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Heat Transfer Enhancement
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Heat Transfer Enhancement

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J: Thermal Management".

Deadline for manuscript submissions: closed (30 April 2019) | Viewed by 77911

Special Issue Editors

Prof. Dr. Mikhail Sheremet

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Guest Editor
Laboratory on Convective Heat and Mass Transfer and Department of Theoretical Mechanics, Tomsk State University, 36 Lenin Ave., 634050 Tomsk, Russia
Interests: heat and mass transfer; natural convection; porous media; phase change materials; computational fluid dynamics; heat transfer enhancement
Special Issues, Collections and Topics in MDPI journals
Prof. Oronzio Manca

E-Mail Website
Guest Editor
Dipartimento di Ingegneria, Università degli Studi della Campania Luigi Vanvitelli, Aversa, CE, Italy
Interests: heat transfer enhancement; heat transfer by nanofluids; thermal control
Special Issues, Collections and Topics in MDPI journals
Prof. Ioan Pop

E-Mail Website
Guest Editor
Faculty of Mathematics and Computer Science, Babeş-Bolyai University, 400084 Cluj-Napoca, Romania
Interests: fluid mechanics; heat transfer; boundary layer; numerical methods

Special Issue Information

Dear Colleagues,

Development of modern engineering applications demands the heat transfer enhancement. At the same time, efficient heat transfer equipment is necessary to reduce energy consumption and improve energy savings. Such techniques allow also to reduce emissions and pollution and to obtain more control in carbon dioxide increase. Heat transfer enhancement is both very attractive and challenging in the research and industry fields. It has a fundamental role in improving energy efficiency, as well as in developing thermal systems with high performances. Heat transfer enhancement techniques can be found in different engineering applications, such as solar energy systems, thermal control, electronics cooling, nuclear reactors, heat exchangers, automotive cooling, refrigeration, chemical process, etc. They are classified as passive methods and active methods. In the first method, no direct application of external power is required, whereas in the second method an external power source is necessary. The effectiveness of heat transfer enhancement techniques is strongly related to the heat transfer mechanisms. This can be due to single-phase free convection and dispersed-flow film boiling. Plate fins, nanofluids, and porous insertions can be considered as examples of passive techniques, while magnetic fields, induced vibrations, and rotations are examples of active techniques. The present Special Issue is a good opportunity to collect original papers on the most recent research activities on the topic to provide useful guidelines for future research directions and engineering applications.

Prof. Dr. Mikhail Sheremet
Prof. Oronzio Manca
Prof. Ioan Pop
Guest Editors

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Keywords

  • heat and mass transfer
  • nanofluids
  • phase change materials
  • porous media
  • turbulent transport
  • heat-generating elements
  • electronics cooling
  • solar collectors

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Published Papers (17 papers)

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Research

20 pages, 3130 KiB  
Article
Thermal and Fluid Dynamic Behaviors of Confined Slot Jets Impinging on an Isothermal Moving Surface with Nanofluids
by Bernardo Buonomo, Oronzio Manca, Nadezhda S. Bondareva and Mikhail A. Sheremet
Energies 2019, 12(11), 2074; https://doi.org/10.3390/en12112074 - 30 May 2019
Cited by 23 | Viewed by 3503
Abstract
A two-dimensional numerical investigation of turbulent convective heat transfer due to a confined slot jet impinging on an isothermal moving surface is accomplished. The confined geometry has an upper adiabatic surface parallel to the heated moving plate and the slot jet is in [...] Read more.
A two-dimensional numerical investigation of turbulent convective heat transfer due to a confined slot jet impinging on an isothermal moving surface is accomplished. The confined geometry has an upper adiabatic surface parallel to the heated moving plate and the slot jet is in the middle of the confining adiabatic wall. The working fluids are pure water or a nanofluid, which in this case was a mixture of water and Al2O3 nanoparticles. The governing equations are written adopting the k-ε turbulence model with enhanced wall treatment and the single-phase model approach for the nanofluids. The numerical model is solved using the finite volume method with the Ansys Fluent code. Two geometric configurations regarding two values of the jet distance from the target surface are considered in the simulations. The concentration of nanoparticles ranges from 0% to 6%, with a single diameter equal to 30 nm, Reynolds numbers ranging from 5000 to 20000, and a moving surface-jet velocity ratio between 0 and 2 are examined in the investigation. The aim is to study the system behaviors by means of local and average Nusselt numbers, local and average friction factor/skin friction factor, stream function, and temperature fields. Results show that the presence of nanoparticles determines an increase in the dimensionless heat transfer but, as expected, does not affect the friction factor. The local and average increase in Nusselt numbers is also due to a combined effect of the moving plate and nanofluids. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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14 pages, 2351 KiB  
Article
Impacts of Non-Uniform Border Temperature Variations on Time-Dependent Nanofluid Free Convection within a Trapezium: Buongiorno’s Nanofluid Model
by Cornelia Revnic, Mohammad Ghalambaz, Teodor Groşan, Mikhail Sheremet and Ioan Pop
Energies 2019, 12(8), 1461; https://doi.org/10.3390/en12081461 - 17 Apr 2019
Cited by 16 | Viewed by 2990
Abstract
The present study develops the influence of inclined border temperature variations on the isotherms, streamlines, and isoconcentrations for unsteady free convection in a trapezoidal region filled with the water-based nanofluid. The considered mathematical nanofluid approach was formulated based on the Buongiorno’s model. The [...] Read more.
The present study develops the influence of inclined border temperature variations on the isotherms, streamlines, and isoconcentrations for unsteady free convection in a trapezoidal region filled with the water-based nanofluid. The considered mathematical nanofluid approach was formulated based on the Buongiorno’s model. The set of governing partial differential equations formulated using non-dimensional primitive variables such as velocity, pressure, temperature, and nanoparticles concentration volume fraction was solved numerically using the finite element method for various magnitudes of control characteristics. It was revealed that control characteristics affected the liquid circulation and energy transport coefficients. The Nusselt number is a growing function of wave number, amplitude, and the Rayleigh number. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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22 pages, 5359 KiB  
Article
Multi-Dimensional Performance Evaluation of Heat Exchanger Surface Enhancements
by Hannes Fugmann, Eric Laurenz and Lena Schnabel
Energies 2019, 12(7), 1406; https://doi.org/10.3390/en12071406 - 11 Apr 2019
Cited by 10 | Viewed by 3859
Abstract
Enhanced heat transfer surfaces allow more energy-efficient, compact and lightweight heat exchangers. Within this study, a method for comparing different types of enhancement and different geometries with multiple objectives is developed in order to evaluate new and existing enhancement designs. The method’s objectives [...] Read more.
Enhanced heat transfer surfaces allow more energy-efficient, compact and lightweight heat exchangers. Within this study, a method for comparing different types of enhancement and different geometries with multiple objectives is developed in order to evaluate new and existing enhancement designs. The method’s objectives are defined as energy, volume, and mass efficiency of the enhancement. They are given in dimensional and non-dimensional form and include limitations due to thermal conductivity within the enhancement. The transformation to an explicit heat transfer rate per dissipated power, volume, or mass is described in detail. The objectives are visualized for different Reynolds numbers to locate beneficial operating conditions. The multi-objective problem is further on reduced to a single-objective problem by means of weighting factors. The implementation of these factors allows a straightforward performance evaluation based on a rough estimation of the energy, volume, and mass importance set by a decision maker. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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23 pages, 37230 KiB  
Article
Mixed Convection and Entropy Generation of an Ag-Water Nanofluid in an Inclined L-Shaped Channel
by Taher Armaghani, Muneer A. Ismael, Ali J. Chamkha and Ioan Pop
Energies 2019, 12(6), 1150; https://doi.org/10.3390/en12061150 - 25 Mar 2019
Cited by 12 | Viewed by 3472
Abstract
This paper investigates the mixed convection and entropy generation of an Ag-water nanofluid in an L-shaped channel fixed at an inclination angle of 30° to the horizontal axis. An isothermal heat source was positioned in the middle of the right inclined wall of [...] Read more.
This paper investigates the mixed convection and entropy generation of an Ag-water nanofluid in an L-shaped channel fixed at an inclination angle of 30° to the horizontal axis. An isothermal heat source was positioned in the middle of the right inclined wall of the channel while the other walls were kept adiabatic. The finite volume method was used for solving the problem’s governing equations. The numerical results were obtained for a range of pertinent parameters: Reynolds number, Richardson number, aspect ratio, and the nanoparticles volume fraction. These results were Re = 50–200; Ri = 0.1, 1, 10; AR = 0.5–0.8; and φ = 0.0–0.06, respectively. The results showed that both the Reynolds and the Richardson numbers enhanced the mean Nusselt number and minimized the rate of entropy generation. It was also found that when AR. increased, the mean Nusselt number was enhanced, and the rate of entropy generation decreased. The nanoparticles volume fraction was predicted to contribute to increasing both the mean Nusselt number and the rate of entropy generation. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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11 pages, 660 KiB  
Article
Heat Transfer at the Interface of Graphene Nanoribbons with Different Relative Orientations and Gaps
by Shahin Mohammad Nejad, Masoud Bozorg Bigdeli, Rajat Srivastava and Matteo Fasano
Energies 2019, 12(5), 796; https://doi.org/10.3390/en12050796 - 27 Feb 2019
Cited by 11 | Viewed by 4072
Abstract
Because of their high thermal conductivity, graphene nanoribbons (GNRs) can be employed as fillers to enhance the thermal transfer properties of composite materials, such as polymer-based ones. However, when the filler loading is higher than the geometric percolation threshold, the interfacial thermal resistance [...] Read more.
Because of their high thermal conductivity, graphene nanoribbons (GNRs) can be employed as fillers to enhance the thermal transfer properties of composite materials, such as polymer-based ones. However, when the filler loading is higher than the geometric percolation threshold, the interfacial thermal resistance between adjacent GNRs may significantly limit the overall thermal transfer through a network of fillers. In this article, reverse non-equilibrium molecular dynamics is used to investigate the impact of the relative orientation (i.e., horizontal and vertical overlap, interplanar spacing and angular displacement) of couples of GNRs on their interfacial thermal resistance. Based on the simulation results, we propose an empirical correlation between the thermal resistance at the interface of adjacent GNRs and their main geometrical parameters, namely the normalized projected overlap and average interplanar spacing. The reported correlation can be beneficial for speeding up bottom-up approaches to the multiscale analysis of the thermal properties of composite materials, particularly when thermally conductive fillers create percolating pathways. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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16 pages, 1558 KiB  
Article
Forced Convection of Fe3O4-Water Nanofluid in a Bifurcating Channel under the Effect of Variable Magnetic Field
by Fatih Selimefendigil, Hakan F. Oztop, Mikhail A. Sheremet and Nidal Abu-Hamdeh
Energies 2019, 12(4), 666; https://doi.org/10.3390/en12040666 - 19 Feb 2019
Cited by 42 | Viewed by 4016
Abstract
In this study, forced convection of Fe 3 O 4 –water nanofluid in a bifurcating channel was numerically studied under the influence of variable magnetic. Galerkin residual finite element method was used for numerical simulations. Effects of various values of Reynolds number (between [...] Read more.
In this study, forced convection of Fe 3 O 4 –water nanofluid in a bifurcating channel was numerically studied under the influence of variable magnetic. Galerkin residual finite element method was used for numerical simulations. Effects of various values of Reynolds number (between 100 and 500), Hartmann number (between 0 and 3), and solid nanoparticle volume fraction (between 0% and 4%) on the convective heat transfer characteristics were analyzed. It was observed that location and size of the re-circulation zones established in the walls of the bifurcating channel strongly influenced by the variable magnetic field and Reynolds number. Average Nusselt number versus Hartmann number showed different characteristics for hot walls of the vertical and horizontal branching channels. The average Nusselt number enhancements were in the range of 12–15% and 9–12% for hot walls of the branching channel in the absence and presence of magnetic field (at Hartmann number of 3). Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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16 pages, 4000 KiB  
Article
Airside Performance of H-Type Finned Tube Banks with Surface Modifications
by Pradhyumn Bhale, Mrinal Kaushik, Jane-Sunn Liaw and Chi-Chuan Wang
Energies 2019, 12(4), 584; https://doi.org/10.3390/en12040584 - 13 Feb 2019
Cited by 8 | Viewed by 3697
Abstract
The present study numerically investigates some novel modifications to augment the performance of the H-type finned tube banks, which are widely used in waste heat recovery in industries. The imposed modifications upon the original H-type finned tube banks include the following: (1) Design [...] Read more.
The present study numerically investigates some novel modifications to augment the performance of the H-type finned tube banks, which are widely used in waste heat recovery in industries. The imposed modifications upon the original H-type finned tube banks include the following: (1) Design 1 contains some triangular cuts at the edge of the original rectangular fin; (2) Design 2 modifies the original rectangular geometry into a trapezoid shape; (3) Design 3 renders the original rectangular cross-section fin thickness into trapezoid cross-section; and (4) Design 4 changes the original rectangular shape into a circular shape. Based on the simulations, it is found that Design 1 shows barely any improvements in the heat transfer performance and surface area reduction. Design 2 can provide some weight saving and surface area reduction at a slightly inferior heat transfer performance. Design 3 can offer up to 14% improvements in the overall heat transfer performance without any pumping power penalty. Yet, Design 4 provides the maximum weight saving as compared to the original reference case. With 3–9% lesser surface area than the reference case, Design 4 still offers marginally higher heat transfer performance. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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13 pages, 5192 KiB  
Article
Influence of Perforated Fin on Flow Characteristics and Thermal Performance in Spiral Finned-Tube Heat Exchanger
by Hyung Ju Lee, Jaiyoung Ryu and Seong Hyuk Lee
Energies 2019, 12(3), 556; https://doi.org/10.3390/en12030556 - 12 Feb 2019
Cited by 32 | Viewed by 11352
Abstract
The present study conducts the numerical investigation of flow characteristics and thermal performance of spiral finned-tube heat exchangers. The effects of location of perforations (90°, 120°, and 150°) on heat transfer and pressure drop are analyzed for the air-side. The commercial computational fluid [...] Read more.
The present study conducts the numerical investigation of flow characteristics and thermal performance of spiral finned-tube heat exchangers. The effects of location of perforations (90°, 120°, and 150°) on heat transfer and pressure drop are analyzed for the air-side. The commercial computational fluid dynamics code ANSYS Fluent (V.17.0) is used for simulations with the RNG k-ε model based on the Reynolds-averaged Navier–Stokes equations. The velocity field, Colburn j-factor, and friction factor are analyzed to evaluate the heat transfer and pressure drop characteristics. Because of the flow through the perforations, the boundary layers on the fin surfaces are interrupted. This results in increased flow disturbances close to the fin, and the heat transfer performance increases compared to the reference case. The pressure drop, which is one of the disadvantages of spiral finned tubes comparing to plate or circular fins, decreases with perforations on the fin. Overall, the cases with perforated fin exhibit greater performance of area goodness factor considering the relationship between the heat transfer and the pressure drop. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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27 pages, 11802 KiB  
Article
Thermal Non-Equilibrium Heat Transfer Modeling of Hybrid Nanofluids in a Structure Composed of the Layers of Solid and Porous Media and Free Nanofluids
by Ali J. Chamkha, Sina Sazegar, Esmael Jamesahar and Mohammad Ghalambaz
Energies 2019, 12(3), 541; https://doi.org/10.3390/en12030541 - 9 Feb 2019
Cited by 58 | Viewed by 4556
Abstract
The free convection heat transfer of hybrid nanofluids in a cavity space composed of a clear flow, porous medium and a solid part is addressed. The cavity is heated from the bottom and cooled from the top. The side walls are well insulated. [...] Read more.
The free convection heat transfer of hybrid nanofluids in a cavity space composed of a clear flow, porous medium and a solid part is addressed. The cavity is heated from the bottom and cooled from the top. The side walls are well insulated. The upper part of the cavity is a clear space with no porous or solid materials and is filled with hybrid nanofluid. The bottom part is divided into two parts of a porous space saturated with the hybrid nanofluid and a solid thermal conductive block. There are conjugate heat transfer mechanisms between the solid block and the porous medium filled with the hybrid nanofluid as well as the hybrid nanofluid in the clear space. For the porous medium model, the local thermal non-equilibrium effects are considered. The hybrid nanofluids contain copper (20 nm) and alumina nanoparticles (40 nm) hybrid nanoparticles. The governing equations for the flow and heat transfer of the hybrid nanofluid in the clear space and the porous medium are introduced. Considering the conjugate heat transfer between the solid block and the hybrid nanofluid fluid in the pores and the porous matrix, appropriate boundary conditions for heat channeling are utilized. The governing equations are transformed into non-dimensional form to generalize the model. The finite element method is employed to solve the equations. The grid check and validation procedure are performed. Subsequently streamlines, isotherms, and Nusselt number are studied as important aspects of flow and heat transfer in the cavity. The increase in the portion of the clear flow part in the cavity enhances heat transfer due to better hybrid nanofluid circulation. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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12 pages, 4828 KiB  
Article
Internal Flow in an Enhanced Tube Having Square-cut Twisted Tape Insert
by Agung Tri Wijayanta, Pranowo, Mirmanto, Budi Kristiawan and Muhammad Aziz
Energies 2019, 12(2), 306; https://doi.org/10.3390/en12020306 - 19 Jan 2019
Cited by 57 | Viewed by 6228
Abstract
In this study, a numerical simulation has been conducted in order to evaluate the thermal hydraulic performance of a turbulent single-phase flow inside an enhanced tube equipped with a square-cut twisted tape (STT) insert. The classical twisted tape (CTT) insert was also investigated [...] Read more.
In this study, a numerical simulation has been conducted in order to evaluate the thermal hydraulic performance of a turbulent single-phase flow inside an enhanced tube equipped with a square-cut twisted tape (STT) insert. The classical twisted tape (CTT) insert was also investigated for comparison. The k-ε renormalized group turbulence model has been utilized as the turbulent model. Various twist ratios (y/W) of 2.7, 4.5, and 6.5 were investigated for the Reynolds number range of 8000–18,000, with water as the working fluid. The numerical results indicated that, in comparison with the plain tube (PT), the tube equipped with the STT with the twist ratios of 2.7, 4.5, and 6.5 led to an increase in the values of the Nusselt number and friction factor in the inner tube by 45.4–80.7% and 2.0–3.3 times, respectively; in addition, the highest thermal performance of 1.23 has been obtained. The results further indicated that the tube equipped with the CTT of the same twist ratios improved the Nusselt number and friction factor in the inner tube by 40.3–74.4% and 1.7–3.0 times, respectively, in comparison with the PT; further, the maximum thermal performance of 1.18 was achieved. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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13 pages, 3609 KiB  
Article
Experimental Study on the Evaporation and Condensation Heat Transfer Characteristics of a Vapor Chamber
by Yanfei Liu, Xiaotian Han, Chaoqun Shen, Feng Yao and Mengchen Zhang
Energies 2019, 12(1), 11; https://doi.org/10.3390/en12010011 - 21 Dec 2018
Cited by 26 | Viewed by 5406
Abstract
A vapor chamber can meet the cooling requirements of high heat flux electronic equipment. In this paper, based on a proposed vapor chamber with a side window, a vapor chamber experimental system was designed to visually study its evaporation and condensation heat transfer [...] Read more.
A vapor chamber can meet the cooling requirements of high heat flux electronic equipment. In this paper, based on a proposed vapor chamber with a side window, a vapor chamber experimental system was designed to visually study its evaporation and condensation heat transfer performance. Using infrared thermal imaging technology, the temperature distribution and the vapor–liquid two-phase interface evolution inside the cavity were experimentally observed. Furthermore, the evaporation and condensation heat transfer coefficients were obtained according to the measured temperature of the liquid near the evaporator surface and the vapor near the condenser surface. The effects of heat load and filling rate on the thermal resistance and the evaporation and condensation heat transfer coefficients are analyzed and discussed. The results indicate that the liquid filling rate that maximized the evaporation heat transfer coefficient was different from the liquid filling rate that maximized the condensation heat transfer coefficient. The vapor chamber showed good heat transfer performance with a liquid filling rate of 33%. According to the infrared thermal images, it was observed that the evaporation/boiling heat transfer could be strengthened by the interference of easily broken bubbles and boiling liquid. When the heat input increased, the uniformity of temperature distribution was improved due to the intensified heat transfer on the evaporator surface. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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17 pages, 24141 KiB  
Article
Impacts of Heat-Conducting Solid Wall and Heat-Generating Element on Free Convection of Al2O3/H2O Nanofluid in a Cavity with Open Border
by Mikhail A. Sheremet, Hakan F. Oztop, Dmitriy V. Gvozdyakov and Mohamed E. Ali
Energies 2018, 11(12), 3434; https://doi.org/10.3390/en11123434 - 7 Dec 2018
Cited by 9 | Viewed by 3076
Abstract
Development of modern electronic devices demands a creation of effective cooling systems in the form of active or passive nature. More optimal technique for an origination of such cooling arrangement is a mathematical simulation taking into account the major physical processes which define [...] Read more.
Development of modern electronic devices demands a creation of effective cooling systems in the form of active or passive nature. More optimal technique for an origination of such cooling arrangement is a mathematical simulation taking into account the major physical processes which define the considered phenomena. Thermogravitational convection in a partially open alumina-water nanoliquid region under the impacts of constant heat generation element and heat-conducting solid wall is analyzed numerically. A solid heat-conducting wall is a left vertical wall cooled from outside, while a local solid element is placed on the base and kept at constant volumetric heat generation. The right border is supposed to be partially open in order to cool the local heater. The considered domain of interest is an electronic cabinet, while the heat-generating element is an electronic chip. Partial differential equations of mathematical physics formulated in non-primitive variables are worked out by the second order finite difference method. Influences of the Rayleigh number, heat-transfer capacity ratio, location of the local heater and nanoparticles volume fraction on liquid circulation and thermal transmission are investigated. It was ascertained that an inclusion of nanosized alumina particles to the base liquid can lead to the average heater temperature decreasing, that depends on the heater location and internal volumetric heat generation. Therefore, an inclusion of nanoparticles inside the host liquid can essentially intensify the heat removal from the heater that is the major challenge in different engineering applications. Moreover, an effect of nanosized alumina particles is more essential in the case of low intensive convective flow and when the heater is placed near the cooling wall. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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15 pages, 974 KiB  
Article
Magnetohydrodynamics Flow Past a Moving Vertical Thin Needle in a Nanofluid with Stability Analysis
by Siti Nur Alwani Salleh, Norfifah Bachok, Norihan Md Arifin, Fadzilah Md Ali and Ioan Pop
Energies 2018, 11(12), 3297; https://doi.org/10.3390/en11123297 - 26 Nov 2018
Cited by 49 | Viewed by 4047
Abstract
In this study, we intend to present the dynamics of a system based on the model of convective heat and mass transfer in magnetohydrodynamics (MHD) flow past a moving vertical thin needle in nanofluid. The problem is formulated in mathematical form by using [...] Read more.
In this study, we intend to present the dynamics of a system based on the model of convective heat and mass transfer in magnetohydrodynamics (MHD) flow past a moving vertical thin needle in nanofluid. The problem is formulated in mathematical form by using Buongiorno’s model with the modified boundary condition. The transformed boundary layer ordinary differential equations are solved numerically using the bvp4c function in MATLAB software. The effects of the involved parameters, including, Brownian motion, thermophoresis, magnetic field, mixed convection, needle size and velocity ratio parameter on the flow, heat and mass transfer coefficients are analyzed. The numerical results obtained for the skin friction coefficients, local Nusselt number and local Sherwood number, as well as the velocity, temperature and concentration profiles are graphically presented and have been discussed in detail. The study reveals that the dual solutions appear when the needle and the buoyancy forces oppose the direction of the fluid motion, and the range of the dual solutions existing depends largely on the needle size and magnetic parameter. The presence of the magnetic field in this model reduces the coefficient of the skin friction and heat transfer, while it increases the coefficient of the mass transfer on the needle surface. A stability analysis has been performed to identify which of the solutions obtained are linearly stable and physically relevant. It is noticed that the upper branch solutions are stable, while the lower branch solutions are not. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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20 pages, 4232 KiB  
Article
A Stability Analysis of Solutions in Boundary Layer Flow and Heat Transfer of Carbon Nanotubes over a Moving Plate with Slip Effect
by Nur Syazana Anuar, Norfifah Bachok and Ioan Pop
Energies 2018, 11(12), 3243; https://doi.org/10.3390/en11123243 - 22 Nov 2018
Cited by 43 | Viewed by 4206
Abstract
The flow and heat transfer characteristics of both single-wall and multi-wall carbon nanotubes (CNTs) with water and kerosene as base fluid on a moving plate with slip effect are studied numerically. By employing similarity transformation, governing equations are transformed into a set of [...] Read more.
The flow and heat transfer characteristics of both single-wall and multi-wall carbon nanotubes (CNTs) with water and kerosene as base fluid on a moving plate with slip effect are studied numerically. By employing similarity transformation, governing equations are transformed into a set of nonlinear ordinary equations. These equations are solved numerically using the bvp4c solver in Matlab which is a very efficient finite difference method. The influence of numerous parameters such as nanoparticle volume fraction, velocity ratio parameter and first order slip parameter on velocity, temperature, skin friction and heat transfer rate are further explored and discussed in the form of graphical and tabular forms. The results reveal that dual solutions exist when the plate and free stream move in the opposite direction and slip parameter was found to widen the range of the possible solutions. However, skin friction coefficients decrease, whereas the heat transfer increases in the presence of slip parameter. Single-wall carbon nanotubes (SWCNTs) give higher skin friction and heat transfer compared to multi-wall carbon nanotubes (MWCNTs) due to the fact that they have higher density and thermal conductivity. A stability analysis is carried out to determine the stability of the solutions obtained. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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15 pages, 5574 KiB  
Article
Numerical Study of Heat Transfer Enhancement of Internal Flow Using Double-Sided Delta-Winglet Tape Insert
by Agung Tri Wijayanta, Muhammad Aziz, Keishi Kariya and Akio Miyara
Energies 2018, 11(11), 3170; https://doi.org/10.3390/en11113170 - 15 Nov 2018
Cited by 41 | Viewed by 4105
Abstract
A numerical study was performed to investigate the thermal performance characteristics of an enhanced tube heat exchanger fitted with punched delta-winglet vortex generators. Computational fluid dynamics modeling was applied using the k–ε renormalized group turbulence model. Benchmarking was performed using the results of [...] Read more.
A numerical study was performed to investigate the thermal performance characteristics of an enhanced tube heat exchanger fitted with punched delta-winglet vortex generators. Computational fluid dynamics modeling was applied using the k–ε renormalized group turbulence model. Benchmarking was performed using the results of the experimental study for a similar geometry. Attack angles of 30°, 50°, and 70° were used to investigate the heat transfer and pressure drop characteristics of the enhanced tube. Flow conditions were considered in the turbulent region in the Reynolds number range of 9100 to 17,400. A smooth tube was employed for evaluating the increment in the Nusselt number and the friction factor characteristics of the enhanced tube. The results show that the Nusselt number, friction factor, and thermal performance factor have a similar tendency. The presence of this insert offers a higher thermal performance factor as compared to that obtained with a plain tube. Vortex development in the flow structure aids in generating a vortex flow, which increases convective heat transfer. In addition, as the angle is varied, it is observed that the largest attack angle provides the highest thermal performance factor. The greatest increase in the Nusselt number and friction factor, respectively, was found to be approximately 3.7 and 10 times greater than those of a smooth tube. Through numerical simulations with the present simulation condition, it is revealed that the thermal performance factor approaches the value of 1.1. Moreover, the numerical and experimental values agree well although they tend to be different at high Reynolds number conditions. The numerical and experimental values both show similar trends in the Nusselt number, friction factor, and thermal performance factor. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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19 pages, 4128 KiB  
Article
MHD Mixed Convection in a Lid-Driven Cavity with a Bottom Trapezoidal Body: Two-Phase Nanofluid Model
by Muhammad Adil Sadiq, Ammar I. Alsabery and Ishak Hashim
Energies 2018, 11(11), 2943; https://doi.org/10.3390/en11112943 - 28 Oct 2018
Cited by 17 | Viewed by 3910
Abstract
The current work examines the effects of a bottom trapezoidal solid body and a magnetic field on mixed convection in a lid-driven square cavity. The Al 2 O 3 -water nanofluid used is assumed to obey Buongiorno’s two-phase model. An isothermal heater is [...] Read more.
The current work examines the effects of a bottom trapezoidal solid body and a magnetic field on mixed convection in a lid-driven square cavity. The Al 2 O 3 -water nanofluid used is assumed to obey Buongiorno’s two-phase model. An isothermal heater is placed on the bottom base of the trapezoid solid body, while the cavity’s vertical walls are kept cold at temperature T c . The top moving wall and the remaining portions of the cavity’s bottom wall are thermally insulated. The Galerkin weighted residual finite element method is employed to solve the dimensionless governing equations. The parameters of interest are the Richardson number ( 0.01 ≤ R i ≤ 100 ), Hartmann number ( 0 ≤ H a ≤ 50 ) , nanoparticle volume fraction ( 0 ≤ ϕ ≤ 0.04 ), and the length of the bottom base of the trapezoidal solid body. The obtained results show that increasing the Richardson number or decreasing the Hartmann number tends to increase the heat transfer rate. In addition, both the thermophoresis and Brownian motion greatly improve the convection heat transfer. It is believed that the current work is a good contribution to many engineering applications such as building design, thermal management of solar energy systems, electronics and heat exchange. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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27 pages, 2483 KiB  
Article
Effects of Non-Homogeneous Nanofluid Model on Natural Convection in a Square Cavity in the Presence of Conducting Solid Block and Corner Heater
by Ammar I. Alsabery, Tahar Tayebi, Ali J. Chamkha and Ishak Hashim
Energies 2018, 11(10), 2507; https://doi.org/10.3390/en11102507 - 20 Sep 2018
Cited by 41 | Viewed by 3341
Abstract
This study investigates numerically the effect of the two-phase nanofluid model due to natural convection within a square cavity along with the existence of a conducting solid block, and a corner heater using the finite difference method (FDM). The top horizontal wall is [...] Read more.
This study investigates numerically the effect of the two-phase nanofluid model due to natural convection within a square cavity along with the existence of a conducting solid block, and a corner heater using the finite difference method (FDM). The top horizontal wall is retained at a cold temperature that is fixed as constant, while the isothermal heater is positioned at the bottom left corner within the square cavity. The remaining fractions of the right vertical wall and the heated wall are set to be adiabatic. The water-based nanofluid, together with Al 2 O 3 nanoparticles, have been evaluated by determining the following parameters: the volume fraction of nanoparticles, thickness of solid block, Rayleigh number, and the solid block thermal conductivity. As a result, the comparative evaluation with outputs reported in publications and prior experimental works has pointed out exceptional agreement with the findings retrieved in this study. The experimental outcomes are graphically illustrated in terms of the average and local Nusselt numbers, isotherms, distribution of nanoparticles, and the streamlines. The findings indicate that an elevation of the thermal conductivity in blocks with a similar size successfully increases the transfer rate of heat, wherein the dominance of conduction has been observed. Full article
(This article belongs to the Special Issue Heat Transfer Enhancement)
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