scholarly journals Thermodynamic Analysis of Fe3O4Nanofluid Flowing Through A Circular Tube

2019 ◽  
Vol 8 (6) ◽  
pp. 530-533 ◽  
Keyword(s):  
Entropy Generation ◽  
Particle Concentration ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Total Entropy ◽  
Particle Volume ◽  
Thermal Entropy

Present work is an experimental study of entropy generation of Fe3O4 -water nanofluid flowing through a circular tube. Flow is maintained in the turbulent region and tube is exposed to constant heat flux along the length. Experiments are conducted to study the entropy generation rate for different conditions such as particle volume concentrations varying from 1% to 6% and also for the different Reynolds numbers varying from 6000 to 22000. Measured data from experimentation is taken as input to calculate thermal entropy and frictional entropy generation separately. Based on these thermal entropy and frictional entropy generation total entropy generation and Bejan number are calculated and results are analyzed. Experimentally, it is proved that the changes in the thermal and frictional entropy generations are converse, such a way that, as particle concentration increases entropy generation due to heat transfer decreases whereas entropy generation due to friction increases. Finally experimental results reveal that there exits an optimum particle volume concentration where the total entropy generation is minimal. The same result has also appended by calculating the Bejan number.

Heat Transfer and Entropy Generation Analyses of Forced Convection Through Porous Media Using Pore Scale Modeling

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Mehrdad Torabi ◽  
Mohsen Torabi ◽  
G. P. Peterson
Keyword(s):  
Entropy Generation ◽  
Reynolds Numbers ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Current Investigation ◽  
Pore Scale ◽  
Cross Sectional ◽  
Scale Modeling ◽  
Performance Evaluation Criterion

The objective of the current investigation is to investigate the entropy generation inside porous media utilizing a pore scale modeling approach. The current investigation improves the thermodynamics performance of the recent analysis (Int. J. Heat Mass Transfer, 2016, 99, pp. 303–316) by considering different cross-sectional configurations and analyzing the thermal system for various Reynolds numbers, porosities, and a comparison between the previous and current investigation. The Nusselt number, the dimensionless volume-averaged entropy generation rate, Bejan number, and performance evaluation criterion (PEC) are all presented and discussed. The dimensionless volume-averaged entropy generation rate was found to increase with increasing Reynolds number, with the increase being higher for lower porosity medium. A slight variation of the dimensionless volume-averaged entropy generation rate is observed for higher Reynolds numbers which is confirmed for both cross-sectional configurations. Examination of the Bejan number demonstrates heat transfer irreversibility (HTI) dominance for most of the Reynolds number ranges examined. The results indicate that the longitudinal elliptical cross-sectional configuration with porosity equals to 0.53 provides superior performance when applying the performance evaluation criterion utilized.

scholarly journals The effects of longitudinal ribs on entropy generation for laminar forced convection in a microchannel

2016 ◽  
Vol 20 (6) ◽  
pp. 1963-1972 ◽  
Author(s):  
Nader Pourmahmoud ◽  
Hosseinali Soltanipour ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Entropy Generation ◽  
Constant Heat Flux ◽  
Wall Heat Flux ◽  
Entropy Generation Rate ◽  
Total Entropy ◽  
Flux Boundary Condition ◽  
Energy Equations

This paper deals with fluid flow, heat transfer and entropy generation in an internally ribbed microchannel. Mass, momentum and energy equations for constant heat flux boundary condition are solved using the finite volume method. Average Nusselt number and Fanning friction factor are reported as a function of rib height at different Reynolds numbers. The effects of non-dimensional rib height, wall heat flux and the Reynolds number on the entropy generation attributed to friction, heat transfer and total entropy generation are explored. The first law indicates that rib height has the great effect on the flow filed and heat transfer. The second law analysis reveals that for any values of Reynolds number and wall heat flux, as rib height grows; the frictional irreversibility increases while, there is a rib height which provides the minimum heat transfer irreversibility. It is found that the optimum rib height with the minimum total entropy generation rate depends on Reynolds number and wall heat flux.

Theoretical and experimental investigation of an organic Rankine cycle for a waste heat recovery system

2009 ◽  
Vol 223 (5) ◽  
pp. 523-533 ◽  
Author(s):  
W Gu ◽  
Y Weng ◽  
Y Wang ◽  
B Zheng
Keyword(s):  
Heat Source ◽  
Entropy Generation ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Entropy Generation Rate ◽  
Working Fluid ◽  
Total Entropy ◽  
Waste Heat Recovery System ◽  
Cycle Efficiency

This article describes and evaluates an organic Rankine cycle (ORC) for a waste heat recovery system by both theoretical and experimental studies. Theoretical analysis of several working fluids shows that cycle efficiency is very sensitive to evaporating pressure, but insensitive to expander inlet temperature. Second law analysis was carried out using R600a as a working fluid and a flow of hot air as a heat source, which is not isothermal, along the evaporator. The result discloses that the evaporator's internal and external entropy generation is the main source of total entropy generation. The effect of the heat source temperature, evaporating pressure, and evaporator size on the entropy generation rate is also presented. The obtained useful power is directly linked to the total entropy generation rate according to the Gouy—Stodola theorem. The ORC testing system was established and operated using R600a as a working fluid and hot water as a heat source. The maximum cycle efficiency of the testing system is 5.2 per cent, and the testing result also proves that cycle efficiency is insensitive to heat source temperature, but sensitive to evaporating pressure. The entropy result also shows that internal and external entropy of the evaporator is the main source of total entropy generation.

scholarly journals Second Law Analysis of Laminar Flow in a Circular Pipe Immersed in an Isothermal Fluid

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Vishal Anand ◽  
Krishna Nelanti
Keyword(s):  
Laminar Flow ◽  
Entropy Generation ◽  
Circular Tube ◽  
Dimensionless Temperature ◽  
Bejan Number ◽  
Uniform Wall Temperature ◽  
Thermal Boundary Conditions ◽  
Fluid Properties ◽  
Isothermal Fluid ◽  
Uniform Wall

Entropy generation and pumping power to heat transfer ratio (PPR) of a laminar flow, for a circular tube immersed in an isothermal fluid, are studied analytically in this paper. Two different fluids, namely, water and ethylene glycol, are chosen to study the influence of fluid properties on entropy generation and PPR. The expressions for dimensionless entropy generation, Bejan number and PPR are derived in a detailed way and their variations with Reynolds number, external Biot number, and the dimensionless temperature difference are illustrated. The results of the analysis are compared with those for a laminar flow in a circular tube with uniform wall temperature boundary condition. Finally, a criterion is established to determine which type of thermal boundary conditions is more suitable for a particular fluid, with respect to its influence on entropy generation.

scholarly journals Effect of corrugated minichannel variable width on entropy generation for convective heat transfer of alpha-Alumina-water nanofluid

2021 ◽  
Vol 2053 (1) ◽  
pp. 012016
Author(s):  
N M Muhammad ◽  
N A C Sidik ◽  
A Saat ◽  
Y Asako ◽  
W M A A Japar ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Entropy Production ◽  
Convective Heat ◽  
Entropy Generation ◽  
Entropy Generation Rate ◽  
Thermal Systems ◽  
Volume Fractions ◽  
Thermal Entropy ◽  
Alpha Alumina

Abstract Energy management and sustainability in thermal systems require maximum utilization of resources with minimal losses. However, it is rarely unattainable due to the ever-increasing need for a high-performance system combined with device size reduction. The numerical study examined convective heat transfer of an alpha-Alumina-water nanofluid in variable-width corrugated minichannel heat sinks. The objective is to study the impact of nanoparticle volume fractions and flow area variation on the entropy generation rate. The determining variables are 0.005 – 0.02 volume fractions, the fluid velocity 3 – 5.5 m/s and heat flux of 85 W/cm2. The numerical results show an acceptable correlation with the experiment results. The results indicate the thermal entropy production drop with an increase in nanoparticles volume fraction. Contrastingly, the frictional resistance entropy suggests the opposite trend due to the turbulence effect on the fluid viscosity. The induction of Alumina-Water nanofluid with enhanced thermal conductivity declined the entropy generation rate compared to water alone. The increase in width ratio by 16% between the cases translates to at least a 9% increase in thermal entropy production. The outcome of this study can provide designers and operators of thermal systems more insight into entropy management in corrugated heatsinks.

scholarly journals Entropy Generation Rates in Two-Dimensional Rayleigh–Taylor Turbulence Mixing

Entropy ◽  
2018 ◽  
Vol 20 (10) ◽  
pp. 738 ◽  
Author(s):  
Xinyu Yang ◽  
Haijiang He ◽  
Jun Xu ◽  
Yikun Wei ◽  
Hua Zhang
Keyword(s):  
Time Evolution ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Two Dimensional ◽  
Spatial Averaging ◽  
Mixing Process ◽  
Thermal Entropy ◽  
Large Gradient ◽  
Turbulence Mixing

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.

scholarly journals Optimal Design of Nanoparticle Enhanced Phan-Thien–Tanner Flow of a Viscoelastic Fluid in a Microchannel

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 895
Author(s):  
Mohammad Abdollahzadeh Jamalabadi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Circular Cross Section ◽  
Major Influence ◽  
Parameter Study ◽  
Bejan Number ◽  
Total Entropy ◽  
Minimum Entropy

The excellent thermal characteristics of nanoparticles have increased their application in the field of heat transfer. In this paper, a thermophysical and geometrical parameter study is performed to minimize the total entropy generation of the viscoelastic flow of nanofluid. Entropy generation with respect to volume fraction (<0.04), the Reynolds number (20,000–100,000), and the diameter of the microchannel (20–20,000 μm) with the circular cross-section under constant flux are calculated. As is shown, most of the entropy generation owes to heat transfer and by increasing the diameter of the channel, the Bejan number increases. The contribution of heat entropy generation in the microchannel is very poor and the major influence of entropy generation is attributable to friction. The maximum quantity of in-channel entropy generation happens in nanofluids with TiO2, CuO, Cu, and Ag nanoparticles, in turn, despite the fact in the microchannel this behavior is inverted, the minimum entropy generation occurs in nanofluids with CuO, Cu, Ag, and TiO2 nanoparticles, in turn. In the channel and microchannel for all nanofluids except water-TiO2, increasing the volume fraction of nanoparticles decreases entropy generation. In the channel and microchannel the total entropy generation increases by augmentation the Reynolds number.

scholarly journals Effects of circular corners and aspect-ratio on entropy generation due to natural convection of nanofluid flows in rectangular cavities

2015 ◽  
Vol 19 (5) ◽  
pp. 1621-1632 ◽  
Author(s):  
Mahmoud Salari ◽  
Ali Mohammadtabar ◽  
Mohammad Mohammadtabar
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Bejan Number ◽  
Total Entropy ◽  
Aspect Ratios ◽  
Corner Radius

In this paper, entropy generation induced by natural convection of cu-water nanofluid in rectangular cavities with different circular corners and different aspect-ratios were numerically investigated. The governing equations were solved using a finite volume approach and the SIMPLE algorithm was used to couple the pressure and velocity fields. The results showed that the total entropy generation increased with the increase of Rayleigh number, irreversibility coefficient, aspect ratio or solid volume fraction while it decreased with the increase of the corner radius. It should be noted that the best way for minimizing entropy generation is decreasing Rayleigh number. This is the first priority for minimizing entropy generation. The other parameters such as radius, volume fraction, etc are placed on the second priority. However, Bejan number had an inverse trend compared with total entropy generation. As an exception, Bejan number and total entropy number had the same trend whenever solid volume fraction increased. Moreover, Nusselt number increased as Rayleigh number, solid volume fraction or aspect ratio increased whereas it decreases with the increase of corner radius.

scholarly journals Analytical Analysis of Heat Transfer and Entropy Generation in a Tube Filled with Double-Layer Porous Media

Entropy ◽  
2020 ◽  
Vol 22 (11) ◽  
pp. 1214 ◽  
Author(s):  
Kun Yang ◽  
Wei Huang ◽  
Xin Li ◽  
Jiabing Wang
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Porous Media ◽  
Nusselt Number ◽  
Double Layer ◽  
Entropy Generation ◽  
Single Layer ◽  
Entropy Generation Rate ◽  
Total Entropy ◽  
Interfacial Radius

The heat transfer and entropy generation in a tube filled with double-layer porous media are analytically investigated. The wall of the tube is subjected to a constant heat flux. The Darcy-Brinkman model is utilized to describe the fluid flow, and the local thermal non-equilibrium model is employed to establish the energy equations. The solutions of the temperature and velocity distributions are analytically derived and validated in limiting case. The analytical solutions of the local and total entropy generation, as well as the Nusselt number, are further derived to analyze the performance of heat transfer and irreversibility of the tube. The influences of the Darcy number, the Biot number, the dimensionless interfacial radius, and the thermal conductivity ratio, on flow and heat transfer are discussed. The results indicate, for the first time, that the Nusselt number for the tube filled with double-layer porous media can be larger than that for the tube filled with single layer porous medium, while the total entropy generation rate for the tube filled with double-layer porous media can be less than that for the tube filled with single layer porous medium. And the dimensionless interfacial radius corresponding to the maximum value of the Nusselt number is different from that corresponding to the minimum value of the total entropy generation rate.

Entropy generation and heat transport analysis of Casson fluid flow with viscous and Joule heating in an inclined porous microchannel

2019 ◽  
Vol 233 (5) ◽  
pp. 1173-1184 ◽  
Author(s):  
BJ Gireesha ◽  
CT Srinivasa ◽  
NS Shashikumar ◽  
Madhu Macha ◽  
JK Singh ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Entropy Generation ◽  
Convective Boundary Condition ◽  
Casson Fluid ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Convective Boundary ◽  
Electrically Conducting ◽  
Number Formula ◽  
The Impact

The combined effects of the magnetic field, suction/injection, and convective boundary condition on heat transfer and entropy generation in an electrically conducting Casson fluid flow through an inclined porous microchannel are scrutinized. The temperature-dependent heat source is also accounted. Numerical simulation for the modelled problem is presented via Runge–Kutta–Felhberg-based shooting technique. Special attention is given to analyze the impact of involved parameters on the profiles of velocity [Formula: see text], temperature [Formula: see text], entropy generation [Formula: see text], and Bejan number [Formula: see text]. It is established that entropy generation rate decreases at the walls with an increase in Hartmann number [Formula: see text], while it increases at the center region of the microchannel.

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