C.V. Raghavarao and S.T.P.T. Srinivas
A parametric spline function approximation is used to study the steady combined convection of a Boussinesq fluid contained between two concentric rotating spheres. A spline…
Abstract
A parametric spline function approximation is used to study the steady combined convection of a Boussinesq fluid contained between two concentric rotating spheres. A spline function which depends on a parameter p > 0 is used for approximation. This approximation gives second order accuracy. The spheres which form the flow region are maintained at uniform but different temperatures and are allowed to rotate about a common vertical axis with different angular velocities. A uniform gravitational field acts in the direction parallel to that of the axis of rotation. The resulting flow patterns, temperature distributions, total heat flux and torque characteristics are presented for various cases considered and it is found that these results are in good agreement with the results of Dallman and Douglass in 1980.
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Syed Saqib Shah, Hakan F. Öztop, Rizwan Ul-Haq and Nidal Abu-Hamdeh
The purpose of this paper is to analyse the buoyancy flow, mass and heat transfer in coaxial duct under Soret and Dufour effect. The combined effects of the thermal-diffusion and…
Abstract
Purpose
The purpose of this paper is to analyse the buoyancy flow, mass and heat transfer in coaxial duct under Soret and Dufour effect. The combined effects of the thermal-diffusion and diffusion-thermo coefficients, as well as the Schmidt number, on natural convection in a heated lower coaxial curve were explored using the proposed physical model. The Dufour and Soret effects are taken into consideration in the energy and concentration equations, respectively.
Design/methodology/approach
The dominating mathematical models are converted into a set of non-linear coupled partial differential equations, which are solved using a numerical approach. The controlling non-linear boundary value problem is numerically solved using the penalty finite element method with Galerkin’s weighted residual scheme over the entire variety of essential parameters.
Findings
It was observed that different parameters were tested such as heat generation or absorption coefficient, buoyancy ratio, Soret coefficient, Dufour coefficient, Lewis number and Rayleigh number. Effect of Rayleigh number, absorption/generation and Dufour coefficient on isotherm are significantly reported. For greater values of Lewis number, maximum mass transfer in duct in the form of molecular particles is produced. Buoyancy ratio parameter decreases the average rate of heat flow and increases its mass transfer.
Originality/value
The main originality of this work is to make an application of Soret and Dufour effects in a coaxial duct in the presence of source sink.
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Mohamed A. Antar and Maged A.I. El‐Shaarawi
The purpose of this paper is to investigate the problem of entropy generation around a spinning/non‐spinning solid sphere subjected to uniform heat flux boundary condition in the…
Abstract
Purpose
The purpose of this paper is to investigate the problem of entropy generation around a spinning/non‐spinning solid sphere subjected to uniform heat flux boundary condition in the forced‐convection regime.
Design/methodology/approach
The governing continuity, momentum, energy and entropy generation equations are numerically solved for a wide range of the controlling parameters; Reynolds number and the dimensionless spin number.
Findings
The dimensionless overall total entropy generation increases with the dimensionless spin number. The effect of increasing the spin number on the fluid‐friction component of entropy generation is more significant compared to its effect on heat transfer entropy generation.
Research limitations/implications
Since the boundary‐layer analysis is used, the flow is presented up to only the point of external flow separation.
Practical implications
Entropy generation analysis can be used to evaluate the design of many heat transfer systems and suggest design improvements.
Originality/value
A review in the open literature indicated that no study is available for the entropy generation in the unconfined flow case about a spinning sphere.
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P. Saikrishnan, Satyajit Roy, H.S. Takhar and R. Ravindran
The purpose of this paper is to study the influence of thermally stratified medium on a free convection flow from a sphere, which is rotating about the vertical axis, immersed in…
Abstract
Purpose
The purpose of this paper is to study the influence of thermally stratified medium on a free convection flow from a sphere, which is rotating about the vertical axis, immersed in a stably thermally stratified medium.
Design/methodology/approach
An implicit finite‐difference scheme in combination with the quasi‐linearization technique is applied to obtain the steady state non‐similar solutions of the governing boundary layer equations for flow and temperature fields.
Findings
The numerical results indicate that the heat transfer rate at the wall decreases significantly with an increasing thermal stratification parameter, but its effect on the skin friction coefficients is rather minimum. In fact, the presence of thermal stratification of the medium influences the heat transfer at wall to be in opposite direction, that is, from fluids to the wall above a certain height. The heat transfer rate increases but the skin frictions decrease with the increase of Prandtl number. In particular, the effect of buoyancy force is much more sensitive for low Prandtl number fluids (Pr = 0.7, air) than that of high Prandtl number fluids (Pr = 7, water). Also the skin friction in rotating direction is less sensitive to the buoyancy force as the buoyancy force acts in the streamwise direction for the present study of thermally stratified medium.
Research limitations/implications
The ambient temperature T∞∞ is assumed to increase linearly with height $h$. The viscous dissipation term, which is usually small for natural convection flows, has been neglected in the energy equation. The flow is assumed to be axi‐symmetric. The Boussinesq approximation is invoked for the fluid properties to relate density changes to temperature changes, and to couple in this way the temperature field to the flow field.
Practical implications
Free convection in a thermally stratified medium occurs in many environmental processes with temperature stratification, and in industrial applications within a closed chamber with heated walls. Also, free convections associated with heat rejection systems for long‐duration deep ocean powder modules where ocean environment is stratified are examples of such type.
Originality/value
The research presented in this paper investigates the free convection flow on a sphere, which is rotating with a constant angular velocity along its vertical axis in a stably thermally stratified fluid.
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M.A. Antar and M.A.I. El‐Shaarawi
Boundary‐layer flow around a spinning liquid sphere moving steadily in a gas stream is investigated numerically. The shear stress exerted on the sphere's surface results in…
Abstract
Boundary‐layer flow around a spinning liquid sphere moving steadily in a gas stream is investigated numerically. The shear stress exerted on the sphere's surface results in surface rotation in the meridional direction in addition to the azimuthal velocity resulting from the spinning of the liquid sphere. The parameters controlling the flow around the sphere are the external flow Reynolds number (Re), the liquid‐to‐gas viscosity ratio (μ*) and the spinning parameter (Rer/Re)2. The effect of these parameters on the velocity components (namely the meridional, radial and azimuthal velocity components) and on the shear stress is shown. Moreover, their effect on the location of external flow point of separation is also demonstrated.
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Henry Gyarteng-Mensah, De-Graft Owusu-Manu, David Edwards, Isaac Baidoo and Hatem El-Gohary
Using a discrete choice experiment (DCE), this study aims to better understand the job preference of postgraduate students studying at the Kwame Nkrumah University of Science and…
Abstract
Purpose
Using a discrete choice experiment (DCE), this study aims to better understand the job preference of postgraduate students studying at the Kwame Nkrumah University of Science and Technology-Institute of Distance Learning, Ghana and also rank the attributes of a job they deem important.
Design/methodology/approach
The research adopted a positivist epistemological design contextualised within a deductive approach and case study strategy. Primary survey data was collected from a stratified random sample of 128 postgraduate students with multi-sectorial career prospects. Sample students were subjected to a DCE in which their stated preferences were collected using closed-ended questionnaires with 28 pairs of hypothetical job profiles. Respondents’ preferences from the DCE data were then modelled using the conditional logit.
Findings
The research reveals that: salary in the range GHC 2,800.00 to GHC 3,400.00 ($1 = GHS 5.3); supportive management; very challenging jobs; and jobs located in the city were the top attributes that were significant and had the most impact in increasing the utility of selecting a particular job. Interestingly, jobs with no extra hours workload were not significant hence, had a negative impact upon student preferences.
Originality/value
This novel research is the first to use a DCE to better elicit preference and trade-offs of postgraduate students in a developing country towards varying job characteristics that have an impact on their future employment decisions. Knowledge advancements made provide invaluable insight to employers and policymakers on the key criteria that should be implemented to retain the best candidate.
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Luxury branding, in the context of tangible luxury consumables, has received academic attention. But the notion remained inconclusive in the context of consumption of luxury…
Abstract
Luxury branding, in the context of tangible luxury consumables, has received academic attention. But the notion remained inconclusive in the context of consumption of luxury intangibles. The travel setting provides an excellent backdrop to explore the complex cognitive process of assigning meaning to the relationship between travellers and luxury travel brands. The shifting image of luxury consumption from elitism to mass aspirational, too, needs to be studied for its transformative implications. The chapter focused on developing a brand relationship scale, namely, TraveLux, in the context of luxury travel consumption and tested its robustness to explain the shared sentiments and emotions of travellers, engaged in luxury travel, across social media. The chapter identifies a four construct instruments capturing the essence of immersive experience, ethnocultural acculturation, passion and excitement and self-congruence as a seedbed of luxury brand affinity for travellers. TraveLux was also found to capture the shared experience of travellers consuming luxury travel brands, thereby establishing a synch between the instrument constructs and manifested human cognition in real-life situations. The study expanded on the volume of literature pertaining to luxury branding in the context of product-oriented industry and addresses the existing void in understanding traveller–brand relationships in luxury travel contexts. The study implicates a theoretical change in branding concept in perceiving luxury brands as price-based exclusivity to a transformative cultural experience. Further extrapolations of the study could be made by incorporating subtle behavioural patterns of travellers in perceiving luxury and subsequent evocation and predisposition towards decision-making.
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Ruben Huertas-Garcia, Juan Carlos Gázquez-Abad and Santiago Forgas-Coll
Adaptive conjoint analysis (ACA) is a market research methodology for measuring utility in business-to-business and customer studies. Based on partial profiles, ACA tailors an…
Abstract
Purpose
Adaptive conjoint analysis (ACA) is a market research methodology for measuring utility in business-to-business and customer studies. Based on partial profiles, ACA tailors an experiment’s design to each respondent depending on their previously stated preferences, ordered in a self-assessment questionnaire. The purpose of this paper is to describe advantages and disadvantages of using a partial-profile randomised experiment, the usual system, and to propose a new design strategy for arranging profiles in blocks that improve its performance.
Design/methodology/approach
The authors propose a comparison between their design with the commonly used designs, as random designs and the so-called “mirror image”, in their resolution capacity for the estimations of main factors and two-factor interactions with the lowest number of profiles.
Findings
Comparing the proposed design over the other two designs highlights certain aspects. The proposed design guarantees more estimation for each experiment than the others and allows the researcher to tailor the design to his or her goals. The authors’ procedure will help researchers to determine an experiment’s resolution capacity before carrying it out, as well as to estimate main factors and two-factor interactions alike.
Originality/value
The authors propose a new design strategy for arranging the profiles in blocks for improving the performance of ACA. This proposal is based on the use of a full-profile approach in which profiles are arranged in two-level factorial designs in blocks of two, and the levels of each factor are codified vectorially.
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Lucas Ioran Marciano, Guilherme Arantes Pedro, Wallyson Ribeiro dos Santos, Geronimo Virginio Tagliaferro, Fabio Rodolfo Miguel Batista and Daniela Helena Pelegrine Guimarães
The purpose of this study is to investigate the influence of light intensity and sources of carbon and nitrogen on the cultivation of Spirulina maxima.
Abstract
Purpose
The purpose of this study is to investigate the influence of light intensity and sources of carbon and nitrogen on the cultivation of Spirulina maxima.
Design/methodology/approach
Cultures were carried out in a modified Zarrouk medium using urea, sodium acetate and glycerol. A Taguchi experimental design was used to evaluate the effect on the production of biocompounds: productivities in biomass, carbohydrates, phycocyanin and biochar were analyzed.
Findings
Statistical data analysis revealed that light intensity and sodium acetate concentration were the most important factors, being significant in three of the four response variables studied. The highest productivities in biomass (46.94 mg.L−1.d−1), carbohydrates (6.11 mg.L−1.d−1), phycocyanin (3.62 mg.L−1.d−1) and biochar (22, 48 mg.L−1.d−1) were achieved in experiment 4 of the Taguchi matrix, highlighting as the ideal condition for the production of biomass, carbohydrates and phycocyanin.
Practical implications
Sodium acetate and urea can be considered, respectively, as potential sources of carbon and nitrogen to increase Spirulina maxima productivity. From the results, an optimized cultivation condition for the sustainable production of bioproducts was obtained.
Originality/value
This work focuses on the study of the influence of light intensity and the use of alternative sources of nitrogen and carbon on the growth of Spirulina maxima, as well as on the influence on the productivity of biomass and biocompounds. There are few studies in the literature focused on the phycocyanin production from microalgae, justifying the need to deepen the subject.
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Development of Research ProblemThe needs, wants, and desires of industrial customers are fulfilled in a market environment epitomised by exchanges between buyers and sellers. Both…
Abstract
Development of Research ProblemThe needs, wants, and desires of industrial customers are fulfilled in a market environment epitomised by exchanges between buyers and sellers. Both of these parties execute strategic moves which are intended to perpetuate their existence as well as optimise the use of available resources. While the over‐riding ambition of the investigator was to identify a model‐form which might serve as a reference for substantiating certain strategic moves by corporate purchasing executives, the more immediate desire was to test empirically the validity of applying such a theory to purchasing. The conceptual model‐form was hypothesised by Berenson. He posited it would answer some of the questions raised by purchasing executives concerning guidelines for establishing purchasing strategy as well as for setting priorities among strategies. The concept was the product life cycle (PLC) theory.