Effects of complex boundary conditions on natural convection of a viscoplastic fluid

Rafiei, Behnam; Masoumi, H.; Aghighi, Mohammad Saeid; Ammar, Amine

doi:10.1108/hff-09-2018-0507

Cited by 8 publications

(6 citation statements)

References 26 publications

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“…For the heated plane: q w = 1.5 MW/m 2 . It is noted that gravity is considered in this study due to the occurring natural convection (Rafiei et al , 2019; Lu et al , 2019).…”

Section: Description Of the Numerical Methodsmentioning

confidence: 99%

Effect of wall conduction on the heat transfer characteristics of supercritical n-decane in a horizontal rectangular pipe for cooling of a scramjet combustor

Xie

Sundén

2020

HFF

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Purpose The purpose of this paper is to numerically study the influence of wall conduction on the heat transfer of supercritical n-decane in the active regenerative cooling channels. Design/methodology/approach A horizontally placed rectangular pipe with a solid zone and another one without a solid zone were used. A drastic variation of thermo-physical properties was emphatically addressed. After the verification of mesh and turbulence models comparing with the experimental results, a mesh number of 4.5 M and the low Reynolds number SST k-ω turbulence model were chosen. The solution of the governing equations and the acquisition of the numerical results were executed by the commercial software FLUENT 2020 R1. Findings The numerical results indicate that there is a heat transfer deterioration (HTD) potential for the upper wall, lower wall and sidewall with the decrease of mass flux. Due to wall conduction, the distribution of the fluid temperature at spanwise-normal planes becomes uniform and this feature also takes advantage of the relatively uniform transverse velocity. For the streamwise-normal planes, the low fluid temperature appears close to the upper wall at the region near the sidewall and vice versa for the region near the centre. Undoubtedly, the secondary flow at the cross-section plays a crucial role in this process and the relatively cool mainstream is affected by the vortices. Originality/value This study warns that the wall conduction must be considered in the practical design and thermal optimization due to the sensibility of thermo-physical properties to the heat flux. The secondary flow caused by the buoyancy force (gravity) plays a significant role in the supercritical heat transfer and mixed convection heat transfer should be further studied.

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“…For the heated plane: q w = 1.5 MW/m 2 . It is noted that gravity is considered in this study due to the occurring natural convection (Rafiei et al , 2019; Lu et al , 2019).…”

Section: Description Of the Numerical Methodsmentioning

confidence: 99%

Effect of wall conduction on the heat transfer characteristics of supercritical n-decane in a horizontal rectangular pipe for cooling of a scramjet combustor

Xie

Sundén

2020

HFF

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“…GFEM had been used extensively in earlier studies for CFD simulations (Basak et al , 2006; Anandalakshmi and Basak, 2015; Biswal and Basak, 2018; Das et al , 2019; Lukose and Basak, 2019; Rafiei et al , 2019). The current work employs GFEM to solve equations (7)–(9) with velocity and different thermal boundary conditions at the walls (equation (10)).…”

Section: Model Formulation Numerical Methodology Finite Element Logistics and Post-processingmentioning

confidence: 99%

“…Average Nusselt number ( Nubtrue¯) and average dimensionless spatial temperature ( trueθ^) are also evaluated via the finite element basis sets. Finite element-based simulations had also been used extensively by various researchers for computational fluid dynamics (CFD)-based studies (Sreedevi et al , 2019; Rafiei et al , 2019; Hajiyan et al , 2019). Current simulations are carried out for Ra = 10 3 −10 5 at Pr = 155.…”

Section: Introductionmentioning

confidence: 99%

Can the shape influence entropy generation for thermal convection of identical fluid mass with identical heating? A finite element introspection

Lukose

Basak

2020

HFF

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Purpose This paper aims to investigate the role of shapes of containers (nine different containers) on entropy generation minimization involving identical cross-sectional area (1 sq. unit) in the presence of identical heating (isothermal). The nine containers are categorized into three classes based on their geometric similarities (Class 1: square, tilted square and parallelogram; Class 2: trapezoidal type 1, trapezoidal type 2 and triangular; Class 3: convex, concave and curved triangular). Design/methodology/approach Galerkin finite element method is used to solve the governing equations for a representative fluid (engine oil: Pr = 155) at Ra = 103–105. In addition, finite element method is used to solve the streamfunction equation and evaluate the entropy generation terms (Sψ and Sθ). Average Nusselt number ( Nub¯) and average dimensionless spatial temperature ( θ^) are also evaluated via the finite element basis sets. Findings Based on larger Nub¯, larger θ^ and optimal Stotal values, containers from each class are preferred as follows: Class 1: parallelogrammic and square, Class 2: trapezoidal type 1 and Class 3: convex (larger θ^, optimum Stotal) and concave (larger Nub¯). Containers with curved walls lead to enhance the thermal performance or efficiency of convection processes. Practical implications Comparison of entropy generation, intensity of thermal mixing ( θ^) and average heat transfer rate give a clear picture for choosing the appropriate containers for processing of fluids at various ranges of Ra. The results based on this study may be useful to select a container (belonging to a specific class or containers with curved or plane walls), which can give optimal thermal performance from the given heat input, thereby leading to energy savings. Originality/value This study depicts that entropy generation associated with the convection process can be reduced via altering the shapes of containers to improve the thermal performance or efficiency for processing of identical mass with identical heat input. The comparative study of nine containers elucidates that the values of local maxima of Sψ (Sψ,max), Sθ (Sθ,max) and magnitude of Stotal vary with change in shapes of the containers (Classes 1–3) at fixed Pr and Ra. Such a comparative study based on entropy generation minimization on optimal heating during convection of fluid is yet to appear in the literature. The outcome of this study depicts that containers with curved walls are instrumental to optimize entropy generation with reasonable thermal processing rates.

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“…Based on the findings of these studies, it can be stated that convection heat transfer diminishes as τ y increases and above a critical yield number Y c ; convection does not occur. Additional investigations on the natural convection of viscoplastic fluids are available in the literature (Sairamu et al, 2013;Patel and Chhabra, 2015;Masoumi et al, 2019;Rafiei et al, 2019;Aghighi et al, 2020a, b;Aghighi et al, 2022).…”

Section: Wall Slip Effects 1275mentioning

confidence: 99%

Wall slip effects in Rayleigh–Bénard convection of viscoplastic materials

Aghighi,

Metivier,

Fakhri

2023

MMMS

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PurposeAccording to the research, viscoplastic fluids are sensitive to slipping. The purpose of this study is to determine whether slip affects the Rayleigh–Bénard convection of viscoplastic fluids in cavities and, if so, under what conditions.Design/methodology/approachThe wall slip was evaluated using a model created for viscoplastic (Bingham) fluids. The coupled conservation equations were solved numerically using the finite element method. Simulations were performed for various parameters: the Rayleigh number, yield number, slip yield number and friction number.FindingsWall slip determines two essential yield stresses: a specific yield stress value beyond which wall slippage is impossible (S_Yc); and a maximum yield stress beyond which convective flow is impossible (Y_c). At low Rayleigh numbers, Y_c is smaller than S_Yc. Hence, the flow attained a stable (conduction) condition before achieving the no-slip condition. However, for more significant Rayleigh numbers Y_c exceeded S_Yc. Thus, the flow will slip at low yield numbers while remaining no-slip at high yield numbers. The possibility of slipping on the wall increases the buoyancy force, facilitating the onset of Rayleigh–Bénard convection.Originality/valueAn essential aspect of this study lies in its comprehensive examination of the effect of slippage on the natural convection flow of viscoplastic materials within a cavity, which has not been previously investigated. This research contributes to a new understanding of the viscoplastic fluid behavior resulting from slipping.

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Effects of complex boundary conditions on natural convection of a viscoplastic fluid

Cited by 8 publications

References 26 publications

Effect of wall conduction on the heat transfer characteristics of supercritical n-decane in a horizontal rectangular pipe for cooling of a scramjet combustor

Effect of wall conduction on the heat transfer characteristics of supercritical n-decane in a horizontal rectangular pipe for cooling of a scramjet combustor

Can the shape influence entropy generation for thermal convection of identical fluid mass with identical heating? A finite element introspection

Wall slip effects in Rayleigh–Bénard convection of viscoplastic materials

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