Entropy Production Analysis Research Articles

Blade redesign based on secondary flow suppression to improve energy efficiency of a centrifugal pump

This paper conducts a systematic study to address the problems of high flow loss and low energy efficiency of centrifugal pumps caused by the development of secondary flow within the impeller. Based on the forces balance in the direction perpendicular to the streamline, theoretical calculations are drawn to redesign blade thickness for a 5-blade centrifugal impeller to suppress the secondary flow. The correlations between the development of internal secondary flow within the impeller and energy efficiency of centrifugal pump under full flow rate conditions are illustrated by numerical simulations validated by experimental tests. Secondary flow coefficient and entropy production rate (EPR) are introduced and extracted to quantitative analysis the secondary flow level and energy loss inside the impeller. Results indicate that the blade redesign methods proposed here can efficiently inhibit the development of secondary flow and improve the energy efficiency. Moreover, the secondary flow coefficient introduced in this paper can quantitatively reflect the intensity of secondary flow under various flow rates of different impellers. Combining with the entropy production analysis of impeller, the consistent change trend of total secondary flow coefficient and entropy production reveals that the improvement of pump energy efficiency benefits from the reduction of turbulence EPR which results from the suppression of internal secondary flow.

Entropy generation analysis of radiative heat transfer in Williamson fluid flowing in a microchannel with nonlinear mixed convection and Joule heating

In this article, the spectral quasi-linearization (SQLM) method is implemented to solve the complicated differential equations governing the nonlinear mixed convective heat transfer of a Williamson fluid through a vertical microchannel. Unlike the conventional Boussinesq approximation, the quadratic Boussinesq approximation is taken into account in the formulation. The effects of Rosseland thermal radiation, Joule heating, and viscous dissipation are described in the thermal analysis subjected to the boundary conditions of convective thermal heating. The analysis of entropy production is also performed. The importance of various parameters governing velocity, Bejan number, temperature, and entropy generation was explored using graphic illustrations. It was found that the nonlinear density change with a temperature significantly affects the heat transport in the microchannel and thus increases the magnitude of the Bejan number and the production of entropy. Entropy production occurs maximum due to the boundary conditions of convection heating at the walls of the microchannel. Furthermore, due to a stronger viscous heating mechanism, the magnitude of the Bejan number is reduced, while the production of entropy increases significantly. As a limiting case of the problem, a comparison was made with results previously published in the literature and excellent agreement was established. The calculations provide a solid reference point for future CFD models and are relevant to the dynamics of polymers in microfluidic devices and the polymer industries.

Energy loss of radial inflow turbine for organic Rankine cycle using mixture based on entropy production method

The radial inflow turbine is the core component of the organic Rankine cycle(ORC) system. Based on the internal flow field of the turbine analyzed by computational fluid dynamics (CFD), the energy dissipation of a radial inflow turbine with variable guide vane is determined by the entropy production analysis method. In the presented work, the mixture of R245fa/R134a is selected as the working fluid, and the effects of tip clearance and mixing ratio on the flow loss characteristics are investigated. The results show that the high entropy production region in the stator is caused by leakage vortex and shock phenomenon, while the passage vortex and leakage vortex are the reasons for the high loss area in the rotor. The total volume entropy production of rotor is mainly composed of the passage zone, which is significantly higher than that of the stator. As the tip clearance increases from 3% to 10%, the total entropy production of stator and rotor increases by 54.5 and 161.7% respectively, and the output power and isentropic efficiency of the turbine decrease by 14.7% and 14.6% respectively. With the increase of R245fa mass fraction, the total volume entropy production of the stator and rotor decreases linearly. Compared with R134a, the turbine isentropic efficiency of R245fa increases by 3.1%.

Research on the Influence of Tip Clearance of Axial-Flow Pump on Energy Characteristics under Pump and Turbine Conditions

In order to study the influence of tip clearance on the performance and energy dissipation of the axial-flow pump and the axial-flow pump as a turbine, and find the location of high dissipation rate, this study took an axial-flow pump model as its research object and designed four tip radial clearance schemes (0, 0.2, 1 and 2 mm). The unsteady calculation simulation of each tip clearance scheme was carried out based on CFD technology. The calculated results were compared with the experimental results, and the simulation results were analyzed using entropy production analysis theory. The results showed that, under both an axial-flow pump and axial-flow pump as turbine operating conditions, increasing the blade tip clearance led to a decrease in hydraulic performance. Compared with the 0 mm clearance, the maximum decreases in pump efficiency, head and shaft power under 2 mm tip clearance were 15.3%, 25.7% and 12.3% under the pump condition, and 12.7%, 18.5% and 28.8% under the turbine condition, respectively. Under the axial-flow pump operating condition, the change in blade tip clearance had a great influence on the total dissipation of the impeller, guide vane and outlet passage, and the maximum variation under the flow rate of 1.0Qdes was 53.9%, 32.1% and 54.2%, respectively. Under the axial-flow pump as a turbine operating condition, the change in blade tip clearance had a great influence on the total dissipation of the impeller and outlet passage, the maximum variation under the flow rate of 1.0Qdes was 22.7% and 17.4%, respectively. Under the design flow rate condition, with the increase in tip clearance, the dissipation rate of the blade surface showed an increasing trend under both the axial-flow pump and axial-flow pump as turbine operating conditions, and areas of high dissipation rate were generated at the rim and clearance.

Hydraulic Performances of a Bulb Turbine with Full Field Reservoir Model Based on Entropy Production Analysis

Hydraulic Performances of a Bulb Turbine with Full Field Reservoir Model Based on Entropy Production Analysis

Entropy Production Analysis of Energy-Efficiency Optimization for Variable-Speed Operation in a Francis Turbine

Entropy Production Analysis of Energy-Efficiency Optimization for Variable-Speed Operation in a Francis Turbine

Effect of a rotating cylinder on the 3D MHD mixed convection in a phase change material filled cubic enclosure

This study displays an exhaustive numerical analysis of entropy production and mixed convection in a 3D cavity filled with a phase change material (PCM) and incorporating a rotating cylinder. The temperature gradient was created between the hot right vertical wall and the cold left while the remaining walls are considered adiabatic. The impacts of various parameters such as the angular rotational velocity (−10 ≤ Ω ≤ 10), vertical position of the cylinder ((0.025 ≤ H ≤ 0.075)) and Hartmann number (0 ≤ Ha ≤ 10) on the convective heat transfer and entropy production were numerically studied in detail. The analysis found evidence to consider the rotating cylinder speed and position as good controlling parameters for the convective heat transfer and melting process in the enclosure. Imposing an angular velocity on the cylinder was found to enhance the heat transfer rate by 21.2% compared to motionless cylinder. In addition, it was noticed that the vertical position of the cylinder can be considered as optimizing parameter of the heat transfer. The application of an external magnetic field lead to the reduction of the heat transfers due to the generated Lorentz force that oppose the Buoyancy effect.

Mixed Convection of Williamson Fluid along an Inclined Porous Microchannel with Chemical Reaction by taking Non-Constant Thermal Conductivity: An Entropy Analysis

Objective: Mixed convection of Williamson fluid along an inclined porous microchannel with the influence of first-order chemical reaction is considered. The thermal conductivity kept varying throughout the flow. Boundaries of the channel are maintained with slip and jump conditions. With these conditions in this present article we are aimed to analyse the velocity, heat transfer and entropy generation in the flow. Method: The non-linear equations which govern the flow are tackled utilizing the bvp4c technique which involves the finite difference method and improved by using the Lobatto III formula. Findings: Fluid flow, heat transfer and entropy production analysis are done for the various estimations of the parameters which are affecting the flow, and the study highlights that non constant thermal conductivity and mixed convection parameters have to be maintained at lower values for the efficient energy transfer in the model. Entropy production shows the dual trend for distinct estimations of Weinsenberg number. Applications: The obtained result in the present study helps industries to analyse the efficient energy transfer in their engineering designs and thermal equipment’s. Also the flow of non- Newtonian fluid has applications in the field of blood flow, lubrication and in many engineering devices such as micro heat exchangers, micro mixers, micro cooling systems. Keywords: Williamson fluid; Inclined microchannel; Variable thermal conductivity; Entropy production; Bejan number

Thermal Characterization of Coolant Maxwell Type Nanofluid Flowing in Parabolic Trough Solar Collector (PTSC) Used Inside Solar Powered Ship Application

Parabolic trough solar collectors (PTSCs) are generally utilized to reach high temperatures in solar-thermal applications. The current work investigates entropy production analysis and the influence of nano solid particles on a parabolic trough surface collector (PTSC) installed within a solar powered ship (SPS). For the current investigation, the non-Newtonian Maxwell type, as well as a porous medium and Darcy–Forchheimer effects, were used. The flow in PTSC was produced by a nonlinear stretching surface, and the Cattaneo–Christov approach was used to assess the thermal boundary layer’s heat flux. Similarity transformation approach has been employed to convert partial differential equations into solvable ordinary differential equations allied to boundary conditions. Partial differential and the boundary conditions have been reduced into a group of non-linear ordinary differential equations. A Keller-box scheme applied to solve approximate solutions of the ordinary differential equations. Single-walled carbon nanotubes -engine oil (SWCNT-EO) and Multiwalled carbon nanotubes/engine oil (MWCNT-EO) nanofluids have been utilized as working fluid. According to the findings, the magnetic parameter led to a reduction in the Nusselt number, as well as an increment in skin friction coefficient. Moreover, total entropy variance over the domain enhanced for flow rates through Reynolds number and viscosity fluctuations were monitored by using Brinkman number. Utilizing SWCNT-EO nanofluid increased the thermal efficiency between 1.6–14.9% in comparison to MWCNT-EO.

Hydraulic components’ matching optimization design and entropy production analysis in a large vertical centrifugal pump

Hydraulic components’ matching optimization design and entropy production analysis in a large vertical centrifugal pump

Entropy production study of an IRS device having diathermic conical funnels with surface radiation

The present study involves the thermodynamic performance and entropy production analysis of an infrared suppression (IRS) system. The IRS device is usually used in ocean liners, warships, and cargo ships to reduce the turbine exhaust temperature. First, the governing differential equations (Navier-Stokes, energy, turbulence, radiation equations) are solved using ANSYS Fluent 19.0 to elucidate the thermodynamic performance of the IRS device. Then entropy production and irreversibilities are calculated in post-processing. The pertinent parameters, viz. Reynolds number at nozzle inlet (6.12 × 105 to 3.11 × 106), the nozzle outlet fluid temperature (400 to 600 K), nozzle overlap, funnel overlap, and the types of guide vanes are varied to analyze the impact of these parameters on entropy generation. The effect of different boundary conditions for funnel walls (i.e., adiabatic, diathermic with or without radiation) on entropy generation is discussed. A comparison of various types of guide vanes is also performed. It is found that entropy production (or irreversibility) is less when mass entrainment is more, i.e., device outlet temperature is less. Moreover, entropy production caused by heat transfer has the main contribution in total entropy production than that caused due to fluid friction. The entropy generation is found to be minimum for zero nozzle overlapping, zero funnel overlapping, diathermic funnel wall with radiation, and QCGV (quarter circular guide vane) type. The mass entertainment is maximum, and device outlet temperature is minimum with the mentioned conditions.

A Comparative Study on the Hydrodynamic-Energy Loss Characteristics between a Ducted Turbine and a Shaftless Ducted Turbine

The shaftless ducted turbine (abbreviated as SDT), as an extraordinary innovation in tidal current power generation applications, has many advantages, and a wide application prospect. The structure of an SDT resembles a ducted turbine (abbreviated as DT), as both contain blades and a duct. However, there are some structural differences between a DT and a SDT, which can cause significant discrepancy in the hydrodynamic characteristics and flow features. The present work compares the detailed hydrodynamic-energy loss characteristics of a DT and a SDT by means of computational fluid dynamics (CFD), performed by solving the 3D steady incompressible Reynolds-averaged Navier-Stokes (RANS) equations in combination with the Menter’s Shear Stress Transport (SST k−ω) turbulence model and entropy production model. The results show the SDT features a higher power level at low tip speed ratio (TSR) and a potential reduction in potential flow resistance and disturbance with respect to the DT. Moreover, a detail entropy production analysis shows the energy loss is closely related to the flow separation and the reverse flow, and other negative flow factors. The entropy production of the SDT is lessened than that of the DT at different TSR. Unlike the DT, the SDT allows a large mass flow of water to leak through the open-center structure, which plays an important role in improving the wake structure and avoiding the negative flow along the central axis.

Irreversibilities in a triple diffusive flow in various porous cavities

Entropy generation minimization approach is a very good method allowing to analyze the engineering systems to exclude technical failure. The present study deals with computational analysis of triple diffusive flow, energy transference and entropy production in different porous cavities from square to triangular through trapezoidal shape. The formulated boundary-value problem has been worked out using the finite element technique and non-primitive variables. The developed computational code has been verified using numerical results of other researchers. Analysis of entropy production due to energy and mass transport, motion friction, and porous material has been performed for different chamber's shapes. Entropy generation analysis in chambers of various geometries under the triple-diffusive flow is a novelty of the present research, where different entropy production mechanisms have been scrutinized for one complex problem. It has been ascertained that average total entropy generation strength raises with buoyancy ratios, Lewis and Rayleigh numbers, but it has the minimum value for the square chamber in comparison with triangular and trapezoidal shapes. Moreover, obtained results characterize a neglecting influence of motion friction on the total entropy generation.

An entropy production analysis for electroosmotic flow and convective heat transfer: a numerical investigation

In the current numerical study, an entropy production analysis is conducted for the electroosmotic flow and convective heat transfer in the microduct. A number of blades are installed inside the system to create the swirl flow and enhance the heat and mass transfer. The results obtained by this investigation are compared with those achieved by other studies to verify the precision of the numerical procedures employed. The length, position, and number of conductive blades, and the electric field intensity are considered as the input parameters. The frictional, thermal, and diffusion types of entropy production are considered as the output parameters. The results show that the frictional entropy production increases, while the thermal entropy production decreases as more number of conductive blades is installed in the system. The amount of diffusion entropy production is very small. In addition by increasing the blade length from 15 to 35 µm, the average velocity in the system increases and accordingly, the frictional entropy production increases up to 140.3% and the thermal entropy production diminishes about 71.2%. By relocating the conductive plate from x = 500 µm to x = 2000 µm toward the outlet section of the system, the frictional entropy production is reduced about 84.4% and the thermal entropy production is boosted up to 261.1%. Increasing the external field strength causes an increase in the frictional entropy production and a decrease in the thermal entropy production.

Analysis of entropy production and activation energy in hydromagnetic rotating flow of nanoliquid with velocity slip and convective conditions

This article investigates entropy production in three-dimensional hydromagnetic rotating flow of nanoliquid with binary chemical mechanism and activation energy impacts. Brownian dispersion and thermophoresis effects are taken into account. Bejan number and entropy production are analyzed through the existence of porous medium, viscous dissipation, magnetic field, thermal radiation and heat source/sink. Velocity slip, convective heat and mass conditions are imposed at the boundary. The nonlinear equations are developed through transformation scheme. Shooting method is utilized to generate the solutions of resulting nonlinear expressions. Salient behaviors of several pertinent variables on velocities, nanoconcentration, entropy production, Bejan number and temperature distributions are examined graphically. Further surface drag forces, heat and mass transfer rates are graphically analyzed via different flow variables. It is observed that heat transfer rate significantly enhances for the higher values of thermal Biot number while an opposite behavior is noted against higher thermophoresis parameter.

Numerical study of the hydrofoil cavitation flow with thermodynamic effects

High-temperature water exhibits evident thermodynamic effects during cavitation, which influences the cavitation flow and generates complex flow characteristics. To reveal the mechanism of thermodynamic effects on the cavitation flow in high-temperature water, a flow around NACA 0015 hydrofoil was simulated. Based on the existing isothermal cavitation model, the thermodynamic effects were considered by correcting evaporation and condensation source terms and coupling physical parameters with temperature. Numerical results obtained from the thermodynamic effect cavitation model agree well with the available experiments. A comparative analysis of performance characteristics, cavitation shape, and interphase mass transfer rate was performed. The thermodynamic effects on the cavitation flow of hydrofoil under different temperature were presented. The existence of the thermodynamic effects lowers the local temperature of the cavitation, reduces the vapor phase volume fraction of the cavitation area, and inhibits the development of cavitation. Moreover, a novel entropy production analysis was conducted to reveal the thermodynamic effects on the energy loss. The difference of local entropy production rate in the cavitation flow with and without thermodynamic effects was revealed. The analyses show that the existence of the thermodynamic effects reduces the energy loss owing to the reduction of the dissipation loss caused by the velocity gradient. When the thermodynamic effects are considered, the energy loss caused by the temperature gradient shows an increase; however, the proportion of this loss is still small.

Second law analysis of heat transfer in swirling flow of Bingham fluid by a rotating disk subjected to suction effect

This framework presents heat transfer analysis for swirling flow of viscoplastic fluid bounded by a permeable rotating disk. Problem formulation is made through constitutive relations of Bingham fluid model. Viscous dissipation effects are pre-served in the mathematical model. Entropy production analysis is made which is yet to be explored for the von-Karman flow of non-Newtonian fluids. Having found the similarity equations, these have been dealt numerically for broad parameter values. The solutions are remarkably influenced by wall suction parameter and Bingham number which measures the fluid yield stress. Akin to earlier numerical results, thermal boundary-layer suppresses upon increasing wall suction velocity. Thermal penetration depth is much enhanced when fluid yield stress becomes large. Higher heat transfer rate can be accomplished by employing higher suction velocity at the disk. However, deterioration in heat transfer is anticipated as fluid yield stress enlarges. Current numerical results are in perfect line with those of an existing article in limiting sense.

Study on characteristics of vortex structures and irreversible losses in the centrifugal pump

The development of flow control methods in the centrifugal pump relies on further understanding of the characteristics of vortex structures and their irreversible losses. In this paper, the detached eddy simulation is conducted on a model centrifugal pump, which shows a good agreement with the experiment. Combining with three generations of vortex identification methods (vorticity, Q criterion, omega and Liutex methods) and entropy production analysis, the results show omega and Liutex methods are highly recommended to analyze the vortex structures. Vorticity is the key factor to promote the energy dissipation, and the irreversible losses of vortex areas can be lower than their surroundings when there exists smaller vorticity or higher rotation strength. Concerning the pressure pulsation induced by vortex shedding, it is unreasonable to analyze this unsteady process via vortex structures identified by iso-surface because of the restriction of the threshold. In comparison, the change of integral length is more related to the pressure pulsation.

Thermal convection and entropy generation of ferrofluid in an enclosure containing a solid body

PurposeThis study/paper aims to deal with thermal convection and entropy production of a ferrofluid in an enclosure having an isothermally warmed solid body placed inside. It should be noted that this research deals with a development of passive cooling system for the electronic devices.Design/methodology/approachThe domain of interest is a square chamber of size L including a rectangular solid block of sizes l1 and l2. Thermal convection of ferrofluid (water–Fe3O4 nanosuspension) is analyzed within this enclosure. The solid body is considered to be isothermal with temperature Th and also its area is L2/9. The vertical borders are cold with temperature Tc and the horizontal boundaries are adiabatic. The flow driven by temperature gradient in the cavity is two-dimensional. The governing equations, formulated in dimensionless primitive variables with corresponding initial and boundary conditions, are worked out by using the finite volume technique with the semi-implicit method for pressure-linked equations algorithm on a uniformly staggered mesh. The influence of nanoparticles volume fraction, aspect ratio of the solid block and an irreversibility ratio on energy transport and flow patterns are examined for the Rayleigh number Ra = 107.FindingsThe results show that the nanoparticles concentration augments the thermal transmission and the entropy production increases also, while the augmentation of temperature difference results in a diminution of entropy production. Finally, lower aspect ratio has the significant impact on heat transfer, isotherms, streamlines and entropy.Originality/valueAn efficient numerical technique has been developed to solve this problem. The originality of this work is to analyze convective energy transport and entropy generation in a chamber with internal block. To the best of the authors’ knowledge, the effects of irreversibility ratio are scrutinized for the first time. The results would benefit scientists and engineers to become familiar with the analysis of convective heat transfer and entropy production in enclosures with internal isothermal blocks, and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.

Analysis of Entropy Production in Structured Chemical Reactors: Optimization for Catalytic Combustion of Air Pollutants.

Optimization of structured reactors is not without some difficulties due to highly random economic issues. In this study, an entropic approach to optimization is proposed. The model of entropy production in a structured catalytic reactor is introduced and discussed. Entropy production due to flow friction, heat and mass transfer and chemical reaction is derived and referred to the process yield. The entropic optimization criterion is applied for the case of catalytic combustion of methane. Several variants of catalytic supports are considered including wire gauzes, classic (long-channel) and short-channel monoliths, packed bed and solid foam. The proposed entropic criterion may indicate technically rational solutions of a reactor process that is as close as possible to the equilibrium, taking into account all the process phenomena such as heat and mass transfer, flow friction and chemical reaction.