Entropy Generation Rate Research Articles

Numerical investigation of the overall thermal and thermodynamic performance of a high concentration ratio parabolic trough solar collector with a novel modified twisted tape insert using supercritical CO2 as the working fluid

Supercritical CO2 (sCO2) is favoured as the next-generation working fluid for advanced high-temperature and high-concentration ratio parabolic trough solar collectors (PTSC) due to the fluid’s low cost, availability and thermal stability at high temperatures. However, the lower thermal transport properties of sCO2 compared to conventional working fluids necessitate heat transfer enhancement of receivers using sCO2. In this study, a combined and extensively validated approach using Monte-Carlo ray tracing for optical analysis and computational fluid dynamics (CFD) for thermal and thermodynamic analysis were used to investigate the overall thermal and thermodynamic performance of a high concentration ratio sCO2-based PTSC with a modified twisted tape (MTT) inserts in the receiver. MTT inserts with twist ratios in the range of 2.0 to 4.0 and width ratios in the range of 0.75 to 0.95 were investigated. Results show enhancement of the heat transfer performance by up to 73% and thermal efficiency by 6%, and reduction of the receiver heat losses and circumferential temperature gradients when the MTT inserts are used. In addition to presenting results using the first law of thermodynamics, this study also considered the second law of thermodynamics by evaluating the entropy generation rates due to heat transfer and fluid friction irreversibilities. Results showed that the use of MTT inserts caused a reduction in the total entropy generation rates, with the lowest irreversibility occurring at a Reynolds number of 1,650,000 for a twist ratio of 2.0 and width ratio of 0.95.

Entropy production on mixed convection stagnation point flow of nonlinear radiative fourth-grade hybrid nanofluid through a stretchable Riga surface

The purpose of the current study is to inspect entropy generation, mixed convective stagnation point flow, and thermal transfer features of nonlinear radiative fourth-grade hybrid nanofluid (NF) confined by a convectively heated Riga surface. The heat transport is examined with the existence of two disparate heat source modulations, variable thermal conductivity, and viscous dissipation. The original flow equations are first transmuted using appropriate transformations into non-dimensional ordinary differential equations, which are then solved via an overlapping grid-based spectral collocation scheme. The upshots of various pertinent parameters on velocity, temperature, entropy generation, and valuable engineering quantities are deliberated. Pivotal results obtained reveal that speedily flow of fluid and skin friction can be accelerated by strong magnetic force, rising mixed convection, and material parameters. Also, convective boundary conditions, along with nonlinear radiation and fluctuating thermal conductivity, are recommended for boosting fluid temperature, rates of entropy generation and heat transport. Thermal mechanism in hybrid NF is dominant over simple NF, which implies that performance of hybrid NF is better than that of simple NF. The outcomes of this study can be useful in enriching thermal performance of the working fluid, assisting in diagnosing causes of incompetency in thermal systems, and discovering suitable means of minimizing entropy generation with the intention of mitigating the loss of useful and scarce energy resources.

FRACTAL FRACTIONAL MODEL OF RADIATIVE HEAT AND MASS TRANSFER CHARACTERISTICS OF TIME DEPENDENT FLOW WITH VARIABLE VISCOSITY, INDUCED MAGNETIC FIELD, DUFOUR AND SORET EFFECTS: AN ENTROPY GENERATION

: In this article, the Caputo Fabrizio fractal fractional order derivatives operator with an exponential kernel was employed to examine the radiative heat and mass transfer characteristics of time dependent flow with variable fluid viscosity, induced magnetic field, Soret and Dufour effects. The local mathematical model for the flow problem is formulated by take into account the impacts of thermal radiation, heat source, and viscous dissipation. The governing equations in-terms of fractal fractional model with an exponential kernel were solved numerically using finite difference method. The influence of flow variables such as induced magnetic field, concentration field, entropy rate, thermal field, and velocity field profiles against the pertinent parameters are discussed through graphs. Increase the values of magnetic Prandtl number results to rises of induced magnetic field. Higher Dufour number significantly grows the thermal field. The fractal fractional parameters enhance the velocity field, thermal field, Bejan number, entropy rate, concentration field and induced magnetic field profiles. The velocity field profiles recede with higher values of fluid variable viscosity parameter whereas the thermal field and induced magnetic field has an opposite effect. Larger Soret number amplifies the concentration field. Increase of Brinkman number, thermal radiation parameter, and magnetic Prandtl number intensifies the entropy generation rate. Increases of Brinkman number, magnetic Prandtl number, Soret number and Dufour number leads to a decrease of Bejan number whereas Bejan number rises with an increase of thermal radiation parameter and heat source

Comparison analysis of entropy and entransy under various conditions of a hollow fiber membrane humidifier (HFMH)

The hollow fiber membrane heat and moisture transfer model is converted equivalently into a series of parallel-plate membranes stacked along the z-axis to simplify the model. A detailed modeling process is described based on the concept of finite difference method. The comparison of experimental values with calculated values ensures the validity of the model. Subsequently, an entransy dissipation model for the heat and moisture transfer process in a hollow fiber membrane humidifier (HFMH) is developed by analogizing heat and moisture conduction to electrical conduction. The variation of heat/moisture transfer capability within the HFMH is investigated from the perspective of “heat/moisture potential energy”. In addition, an entropy generation model for the HFMH is established to study the irreversible losses in the heat and moisture transfer process caused by irreversibility. The performance, entropy generation rate, and entransy dissipation rate of the HFMH under different conditions are comparatively analyzed. It can be found that the heat/moisture transfer performance of the humidifier can be improved by adjusting the operating conditions to increase the heat/moisture transfer driving force. However, the irreversible losses increase due to a higher heat/moisture transfer energy grade. The sensible and latent effectiveness can be enhanced by 20.9%–85.2 %, while the equivalent resistance can be reduced by 16.2%–42.0 % via optimizing the geometry structures and membrane properties. In the hot-dry region, the heat and moisture transfer increase by 25.9%–89.8 %, while the equivalent resistances decrease by 20.8%–66.0 %. In addition, the minimum equivalent resistances correspond to the optimal HFMH performance. The entransy analysis avoids the “paradox” of entropy analysis.

Numerical investigation on mixed convection for laminar molten salt in horizontal square tubes

Molten salts are the key working media in nuclear and new energy fields. However, the mixed convection of molten salt is rarely investigated. The mixed convection of laminar flow in horizontal square tubes with constant heat flux is analyzed using Fluent software for the first time. The effects of heat flux, inlet temperature and Reynolds number on the flow and heat transfer performances are evaluated. It is found that as the buoyancy force increases, the friction factor, flow entropy generation rate, Nusselt number, and exergy efficiency increase, while the heat transfer entropy generation rate and exergy loss decrease. Compared to the forced convection, the maximum local friction factor, flow entropy generation rate, mean Nusselt number and mean exergy efficiency for mixed convection increase by 25.8%, 50.5%, 109.0% and 7.6%, respectively. Moreover, the maximum mean heat transfer entropy generation rate and exergy loss decrease by 56.1% and 57.3%, respectively. In addition, approximately 42% of the friction factor predicted by Fluent and 30% of the heat transfer predicted by Fluent exceed 20.0% uncertainties of conventional correlations. Therefore, an accurate friction factor correlation with 12.9% uncertainty and an accurate heat transfer correlation with 9.1% uncertainty are proposed.

Comparative assessment of aerodynamic losses in turbine stages with supercritical carbon dioxide and steam

To investigate the aerodynamic loss mechanisms in supercritical carbon dioxide turbine (CT) and steam turbine (ST) stages, entropy generation and entropy generation rate are used to analyze various losses in stage passages. The results reveal that under sealing clearance at 2.5 % blade height, the leakage losses of CT and ST constitute over 7 % of total available energy. Rotor and stator losses of CT and ST decrease as the Mach number of stage outlet increases. The endwall losses of CT and ST rotor are both predominant, constituting over 1.78 % of total available energy, with lower endwall losses of CT rotor. Furthermore, the stator profile loss of CT represents the majority of stator loss and is notably higher than that of ST. The impact loss and separation loss are more pronounced in CT. The conclusions will provide direction, guidance, and data support for the design and optimization of CT and ST.

Thermodynamic survey of a reactive MHD couple stress fluid through saturated porous substances with convective boundary conditions

This study explores the thermodynamic behavior of a reactive hydromagnetic liquid flowing through permeable materials, with convective cooling applied to the walls. This study holds practical significance in optimization of thermal management systems and it is crucial for enhancing the efficiency of controlling thermal runaway. The flow is modeled as a system of partial differential equations which are numerically solved. The modified Adomian Decomposition Method and Pade approximation technique are utilized in solving the equations. The results acquired for velocity and temperature distributions are thereby employed to estimate entropy generation rate with critical values over numerous effects of various boundaries over improvement of thermal runaway utilizing Pade approximation technique to show the significant impact of convective cooling term (Biot number) and other thermophysical parameters on the fluid flow. The outcomes show that fluid velocity continuously increases with rising values of inverse couple stress and fluid temperature increases Biot number.

Analysis of Thermal Mixing and Entropy Generation during Natural Convection Flows in Arbitrary Eccentric Annulus

The present study presents a computational investigation into the thermal mixing along with entropy generation throughout the natural convection flow within an arbitrarily eccentric annulus. Salt water is filled inside the eccentric annulus, in which the outer and inner cylinders have Tc and Th constant temperatures. The Boussinesq approximation is used to develop the governing equations for the natural convection flow, which are then solved on a structured quadrilateral mesh using the OpenFOAM software package (FOAM-Extend 4.0). The computational simulations are performed for Rayleigh numbers (Ra=103–105), eccentricity (ϵ=0,0.4,0.8), angular positions (φ=0∘,45∘,90∘), and Prandtl number (Pr=10, salt water). The computational results are visualized in terms of streamlines, isotherms, and entropy generation caused by fluid friction and heat transfer. Additionally, a thorough examination of the variations in the average and local Nusselt numbers, circulation intensity with eccentricities, and angular positions is provided. The optimal state of heat transfer is shown to be influenced by the eccentricity, angular positions, uniform temperature sources, and Boussinesq state. Moreover, the rate of thermal mixing and the production of total entropy increase as Ra increases. It is found that, compared to a concentric annulus, an eccentric annulus has a higher rate of thermal mixing and entropy generation. The findings show which configurations and types of eccentric annulus are ideal and could be used in any thermal processing activity where a salt fluid (Pr=10) is involved.

Assessment of thermohydraulic performance and entropy generation in an evacuated tube solar collector employing pure water and nanofluids as working fluids

This study conducts a numerical comparison of the thermal performance of three distinct working fluids (pure water, TiO2, and SiO2 water-based nanofluids) within an evacuated tube solar collector using Computational Fluid Dynamics. The study evaluates thermohydraulic performance alongside global and local entropy generation rates, while considering variations in solar radiation values and inlet mass flow rates. Results indicate that nanofluids demonstrate superior performance under low solar radiation, exhibiting higher outlet temperatures, velocities, thermal efficiency, and exergy efficiency compared to pure water. However, at the higher solar radiation level, the efficiency of SiO2 water-based nanofluid diminishes due to its impact on specific heat. Furthermore, the entropy generation analysis reveals significant reductions with TiO2 water-based nanofluid in all the phenomena considered (up to 79 %). The SiO2 nanofluid performance aligns closely with pure water under high radiation value. This investigation offers valuable insights into the utilization of nanofluids in solar collectors across diverse operating conditions, emphasizing their pivotal role in enhancing overall performance.

Performance evaluation criteria based on the first and second laws of thermodynamics

Numerical simulations were conducted to investigate the correlation between assessments based on the total entropy generation rate criterion and the thermal resistance criterion in the context of evaluating heat transfer performance. This study focused on a parallel plate channel heat sink with the lower wall subjected to a constant heat flux, under various flow constraints. The flow was assumed to be laminar and fully developed. The energy equation was discretized using the control volume-based power law scheme, and the resulting algebraic equations were solved by the line-by-line method. Optimal channel heights which lead to minimize irreversibility and temperature difference between heated wall and inlet fluid temperatures were determined by both the total entropy generation rate and thermal resistance criteria under four distinct flow constraints: identical mass flow rate, identical inlet velocity, identical pumping power, and identical pressure drop. The investigation revealed a lack of significant correlation between the optimal channel heights derived from assessments based on the total entropy generation rate and thermal resistance. Consequently, the utilization of the total entropy generation rate criterion for evaluating heat transfer performance, based in the second law of thermodynamics, instead of the thermal resistance criterion, based in the first law of thermodynamics, was deemed inappropriate. The total entropy generation rate criterion was based on the minimization of the irreversibility and served as an indicator of heat transfer quality. As a recommendation, it is suggested that results obtained from both the total entropy generation rate and thermal resistance criteria for assessing heat transfer performance be presented separately for each specific application.

Study on the Tip Leakage Loss Mechanism of a Compressor Cascade Using the Enhanced Delay Detached Eddy Simulation Method.

The leakage flow has a significant impact on the aerodynamic losses and efficiency of the compressor. This paper investigates the loss mechanism in the tip region based on a high-load cantilevered stator cascade. Firstly, a high-fidelity flow field structure was obtained based on the Enhanced Delay Detached Eddy Simulation (EDDES) method. Subsequently, the Liutex method was employed to study the vortex structures in the tip region. The results indicate the presence of a tip leakage vortex (TLV), passage vortex (PV), and induced vortex (IV) in the tip region. At i=4°,8°, the induced vortex interacts with the PV and low-energy fluid, forming a "three-shape" mixed vortex. Finally, a qualitative and quantitative analysis of the loss sources in the tip flow field was conducted based on the entropy generation rate, and the impact of the incidence on the losses was explored. The loss sources in the tip flow field included endwall loss, blade profile loss, wake loss, and secondary flow loss. At i=0°, the loss primarily originated from the endwall and blade profile, accounting for 40% and 39%, respectively. As the incidence increased, the absolute value of losses increased, and the proportion of loss caused by secondary flow significantly increased. At i=8°, the proportion of secondary flow loss reached 47%, indicating the most significant impact.

Entropy generation and heat transfer analysis of Eyring-Powell nanofluid flow through inclined microchannel subjected to magnetohydrodynamics and heat generation

The current study is inspired to investigate the influences of essential flow dynamics including magnetic field, variable dynamic viscosity, Joule heating, viscous dissipation, porous medium dissipation, heat source, thermal radiation, and convective heating on the mixed convection flow of Eyring-Powell Cu − water nanofluid trough an inclined microchannel in the presence of Darcy-Forchheimer porous medium. The governing mathematical model equations are formulated, converted into dimensionless and thereafter solved numerically in the MATLAB software via Bvp4c-package. The influences of the embedded dimensionless parameters on heat transfer behaviours and entropy generations are displayed trough graphs as well as their physical interpretations are discussed in detail. Consequently, it is revealed that the performance of microchannel thermal system is improved by factors such as injection/suction of fluids, Eyring-Powell fluid, magnetic field, non-Darcy porous medium, Cu − nanoparticles, thermal radiation and convective heating. The drag coefficient and Nusselt number augment with viscous dissipation, variable dynamic viscosity, Darcy porous medium, angle of inclination, Prandtl number and heat source. Moreover, the Nusselt number at around the left and right walls vicinity shows an opposite behaviour with escalating values of the Biot number and thus convective transfer of heat around the microchannel walls is remarkably important. Furthermore, the minimization of net entropy generation rate is achieved with Eyring-Powell fluid, magnetic field, Cu − nanoparticles, thermal radiation and convective heating but it escalates with variable dynamic viscosity, viscous dissipation, angle of inclination, heat source and Prandtl number. Indeed, the irreversibility due to the robust influence of porous medium shows dual behaviours on the net entropy generation rate. Finally, the numerical results are also validated by comparing with the results of already existing literatures and hence, a sounding agreement is attained.

Numerical investigations on the entropy generation and heat transfer of an unsteady micropolar hybrid nanofluid flow over an inclined stretching surface

Studies on stagnation point flow on inclined surfaces have gained momentum in recent times due to its application in a variety of fields. This study aims at the heat transfer properties of an incompressible unsteady stagnation point flow of a non-Newtonian micropolar hybrid nanofluid over an inclined stretching sheet with thermal radiation, viscous dissipation, and Joule heating. The governing equations of the problem are transformed into a system of ordinary differential equations by employing similarity variables. They are then solved numerically using the Runge-Kutta 4 th order method along with the shooting approach. Numerical solutions on velocity, microrotation, and temperature distribution along with entropy generation and Bejan number are consolidated graphically and those on heat transfer rate and skin friction coefficient are tabulated. The results indicate that the heat transfer rate is higher in hybrid nanofluid as compared to that of mononanofluid, the angle of inclination of the sheet is unfavorable for the velocity profile, and the temperature of the hybrid nanofluid escalates with a rise in viscous dissipation. Entropy generation rate is reduced when the Hartmann number is increased and the Bejan number diminishes with elevating viscous dissipation. The results were validated using existing studies and comparing heat transfer rate values between the present results and the results obtained from NDSolve.

Irreversibility of Al2O3-Ag hybrid nanoparticles in mixture base fluid on microchannel with variable viscosity, buoyancy forces, and suction/injection effects: An analytical study

The development of inherent irreversibility in the system is caused by single phase Poiseuille flow considering hybrid nanoparticles (Al2O3-Ag) and mixture fluid (water and ethylene glycol H2O50%-C2H6O250%) in the upright microchannel with unequal viscosity. Taking into account the buoyancy force, suction/injection at the walls, and the form factor and geometry of the nanoparticles. The modeling is based on nonlinear PDEs such as continuity, momentum, and heat equations, which are then transformed to a system of nonlinear ODEs using similarity transformations and solved numerically and analytically. The analytical solution was built using the Differential Transform Method (DTM), and the current results in specific cases are compared to results obtained by the HAM-based Mathematica package, the Runge-Kutta Fehlberg 4th-5th order (RKF45), and those available in literature. The effects of active parameters are investigated on the velocity and temperature, entropy generation and Bejan number. The outcomes of the present analysis reveal that the nanoparticles volume fraction, thermal radiation and Biot number acts to enhance the cooling of the system through the release of thermal energy. in addition, the enhancement in variable viscosity parameter, causes a rise in the irreversibility rate, which in turn boosts the rates of entropy generation and Bejan number. On the other hand, Irreversibility due to heat transfer is dominant in the centerline of the microchannel, while fluid friction irreversibility dominates its walls.

Neural network and thermodynamic optimization of magnetized hybrid nanofluid dissipative radiative convective flow with energy activation

This article, motivated by hybrid magnetic coating manufacturing developments, utilizes a neural network-based computational program to study the dynamics of hybrid magnetic nanofluids with entropy generation. A new physico-chemo-mathematical model has been presented to simulate the hybrid magnetic nano-coating flow along a stretching surface to a porous medium with viscous heating. A Rosseland flux model is used for radiation heat transfer and Darcy’s model for the isotropic porous medium. The stretching sheet is porous, and wall suction or injection are possible. A robust neural network has been deployed to optimize the physical parameters controlling the transport characteristics of hybrid nanofluids. Specifically, two hybrid nanoparticle combinations are addressed, namely graphite oxide (GO)-molybdenum disulfide ( Mo S 2 ) and copper (Cu)-silicon dioxide ( Si O 2 ), both with engine oil as the base fluid. The dimensional boundary layer model is transformed via suitable scaling variables from a partial differential system into a dimensionless non-linear coupled ordinary differential system. The transformed boundary value problem is solved numerically with the BVP4C subroutine in the symbolic software MATLAB, which achieves exceptional accuracy. Validation with previous simpler studies is conducted and a good correlation is obtained. The neural network optimization analysis incorporates Bayesian regularization as the training algorithm. The Bejan entropy generation minimization (EGM) analysis shows that with increasing radiation parameter R d , both entropy generation rate and Bejan number are increased. Furthermore, an elevation in Brinkman number Br leads to an upsurge in entropy generation rate and a downtrend in the Bejan number. The numerical solution of the boundary value problem reveals that with an increment in nanoparticle solid volume fraction φ 2 , magnetic parameter M , inverse permeability parameter ϵ , surface injection parameter ( s < 0 ) , Eckert number Ec and radiation parameter R d and with a decrement in suction parameter ( s > 0 ) and Prandtl number Pr , there is a strong enhancement in temperature magnitude and thermal boundary layer thickness. With greater nanoparticle solid volume fraction φ 2 , magnetic parameter M , inverse permeability parameter ϵ , suction parameter s and a reduction in thermal buoyancy parameter λ , strong flow deceleration is induced, and momentum boundary layer thickness is increased. The skin friction coefficient is substantially boosted with lower values of magnetic parameter M , inverse permeability parameter ϵ , suction parameter s and higher values of thermal buoyancy parameter λ . There is a significant decrement also computed in Nusselt number with a greater radiation parameter R d . The simulations provide a good benchmark for future extensions that may consider non-Newtonian behavior.

Electroosmotic microchannel flow of blood conveying copper and cupric nanoparticles: Ciliary motion experiencing entropy generation using backpropagated networks

AbstractA novel mathematical model for a hybrid (Cu–CuO/blood) Jeffrey nanofluid passing a vertical symmetric microchannel along with an electroosmosis pump is presented. The focuses on the advancement of mathematical modeling techniques, its comprehensive analysis of microfluidic system dynamics, and its potential to inform the optimal design of devices using nanofluids with broad applications in various fields. Arrhenius's law is used to analyze endothermic–exothermic reactions and activation energy. The governing partial differential equations of the fixed frame are transformed into ordinary differential equations of the wave frame using self‐similarity transformations. Low Reynolds number and long‐wavelength approximations helped to find solutions of the equations by applying a suitable BVP solver in MATLAB. The fluid's velocity, temperature, concentration, and electroosmosis properties are studied graphically. Two‐dimensional contour plots of fluid velocity and three‐dimensional surface plots of fluid properties are discussed. Physically significant quantities of mass transfer rate, skin friction coefficient, entropy generation, and heat transfer rate are studied using contour plots. Artificial neural network simulation using Bayesian regularization backpropagation algorithms is analyzed for training state, error histogram, fit, performance, and regression plots. Conclusively, the comprehensive analysis of the fluid dynamics, entropy generation, mass and heat transfer, and in the microchannel, coupled with the successful implementation of artificial neural network simulation, contributes to an improved understanding of the system's behavior. Entropy generation was raised for enhanced Brownian motion number and reduced values of thermophoresis, activation energy, and endothermic–exothermic reaction parameters. This study's results can be used to improve the efficiency and effectiveness of microfluidic devices used in fields as diverse as electrical cooling and medicine delivery.

Thermo-hydraulic and entropy generation analysis of nanofluid flow with variable properties in various duct cross sections: a 3-D two-phase approach

A three-dimensional computational fluid dynamics (CFD) study is carried out to explore the effect of duct cross section on the thermo-hydraulic performance of various ducts. A finite volume-based scheme with an SST k-omega model and mixture model (two-phase model) was used to obtain more realistic results. A two-phase mixture model was used to consider the movement between base fluid and nanoparticles. Al2O3 nanoparticle having a volume fraction of 0.01% and 42 nm as particle size, the heat transfer and friction factor characteristic are studied for turbulent flow regime (3000 < Re < 9000) with variable thermo-physical properties. A maximum enhancement of 86% in heat transfer rate is obtained for the serpentine duct compared to the conventional circular duct at Re = 4500. Owing to a significantly lower increase in pressure drop, the elliptical duct has the highest thermo-hydraulic performance parameter of 1.54 relative to the circular duct. Further, to analyze the heat transfer quality, the entropy generation rate is studied, and it is observed that the square duct reported the highest with an increase of 60% and the elliptical duct the lowest with a reduction of 54% relative to the circular duct. This study can aid in choosing the duct geometry to enhance the heat transfer rate with nanofluid for applications such as solar-thermal, heat exchangers, etc.

Fluid–structure-interactive elasto- and thermo-hydrodynamics of electrokinetic binary fluid flows in compliant micro-confinements

We explore the intricate two-way fluid structure interaction arising due to the flow of a binary system of immiscible Newtonian fluids, composed of upper electrically conducting and lower electrically insulating fluids, flowing within a compliant microchannel, whose walls behave as linear elastic solids. The transport of the fluids along the domain occurs due to the collective impact of pressure gradient and applied electric field. We solve the closed-form system of equations and obtain semi-analytical expressions for the velocity fields and channel wall deformation from the coupled elasto-hydrodynamic problem. We then delineate the effect of four pivotal parameters: (a) Debye–Hückel parameter κ¯, (b) upper wall slip length, ls¯, (c) viscosity ratio, μr, and (d) elasticity ratio, Nr, on the morphological evolution of the wall deformation characteristics and the spatial distribution of the velocity profile of the fluids. Observations establish a positive co-relationship of wall deformation with fluid pressure, showcasing an increased collapsibility with augmented pressure gradients. Consequently, the channel walls show enhanced deformation with a decrease in κ¯, ls¯, μr and with an increase in Nr. We also demonstrate from our model that by properly tuning the applied pressure gradient and electric field, it is possible to achieve counterflow of the two fluids. We also consider the effect of heat generation in the fluids due to viscous dissipation and Joule heating, which dissipates to the surrounding by the mechanism of conjugate heat transfer. Accordingly, we provide semi-analytical expressions for the temperature profile distribution within the channel, and discuss their variation with three thermo-physical parameters: (a) Biot number of the top wall (Bi1), (b) Peclet number of the top fluid (Pe1), and (c) ratio of the thermal conductivities of the upper conducting fluid to that of the upper solid wall (kr2). We establish from our investigation that with the increase in Pe1 and with the decrease in Bi1 and kr2, the overall system temperature enhances. Finally, in order to design a thermally efficient system, we compute the global entropy generation rate in the system and evaluate optimum values of, Pe1, Bi1, and kr2 for which the system exhibits highest second law efficiency. We expect our findings to contribute toward the development of optimized microfluidic devices fabricated from deformable elastic materials.

An Effective Flux Framework for Linear Irreversible Heat Engines: Case Study of a Thermoelectric Generator.

We consider an autonomous heat engine in simultaneous contact with a hot and a cold reservoir and describe it within a linear irreversible framework. In a tight-coupling approximation, the rate of entropy generation is effectively written in terms of a single thermal flux that is a homogeneous function of the hot and cold fluxes. The specific algebraic forms of the effective flux are deduced for scenarios containing internal and external irreversibilities for the typical example of a thermoelectric generator.

Improving the hydraulic performance of a high-speed submersible axial flow pump based on CFD technology

The hydraulic performance of a high-speed submersible axial flow pump is investigated to reduce its energy consumption. A more efficient and stable optimization method that combines parametric design, computational fluid dynamics, and a computer algorithm is proposed. The main aim is to broaden the high-efficiency operating zone, so the average efficiency under multiple conditions is optimized while considering rotor–stator matching. The design-of-experiments method and a radial-basis-function neural network are combined to form the optimization platform, and automatic optimization of the pump design is realized through repeated execution of design and simulation. The flow loss mechanism inside the pump is studied in depth via the entropy generation rate, and regression analysis shows that the pump efficiency is influenced mainly by the blade angles. After optimization, the target efficiency is increased by 8.34%, and the flow field distribution shows that the channel vortex and hydraulic loss are controlled effectively. Finally, the results are validated by experiment. The proposed optimization approach has advantages in saving manpower and obtaining globally optimal solutions.