Yuan Ma, Hui Tang and Chenglei Wang
This study aims at investigating the heat transfer characteristics of a nonsquare enclosure when hydrodynamic resistance is altered discontinuously along its inner surface…
Abstract
Purpose
This study aims at investigating the heat transfer characteristics of a nonsquare enclosure when hydrodynamic resistance is altered discontinuously along its inner surface. Particularly, it focuses on investigating how several essential factors collaboratively influence the natural convection, including the Rayleigh number (Ra), the aspect ratio (AR), the nanoparticle volume fraction (ϕ) and the locations of changing hydrodynamic resistance.
Design/methodology/approach
To achieve these objectives, an L-shaped enclosure of various AR is adopted, while zero local shear resistance is applied and modeled by stress-free (SF) patches of four distinct arrangements (corresponding to Cases 1–4). The nanofluid is modeled by Buongiorno’s two-phase model. The effects are explored using an in-house numerical framework based on a hybrid lattice Boltzmann-finite difference method with the total variation minimization scheme.
Findings
The results show that when Ra is sufficiently large, i.e. Ra = 105, SF patches can generally enhance the heat transfer performance regardless of other factors. However, the ways of achieving those enhancements are different, which mainly depend on the arrangement of the SF patches and AR but are nearly independent of ϕ. The maximum improvement of heat transfer can be achieved in Case 3 with AR = 0.6, Ra = 105 and ϕ = 0.04, where the averaged Nusselt number is enhanced by 8.89%.
Originality/value
This study presents a new scenario where the SF patches of various arrangements are applied to enhance the nanofluid natural convection of a nonsquared enclosure, and it reveals how the improvement is achieved and cooperatively affected by several important factors.
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Keywords
Mohamed Ouni, Fatih Selimefendigil, Besbes Hatem, Lioua Kolsi and Mohamed Omri
The purpose of this study is to analyze the impacts of combined utilization of multi-jet impinging cooling of nanofluids with magnetic field and porous layer on the cooling…
Abstract
Purpose
The purpose of this study is to analyze the impacts of combined utilization of multi-jet impinging cooling of nanofluids with magnetic field and porous layer on the cooling performance, as effective cooling with impinging jets are obtained for various energy systems, including photovoltaic panels, electronic cooling and many other convective heat transfer applications.
Design/methodology/approach
Finite element method is used to explore the magnetic field effects with the inclusion of porous layer on the cooling performance efficiency of slot nanojet impingement system. Impacts of pertinent parameters such as Reynolds number (Re between 250 and 1,000), strength of magnetic field (Ha between 0 and 30), permeability of the porous layer (Da between 0.001 and 0.1) on the cooling performance for flat and wavy surface configurations are explored.
Findings
It is observed that the average Nusselt number (Nu) rises by about 17% and 20.4% for flat and wavy configuration while temperature drop of 4 K is obtained when Re is increased to 1,000 from 250. By using magnetic field at the highest strength, the average Nu rises by about 29% and 7% for flat and wavy cases. Porous layer permeability is an effective way of controlling the cooling performance while up to 44.5% variations in the average Nu is obtained by varying its value. An optimization routine is used to achieve the highest cooling rate while the optimum parameter set is obtained as (Re, Ha, Da, γ, sx) = (1,000, 30, 0.07558, 86.28, 2.585) for flat surface and (Re, Ha, Da, γ, sx) = (1,000, 30, 0.07558, 71.85, 2.329) for wavy surface configurations.
Originality/value
In thermal systems, cooling system design is important for thermal management of various energy systems, including fuel cells, photovoltaic panels, electronic cooling and many others. Impinging jets are considered as effective way of cooling because of its ability to give higher local heat transfer coefficients. This paper offers novel control tools, such as magnetic field, installation of porous layer and hybrid nano-liquid utilization for control of cooling performance with multiple impinging jets.
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Emre Burak Ekmekcioglu, Mahmure Yelda Erdogan and Alptekin Sokmen
The purpose of this study is to test the moderating role of career-enhancing strategies (CESs) in the relationship between career commitment (CC) and subjective career success…
Abstract
Purpose
The purpose of this study is to test the moderating role of career-enhancing strategies (CESs) in the relationship between career commitment (CC) and subjective career success (CS).
Design/methodology/approach
Data were collected from 217 full-time employees working for three different sectors in Ankara, Turkey. The participants were asked to respond to a self-reported survey. The hypotheses were tested using a hierarchical regression analysis.
Findings
The results indicated that CC had a significant and positive effect on subjective CS. Furthermore, the positive relationship between CC and subjective CS was stronger for employees with a high level of self-nomination and for employees with a high level of networking. However, creating career opportunities did not moderate the effects of CC on subjective CS.
Research limitations/implications
Because this study had a cross-sectional research design, causality cannot be established among the study variables.
Practical implications
The findings suggest a better understanding of the way CC is able to affect subjective CS through the networking and self-nomination CESs.
Originality/value
This study is original, in that no previous studies have investigated the moderating role of CESs in the relationship between CC and subjective CS.