Optimal behavior of viscoelastic flow at resonant frequencies

The global entropy generation rate in the zero-mean oscillatory flow of a Maxwell fluid in a pipe is analyzed with the aim at determining its behavior at resonant flow conditions. This quantity is calculated explicitly using the analytic expression for the velocity field and assuming isothermal conditions. The global entropy generation rate shows well-defined peaks at the resonant frequencies where the flow displays maximum velocities. It was found that resonant frequencies can be considered optimal in the sense that they maximize the power transmitted to the pulsating flow at the expense of maximum dissipation.Comment: Paper accepted to be published in Phys. Rev.

Effect of Thermal Radiation on the Entropy Generation of Hydromagnetic Flow Through Porous Channel

In this study, effect of thermal radiation on the entropy generation rate of a hydromagnetic incompressible viscous flow through porous channel has been studied. The governing equations are formulated, non-dimensionalized and solved by Adomian decomposition and Differential Transform methods. The obtained velocity and temperature profiles are used to compute the entropy generation rate and Bejan number. The influence of various flow parameters on the velocity, temperature, entropy generation rate and Bejan number are discussed graphicall

Second Law Analysis of a Reactive MHD Couple Stress Fluid Through Porous Medium

In this work, effect of magnetic field on the entropy generation rate of a reactive couple stress fluid through porous medium is investigated. The equations governing the fluid flow are formulated, nondimensionalised and solved using the rapidly convergent semi-analytical Adomian decomposition method (ADM). The obtained velocity and temperature profiles are utilised to compute the entropy generation rate, irreversibility ratio and Bejan number. The effects of pertinent flow parameters on velocity, temperature, entropy generation rate and Bejan number are analyzed graphically�

Entropy Generation Rate for Profiled Endwall Design in Turbines

This thesis investigates the use of entropy generation rate as a design variable for Profiled Endwalls (PEW) to reduce secondary loss in turbines. Entropy generation rate is a measure of the local loss production in the machine, therefore any reduction in this variable leads to a reduction of the losses at their source. To that end, a numerical investigation was conducted to calculate the entropy generation rate via Computational Fluid Dynamics (CFD) by solving the Reynolds-Averaged Navier-Stokes Equations (RANS) in three dimensions, for the so-called Durham Cascade. This was part of a PEW Design System optimisation that used the entropy generation rate as a design variable in a Genetic Algorithm (GA) coupled with CFD validated against experimental measurements. After 3000 evaluations and 48000h CPU using the Hamilton High Performance Computing Service, the result was a new PEW denominated E2 that reduced the predicted entropy generation rate by 9.7% compared to the planar case (P0). An experimental campaign that consisted of axial traverses using a 5-hole probe, confirmed that the E2 reduced the stagnation pressure loss coefficient by 0.0241 compared to P0. Two loss reduction mechanisms were identified: reduced vortex interaction of the suction side horseshoe vortex (SSHV) with the pressure side horseshoe vortex (PSHV); and delayed blade suction side boundary layer separation. The first use of entropy generation rate as a design variable for iterative design optimisation has been explored and its use recommended for PEW design

Entropy characterisation of overstressed capacitors for lifetime prediction

We propose a method to monitor the ageing and damage of capacitors based on their irreversible entropy generation rate. We overstressed several electrolytic capacitors in the range of 33 µF–100 µF and monitored their entropy generation rate View the MathML source(t ). We found a strong relationship between capacitor degradation and View the MathML source(t ). Therefore, we proposed a threshold for View the MathML source(t ) as an indicator of capacitor time-to-failure. This magnitude is related to both capacitor parameters and to a damage indicator such as entropy. Our method goes beyond the typical statistical laws for lifetime prediction provided by manufacturers. We validated the model as a function of capacitance, geometry, and rated voltage. Moreover, we identified different failure modes, such as heating, electrolyte dry-up and gasification from the dependence of View the MathML source(T) with temperature, T. Our method was implemented in cheap electrolytic capacitors but can be easily applied to any type of capacitor, supercapacitor, battery, or fuel cell.Peer ReviewedPostprint (author's final draft

A thermodynamic analysis of forced convection through porous media using pore scale modeling

The flow thorough porous media is analyzed from a thermodynamic perspective, with a particular focus on the entropy generation inside the porous media, using a pore scale modeling approach. A single representative elementary volume was utilized to reduce the CPU time. Periodic boundary conditions were employed for the vertical boundaries, by re-injecting the velocity and temperature profiles from the outlet to the inlet and iterating. The entropy generation was determined for both circular and square cross-sectional configurations, and the effects of different Reynolds numbers, assuming Darcy and Forchheimer regimes, were also taken into account. Three porosities were evaluated and discussed for each cross-sectional configuration, and streamlines, isothermal lines and the local entropy generation rate contours were determined and compared. The local entropy generation rate contours indicated that the highest entropy generation regions were close to the inlet for low Reynolds flows and near the central cylinder for high Reynolds flows. Increasing Reynolds number from 100 to 200 reveals disturbances in the dimensionless volume averaged entropy generation rate trend that may be due to a change in the fluid flow regime. According to Bejan number evaluation for both cross-section configurations, it is demonstrated that is mainly provoked by the heat transfer irreversibility. A performance evaluation criterion parameter was calculated for different case-studies. By this parameter, conditions for obtaining the least entropy generation and the highest Nusselt number could be achieved simultaneously. Indeed, this parameter utilizes both the first and the second laws of thermodynamics to present the best case-study. According to the performance evaluation criterion, it is indicated that the square cross-section configuration with o=0.64 exhibits better thermal performance for low Reynolds number flows. A comparison between the equal porosity cases for two different cross-sectional configurations indicated that the square cross-section demonstrated a higher performance evaluation criterion than the circular cross-section, for a variety of different Reynolds numbers

Non-equilibrium thermodynamic analysis of double diffusive, nanofluid forced convection in microreactors with radiation effects

This paper presents a theoretical investigation of the second law performance of double diffusive forced convection in microreactors with the inclusion of nanofluid and radiation effects. The investigated microreactors consist of a single microchannel, fully filled by a porous medium. The transport of heat and mass are analysed by including the thick walls and a first order, catalytic chemical reaction on the internal surfaces of the microchannel. Two sets of thermal boundary conditions are considered on the external surfaces of the microchannel; (1) constant temperature and (2) constant heat flux boundary condition on the lower wall and convective boundary condition on the upper wall. The local thermal non-equilibrium approach is taken to thermally analyse the porous section of the system. The mass dispersion equation is coupled with the transport of heat in the nanofluid flow through consideration of Soret effect. The problem is analytically solved and illustrations of the temperature fields, Nusselt number, total entropy generation rate and performance evaluation criterion (PEC) are provided. It is shown that the radiation effect tends to modify the thermal behaviour within the porous section of the system. The radiation parameter also reduces the overall temperature of the system. It is further demonstrated that, expectedly, the nanoparticles reduce the temperature of the system and increase the Nusselt number. The total entropy generation rate and consequently PEC shows a strong relation with radiation parameter and volumetric concentration of nanoparticles

Irreversibility analysis for reactive third-grade fluid flow and heat transfer with convective wall cooling

Inherent irreversibility in the flow of a reactive third grade fluid though a channel with convective heating is examined. It is well known that heat dissipated from the exothermic chemical reaction passes through fluid in an irreversible manner and as a result entropy is generated continuously within the channel. Analytical solutions of the resulting dimensionless non-linear boundary-value-problems arising from the governing equations were obtained by using a perturbation method. These solutions are utilized to obtain the entropy generation rate and Bejan number for the system. The influence of various important parameters on the entropy generation rate and Bejan number are shown graphically and discussed accordingly

Effects of temperature-dependent viscosity variation on entropy generation, heat and fluid flow through a porous-saturated duct of rectangular cross-section

Effect of temperature-dependent viscosity on fully developed forced convection in a duct of rectangular cross-section occupied by a fluid-saturated porous medium is investigated analytically. The Darcy flow model is applied and the viscosity-temperature relation is assumed to be an inverse-linear one. The case of uniform heat flux on the walls, i.e. the H boundary condition in the terminology of Kays and Crawford, is treated. For the case of a fluid whose viscosity decreases with temperature, it is found that the effect of the variation is to increase the Nusselt number for heated walls. Having found the velocity and the temperature distribution, the second law of thermodynamics is invoked to find the local and average entropy generation rate. Expressions for the entropy generation rate, the Bejan number, the heat transfer irreversibility, and the fluid flow irreversibility are presented in terms of the Brinkman number, the Péclet number, the viscosity variation number, the dimensionless wall heat flux, and the aspect ratio (width to height ratio). These expressions let a parametric study of the problem based on which it is observed that the entropy generated due to flow in a duct of square cross-section is more than those of rectangular counterparts while increasing the aspect ratio decreases the entropy generation rate similar to what previously reported for the clear flow case

Thermodynamics Analysis of Radiative Hydromagnetic Couple Stress Fluid through a Channel

This work applies second law of thermodynamics to analyse the effect of radiation on electrically conducting couple stress fluid through a channel. A constant magnetic field is introduced across the flow channel and the resulting Navier- Stokes and energy equations are non-dimensionalized and solved using Adomian decomposition method (ADM) and differential transform method (DTM). The obtained velocity and temperature profiles are used to calculate the entropy generation rate and irreversibility ratio. The effects of radiation, magnetic field and couple stress parameters on the velocity, temperature, entropy generation rate and Bejan number are discussed with the aid of graphs. From the study, it is observed that increase in magnetic field and couple stress parameters reduces the fluid velocity while an increase in radiation parameter reduces the temperature of the fluid. Furthermore, radiation parameter increases entropy generation as heat transfer dominates irreversibility