E-Mail Alert

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

Journal Browser

Journal Browser

Special Issue "Entropy Generation and Heat Transfer"

A special issue of Entropy (ISSN 1099-4300).

Deadline for manuscript submissions: 30 April 2019

Special Issue Editor

Guest Editor
Prof. Dr. José Miguel Mateos Roco

Department of Applied Physics, Faculty of Science, University of Salamanca, Plaza de la Merced, s/n, 37008 SALAMANCA, Spain
Website | E-Mail
Interests: thermodynamics; statistical physics

Special Issue Information

Dear Colleagues,

The evaluation of entropy generation has been a research issue since the foundation of Thermodynamics as a physical theory related to the analysis and performance of heat devices. As a matter of fact, the cornerstone Clausius theorem of Thermodynamics ascribed entropy generation to unavoidable irreversibilities of real processes, which do not allow heat devices to perform the quasistatic upper bound efficiency.

The aim of the evaluation of entropy generation requires the proposal of models that feature heat transfer processes, taking into account the finite size of actual devices and the finite speeds of real processes. Moreover, the eventual optimization of a suitable functional with respect to the characteristic parameters of the model, allows to obtain more realistic bounds for the performance of real heat devices.

This purpose to describe accurately efficient real-life devices has brought a great variety of models and optimization criteria according to the different nature and scales of the involved processes: from quantum, to macroscopic passing through mesoscopic levels. Then, for this Special Issue aimed to provide a panoramic view (including physics, engineering oriented papers and others) of the research carried out in this field, submissions related with modeling and optimization of real heat devices are welcome.

Prof. Dr. José Miguel Mateos Roco
Guest Editor

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 1600 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

  • Heat devices
  • Mesoscopic energy converters
  • Quantum heat devices
  • Finite time thermodynamics
  • Irreversible thermodynamics
  • Energy dissipation
  • Finite size constraints
  • Finite time contraints
  • Quantum thermodynamics
  • Thermodynamic optimization
  • Entropy generation minimization
  • Stochastic thermodynamics

Published Papers (17 papers)

View options order results:
result details:
Displaying articles 1-17
Export citation of selected articles as:

Editorial

Jump to: Research

Open AccessEditorial How to Teach Heat Transfer More Systematically by Involving Entropy
Entropy 2018, 20(10), 791; https://doi.org/10.3390/e20100791
Received: 11 September 2018 / Accepted: 8 October 2018 / Published: 15 October 2018
PDF Full-text (2427 KB) | HTML Full-text | XML Full-text
Abstract
In order to teach heat transfer systematically and with a clear physical background, it is recommended that entropy should not be ignored as a fundamental quantity. Heat transfer processes are characterized by introducing the so-called “entropic potential” of the transferred energy, and an
[...] Read more.
In order to teach heat transfer systematically and with a clear physical background, it is recommended that entropy should not be ignored as a fundamental quantity. Heat transfer processes are characterized by introducing the so-called “entropic potential” of the transferred energy, and an assessment number is based on this new quantity. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Research

Jump to: Editorial

Open AccessArticle How to Construct a Combined S-CO2 Cycle for Coal Fired Power Plant?
Entropy 2019, 21(1), 19; https://doi.org/10.3390/e21010019
Received: 29 November 2018 / Revised: 22 December 2018 / Accepted: 23 December 2018 / Published: 27 December 2018
PDF Full-text (2535 KB) | HTML Full-text | XML Full-text
Abstract
It is difficult to recover the residual heat from flue gas when supercritical carbon dioxide (S-CO2) cycle is used for a coal fired power plant, due to the higher CO2 temperature in tail flue and the limited air temperature in
[...] Read more.
It is difficult to recover the residual heat from flue gas when supercritical carbon dioxide (S-CO2) cycle is used for a coal fired power plant, due to the higher CO2 temperature in tail flue and the limited air temperature in air preheater. The combined cycle is helpful for residual heat recovery. Thus, it is important to build an efficient bottom cycle. In this paper, we proposed a novel exergy destruction control strategy during residual heat recovery to equal and minimize the exergy destruction for different bottom cycles. Five bottom cycles are analyzed to identify their differences in thermal efficiencies (ηth,b), and the CO2 temperature entering the bottom cycle heater (T4b) etc. We show that the exergy destruction can be minimized by a suitable pinch temperature between flue gas and CO2 in the heater via adjusting T4b. Among the five bottom cycles, either the recompression cycle (RC) or the partial cooling cycle (PACC) exhibits good performance. The power generation efficiency is 47.04% when the vapor parameters of CO2 are 620/30 MPa, with the double-reheating-recompression cycle as the top cycle, and RC as the bottom cycle. Such efficiency is higher than that of the supercritical water cycle power plant. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle A Simple Thermodynamic Model of the Internal Convective Zone of the Earth
Entropy 2018, 20(12), 985; https://doi.org/10.3390/e20120985
Received: 29 November 2018 / Revised: 8 December 2018 / Accepted: 14 December 2018 / Published: 18 December 2018
PDF Full-text (465 KB) | HTML Full-text | XML Full-text
Abstract
As it is well known both atmospheric and mantle convection are very complex phenomena. The dynamical description of these processes is a very difficult task involving complicated 2-D or 3-D mathematical models. However, a first approximation to these phenomena can be by means
[...] Read more.
As it is well known both atmospheric and mantle convection are very complex phenomena. The dynamical description of these processes is a very difficult task involving complicated 2-D or 3-D mathematical models. However, a first approximation to these phenomena can be by means of simplified thermodynamic models where the restriction imposed by the laws of thermodynamics play an important role. An example of this approach is the model proposed by Gordon and Zarmi in 1989 to emulate the convective cells of the atmospheric air by using finite-time thermodynamics (FTT). In the present article we use the FTT Gordon-Zarmi model to coarsely describe the convection in the Earth’s mantle. Our results permit the existence of two layers of convective cells along the mantle. Besides the model reasonably reproduce the temperatures of the main discontinuities in the mantle, such as the 410 km-discontinuity, the Repetti transition zone and the so-called D-Layer. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Irreversibility Analysis of Dissipative Fluid Flow Over A Curved Surface Stimulated by Variable Thermal Conductivity and Uniform Magnetic Field: Utilization of Generalized Differential Quadrature Method
Entropy 2018, 20(12), 943; https://doi.org/10.3390/e20120943
Received: 10 October 2018 / Revised: 18 November 2018 / Accepted: 3 December 2018 / Published: 7 December 2018
PDF Full-text (3867 KB) | HTML Full-text | XML Full-text
Abstract
The effects of variable thermal conductivity on heat transfer and entropy generation in a flow over a curved surface are investigated in the present study. In addition, the effects of energy dissipation and Ohmic heating are also incorporated in the modelling of the
[...] Read more.
The effects of variable thermal conductivity on heat transfer and entropy generation in a flow over a curved surface are investigated in the present study. In addition, the effects of energy dissipation and Ohmic heating are also incorporated in the modelling of the energy equation. Appropriate transformations are used to develop the self-similar equations from the governing equations of momentum and energy. The resulting self-similar equations are then solved by the Generalized Differential Quadrature Method (GDQM). For the validation and precision of the developed numerical solution, the resulting equations are also solved numerically using the Runge-Kutta-Fehlberg method (RKFM). An excellent agreement is found between the numerical results of the two methods. To examine the impacts of emerging physical parameters on velocity, temperature distribution and entropy generation, the numerical results are plotted against the various values of physical flow parameters and discussed physically in detail. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Entropy Analysis of 3D Non-Newtonian MHD Nanofluid Flow with Nonlinear Thermal Radiation Past over Exponential Stretched Surface
Entropy 2018, 20(12), 930; https://doi.org/10.3390/e20120930
Received: 29 October 2018 / Revised: 28 November 2018 / Accepted: 2 December 2018 / Published: 5 December 2018
PDF Full-text (6386 KB) | HTML Full-text | XML Full-text
Abstract
The present study characterizes the flow of three-dimensional viscoelastic magnetohydrodynamic (MHD) nanofluids flow with entropy generation analysis past an exponentially permeable stretched surface with simultaneous impacts of chemical reaction and heat generation/absorption. The analysis was conducted with additional effects nonlinear thermal radiation and
[...] Read more.
The present study characterizes the flow of three-dimensional viscoelastic magnetohydrodynamic (MHD) nanofluids flow with entropy generation analysis past an exponentially permeable stretched surface with simultaneous impacts of chemical reaction and heat generation/absorption. The analysis was conducted with additional effects nonlinear thermal radiation and convective heat and mass boundary conditions. Apposite transformations were considered to transform the presented mathematical model to a system of differential equations. Analytical solutions of the proposed model were developed via a well-known homotopy analysis scheme. The numerically calculated values of the dimensionless drag coefficient, local Nusselt number, and mass transfer Nusselt number are presented, with physical insights. The graphs depicting the consequences of numerous parameters on involved distributions with requisite deliberations were also a part of this model. It is seen that the Bejan number is an increasing function of the thermal radiation parameter. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Entropy Density Acceleration and Minimum Dissipation Principle: Correlation with Heat and Matter Transfer in Glucose Catabolism
Entropy 2018, 20(12), 929; https://doi.org/10.3390/e20120929
Received: 7 November 2018 / Revised: 2 December 2018 / Accepted: 3 December 2018 / Published: 5 December 2018
PDF Full-text (2182 KB) | HTML Full-text | XML Full-text
Abstract
The heat and matter transfer during glucose catabolism in living systems and their relation with entropy production are a challenging subject of the classical thermodynamics applied to biology. In this respect, an analogy between mechanics and thermodynamics has been performed via the definition
[...] Read more.
The heat and matter transfer during glucose catabolism in living systems and their relation with entropy production are a challenging subject of the classical thermodynamics applied to biology. In this respect, an analogy between mechanics and thermodynamics has been performed via the definition of the entropy density acceleration expressed by the time derivative of the rate of entropy density and related to heat and matter transfer in minimum living systems. Cells are regarded as open thermodynamic systems that exchange heat and matter resulting from irreversible processes with the intercellular environment. Prigogine’s minimum energy dissipation principle is reformulated using the notion of entropy density acceleration applied to glucose catabolism. It is shown that, for out-of-equilibrium states, the calculated entropy density acceleration for a single cell is finite and negative and approaches as a function of time a zero value at global thermodynamic equilibrium for heat and matter transfer independently of the cell type and the metabolic pathway. These results could be important for a deeper understanding of entropy generation and its correlation with heat transfer in cell biology with special regard to glucose catabolism representing the prototype of irreversible reactions and a crucial metabolic pathway in stem cells and cancer stem cells. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Optimization and Stability of Heat Engines: The Role of Entropy Evolution
Entropy 2018, 20(11), 865; https://doi.org/10.3390/e20110865
Received: 23 October 2018 / Revised: 5 November 2018 / Accepted: 7 November 2018 / Published: 9 November 2018
PDF Full-text (2042 KB) | HTML Full-text | XML Full-text
Abstract
Local stability of maximum power and maximum compromise (Omega) operation regimes dynamic evolution for a low-dissipation heat engine is analyzed. The thermodynamic behavior of trajectories to the stationary state, after perturbing the operation regime, display a trade-off between stability, entropy production, efficiency and
[...] Read more.
Local stability of maximum power and maximum compromise (Omega) operation regimes dynamic evolution for a low-dissipation heat engine is analyzed. The thermodynamic behavior of trajectories to the stationary state, after perturbing the operation regime, display a trade-off between stability, entropy production, efficiency and power output. This allows considering stability and optimization as connected pieces of a single phenomenon. Trajectories inside the basin of attraction display the smallest entropy drops. Additionally, it was found that time constraints, related with irreversible and endoreversible behaviors, influence the thermodynamic evolution of relaxation trajectories. The behavior of the evolution in terms of the symmetries of the model and the applied thermal gradients was analyzed. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Entropy and Entransy Dissipation Analysis of a Basic Organic Rankine Cycles (ORCs) to Recover Low-Grade Waste Heat Using Mixture Working Fluids
Entropy 2018, 20(11), 818; https://doi.org/10.3390/e20110818
Received: 16 September 2018 / Revised: 19 October 2018 / Accepted: 19 October 2018 / Published: 24 October 2018
Cited by 1 | PDF Full-text (4907 KB) | HTML Full-text | XML Full-text
Abstract
Mixture working fluids can reduce effectively energy loss at heat sources and heat sinks, and therefore enhance the organic Rankine cycle (ORC) performance. The entropy and entransy dissipation analyses of a basic ORC system to recover low-grade waste heat using three mixture working
[...] Read more.
Mixture working fluids can reduce effectively energy loss at heat sources and heat sinks, and therefore enhance the organic Rankine cycle (ORC) performance. The entropy and entransy dissipation analyses of a basic ORC system to recover low-grade waste heat using three mixture working fluids (R245fa/R227ea, R245fa/R152a and R245fa/pentane) have been investigated in this study. The basic ORC includes four components: an expander, a condenser, a pump and an evaporator. The heat source temperature is 120 °C while the condenser temperature is 20 °C. The effects of four operating parameters (evaporator outlet temperature, condenser temperature, pinch point temperature difference, degree of superheat), as well as the mass fraction, on entransy dissipation and entropy generation were examined. Results demonstrated that the entransy dissipation is insensitive to the mass fraction of R245fa. The entropy generation distributions at the evaporator for R245/pentane, R245fa/R152a and R245fa/R227ea are in ranges of 66–74%, 68–80% and 66–75%, respectively, with the corresponding entropy generation at the condenser ranges of 13–21%, 4–17% and 11–21%, respectively, while those at the expander for R245/pentane, R245fa/R152a and R245fa/R227ea are approaching 13%, 15% and 14%, respectively. The optimal mass fraction of R245fa for the minimum entropy generation is 0.6 using R245fa/R152a. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Entropy Generation Rates in Two-Dimensional Rayleigh–Taylor Turbulence Mixing
Entropy 2018, 20(10), 738; https://doi.org/10.3390/e20100738
Received: 20 August 2018 / Revised: 13 September 2018 / Accepted: 17 September 2018 / Published: 26 September 2018
PDF Full-text (3103 KB) | HTML Full-text | XML Full-text
Abstract
Entropy generation rates in two-dimensional Rayleigh–Taylor (RT) turbulence mixing are investigated by numerical calculation. We mainly focus on the behavior of thermal entropy generation and viscous entropy generation of global quantities with time evolution in Rayleigh–Taylor turbulence mixing. Our results mainly indicate that,
[...] Read more.
Entropy generation rates in two-dimensional Rayleigh–Taylor (RT) turbulence mixing are investigated by numerical calculation. We mainly focus on the behavior of thermal entropy generation and viscous entropy generation of global quantities with time evolution in Rayleigh–Taylor turbulence mixing. Our results mainly indicate that, with time evolution, the intense viscous entropy generation rate s u and the intense thermal entropy generation rate S θ occur in the large gradient of velocity and interfaces between hot and cold fluids in the RT mixing process. Furthermore, it is also noted that the mixed changing gradient of two quantities from the center of the region to both sides decrease as time evolves, and that the viscous entropy generation rate S u V and thermal entropy generation rate S θ V constantly increase with time evolution; the thermal entropy generation rate S θ V with time evolution always dominates in the entropy generation of the RT mixing region. It is further found that a “smooth” function S u V t 1 / 2 and a linear function S θ V t are achieved in the spatial averaging entropy generation of RT mixing process, respectively. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Transpiration and Viscous Dissipation Effects on Entropy Generation in Hybrid Nanofluid Flow over a Nonlinear Radially Stretching Disk
Entropy 2018, 20(9), 668; https://doi.org/10.3390/e20090668
Received: 1 July 2018 / Revised: 14 August 2018 / Accepted: 17 August 2018 / Published: 4 September 2018
Cited by 1 | PDF Full-text (7130 KB) | HTML Full-text | XML Full-text
Abstract
The present research work explores the effects of suction/injection and viscous dissipation on entropy generation in the boundary layer flow of a hybrid nanofluid (Cu–Al2O3–H2O) over a nonlinear radially stretching porous disk. The energy dissipation function is
[...] Read more.
The present research work explores the effects of suction/injection and viscous dissipation on entropy generation in the boundary layer flow of a hybrid nanofluid (Cu–Al2O3–H2O) over a nonlinear radially stretching porous disk. The energy dissipation function is added in the energy equation in order to incorporate the effects of viscous dissipation. The Tiwari and Das model is used in this work. The flow, heat transfer, and entropy generation analysis have been performed using a modified form of the Maxwell Garnett (MG) and Brinkman nanofluid model for effective thermal conductivity and dynamic viscosity, respectively. Suitable transformations are utilized to obtain a set of self-similar ordinary differential equations. Numerical solutions are obtained using shooting and bvp4c Matlab solver. The comparison of solutions shows excellent agreement. To examine the effects of principal flow parameters like suction/injection, the Eckert number, and solid volume fraction, different graphs are plotted and discussed. It is concluded that entropy generation inside the boundary layer of a hybrid nanofluid is high compared to a convectional nanofluid. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Second Law Analysis of Dissipative Flow over a Riga Plate with Non-Linear Rosseland Thermal Radiation and Variable Transport Properties
Entropy 2018, 20(8), 615; https://doi.org/10.3390/e20080615
Received: 17 July 2018 / Revised: 7 August 2018 / Accepted: 15 August 2018 / Published: 18 August 2018
PDF Full-text (7393 KB) | HTML Full-text | XML Full-text
Abstract
In this article, we investigated entropy generation and heat transfer analysis in a viscous flow induced by a horizontally moving Riga plate in the presence of strong suction. The viscosity and thermal conductivity of the fluid are taken to be temperature dependent. The
[...] Read more.
In this article, we investigated entropy generation and heat transfer analysis in a viscous flow induced by a horizontally moving Riga plate in the presence of strong suction. The viscosity and thermal conductivity of the fluid are taken to be temperature dependent. The frictional heating function and non-linear radiation terms are also incorporated in the entropy generation and energy equation. The partial differential equations which model the flow are converted into dimensionless form by using proper transformations. Further, the dimensionless equations are reduced by imposing the conditions of strong suction. Numerical solutions are obtained using MATLAB boundary value solver bvp4c and used to evaluate the entropy generation number. The influences of physical flow parameters arise in the mathematical modeling are demonstrated through various graphs. The analysis reveals that velocity decays whereas entropy generation increases with rising values of variable viscosity parameter. Furthermore, entropy generation decays with increasing variable thermal conductivity parameter. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Thermo-Fluid Characteristics of High Temperature Molten Salt Flowing in Single-Leaf Type Hollow Paddles
Entropy 2018, 20(8), 581; https://doi.org/10.3390/e20080581
Received: 8 July 2018 / Revised: 2 August 2018 / Accepted: 5 August 2018 / Published: 7 August 2018
PDF Full-text (7878 KB) | HTML Full-text | XML Full-text
Abstract
A single-leaf type paddle heat exchanger with molten salt as the working fluid is a proper option in high temperature heating processes of materials. In this paper, based on computational fluid dynamics (CFD) simulations, we present the thermo-fluid characteristics of high temperature molten
[...] Read more.
A single-leaf type paddle heat exchanger with molten salt as the working fluid is a proper option in high temperature heating processes of materials. In this paper, based on computational fluid dynamics (CFD) simulations, we present the thermo-fluid characteristics of high temperature molten salt flowing in single-leaf type hollow paddles in the view of both the first law and the second law of thermodynamics. The results show that the heat transfer rate of the hollow paddles is significantly greater than that of solid paddles. The penalty of the heat transfer enhancement is additional pressure drop and larger total irreversibility (i.e., total entropy generation rate). Increasing the volume of the fluid space helps to enhance the heat transfer, but there exists an upper limit. Hollow paddles are more favorable in heat transfer enhancement for designs with a larger height of the paddles, flow rate of molten salt and material-side heat transfer coefficient. The diameter of the flow holes influences the pressure drop strongly, but their position is not important for heat transfer in the studied range. Other measures of modifying the fluid flow and heat transfer like internal baffles, more flow holes or multiple channels for small fluid volume are further discussed. For few baffles, their effects are limited. More flow holes reduce the pressure drop obviously. For the hollow paddles with small fluid volume, it is possible to increase the heat transfer rate with more fluid channels. The trade-off among fluid flow, heat transfer and mechanical strength is necessary. The thermo-fluid characteristics revealed in this paper will provide guidance for practical designs. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Entropy Generation Due to the Heat Transfer for Evolving Spherical Objects
Entropy 2018, 20(8), 562; https://doi.org/10.3390/e20080562
Received: 5 July 2018 / Revised: 23 July 2018 / Accepted: 25 July 2018 / Published: 28 July 2018
PDF Full-text (5648 KB) | HTML Full-text | XML Full-text
Abstract
Heat transfer accompanying entropy generation for the evolving mini and microbubbles in solution is discussed based on the explicit solutions for the hydrodynamic equations related to the bubble motion. Even though the pressure difference between the gas inside the bubble and liquid outside
[...] Read more.
Heat transfer accompanying entropy generation for the evolving mini and microbubbles in solution is discussed based on the explicit solutions for the hydrodynamic equations related to the bubble motion. Even though the pressure difference between the gas inside the bubble and liquid outside the bubble is a major driving force for bubble evolution, the heat transfer by conduction at the bubble-liquid interface affects the delicate evolution of the bubble, especially for sonoluminescing the gas bubble in sulfuric acid solution. On the other hand, our explicit solutions for the continuity, Euler equation, and Newtonian gravitational equation reveal that supernovae evolve by the gravitational force radiating heat in space during the expanding or collapsing phase. In this article, how the entropy generation due to heat transfer affects the bubble motion delicately and how heat transfer is generated by gravitational energy and evolving speed for the supernovae will be discussed. The heat transfer experienced by the bubble and supernovae during their evolution produces a positive entropy generation rate. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Thermal Characteristics of Staggered Double-Layer Microchannel Heat Sink
Entropy 2018, 20(7), 537; https://doi.org/10.3390/e20070537
Received: 14 June 2018 / Revised: 5 July 2018 / Accepted: 12 July 2018 / Published: 19 July 2018
Cited by 1 | PDF Full-text (1678 KB) | HTML Full-text | XML Full-text
Abstract
The present work numerically studies the thermal characteristics of a staggered double-layer microchannel heat sink (DLMCHS) with an offset between the upper layer of microchannels and lower layer of microchannels in the width direction, and investigates effects of inlet velocity and geometric parameters
[...] Read more.
The present work numerically studies the thermal characteristics of a staggered double-layer microchannel heat sink (DLMCHS) with an offset between the upper layer of microchannels and lower layer of microchannels in the width direction, and investigates effects of inlet velocity and geometric parameters including the offset of the two layers of microchannels, vertical rib thickness and microchannel aspect ratio on the thermal resistance of the staggered DLMCHS. The present work found that the thermal resistance of the staggered DLMCHS increases with the increasing offset value when the vertical rib thickness is small, but decreases firstly and then increases as the offset value increases when the vertical rib thickness is large enough. Furthermore, the thermal resistance of the staggered DLMCHS decreases with the increasing offset when the aspect ratio is small, but increases with the increasing offset when the aspect ratio is large enough. Thus, for the DLMCHS with a small microchannel aspect ratio and large vertical rib thickness, the offset between the upper layer of microchannels and the lower layer of microchannels in the width direction is a potential method to reduce thermal resistance and improve the thermal performance of the DLMCHS. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Refrigeration Performance and Entropy Generation Analysis for Reciprocating Magnetic Refrigerator with Gd Plates
Entropy 2018, 20(6), 427; https://doi.org/10.3390/e20060427
Received: 19 April 2018 / Revised: 19 May 2018 / Accepted: 29 May 2018 / Published: 1 June 2018
Cited by 1 | PDF Full-text (10295 KB) | HTML Full-text | XML Full-text
Abstract
In the current work, a novel 2D numerical model of stationary grids was developed for reciprocating magnetic refrigerators, with Gd plates, in which the magneto-caloric properties, derived from the Weiss molecular field theory, were adopted for the built-in energy source of the magneto-caloric
[...] Read more.
In the current work, a novel 2D numerical model of stationary grids was developed for reciprocating magnetic refrigerators, with Gd plates, in which the magneto-caloric properties, derived from the Weiss molecular field theory, were adopted for the built-in energy source of the magneto-caloric effect. The numerical simulation was conducted under the conditions of different structural and operational parameters, and the effects of the relative fluid displacement (φ) on the specific refrigeration capacity (qref) and the Coefficient of Performance (COP) were obtained. Besides the variations of entropy, the generation rate and number were studied and the contours of the local entropy generation rate are presented for discussion. From the current work, it is found that with an increase in φ, both the qref and COP followed the convex variation trend, while the entropy generation number (Ns) varied concavely. As for the current cases, the maximal qref and COP were equal to 151.2 kW/m3 and 9.11, respectively, while the lowest Ns was the value of 2.4 × 10−4 K−1. However, the optimal φ for the largest qref and COP, and for the lowest Ns, were inconsistent, thus, some compromises need be made in the optimization of magnetic refrigerators. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Entropy Generation on Nanofluid Thin Film Flow of Eyring–Powell Fluid with Thermal Radiation and MHD Effect on an Unsteady Porous Stretching Sheet
Entropy 2018, 20(6), 412; https://doi.org/10.3390/e20060412
Received: 26 March 2018 / Revised: 3 May 2018 / Accepted: 14 May 2018 / Published: 28 May 2018
Cited by 8 | PDF Full-text (1155 KB) | HTML Full-text | XML Full-text
Abstract
This research paper investigates entropy generation analysis on two-dimensional nanofluid film flow of Eyring–Powell fluid with heat amd mass transmission over an unsteady porous stretching sheet in the existence of uniform magnetic field (MHD). The flow of liquid films are taken under the
[...] Read more.
This research paper investigates entropy generation analysis on two-dimensional nanofluid film flow of Eyring–Powell fluid with heat amd mass transmission over an unsteady porous stretching sheet in the existence of uniform magnetic field (MHD). The flow of liquid films are taken under the impact of thermal radiation. The basic time dependent equations of heat transfer, momentum and mass transfer are modeled and converted to a system of differential equations by employing appropriate similarity transformation with unsteady dimensionless parameters. Entropy analysis is the main focus in this work and the impact of physical parameters on the entropy profile are discussed in detail. The influence of thermophoresis and Brownian motion has been taken in the nanofluids model. An optima approach has been applied to acquire the solution of modeled problem. The convergence of the HAM (Homotopy Analysis Method) has been presented numerically. The disparity of the Nusslet number, Skin friction, Sherwood number and their influence on the velocity, heat and concentration fields has been scrutinized. Moreover, for comprehension, the physical presentation of the embedded parameters are explored analytically for entropy generation and discussed. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Open AccessArticle Effective Boundary Slip Induced by Surface Roughness and Their Coupled Effect on Convective Heat Transfer of Liquid Flow
Entropy 2018, 20(5), 334; https://doi.org/10.3390/e20050334
Received: 29 March 2018 / Revised: 22 April 2018 / Accepted: 25 April 2018 / Published: 2 May 2018
Cited by 2 | PDF Full-text (1517 KB) | HTML Full-text | XML Full-text
Abstract
As a significant interfacial property for micro/nano fluidic system, the effective boundary slip can be induced by the surface roughness. However, the effect of surface roughness on the effective slip is still not clear, both increased and decreased effective boundary slip were found
[...] Read more.
As a significant interfacial property for micro/nano fluidic system, the effective boundary slip can be induced by the surface roughness. However, the effect of surface roughness on the effective slip is still not clear, both increased and decreased effective boundary slip were found with increased roughness. The present work develops a simplified model to study the effect of surface roughness on the effective boundary slip. In the created rough models, the reference position of the rough surfaces to determinate effective boundary slip was set based on ISO/ASME standard and the surface roughness parameters including Ra (arithmetical mean deviation of the assessed profile), Rsm (mean width of the assessed profile elements) and shape of the texture varied to form different surface roughness. Then, the effective boundary slip of fluid flow through the rough surface was analyzed by using COMSOL 5.3. The results show that the effective boundary slip induced by surface roughness of fully wetted rough surface keeps negative and further decreases with increasing Ra or decreasing Rsm. Different shape of roughness texture also results in different effective slip. A simplified corrected method for the measured effective boundary slip was developed and proved to be efficient when the Rsm is no larger than 200 nm. Another important finding in the present work is that the convective heat transfer firstly increases followed by an unobvious change with increasing Ra, while the effective boundary slip keeps decreasing. It is believed that the increasing Ra enlarges the area of solid-liquid interface for convective heat transfer, however, when Ra is large enough, the decreasing roughness-induced effective boundary slip counteracts the enhancement effect of roughness itself on the convective heat transfer. Full article
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
Figures

Figure 1

Entropy EISSN 1099-4300 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top