Main Channel Flow Research Articles

Wettability impacts residual trapping of immiscible fluids during cyclic injection

Understanding the hysteretic behaviour in fluid–fluid displacement processes in porous media is critical in many engineering applications. In this work, we study the quasi-static immiscible displacement process in two-dimensional porous media during cyclic injections in the context of carbon geosequestration. The role of wettability on the residual trapping of CO $_2$ is investigated numerically using an extended interface tracking algorithm. Despite that higher CO $_2$ saturation can be achieved in CO $_2$ -wet porous media after the first CO $_2$ injection, the majority of CO $_2$ is found to be unstable and can be mobilised during subsequent water injection processes. An improvement in the residual trapping of CO $_2$ is observed as the number of injection cycles increases, which is associated with the dispersion of continuous CO $_2$ ganglia into numerous smaller blobs. Compared with either water-wet or CO $_2$ -wet porous media, it is found that less CO $_2$ is trapped within the neutral-wet ones at equilibrium state after a sufficient number of injection cycles. The hysteretic behaviour of saturation between water/CO $_2$ injection cycles is found to follow an exponential decay, which eventually reaches a finite value. This process corresponds to the shift of the mobile region during displacement from typical capillary fingering to a less ramified regime, which ultimately converges towards main flow channels. This work highlights the hysteretic behaviour during cyclic injections, providing insights on the wettability impacts on multiphase flow in porous media, which is of great importance in applications such as carbon geosequestration and geological hydrogen storage.

Three-dimensional numerical study for determining the optimum diversion angle of bifurcating channels

Water diversion to bifurcating canals has been attracting interest from water engineering researchers for decades. It can be described by the size of the separation zone in the intake channel and the quantity of flow rate into the bifurcating channel based on the diversion angle. The present study is an attempt to determine the optimum diversion angle of bifurcating channels that can achieve the minimum separation zone size in the intake channel and maximum discharge in the bifurcating channel. The study’s objectives were achieved by using the theoretical three-dimensional (3D) ANSYS 16 software to investigate the diverted flow into bifurcating channels with different diversion angles (90, 75, 60, 45, 30, and 15-degrees). Theoretical expected flow characteristics have been validated by experimental work. According to the findings, the ANSYS 16 software is a good tool for calculating bifurcating channel flow patterns. The final results proved that the 15-degree diversion angle has the optimum impact on the diverted flow. In addition, it achieves a maximum flow rate in the bifurcating channel (about 8.1 L/s), which represents nearly 49.4% of the main channel flow. It also provides a negligible separation zone with respect to the other diversion angles of the bifurcating channel. As a result, the efficiency of distributing, transporting, and controlling the limited amount of water available will improve.

Influence of Emulsification Characteristics on the Pressure Dynamics during Chemical Flooding for Oil Recovery

Chemical flooding agents, especially surfactant-based flooding oil agents, have been widely studied due to their excellent emulsification ability. Nevertheless, there are many evaluation methods for chemical flooding agents, and the focus of each test is different. How to combine routine testing with reservoir conditions is an urgent problem to be solved. In this study, different kinds of chemical flooding agents were evaluated for interfacial tension (IFT), minimum emulsification speed, emulsification state, droplet size distribution, viscoelasticity, apparent viscosity in porous media, stability, and flooding efficiency. The influence of their characteristics on the pressure dynamics during flooding is analyzed, and the mechanism in the different stages of chemical flooding is clarified. A comprehensive analysis of IFT and the minimum emulsification speed is needed to evaluate the emulsification ability. The apparent viscosity when W/O emulsion flows through porous media is more accurate to evaluate the viscosity reduction of the chemical flooding agents than the traditional viscosity test. The chemical flooding dynamics is mainly divided into three stages: pressure increase (emulsification ability), pressure decrease (fluidity of formed oil in water (O/W) emulsion), and pressure stabilization (flooding efficiency). The stronger the emulsification ability, the faster the pressure increase and the wider the main flow channel. The easier the O/W emulsion is formed, the smaller the droplet size, the stronger the elastic deformation ability, and the higher the oil flooding efficiency. The smaller the droplet size and the stronger the viscoelasticity of O/W emulsion, the lower the maximum pressure in the flooding process and the slower the pressure decrease in the middle stage. Therefore, the evaluation of chemical flooding agents should mainly consider their emulsification ability and the formed O/W emulsion droplet size, viscoelasticity, and stability. This study clarified the evaluation focus of chemical flooding, and laid a foundation for the research and development and screening of chemical flooding agents, and the dynamic analysis of chemical flooding.

Influence of operating parameters on the vortex structure in the main flow passage of the helico-axial multiphase pump

The flow is extremely complex within the main flow channel during the operation of the multiphase pump, resulting in constant changes in the vortex structure, disrupting the orderly flow of the existing flow field, and reducing the performance of the pump. Numerical calculations, supplemented by experimental verification, are used as the main method for investigating influencing factors that affect the vortex structure in the impeller passage of the pump, and vortex structure present on isosurfaces is selected based on Q criterion to study the evolution of vortex structures under different working conditions. Results indicate that the flow rate affects vortex structure generation on the suction side and trailing edge of the blade. With an increase in flow rate, the vortex becomes complete from fine broken structures. Speed has a greater influence on vortex structures in inlet and outlet areas: the higher the speed, the larger the vortex structure attached to the impeller leading edge. The vortex structure is separated from the blade surface at two-thirds of the impeller under gas–liquid two-phase working condition, with an increase in inlet gas void fraction, and the vortex structure expands to the center of impeller passage. Therefore, exploring evolutions of the vortex structure can provide a certain theoretical basis for improving the stability of multiphase pump internal flow.

Exploring the role of the structural heterogeneity of fractured carbonate reservoirs in contact with dissolved CO2 based on fracture-water-rock simulation experiments

Based on the geological background of ultra-deep fractured carbonate reservoirs in the Shunbei oil and gas field, the objective of this study was to clarify the interactions between fractured carbonate reservoirs and formation fluids (brine with dissolved CO2) under deep strata, and the potential impact of these interactions on reservoirs. In this study, high-temperature and high-pressure simulation experiments and numerical simulations based on the Yijianfang Formation in the Shunbei area were designed to investigate the influence of temperature, pressure, fluid, and structural heterogeneity on fluid transport and mass transfer, calculate the ion diffusion characteristics and the trend of mineral dissolution/precipitation along the fractures, and clarify the change in the reservoir space. The results indicated that the volume of the main fracture increased after the reaction between an acidic solution and a formation sample, the permeability of the sample increased by orders of magnitude, and its porosity increased accordingly. The overall reaction during the experimental period was dominated by the dissolution of calcium carbonate, and no calcium carbonate precipitated. The structural heterogeneity and hydraulic properties of the sample make the main flow channel a main fracture. The flow and reaction processes in the flow channel promoted each other. The effects of temperature and pressure on the overall reservoir space were insignificant. Branch fractures or microfractures can weaken the main fluid flow rate and tend to result in the accumulation of solutes, the ends of which may be potential locations for mineral precipitation. Therefore, the priority exploration location for deep and ultra-deep fractured reservoirs should be the main fractures upstream of the fluid flow.

Turbulence structure and bank erosion process in a dredged channel

AbstractRiverbank erosion has significant geomorphological as well as anthropogenic consequences. The geomorphological impacts include form changes such as lateral channel migration, meanders, channel expansion, etc. The anthropogenic effects include the threat to floodplain human habitation, agricultural land, and stability of instream hydraulic structures and buried pipelines. Channel dredging for the extraction of sand and gravel has seen a multi‐fold rise in the last few decades. Therefore, riverbank erosion response to channel mining gains importance in river basin management. Sandpits dredged in the riverbeds can significantly impact the downstream riverbank stability. In order to assess these impacts, we conducted a series of experiments at a laboratory scale in a recirculating water flume. Three riverbank slopes, 25° (gentle), 31° (equal to the angle of repose of the bank sediments), and 40° (steeper than the angle of repose), were tested along with a sandpit. Remarkable changes in the turbulence structure of riverbank flow were found due to the channel pit. Pit excavation directly impacts the fluvial erosion characteristics of the riverbank. Pit action increases the Reynolds shear stress fields in the near‐bank flow, which causes progressive fluvial erosion of the berm at the bank toe. The erosivity of the main channel flow in the riverbank also leads to channel degradation, which increases the exposed height of the bank slope. Pit dredging leads to the generation of stronger ejection bursts which provide a mechanism for berm sediment mobility and erosion. The hydro morphological response of the riverbank due to sand mining was analysed, and process understandings are presented in the paper.

Identification of a Function to Fit the Flow Duration Curve and Parameterization of a Semi-Arid Region in North China

The discharge process has undergone major changes in many river basins throughout the world as a result of the simultaneous influences of global climate change and human activity. Flow duration curves (FDCs) are crucial indicators of river basins’ hydrological processes. However, it is challenging to compare FDCs in a quantitative way. This study will identify the best function with which to fit the flow duration curve in a semi-arid region of North China, so as to quantify the FDC, and parameterize the function of the FDC of the region in order to describe the FDCs of ungauged basins. In this work, six small- and medium-sized catchments in North China are selected as the study area, and three functions, i.e., log normal, generalized Pareto and H2018 functions, were chosen to fit the FDC at nineteen hydrological stations. The relationship between the parameters of the FDC and the basin characteristics, such as the climatic factors and geographical features, were analyzed. A regression formula of the parameters of the FDC function was established, and its spatial and temporal distributions were examined. Based on the evaluation of four indicators, the Nash–Sutcliffe efficiency, the root mean square relative error, the logarithmic Nash efficiency coefficient and the coefficient of determination, the results demonstrate that the H2018 function can match FDCs the best. Through the annual runoff, annual precipitation, precipitation in summer, potential evapotranspiration, catchment area, mean elevation, length of the main channel and maximum flow frequency, the parameters of a, b, and k in the H2018 function can be formulated. The regression formula constructed in this study can obtain a regional flow duration curve with satisfactory performance, which provides a reference for the validation of remote-sensing-based runoff data in ungauged regions.

Study on fracture evolution model of the enhanced geothermal system under thermal-hydraulic-chemical-deformation coupling

The fractures are the main flow and heat transfer channel for fluids in deep high-temperature enhanced geothermal systems (EGS). The deformation of the fracture controlled by reactive flow is a common phenomenon during geothermal development, which might lead to a reduction in the system's thermal performance and operating life.While most previous research focuses on the influence of fracture deformation on system heat extraction performance, conversely the fracture deformation mechanism caused by the reactive flow is ignored. In this paper, a coupled thermal-hydraulic-chemical-deformation (THCD) model is established to investigate the fracture deformation mechanism. The deformation behavior of quartz and anorthite is compared, and the Damkohler number (Da) is adopted to explore the reaction mechanism. Meanwhile, the influence mechanism of concentration and temperature on fracture deformation is also analyzed. Results show that the Da at the fracture surface is 10−12 -10−8, which means that the deformation of the fracture is controlled by the reaction rate. Compared with the concentration, the influence of temperature on fracture deformation is complex, and there is an inflection point. The inflection point is governed by the mineral reaction kinetics. These results provide significant references for the efficient heat extraction of the EGS.

Mathematical modeling of the operating mode of the South Golodnostepsk main channel

The article presents the results of a study of operation and considers the application of mathematical modeling to the movement of water flow in the South Golodnostepsk main channel. A convenient, simple and cheap mathematical apparatus is proposed, which gives sufficiently reliable predictive results for making the right decisions in emergency situations during the operation of the South Golodnostepsk main channel. It is also given to apply recommendations for the numerical calculation of other irrigation channel in the region.

Numerical Study of the Purge Flow’s Effect on the Loss Mechanism of the Blocking and Shear Effects

The loss mechanism of shear and upstream blockage caused by the interaction of the purged flow and ingested gas needs to be systematically studied to optimize the flow near the rim. In order to study the causes and influence factors of blocking and shearing effects and quantify their losses reasonably, the three-dimensional unsteady numerical method validated by the experiment data was adopted to study the turbine with three kinds of sealing structures. The block and shear loss are quantified by integrating the dissipation coefficient in the volume where the specific aerodynamic loss occurs. The result indicated that there was a larger radial velocity and smaller tangential velocity of the purged flow relative to the main flow caused the blocking effect. Therefore, its loss is affected by the seal flow and seal structure. The shear effect is mainly affected by the tangential velocity gradient and the axial velocity gradient near the cavity exit. The contribution of the tangential velocity gradient to shear loss is increased with the enlarged sealing efficiency. Through research, it is clear that increasing the purge flow’s tangential velocity is beneficial to reducing the shear loss and has a positive significance for weakening the blocking effect in the main flow channel. Furthermore, the influence of sealing structure on blocking and shear effect must be particularly considered since both are related to sealing efficiency.

Investigation on permeability anisotropy in unconsolidated hydrate-bearing sediments based on pore-scale numerical simulation: Effect of mineral particle shape and pore-filling

Resulting from the preferential alignment of sediment particles, permeability anisotropy of unconsolidated strata is an essential parameter for natural gas hydrate (NGH) exploitation. Fundamentally, the effect of mineral particle shape and pore-filling NGH on the permeability anisotropy are considered in this study. A simulation with combining methods of particle flow code and computational fluid dynamics is conducted to construct a series of numerical samples and calculate the anisotropic permeabilities. Different particles shapes and hydrate saturations are preinstalled in these samples. It is firstly proved that the elongated particles have little effect on permeability anisotropy. Meanwhile, the preferential alignment of plate-shaped particles is the main reason for permeability anisotropy. In principle, the difference between intermediate orthogonal axes and short orthogonal axes of plate-shaped particles makes the tortuosity different in directions, thus inducing the permeability anisotropy. The anisotropy ratio decreases with the increase of hydrate saturation, which is caused by the nonlinear decline of main channel flow resulting from the thrombus-like hydrate particles. The results provide an insight into the formation mechanism of permeability anisotropy and display potential application value in NGH exploitation, groundwater environment protection and geological disaster prevention.

Numerical Study of Sedimentation and Flow Pattern at the Open Channel Intake

Generally, open channel lateral intake structures are extensively used in the water and environmental projects. The passing flow at side intakes is mostly turbulence containing vertical and horizontal spiral currents causing sediment problems. The flow separation region in the intake channel is critical for sediment and water distribution during the diversion. It denotes a large reduction in the possible breadth of the lateral branch's incoming flow, as well as a place where sediment has collected, obstructing the deviated flow. This study aims to reduce and control sediment problems at the lateral intake by improving the flow pattern at this area using three-dimensional numerical models simulated in CFD, ANSYS Fluent software. The correctness of the three-dimensional numerical model was validated by a previous experimental study that showed good accuracy. Different discharge ratios and a range of shape designs were used to simulate the flow pattern at the intake channel junction. The findings demonstrated that the separation zone measurements minimize as the discharge ratio increases. Based on the changing the intake entrance shape results, cutting the outer boundary of the canal entrance widens the separation area, as well as an additional separation spot as the cutting size grows. In contrast with the internal chamfered angle models of the intake inlet, the separation area dimensions are reduced. The chamfered and rounded inner intake edge model with 30o angle to the main channel flow direction and the length of the chamfered side that normal to the flow direction (c value ) equal to three-quarters of the intake width was noticed to be the best design for lessening separation extent in this study. Thereby, the reduction ratio of the separation area width and length reaches in this case to 90% and 72%, respectively.

Association Between Blood Flow Pattern and Rupture Risk of Abdominal Aortic Aneurysm Based on Computational Fluid Dynamics

This study aimed to derive a novel classification of blood flow pattern in abdominal aortic aneurysms (AAA) based on computational fluid dynamics (CFDs), and to determine the predictive value of flow patterns in AAA rupture. This was an age and sex matched case control study. Cases were identified as patients who underwent emergency endovascular or open repair due to ruptured or AAA at risk of impending rupture. Controls were age and sex matched with patients with an AAA who were asymptomatic and had a confirmed unruptured AAA from computed tomography angiography images from the same period. Classification of blood flow pattern (type I: non-helical main flow channel with multiple vortices; type II: non-helical main flow channel with single vortices; and type III, helical main flow channel with helical vortices) and haemodynamic parameters (areas of low wall shear stress [AlowWSS], aneurysm pressure drop [Δ pressure], etc) were derived from CFD analyses. Multivariable regression was used to determine independent AAA rupture risk factors. The incremental discriminant and reclassification abilities for AAA rupture were compared among different models. Fifty-three ruptured and 53 intact AAA patients were included. Ruptured AAA showed a higher prevalence of type III flow pattern than intact AAA (60.4% vs. 15.1%; p < .001). Type III flow pattern was associated with a significantly increased risk of aneurysm rupture (odds ratio 10.22, 95% confidence interval 3.43 – 30.49). Among all predicting models, the combination of AAA diameter, haemodynamic parameters (AlowWSS or Δ pressure), and flow pattern showed highest discriminant abilities in both the overall population (c-index = 0.862) and subgroup patients with AAAs < 55 mm (c-index = 0.972). Compared with AAA diameter, adding the flow pattern could significantly improve the reclassification abilities in both the overall population (net reclassification index [NRI] = 0.321; p < .001) and the subgroup of AAAs < 55 mm (NRI = 0.732; p < .001). Type III flow pattern was associated with a significantly increased risk of AAA rupture. The integration of blood flow pattern may improve the identification of high risk aneurysms in both overall population and in those with AAAs < 55 mm.

Flow Visualization of Transition From Linear to Nonlinear Flow Regimes in Rock Fractures

AbstractThis study made the first experimental attempt to visualize the transition processes from linear to nonlinear flow regimes in rough‐walled rock fractures for a better understanding of the evolution of flow regimes in rock fractures. The experiments visualized the narrowing of the mainstream channel associated with eddies enlarged near the fracture wall with increasing applied flux. The measured fluid velocity field showed that these flow structures resulted in a significant increase in fluid velocity in the narrowed main flow channel and a relatively small velocity in the enlarged eddy zone. The order‐of‐magnitude analysis of local inertial and viscous forces, using measured fluid velocity vectors, showed that inertial forces overwhelmed viscous forces in the narrowed mainstream channel of rough‐walled segments, which led to the transition to nonlinear flow in rough‐walled fractures. The quantitative comparison between measured fluid velocity and the numerical simulations showed good agreement. This study demonstrates that the micro‐PIV technique can serve for phenomenon‐based experimental research on fluid flow and solute transport in rock fractures.

Silver Carp (Hypophthalmichthys molitrix) (Asian Silver Carp) Presence in Danube Delta and Romania-A Review with Data on Natural Reproduction.

The Danube River has a large hydrographical basin, being the second largest river in Europe. The main channel flows through seven European countries with many species of fish inhabiting it. In this review we focused on the invasive species silver carp (Hypophthalmichthys molitrix), which plays an important ecological and economic role in its original habitat, but since introduced in Europe’s rivers, the species has posed a serious ecological risk under global warming. In this review paper, we gathered data regarding silver carp, such as when and how it entered the Danube Delta and the water temperature suitable for its growth and reproduction, mainly in the context of global warming, as well as the nature of nutrition and the ecological risk the species poses.

Mass transfer between recirculation zone and main flow domain in fractures: Is the first order rate law valid?

• Recirculation zones (RZs) are present and grow with Reynolds number ( Re ) in fractures when inertial forces are significant. • Mass transfer between RZ and main flow channel results in a late time tailing in residence time distributions. • The first order rate law is robust for describing mass transfer between RZs and main flow channel. A better understanding of solute transport in fractures with immobile zones is critical for many geophysical processes and engineering applications. Although the roles of immobile zones in capturing and releasing solutes leading to non-Fickian transport are well-acknowledged, the mass transfer between immobile and mobile domains using the first order rate law has never been explicitly validated. To this end, we solved fluid flow and solute transport through direct numerical simulations with Reynolds number ( Re ) ranging from 10 to 40, where one kind of immobile zone, i.e., recirculation zones (RZs), are noticeably present and grow with Re . By fitting the analytical solution using the first order rate law to the numerically-derived concentration in RZs, we find that the first order rate law is applicable whenever RZs are noticeably present. Moreover, the mass transfer coefficient increases with Re , and decreases from upstream to downstream in the direction of fluid flow. Hence, the mass transfer coefficient should be precisely determined to accurately capture non-Fickian transport via the first order rate law.

Well-pattern optimization of CH4 transport associated with supercritical CO2 flooding

Injecting supercritical CO2 into depleted gas reservoirs enables additional CH4 to be extracted, a process known as CO2 enhanced gas recovery (CO2-EGR). Optimization of the well pattern is another method used to enhance gas reservoir exploitation. The focus of the present work is to address the arrangement of the well pattern when using CO2-EGR. For this purpose, mathematical models with five-spot and seven-spot well patterns are established in steady and unsteady conditions, and their results are validated against previously published models. For the first time, equipotential and streamline charts of the well pattern in CO2-EGR are derived from these models. As a result, the main flow channel of the well pattern is clarified, and the distributions of formation pressure and seepage velocity are determined. Moreover, the relationships between the gas production rate and well pattern parameters such as the producing pressure drop, permeability, formation pressure, temperature, and well spacing are investigated and the factors that influence the recovery ratio are examined. Finally, an optimization strategy for the well pattern parameters in CO2-EGR is proposed to enhance the gas production rate and recovery factor.

Porous geopolymer with controllable interconnected pores—a viable permeable reactive barrier filler for lead pollutant removal

Most of the commonly used traditional permeable reactive barrier (PRB) fillers have many drawbacks, such as poor retention of hydraulic conductivity, high cost, and a complex preparation process. Porous geopolymers (PGPs) with controllable pore structures could circumvent these drawbacks owing to their high adsorption capacity, cost-effective synthesis, and good chemical stability. In this study, based on our previous research, the “foaming-liquid film” balance control method was proposed and used to fabricate three PGPs with gradient pore connectivity. The influence of pore structure on the Pb2+ removal performance and migration mechanism were investigated by conducting both batch and column experiments. Closed, dead-end, capillary, and interconnected pores exist in the PGPs, and results indicated that interconnected pores effectively promote the migration of solute in the main flow channels to the deeper matrix, thereby enhancing the long-term dynamic removal efficiency. At breakthrough, the Pb2+ uptake of PGP-3 reached 146 mg g−1. Further, the proposed “foaming-liquid film” balance control method is effective to prepare PGPs with controllable connectivity, and the PGP-PRBs with a high proportion of interconnected pores exhibit excellent performance for the removal of heavy metals, which is advantageous for their future applications in groundwater decontamination.

Flow structures and circulation due to meandering geometry in a stratified sea strait

Combining with local topography (i.e., the presence of a bar or a sill on the bottom and the shape of the coastline), the meandering geometry of straits, which have more complex geomorphological formations compared to rivers, reveals different circulation patterns in the coastal region and central part of the strait. Identifying circulation patterns in meanders is crucial to managing those waterways in several aspects (i.e. monitoring the transport of contamination, wastewater outfall, etc.). In the present study, the flow circulations in some meanders of a strait (the Bosphorus), which presents a two-layered flow, are analyzed using the calibrated 3D model. Each of the four selected meanders has a unique shape: 1) expansion on both sides, 2) expansion on one side, 3) with a constant width, and 4) an estuary connected from one side.The results showed the decisive role of some characteristic morphological formations (i.e. headland, bars on the bottom, the shape of coastline) in creating reversing flow in a meander rather than adverse along channel pressure gradient due to the sudden expansion. While extreme water level differences between both entrances of the strait reveal unidirectional flow in the main channel, the reversals may develop in the shallowness of the meanders depending on the coastline shape (e.g. smoothness), presence of a local bar, and the presence of a headland. Besides this, in the case of a meander that has expansion at both sides, the flow separates from the main channel and circulates in opposite direction either clockwise or counterclockwise in the expanded sections. The annual flow profiles show a notable difference between the main channel and the coastal part of the meanders for a significant amount of time. For the low composite Froude numbers (G2) around or less than 0.3, the main channel flow is two-layered with the upper layer flowing south and the lower layer flowing north. In the shallowness of the expansions, however, it is unidirectional. For higher G2s (> 0.6), however, it is unidirectional both in the main channel and in the expansions of the meanders.

Analysis of Entropy Generation and Potential Inhibition in an Aeroengine System Environment

From a system perspective, the entropy generation of an aeroengine is directly related to the thermal efficiency when the Brayton cycle pressure ratio and maximum temperature remain constant. The lower the entropy generation of the engine is, the higher the thermal efficiency. However, the secondary air system of the engine generates a large quantity of entropy compared to the components of the main flow channel, because the irreversible losses of the internal flow and heat exchange between the air system components generate considerable entropy within the system. In this study, the theoretical method is used to build entropy generation model for different characteristics of air system components during the aerothermal process. In this basis, an integrated model of the whole engine is introduced to identify the key components for entropy generation in the system environment. The results show that the labyrinth at outlet of unloading cavity is recognized as the one that generates the most entropy in the entire aeroengine system, and the total entropy generation of the system is highly related to this component. Besides, in the system environment, entropy generation is the sum of the local entropy generated by the components and the total entropy generated by mixing of airflows in each component. High local entropy generated by components does not necessarily result in a high system entropy production, and vice versa. Therefore, when the minimum system entropy generation is the design goal, the most critical operations for entropy generation should be identified according to the corresponding sensitivity and parameter variation range, and the design should be improved accordingly.