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1095 KiB

Open AccessArticle

A LiBr-H₂O Absorption Refrigerator Incorporating a Thermally Activated Solution Pumping Mechanism

by Ian W. Eames

Entropy 2017, 19(3), 90; https://doi.org/10.3390/e19030090 - 26 Feb 2017

Cited by 5 | Viewed by 7190

This paper provides an illustrated description of a proposed LiBr-H₂O vapour absorption refrigerator which uses a thermally activated solution pumping mechanism that combines controlled variations in generator vapour pressure with changes it produces in static-head pressure difference to circulate the absorbent [...] Read more.

This paper provides an illustrated description of a proposed LiBr-H₂O vapour absorption refrigerator which uses a thermally activated solution pumping mechanism that combines controlled variations in generator vapour pressure with changes it produces in static-head pressure difference to circulate the absorbent solution between the generator and absorber vessels. The proposed system is different and potentially more efficient than a bubble pump system previously proposed and avoids the need for an electrically powered circulation pump found in most conventional LiBr absorption refrigerators. The paper goes on to provide a sample set of calculations that show that the coefficient of performance values of the proposed cycle are similar to those found for conventional cycles. The theoretical results compare favourably with some preliminary experimental results, which are also presented for the first time in this paper. The paper ends by proposing an outline design for an innovative steam valve, which is a key component needed to control the solution pumping mechanism. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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12388 KiB

Open AccessArticle

Response Surface Methodology Control Rod Position Optimization of a Pressurized Water Reactor Core Considering Both High Safety and Low Energy Dissipation

by Yi-Ning Zhang, Hao-Chun Zhang, Hai-Yan Yu and Chao Ma

Entropy 2017, 19(2), 63; https://doi.org/10.3390/e19020063 - 10 Feb 2017

Cited by 5 | Viewed by 5154

Abstract

Response Surface Methodology (RSM) is introduced to optimize the control rod positions in a pressurized water reactor (PWR) core. The widely used 3D-IAEA benchmark problem is selected as the typical PWR core and the neutron flux field is solved. Besides, some additional thermal [...] Read more.

Response Surface Methodology (RSM) is introduced to optimize the control rod positions in a pressurized water reactor (PWR) core. The widely used 3D-IAEA benchmark problem is selected as the typical PWR core and the neutron flux field is solved. Besides, some additional thermal parameters are assumed to obtain the temperature distribution. Then the total and local entropy production is calculated to evaluate the energy dissipation. Using RSM, three directions of optimization are taken, which aim to determine the minimum of power peak factor P_max, peak temperature T_max and total entropy production S_tot. These parameters reflect the safety and energy dissipation in the core. Finally, an optimization scheme was obtained, which reduced P_max, T_max and S_tot by 23%, 8.7% and 16%, respectively. The optimization results are satisfactory. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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335 KiB

Open AccessArticle

Scaling Relations of Lognormal Type Growth Process with an Extremal Principle of Entropy

by Zi-Niu Wu, Juan Li and Chen-Yuan Bai

Entropy 2017, 19(2), 56; https://doi.org/10.3390/e19020056 - 27 Jan 2017

Cited by 5 | Viewed by 6710

Abstract

The scale, inflexion point and maximum point are important scaling parameters for studying growth phenomena with a size following the lognormal function. The width of the size function and its entropy depend on the scale parameter (or the standard deviation) and measure the [...] Read more.

The scale, inflexion point and maximum point are important scaling parameters for studying growth phenomena with a size following the lognormal function. The width of the size function and its entropy depend on the scale parameter (or the standard deviation) and measure the relative importance of production and dissipation involved in the growth process. The Shannon entropy increases monotonically with the scale parameter, but the slope has a minimum at p 6/6. This value has been used previously to study spreading of spray and epidemical cases. In this paper, this approach of minimizing this entropy slope is discussed in a broader sense and applied to obtain the relationship between the inflexion point and maximum point. It is shown that this relationship is determined by the base of natural logarithm e ' 2.718 and exhibits some geometrical similarity to the minimal surface energy principle. The known data from a number of problems, including the swirling rate of the bathtub vortex, more data of droplet splashing, population growth, distribution of strokes in Chinese language characters and velocity profile of a turbulent jet, are used to assess to what extent the approach of minimizing the entropy slope can be regarded as useful. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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29008 KiB

Open AccessArticle

by Lei Zhang, Weilin Zhuge, Yangjun Zhang and Tao Chen

Entropy 2017, 19(1), 25; https://doi.org/10.3390/e19010025 - 14 Jan 2017

Cited by 12 | Viewed by 7291

Abstract

Organic Rankine Cycles using radial turbines as expanders are considered as one of the most efficient technologies to convert heavy-duty diesel engine waste heat into useful work. Turbine similarity design based on the existing air turbine profiles is time saving. Due to totally [...] Read more.

Organic Rankine Cycles using radial turbines as expanders are considered as one of the most efficient technologies to convert heavy-duty diesel engine waste heat into useful work. Turbine similarity design based on the existing air turbine profiles is time saving. Due to totally different thermodynamic properties between organic fluids and air, its influence on turbine performance and loss mechanisms need to be analyzed. This paper numerically simulated a radial turbine under similar conditions between R245fa and air, and compared the differences of the turbine performance and loss mechanisms. Larger specific heat ratio of air leads to air turbine operating at higher pressure ratios. As R245fa gas constant is only about one-fifth of air gas constant, reduced rotating speeds of R245fa turbine are only 0.4-fold of those of air turbine, and reduced mass flow rates are about twice of those of air turbine. When using R245fa as working fluid, the nozzle shock wave losses decrease but rotor suction surface separation vortex losses increase, and eventually leads that isentropic efficiencies of R245fa turbine in the commonly used velocity ratio range from 0.5 to 0.9 are 3%–4% lower than those of air turbine. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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1977 KiB

Open AccessArticle

Entropy Generation in Magnetohydrodynamic Mixed Convection Flow over an Inclined Stretching Sheet

by Muhammad Idrees Afridi, Muhammad Qasim, Ilyas Khan, Sharidan Shafie and Ali Saleh Alshomrani

Entropy 2017, 19(1), 10; https://doi.org/10.3390/e19010010 - 28 Dec 2016

Cited by 42 | Viewed by 6739

Abstract

This research focuses on entropy generation rate per unit volume in magneto-hydrodynamic (MHD) mixed convection boundary layer flow of a viscous fluid over an inclined stretching sheet. Analysis has been performed in the presence of viscous dissipation and non-isothermal boundary conditions. The governing [...] Read more.

This research focuses on entropy generation rate per unit volume in magneto-hydrodynamic (MHD) mixed convection boundary layer flow of a viscous fluid over an inclined stretching sheet. Analysis has been performed in the presence of viscous dissipation and non-isothermal boundary conditions. The governing boundary layer equations are transformed into ordinary differential equations by an appropriate similarity transformation. The transformed coupled nonlinear ordinary differential equations are then solved numerically by a shooting technique along with the Runge-Kutta method. Expressions for entropy generation (Ns) and Bejan number (Be) in the form of dimensionless variables are also obtained. Impact of various physical parameters on the quantities of interest is seen. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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2182 KiB

Open AccessArticle

Numerical Study of Entropy Generation in Mixed MHD Convection in a Square Lid-Driven Cavity Filled with Darcy–Brinkman–Forchheimer Porous Medium

by Rahma Bouabda, Mounir Bouabid, Ammar Ben Brahim and Mourad Magherbi

Entropy 2016, 18(12), 436; https://doi.org/10.3390/e18120436 - 06 Dec 2016

Cited by 6 | Viewed by 4723

Abstract

This investigation deals with the numerical simulation of entropy generation at mixed convection flow in a lid-driven saturated porous cavity submitted to a magnetic field. The magnetic field is applied in the direction that is normal to the cavity cross section. The governing [...] Read more.

This investigation deals with the numerical simulation of entropy generation at mixed convection flow in a lid-driven saturated porous cavity submitted to a magnetic field. The magnetic field is applied in the direction that is normal to the cavity cross section. The governing equations, written in the Darcy–Brinkman–Forchheimer formulation, are solved using a numerical code based on the Control Volume Finite Element Method. The flow structure and heat transfer are presented in the form of streamlines, isotherms and average Nusselt number. The entropy generation was studied for various values of Darcy number (10⁻³ ≤ Da ≤ 1) and for a range of Hartmann number (0 ≤ Ha ≤ 10²). It was found that entropy generation is affected by the variations of the considered dimensionless physical parameters. Moreover, the form drag related to the Forchheimer effect remains significant until a critical Hartmann number value. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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1201 KiB

Open AccessArticle

Energy Efficiency Improvement in a Modified Ethanol Process from Acetic Acid

by Young Han Kim

Entropy 2016, 18(12), 422; https://doi.org/10.3390/e18120422 - 24 Nov 2016

Cited by 2 | Viewed by 7994

Abstract

For the high utilization of abundant lignocellulose, which is difficult to directly convert into ethanol, an energy-efficient ethanol production process using acetic acid was examined, and its energy saving performance, economics, and thermodynamic efficiency were compared with the conventional process. The raw ethanol [...] Read more.

For the high utilization of abundant lignocellulose, which is difficult to directly convert into ethanol, an energy-efficient ethanol production process using acetic acid was examined, and its energy saving performance, economics, and thermodynamic efficiency were compared with the conventional process. The raw ethanol synthesized from acetic acid and hydrogen was fed to the proposed ethanol concentration process. The proposed process utilized an extended divided wall column (DWC), for which the performance was investigated with the HYSYS simulation. The performance improvement of the proposed process includes a 27% saving in heating duty and a 41% reduction in cooling duty. The economics shows a 16% saving in investment cost and a 24% decrease in utility cost over the conventional ethanol concentration process. The exergy analysis shows a 9.6% improvement in thermodynamic efficiency for the proposed process. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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234 KiB

Open AccessArticle

On Thermodynamics Problems in the Single-Phase-Lagging Heat Conduction Model

by Shu-Nan Li and Bing-Yang Cao

Entropy 2016, 18(11), 391; https://doi.org/10.3390/e18110391 - 09 Nov 2016

Cited by 3 | Viewed by 4073

Abstract

Thermodynamics problems for the single-phase-lagging (SPL) model have not been much studied. In this paper, the violation of the second law of thermodynamics by the SPL model is studied from two perspectives, which are the negative entropy production rate and breaking equilibrium spontaneously. [...] Read more.

Thermodynamics problems for the single-phase-lagging (SPL) model have not been much studied. In this paper, the violation of the second law of thermodynamics by the SPL model is studied from two perspectives, which are the negative entropy production rate and breaking equilibrium spontaneously. The methods for the SPL model to avoid the negative entropy production rate are proposed, which are extended irreversible thermodynamics and the thermal relaxation time. Modifying the entropy production rate positive or zero is not enough to avoid the violation of the second law of thermodynamics for the SPL model, because the SPL model could cause breaking equilibrium spontaneously in some special circumstances. As comparison, it is shown that Fourier’s law and the CV model cannot break equilibrium spontaneously by analyzing mathematical energy integral. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

4063 KiB

Open AccessArticle

Analysis of Entropy Generation in Mixed Convective Peristaltic Flow of Nanofluid

by Tasawar Hayat, Sadaf Nawaz, Ahmed Alsaedi and Maimona Rafiq

Entropy 2016, 18(10), 355; https://doi.org/10.3390/e18100355 - 30 Sep 2016

Cited by 17 | Viewed by 5799

Abstract

This article examines entropy generation in the peristaltic transport of nanofluid in a channel with flexible walls. Single walled carbon nanotubes (SWCNT) and multiple walled carbon nanotubes (MWCNT) with water as base fluid are utilized in this study. Mixed convection is also considered [...] Read more.

This article examines entropy generation in the peristaltic transport of nanofluid in a channel with flexible walls. Single walled carbon nanotubes (SWCNT) and multiple walled carbon nanotubes (MWCNT) with water as base fluid are utilized in this study. Mixed convection is also considered in the present analysis. Viscous dissipation effect is present. Moreover, slip conditions are encountered for both velocity and temperature at the boundaries. Analysis is prepared in the presence of long wavelength and small Reynolds number assumptions. Two phase model for nanofluids are employed. Nonlinear system of equations for small Grashof number is solved. Velocity and temperature are examined for different parameters via graphs. Streamlines are also constructed to analyze the trapping. Results show that axial velocity and temperature of the nanofluid decrease when we enhance the nanoparticle volume fraction. Moreover, the wall elastance parameter shows increase in axial velocity and temperature, whereas decrease in both quantities is noticed for damping coefficient. Decrease is notified in Entropy generation and Bejan number for increasing values of nanoparticle volume fraction. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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4958 KiB

Open AccessArticle

Heat Transfer and Entropy Generation of Non-Newtonian Laminar Flow in Microchannels with Four Flow Control Structures

by Ke Yang, Di Zhang, Yonghui Xie and Gongnan Xie

Entropy 2016, 18(8), 302; https://doi.org/10.3390/e18080302 - 12 Aug 2016

Cited by 6 | Viewed by 5015

Abstract

Flow characteristics and heat transfer performances of carboxymethyl cellulose (CMC) aqueous solutions in the microchannels with flow control structures were investigated in this study. The researches were carried out with various flow rates and concentrations of the CMC aqueous solutions. The results reveal [...] Read more.

Flow characteristics and heat transfer performances of carboxymethyl cellulose (CMC) aqueous solutions in the microchannels with flow control structures were investigated in this study. The researches were carried out with various flow rates and concentrations of the CMC aqueous solutions. The results reveal that the pin-finned microchannel has the most uniform temperature distribution on the structured walls, and the average temperature on the structured wall reaches the minimum value in cylinder-ribbed microchannels at the same flow rate and CMC concentration. Moreover, the protruded microchannel obtains the minimum relative Fanning friction factor f/f₀, while, the maximum f/f₀ is observed in the cylinder-ribbed microchannel. Furthermore, the minimum f/f₀ is reached at the cases with CMC2000, and also, the relative Nusselt number Nu/Nu₀ of CMC2000 cases is larger than that of other cases in the four structured microchannels. Therefore, 2000 ppm is the recommended concentration of CMC aqueous solutions in all the cases with different flow rates and flow control structures. Pin-finned microchannels are preferred in low flow rate cases, while, V-grooved microchannels have the minimum relative entropy generation S’/S₀’ and best thermal performance TP at CMC2000 in high flow rates. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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4767 KiB

Open AccessArticle

A Critical Reassessment of the Hess–Murray Law

by Enrico Sciubba

Entropy 2016, 18(8), 283; https://doi.org/10.3390/e18080283 - 05 Aug 2016

Cited by 19 | Viewed by 8249

Abstract

The Hess–Murray law is a correlation between the radii of successive branchings in bi/trifurcated vessels in biological tissues. First proposed by the Swiss physiologist and Nobel laureate Walter Rudolf Hess in his 1914 doctoral thesis and published in 1917, the law was “rediscovered” [...] Read more.

The Hess–Murray law is a correlation between the radii of successive branchings in bi/trifurcated vessels in biological tissues. First proposed by the Swiss physiologist and Nobel laureate Walter Rudolf Hess in his 1914 doctoral thesis and published in 1917, the law was “rediscovered” by the American physiologist Cecil Dunmore Murray in 1926. The law is based on the assumption that blood or lymph circulation in living organisms is governed by a “work minimization” principle that—under a certain set of specified conditions—leads to an “optimal branching ratio” of

\frac{r_{i + 1}}{r_{i}} = \frac{1}{\sqrt[3]{2}} = 0.7937

. This “cubic root of 2” correlation underwent extensive theoretical and experimental reassessment in the second half of the 20th century, and the results indicate that—under a well-defined series of conditions—the law is sufficiently accurate for the smallest vessels (r of the order of fractions of millimeter) but fails for the larger ones; moreover, it cannot be successfully extended to turbulent flows. Recent comparisons with numerical investigations of branched flows led to similar conclusions. More recently, the Hess–Murray law came back into the limelight when it was taken as a founding paradigm of the Constructal Law, a theory that employs physical intuition and mathematical reasoning to derive “optimal paths” for the transport of matter and energy between a source and a sink, regardless of the mode of transportation (continuous, like in convection and conduction, or discrete, like in the transportation of goods and people). This paper examines the foundation of the law and argues that both for natural flows and for engineering designs, a minimization of the irreversibility under physically sound boundary conditions leads to somewhat different results. It is also shown that, in the light of an exergy-based resource analysis, an amended version of the Hess–Murray law may still hold an important position in engineering and biological sciences. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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3798 KiB

Open AccessArticle

Entropy Generation through Non-Equilibrium Ordered Structures in Corner Flows with Sidewall Mass Injection

by LaVar King Isaacson

Entropy 2016, 18(8), 279; https://doi.org/10.3390/e18080279 - 28 Jul 2016

Cited by 2 | Viewed by 5495

Abstract

Additional entropy generation rates through non-equilibrium ordered structures are predicted for corner flows with sidewall mass injection. Well-defined non-equilibrium ordered structures are predicted at a normalized vertical station of approximately eighteen percent of the boundary-layer thickness. These structures are in addition to the [...] Read more.

Additional entropy generation rates through non-equilibrium ordered structures are predicted for corner flows with sidewall mass injection. Well-defined non-equilibrium ordered structures are predicted at a normalized vertical station of approximately eighteen percent of the boundary-layer thickness. These structures are in addition to the ordered structures previously reported at approximately thirty-eight percent of the boundary layer thickness. The computational procedure is used to determine the entropy generation rate for each spectral velocity component at each of several stream wise stations and for each of several injection velocity values. Application of the procedure to possible thermal system processes is discussed. These results indicate that cooling sidewall mass injection into a horizontal laminar boundary layer may actually increase the heat transfer to the horizontal surface. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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Review

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1228 KiB

Open AccessReview

Nonequilibrium Thermodynamics of Ion Flux through Membrane Channels

by Chi-Pan Hsieh

Entropy 2017, 19(1), 40; https://doi.org/10.3390/e19010040 - 19 Jan 2017

Cited by 3 | Viewed by 6336

Abstract

Ion flux through membrane channels is passively driven by the electrochemical potential differences across the cell membrane. Nonequilibrium thermodynamics has been successful in explaining transport mechanisms, including the ion transport phenomenon. However, physiologists may not be familiar with biophysical concepts based on the [...] Read more.

Ion flux through membrane channels is passively driven by the electrochemical potential differences across the cell membrane. Nonequilibrium thermodynamics has been successful in explaining transport mechanisms, including the ion transport phenomenon. However, physiologists may not be familiar with biophysical concepts based on the view of entropy production. In this paper, I have reviewed the physical meanings and connections between nonequilibrium thermodynamics and the expressions commonly used in describing ion fluxes in membrane physiology. The fluctuation theorem can be applied to interpret the flux ratio in the small molecular systems. The multi-ion single-file feature of the ion channel facilitates the utilization of the natural tendency of electrochemical driving force to couple specific biophysical processes and biochemical reactions on the membrane. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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13147 KiB

Open AccessReview

Generalized Thermodynamic Optimization for Iron and Steel Production Processes: Theoretical Exploration and Application Cases

by Lingen Chen, Huijun Feng and Zhihui Xie

Entropy 2016, 18(10), 353; https://doi.org/10.3390/e18100353 - 29 Sep 2016

Cited by 125 | Viewed by 15883

Abstract

Combining modern thermodynamics theory branches, including finite time thermodynamics or entropy generation minimization, constructal theory and entransy theory, with metallurgical process engineering, this paper provides a new exploration on generalized thermodynamic optimization theory for iron and steel production processes. The theoretical core is [...] Read more.

Combining modern thermodynamics theory branches, including finite time thermodynamics or entropy generation minimization, constructal theory and entransy theory, with metallurgical process engineering, this paper provides a new exploration on generalized thermodynamic optimization theory for iron and steel production processes. The theoretical core is to thermodynamically optimize performances of elemental packages, working procedure modules, functional subsystems, and whole process of iron and steel production processes with real finite-resource and/or finite-size constraints with various irreversibilities toward saving energy, decreasing consumption, reducing emission and increasing yield, and to achieve the comprehensive coordination among the material flow, energy flow and environment of the hierarchical process systems. A series of application cases of the theory are reviewed. It can provide a new angle of view for the iron and steel production processes from thermodynamics, and can also provide some guidelines for other process industries. Full article

(This article belongs to the Special Issue Advances in Applied Thermodynamics II)

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