Entropy Production Analysis Research Articles

Influence Mechanism of Trimming Impeller Diameter in a Centrifugal Pump by Computational Fluid Dynamics Investigation

Abstract Trimming the impeller diameter of a centrifugal pump is the easiest and most economical way to adjust its efficient operating range based on its original performance. Three impellers obtained by trimming the diameter are investigated. Energy performance, internal flow field, and entropy production analysis have been discussed in different cases. The results show that trimming the impeller diameter causes a great change in the energy performance of centrifugal pumps. The turbulent kinetic energy (TKE) distribution and entropy production also change significantly. The best efficiency point (BEP) shifts to low flowrate with trimming impeller diameter. The BEP shift rate was 6.67% and 20% for trimming amounts of 5.15% and 10.29%, respectively. As the impeller diameter decreases, the backflow phenomenon that occurs at the diffuser inlet at low flowrate improves. The ratio of mechanical energy to kinetic energy and pressure energy is not constant for pumps with different impeller diameters. The energy performance changes are mainly caused by flow changes inside the impeller, chamber, and diffuser. The results could be referred to as the design and selection of centrifugal pumps.

Turbulent double-diffusive convection and implementation of entropy production rate due to the mean and the fluctuating flow field

The present study performs a CFD-based analysis of entropy production due to conjugate turbulent heat and mass transfer. For the turbulent regime, the instantaneous temperature, concentration, and velocity fields are resolved into time-averaged mean and fluctuating parts. Thus, six different terms of entropy production arise due to this mode of temperature and species transfer. Unfortunately, such a model does not exist and a new approach is therefore needed which makes this problem more challenging. Hence, the overall aim of this paper is twofold: First, is to develop a new approach to cope with the entropy production that takes into account all the six different terms due to temperature and species transport. Second, is to carry out a numerical simulation of double-diffusive free convection inside a square cavity. On the basis of asymptotic considerations, a new formula that expresses entropy production due to fluctuating concentration gradients was derived. Depending on the Rayleigh number and the buoyancy ratio, the total entropy increased significantly when the fluctuating terms were accounted for. Total entropy was found to increase by up 27% for N = +5.0 and Rayleigh number of 109. However, it increased by 38% when N = +1.0 and Ra = 1010.

Theoretical analysis of entropy production in exothermic/endothermic reactive magnetized nanofluid flow through curved porous space with variable permeability and porosity

In current analysis, flow of magnetized nanofluids in porous curved stretchable surface with variable characteristics has been inspected by imposing the thermal radiation, and activation energy. The exothermic/endothermic reactive effect is included along with Buongiorno nanofluid model to investigate the thermal performance more extensively. The Lorentz force characteristics that cause the interaction of magnetic field with nanoliquid motion is further investigated. Additionally, production of entropy in the porous curved system because of irreversible process has been considered here. The modeled systems for considered model are firstly transformed into ODEs via appropriate variables and then computed by employing NDSolve technique using tool of Mathematica. Flow fields variation against relevant variables is inspected via tables and sketches. The key outcome of analysis is that, the entropy rate upsurges for higher local inertia parameter, radiation variable and Brinkman number.

A stable and causal model of magnetohydrodynamics

We formulate the theory of first-order dissipative magnetohydrodynamics in an arbitrary hydrodynamic frame under the assumption of parity-invariance and discrete charge symmetry. We study the mode spectrum of Alfvén and magnetosonic waves as well as the spectrum of gapped excitations and derive constraints on the transport coefficients such that generic equilibrium states with constant magnetic fields are stable and causal under linearised perturbations. We solve these constraints for a specific equation of state and show that there exists a large family of hydrodynamic frames that renders the linear fluctuations stable and causal. This theory does not require introducing new dynamical degrees of freedom and therefore is a promising and simpler alternative to Müller-Israel-Stewart-type theories. Together with a detailed analysis of transport, entropy production and Kubo formulae, the theory presented here is well suited for studying dissipative effects in various contexts ranging from heavy-ion collisions to astrophysics.

An analytical approach to entropy production in MHD mixed convection micropolar fluid flow over an inclined porous stretching sheet

This analytical analysis examines the MHD micropolar fluid flow and mixed convection features using entropy production analysis of an inclined porous stretching sheet. Flow field and heat transfer analysis are presented to consider thermal radiation, heat source/sink, Lorentz, and buoyancy forces. The PDEs system is transformed by appropriate similarity variables, turned into a system of high non-linearity coupling ODEs, and then solved with the help of an analytical approach. An analytical approach can provide exact explicit solutions for the flow field, heat transport, entropy production, the local skin friction coefficient, the local couple stress coefficient, and the local Nusselt number. It is shown that the magnetic field, mixed convection, and sheet inclination effects can be incorporated together into a single parameter, which is called the magneto-buoyancy-inclination parameter here. In other words, this parameter controls the boundary layer flow. In addition, an experimental procedure called Box-Behnken design (BBD) was employed to analyze the influence of material (K), radiation (Rd), and buoyancy (Λ) parameters on entropy production in MHD micropolar fluid flow over the sheet. In order to estimate accurately the optimum entropy generation containing K, Rd, and Λ, we used a quadratic regression model. Based on the results of this investigation, the value of the entropy generation number became larger by decreasing the magneto-buoyancy-inclination parameter. Further, the magnitude of the local couple stress coefficient is reduced as the heat source parameter increases.

Numerical Study for Flow Loss Characteristic of an Axial-Flow Pump as Turbine via Entropy Production Analysis

Low-head vertical axial-flow pump as turbine (PAT) devices play a vital part in the development of clean energy for hydropower in plain areas. The traditional method of evaluating the flow loss in hydraulic machinery is calculated by the pressure drop method, the limitation of which is that the location of the occurrence of large losses cannot be accurately determined. In this paper, entropy production theory is introduced to evaluate the irreversible losses in the axial-flow PAT from the perspective of the second law of thermodynamics. A three-dimensional model of the axial-flow PAT is established and solved numerically using the Reynolds time-averaged equation, and the turbulence model is adopted as Shear Stress Transport–Curvature Correction (SST-CC) model. The validity of the entropy production theory to evaluate the energy loss distribution of the axial-flow PAT is illustrated by comparing the flow loss calculated by the pressure drop and the entropy production theory, respectively. The entropy production by turbulent dissipative dominates the total entropy production in the whole flow conduit, and the turbulent dissipative entropy accounts for the smallest percentage of the whole conduit entropy production at the optimal working condition Qbep, which is 51%. The impeller and the dustpan-shaped conduit are the essential sources of hydraulic loss in the entire flow conduit of the axial-flow PAT, and most of the energy loss of the impeller occurs at the blade leading edge, the trailing edge, and the flow separation zone near the suction surface. The energy loss of the dustpan-shaped conduit results from the high-speed flow from the impeller outlet to dustpan-shaped conduit to form a vortex, backflow and other chaotic flow patterns. Flow impact, flow separation, vortex and backflow are the main causes of high entropy production and energy loss.

Cavitation Suppression and Design Optimization in a Cryogenic Liquid Turbine Expander Based on Thermodynamic Cavitation and Entropy Production Analysis

Abstract Cryogenic liquid turbine expanders have emerged quite recently as a replacement of J–T valve for enhancing energy efficiency of industrial systems, such as air separation units (ASUs) and Supercritical Compressed Air Energy Storage systems. In the liquid turbine expander, the rotating impeller-induced swirling flow and cavitation are essentially significant and intensive, which requests some in-depth work toward a thorough understanding flow physics and then effective attenuation. This study aims at effectively mitigating the swirling flow and cavitation. The entropy production analysis method (EPAM) is proposed to characterize the swirling flow and cavitation. It is then incorporated with the improved cavitation and turbulence models and validated through the simulation of the Hord's liquid nitrogen hydrofoil. To mitigate the swirling flow and subsequent cavitation, the design optimization method is developed, in which a novel optimization objective function is constituted by incorporating the local entropy production rate and vapor volume fraction to capture the mechanical energy dissipation and cryogenic cavitating flow physics; the non-uniform relational B-Splines and free form deformation (NURBS–FFD) parametric method is used to facilitate a flexible variation in impeller blade and diffuser vane geometries. It is solved within cfx frame by means of the particle swarm optimization (PSO) algorithm coupling the Kriging-based adaptive surrogate model. With the design optimization, the impeller and vaned diffuser tube geometries are collaboratively fine-tuned, and the mechanical energy dissipation and cavitating flow across both the impeller and vaned diffuser tube is effectively mitigated.

Research on Energy Loss Characteristics of Pump-Turbine during Abnormal Shutdown

Pumped-storage hydropower (PSH) stations are an efficient emission-free technology to balance renewable energy generation instabilities. The pump-turbine is a core component of PSH stations requiring frequent start-up, shutdown, and working conditions for regulation tasks, making it prone to instabilities. Based on entropy production theory and vortex dynamics, we analyzed the energy loss characteristics for three working conditions of the pump, pump brake, and turbine when shutting down the pump-turbine. The results showed that the entropy production and vorticity of the spiral casing and draft tube remain almost constant, while the entropy production and vorticity of the runner region substantially change from the late pump braking to the late turbine condition. The entropy production and vorticity are derived from the guide vane transitioning to the runner flow channel through the vaneless space. The change law of energy loss through entropy production agrees with the change law of internal flow turbulence through vorticity. The entropy production analysis can quantify the energy loss and mark its location, while the vorticity analysis can quantify the degree of flow disturbance and show its location. The entropy production theory and vortex dynamics combination provide insights into the connection between undesirable flow phenomena and energy loss.

Performance analysis of geometrically optimized PaT at turbine mode: A perspective of entropy production evaluation

In the field of hydroelectric power, Pump as Turbine (PaT) is an important tool to achieve recycling the redundant kinetic energy in small stream/rivers. However, due to the contradiction between the reverse fluid flow working at turbine mode and the designed flow passage of pump geometry, the internal hydraulic loss in PaT is excessive. As a result, it renders the PaT performance extremely low affecting its wide applications with the demand of high efficiency operation. Therefore, this paper aims to optimize the geometric parameters of the impeller in PaT turbine mode under three different typical flow conditions (i.e. rated, best efficiency, and overload working conditions). After the geometric optimization, the internal energy losses among the flow passages are analyzed by using the entropy production method. The results show that the impeller passage exhibits obviously higher entropy loss in comparison to the volute and the outlet pipe. Inside the impeller, the blade leading and trailing edges on both suction and pressure sides are the locations where the majority of the impeller energy losses occur, and the high entropy area is concentrated at the impeller inlet area. Moreover, The energy loss gradually decreases from blade leading edge (BLE) to blade trailing edge (BTE), and the entropy production decreases from the blade pressure side (PS) to the blade suction side (SS) due to the large mixing flow loss from PS to SS. It is concluded that the entropy production analysis is effective in explaining the PaT power losses caused by the geometric mismatch of different components including inlet, impeller, and outlet, providing the reference value for the geometric optimization of other turbine machinery.

Heat transfer performance of microchannels with round grooves and ribs based on field synergy principle and entropy production analysis

ABSTRACT Four kinds of microchannels with round grooves and ribs were designed: round grooves (round), round grooves and single–sided ribs (round–single), round grooves and odd-symmetric ribs (round–odd), and round grooves and doubly symmetric ribs (round–double). The effects of rib arrangement on the heat transfer performance of microchannels with round grooves and ribs were numerically investigated and then compared with the microchannel with no grooves or ribs. The heat transfer characteristics were analyzed and compared in accordance with the field synergy principle and entropy production. Results indicate that the heat transfer field of round and round–double microchannels exhibited the smallest synergy angle (α) and the best field synergy. The round–double microchannel produced the lowest entropy caused by heat transfer and had a minimal irreversible loss; thus, it exhibited the best heat transfer performance.

Analysis of entropy production in a bi-convective magnetized and radiative hybrid nanofluid flow using temperature-sensitive base fluid (water) properties

The heat transport characteristics, flow features, and entropy-production of bi-convection buoyancy induced, radiation-assisted hydro-magnetic hybrid nanofluid flow with thermal sink/source effects are inspected in this study. The physical characteristics of hybrid nanofluids (water-hosted) are inherited from the base liquid (water) and none has considered the physical characteristics of base liquid (water) in the study of temperature-sensorial hybrid nanofluid investigations, though the water physical characteristics are not constants in temperature variations. So, the temperature-sensorial attributes of base liquid (water) are taken into account for this hybrid nanofluid (Cu+{Al}_{2}{O}_{3}+text{water}) flow analysis. The mathematical forms of the flow configuration (i.e., the set of coupled, nonlinear PDE form of governing equations) are solved by utilizing the subsequent tasks: (i) congenial transformation; (ii) quasilinearization; (iii) methods of finite differences to form block matrix system, and (iv) Varga’s iterative algorithm. The preciseness of the whole numerical procedure is ensured by restricting the computation to follow strict convergence conditions. Finally, the numerically extracted results representing the impacts of various salient parameters on different profiles (F, G, H), gradients, and entropy production are exhibited in physical figures for better perception. A few noticeable results are highlighted as: velocity graph shows contrast behaviour under assisting and opposing buoyancy; temperature (G(xi ,eta )) is dropping for heightening heat source (Q) surface friction remarkably declines with the outlying magnetic field (St); thermal transport confronts drastic abatement under radiation ({R}_{1}), and St; the characteristics Reynolds and Brinkman numbers promote entropy. Furthermore, the bounding surface acts as a strong source of {S}_{G}-production. Summarizations are listed at the end to quantify percentage variations.

Energy Characteristics of a Bidirectional Axial-Flow Pump with Two Impeller Airfoils Based on Entropy Production Analysis.

This research sought to determine the spatial distribution of hydraulic losses for a bidirectional axial-flow pump with arc- and S-shaped impellers. The unsteady Reynolds time-averaged Stokes (URANS) approach with the SST k-omega model was used to predict the internal flow field. The total entropy production (TEP) and total entropy production rate (TEPR) were used to evaluate the overall and local hydraulic losses. The results show that the distribution of TEP and TEPR was similar for both impeller cases. Under a forward condition, TEP mainly comes from the impeller and elbow pipe. The high TEPR inside the impeller can be found near the shroud, and it shifts from the leading edge to the trailing edge with an increase in the flow rate due to the decline in the attack angle. The high TEPR inside the elbow pipe can be seen near the inlet, and the area shrinks with an increase in the flow rate caused by a reduction in the velocity circulation. Under the reverse condition, TEP mainly comes from the impeller and the straight pipe. The TEPR of the region near the shroud is obviously higher than for other regions, and the area of high TEPR near the suction side shrinks with an increase in the flow rate. The high TEPR of the straight pipe can be found near the inlet, and declines in the flow direction. These results provide a theoretical reference for future work to optimize the design of the bidirectional axial-flow pump.

Three-dimensional analysis of heat transfer and entropy production of jet impingement hybrid nanofluid cooling a porous media-filled heat sink

ABSTRACT In this study, a numerical assessment was carried out on heat transfer and entropy production of a three-dimensional heat sink exposed to an impinging jet, where the area between the heat sink fins is filled with aluminum foam saturated with A L 2 O 3 − C u / w a t e r hybrid nanofluid. Darcy-Brinkman-Forchheimer’s model with the local thermal equilibrium was considered. The effects of various important parameters such as Reynolds number 400 ≤ R e ≤ 1600 , volumetric concentrations 1 % ≤ φ h n f ≤ 5 % , Darcy number 10 − 5 ≤ D a ≤ 10 − 1 , porosity 0.1 ≤ ε ≤ 0.6 , and the diameter of nanoparticles 20 n m ≤ d n ≤ 60 n m on fluid flow, heat transfer, drop pressure, and entropy generation were investigated. A finite-volume approach with SIMPLE algorithm was employed to solve continuity, momentum, energy, and entropy equations with the help of the Ansys-Fluent 14.5 program. Regarding the validation of the computational approach used in this paper, a strong consensus has been reached with other findings available in the literature. Outcomes indicated that boosting Darcy number D a and porosity ε of the used porous material helps increase the heat exchange rate by up to 72 % and 40 % , respectively. On the other hand, we obtained a 7 % enhancement in the heat transmission rate when using nanoparticles with a diameter d n of 20 n m instead of nanoparticles with a diameter of 60 nm. Furthermore, it has been demonstrated that boosting D a , ε and d n minimize drop pressure by various proportions. Based on the entropy production analysis, it is possible to infer that entropy due to heat transfer is more dominant than other types of entropy with all parameters analyzed. Also, it can be deducted that as the values of ε and D a grow and the values of d n decline, the total entropy production ( S p , t ) rises up to 55 % , 75 % and 3 % , respectively. The same findings were reached with the Bejan number B e , but different percentages. Finally, three correlations of Nusselt number with several variables with an error not exceeding 15 % have been suggested. The proposed study’s findings may be utilized to define appropriate process factors for improved thermodynamic efficiency of heat sinks using hybrid nanofluids and porous media.

Analysis of Entropy Generation in Micropolar Magneto-Nanoliquid Material with Activation Energy and Nonlinear Radiation

This study investigates entropy production analysis in the flow of micropolar nanoliquid due to its application in thermal engineering systems for the identification of the factors which causes the destruction in the available energy and consequently affects overall performance of the thermal devices. The model is built on a two-dimensional porous stretching sheet with an incompressible fluid assumption and steady with the influence of variable thermal conductivity, nonlinear thermal radiation, haphazard motion and thermo-migration tiny particles. A prescribed surface temperature is adopted as the thermal heating condition while the impact of the reaction order and activation energy are incorporated into the concentration field. The model equations are restructured to ordinary derivative system, which is computationally solved by Fehlberg Runge-Kutta technique. The results agree well with previous outcomes for limiting situations while the effects of the embedded terms are presented graphs. The analysis reveals that a rise in variable thermal conductivity, the material term and viscous dissipation leads to a rise in the irreversibility process.

Research on flow resistance characteristics of reactor coolant pump under large break LOCA at inlet

In the event of a large break loss-of-coolant accident (LBLOCA) at the inlet of the nuclear Reactor Coolant Pump (RCP), the RCP is likely to enter an extreme working condition of the reverse pump mode. In this mode, the pump actually acts as a stopper to the coolant out of the circulation system. When the flow rate remains constant, the head reflects the flow resistance capacity. In previous studies, we have found that the head of the RCP increases and then decreases with increasing cavitation under the reverse pump mode. Objective to research into this situation, numerical simulation of the RCP under the reverse pump mode has been used to analyze the flow resistance characteristics inside the impeller. Results show that the high-velocity flow generated by the cavitation region is the crucial factor causing the variation in pump head in comparison with the vapor volume fractions of the impeller blade surface. To investigate the effect of high-velocity flow on the pump head under different cavitation conditions and to even better reveal the flow resistance characteristics, entropy production analysis and vorticity analysis are carried out for the internal flow field of the impeller.

Entropy production analysis for energy dissipation of a vertical mixed-flow pump device under asymmetric inflow conditions

To investigate the influence of the inflow angle on the hydraulic loss and internal flow fields of a vertical mixed-flow pump device, unsteady numerical simulations were performed under different inflow angles ( θ = 0°, 10°, 20°, and 30°). The calculation results were validated using an external characteristic test at an inflow angle of 0°. The entropy production theory was applied to analyse the energy loss and dissipation rate distribution in a vertical mixed-flow pump device under different inflow angles. Influenced by asymmetric inflow, the design point of the external characteristics deviated towards the overload flow rate, and the maximum deviations were obtained under 1.2 Q des, whereas the influence of the inflow angle on the internal flow fields was the most significant under the part-load flow rate. When the inflow angle increased from 0° to 30°, the total entropy production in the pump device increased by 18.35% under 0.6 Q des, and indirect dissipation accounted for the largest proportion. The internal flow patterns in the impeller and guide vane were also distorted by asymmetric inflow. The indirect dissipation rate on the suction side of the impeller blade, interface between the impeller and diffuser, and pressure side of the guide vane increased significantly with an increase in the inflow angle. To restrain the influence of asymmetric inflow, it is of great significance to optimise the hydraulic design structure of the inflow runner. In this study, a middle spacer pier was used to improve the operational efficiency of the pump device.

Passive odd viscoelasticity.

Active chiral viscoelastic materials exhibit elastic responses perpendicular to the applied stresses, referred to as odd elasticity. We use a covariant formulation of viscoelasticity combined with an entropy production analysis to show that odd elasticity is not only present in active systems but also in broad classes of passive chiral viscoelastic fluids. In addition, we demonstrate that linear viscoelastic chiral solids require activity in order to manifest odd elastic responses. To model the phenomenon of passive odd viscoelasticity we propose a chiral extension of Jeffreys model. We apply our covariant formalism in order to derive the dispersion relations of hydrodynamic modes and obtain clear imprints of odd viscoelastic behavior.

Raising thermal efficiency of solar water‐pump using Oldroyd‐B nanofluids' flow: An optimal thermal application

AbstractIt is well known that solar energy is the main source of thermal energy coming from the sun responsible for huge operations in engineering studies. It can be seen in the technology of photovoltaic cells, solar streetlights, solar energy plates, and solar water pumping. This study is for investigating solar radiation as well as a method to improve the performance of the solar water pump (SWP) with the use of solar radiation along with nanotechnology. The thermal transfer performance of the pump is checked for the case of many impacts including heat radiations and variable thermal conductivity. An Oldroyd‐B nanofluid with entropy production analysis has been scrutinized as a working coolant liquid in the system. Graphene oxide (GO) and Cu nanoparticles have been employed in engine oil (EO) as the base liquid. It is noticed that the heat transfer performance of SWP increases in the case of amplification in thermal radiation and temperature‐dependent thermal conductivity characteristics. In comparison to low thermal conductivity nanofluid, high thermal conductivity nanofluid provides the best capability for heat transmission. The thermal efficiency of the used (GO/EG) nanofluid has been enhanced by between 7.70% and 26.68% than (Cu/EO) nanofluid.

On the cavitation-induced collapse erosion of a turbofan fuel pump

Cavitation is a challenging flow phenomenon that can adversely affect the hydraulic performance of centrifugal pumps. In this study, numerical investigations were carried out incorporating the Zwart cavitation model derived from Rayleigh–Plesset equation with the Navier–Stokes equations to study a damaged turbofan pump. Pressure fluctuation was analyzed with fast Fourier transform (FFT) in both non-cavitation and cavitation flow fields. The entropy production theory was used to further analyze the positions of vortex cores and energy-loss behaviors inside the pump. The results demonstrate that the numerically predicted positions of vortex cores in high-pressure regions agree well with the erosion positions determined under real working conditions. Herein, through combined analysis of the pressure contours and the vortex-core locations, we demonstrate that the erosion failure of the surface is caused by fatigue failure due to the collapse of cavities at vortex cores. The percentages of different kinds of entropy production rates under different mass flow rates in the whole calculation domain were calculated, and it was found that the impeller suffered the most energy loss. The results of the entropy production analysis can provide guidance for subsequent optimization of turbofan pumps.

Entropy production and lumping of species can effectively reduce complex cell signaling pathways

A complicated issue in many cell signaling pathways is mainly related to the number of state variables and parameters. This is computationally very expensive, it may sometimes difficult to predict their model dynamics. Such problems in cell signaling pathways can be simplified and analyzed easily based on model reduction approaches. In this work, we suggest a model reduction technique based on entropy production analysis and lumping of isolated species. The proposed approach provides an improvement in the field of cell signaling pathways. We apply this technique to minimize the number of reactions and elements for the elongation factors EF–Tu and EF–Ts pathways. Computational simulations are computed for the given initial values and parameters. The results provide accuracy and important agreement between the original and reduced models. More interestingly, the model approaches here may apply to a variety of complex cell signaling networks and may use for theoretical and practical purposes.