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The magneto hydro-dynamic flows are of great importance in the industries such as food processing, power generation and in investigating the behavior of boundary layer convection. In this article, the magneto hydrodynamic flow of Newtonian fluid in rectangular cavity under the effect of applied magnetic filed is investigated. In the rectangular cavity, three semi circular cylinders are placed as obstacles to create unsteadiness in the flow path. Computational fluid dynamics model is built to analyze and observe the flow behavior in presence of 10 Ampere per meter. Furthermore, velocity profiles in vertical and horizontal directions, streamlines patterns, pressure distribution profile, vorticity profile, and viscous stress are presented. These profiles are discussed with and without the presence of strong magnetization force and flow behavior is investigated. The model is designed and compute in COMSOL-Multiphysics. It is concluded that presence of high magnetization force enhance the surface velocity to 1.87 m/s in horizontal direction and 0.86 m/s in vertical direction. Swirling flow pattern in streamlines increase with high magnetic force. The exerted pressure on wall of cavity has augmented to 2.39 Pa with increment in magnetic field. Moreover, obtained results are in complete agreement with already published work. [ABSTRACT FROM AUTHOR]

Feed spacers are incorporated in membrane modules to enhance fluid mixing, thereby enhancing membrane flux. Previous experimental work showed that triply periodic minimal surfaces (TPMS)-based spacers induce significant improvements in membrane distillation (MD) performance, which was attributed to the suppression of membrane boundary layer, reducing heat and mass transfer resistance. To corroborate those findings, in this study, we assess the performance of TPMS spacers in direct contact MD (DCMD) modules using computational fluid dynamics (CFD). Results showed that the Fischer-Koch S TPMS spacer topology achieved twice the flux of the empty channel case and exhibited a 13 % increment in flux compared to the net-type spacer, but this improvement was accompanied by a higher pressure drop in the feed channel. Therefore, a normalized power ratio (NPR) was used to evaluate the overall performance of spacers. For Reynold number (Re) ranging between 200 and 1200, Fischer-Koch S spacer had a 12 % improvement in NPR compared to the net-type spacer and resulted in higher shear stress near the membrane surface, indicating a promising mean for mitigating fouling in membrane distillation. This research highlights the importance of utilizing novel spacers in membrane distillation and showcases the power of CFD tools in optimizing the process. • CFD proves valuable in optimizing DCMD performance. • TPMS spacer enhances DCMD flux by improving fluid mixing. • Shear stress enhancement with Fischer-Koch S spacer can reduce membrane fouling. • Fischer-Koch S excels-2× flux vs. empty channel, 13 % increment over net-type. • Fischer-Koch S spacer shows 12 % NPR improvement over net-type at Re 200–1200. [ABSTRACT FROM AUTHOR]

This numerical study investigates the effect of CaCO 3 deposition on the performance of direct contact membrane distillation (DCMD). It is the first numerical study to directly evaluate the deposition and film thickness of CaCO 3 on the membrane surface. Therefore, a 3D computational fluid dynamics (CFD) model, which combines momentum, heat, species transport reaction, and the Eulerian wall film model, is used to analyze the CaCO 3 mass deposition rate and scaling deposition thickness on the membrane surface. HSC Chemical Software is used to evaluate the ion compositions and reaction kinetics, including the activation energy (E a) and pre-exponential factor (A r). The CFD model is validated with experimental results. The results reveal that the CaCO 3 deposition rate increases significantly at a high temperature, velocity, and salinity of the solution. The CaCO 3 mass deposition increased by 15 times and scaling deposition thickness increased from 0.05 nm to 1 nm when the temperature was raised from 318.15 K to 348.15 K, whereas an increase of approximately 25 % in deposition was observed with an increase in velocity from 0.17 to 1.38 m/s at a concentration of calcium (Ca+2) ions, 0.03 % and bicarbonate (HCO 3 −) ions 0.004 %. The results also indicate that CaCO 3 deposition decreases the flux and efficiency of the DCMD by 2 % with a low concentration of Ca+2 ions, 0.03 %, and HCO 3 − ions, 0.004 %. The findings indicate that the high feed salinity (75.23 g/l) increases CaCO 3 mass deposition and scaling deposition thickness on the membrane surface due to the high concentration of Ca+2 ions, 0.07 %, and HCO 3 − ions, 0.01 %, significantly reducing the permeate flux by 14 %. The study's model development and implementation can be adjusted to offer guidance for studying the MD process in treating high saline water with fouling issues. • CFD model is developed to evaluate CaCO 3 deposition on the membrane surface • A species transport reaction and Eulerian film models were utilized to evaluate the CaCO 3 deposition on DCMD. • HSC Chemical software evaluates the composition of ions and the Arrhenius constants (E a , and A r). • High feed salinity (75.23 g/l) gives high CaCO 3 deposition and reduces the flux by 14 %. • High temperature strongly affects the CaCO 3 deposition on the membrane surface compared to the high velocity. [ABSTRACT FROM AUTHOR]

Highlights • Two validated CFD models were developed to simulate FS and HF modules. • Two-level full factorial design and analysis tool was utilized. • Influence of four DCMD operating parameters were investigated. • FS membrane module showed better performance than the HF membrane module. • Flow in permeate channel is critical to enhance permeate flux in the HF module. Abstract The effects of select system parameters on the performance of direct contact membrane distillation (DCMD), in terms of permeate flux (J) and temperature polarization coefficient (TPC), were investigated and compared for flat-sheet (FS) and hollow-fiber (HF) modules. Three-dimensional (3D) computational fluid dynamics (CFD) models were developed and validated using experimental data. Then, a two-level full factorial design tool was used to design the simulation runs to investigate the effects of four selected process parameters on flux and TPC. These are: feed inlet temperature (T f), permeate inlet temperature (T p) and Reynolds number on the feed (Re f) and permeate (Re p) sides. The effect of each factor and the interactions thereof were assessed based on data obtained from the CFD models. Although all four parameters showed a significant influence on flux and TPC , their interactions had different effects on the HF and FS modules. For instance, since the permeate stream temperature increases much faster along the permeate channel in the HF module than in the FS module, Re p has a more substantial impact in the HF module. At higher Re p values, higher T f results in further enhancement in permeate flux in the HF module. Furthermore, the CFD model results indicate that the FS module generally showed better performance, in terms of permeate flux, than the HF module under the same DCMD process conditions. In the CFD model runs which yielded the highest flux in both HF and FS modules, the permeate outlet temperatures from the HF and FS modules were 21.72 °C and 18.53 °C, respectively, under the same operating conditions. Generally, the HF module exhibited about 21% lower flux than the FS module. [ABSTRACT FROM AUTHOR]

Abstract The critical factors and interactions which affect the module-level performance of permeate gap membrane distillation (PGMD) were investigated. A three-dimensional computational fluid dynamics (CFD) model was developed for the PGMD configuration, and the model was validated using experimental data. The realizable k- ε turbulence model was applied for the flow in the feed and coolant channels. A two-level full factorial design tool was utilized to plan additional simulation trials to examine the effects of four selected parameters (i.e., factors) on permeate flux and thermal efficiency, both of which represent performance indicators of PGMD. Permeate gap conductivity (k gap), permeate gap thickness (δ gap), module length (L module), and membrane distillation coefficient (B m) were the selected factors for the analysis. The effect of each factor and their interactions were evaluated. B m was found to be the most influential factor for both performance indicators, followed by k gap and δ gap. The factorial analysis indicated that the influence of each variable depends on its interactions with other factors. The effect of k gap was more significant for membranes with higher B m because the gap resistance becomes dominant at high B m. Similarly, δ gap is inversely proportional to the permeate flux and only significant for membranes with high B m. Highlights • A validated CFD model was developed to model PGMD configuration. • Realizable k- ε turbulence model was applied in the feed and permeate channels. • Two-level full factorial design and analysis tool was utilized. • Effect of four PGMD configuration parameters were investigated. • Membrane distillation coefficient has the most important effect on PGMD performance. [ABSTRACT FROM AUTHOR]

A two-dimensional computational fluid dynamics (CFD) model was developed and validated to estimate the liquid entry pressure (LEP) of hydrophobic membranes used for membrane distillation (MD). The volume of fluid (VOF) approach was employed to model the pore wetting process at pore-scale. As a result, the water/air interface could be identified at the pore entrance and then monitored through the pore in the course of gradually increased liquid water pressure at the feed side of the membrane. The contact angle ( θ ), pore length (L), pore entrance sharpness ( r s ) and pore throat geometry were studied for their effects on wetting using the CFD model. Additionally, the impact of applying permeate-side vacuum on the LEP was assessed, in comparison to feed-side-only trans-membrane pressure. An accurate LEP estimation with a high-resolution capillary effect monitoring strategy was achieved using the CFD tool. Pore throat geometry variation, θ , r s and L were all found to have a significant effect on LEP. Air-mixed layer formation was observed in the case of superhydrophobic membranes. Permeate-side vacuum resulted in earlier wetting, compared to atmospheric pressure outlet, but only for one pore geometry. The results of this work provide an insight for understanding the wetting progress through a membrane's micropore, enabling better mitigation of premature wetting in MD membranes. [ABSTRACT FROM AUTHOR]

Predicting the performance of a full-scale direct contact membrane distillation (DCMD) module based on experimental lab-scale results is rather difficult, since the DCMD performance is dependent on many different process parameters. Hence, there is a need for a methodology to perform DCMD system up-scaling based on lab-scale experimental results. In this study, we devise an approach to scale up the performance of DCMD systems by using the Buckingham's Pi theorem to group the DCMD process parameters into eight relevant dimensionless groups. Experimental data obtained from literature at various module dimensions were used to evaluate the developed dimensionless groups. An experimentally validated computational fluid dynamics (CFD) model was also developed and used to extend the coverage of operational parameters beyond the available experimental data. Then, two empirical dimensionless correlations were created, using multiple nonlinear regression analysis, and then validated, to enable the prediction of flux and pressure drop in DCMD systems at any scale. • Buckingham Pi-theorem used to model DCMD performance with dimensionless parameters. • DCMD process performance represented by eight dimensionless groups • Reliability of predicted relationships confirmed with experimental and CFD data. • Generated correlations predicted MD performance for small and large-scale modules. • Proposed approach can be extended to other MD configurations. [ABSTRACT FROM AUTHOR]

This study introduces and evaluates a novel Concentrated Photovoltaic (CPV)-assisted Direct Contact Membrane Distillation (DCMD) system, examining its efficiency and energy output under varying operational conditions. A Computational Fluid Dynamics (CFD) model, validated with experimental data, assesses the system's performance at different concentration ratios ranging from 1x to 10x and 25x to 100x, flow patterns (counterflow and parallel flow) at different Reynolds numbers (30–1200). This study investigates the seasonal performance of the CPV-DCMD system, providing valuable insights into its reliability and sustainability throughout the year. Results show increased mass flux and electric power with higher concentration ratios, especially at lower Reynolds numbers. In the counter-flow arrangement, the mass flux increases notably under specific conditions, while seasonal analysis reveals peak flux during summer and autumn afternoons. Electric power output follows a consistent trend across seasons, with high output observed during noon hours. The study demonstrates the system's energy efficiency, with notable energy gain compared to consumption across diverse operational conditions. Overall, the findings provide insights into optimizing the performance of CPV-assisted DCMD systems for sustainable energy generation and water desalination applications. • Introduction of a new design, unifying CPV and DCMD units into a single module. • CFD model analyzing parametric and seasonal performance of a CPV-assisted DCMD system. • Higher flux is gained with low flow/high CR due to solar heat absorption; high power gained at high flow. • In counter-flow, mass flux rises by 29 % at Re-60 and CR-10x due to high local delta T variations. • CPV-assisted DCMD system exhibits notably high energy gain versus consumption in all conditions. [ABSTRACT FROM AUTHOR]

Pore wetting phenomenon plays a critical role in a porous media and is critical in various processes. For instance, liquid entry pressure (LEP) is one of the critical characteristics of hydrophobic membranes used in membrane distillation (MD) processes. In this study, pore-scale models were developed to assess the accuracy of two multiphase flow computational fluid dynamics (CFD) methods, as modeling tools for predicting two-phase flow in microporous MD membranes. Finite element method (FEM)-based phase field (PF) method (which was applied in the COMSOL package) and finite volume method (FVM)-based volume of fluid (VOF) method (which was applied in Star-CCM+) were the selected CFD tools for the implementation. The boundary conditions of the models were first set based on the experimental procedure for measuring the LEP, as given in the literature. Then, the models were used to capture the LEP under the gradually increased water pressure. Critical tuning of CFD parameters of each tool (such as mesh size, mesh type, and interface thickness) was conducted to investigate their influence on the LEP prediction accuracy and the water/air interface representation at the pore entrance. CFD model results were presented and compared with both experimental LEP data and the calculated value using the Young-Laplace equation (YLE). Both CFD tools were capable of capturing the water/air interface. LEP result from the VOF model showed good agreement with the experimental data, but the PF model overestimated the LEP value closer to the theoretical YLE value. For both approaches, the adjustment of the interface thickness was critical. In the VOF method, a realistic interface thickness could be achieved by adjusting both mesh size and time step simultaneously. In contrast, PF simulations were less mesh sensitive. The accuracy of the VOF model was better due to its mass conservation condition at the interface. Unlabelled Image • PF and VOF methods are used to model two-phase flow along a hydrophobic pore. • The capabilities of two commercial codes are assessed on pore-scale. • VOF model results are in good agreement with the experimental data. • PF model deviates from experimental data due to its non-conservative structure. • Modeling pore wetting in membrane distillation is a key application. [ABSTRACT FROM AUTHOR]

The motivation of this computational research is to comprehensively analyze the performance of the air gap membrane distillation (AGMD) process by varying the membrane porosity at different inlet feed temperatures (T feed) in counter-current and co-current flow regimes. This computational study also includes the comparative study of different membrane materials with different porosities. In this research work, a detailed theoretical model for porous medium with phase change is formulated and presented to evaluate the permeate mass flux, heat flux, and evaporation efficiency of the AGMD technique. Additionally, a CFD numerical model is successfully developed and validated with the previously published data. The results reveal that high evaporation efficiency is achieved at about 90 %, 92 %, and 94 % with 90 % membrane porosity at different inlet feed temperatures of 50 °C, 60 °C, and 75 °C, respectively, in both flow regimes. Also, transported mass flux was enhanced by 43 % at T feed , 50 °C with high porosity, while it increased by 65 % at T feed , 75 °C. The AGMD thermal performance using PVDF and PTFE flat sheet membranes is comparable with the same membrane thickness and at the same porosity; however, PTFE offers relatively high evaporation efficiency and mass flux, especially at low inlet feed temperature (50 °C). • Numerical model is formulated for porous membranes with phase change. • Integrated CFD model with phase change in a porous medium is developed. • Model applied to air gap membrane distillation • High porosity and feed temperature promote high efficiency and permeate flux. • Membrane porosity dominated efficiency while feed temperature dominated mass flux. [ABSTRACT FROM AUTHOR]

In this paper, the hydrodynamics and wall-to-bed heat transfer of gas–solid flow in a conical fluidized bed were simulated using the Eulerian–Eulerian model. Sand with a diameter of 560 μm was used as bed material where its properties were calculated by applying the kinetic theory of granular flow (KTGF). Different amounts of slip between particle and wall were given by varying the specularity coefficient. The effect of different values of specularity coefficient (0, 0.2, 0.5, and 1.0) on hydrodynamic and wall-to-bed heat transfer at superficial gas velocity of 0.65 m/s was investigated. It was found that the wall-to-bed heat transfer coefficient decreases with increasing specularity coefficient. The specularity coefficient had no clear effect on the bed pressure drop. Different values of specularity coefficient resulted in almost the same hydrodynamic behavior near the wall and the center of bed. [ABSTRACT FROM AUTHOR]

Numerical simulations of conical fluidized bed combustors were carried out to estimate the effect of collision elasticity, parameterized by the particle-to-particle and particle-to-wall coefficients of restitution, upon the combustor’s hydrodynamics and heat transfer. The Eulerian–Eulerian two-fluid model was used to simulate the hydrodynamics and heat transfer in the combustor, and solid phase properties were calculated by applying the kinetic theory of granular flow (KTGF). Sand of size 560 μ m was used as a bed material and air was used as a fluidized gas, introduced at the velocity of 3 m/s at the combustor inlet. In the simulations, increasing the particle-to-particle restitution coefficient increased the bed pressure drop and caused significant changes to other hydrodynamics parameters. Oppositely increasing the particle-to-wall coefficient of restitution decreased the bed pressure drop. Changes to either the coefficients studied had little effect on heat transfer. [ABSTRACT FROM AUTHOR]

In recent decades, more emphasis has been given to produce clean energy from wastes and other renewable sources due to the rise in crude oil price and greenhouse gas emission. Fluidized bed combustors (FBC) are becoming the core of ‘clean wastes technology’ for power production, owing to their efficient and clean burning of coal and other solid fuels including biomass and other wastes, in an environment friendly manner with reduced pollutants. It is important to understand the mechanism of heat transfer and the effect of operating parameters on the heat transfer process for proper design of fluidized-bed reactors and for control the temperature at desired value. The scope of this paper is reviewing the heat transfer process in different types of fluidized bed combustors as well as the important operating conditions affecting the process. This paper covers both experimental and numerical studies related to the heat transfer process in different types of fluidized bed combustors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Analytical model integrated with CFD model is developed for EMF-DCMD process. • EMF would eliminate the need for increasing the feed velocity to promote turbulence. • EMF promoted the feed turbulence that significantly improved DCMD performance. • DCMD Electro-thermo-fluid model is successfully developed and validated experimentally. • EMF depicted a significant impact on the feed turbulence and a slight thermal impact. Using an advanced CFD model, this study attempts to determine how electromagnetic field (EMF) affects the performance of the direct contact membrane distillation (DCMD) process. The influence of electromagnetic fields (EMF) on the permeate flow, evaporation efficiency (EE), and temperature polarization coefficient (TPC) of the DCMD process are studied using a thorough theoretical model linked with a CFD model. Experiments conducted in-house with and without the EMF influence are used to verify the CFD model. High magnetic potency propagates the turbulence in the feed channel, hence boosting the driving force and transport phenomena for vapor transport to the permeate side. Permeate flux increased by 30%, and EE increased by 15% when the magnetic field strength was raised from 0 to 0.5 T, particularly at a lower intake feed velocity (0.02 m/s) and temperature of 333.05 K. In contrast, with the same magnetic potency (0.5 T) at a higher velocity at an input feed temperature, there is less improvement in EE (5%) and permeate flux (12%) due to the elevated turbulence intensity at high feed velocity. This research contributes to studies aimed at elucidating how electromagnetic fields affect separation processes such as MD, opening the door for more tuning and use of the fascinating phenomenon. [ABSTRACT FROM AUTHOR]

Wetting phenomenon inside the pore is a significant obstacle hindering membrane distillation (MD) from being fully industrialized. Herein, a new equation is provided for the users, using the combination of computational fluid dynamics (CFD) and genetic programming (GP) tools for estimation of liquid entry pressure (LEP), a parameter closely related to pore wetting. CFD was applied to model the wetting process inside the pore during the gradual increase in feed pressure at different scenarios in which contact angle, pore radius and membrane thickness were changed. Afterwards, GP as an intelligent method was employed to provide a computer program estimating LEP in the whole ranges in which CFD modeling was carried out. Moreover, validation was done using experimental data and then the influence of effective parameters on LEP was studied. This work provides an explicit formula for estimation of LEP in a closer agreement with the experimental data in comparison to the Young-Laplace equation. In addition, the influence of the membrane thickness was added to the equation, providing a more realistic formula for LEP estimation. Unlabelled Image • A CFD-GP model was presented for estimating LEP, considering the thickness of membrane. • The model provided an explicit formula for estimation of LEP. • The influence of effective parameters on LEP was studied using the developed model. [ABSTRACT FROM AUTHOR]