Total Entropy Generation Research Articles

Influence of magnetic field inclination angles on hybrid nanofluids: Enhanced MHD double-diffusive mixed convection and entropy generation in a trapezoidal enclosure

This current numerical investigation is focused on analyzing the influences of various magnetic field inclination angles on mixed convective heat and mass transfer along with entropy generation in a lid-driven trapezoidal enclosure with double rotating cylinders inside by highlighting significant correlations between system’s input & output parameters. In this study, the effects of three types of SWCNT-Cu-–water hybrid-nanofluids composed of various ratios of nanoparticles in water are observed along with the individual impacts of SWCNT-water, Cu-water, and –water nanofluids. Galerkin weighted residual finite element method is used to solve the governing Navier-Stokes, thermal energy, and mass conservation equations numerically to get the results in forms of average Nusselt number, average Sherwood number, average entropy generation, and average temperature. The optimum conditions are identified to get the best results and these results are also represented in the forms of streamlines, isotherm, and isoconcentration contours for several parameters to get a better insight into heat and mass transfer. In most cases, maximum heat, and mass transfer along with maximum average total entropy generation occur if the magnetic field is assigned at an inclined angle with respect to the horizontal axis for each type of fluid in this current framework.

Variations of MHD double-diffusive mixed convection and entropy generation in various nanofluids and hybrid nanofluids due to the deviation of the spinning of double rotating cylinders

The current numerical study aims to investigate the effects of various rotating speeds of rotating cylinders on mixed convection and entropy generation in a lid-driven trapezoidal enclosure for fixed magnetic field inclination angle. Several water-based hybrid nanofluids are used as governing fluids. In this work, the impacts of SWCNT-water, Cu-water, and Al2O3-water nanofluids individually, as well as the effects of three different types of SWCNT-Cu-Al2O3-water hybrid nanofluids are examined. The average Nusselt number, average Sherwood number, average temperature, and average entropy generation because of heat transfer, diffusion, fluid friction, and the applied magnetic field as well as total entropy generation and Bejan number are evaluated as output parameters for different values of governing parameters. The Galerkin weighted residual finite element method is used to numerically solve the governing Navier-Stokes, thermal energy, and mass conservation equations. The optimal values of each governing parameter are established in order to produce the best results for the output parameters. To inspect the thermal and flow field within the trapezoidal enclosure as well as the variations in mass concentrations, isotherm contours, streamlines and isoconcentration contours are studied. Better performance is found for higher rotating speed regardless of other parameters.

Influence of nanofluids on the thermal performance and entropy generation of varied geometry microchannel heat sink

A microchannel heat sink (MCHS) is a compact, effective cooling device that meets the heat dissipation requirements of high-power electronic equipment. This paper investigates the impact of utilizing Al2O3/water, MgO/water, and TiO2/water nanofluids in a rectangular MCHS. To ensure an acceptable comparison, the flow rate is kept constant at 2 m/s. The heat sink base is subjected to 90W of steady heat dissipation, which produces the desired performance result. The vol. concentration of nanofluids ranges from 0 to 8%. The study covers a wide range of MCHS geometries; channel height (Hch) and its width (Wch) ranging from 200 to 800 μm and 100–500 μm respectively. The problem is modeled, validated, and analyzed. The use of nanofluids maximizes the heat transfer performance to 24.95% and minimizes thermal resistance and total entropy generation (TEG) to 15.01%, and 19.96% respectively. TEG decreases to 53.15% when Hch increases and the same increases to 198% when Wch increases. Nanofluids at highest vol. concentration as well as increase in Hch and Wch penalize the system maximum by demanding more pumping power (Ω) by 25.58%, 173.36%, and 39% respectively. Al2O3/water and MgO/water nanofluids deliver better performance and are recommended for future applications. Finally, the authors suggest concentration and geometric parameter ranges for optimality of the thermal performance.

Modeling and numerical analysis of micropolar hybrid-nanofluid flow subject to entropy generation

The regulation of energy associated with heat transfer is the most important problem in the food processing, chemical and biomedical engineering industries. Therefore, this investigation explores the heat transfer qualities of micropolar hybrid-nanofluid also considering entropy generation which has recently become central focus of research in the field of heat transfer processes. The purpose of this analysis is to explore the influence of magnetohydrodynamics (MHD), viscous dissipation, and heat radiation on the flow of hybrid-nanofluid with micropolar properties above an exponentially shrinking/stretching sheet. A mathematical model is constructed and the solution is acquired by utilizing numerical technique bvp-4c in MATLAB. The befitting usage of the second law of thermal physics helped in conducting the entropy production analysis. The study obtains numerical results for the governing equations, which reveal dual solutions when analyzing a shrinking sheet, contrary to a stretching sheet. The paper presents graphical depictions of the influence of different attributes upon micro-rotation, velocity, surface-friction, temperature, Nusselt number and also the entropy generation plus the Bejan number. Moreover, a comparison of heat transfer rates between conventional nanomaterial and hybrid-nanofluid is provided. The study concludes that dual solutions appear and the wall shear stress coefficient decreases as the values of micropolar parameter [Formula: see text] increase with critical values of [Formula: see text] being [Formula: see text], [Formula: see text] and [Formula: see text]. Also thermal irreversibility, which results from fluid friction near the sheet rather than far from it, is more dominant than total entropy generation.

Entropy Generation Analysis on a Metal Foam in an Automotive Exhaust Line with Thermoelectric Generator

Abstract In the present paper, an entropy generation analysis on a 2-D steady state problem in convective regime of an aluminum foam partially and totally filled channel with an external TEG element is solved in numerical way. The numerical analyses are accomplished with the assumption of the local thermal equilibrium (LTE) hypothesis in order to model the metal foam and heat transfer inside the channel. The working fluid is exhaust gas characterized by the same properties of the air in correspondence to the TEG upper surface temperature. The TEG is considered as a solid component characterized by an internal energy generation. The thermophysical properties are assumed temperature independent. Ansys-Fluent code is employed in order to resolve the governing equations for exhaust gas, metal foam and TEG. Different exhaust gas mass flow rates on the inlet section are assumed. Several thicknesses of aluminum foam values are employed. The porous media are characterized by a porosity from 0.90 to 0.978 and number of pores per inch (PPI) equal to 5, 10, 20, 40. Results are given in terms of global entropy generations related to the thermal and viscous effects. The total global entropy generation increases with increasing of exhaust gas flow rate for all pore density and porosity values. Bejan number decreases with the increment of mass flow rate and thickness. It increases when the porosity value increases whereas at high mass flow rate and for assigned porosity the values present small difference for different pore density values.

Entropy optimization and response surface methodology of blood hybrid nanofluid flow through composite stenosis artery with magnetized nanoparticles (Au-Ta) for drug delivery application

Entropy creation by a blood-hybrid nanofluid flow with gold-tantalum nanoparticles in a tilted cylindrical artery with composite stenosis under the influence of Joule heating, body acceleration, and thermal radiation is the focus of this research. Using the Sisko fluid model, the non-Newtonian behaviour of blood is investigated. The finite difference (FD) approach is used to solve the equations of motion and entropy for a system subject to certain constraints. The optimal heat transfer rate with respect to radiation, Hartmann number, and nanoparticle volume fraction is calculated using a response surface technique and sensitivity analysis. The impacts of significant parameters such as Hartmann number, angle parameter, nanoparticle volume fraction, body acceleration amplitude, radiation, and Reynolds number on the velocity, temperature, entropy generation, flow rate, shear stress of wall, and heat transfer rate are exhibited via the graphs and tables. Present results disclose that the flow rate profile increase by improving the Womersley number and the opposite nature is noticed in nanoparticle volume fraction. The total entropy generation reduces by improving radiation. The Hartmann number expose a positive sensitivity for all level of nanoparticle volume fraction. The sensitivity analysis revealed that the radiation and nanoparticle volume fraction showed a negative sensitivity for all magnetic field levels. It is seen that the presence of hybrid nanoparticles in the bloodstream leads to a more substantial reduction in the axial velocity of blood compared to Sisko blood. An increase in the volume fraction results in a noticeable decrease in the volumetric flow rate in the axial direction, while higher values of infinite shear rate viscosity lead to a significant reduction in the magnitude of the blood flow pattern. The blood temperature exhibits a linear increase with respect to the volume fraction of hybrid nanoparticles. Specifically, utilizing a hybrid nanofluid with a volume fraction of 3% leads to a 2.01316% higher temperature compared to the base fluid (blood). Similarly, a 5% volume fraction corresponds to a temperature increase of 3.45093%.

Artificial intelligence-based entropy generation investigation of two-phase nanofluid flow in a heatsink with pin fins

It is crucial to assess the efficiency of using entropy generation (EYG) in energy-consuming devices. In this article, a study is done on the EYG of laminar water/alumina nanofluid (NFD) in a heatsink (HTK) with circular pin fins. The NFD enters the middle of the HTK and exits around it and passes through the pin fins. The bottom portion of the HTK is subjected to a steady flux, and the temperature of the HTK is lowered by the cold NFD. By changing the diameter and height of pin fins and their distance, the values ​​of thermal EYG (TEYG), frictional EYG (FEYG), and total EYG (TOEYG) are estimated and the contours of temperature and NFD flow are presented. An optimization is performed on the results by using the response surface method (RSM) in the range of the studied variables to obtain minimum amounts of EYG and HTK temperature. The finite element method (FEM) and the two-phase mixture method are utilized to simulate the NFD flow. The findings show that increasing the height of the pin fins decreases thermal and TOEYG while increasing FEYG. Enhancing the distance between the pin fins, leads to a slight decrease in thermal and TOEYG.

Control of hybrid nanofluid natural convection with entropy generation: A LBM analysis based on the irreversibility of thermodynamic laws

This article analyzes the irreversibility of the natural convection of water/copper nanofluids in a square enclosure. Thermal entropy generation, frictional entropy generation, and total entropy generation are examined by changing the Hartmann number, thickness and length of baffles, and magnetic field with inclinations angle. Three baffles are mounted on the hot wall of the enclosure. The wall in front of the hot wall is cold and the other walls are insulated. The numerical method is employed for this analysis using the Lattice Boltzmann method. The results of this study demonstrate that an increment in the Ha reduces the horizontal and vertical velocity components ​​of the water/copper nanofluids in the enclosure and reduces the temperature gradient. Also, an enhancement in the Ha reduces all types of ETG. An increment in the angle of the magnetic field enhances thermal entropy generation, frictional entropy generation, and total entropy generation. Enhancing the magnetic field, first decreases and then increases the Bejan number.

Enhancing Heat Transfer in Blood Hybrid Nanofluid Flow with Ag–TiO2 Nanoparticles and Electrical Field in a Tilted Cylindrical W-Shape Stenosis Artery: A Finite Difference Approach

The present research examines the unsteady sensitivity analysis and entropy generation of blood-based silver–titanium dioxide flow in a tilted cylindrical W-shape symmetric stenosis artery. The study considers various factors such as the electric field, joule heating, viscous dissipation, and heat source, while taking into account a two-dimensional pulsatile blood flow and periodic body acceleration. The finite difference method is employed to solve the governing equations due to the highly nonlinear nature of the flow equations, which requires a robust numerical technique. The utilization of the response surface methodology is commonly observed in optimization procedures. Drawing inspiration from drug delivery techniques used in cardiovascular therapies, it has been proposed to infuse blood with a uniform distribution of biocompatible nanoparticles. The figures depict the effects of significant parameters on the flow field, such as the electric field, Hartmann number, nanoparticle volume fraction, body acceleration amplitude, Reynolds number, Grashof number, and thermal radiation, on velocity, temperature (nondimensional), entropy generation, flow rate, resistance to flow, wall shear stress, and Nusselt number. The velocity and temperature profiles improve with higher values of the wall slip parameter. The flow rate profiles increase with an increment in wall velocity but decrease with the Womersley number. Increasing the intensity of radiation and decreasing magnetic fields both result in a decrease in the rate of heat transfer. The blood temperature is higher with the inclusion of hybrid nanoparticles than the unitary nanoparticles. The total entropy generation profiles increase for higher values of the Brickman number and temperature difference parameters. Unitary nanoparticles exhibit a slightly higher total entropy generation than hybrid nanoparticles, particularly when positioned slightly away from the center of the artery. The total entropy production decreases by 17.97% when the thermal radiation is increased from absence to 3. In contrast, increasing the amplitude of body acceleration from 0.5 to 2 results in a significant enhancement of 76.14% in the total entropy production.

Working mechanism and characteristics analysis of a novel configuration of a supersonic ejector

The growing awareness of utilizing low-grade energy has encouraged the scientific community to conduct research on supersonic ejectors. Most previous studies have investigated on the geometry parameters or profiles of supersonic ejectors, but few studies have focused on improving the ejector configuration. This paper presents a novel configuration of a supersonic ejector which has the advantage of better performance than the conventional ejector in double-choking mode. First, the novel configuration and its working mechanism are presented, and the entropy generation of the primary fluid is compared theoretically between the novel and conventional configurations. Second, validation of the novel configuration mechanism is performed using CFD. The velocity and pressure distribution, performance characteristics, and entropy generation at different outlet pressures are presented and analyzed in comparison to the conventional ejector. The normal shock intensity in the novel configuration is reduced and the total entropy generation decreased, thereby improving the ejector's performance. Finally, the impact of the geometric parameters of the novel configuration is evaluated, pointing out its limits and the need of further investigation and experimental studies for optimal design.

MHD Mixed Convection of Non-Newtonian Bingham Nanofluid in a Wavy Enclosure with Temperature-Dependent Thermophysical Properties: A Sensitivity Analysis by Response Surface Methodology

The numerical investigation of magneto-hydrodynamic (MHD) mixed convection flow and entropy formation of non-Newtonian Bingham fluid in a lid-driven wavy square cavity filled with nanofluid was investigated by the finite volume method (FVM). The numerical data-based temperature and nanoparticle size-dependent correlations for the Al2O3-water nanofluids are used here. The physical model is a two-dimensional wavy square cavity with thermally adiabatic horizontal boundaries, while the right and left vertical walls maintain a temperature of TC and TH, respectively. The top wall has a steady speed of u=u0. Pertinent non-dimensional parameters such as Reynolds number (Re=10,100,200,400), Hartmann number (Ha=0,10,20), Bingham number (Bn=0,2,5,10,50,100,200), nanoparticle volume fraction (ϕ=0,0.02,0.04), and Prandtl number (Pr=6.2) have been simulated numerically. The Richardson number Ri is calculated by combining the values of Re with a fixed value of Gr, which is the governing factor for the mixed convective flow. Using the Response Surface Methodology (RSM) method, the correlation equations are obtained using the input parameters for the average Nusselt number (Nu¯), total entropy generation (Es)t, and Bejan number (Beavg). The interactive effects of the pertinent parameters on the heat transfer rate are presented by plotting the response surfaces and the contours obtained from the RSM. The sensitivity of the output response to the input parameters is also tested. According to the findings, the mean Nusselt numbers (Nu¯) drop when Ha and Bn are increased and grow when Re and ϕ are augmented. It is found that (Es)t is reduced by raising Ha, but (Es)t rises with the augmentation of ϕ and Re. It is also found that the ϕ and Re numbers have a positive sensitivity to the Nu¯, while the sensitivity of the Ha and Bn numbers is negative.

Numerical studies for effect of geometrical parameters on water jet pump performance via entropy generation analysis

This paper presented an implementation of entropy generation analysis in the main flow field of a water jet pump via the CFD method. This study aimed to identify the inefficient location of energy conversion and to analyse entropy generation sources in each region of the water jet pump. The 2D-axisymmetric model and realisable k-ε (RKE) turbulence model at steady-state conditions were performed to validate jet pump performance and to assess the entropy generation. Likewise, the effects of the projection ratio and throat-aspect ratio as independent parameters were investigated. As a result, the throat is the most inefficient part due to the high total entropy generation rate, following by diffuser part. Also, the entropy generation rate was assessed dominant than viscous dissipation due to the turbulent dissipation, which was caused by a turbulent shear stress layer of mixing the streams. In conclusion, the projection ratio influenced the growth of the shear stress layer as well as the entropy generation. Further, the throat-aspect ratio affected the distribution of entropy generation in the throat section. An appropriate combination of both parameters has an impact on the jet pump performance improvements reducing the entropy generation rate in the future.

Local hydrothermal characteristics and temperature uniformity improvement of microchannel heat sink with non-uniformly distributed grooves

In order to improve the temperature uniformity of bottom walls, a novel design of microchannel heat sink with From-Sparse-To-Dense embowed grooves (MC-FSTD) was proposed as well as a comparative one with From-Dense-To-Sparse embowed grooves (MC-FDTS). The local hydrothermal characteristics and temperature distribution variance of bottom wall of microchannel heat sinks were numerically investigated for Reynolds number (Re) ranging from 100 to 800. The results showed that the denser grooves led to lower flow velocity, lower local friction factor and higher local pressure as well as the lower bottom wall temperature (Tw) and higher local Nusselt number (Nuz). The local Nusselt number and the bottom wall temperature of MC-FSTD were 2.17 times higher and 9.1K lower than that of MC-SC at z = 10 mm, respectively. MC-FSTD also had the most uniform temperature of the bottom wall and the corresponding temperature variance was 6.42 times lower than that of MC-SC at Re = 795.38. The heat transfer entropy generation rate and the total entropy generation rate of MC-FSTD were also the lowest with an acceptable friction entropy generation rate. Finally, the effects of the decreasing magnitude (Li) of the distance between two adjacent grooves on the local hydrothermal characteristics and temperature uniformity of MC-FSTD were explored and the total entropy generation rate was further reduced to 5.22 × 10−4 W/K at Li = 0.015 mm and Re = 795.38.

Numerical analysis of entropy generation in a solar desalination plant with nanofluid and a layer of phase change material in its reservoir

The acquisition of drinking water is discussed in this paper by three-dimensional modeling of a solar desalination plant focusing on renewable energies. The reservoir of the desalination plant contains aluminum nanoparticles with a constant weight percent. A layer of n-Eicosane phase change material (PCM) with various thicknesses is used at the bottom of the desalination plant reservoir. The objective of the present paper is to examine the entropy generation, including frictional, thermal, and total entropy generation in the flow of steam and air inside the desalination plant and the use of the PCM layer. The angle of the glass changes from 10 to 45°, and the thickness of the PCM layer varies during the day. The nanofluid flow is assumed to be two-phase, and the finite element method (FEM) is employed to solve the equations using COMSOL software. The results show that increasing the glass angle enhances the frictional entropy generation, and decreases the thermal entropy generation. Using PCM with a thickness of 50 mm reduces the thermal entropy generation in the steam, especially in the afternoon. The amount of PMC thickness changes the total entropy generation in the PMC.

Entropy Generation Minimization of Two-Phase Flow Irreversibilities in Hydrocarbon Reservoirs

The efficient use of available energy in hydrocarbon extraction processes is essential to reducing overall emissions in the petroleum industry. The inefficient design of an extraction process leads to higher emissions per unit mass of hydrocarbon recovery. Fluid friction and heat transfer are irreversible processes that are vital in decreasing the overall system’s operational efficiency. To reduce these irreversible energy losses in the petroleum reservoir production’s life, contributing factors such as the characteristic features of a reservoir formation, reservoir fluids, and production rate are investigated in this paper. This study examines irreversible energy loss in porous media and wellbore formations using entropy generation minimization at various stages of production and thermodynamic conditions, eventually achieving higher hydrocarbon recovery factors. Entropy production is used to develop predictive models that calculate reservoir and wellbore energy losses for multiphase flow. The proposed models consider oil and water as the working fluids in a porous medium and a wellbore. This paper also investigates the thermophysical effects around the wellbore by incorporating Hawkin’s model. A sensitivity analysis assessed the impact of rock and fluid properties and thermodynamic conditions such as temperature, wettability, and capillary pressure on the total entropy generation. The findings reveal that the capillary pressure significantly impacts the oil and water recovery factor and total entropy production. Additionally, the capillary pressure strongly influences the reservoir production life. The two-phase models show that as the recovery factor increases, the total entropy production decreases at lower production rates. This article helps to address the impact of irreversible processes on multiphase hydrocarbon reservoir operational efficiency. Furthermore, the results obtained from the numerical-simulation model open up a new research area for scholars to maximize the recovery factor using entropy generation minimization in heterogeneous reservoirs.

Numerical Simulation of MHD Natural Convection and Entropy Generation in Semicircular Cavity Based on LBM

To study the natural convection and entropy generation of a semicircular cavity containing a heat source under the magnetic field, based on the single-phase lattice Boltzmann method, a closed cavity model with a heat source in the upper semicircular (Case 1) and lower semicircular cavity (Case 2) is proposed. The cavity is filled with CuO-H2O nanofluid, and the hot heat source is placed in the center of the cavity. The effects of Rayleigh number, Hartmann number and magnetic field inclination on the average Nusselt number and the entropy generation of the semicircular cavity are studied. The results show that the increase in the Rayleigh number can promote the heat transfer performance and entropy generation of nanofluids. When the Hartmann number is less than 30, the increasing function of the Hartmann number at the time of total entropy generation reaches its maximum when the Hartmann number reaches 30. As the Hartmann number increases, the total entropy generation is the decreasing function of the Hartmann number. The larger the Hartmann number, the greater the influence of the magnetic field angle system. Under the same Hartman number, with the increase in the Rayleigh number, the flow function of Case 2 increases by 29% compared with that of Case 1. The average Nusselt number of heat source surfaces in Case 2 increases by 5.77% compared with Case 1.

Distributed heat release effects on entropy generation by premixed, laminar flames

This article studies the generation of entropy disturbances by laminar premixed flames. The total entropy generation equals the integrated ratio of the local heat release rate and the local temperature, namely, [Formula: see text]. Due to this path dependency, evaluating this integral requires an understanding of how the heat release is distributed in the temperature space. Several studies evaluate the local entropy generation as [Formula: see text], where [Formula: see text] refers to the burned gas temperature, implicitly assuming all the heat release occurs at [Formula: see text]. Such an approximation is motivated by the high activation energy nature of combustion chemistry. This work evaluates this assumption by comparing it to results from one-dimensional premixed flame calculations for hydrogen, methane, and propane-air flames over a range of pressures, equivalence ratios, and preheat temperatures, quantified via the ratio [Formula: see text]. We show that this assumption is quite reasonable for methane and propane-air flames (with errors ranging from 5% to 25%) but deviates significantly from the exact results for hydrogen flames (where errors can be as high as 50%). In general, the peak heat release moves to lower temperatures as preheat temperature is increased. Noting that the temperature sensitivity of heat release is directly related to the activation energy, we use Law's approach to extract global activation energies and show that the deviations of [Formula: see text] from unity can be approximately correlated with [Formula: see text]. Finally, we show that significant improvements in entropy generation calculations can be obtained by estimating [Formula: see text] using [Formula: see text], where [Formula: see text] is the temperature at which the reaction rate peaks. This estimation leads to predictions of ∼5% within the exact value for the hydrocarbon cases but can still be in significant error for hydrogen at certain conditions.

Entropy minimization of the non-Newtonian bio-hybrid (Fe3O4-CuO/blood) nanofluid flow over a linear extending sheet by means of induced magnetic field

The physiological system loses heat energy through the bloodstream to nearby cells. Such energy loss can lead to a quick death, anemia, severe hypothermia and high or low blood pressure to heart surgery. As a result, biomedical engineers and physicians are increasingly attracted to the study of entropy production to calculate the energy loss of biological systems. Furthermore, the thermodynamic state of entropy production is used to access cancer cells during chemotherapy treatment and heat transfer in tissues. The current model intends to explore the significance of the non-Fourier heat flux model on Eyring–Powell/Maxwell hybrid nanofluid (Fe3O4–CuO/blood) flow in a linear extending sheet with induced magnetic field and entropy generation. Suitable self-similarity variables are performed to convert momentum and thermal equations determined using the homotopy perturbation method into ordinary differential equations. The significance of distinct physical parameters such as thermal relaxation parameter, volume fraction, fluid parameter, magnetic Prandtl number, Biot number, Brinkman number, heat source, Eckert number, radiation and heat source on velocity, temperature, skin friction coefficient, Nusselt number, entropy production, streamlines and isotherm are represented through figures. It is recognized that the fluid friction irreversibility is comparatively higher than thermal irreversibility and highly dominates the total entropy generation. The nanoparticle volume fraction diminishes the velocity and induced magnetic field of both Eyring–Powell and Maxwell hybrid nanofluid. Fluid friction irreversibility is more in Maxwell fluid compared to the Eyring–Powell fluid.

High-dimensional CFD optimization of a low-flow coefficient S–CO2 centrifugal compressor for enhanced oil recovery systems

The design of low-flow coefficient (∼0.01) centrifugal compressors with supercritical CO2 as working fluid is still a challenge for engineers due to its increased friction losses at the impeller. However, the reinjection pressure required for Enhanced Oil Recovery (EOR) systems is achieved by compression trains with stages of high-Pressure Ratios (PR > 3) which can only be obtained by lowering the flow coefficient of the equipment. The carbon dioxide mitigation, due to the reinjection process, also increases oil productivity and extraction lifetime. A four-staged compression system was considered and the preliminary geometry of its last stage was considered herein after a 1D optimization that decreased the total required power of the system. In order to further increase the systems' performance, a CFD model was developed and submitted to Sensitivity Analysis (SA) and parametric optimization procedure, considering polar angles, meridional profile and vaneless diffuser passage (25 variables). The assessment of the sequential SA using, Morris' screening method Design of Experiment (DoE) and SS-ANOVA for variable ranking and response surface training, has exposed the method's limitation in recognizing interaction between variables since low-quality Response Surfaces (RS) were trained. However, the Incremental Space Filler (ISF) sampling has complemented the sample space screening, guarantying adequate RS at a low computational cost. This indirect optimization strategy that increased the equipment's polytropic efficiency by 1.19%, diminishing total entropy generation by 8.5% can deliver important cost reductions to the operation of EOR compression systems. The ‘entropy-guided’ phenomenology analysis strategy combined with SA results, identified that the narrowing of the vaneless diffuser has extinguished the recirculation present in the original geometry's impeller/diffuser interface region, which was the largest difference in the entropy histogram. Moreover, the enlargement of the impeller's meridional profile has smoothed the fluid flow change of direction (from axial to radial) and displaced the swirl structures that restricted the fluid flow in the main passage.

Numerical Analysis of Energy Loss in Stall Zone for Full Tubular Pump Based on Entropy Generation Theory

As a low-head and non-drive pump, the head reduction and stall advance are the key factors that restrict the popularization and application of the full tubular pump (FTP). In this paper, the shear stress transport (SST) k-ω turbulence model is used for the numerical calculation of the FTP. Additionally, based on the entropy generation theory, the energy loss and main distribution zones of the FTP under all working conditions are analyzed, and the mechanism of inducing its stall advance is explored. By comparison, we found that there is little difference between the numerical simulation results and the model test. Turbulence entropy generation has a high proportion under small flow conditions, which is mainly reflected in the outlet flow separation zone of the suction surface of the impeller blade, the guide vane inlet zone where inlet deviation exists, and the trailing edge of the guide vane where the flow separation exists. Compared with the axial flow pump (AFP), when the flow rate decreases, the clearance reflow between the stator and rotor induces the deterioration of the flow at the impeller inlet, and the turbulent entropy generation in the impeller channel increases rapidly, making the FTP enter the stall zone ahead of time. The clearance backflow affects the flow pattern of the inlet pipe, making the turbulence entropy generation in the outlet area of the inlet pipe increase. The total entropy generation in the stator–rotor region is little affected by the pump flow conditions, and it is mainly affected by different stator–rotor backflow clearance dimensions. This study can provide a reference for exploring the energy loss of the FTP and revealing its stall characteristics.