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Energies
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Convection Process and Entropy Generation in Different Fluids
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Convection Process and Entropy Generation in Different Fluids

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

Deadline for manuscript submissions: closed (20 November 2020) | Viewed by 19352

Special Issue Editor

Dr. Gholamreza Kefayati

E-Mail Website
Guest Editor
School of Engineering, University of Tasmania, Hobart Tasmania, TAS 7001, Australia
Interests: CFD; heat and mass transfer; nanofluid; MHD; ferrofluid; non-Newtonian fluid
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Different kinds of convection process—natural, forced, and mixed convection—are present in various industries where heat and mass transfer play a key role. In the cited industries, the studied fluid can be Newtonian or non-Newtonian, and the character has an important impact on heat and mass transfer, as well as fluid flow behavior. In addition, it is crucial to manage the energy loss in the convection process, and one of the common ways in this area is studying entropy generation and minimizing the value in order to optimize the process.

This Special Issue invites original research papers to address studies into the various types of convection process numerically and experimentally for different Newtonian and non-Newtonian fluids, nanofluids, ferrofluids, MHD, and multiphase flows. Further, authors are encouraged to submit papers addressing entropy generation in a convection process.

Prof. Gholamreza Kefayati
Guest Editor

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Keywords

  • natural convection
  • mixed convection
  • entropy generation
  • newtonian and non-newtonian fluids
  • nanofluids
  • MHD
  • computational method

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Published Papers (6 papers)

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Research

20 pages, 3812 KiB  
Article
An Analytical Model for Natural Convection in a Rectangular Enclosure with Differentially Heated Vertical Walls
by Alberto Fichera, Manuel Marcoux, Arturo Pagano and Rosaria Volpe
Energies 2020, 13(12), 3220; https://doi.org/10.3390/en13123220 - 21 Jun 2020
Cited by 3 | Viewed by 2695
Abstract
This paper proposes an analytical model for natural convection in a closed rectangular enclosure filled by a fluid, with imposed heat fluxes at the vertical walls and adiabatic horizontal walls. The analytical model offers a simplified, but easy to handle, description of the [...] Read more.
This paper proposes an analytical model for natural convection in a closed rectangular enclosure filled by a fluid, with imposed heat fluxes at the vertical walls and adiabatic horizontal walls. The analytical model offers a simplified, but easy to handle, description of the temperature and velocity fields. The predicted temperature, velocity, and pressure fields are shown to be in agreement with those obtained from a reliable numerical model. The Nusselt numbers for both the analytical and numerical solutions are then calculated and compared, varying both the aspect ratio of the enclosure and the Rayleigh number. Based on the comparisons, it is possible to assess the dependence of the reliability of the analytical model on the aspect ratio of the enclosure, showing that the prediction error rapidly decreases with the increase of the enclosure slenderness. Full article
(This article belongs to the Special Issue Convection Process and Entropy Generation in Different Fluids)
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16 pages, 4751 KiB  
Article
Energy and Exergy Analysis of Using Turbulator in a Parabolic Trough Solar Collector Filled with Mesoporous Silica Modified with Copper Nanoparticles Hybrid Nanofluid
by Sara Rostami, Amin Shahsavar, Gholamreza Kefayati and Aysan Shahsavar Goldanlou
Energies 2020, 13(11), 2946; https://doi.org/10.3390/en13112946 - 8 Jun 2020
Cited by 35 | Viewed by 3472
Abstract
Designing the most efficient parabolic trough solar collector (PTSC) is still a demanding and challenging research area in solar energy systems. Two effective recommended methods for this purpose that increase the thermal characteristics of PTSCs are adding turbulators and nanofluids. To study the [...] Read more.
Designing the most efficient parabolic trough solar collector (PTSC) is still a demanding and challenging research area in solar energy systems. Two effective recommended methods for this purpose that increase the thermal characteristics of PTSCs are adding turbulators and nanofluids. To study the effects of the two approaches on the energy efficiency of PTSCs, a stainless steel turbulator was used and solid nanoparticles of Cu/SBA-15 were added to the water with the volume concentrations of 0.019% to 0.075%. The generated turbulence in the fluid flow was modeled by the SST k–ω turbulent model. The results in daylight demonstrated that energy efficiency increases steadily by 11:30 a.m., and then, starts to drop gradually due to more irradiations at noon. It was observed that applying the turbulator to the studied PTSC has a significant influence on the enhancement of energy efficiency. Adding the nanoparticles augmented the average Nusselt number inside the solar collector in various studied Reynolds numbers. It was also found that the increase in volume concentrations of nanoparticles enhances heat transfer regularly. Full article
(This article belongs to the Special Issue Convection Process and Entropy Generation in Different Fluids)
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23 pages, 5044 KiB  
Article
Axisymmetric Natural Convection of Liquid Metal in an Annular Enclosure under the Influence of Azimuthal Magnetic Field
by Takuya Masuda and Toshio Tagawa
Energies 2020, 13(11), 2896; https://doi.org/10.3390/en13112896 - 5 Jun 2020
Cited by 6 | Viewed by 2560
Abstract
Natural convection of liquid metal in an annular enclosure under the influence of azimuthal static magnetic field was numerically studied. The liquid metal in the enclosure whose cross-sectional area is square was heated from an inner vertical wall and cooled from an outer [...] Read more.
Natural convection of liquid metal in an annular enclosure under the influence of azimuthal static magnetic field was numerically studied. The liquid metal in the enclosure whose cross-sectional area is square was heated from an inner vertical wall and cooled from an outer vertical wall both isothermally whereas the other two horizontal walls were assumed to be adiabatic. The static azimuthal magnetic field was imposed by a long straight electric coil that was located at the central axis of the annular enclosure. The computations were carried out for the Prandtl number 0.025, the Rayleigh number 104, 5 × 105 and 107, and the Hartmann number 0–100,000 by using an in-house code. It was found that the contour map of the electric potential was similar to that of the Stokes stream function of the velocity regardless of the Hartmann number. Likewise, the contour map of the pressure was similar to the Stokes stream function of the electric current density in the case of the high Hartmann number. The average Nusselt number was decreased in proportion to the square of the Hartmann number in the high Hartmann number regime. Full article
(This article belongs to the Special Issue Convection Process and Entropy Generation in Different Fluids)
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17 pages, 4254 KiB  
Article
Study on Surface Condensate Water Removal and Heat Transfer Performance of a Minichannel Heat Exchanger
by Xiuli Liu, Hua Chen, Xiaolin Wang and Gholamreza Kefayati
Energies 2020, 13(5), 1065; https://doi.org/10.3390/en13051065 - 1 Mar 2020
Cited by 8 | Viewed by 3357
Abstract
The condensate on the surface of the minichannel heat exchanger generated during air cooling substantially reduces the heat transfer performance as it works as an evaporator in the air-conditioning system. This has received much attention in scientific communities. In this paper, the effect [...] Read more.
The condensate on the surface of the minichannel heat exchanger generated during air cooling substantially reduces the heat transfer performance as it works as an evaporator in the air-conditioning system. This has received much attention in scientific communities. In this paper, the effect of operating parameters on the heat transfer performance of a minichannel heat exchanger (MHE) is investigated under an evaporator working condition. An experimental MHE test system is developed for this purpose, and extensive experimental studies are conducted under a wide range of working conditions using the water-cooling method. The inlet air temperature shows a large effect on the overall heat transfer coefficient, while the inlet air relative humidity shows a large effect on the condensate aggregation rate. The airside heat transfer coefficient increases from 66 to 81 W/(m2·K) when the inlet air temperature increases from 30 to 35 °C. While the condensate aggregation rate on the MHE surface increases by up to 1.8 times when the relative humidity increases from 50% to 70%. The optimal air velocity, 2.5 m/s, is identified in terms of the heat transfer rate and airside heat transfer coefficient of the MHE. It is also found that the heat transfer rate and overall heat transfer coefficient increase as the air velocity increases from 1.5 to 2.5 m/s and decreases above 2.5 m/s. Furthermore, a large amount of condensate accumulates on the MHE surface lowering the MHE heat transfer. The inclined installation angle of the MHE in the wind tunnel effectively enhances heat transfer performance on the MHE surface. The experimental results provide useful information for reducing condensate accumulation and enhancing microchannel heat transfer. Full article
(This article belongs to the Special Issue Convection Process and Entropy Generation in Different Fluids)
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19 pages, 4656 KiB  
Article
Dynamic and Economic Investigation of a Solar Thermal-Driven Two-Bed Adsorption Chiller under Perth Climatic Conditions
by Ali Alahmer, Xiaolin Wang and K. C. Amanul Alam
Energies 2020, 13(4), 1005; https://doi.org/10.3390/en13041005 - 24 Feb 2020
Cited by 44 | Viewed by 3763
Abstract
Performance assessment of a two-bed silica gel-water adsorption refrigeration system driven by solar thermal energy is carried out under a climatic condition typical of Perth, Australia. A Fourier series is used to simulate solar radiation based on the actual data obtained from Meteonorm [...] Read more.
Performance assessment of a two-bed silica gel-water adsorption refrigeration system driven by solar thermal energy is carried out under a climatic condition typical of Perth, Australia. A Fourier series is used to simulate solar radiation based on the actual data obtained from Meteonorm software, version 7.0 for Perth, Australia. Two economic methodologies, Payback Period and Life-Cycle Saving are used to evaluate the system economics and optimize the need for solar collector areas. The analysis showed that the order of Fourier series did not have a significant impact on the simulation radiation data and a three-order Fourier series was good enough to approximate the actual solar radiation. For a typical summer day, the average cooling capacity of the chiller at peak hour (13:00) is around 11 kW while the cyclic chiller system coefficient of performance (COP) and solar system COP are around 0.5 and 0.3, respectively. The economic analysis showed that the payback period for the solar adsorption system studied was about 11 years and the optimal solar collector area was around 38 m2 if a compound parabolic collector (CPC) panel was used. The study indicated that the utilization of the solar-driven adsorption cooling is economically and technically viable for weather conditions like those in Perth, Australia. Full article
(This article belongs to the Special Issue Convection Process and Entropy Generation in Different Fluids)
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20 pages, 5587 KiB  
Article
Dual Solutions and Stability Analysis of Micropolar Nanofluid Flow with Slip Effect on Stretching/Shrinking Surfaces
by Sumera Dero, Azizah Mohd Rohni, Azizan Saaban and Ilyas Khan
Energies 2019, 12(23), 4529; https://doi.org/10.3390/en12234529 - 28 Nov 2019
Cited by 25 | Viewed by 2703
Abstract
The purpose of the present paper is to investigate the micropolar nanofluid flow on permeable stretching and shrinking surfaces with the velocity, thermal and concentration slip effects. Furthermore, the thermal radiation effect has also been considered. Boundary layer momentum, angular velocity, heat and [...] Read more.
The purpose of the present paper is to investigate the micropolar nanofluid flow on permeable stretching and shrinking surfaces with the velocity, thermal and concentration slip effects. Furthermore, the thermal radiation effect has also been considered. Boundary layer momentum, angular velocity, heat and mass transfer equations are converted to non-linear ordinary differential equations (ODEs). Then, the obtained ODEs are solved by applying the shooting method and in the results, the dual solutions are obtained in the certain ranges of pertinent parameters in both cases of shrinking and stretching surfaces. Due to the presence of the dual solutions, stability analysis is done and it was found that the first solution is stable and physically feasible. The results are also compared with previously published literature and found to be in excellent agreement. Moreover, the obtained results reveal the angular velocity increases in the first solution when the value of micropolar parameter increases. The velocity of nanofluid flow decreases in the first solution as the velocity slip parameter increases, whereas the temperature profiles increase in both solutions when thermal radiation, Brownian motion and the thermophoresis parameters are increased. Concentration profile increases by increasing N t and decreases by increasing N b . Full article
(This article belongs to the Special Issue Convection Process and Entropy Generation in Different Fluids)
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