E-Mail Alert

Add your e-mail address to receive forthcoming issues of this journal:

Journal Browser

Journal Browser

Special Issue "Non-Equilibrium Thermodynamics of Micro Technologies"

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Thermodynamics".

Deadline for manuscript submissions: closed (10 December 2018)

Special Issue Editors

Guest Editor
Prof. Dr. S. Mostafa Ghiaasiaan

Heat Transfer, Combustion and Energy Systems, The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
Website | E-Mail
Guest Editor
Prof. Dr. Somchai Wongwises

Mechanical Engineering, Department of Mechanical Engineering, King Mongkut's University of Technology Thonburi, Bangkok 10140, Thailand
Website | E-Mail
Guest Editor
Dr. Nader Karimi

Lecturer in Mechanical Engineering, School of Engineering, University of Glasgow, Glasgow G12 8QQ, UK
Website | E-Mail
Guest Editor
Dr. Mohsen Torabi

The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
Website | E-Mail

Special Issue Information

Dear Colleagues,

Miniaturized thermofluid systems have recently gained significant attention from theoretical and experimental viewpoints. This is, mainly, due to the increasing applications of these systems in micro manufactured devices. Recently, micro heat sink thermal systems, such as microchannels and microtubes, have been used for a wide range of thermal and biological purposes. Among these, microchannels filled with porous materials have received particular attention as they feature favorable characteristics for cooling and pumping technologies in biomedical engineering. Utilization of microchannels has further resulted in the development of the so-called ‘microreactors’ for chemical process intensification. These devices build upon the technological progress in the general fields of microchannels and micro-thermofluids to accommodate homogenous or heterogonous chemical reactions. Micro porous tubes have also been used for miniaturized cryocoolers. The applications of microreactors and miniaturized cryocoolers are now at their most extensive and include applications in combustion, hydrogen, cryogenic and syngas production and industrial chemicals. These devices can also involve multiple reactants and exothermic/endothermic stages. Therefore, they should feature very efficient mixing and heat transfer characteristics.

Second law analysis and entropy generation minimization have started to be employed in the design and optimization of various thermal and thermochemical systems. These include microchannels and microtubes with applications in micro thermal, mechanical, chemical and biological systems. Further developments in this front call for a more rigorous understanding and modeling of thermodynamic processes in micro devices under highly irreversible conditions.

This Special Issue aims to be the forum for the presentation of the novel non-equilibrium thermodynamic investigations in the broad area of micro-technology. In particular, heat and mass transfer and entropy generation investigations in microchannels, microreactors, microcryocoolers, and micro-thermofluids fall within the scope of this Special Issue.

Prof. Dr. S. Mostafa Ghiaasiaan
Prof. Dr. Somchai Wongwises
Dr. Nader Karimi
Dr. Mohsen Torabi
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Entropy generation

  • Micro thermofluids

  • Micro channels

  • Miniaturized cryocoolers

  • Micro reactors

Published Papers (8 papers)

View options order results:
result details:
Displaying articles 1-8
Export citation of selected articles as:

Research

Open AccessArticle Flow and Heat Transfer in the Tree-Like Branching Microchannel with/without Dimples
Entropy 2018, 20(5), 379; https://doi.org/10.3390/e20050379
Received: 2 April 2018 / Revised: 10 May 2018 / Accepted: 16 May 2018 / Published: 18 May 2018
Cited by 1 | PDF Full-text (29306 KB) | HTML Full-text | XML Full-text
Abstract
This work displays a numerical and experimental investigation on the flow and heat transfer in tree-like branching microchannels and studies the effects of dimples on the heat transfer enhancement. The numerical approach is certified by a smooth branching microchannel experiment. The verification result
[...] Read more.
This work displays a numerical and experimental investigation on the flow and heat transfer in tree-like branching microchannels and studies the effects of dimples on the heat transfer enhancement. The numerical approach is certified by a smooth branching microchannel experiment. The verification result shows that the SSG turbulence model can provide a reasonable prediction. Thus, further research on the convective heat transfer in dimpled branching microchannels is conducted with the SSG turbulence model. The results indicate that the dimples can significantly improve the averaged heat transfer performance of branching microchannels, and the heat transfer increment of the branch segment increases with the increase in the branching level. However, the flow dead zones in some dimples at bifurcations and bends suppress the turbulent flow and heat transfer. Furthermore, the Nu number ratio (Nua/Nus) and thermal enhancement factor (η) both monotonously decrease as the Re number increases, while the friction factor ratio (fa/fs) changes nonlinearly. The entropy generation rates of S ˙ t and S ˙ p in all dimpled cases are lower than those in the smooth case, and the dimpled case with the streamwise spacing to diameter ratio s/D = 3 obtains the lowest value of augmentation entropy generation (Ns) under the high Re number conditions. Nua/Nus, fa/fs, and η decline with the increase in the streamwise spacing to diameter ratio (s/D) from 3 to 9; therefore, the dimpled case with s/D = 3 shows the best overall thermal performance. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Figure 1

Open AccessArticle Performance of Segmented Thermoelectric Cooler Micro-Elements with Different Geometric Shapes and Temperature-Dependent Properties
Entropy 2018, 20(2), 118; https://doi.org/10.3390/e20020118
Received: 31 December 2017 / Revised: 7 February 2018 / Accepted: 8 February 2018 / Published: 11 February 2018
PDF Full-text (2222 KB) | HTML Full-text | XML Full-text
Abstract
In this work, the influences of the Thomson effect and the geometry of the p-type segmented leg on the performance of a segmented thermoelectric microcooler (STEMC) were examined. The effects of geometry and the material configuration of the p-type segmented leg on the
[...] Read more.
In this work, the influences of the Thomson effect and the geometry of the p-type segmented leg on the performance of a segmented thermoelectric microcooler (STEMC) were examined. The effects of geometry and the material configuration of the p-type segmented leg on the cooling power ( Q c ) and coefficient of performance ( C O P ) were investigated. The influence of the cross-sectional area ratio of the two joined segments on the device performance was also evaluated. We analyzed a one-dimensional p-type segmented leg model composed of two different semiconductor materials, B i 2 T e 3 and ( B i 0.5 S b 0.5 ) 2 T e 3 . Considering the three most common p-type leg geometries, we studied both single-material systems (using the same material for both segments) and segmented systems (using different materials for each segment). The C O P , Q c and temperature profile were evaluated for each of the modeled geometric configurations under a fixed temperature gradient of Δ T = 30 K. The performances of the STEMC were evaluated using two models, namely the constant-properties material (CPM) and temperature-dependent properties material (TDPM) models, considering the thermal conductivity ( κ ( T ) ), electrical conductivity ( σ ( T ) ) and Seebeck coefficient ( α ( T ) ). We considered the influence of the Thomson effect on C O P and Q c using the TDPM model. The results revealed the optimal material configurations for use in each segment of the p-type leg. According to the proposed geometric models, the optimal leg geometry and electrical current for maximum performance were determined. After consideration of the Thomson effect, the STEMC system was found to deliver a maximum cooling power that was 5.10 % higher than that of the single-material system. The results showed that the inverse system (where the material with a higher Seebeck coefficient is used for the first segment) delivered a higher performance than the direct system, with improvements in the C O P and Q c of 6.67 % and 29.25 % , respectively. Finally, analysis of the relationship between the areas of the STEMC segments demonstrated that increasing the cross-sectional area in the second segment led to improvements in the C O P and Q c of 16.67 % and 8.03 % , respectively. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Graphical abstract

Open AccessArticle Assesment of Thermodynamic Irreversibility in a Micro-Scale Viscous Dissipative Circular Couette Flow
Entropy 2018, 20(1), 50; https://doi.org/10.3390/e20010050
Received: 18 December 2017 / Revised: 8 January 2018 / Accepted: 10 January 2018 / Published: 11 January 2018
PDF Full-text (2519 KB) | HTML Full-text | XML Full-text
Abstract
We investigate the effect of viscous dissipation on the thermal transport characteristics of heat and its consequence in terms of the entropy-generation rate in a circular Couette flow. We consider the flow of a Newtonian fluid through a narrow annular space between two
[...] Read more.
We investigate the effect of viscous dissipation on the thermal transport characteristics of heat and its consequence in terms of the entropy-generation rate in a circular Couette flow. We consider the flow of a Newtonian fluid through a narrow annular space between two asymmetrically-heated concentric micro-cylinders where the inner cylinder is rotating at a constant speed. Employing an analytical methodology, we demonstrate the temperature distribution and its consequential effects on the heat-transfer and entropy-generation behaviour in the annulus. We bring out the momentous effect of viscous dissipation on the underlying transport of heat as modulated by the degree of thermal asymmetries. Our results also show that the variation of the Nusselt number exhibits an unbounded swing for some values of the Brinkman number and degrees of asymmetrical wall heating. We explain the appearance of unbounded swing on the variation of the Nusselt number from the energy balance in the flow field as well as from the second law of thermodynamics. We believe that the insights obtained from the present analysis may improve the design of micro-rotating devices/systems. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Graphical abstract

Open AccessFeature PaperArticle Impact of Microgroove Shape on Flat Miniature Heat Pipe Efficiency
Entropy 2018, 20(1), 44; https://doi.org/10.3390/e20010044
Received: 27 October 2017 / Revised: 7 January 2018 / Accepted: 9 January 2018 / Published: 11 January 2018
Cited by 1 | PDF Full-text (5213 KB) | HTML Full-text | XML Full-text
Abstract
Miniature heat pipes are considered to be an innovative solution able to dissipate high heat with low working fluid fill charge, provide automatic temperature control, and operate with minimum energy consumption and low noise levels. A theoretical analysis on heat pipe thermal performance
[...] Read more.
Miniature heat pipes are considered to be an innovative solution able to dissipate high heat with low working fluid fill charge, provide automatic temperature control, and operate with minimum energy consumption and low noise levels. A theoretical analysis on heat pipe thermal performance using Deionized water or n-pentane as the working fluid has been carried out. Analysis on the maximum heat and capillary limitation is conducted for three microgroove cross sections: rectangular, triangular, and trapezoidal. The effect of microgroove height and width, effective length, trapezoidal microgroove inclination angle, and microgroove shape on heat pipe performance is analysed. Theoretical and experimental investigations of the heat pipes’ heat transport limitations and thermal resistances are conducted. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Figure 1

Open AccessArticle Leakage Evaluation by Virtual Entropy Generation (VEG) Method
Entropy 2018, 20(1), 14; https://doi.org/10.3390/e20010014
Received: 15 November 2017 / Revised: 23 December 2017 / Accepted: 28 December 2017 / Published: 29 December 2017
Cited by 3 | PDF Full-text (1925 KB) | HTML Full-text | XML Full-text
Abstract
Leakage through microscale or nanoscale cracks is usually hard to observe, difficult to control, and causes significant economic loss. In the present research, the leakage in a pipe was evaluated by the virtual entropy generation (VEG) method. In virtual entropy generation method, the
[...] Read more.
Leakage through microscale or nanoscale cracks is usually hard to observe, difficult to control, and causes significant economic loss. In the present research, the leakage in a pipe was evaluated by the virtual entropy generation (VEG) method. In virtual entropy generation method, the “measured entropy generation” is forced to follow the “experimental second law of thermodynamics”. Taking the leakage as the source virtual entropy generation, a new pipe leakage evaluation criterion was analytically derived, which indicates that the mass leakage rate should be smaller than the pressure drop rate inside a pipe. A numerical study based on computational fluid dynamics showed the existence of an unrealistic virtual entropy generation at a high mass leakage rate. Finally, the new criterion was used in the evaluation of leakage available in the literature. These results could be useful for leakage control or industry criteria design in the future. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Graphical abstract

Open AccessArticle Analysis and Optimization of Trapezoidal Grooved Microchannel Heat Sink Using Nanofluids in a Micro Solar Cell
Entropy 2018, 20(1), 9; https://doi.org/10.3390/e20010009
Received: 15 November 2017 / Revised: 7 December 2017 / Accepted: 20 December 2017 / Published: 25 December 2017
Cited by 1 | PDF Full-text (8088 KB) | HTML Full-text | XML Full-text
Abstract
It is necessary to control the temperature of solar cells for enhancing efficiency with increasing concentrations of multiple photovoltaic systems. A heterogeneous two-phase model was established after considering the interacting between temperature, viscosity, the flow of nanofluid, and the motion of nanoparticles in
[...] Read more.
It is necessary to control the temperature of solar cells for enhancing efficiency with increasing concentrations of multiple photovoltaic systems. A heterogeneous two-phase model was established after considering the interacting between temperature, viscosity, the flow of nanofluid, and the motion of nanoparticles in the nanofluid, in order to study the microchannel heat sink (MCHS) using Al2O3-water nanofluid as coolant in the photovoltaic system. Numerical simulations were carried out to investigate the thermal performance of MCHS with a series of trapezoidal grooves. The numerical results showed us that, (1) better thermal performance of MCSH using nanofluid can be achieved from a heterogeneous two-phase model than that from single-phase model; (2) The effects of flow field, volume fraction, nanoparticle size on the heat transfer enhancement in MCHS were interpreted by a non-dimensional parameter NBT (i.e., ratio of Brownian diffusion and thermophoretic diffusion). In addition, the geometrical parameters of MCHS and the physical parameters of the nanofluid were optimized. This can provide a sound foundation for the design of MCHS. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Figure 1

Open AccessArticle Non-Equilibrium Thermodynamic Analysis of Double Diffusive, Nanofluid Forced Convection in Catalytic Microreactors with Radiation Effects
Entropy 2017, 19(12), 690; https://doi.org/10.3390/e19120690
Received: 11 October 2017 / Revised: 27 November 2017 / Accepted: 14 December 2017 / Published: 15 December 2017
Cited by 1 | PDF Full-text (2420 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a theoretical investigation of the second law performance of double diffusive forced convection in microreactors with the inclusion of nanofluid and radiation effects. The investigated microreactors consist of a single microchannel, fully filled by a porous medium. The transport of
[...] Read more.
This paper presents a theoretical investigation of the second law performance of double diffusive forced convection in microreactors with the inclusion of nanofluid and radiation effects. The investigated microreactors consist of a single microchannel, fully filled by a porous medium. The transport of heat and mass are analysed by including the thick walls and a first order, catalytic chemical reaction on the internal surfaces of the microchannel. Two sets of thermal boundary conditions are considered on the external surfaces of the microchannel; (1) constant temperature and (2) constant heat flux boundary condition on the lower wall and convective boundary condition on the upper wall. The local thermal non-equilibrium approach is taken to thermally analyse the porous section of the system. The mass dispersion equation is coupled with the transport of heat in the nanofluid flow through consideration of Soret effect. The problem is analytically solved and illustrations of the temperature fields, Nusselt number, total entropy generation rate and performance evaluation criterion (PEC) are provided. It is shown that the radiation effect tends to modify the thermal behaviour within the porous section of the system. The radiation parameter also reduces the overall temperature of the system. It is further demonstrated that, expectedly, the nanoparticles reduce the temperature of the system and increase the Nusselt number. The total entropy generation rate and consequently PEC shows a strong relation with radiation parameter and volumetric concentration of nanoparticles. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Figure 1

Open AccessArticle Atangana–Baleanu and Caputo Fabrizio Analysis of Fractional Derivatives for Heat and Mass Transfer of Second Grade Fluids over a Vertical Plate: A Comparative Study
Entropy 2017, 19(8), 279; https://doi.org/10.3390/e19080279
Received: 4 May 2017 / Revised: 11 June 2017 / Accepted: 12 June 2017 / Published: 18 August 2017
Cited by 20 | PDF Full-text (1732 KB) | HTML Full-text | XML Full-text
Abstract
This communication addresses a comparison of newly presented non-integer order derivatives with and without singular kernel, namely Michele Caputo–Mauro Fabrizio (CF) CF(β/tβ) and Atangana–Baleanu (AB) AB(α/tα
[...] Read more.
This communication addresses a comparison of newly presented non-integer order derivatives with and without singular kernel, namely Michele Caputo–Mauro Fabrizio (CF) C F ( β / t β ) and Atangana–Baleanu (AB) A B ( α / t α ) fractional derivatives. For this purpose, second grade fluids flow with combined gradients of mass concentration and temperature distribution over a vertical flat plate is considered. The problem is first written in non-dimensional form and then based on AB and CF fractional derivatives, it is developed in fractional form, and then using the Laplace transform technique, exact solutions are established for both cases of AB and CF derivatives. They are then expressed in terms of newly defined M-function M q p ( z ) and generalized Hyper-geometric function p Ψ q ( z ) . The obtained exact solutions are plotted graphically for several pertinent parameters and an interesting comparison is made between AB and CF derivatives results with various similarities and differences. Full article
(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)
Figures

Figure 1

Back to Top