Solid Mass Transfer Research Articles

Measuring the liquid-solid mass transfer coefficient in packed beds using [formula omitted] relaxation exchange NMR

Direct measurement of the liquid–solid mass transfer coefficient in packed beds is achieved using T2-T2 relaxation exchange NMR. This method directly probes molecular exchange between intra- and inter-pellet fluid, rather than requiring a net flux between phases as in conventional methods. Mass transfer coefficients measured using the NMR method are compared with literature values and two widely used correlations. For Reynolds number, Re, less than 0.2, the mass transfer coefficients measured using NMR show excellent agreement with the correlations over the flow conditions for which they were developed. The approach also enables the quantification of mass transfer in the limit of, and at, zero flow. At Re= 0, the Sherwood number in packed beds with voidage of 0.41 determined by NMR is found to approach 9, in good agreement with previously reported results, but significantly greater than that predicted by extrapolating well-known correlations beyond their range of validity to Re= 0.

Leloir glycosyltransferases enabled to flow synthesis: Continuous production of the natural C-glycoside nothofagin.

C‐glycosyltransferase (CGT) and sucrose synthase (SuSy), each fused to the cationic binding module Z basic2, were co‐immobilized on anionic carrier (ReliSorb SP400) and assessed for continuous production of the natural C‐glycoside nothofagin. The overall reaction was 3ʹ‐C‐β‐glycosylation of the polyphenol phloretin from uridine 5ʹ‐diphosphate (UDP)‐glucose that was released in situ from sucrose and UDP. Using solid catalyst optimized for total (∼28 mg/g) as well as relative protein loading (CGT/SuSy = ∼1) and assembled into a packed bed (1 ml), we demonstrate flow synthesis of nothofagin (up to 52 mg/ml; 120 mM) from phloretin (≥95% conversion) solubilized by inclusion complexation in hydroxypropyl β‐cyclodextrin. About 1.8 g nothofagin (90 ml; 12–26 mg/ml) were produced continuously over 90 reactor cycles (2.3 h/cycle) with a space‐time yield of approximately 11 mg/(ml h) and a total enzyme turnover number of up to 2.9 × 103 mg/mg (=3.8 × 105 mol/mol). The co‐immobilized enzymes exhibited useful effectiveness (∼40% of the enzymes in solution), with limitations on the conversion rate arising partly from external liquid–solid mass transfer of UDP under packed‐bed flow conditions. The operational half‐life of the catalyst (∼200 h; 30°C) was governed by the binding stability of the glycosyltransferases (≤35% loss of activity) on the solid carrier. Collectively, the current study shows integrated process technology for flow synthesis with co‐immobilized sugar nucleotide‐dependent glycosyltransferases, using efficient glycosylation from sucrose via the internally recycled UDP‐glucose. This provides a basis from engineering science to promote glycosyltransferase applications for natural product glycosides and oligosaccharides.

A Fundamental Investigation of Gas/Solid Heat and Mass Transfer in Structured Catalysts Based on Periodic Open Cellular Structures (POCS).

In this work, we investigate the gas–solid heat and mass transfer in catalytically activated periodic open cellular structures, which are considered a promising solution for intensification of catalytic processes limited by external transport, aiming at the derivation of suitable correlations. Computational fluid dynamics is employed to investigate the Tetrakaidekahedral and Diamond lattice structures. The influence of the morphological features and flow conditions on the external transport properties is assessed. The strut diameter is an adequate characteristic length for the formulation of heat and mass transfer correlations; accordingly, a power-law dependence of the Sherwood number to the Reynolds number between 0.33 and 0.67 was found according to the flow regimes in the range 1–128 of the Reynolds number. An additional −1.5-order dependence on the porosity is found. The formulated correlations are in good agreement with the simulation results and allow for the accurate evaluation of the external transfer coefficients for POCS.

Study of Liquid-Solid Mass Transfer and Hydrodynamics in Micropacked Bed with Gas-Liquid Flow.

The volumetric liquid–solid (L-S) mass transfer coefficient under gas–liquid (G-L) two-phase flow in a silicon-chip-based micropacked bed reactor (MPBR) was studied using the copper dissolution method and was related to the reactor hydrodynamic behavior. Using a high-speed camera and a robust computational image analysis method that selectively analyzed the bed voidage around the copper particles, the observed hydrodynamics were directly related to the L-S mass transfer rates in the MPBR. This hydrodynamic study revealed different pulsing structures inside the packed copper bed depending on the flow patterns established preceding the packed bed upon increasing gas velocity. A “liquid-dominated slug” flow regime was associated with an upstream slug flow feed. A “sparse slug” flow regime developed with an upstream slug-annular flow feed. At higher gas velocity, a “gas continuous with pulsing” regime developed with an annular flow feed, which had similar features to the pulsing flow in macroscale packed beds, but it was sensitive and easily destabilized by disturbances from upstream or downstream pressure fluctuations. The volumetric L-S mass transfer coefficient decreased with increasing gas velocity under the liquid-dominated slug flow regime and became rather less affected under the sparse slug flow regime. By resolving the transition from the liquid-dominated slug flow to the sparse slug flow and capturing the onset of the gas-continuous with pulsing regime, we gained new insights into the hydrodynamic effects of G-L flows on the L-S mass transfer rates in a MPBR.

A comprehensive two-phase proton exchange membrane fuel cell model coupled with anisotropic properties and mechanical deformation of the gas diffusion layer

Adequate mechanical compression applied to a proton exchange membrane fuel cell is essential for enhancing performance and durability. The compression not only improves the intimate contact between each layer component, but also causes significant deformation of the gas diffusion layer (GDL). As a result, the level of compression results in changes of electrical and thermal contact resistances, and anisotropic distribution of porosity and tortuosity in the GDL. To improve the fundamental understanding of the compression effect, a comprehensive two-phase model coupling solid mechanics, heat and mass transfer, and electrochemical reactions is developed. First, the model results are validated and show good agreement with the experimental data at baseline operating conditions of 80 °C, 200 kPa, 80% relative humidity, and 20% compression strain ratio with hydrogen and air. Then, oxygen, temperature and liquid saturation distribution at low, intermediate and high current densities are studied at the baseline compression level (20% strain). Finally, five compression strain ratios ranging from 5%, 10%, 15%, 20% and 25% are investigated to study the effect on stress distribution, transport properties, and fuel cell performance. Our results indicate that significant GDL deformation and channel intrusion are caused by land and rib distribution. As a combined effect from heat and mass transport, the liquid water condensation tends to initiate near the rib/GDL interface and can reach near 30% saturation at high current density. In addition, significant difference of in-plane temperature, oxygen, current, and load distributions can be observed due to the geometric aspect ratio and anisotropic GDL properties. A compression strain ratio of 20% is found to have an optimal performance balancing between high contact resistance caused by low compression and high transport resistance due to high compression. The findings of this study provide a new insight to the understanding the complicated coupling effect between mechanical, thermal, mass transport, and electrochemical multiphysics.

Liquid–Solid Mass Transfer in Adsorption Systems—An Overlooked Resistance?

In liquid-solid adsorption, fluid film diffusion is typically faster than intraparticle diffusion, especially for microporous adsorbents. However, fluid film diffusion might play a significant role in the overall rate of the process for mesoporous-macroporous and non-porous solids. In most adsorption modeling studies, the fluid film diffusion step is typically ignored, which is not always justified. This article critically discusses the theory behind the liquid-solid mass-transfer coefficient in stirred vessels and presents the dissolution and adsorption methods adopted for estimating its value. Then, starting from the definition of the Biot number, an original analysis is developed with reference to selected studies. Surface versus pore diffusion of the adsorbate in the adsorbent is taken into account, and external versus internal mass-transfer resistance is considered to put the fluid film resistance back in the picture when needed. Iso-Biot charts where the operating points can be visualized are presented as well.

Thermodynamic and mathematical analysis of modified Luikov's equations for simultaneous heat and mass transfer

Interface thermodynamic and mathematical analysis of modified Luikov equations (MLEs) for simultaneous heat and mass transfer in solids were developed. The thermodynamic relations at interface show that air-(wet solid) equilibrium relation may be mathematically approximated by two linear segments. These linear relations conduced to the possibility that MLEs have analytical solution for 1D rectangular, 1D radial cylindrical and 1D radial spherical coordinates system; and, the existence of a topology between solutions. The implications of MLEs thermodynamic and mathematical analysis on lumped equations were discussed. Experimental evolution of moisture and temperature during potato drying were compared with MLEs analytical (for one single linear stage at interface) and numerical (for the 2 linear stages) solutions.

Vacuum pressure swing adsorption process for coalbed methane enrichment

The enrichment of low concentration coalbed methane using adsorption process with activated carbon adsorbent was studied in this work. Adsorption isotherms of methane, nitrogen and carbon dioxide on activated carbon were measured by volumetric method, meanwhile a series of breakthrough tests with single component, binary components and three components feed mixture has been performed for exploring dynamic adsorption behaviors. Moreover, a rigorous mathematical model of adsorption bed containing mass, energy, and momentum conservation equation as well as dual-site Langmuir model with the Linear driving force model for gas–solid phase mass transfer has been proposed for numerical modeling and simulation of fixed bed breakthrough process and vacuum pressure swing adsorption process. Furthermore, the lumped mass transfer coefficient of methane, nitrogen and carbon dioxide on activated carbon adsorbent has been determined to be 0.3 s −1 , 1.0 s −1 and 0.06 s −1 by fitting the breakthrough curves using numerical calculation. Additionally, a six bed VPSA process with twelve step cycle sequence has been proposed and investigated for low concentration coalbed methane enrichment. Results demonstrated that the methane molar fraction in feed mixture ranged from 10% to 50% could be enriched to 32.15% to 88.75% methane in heavy product gas with a methane recovery higher than 83% under the adsorption pressure of 3 bar (1 bar = 10 5 Pa) and desorption pressure of 0.1 bar. Energy consumption of this VPSA process was varied from 0.165 kW·h·m − 3 CH 4 to 0.649 kW·h·m − 3 CH 4 . Finally, a dual-stage VPSA process has been successfully developed to upgrade a low concentration coalbed methane containing 20% methane to a target product gas with methane purity higher than 90%, meanwhile the total methane recovery was up to 98.71% with a total energy consumption of 0.504 kW·h·m − 3 CH 4 .

Liquid-solid mass transfer in a rotating packed bed reactor with structured foam packing

A rotating packed bed (RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid–solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid–solid mass transfer coefficient (kLS) have been investigated. The correlation for predicting kLS was proposed, and the deviation between the experimental and predicted values was within ± 12%. The liquid–solid volumetric mass transfer coefficient (kLSaLS) ranged from 0.04–0.14 1−1, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.

Experimental and modeling studies on the Ru/C catalyzed levulinic acid hydrogenation to γ-valerolactone in packed bed microreactors

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was performed in perfluoroalkoxy alkane capillary microreactors packed with a carbon-supported ruthenium (Ru/C) catalyst with an average particle diameter of 0.3 or 0.45 mm. The reaction was executed under an upstream gas–liquid slug flow with 1,4-dioxane as the solvent and H2 as the hydrogen donor in the gas phase. Operating conditions (i.e., flow rate and gas to liquid flow ratio, pressure, temperature and catalyst particle size) were varied in the microreactor to determine the influence of mass transfer and kinetic characteristics on the reaction performance. At 130 °C, 12 bar H2 and a weight hourly space velocity of the liquid feed (WHSV) of 3.0 gfeed/(gcat·h), 100% LA conversion and 84% GVL yield were obtained. Under the conditions tested (70–130 °C and 9–15 bar) the reaction rate was affected by mass transfer, given the notable effect of the mixture flow rate and catalyst particle size on the LA conversion and GVL yield at a certain WHSV. A microreactor model was developed by considering gas–liquid–solid mass transfer therein and the reaction kinetics estimated from the literature correlations and data. This model well describes the measured LA conversion for varying operating conditions, provided that the internal diffusion and kinetic rates were not considered rate limiting. Liquid–solid mass transfer of hydrogen towards the external catalyst surface was thus found dominant in most experiments. The developed model can aid in the further optimization of the Ru/C catalyzed levulinic acid hydrogenation in packed bed microreactors.

Influences of top clearance and liquid throughput on the performances of an external loop airlift slurry reactor integrated mixing and separation

Abstract A new developed external loop airlift slurry reactor, which was integrated with gas–liquid–solid three-phase mixing, mass transfer, and liquid–solid separation simultaneously, was deemed to be a promising slurry reactor due to its prominent advantages such as achieving continuous separation of clear liquid from slurry and cyclic utilization of solid particles without any extra energy, energy-saving, and intrinsic safety design. The principal operating parameters, including gas separator volume, handling capacity, and superficial gas velocity, are systematically investigated here to promote the capabilities of mixing, mass transfer, and yield in the pilot external loop airlift slurry reactor. The influences of top clearance and throughput of the clear liquid on flow regime and gas holdup in the riser, liquid circulating velocity, and volumetric mass transfer coefficient with a typical high solid holdup and free of particles are examined experimentally. It was found that increasing the gas separator volume could promote the liquid circulating velocity by about 14.0% at most. Increasing the handling capacity of the clear liquid from 0.9 m3·h−1 to 3.0 m3·h−1 not only could increase the output without any adverse consequences, but also could enhance the liquid circulating velocity as much as 97.3%. Typical operating conditions investigated here can provide some necessary data and guidelines for this new external loop airlift slurry reactor to upgrade its performances.

Study on Loose-Coupling Methods for Aircraft Thermal Anti-Icing System

To simulate aircraft thermal anti-icing systems and solve the conjugate heat transfer of air-droplet flow and solid skin, the heat and mass transfer model of the runback water on the anti-icing surface was combined with the heat conduction equation of the skin by loosely coupled methods. According to the boundary conditions used for the runback water conservation equations, two loose-coupling methods for the heat exchange between the runback water and the solid skin were developed based on surface heat flow and surface temperature, respectively. The anti-icing and ice accretion results of a NACA 0012 electro-thermal anti-icing system were obtained by the two loose-coupling methods. The heat flow-based method directly solves the thermodynamic model of the runback water without any extra assumptions, but the convergence rate is relatively slow. On the other hand, the temperature-based method achieves higher calculation speed, but the freezing point is extended to an artificial temperature range between water and ice phases. When the value of the artificial temperature range is small, the results obtained by the temperature-based method are consistent with those of the heat flow-based method, indicating that the effect of freezing point extension can be ignored for thermal anti-icing simulation. Furthermore, the solutions of the two methods are in acceptable and comparable agreement with the experimental and simulative results in the literature, confirming their feasibility and effectiveness. In addition, it is found that the ice thicknesses and ice shapes rise obviously near the runback water limits as a result of the transverse heat conduction of the solid skin.

Modeling and Optimization for Gas Distribution Patterns on Biomass Gasification Performance of a Bubbling Spout Fluidized Bed

Gas distribution patterns exert a great impact on the gas–solid flow, heat and mass transfer, and reaction characteristics and thus affect significantly the thermal conversion efficiency inside the...

Selection of suitable model for the supercritical fluid extraction of carrot seed oil: A parametric study

To investigate suitable model for supercritical fluid extraction of carrot seed oil, different mathematical models are selected from literature and solved using COMSOL Multiphysics software. Operating parameters such as pressure, temperature, solvent flow rate, and addition of co-solvent are varied in ranges as 200–400 bar, 50–70 °C, 5–15 g/min, and 0–10 wt%, respectively. Solvent and solid phase mass transfer coefficients, easily accessible oil content and equilibrium constant are considered as tuning parameters to fit the model with experimental data. Oil yield is increased with pressure (400 bar) and temperature (70 °C) whereas, its value is highest at the solvent flow rate of 10 g/min, and co-solvent of 5 wt%. Thus, these values of parameters are considered as optimum points.

Experimental investigation of hydrodynamics and chromium(VI) adsorption in continuous countercurrent fluidized column

Continuous countercurrent fluidized column is fabricated to study the hydrodynamics and mass transfer of chromium(VI) ion from chromium aqueous solution to activated carbon. Hydrodynamics studies including pressure drop, holdup, and the flow pattern are studied. Batch adsorption studies are conducted to find the equilibrium time and effect of mass of adsorbent. Maximum percentage removal is obtained at maximum flow rates of water (1.42 cm/s) and solid particles (24.6 g/s) from the range of parameters studied in this work. For a given water velocity, the total pressure drop linearly increases along the length of the column because of the increase in frictional loss. Also, with an increase in water velocity, the solid holdup increases in the column. The percentage removal of chromium(VI) increased up to 60% along the length of the column because of the increased contact time between the adsorbent and the adsorbate. An empirical correlation is proposed to predict the solid holdup and mass transfer coefficient.

Coarse-grained CFD-DEM simulation of biomass gasification in a fluidized bed reactor

Gas-solid fluidized beds play an important role in many industrial operations. However, there still is a lack of knowledge concerning the processes inside the bed, which impedes proper designing and upscaling of fluidized bed reactors. In this work, biomass steam gasification in a fluidized bed reactor is investigated with a coarse-grained CFD-DEM approach.The numerical model in the Eulerian-Lagrangian framework treats the gas phase as a continuum and describes the particle interactions with the discrete element method (DEM). The non-spherical shape of the particles is accounted for in the momentum exchange calculation with the gas phase. The considered systems consist of steam as the fluidization gas, entering the bottom region of the three dimensional reactor geometry through inclined nozzles in an inner duct at the center axis. The wood pellets are fed into the reactor from the top of the freeboard together with a nitrogen purge gas stream. Over time, different operation modes occur, since there is no solids removal from the gasifier and unconverted material is continuously added to the bed.Three different operation modes are investigated. For the start-up procedure, the reactor is filled with 2.565 kg of sand particles. The inert material is allowed to settle for three seconds and is fluidized for another three seconds until quasi steady-state is achieved. Afterwards, the wood pellets are added for 35 s at a rate of one pellet every two seconds and undergo the processes of heating, drying, pyrolysis and char conversion. From the simulation results and literature correlations, the average time intervals for pyrolysis and char conversion, as well as the respective particle properties (temperature, diameter, density) are estimated. With the knowledge of the average composition of reactive material in the reactor, variable operating points can be simulated.The other two cases investigated are after approximately 20 and 50 h of operating time. Additionally to the start-up procedure, 0.6 and 1.5 kg of inert residue are added to the sand particles. Again, the inert material is allowed to settle for three seconds and is fluidized for another three seconds. Subsequently, the average reactive material obtained from the start-up simulations is patched into the fluidized bed and wood pellets are fed to the freeboard.The following phenomena are implemented in the numerical model: gas-solid momentum exchange, solids collisional behavior, heat and mass transfer, particle shrinkage and change in material properties, pyrolysis, as well as homogeneous and heterogeneous chemical reactions.Simulation results are analyzed both qualitatively and quantitatively. The particle flow fields and the mixing between sand, residue, and wood are investigated for different fillings of the reactor. Bed pressure drop, product gas composition, and temperature are compared to experimental data in order to validate the numerical model.The results show, that the bed pressure drop, the gas composition, and the conversion time obtained with the numerical simulation agree well with experimental observations and literature correlations. This indicates that the proposed model can make a significant contribution towards understanding and improving the internal processes in fluidized bed reactors for biomass gasification and combustion.

Migration behaviors and kinetics of phosphorus during coal-based reduction of high-phosphorus oolitic iron ore

To understand the migration mechanisms of phosphorus (P) during coal-based reduction, a high-phosphorus oolitic iron ore was reduced by coal under various experimental conditions. The migration characteristics and kinetics of P were investigated by a field-emission electron probe microanalyzer (FE-EPMA) and using the basic principle of solid phase mass transfer, respectively. Experimental results showed that the P transferred from the slag to the metallic phase during reduction, and the migration process could be divided into three stages: phosphorus diffusing from the slag to the metallic interface, the formation of Fe-P compounds at the slag-metal interface and P diffusing from the slag-metal interface to the metallic interior. The reduction time and temperature significantly influenced the phosphorus content of the metallic and slag phases. The P content of the metallic phase increased with increasing reduction time and temperature, while that of the slag phase gradually decreased. The P diffusion constant and activation energy were determined and a migration kinetics model of P in coal-based reduction was proposed. P diffusion in the metallic phase was the controlling step of the P migration.

Improved Gas–Solids Mass Transfer in Fluidized Beds: Confined Fluidization in Chemical-Looping Combustion

© 2019 American Chemical Society. Fluidized bed processes with reactive bed material have become increasingly popular as research topics, with applications such as chemical-looping technologies, oxygen carrier aided combustion, and fluidized bed gasification being extensively investigated. When used at commercial scale the performance of such processes may be limited not by gas-solid reactivity, but by mass transfer of reactants from bubbles to the emulsion phase. In an effort to break down the two-phase flow structure, and thereby increase the bubble-emulsion mass transfer coefficient, spherical packing material was added to a fluidized bed using ilmenite as bed material. Two types of packing were tested: expanded clay aggregate (ECA) and aluminum silicate balls (ASB). Both packings had a diameter of about 12 mm but drastically different bulk densities of 240 kg/m 3 and 1400 kg/m 3 , respectively. These were tested in chemical-looping-combustion batch experiments using a stainless-steel reactor with a diameter of 78 mm, with syngas or carbon monoxide as fuel at 915 °C. The lighter packing formed a floating plug while the heavier remained stationary at the reactor bottom. To compare the confined fluidized bed to a reference conventional one, a simple reaction model was implemented based on the experiments. It showed that in the confined fluidized bed the associated effective reaction rate constant increased by up to a factor of 2 for a given bed mass. Further, up to 4 times less oxygen carrier bed mass was needed to achieve the same gas conversion, at a lower total pressure drop. Experiments with only carbon monoxide showed similar gains when using aluminum silicate balls, indicating that catalysis of the water gas shift reaction was not the main factor for improved gas conversion. It can be concluded that the concept of confined fluidization has great potential to increase mass transfer in fluidized beds with active bed material.

Millimeter-Wave Gyrotron System for Research and Application Development. Part 2. High-Temperature Processes in Polycrystalline Dielectric Materials

Gyrotron systems operated at frequencies of 24 to 30 GHz with an output power of 3 to 15 kW have been used at the Institute of Applied Physics of the Russian Academy of Sciences for more than 20 years for the studies of high-temperature processes in polycrystalline dielectric materials under intense electromagnetic irradiation. The research has mostly been focused on the study of the physically specific features of diffusive mass transfer in solids and on the possible use of these features for applications. A distinguishing feature of the studied processes is a significant enhancement of their rates compared to similar processes performed with the use of conventional heating methods. Examples of enhanced sintering of a broad range of ceramic materials, including optical and laser ceramics and composition-graded metal–ceramic products are considered. The principles of the developed method of ultrafast sintering of oxide ceramics with rates exceeding those typical of the conventional methods by two or three orders of magnitude are described. The development of this method has resulted from a purposeful use of the functional capabilities of the gyrotron systems and the engineering solutions implemented therein.

Increasing Gas–Solids Mass Transfer in Fluidized Beds by Application of Confined Fluidization—A Feasibility Study

Fluidized bed applications where the bed material plays an active role in chemical reactions, e.g. chemical looping combustion, have seen an increase in interest over the past decade. When these processes are to be scaled up to industrial or utility scale mass transfer between the gas and solids phases can become a limitation for conversion. Confined fluidized beds were conceptualized for other purposes in the 1960’s but are yet to be applied to these recent technologies. Here it is investigated if they can prove useful to increase mass transfer but also if they are feasible from other perspectives such as pressure drop increase and solids throughflow. Four spherical packing solids, 6.35–25.4 mm in diameter at two different densities, were tested. For mass transfer experiments the fluidizing air was humidified and the water adsorption rate onto silica gel particles acting as fluidizing solids was measured. Olivine sand was used in further experiments measuring segregation of solids and packing, and maximum vertical crossflow of solids. It was found that mass transfer increased by a factor of 1.9–3.8 with packing solids as compared to a non-packed reference. With high-density packing, fluidizing solids voidage inside the packing was found to be up to 58% higher than in a conventional fluidized bed. Low density packing material favoured its flotsam segregation and with it higher fluidization velocities yield better mixing between packing and fluidizing solids. Maximum vertical cross-flow was found to be significantly higher with low density packing that fluidized, than with stationary high-density packing. Conclusively, the prospect of using confined fluidized beds for improving mass transfer looks promising from both performance and practical standpoints.