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Article
Publication date: 2 October 2020

Faraz Hoseininejad, Saeed Dinarvand and Mohammad Eftekhari Yazdi

This study aims to investigate numerically the problem of conjugate conduction and mixed convection heat transfer of a nanofluid in a rotational/stationary circular enclosure…

Abstract

Purpose

This study aims to investigate numerically the problem of conjugate conduction and mixed convection heat transfer of a nanofluid in a rotational/stationary circular enclosure using a two-phase mixture model.

Design/methodology/approach

Hot and cold surfaces on the wall or inside the enclosure (heater and cooler) are maintained at constant temperature of Th and Tc, respectively, whereas other parts are thermally insulated. To examine the effects of various parameters such as Richardson number (0.01 = Ri =100), thermal conductivity ratio of solid to base fluid (1 = Kr = 100), volume fraction of nanoparticle (0 = φ = 0.05), insertion of conductive covers (C.Cs) around the heater in a different shape (triangular, circular or square), segmentation and arrangement of the conductive blocks (C.Bs) and rotation direction of the enclosure on the flow structure and heat transfer rate, two-dimensional equations of mass, momentum and energy conservation, as well as volume fraction, are solved using finite volume method and Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm.

Findings

The results show that inserting C.C around heater can increase or decrease heat transfer rate, and it depends on thermal conductivity ratio of solid to pure fluid. Also, it is found that by the division of C.B and location of its portions in a horizontal configuration, heat transfer rate reduces. Moreover, it is observed that external heating and cooling of the enclosure causes enhancement of heat transfer relative to that of internal heating and cooling. Finally, results illustrate that under the condition that cylinders rotate in the same direction, the heat transfer rate increases as compared to those that rotate in the opposite direction. Hence rotation direction of cylinders can be used as a desired parameter for controlling heat transfer rate.

Originality/value

A comprehensive report of results for the problem of conjugate conduction and mixed convection heat transfer in a circular cylinder containing different shapes of C.C, conducting obstacle and heater and cooler has been presented. An efficient numerical technique has been developed to solve this problem. The achievements of this paper are purely original, and the numerical results were never published by any researcher.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 31 March 2020

Nandkishor Sah and Mohan Jagadeesh Kumar Mandapati

Use of packed beds, enhanced tubes, nano-fluids and artificial ribs are few passive techniques to increase heat transfer in solar air heaters (SAHs). Artificial ribs attached to…

Abstract

Purpose

Use of packed beds, enhanced tubes, nano-fluids and artificial ribs are few passive techniques to increase heat transfer in solar air heaters (SAHs). Artificial ribs attached to the absorber plate of the SAH will enhance the turbulence near the plate. Experimental analyses are conducted to find the thermal performance of SAH with ribs of regular geometries including rectangular, semi-circular and triangular in cross section. This paper aims to present the improvement in thermal performance of SAH with modified-arc.

Design/methodology/approach

Absorber plates are designed with ribs of rectangular, triangular, semi-circular and modified-arc in cross-section using existing data in literature. Physical dimensions of the ribs are designed by adapting procedure from literature. Absorber plates are manufactured with ribs and coated with blackboard paint and fixed to the existing SAH. Experiments are conducted with a variable-speed blower fixed to the inlet section of the SAH, which is used to supply air at different mass flow rates in a range between 0.495 and 0.557 kg/min.

Findings

Efficiency is found to be a strong function of mass flow rate of air through the SAH from the present experimental investigations. It was found that use of modified-arc ribs enhanced the efficiency of SAH by 105.35 per cent compared to SAH with plane absorber plate. Efficiency of SAH with modified-arc ribs is found to be higher by 24.43, 45.61 and 63.21 per cent, respectively, for SAH with semi-circular, rectangular and triangular arc ribs on its absorber plate.

Research limitations/implications

Experiments on SAH are conducted during daytime from 9:00 am to 5:00 pm in open atmospheric conditions. Solar intensity is continuously changing during the experimentation from morning to evening. Calculations are made based on the observations with average values of solar intensity and temperature readings. More accurate values of SAH efficiency can be obtained with constant heat supply to the absorber plate by simulating the experimental setup in indoor conditions. Temperature and flow rate observations could be more accurate with sophisticated instrumentation rather than using simple thermocouples and orifice meters.

Social implications

SAHs are basically used to supply hot air for both rural and industrial applications. These are used for crop drying, preheating of air, removal of moisture from leather, chemicals, etc. Conventionally, formers in India are using open sun drying to remove moisture from agricultural products. In this method, the moisture can be removed up to a level of 20 to 25 per cent. Use of SAH can remove moisture up to below 5 per cent and process is clean without reducing the quality of agricultural products. Enhancing the efficiency of SAHs will surely increase its usage by formers for crop drying.

Originality/value

Use of artificial ribs on absorber plate of SAH is most economical among many of the active and passive techniques. Numerical and experimental investigations are found in literature with regular cross-sectional ribs, including rectangular, triangular and semi-circular. The present work proposed new shape of the ribs named as modified-arc, which was not presented in the literature. Experimental analysis proved that the use of modified-arc makes the SAH more efficient in heat transfer.

Details

World Journal of Engineering, vol. 17 no. 3
Type: Research Article
ISSN: 1708-5284

Keywords

Article
Publication date: 7 June 2023

Nirmalendu Biswas, Dipak Kumar Mandal, Nirmal K. Manna, Rama S.R. Gorla and Ali J. Chamkha

This study aims to investigate the impact of different heater geometries (flat, rectangular, semi-elliptical and triangular) on hybrid nanofluidic (Cu–Al2O3–H2O) convection in…

Abstract

Purpose

This study aims to investigate the impact of different heater geometries (flat, rectangular, semi-elliptical and triangular) on hybrid nanofluidic (Cu–Al2O3–H2O) convection in novel umbrella-shaped porous thermal systems. The system is top-cooled, and the identical heater surfaces are provided centrally at the bottom to identify the most enhanced configuration.

Design/methodology/approach

The thermal-fluid flow analysis is performed using a finite volume-based indigenous code, solving the nonlinear coupled transport equations with the Darcy number (10–5 ≤ Da ≤ 10–1), modified Rayleigh number (10 ≤ Ram ≤ 104) and Hartmann number (0 ≤ Ha ≤ 70) as the dimensionless operating parameters. The semi-implicit method for pressure linked equations algorithm is used to solve the discretized transport equations over staggered nonuniform meshes.

Findings

The study demonstrates that altering the heater surface geometry improves heat transfer by up to 224% compared with a flat surface configuration. The triangular-shaped heating surface is the most effective in enhancing both heat transfer and flow strength. In general, flow strength and heat transfer increase with rising Ram and decrease with increasing Da and Ha. The study also proposes a mathematical correlation to predict thermal characteristics by integrating all geometric and flow control variables.

Research limitations/implications

The present concept can be extended to further explore thermal performance with different curvature effects, orientations, boundary conditions, etc., numerically or experimentally.

Practical implications

The present geometry configurations can be applied in various engineering applications such as heat exchangers, crystallization, micro-electronic devices, energy storage systems, mixing processes, food processing and different biomedical systems (blood flow control, cancer treatment, medical equipment, targeted drug delivery, etc.).

Originality/value

This investigation contributes by exploring the effect of various geometric shapes of the heated bottom on the hydromagnetic convection of Cu–Al2O3–H2O hybrid nanofluid flow in a complex umbrella-shaped porous thermal system involving curved surfaces and multiphysical conditions.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 33 no. 9
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 9 April 2019

Mohsen Izadi, Nemat M. Maleki, Ioan Pop and S.A.M. Mehryan

This paper aims to numerically investigate the natural convection heat transfer of a hybrid nanofluid into a porous cavity exposed to a variable magnetic field.

Abstract

Purpose

This paper aims to numerically investigate the natural convection heat transfer of a hybrid nanofluid into a porous cavity exposed to a variable magnetic field.

Design/methodology/approach

The non-linear elliptical governing equations have been solved numerically using control volume based finite element method. The effects of different governing parameters including Rayleigh number (Ra = 103 − 106), Hartman number (Ha = 0 − 50), volume fraction of nanoparticles (φ = 0 − 0.02), curvature of horizontal isolated wall (a = 0.85 − 1.15), porosity coefficient (ε = 0.1 − 0.9) and Darcy number (Da = 10−5 − 10−1) have been studied.

Findings

The results indicate that at low Darcy numbers close to 0, the average Nusselt number Nua enhances as porosity coefficient increases. For a = 1 and a = 1.15 in comparison with a = 0.85, the stretching of the isothermal lines is maintained from the left side to the right side and vice versa, which indicates increased natural convection heat transfer for this configuration of the top and bottom walls. In addition, at higher Rayleigh numbers, by increasing the Hartmann number, a significant decrease is observed in the Nusselt number, which can be attributed to the decreased power of the flow.

Originality/value

The authors believe that all the results, both numerical and asymptotic, are original and have not been published elsewhere.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 17 July 2019

A.S. Dogonchi, Muhammad Waqas, M. Mudassar Gulzar, M. Hashemi-Tilehnoee, Seyyed Masoud Seyyedi and D.D. Ganji

The purpose of this research is to describe the importance of the Cattaneo–Christov theory of heat conduction in a triangular enclosure with a semi-circular heater. Analysis…

Abstract

Purpose

The purpose of this research is to describe the importance of the Cattaneo–Christov theory of heat conduction in a triangular enclosure with a semi-circular heater. Analysis subjected to Fe3O4-H2O nanofluid is reported. Viscosity dependent on magnetic field is taken into consideration to simulate ferrofluid viscosity. Besides, heat generation and shape factor of nanoparticles are also considered.

Design/methodology/approach

The well-known control volume finite element method is used for simulations.

Findings

The outcomes reveal that the magnetic field can be introduced to the system as a controlling element.

Originality/value

No such analysis exists in the literature.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 11
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 24 July 2018

Yuhui Wei, Zhaowei Su, Huashan Lu and Xue Mei Ding

The purpose of this paper is to develop an efficient termination control strategy of air-vented dryer in term of energy saving, improving smoothness and reducing microscopic…

Abstract

Purpose

The purpose of this paper is to develop an efficient termination control strategy of air-vented dryer in term of energy saving, improving smoothness and reducing microscopic damage of fiber.

Design/methodology/approach

A simple, low cost termination control strategy is developed by testing the instantaneous humidity of exhaust air and then deducing the drying degree of fabric in process. The practicability evaluation of this novel strategy was investigated by using both experimental and mathematical approaches. The effect of termination control strategy on drying efficiency and fabric apparent properties were also discussed.

Findings

Termination control strategy significantly affects drying time, energy consumption, smoothness and microscopic of fiber. Specially, a novel termination control strategy that the combination of equilibrium moisture content of fabric in ambient environment and relative humidity of exhaust air in exhaust duct is workable and can save 25.2 percent of energy consumption, 26.7 percent of the drying time and improve 0.7 grade of the appearance smoothness, as well as significantly reduce the microscopic damage of fiber compare to the original control strategy of dryer. This indicates possible ways to minimize drying energy consumption and dryer damage by reducing unnecessary migrate out of the water from the clothes.

Practical implications

The paper is helpful in not only the development of new drying product but also the optimization of appearance smoothness of fabric after drying and reduce the microscopic damage of fiber.

Originality/value

A novel termination control strategy of dryer is applied to improve drying efficiency of dryer and reduce fabric damage.

Details

International Journal of Clothing Science and Technology, vol. 30 no. 3
Type: Research Article
ISSN: 0955-6222

Keywords

Article
Publication date: 29 October 2021

Abdelraheem M. Aly and Shreen El-Sapa

The purpose of this paper is to work out the magnetic forces on heat/mass transmission in a cavity filled with a nanofluid and wavy porous medium by applying the incompressible…

89

Abstract

Purpose

The purpose of this paper is to work out the magnetic forces on heat/mass transmission in a cavity filled with a nanofluid and wavy porous medium by applying the incompressible smoothed particle hydrodynamics (ISPH) method.

Design/methodology/approach

The cavity is filled by a nanofluid and an undulating layer of a porous medium. The inserted two circular cylinders are rotated around the cavity’s center by a uniform circular velocity. The outer circular cylinder has four gates, and it carries two different boundary conditions. The inner circular cylinder is carrying Th and Ch. The Lagrangian description of the dimensionless regulating equations is solved numerically by the ISPH method.

Findings

The major outcomes of the completed numerical simulations illustrated the significance of the wavy porous layer in declining the nanofluid movements, temperature and concentration in a cavity. The nanofluid movements are declining by an increase in nanoparticle parameter and Hartmann number. The variations on the boundary conditions of an outer circular cylinder are changing the lineaments of heat/mass transfer in a cavity.

Originality/value

The originality of this study is investigating the dual rotations of the cylinders on magnetohydrodynamics thermosolutal convection of a nanofluid in a cavity saturated by two wavy horizontal porous layers.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 13 June 2019

Zafar Namazian and S.A.M. Mehryan

The purpose of this study is to numerically study the heat transfer of free convection of a magnetizable micropolar nanofluid inside a semicircular enclosure.

Abstract

Purpose

The purpose of this study is to numerically study the heat transfer of free convection of a magnetizable micropolar nanofluid inside a semicircular enclosure.

Design/methodology/approach

The flow domain is under simultaneous influences of two non-uniform magnetic fields generated by current carrying wires. The directions of the currents are the same. Although the geometry is symmetric, it is physically asymmetric. The impacts of key parameters, including Rayleigh number Ra = 103-106, Hartman number Ha = 0-50, vortex viscosity parameter Δ = 0-4, nanoparticles volume fraction φ = 0-0.04 and magnetic number Mnf = 0-1000, on the macro- and micro-scales flows, temperature and heat transfer rate are studied.

Finding

The outcomes show that dispersing of the nanoparticles in the host fluid increases the strength of macro- and micro-scale flows. When Mnf = 0, the increment of the vortex viscosity parameter increases the strength of the particles micro-rotations, while this characteristic is decreased by growing Δ for Mnf ≠ 0. The increment of Δ and Ha decreases the rate of heat transfer. The increment of Ha decreases the enhancement percentage of heat transfer rate because of dispersing nanoparticles, known as En parameter. In addition, the value of Δ has no effect on En. Moreover, the average Nusselt number Nuavg and En remain constant by increasing the magnetic number Mnf for different volume fraction values.

Originality/value

The authors believe that all of the results, both numerical and asymptotic, are original and have not been published elsewhere yet.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 10
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 7 May 2021

Mohammad M. Rahman, Ziad Saghir and Ioan Pop

This paper aims to investigate numerically the free convective heat transfer efficiency inside a rectotrapezoidal enclosure filled with Al2O3–Cu/water hybrid fluid. The bottom…

Abstract

Purpose

This paper aims to investigate numerically the free convective heat transfer efficiency inside a rectotrapezoidal enclosure filled with Al2O3–Cu/water hybrid fluid. The bottom wall of the cavity is uniformly heated, the upper horizontal wall is insulated, and the remaining walls are considered cold. A new thermophysical relation determining the thermal conductivity of the hybrid nanofluid has been established, which produced results those match with experimental ones.

Design/methodology/approach

The governing partial differential equations are solved using the finite element method of Galerkin type. The simulated results in terms of streamlines, heat lines and isotherms are displayed for various values of the model parameters, which govern the flow.

Findings

The Nusselt number, friction factor and the thermal efficiency index are also determined for the pertinent parameters varying different ratios of the hybrid nanoparticles. The simulated results showed that thermal buoyancy significantly controls the heat transfer, friction factor and thermal efficiency index. The highest thermal efficiency is obtained for the lowest Rayleigh number.

Practical implications

This theoretical study is significantly relevant to the applications of the hybrid nanofluids electronic devices cooled by fans, manufacturing process, renewable energies, nuclear reactors, electronic cooling, lubrication, refrigeration, combustion, medicine, thermal storage, etc.

Originality/value

The results showed that nanoparticle loading intensified the rate of heat transfer and thermal efficiency index at the expense of the higher friction factor or higher pumping power. The results further show that the heat transmission in Al2O3–Cu/water hybrid nanofluid at a fixed value of intensified $\phi_{hnf}$ compared to the Al2O3/water nanofluid when an amount of higher conductivity nanoparticles (Cu) added to it. Besides, the rate of heat transfer in Cu/water nanofluid declines when the lower thermal conductivity Al2O3 nanoparticles are added to the mixture.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 24 September 2019

Tahar Tayebi and Ali J. Chamkha

The purpose of this paper is to study the influence of magnetic field on entropy generation and natural convection inside an enclosure filled with a hybrid nanofluid and having a…

Abstract

Purpose

The purpose of this paper is to study the influence of magnetic field on entropy generation and natural convection inside an enclosure filled with a hybrid nanofluid and having a conducting wavy solid block. Also, the effect of fluid–solid thermal conductivity ratio is investigated.

Design/methodology/approach

The governing equations that are formulated in the dimensionless form are discretized via finite volume method. The velocity–pressure coupling is assured by the SIMPLE algorithm. Heat transfer balance is used to verify the convergence. The validation of the numerical results was performed by comparing qualitatively and quantitatively the results with previously published investigations.

Findings

The results indicate that the magnetic field and the conductivity ratio of the wavy solid block can significantly affect the dynamic and thermal field and, consequently, the heat transfer rate and entropy generation because of heat transfer, fluid friction and magnetic force.

Originality/value

To the best of the authors’ knowledge, the present numerical study is the first attempt to use hybrid nanofluid for studying the entropy generation because of magnetohydrodynamic natural convective flow in a square cavity with the presence of a wavy circular conductive cylinder. Irreversibilities due to magnetic effect are taken into account. The effect of fluid–solid thermal conductivity ratio is considered.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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