimentally.
Originality/value
A pioneering numerical investigation on the structural influence of hot solid block on the convective nanofluid flow, energy transport and entropy production in an annular space has been analyzed. The results in the present study are novel, related to various modern industrial applications. These results could be used as a firsthand information for the design engineers to obtain highly efficient thermal systems.
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Jorge Lopez, Robert Hoffmann, Graham Emslie and Roseanne Armitage
Sleep disturbances, present in more than 90% of major depressive disorder (MDD) patients, are moderated by sex in adult MDD. In particular, slow-wave electroencephalographic…
Abstract
Sleep disturbances, present in more than 90% of major depressive disorder (MDD) patients, are moderated by sex in adult MDD. In particular, slow-wave electroencephalographic activity (SWA; 0.5-4 Hz) accumulation is low and dissipation impaired. This SWA abnormality in depressed adult males does not change with age, suggesting that SWA abnormality appears at early ages. The present study evaluated sex differences in SWA in adolescents with MDD compared to healthy controls. We evaluated regularized sleep-wake schedules at home for 5-7 days, followed by two consecutive nights of sleep EEG recording. The study included 104 participants, 52 symptomatic and depressed subjects (MDD: 20 males and 32 females) and 52 healthy controls (HC: 20 males and 32 females), aged 13-18 years. SWA power and dissipation, and duration and latencies to each Non-Rapid Eye Movement (NREM) sleep period were calculated for each group. Results showed that SWA accumulation in the first NREM period was lower and its dissipation across the night more irregular in MDD males compared to HC males (P<0.009). By contrast, SWA was equivalent in MDD and HC females. In conclusion, as reported in adult MDD, the accumulation and dissipation of SWA was abnormal in depressed adolescents, but only in males. SWA abnormalities in adolescent MDD may relate to different depressive symptoms in females and males. These results underscore the need to develop sex-specific therapies to enhance and restore SWA in depressed adolescents.
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This study aims to focus on a specific project marketing concept, i.e. “discontinuity,” and analyzes how this concept emerged in project marketing, becoming its key scholarly…
Abstract
Purpose
This study aims to focus on a specific project marketing concept, i.e. “discontinuity,” and analyzes how this concept emerged in project marketing, becoming its key scholarly embodiment, how it became decoupled from the increasingly service-intensive project business practice and what the relevance of discontinuity is for project marketers moving forward.
Design/methodology/approach
This study is built on a systematic literature review of 31 years (1993–2023) of publishing data from major marketing and management journals.
Findings
This study provides three findings. First, the author reveals the risks related to marketing scholars and practitioners losing sight of each other as business practices evolve much faster than scholarly research can keep up. Second, the author highlights the role of interdisciplinary collaboration in advancing conceptual innovations. Finally, the research elucidates the need for broader metatheoretical reflection to keep this research tradition on an upward trajectory.
Research limitations/implications
The aim of this study is not to criticize project marketing, as many strands of business-to-business (B2B) marketing face the same challenge, but to elucidate a need for conceptual innovations, collaboration with practitioners and other disciplines and broader metatheoretical reflection to keep this research tradition on an upward trajectory.
Originality/value
This study makes several contributions to the project marketing research tradition. First, it reviews the emergence and dissipation of the concept of discontinuity, drawing on semantical, etymological and epistemological insights. It also reflects on recent disruptions in the marketplace and envisions future research trajectories for this elusive concept. In addition, the author develops a conceptual framework that combines project types with exchange elements in project and service businesses. This conceptual framework helps elucidate what part of the exchange is continuing and what is discontinuing in the resulting business relationships. Furthermore, the research contributes to B2B marketing more broadly by highlighting the fleeting correspondence between theory and the real world. It underscores the need for constant updates to maintain relevance.
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Leiting Zhao, Kan Liu, Donghui Liu and Zheming Jin
This study aims to improve the availability of regenerative braking for urban metro vehicles by introducing a sensorless operational temperature estimation method for the braking…
Abstract
Purpose
This study aims to improve the availability of regenerative braking for urban metro vehicles by introducing a sensorless operational temperature estimation method for the braking resistor (BR) onboard the vehicle, which overcomes the vulnerability of having conventional temperature sensor.
Design/methodology/approach
In this study, the energy model based sensorless estimation method is developed. By analyzing the structure and the convection dissipation process of the BR onboard the vehicle, the energy-based operational temperature model of the BR and its cooling domain is established. By adopting Newton's law of cooling and the law of conservation of energy, the energy and temperature dynamic of the BR can be stated. To minimize the use of all kinds of sensors (including both thermal and electrical), a novel regenerative braking power calculation method is proposed, which involves only the voltage of DC traction network and the duty cycle of the chopping circuit; both of them are available for the traction control unit (TCU) of the vehicle. By utilizing a real-time iterative calculation and updating the parameter of the energy model, the operational temperature of the BR can be obtained and monitored in a sensorless manner.
Findings
In this study, a sensorless estimation/monitoring method of the operational temperature of BR is proposed. The results show that it is possible to utilize the existing electrical sensors that is mandatory for the traction unit’s operation to estimate the operational temperature of BR, instead of adding dedicated thermal sensors. The results also validate the effectiveness of the proposal is acceptable for the engineering practical.
Originality/value
The proposal of this study provides novel concepts for the sensorless operational temperature monitoring of BR onboard rolling stocks. The proposed method only involves quasi-global electrical variable and the internal control signal within the TCU.
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William H. Kaempfer, Edward Tower and Thomas D. Willett
We consider a domestic monopolist who is protected by an import quota on the product he produces. He faces a domestic demand curve which is characterized by a constant price…
Abstract
We consider a domestic monopolist who is protected by an import quota on the product he produces. He faces a domestic demand curve which is characterized by a constant price elasticity. He is unable to export and has an upward sloping marginal cost curve. We demonstrate that in this case his employment of labor rises with the import quota until imports rise to a fraction lie of domestic output where e is the elasticity of domestic demand. Thus, the employment maximizing quota sets permissible imports at a fraction of domestic output which is at least as high as the reciprocal of the elasticity of demand. We also make a case for liberalizing all the way right away, "cold turkey liberalization. "
This study examines put-call-futures parity in KOSPI 200 index futures and options markets for the sampling period between January of 2011 and December of 2013 in order to…
Abstract
This study examines put-call-futures parity in KOSPI 200 index futures and options markets for the sampling period between January of 2011 and December of 2013 in order to investigate whether option multiplier increasing affects on the arbitragee efficiency of an index option market and permanent relationship between futures and options markets by analyzing minute by minute historical index option and future intraday trading data.
What we find is that the arbitrage opportunities associated with put-call-futures parity increase to 5.16% from 1.75% after increasing option multiplier. Although there is no significant change of discrepancies in ATM options, a slight decrease of mispricing is found in the moneyness where call option is OTM. It turns out, however, that the arbitrage opportunities increase by 3.4 times in the moneyness below 0.97 or above 1.03, after increasing multiplier. Also ex-ante analysis shows that most of arbitrage opportunities disappear within one minute, but the speed of dissipation becomes to decrease in the moneyness where the liquidity of ITM options declines to be a very low level. Overall our results suggest that the arbitrage efficiency in the KOSPI 200 index option markets might be deteriorated after an increasing of option multiplier.
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Amar Messas, Karim Benyahi, Arezki Adjrad, Youcef Bouafia and Sarah Benakli
The purpose of this study, is to deals with capacity design (strong column – weak beam) in reinforced concrete frames, slightly slender, which depends on the determination of a…
Abstract
Purpose
The purpose of this study, is to deals with capacity design (strong column – weak beam) in reinforced concrete frames, slightly slender, which depends on the determination of a capacity ratio necessary to reach a structural plastic mechanism. To find the capacity ratio allowing to achieve a fairly ductile behavior in reinforced concrete frames, it is necessary to validate this concept by a non-linear static analysis (push-over). However, this analysis is carried out by the use of the ETABS software, and by the introduction into the beams and columns of plastic hinges according to FEMA-356 code.
Design/methodology/approach
This approach makes it possible to assess seismic performance, which facilitates the establishment of a system for detecting the plasticization mechanisms of structures. It is also necessary to use a probabilistic method allowing to treat the dimensioning by the identification of the most probable mechanisms and to take only those that contribute the most to the probability of global failure of the structural system.
Findings
In this study, three reinforced concrete frame buildings with different numbers of floors were analyzed by varying the capacity ratio of the elements. The results obtained indicate that it is strongly recommended to increase the ratio of the resistant moments of the columns on those of the beams for the Algerian seismic regulation (RPA code), knowing that the frameworks in reinforced concrete are widespread in the country.
Originality/value
The main interest of this paper is to criticize the resistance condition required by RPA code, which must be the subject of particular attention to reach a mechanism of favorable collapse. This study recommends, on the basis of a reliability analysis, the use of a capacity dimensioning ratio greater than or equal to two, making it possible to have a sufficiently low probability of failure to ensure a level of security for users.
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