Editorial

4 pages, 169 KiB

Open AccessEditorial

Non-Equilibrium Thermodynamics of Micro Technologies

by Mohsen Torabi, Nader Karimi, Mostafa Ghiaasiaan and Somchai Wongwises

Entropy 2019, 21(5), 501; https://doi.org/10.3390/e21050501 - 17 May 2019

Cited by 2 | Viewed by 2561

This is the Editorial article summarizing the scope and contents of the Special Issue, Non-Equilibrium Thermodynamics of Micro Technologies. Full article

(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)

Research

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16 pages, 4977 KiB

Open AccessArticle

Numerical Study of Double-Layered Microchannel Heat Sinks with Different Cross-Sectional Shapes

by Daxiang Deng, Guang Pi, Weixun Zhang, Peng Wang and Ting Fu

Entropy 2019, 21(1), 16; https://doi.org/10.3390/e21010016 - 25 Dec 2018

Cited by 21 | Viewed by 5373

Abstract

This work numerically studies the thermal and hydraulic performance of double-layered microchannel heat sinks (DL-MCHS) for their application in the cooling of high heat flux microelectronic devices. The superiority of double-layered microchannel heat sinks was assessed by a comparison with a single-layered microchannel [...] Read more.

This work numerically studies the thermal and hydraulic performance of double-layered microchannel heat sinks (DL-MCHS) for their application in the cooling of high heat flux microelectronic devices. The superiority of double-layered microchannel heat sinks was assessed by a comparison with a single-layered microchannel heat sink (SL-MCHS) with the same triangular microchannels. Five DL-MCHSs with different cross-sectional shapes—triangular, rectangular, trapezoidal, circular and reentrant Ω-shaped—were explored and compared. The results showed that DL-MCHS decreased wall temperatures and thermal resistance considerably, induced much more uniform wall temperature distribution, and reduced the pressure drop and pumping power in comparison with SL-MCHS. The DL-MCHS with trapezoidal microchannels performed the worst with regard to thermal resistance, pressure drop, and pumping power. The DL-MCHS with rectangular microchannels produced the best overall thermal performance and seemed to be the optimum when thermal performance was the prime concern. Nevertheless, the DL-MCHS with reentrant Ω-shaped microchannels should be selected when pumping power consumption was the most important consideration. Full article

(This article belongs to the Special Issue Non-Equilibrium Thermodynamics of Micro Technologies)

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22 pages, 29306 KiB

Open AccessArticle

Flow and Heat Transfer in the Tree-Like Branching Microchannel with/without Dimples

by Linqi Shui, Jianhui Sun, Feng Gao and Chunyan Zhang

Entropy 2018, 20(5), 379; https://doi.org/10.3390/e20050379 - 18 May 2018

Cited by 9 | Viewed by 4404

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 (Nu_a/Nu_s) and thermal enhancement factor (η) both monotonously decrease as the Re number increases, while the friction factor ratio (f_a/f_s) changes nonlinearly. The entropy generation rates of

{\dot{S}}_{t}

and

{\dot{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 (N_s) under the high Re number conditions. Nu_a/Nu_s, f_a/f_s, 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)

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17 pages, 2222 KiB

Open AccessArticle

Performance of Segmented Thermoelectric Cooler Micro-Elements with Different Geometric Shapes and Temperature-Dependent Properties

by Carlos Alberto Badillo-Ruiz, Miguel Angel Olivares-Robles and Pablo Eduardo Ruiz-Ortega

Entropy 2018, 20(2), 118; https://doi.org/10.3390/e20020118 - 11 Feb 2018

Cited by 13 | Viewed by 4786

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)

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18 pages, 2519 KiB

Open AccessArticle

Assesment of Thermodynamic Irreversibility in a Micro-Scale Viscous Dissipative Circular Couette Flow

by Pranab Kumar Mondal and Somchai Wongwises

Entropy 2018, 20(1), 50; https://doi.org/10.3390/e20010050 - 11 Jan 2018

Cited by 9 | Viewed by 3220

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)

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18 pages, 5213 KiB

Open AccessFeature PaperArticle

Impact of Microgroove Shape on Flat Miniature Heat Pipe Efficiency

by François Ternet, Hasna Louahlia-Gualous and Stéphane Le Masson

Entropy 2018, 20(1), 44; https://doi.org/10.3390/e20010044 - 11 Jan 2018

Cited by 11 | Viewed by 5021

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)

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1925 KiB

Open AccessArticle

Leakage Evaluation by Virtual Entropy Generation (VEG) Method

by Zhichao Zhang, Corina Drapaca, Zhifeng Zhang, Shuaifang Zhang, Shimei Sun and Hui Liu

Entropy 2018, 20(1), 14; https://doi.org/10.3390/e20010014 - 29 Dec 2017

Cited by 9 | Viewed by 4167

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)

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8088 KiB

Open AccessArticle

Analysis and Optimization of Trapezoidal Grooved Microchannel Heat Sink Using Nanofluids in a Micro Solar Cell

by Ruijin Wang, Wen Wang, Jiawei Wang and Zefei Zhu

Entropy 2018, 20(1), 9; https://doi.org/10.3390/e20010009 - 25 Dec 2017

Cited by 17 | Viewed by 5588

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 N_BT (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)

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2420 KiB

Open AccessArticle

Non-Equilibrium Thermodynamic Analysis of Double Diffusive, Nanofluid Forced Convection in Catalytic Microreactors with Radiation Effects

by Lilian Govone, Mohsen Torabi, Graeme Hunt and Nader Karimi

Entropy 2017, 19(12), 690; https://doi.org/10.3390/e19120690 - 15 Dec 2017

Cited by 11 | Viewed by 4256

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)

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1732 KiB

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

by Arshad Khan, Kashif Ali Abro, Asifa Tassaddiq and Ilyas Khan

Entropy 2017, 19(8), 279; https://doi.org/10.3390/e19080279 - 18 Aug 2017

Cited by 90 | Viewed by 7362

Abstract

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} (\partial^{β} / \partial t^{β})

and Atangana–Baleanu (AB) [...] 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} (\partial^{β} / \partial t^{β})

and Atangana–Baleanu (AB)

^{A B} (\partial^{α} / \partial 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)

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