Entropy Generation Analysis Research Articles

Efficiency and Irreversibility Analysis of MHD Unsteady Fluid Flow with Heat and Mass Transfer

In this paper the analysis of entropy generation of unsteady MHD fluid flow passing through the stretching sheet under the influence of Soret and the chemical reaction has been investigated. The multiple slip effects, suction/injection are considered to analyze the entropy generation rate. The non-linear governing equations are transformed into the first order differential equations using suitable similarity transformations. The resulting boundary value problem is solved by using the MATLAB built in bvp4c solver technique. Numerical values of skin friction coefficient, Nusselt number, Sherwood number and irreversibility ratios are shown in tabular form. Further uniqueness of this work is to find the various irreversibility ratios at the surface due to the effect of thermal and mass diffusion, magnetic field, combined effect of heat and mass transfer over total entropy generation number. It is noticed that to reduce the irreversibility and to boast up the efficiency we have to control the values of chemical reaction parameter (K1), Prandtl number and suction/injection parameter. Irreversibility due to combined effect of heat and mass transfer contributes more wastage than others.

Unsteady response of performance for centrifugal compressor under pulsating backpressure condition

The intermittent throttling effects of intake valves of internal combustion engine generate pulsations at compressor exit, which has a great impact on the compressor performance. In this paper, the influence of pulsation on the compressor is studied via unsteady 3-D numerical method validated by experiments. Results show that the cycle-average efficiency is lower than the quasi-steady value. The impeller is confirmed as the main reason for efficiency deterioration according to entropy generation analysis, due to the difference of secondary flow patterns. The tip leakage vortex at impeller inlet is alleviated at pulsating condition because of inertia effect, resulting in a lower velocity thus higher incidence angle near splitter. The stronger separation and tip leakage flow at splitter leading edge lead to the wake with higher losses. Moreover, the circumferential distortion at the impeller exit is found to be weaker under pulsation. It is caused by two reasons: the flow field, which is closer to the quasi-steady one with a higher mass flow rate due to the lagging effect; the additional pressure gradient in volute caused by propagation of pulse. It results in an evener flow field and improves impeller stability. Specifically, the recirculation region at impeller inlet shrinks 5% under pulsation.

Mass-based hybrid nanofluid model for entropy generation analysis of flow upon a convectively-warmed moving wedge

In this research, the steady incompressible laminar two-dimensional hybrid nanofluid flow upon a convectively-warmed moving wedge with radiative transition has been studied numerically. The nanoparticles are the magnetite (Fe3O4) and the graphene oxide (GO), in two research parts of spherical and non-spherical (brick, cylinder, platelet, and disk) shapes, suspended in the pure water as base fluid. Three main geometries of the well-known Falkner-Skan problem including: (i) the flat plat (named Blasius flow), (ii) the wedge, and (iii) the vertical plate (named Hiemenz stagnation flow) have been considered to present a comprehensive development of this significant problem. The applied methodology is according to the single-phase Tiwari-Das hybrid nanofluid model considering the masses of nanoparticles and base fluid instead the volume concentration of first and second nanoparticles. For the first time, the mentioned mass-based method will be utilized in combination with the entropy generation analysis. The governing dimensional PDEs are varied to a system of non-dimensional ODEs with the use of similarity transformation technique which is then solved numerically through Runge–Kutta–Fehlberg method coupled with a conventional shooting procedure. The effect of the governing parameters on the hybrid nanofluid velocity, the temperature distribution, the skin friction coefficient, the Nusselt number, the entropy generation, and the Bejan number has been investigated and interpreted through the tabular and graphical results. A reliable treatment of the mass-based method for the hybrid nanofluid flow, the heat transfer and especially the entropy analysis is the substantial achievement of the present research; although, the detailed results have been presented and discussed in the article's body. Certainly, new modeling and approaches for the hybrid nanofluid can be dramatically beneficial in the various industries in which the cooling technologies are vital

Magneto-turbulent natural convection and entropy generation analyses in liquid sodium-filled cavity partially heated and cooled from sidewalls with circular blocks

Liquid sodium is a promising candidate working fluid in the new solar system and high-density heat sources in industrial applications. In this study free convective flow, heat transfer, and entropy generation of liquid sodium in a hot square enclosure with 16 and 64 cylindrical solid blocks are studied. The cavity is partially heated and cooled from sidewalls with three different locations of heater and cooler named CONF1–3. The effects of the magnetic field in the form of Hartmann number (Ha = 0 and 100), and flow condition in the form of the Rayleigh number (Ra = 106, and 107) are investigated. For tuning the CFD code primitive parameter, the dimensionless forms of the governing equations are used. The ANSYS Fluent equations solver conjugated with a nondimesionlization scheme are used in the turbulent region due to the behavior of liquid metal. The grid verification and validation tests are carried out to ensure the accuracy of the data. Two correlations for average Nusselt number and entropy generation are proposed to simplify calculations. The results discovered that the average Nusselt number and entropy generation increase with increasing the Rayleigh number for each value of the Hartmann number.

Numerical analysis of entropy generation and induced magnetic field on unsteady stagnation flow with suction/injection

The core part of current model is to analyze the entropy generation and 2-dimensional unsteady stagnation flow with suction/injection constraint present in the boundary. Further, the induced magnetic field has applied with this flow model, which is formed by the motion of fluid that conducts electrically. The time-dependent partial differential equations (PDE) of the recent model are first converted to non-linear ordinary differential equations (ODE) using suitable similarity variables. We obtain solutions numerically using inbuilt shooting technic. We demonstrate the results using the graphs, tables and discussed them in detail. It is found that as the injection parameter is responsible for the thinning of the boundary layer, induced magnetic boundary layer; Suction, and unsteady constraints decelerate Bejan number; and the unsteady parameter decelerates the profiles and the temperature distributions accelerate by the

Effects of heated block comprised porous stratum and micropolar hybrid nanofluid on convective heat transfer and entropy generation in a square enclosure

AbstractA numerical study is performed to explore the effects on heat convection and entropy gthe eneration due to porous stratum and heated block in an enclosure saturated with micropolar hybrid nanofluid. Constant heat flux through half of the length of the square enclosure is centrally placed at the bottom wall and the top wall is isothermally cooled while vertical walls are insulated. The Cu‐Al2O3/water hybrid nanofluid is considered a micropolar fluid (MF) with constant physical properties. The Boussinesq approximation is implemented on the density variation and convection within the porous layer is regulated with the Darcy–Brinkman model. The governing nondimensional equations are solved with the finite difference method (FDM). Effects of various key parameters on isotherms, streamlines, local Nusselt number, and average Nusselt number are discussed numerically and analyzed through graphs. The entropy generation analysis (EGA) has been done with local and average Bejan numbers, local entropy generation, and entropy generation numbers. The heat convection from the heat flux enhances with the increase in the volume fraction of the hybrid nanoparticles (), Rayleigh number (Ra), and Darcy's number (Da) while attenuating by increasing the vortex viscosity K0. The domination of the heat transfer irreversibility over the frictional irreversibility upraises with K0 and . With an increase in the porous stratum's thickness, the average value of the Bejan's number enhances, and a decline in the entropy generation number Ns.

Entropy Generation Analysis of the Flow Boiling in Microgravity Field.

Entropy generation analysis of the flow boiling in microgravity field is conducted in this paper. A new entropy generation model based on the flow pattern and the phase change process is developed in this study. The velocity ranges from 1 m/s to 4 m/s, and the heat flux ranges from 10,000 W/m2 to 50,000 W/m2, so as to investigate their influence on irreversibility during flow boiling in the tunnel. A phase–change model verified by the Stefan problem is employed in this paper to simulate the phase–change process in boiling. The numerical simulations are carried out on ANSYS-FLUENT. The entropy generation produced by the heat transfer, viscous dissipation, turbulent dissipation, and phase change are observed at different working conditions. Moreover, the Be number and a new evaluation number, EP, are introduced in this paper to investigate the performance of the boiling phenomenon. The following conclusions are obtained: (1) a high local entropy generation will be obtained when only heat conduction in vapor occurs near the hot wall, whereas a low local entropy generation will be obtained when heat conduction in water or evaporation occurs near the hot wall; (2) the entropy generation and the Be number are positively correlated with the heat flux, which indicates that the heat transfer entropy generation becomes the major contributor of the total entropy generation with the increase of the heat flux; (3) the transition of the boiling status shows different trends at different velocities, which affects the irreversibility in the tunnel; (4) the critical heat flux (CHF) is the optimal choice under the comprehensive consideration of the first law and the second law of the thermodynamics.

The Exergy Losses Analysis in Adiabatic Combustion Systems including the Exhaust Gas Exergy.

The entropy generation analysis of adiabatic combustion systems was performed to quantify the exergy losses which are mainly the exergy destroyed during combustion inside the chamber and in the exhaust gases. The purpose of the present work was therefore: (a) to extend the exergy destruction analysis by including the exhaust gas exergy while applying the hybrid filtered Eulerian stochastic field (ESF) method coupled with the FGM chemistry tabulation strategy; (b) to introduce a novel method for evaluating the exergy content of exhaust gases; and (c) to highlight a link between exhaust gas exergy and combustion emissions. In this work, the adiabatic Sandia flames E and F were chosen as application combustion systems. First, the numerical results of the flow and scalar fields were validated by comparison with the experimental data. The under-utilization of eight stochastic fields (SFs), the flow field results and the associated scalar fields for the flame E show excellent agreement contrary to flame F. Then, the different exergy losses were calculated and analyzed. The heat transfer and chemical reaction are the main factors responsible for the exergy destruction during combustion. The chemical exergy of the exhaust gases shows a strong relation between the exergy losses and combustion emission as well as the gas exhaust temperature.

Computational Fluid Dynamics-Based Analysis of Entropy Generation on Laminar Natural Convection in Enclosures With Partitioned Walls and for Different Heating Positions

Abstract A numerical investigation is performed to analyze air's steady natural convection phenomena in an enclosure with partial active sidewalls. A partition is attached to the hot wall for different active locations to study the effect of the partition position on the heat transfer. First, a finite volume method solves the coupled equations of continuity, momentum, and energy. The SIMPLE algorithm is used to solve the pressure velocities coupling iteratively. Second, based on the obtained dimensionless velocity and temperature values, the distributions of the local entropy generation due to heat transfer and fluid friction and the total entropy generation are determined for different parameters. The results are presented graphically in streamlines, isotherms, and average Nusselt numbers. Three different configurations of active region arrangement are considered in this study, while the partition length has been changed. In order to identify the optimum location of the partition for better heat transfer, the effect of entropy generation has been studied. The heat transfer rate decreases with the increased partition length, especially for l = L/2. Thus, the maximum average Nusselt number occurs for the middle–middle arrangement, while the minimum one occurs for the bottom–bottom arrangement. The numerical investigations in this analysis are made over a wide range of parameters, Rayleigh number 103 to 105, dimensionless partitions length (l = L/8, L/4, L/2), and irreversibility coefficients 10−4< ϕ < 10−2; however, the Prandtl numbers was fixed to 0.71.

Entropy Generation Analysis on Confined Impinging Slot Jets with Nanofluids in Metal Foam

In this paper a numerical entropy generation analysis on confined slot impinging jets made up of a totally filled configuration of metal foam in mixed convection is presented. A two-dimensional domain is assumed and several Peclet numbers (equal to 350, 750, 1500) are considered. Rayleigh numbers is imposed equal to 30000. The employed working fluids are pure water or Al2O3/water based nanofluids. The nanoparticle volume concentrations are in a range from 0% to 4% and the nanoparticle diameter is varied in a range from 20 nm to 80nm. The target surface is characterized by a constant temperature, estimated starting to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. The thermal and fluid dynamic properties of nanofluids are evaluated by a single-phase model method. The model of local thermal non equilibrium (LTNE) is considere in order to simulate the behavior of the metal foam characterized by a number of pores per inch (PPI) equal to 5, 10, 20, 40 and a porosity around 0.90. The data in terms of total global entropy generation related to the thermal and viscous effects are given Results show increasing values of the total entropy generation for increasing values of Peclet number and nanoparticle concentration. This behaviour is more evident at higher Peclet number values. In addition, the total entropy generation increases with the increase of PPI in corresponding to the same porosity value.

Entropy generation minimization on electromagnetohydrodynamic radiative Casson nanofluid flow over a melting Riga plate

AbstractMinimizing entropy generation is a technique that helps improve the effectiveness of real processes by studying the associated irreversibility of system performance of nanofluid. This study examines the entropy generation analysis of electromagnetohydrodynamic radiative Casson flow induced by a stretching Riga plate in a non‐Darcian porous medium under the influence of internal energy change, Arrhenius activation energy, chemical reaction, and melting heat transfer. The thermophysical features of the fluid are assumed constant in most of the literature. However, this current research bridges this gap by considering viscosity, conductivity, and diffusivity as temperature‐dependent variables. Also, the exponential decaying Grinberg term is used as a resistive force in this investigation due to the electromagnetic properties of the Riga plate in the momentum conservation equation. Some suitable dimensionless variables are introduced to remodel the transport equations into unitless ones and then solved numerically by employing Galerkin Weighted Residual Method. Analyses reveal that the Casson parameter declines the fluid velocity, while the existence of the melting parameter has the opposite effect. Also, this article includes some future recommendations.

A flow analysis of gamma-alumina nanoparticles near a solid sphere

ABSTRACT Prandtl number exhibits a primary role in regulating thermal or momentum boundary layer regions. Therefore, keeping such a comprehensive spectrum in view we contemplated the significance of an effective Prandtl number model on natural convection flow of non-uniform viscosity with steady, 2D, incompressible nano-liquids of and towards a solid heated sphere. To renovate the PDEs into a system of ODEs a felicitous transformation has been employed. The converted non-linear equations are executed numerically via BVP4C. Main findings reveal that nanoparticle volume fraction parameter augments the velocity component for both cases of effective and non-effective Prandtl numbers. A comparison reveals that offers better thermal transfer enhancement than . Entropy generation analysis is also perceived and the behavior of Grashof number is also presented.

Entropy generation for MHD two phase blood flow through a curved permeable artery having variable viscosity with heat and mass transfer

Present study deals with the analysis of entropy generation of MHD blood flow through a stenosed permeable curved artery with heat source and chemical reaction. Blood flow is considered in two-phases; core and plasma region, respectively. Viscosity of the core region is considered as temperature-dependent, while constant viscosity is considered in plasma region. The governing equations of the proposed two-phase blood flow model are considered in the toroidal coordinate system. The second-order finite difference method is adopted to solve governing equations with 10−6 tolerance in the iteration process. A comparative study of darcy number (Da) is performed to understand the influence of permeable and impermeable wall conditions. The effect of various physical parameters such as magnetic field (M), viscosity variation parameter (λ1), Darcy number (Da), Brinkman number (Br), heat source (H), chemical reaction parameter (ξ) etc. are displayed graphically on the flow velocity, temperature, concentration, wall shear stress (WSS), frictional resistance profile and entropy generation profiles. A comparison with published work has also been displayed through the graph to validate the present model, and it is in fair agreement with the existing work. The present study suggested that the curvature and permeability of the arterial wall raise the risk of atherosclerosis formation, while the implication of heat source on the blood flow lower this risk. Clinical researchers and biologists can use the current mathematical research to lower the risk of lipid deposition and predict the risk of cardiovascular disease, and then diagnose patients based on risk.

Experimental investigation and numerical investigations of heat transfer enhancement in a tube with punched winglets

As an effective technology to reduce flow resistance, drilling holes on the surface of vortex generators had been studied extensively. In this paper, thermal performance of punched rectangular winglet vortex generators (PRWVGs) in turbulent regime (Reynolds number was in the range of 9,090∼21,210) was studied experimentally and numerically. Air was applied as the working fluid. The PRWVGs were inserted into the tube with three attack angles (α=30°,45°,60°). The punched holes were set in three different positions (g=3mm,5mm,7mm) in the vertical direction and at three different hole heights (d=1mm,3mm,6mm). The performance of PRWVGs was quantified by the heat transfer coefficient ratio (h/h0), the friction factor ratio (f/f0), and a combined thermal enhancement factor (TEF) of the two. The results revealed that h/h0 as well as f/f0 values of PRWVGs compared with those of planar VGs (without holes) were reduced. The flow and temperature fields of different cases were obtained by numerical simulations, and the experimental results were verified by analyzing the fluid flow behaviors. The results showed that the jet flow (defined as a jet emanating from the punched hole of a VG), would enhance the heat transfer efficiency in the recirculation area. And the TEF value of VGs was improved by punching holes on the surface of VGs. However, the shape of the jet flow depended on the position of the hole. When the position of the hole was lower in the vertical direction, the jet flow was effective in increasing its TEF value. Additionally, the size of the hole had a large effect on the TEF value. Besides, entropy generation analysis showed that PRWVGs were thermodynamically advantageous. Whend=1mm,w=5mm, the Bejan number reached the minimum. Under this condition, the proposed PRWVGs performed best in practice. When the height of the hole was d=1mm, TEF was the maximum, which was 1.25 at α=45° and Re=9,090.

Performance of Graphene and Diamond Nanoparticles on EMHD Peristaltic Flow Model with Entropy Generation Analysis

Performance of Graphene and Diamond Nanoparticles on EMHD Peristaltic Flow Model with Entropy Generation Analysis

Analysis of thermo-magnetic convection and entropy generation of Al2O3-water nanofluid in a partially heated wavy electronic cabinet

A computational analysis has been performed to study the effect of magnetic parameter on magneto-natural convection and entropy generation inside a wavy cabinet filled by Al2O3-H2O nanosuspension. The vertical boundaries of the cavity are designed as wavy and kept at cooled temperature (Tc), while the horizontal borders are modeled as flat and supposed to be thermally insulated except the centrally heated portion on the bottom wall. The higher constant temperature (Th) of the isothermal line source can supply thermal energy in uniform manner. The transformed dimensionless governing equations were solved using finite volume technique along with power-law scheme. The system was optimized for significant variety of controlling parameters namely, number of undulations (N = 0–3), volume fraction of nanosuspension (ϕ = 0.0–0.04), magnetic parameter (Ha = 0 and 50), magnetic tilted angle (ζ = 0°–90°) and dimensionless heat difference (Ω = 0.001–0.1). The numerical results are analyzed for streamlines, isotherms, entropy isolines, overall Nusselt number and average entropy production strength. From this study, it is noticeable that growth of undulation number causes the reduction of convective heat transfer rate as well as average entropy production intensity. Further, the findings elucidate that the average entropy production intensity and overall heat transfer rate are decreased upon growing magnetic parameter.

Entropy Generation Analysis of Peristaltic Flow of Nanomaterial in a Rotating Medium through Generalized Complaint Walls of Micro-Channel with Radiation and Heat Flux Effects.

This study discusses entropy generation analysis for a peristaltic flow in a rotating medium with generalized complaint walls. The goal of the current analysis is to understand the fluid flow phenomena particular to micro devices. Nano materials with a size less than 100 nm have applications in micro heat exchangers to cool electronic circuits, blood analyzers, biological cell separations, etc. For this study, we considered the effects of radiation, viscous dissipation and heat flux on the flow of nanomaterial inside a cylindrical micro-channel. To investigate the slip effects on the flow, the second order slip condition for axial velocity, the first order slip condition for secondary velocity and the thermal slip conditions were used. The flow was governed by partial differential equations (PDE’s), which were turned into a system of coupled ordinary differential equations (ODE’s) that were highly non-linear and numerically solved using the NDSolve command in Mathematica. The impacts of different involved parameters on the flow field were investigated with the aid of graphical illustrations. Entropy generation and the Bejan number were given special attention, and it was found that they decreased as the Hartman number, rotation, and radiation parameters increased.

Entropy generation analysis of three dimensional mixed convection flow of couple stress nanofluid with non-Fourier’s heat and non-Fick’s mass flux model

The current study concentrated on the analysis of entropy generation in three dimensional mixed convection flow of couple stress nanofluid under the effect of high order velocity slip flow, passive and active control conditions. The problem advances more significance with the effect of non-Fourier’s heat, and non-Fick’s mass flux model to scrutinize the heat and mass transport rate. The high-order partial differential equations obtained from the designed problem are transmuted into higher order ordinary differential equations using similarity conversion and lastly solved by using bvp4c. Through this investigation how governing parameters have affected the flow problem were examined and offered in graphical and tabular form. It is discovered that the occurrence of couple stress inflow problem upsurges the velocity of the fluid and on the other hand it causes a reduction in the entropy production. Likewise, it is detected that temperature improves by snowballing the Hartman parameter. Moreover, the temperature and concentration disseminations are greater all for the situation of an active control while correlated with a case of passive control. Also, the same is true for numerical results of Nusselt number and Sherwood number that is due to an active control is greater than all for the case of passive control. Furthermore, this theoretical and numerical deliberation bears the potential to beneficial in the field of bio-fluid dynamics.

An entropy generation analysis of horizontal convection under the centrifugal buoyancy approximation

An entropy generation analysis is conducted for horizontal convection under the centrifugal buoyancy and the Boussinesq approximations in a relatively shallow enclosure at a fixed Prandtl number of unity to characterise irreversible losses across the conduction and convection-dominated regimes using the Bejan number (Be). A variable irreversibility distribution factor is expressed for the entropy generation analysis as a ratio of the Brinkman number (Br) and the Gay-Lussac (Ga) parameter for the first time. Governing equations are solved numerically using a high-order nodal spectral-element method. Calculations are performed at a fixed Br = 2 × 10−5 over the physical range of the Gay-Lussac parameter 0 ≤ Ga ≤ 2 up to Ra = 5 × 108. As expected, increasing the Rayleigh number shifts the flow toward a convection-dominated regime; however it is found that increasing the Gay-Lussac parameter draws the heat transfer mechanism back to a conduction-dominated state. In other words, advection related buoyancy effects act to keep the buoyancy-driven flow in conduction-dominated regime. The entropy generation analysis indicates that at Ga ≳ 0.5 conduction and convection are in balance at Ra ≈ 6 × 105, while under the conventional Boussinesq approximation (Ga = 0), heat transfer is convection-dominated. The transition of the average Bejan number from conduction to convection-dominated regime follows closely to a reciprocal scaling against Rayleigh number Beave~Ra−1 when Ga = 0 but the same process scales with Beave~Ra−0.5 relation at Ga = 2.

Numerical investigation on the loss audit of Wells turbine with exergy analysis

As one of the most promising methods for harnessing ocean wave energy, the oscillating water column device has been intensively investigated, especially the Wells turbine within the device. However, owing to the low efficiency of the Wells turbine, it is essential to provide a deep insight into the loss audit and loss quantification. The scope of this work is to explore the main loss mechanisms due to the irreversibility. The aerodynamic losses and associated flow behaviors within four typical working conditions were quantified and analyzed in detail based on entropy generation and exergy analysis. The loss weight of the Wells turbine indicates that the secondary flow loss coupled with the friction loss is the largest, 34%, under the stall condition. The blade tip streamlines show that a large-scale vortex structure on the blade suction caused by the interaction of the leakage flow and the suction side flow is one of the main reasons of the decreasing blade loading and growth of low-energy fluids. Moreover, the exergy loss gradually increases with the increasing angle of attack, leading to a dramatic drop of the second law efficiency from 0.52 at the maximum torque point to 0.22 at the stall condition.