Effect Of Flow Configuration Research Articles

Assessment of ultrasound-assisted forward osmosis process performance for seawater desalination using experimental factorial design

The effect of ultrasound on water flux through forward osmosis membrane for seawater desalination was investigated using the factorial design approach. Sodium chloride (NaCl) was used to simulate the dissolved solids content. In every test, the initial draw solution (DS) concentration was fixed at 4.5 M for NaCl and 2 M for MgCl2. Parameters considered in the investigation included membrane crossflow velocity (0.25 and 1.0 cm/s), flow configuration (co-current versus counter-current), direction of ultrasound waves relative to the membrane side (active layer versus support layer), and type of draw solution (NaCl versus MgCl2). A two-level factorial design was considered in the analysis of the results obtained from the experimental work. Based on the factorial design analysis, crossflow velocity and use of ultrasound have a positive effect on water flux enhancement for both draw solutions. However, the velocity effect on water flux enhancement was more pronounced than that of the use of ultrasound. The effect of flow configuration was statistically insignificant for both draw solutions. The interaction effect between crossflow velocity and ultrasound was statistically significant for both draw solutions. However, the interaction between crossflow velocity and flow configuration was only significant for the case of MgCl2. The three-way interaction was insignificant for both draw solutions. The developed factorial model equations were used to predict other flux data in ultrasound-assisted FO systems and showed adequate representation of these data at relatively similar conditions after adjustment of the model for the baseline conditions of the evaluated cases.

Studies on the effect of flow configuration on the temperature distribution and performance in a high current density region of solid oxide fuel cell

• Three different flow configurations of solid oxide fuel cell have been compared. • The temperature distribution at 6000 A/m 2 were analyzed. • In counter-flow, the most uniform temperature distribution was formed. • The power density is 5% higher in counter-flow than the other configurations. • Counter-flow presents the best efficiency of up to 3.35%. The effect of temperature distribution on the performance of solid oxide fuel cells (SOFCs) is analyzed for various channel designs in a high current density region. By considering heat accumulation due to local electrochemical reactions and cooling due to flow patterns, the heat distributions in three flow configurations (co-flow, counter-flow, and cross-flow) are analyzed, with the most appropriate channel in the high power region selected. The average operating temperature of the cell is the highest for the counter-flow configuration and the lowest for co-flow. The temperature of the counter-flow configuration is approximately 10 K higher than that of co-flow. The temperature distribution of counter-flow configuration, however, is the most uniform among different flow patterns. The maximum temperature difference in the counter-flow channel is approximately 8 K, but that in co-flow is approximately 22 K. Furthermore, the performance of the cell using the counter-flow configuration is the best in that it shows 5% higher power density and 3.35% higher system efficiency than the other flow configurations. Therefore, the counter-flow configuration is superior at high power because it has the lowest temperature gradient and the best cell performance. This paper contributes to the commercialization of the fuel cell by presenting appropriate parameters for temperature regulation and suitable flow configuration for operation at high power.

Effects of Contact Time and Flow Configuration on the Acid Mine Drainage Remediation Capabilities of Pervious Concrete

This paper investigates the Acid Mine Drainage (AMD) remediation capabilities of pozzolanic pervious concrete Permeable Reactive Barriers (PRBs) with a specific focus on the effects of flow configuration and contact time on the remediation efficiency. Raw AMD was collected from an abandoned coal mine. Two flow configurations, gravity flow and column flow, were tested at a laboratory scale with gradually increasing contact times. The gravity flow configuration with two orders of magnitude less liquid-concrete contact time achieved AMD treated water quality equivalent to the high retention column flow configuration. Concentrations of iron, aluminium, sulphate, magnesium and sodium were reduced by more than 99%, 80%, 17%, 22% and 20%, respectively, at the tested limits while calcium and potassium concentrations were increased by up to 16% and 300%, respectively. The study findings indicate that the lifecycle costs of pervious concrete PRBs can be significantly reduced when the PRBs are operated under gravity flow.

Effect of Flow Configuration on Nitrifiers in Biological Activated Carbon Filters for Potable Water Production.

Up-flow biological activated carbon (BAC) filters have been empirically employed in drinking water treatment plants (DWTPs) to address the challenges of its down-flow counterparts (e.g., high head loss and insufficient use of BAC beds), yet their performances and mechanisms toward ammonia removal are not fully evaluated. This study characterized the occurrence, distribution, and diversities of nitrifiers in up-flow and down-flow BAC filters by investigating 18 full-scale drinking water treatment trains in different geographic locations. Quantitative polymerase chain reaction analysis of gene markers of target microorganisms demonstrated higher numbers of total bacteria, ammonia-oxidizing bacteria (AOB), and Nitrospira in the up-flow filters relative to the down-flow filters (P < 0.05), implying enhanced biological activities and nitrification potential within up-flow filters. The dominance of ammonia-oxidizing archaea (AOA) over AOB (i.e., 1.3-4.0 log10 gene copies higher) in 17 BAC filters illustrated the critical role of AOA in drinking water nitrification. Stratification of biomass was mainly found in the down-flow filters rather than the up-flow filters, suggesting better mixing of filter media across up-flow filter beds. Analysis of similarity results revealed that the AOA and Nitrospira community compositions were mainly affected by water sources and locations (P < 0.05) but not flow configurations. These results provide insight into nitrification mechanisms in BAC filters with different flow configurations in real-world DWTPs.

Experiments on a novel membrane-based liquid desiccant dehumidifier for hybrid air conditioner

A novel membrane dehumidifier is proposed for hybrid air conditioning system for which investigations are carried out for hot and humid climatic conditions. With separate cooling arrangements for air and desiccant, efficient control of both temperature and specific humidity is possible. In the present study, the effects of flow configurations, and operating parameters of air, cooling water and desiccant on the performance of the dehumidifier are investigated. The performance is presented in terms of moisture removal rate, and sensible, latent and total effectiveness. The configuration with cooling water flow in parallel and counter to air and desiccant respectively is found to be optimum for the dehumidifier. It is also found that the sensible effectiveness of the dehumidifier is independent of the changes in the operating parameters of desiccant.

Effect of flow configuration on the performance of spiral-wound heat exchanger

The effects of flow configuration on the heat transfer performance of a spiral wound heat exchanger were experimentally investigated. The spiral-wound heat exchanger was made from stainless steel tubes of 6 mm outside diameter and consisted of 4 helical coils centrally connected in series, with a longitudinal and transverse pitch of 12 mm. Three air flow configurations were tested, namely axial, radial, and mixed axial-radial flows. The overall heat transfer coefficient was determined from the experimental data and the shell-side convection heat transfer coefficient was calculated from the tube-side convection heat transfer coefficient and the total thermal resistance. The measurements were conducted for tube-side Reynolds number in the range of 9000–10,000 (for water flow inside the tubes) and shell-side Reynolds number in the range of 500–6000 (for air flow outside the tubes based on maximum velocity). The results showed that the mixed axial-radial flow configuration has the highest heat transfer coefficient and pressure drop followed by the axial and radial flow configurations. Correlations of Nusselt number, Colburn-j factor, and friction factor were developed for the different flow configurations and a comparison with the Nusselt number correlations for heat transfer over bank of tubes was presented. The correlations are in good agreement with experimental data and has correlation coefficient in the range of 78–98%.

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

Effect of Design Parameters on the Internal Steam Reforming of Methane in Solid Oxide Fuel Cell Systems

The operation of solid oxide fuel cell systems with the internal steam reforming of methane over supported nickel catalysts is studied. A mathematical model including heterogeneous chemistry, electro-chemistry, mass transport, and porous media transport is developed to explore the thermal energy coupling between the steam reforming and the electrochemical reactions, independent of the geometrical structure. The role of catalyst activity, inlet temperature, current density, and operating pressure in the system behavior is evaluated. A sensitivity analysis is also performed for different design parameters. The effect of flow configuration on the operation of the system is analyzed and compared based on multiple performance criteria. It is shown that the internal steam reforming within the fuel cell system can result in an overall auto-thermal operation which increases efficiency and simplifies the design process. However, a local cooling effect may occur close to the entrance of the reformer. The use of less active catalysts can cause the slippage of the methane. To reduce both the overall temperature increase across the fuel cell and the local cooling caused by the endothermic steam reforming reactions, increasing the operating pressure is found to be an effective approach. High system efficiency is obtained with increasing the operating pressure or decreasing the current density. The more efficient system is found for a co-flow configuration, while significant temperature gradients near the entrance of the reformer are not desirable for ceramic solid oxide fuel cell systems.

Removal of antibiotics and antibiotic resistance genes from domestic sewage by constructed wetlands: Effect of flow configuration and plant species

This study aims to investigate the removal of antibiotics and antibiotic resistance genes (ARGs) in raw domestic wastewater by various mesocosm-scale constructed wetlands (CWs) with different flow configurations or plant species including the constructed wetland with or without plant. Six mesocosm-scale CWs with three flow types (surface flow, horizontal subsurface flow and vertical subsurface flow) and two plant species (Thaliadealbata Fraser and Iris tectorum Maxim) were set up in the outdoor. 8 antibiotics including erythromycin-H2O (ETM-H2O), monensin (MON), clarithromycin (CTM), leucomycin (LCM), sulfamethoxazole (SMX), trimethoprim (TMP), sulfamethazine (SMZ) and sulfapyridine (SPD) and 12 genes including three sulfonamide resistance genes (sul1, sul2 and sul3), four tetracycline resistance genes (tetG, tetM, tetO and tetX), two macrolide resistance genes (ermB and ermC), two chloramphenicol resistance genes (cmlA and floR) and 16S rRNA (bacteria) were determined in different matrices (water, particle, substrate and plant phases) from the mesocosm-scale systems. The aqueous removal efficiencies of total antibiotics ranged from 75.8 to 98.6%, while those of total ARGs varied between 63.9 and 84.0% by the mesocosm-scale CWs. The presence of plants was beneficial to the removal of pollutants, and the subsurface flow CWs had higher pollutant removal than the surface flow CWs, especially for antibiotics. According to the mass balance analysis, the masses of all detected antibiotics during the operation period were 247,000, 4920–10,600, 0.05–0.41 and 3500–60,000μg in influent, substrate, plant and effluent of the mesocosm-scale CWs. In the CWs, biodegradation, substrate adsorption and plant uptake all played certain roles in reducing the loadings of nutrients, antibiotics and ARGs, but biodegradation was the most important process in the removal of these pollutants.

Effect of flow configuration on Darcian and Forchheimer permeabilities determination in a porous composite tube

Using Fuel Cell on board of aircraft imposes to extract light species (such as Hydrogen and light hydrocarbons) from the liquid fuel which is stored and used, possibly at temperatures where a fuel pyrolysis occurs. Natural porosity of composite material could be used to filtrate the selected species. Hence the permeability of the porous media becomes one of the key parameter to be accurately measured. It is often determined experimentally in laboratory with disc samples (outlet of the flow is achieved through the porous material) and normal flow. However, this configuration is far from the realistic one consisting of tubes (a main flow is found additionally to the one through the material, tangential permeability). Therefore, the effect of a second outlet on the Darcy's and Forchheimer's permeabilities characterization should be studied (despite the permeability is an intrinsic property of the material itself and it should not be dependent on the test apparatus). This paper focuses on a new way of using an existing test bench for the determination of Darcy's and Forchheimer's permeabilities of C/SiC porous composite tube by taking two outlets into account. Operating parameters (temperature, pressure and mass flow rate) are measured for three different configurations: i) primary outlet (P.O) is 0% open ii) P.O is 50% open and iii) P.O is 100% open. Then Darcy's and Forchheimer's permeabilities are computed by ISO and P2 methods using a direct search algorithm. Obtained results from different methods are compared and discussed. They are in agreement with the literature data which guarantees the reliability of the test bench and of related measures.

Computational Analysis of Particle Nucleation in Dilution Tunnels: Effects of Flow Configuration and Tunnel Geometry

Measurement of fine particle emission from combustion sources is important to understand their health effects, and to develop emissions regulations. Dilution sampling is the most commonly used technique to measure particle number distribution because it simulates the mixing and cooling of combustion exhaust with atmospheric air, which drives nucleation and condensation of semi volatile material. Experiments suggest that the measured size distribution is dependent on the dilution ratio used and the tunnel design. In the present work, computational analysis using a large-eddy-simulation (LES) based model is performed to investigate the effect of tunnel flow and geometric parameters on H2SO4-H2O binary nucleation inside dilution tunnels. Model predictions suggest that the experimental trends are likely due to differences in the intensity of turbulent mixing inside the tunnels. It is found that the interaction of dilution air and combustion exhaust in the mixing layer greatly impacts the extent of nucleation. In general, a cross-flow interaction with enhanced turbulent mixing leads to greater number of nucleation-mode particles than an axial-flow interaction of combustion sample and dilution air.Copyright 2014 American Association for Aerosol Research

Design of an ion transport membrane reactor for gas turbine combustion application

The use of ion transport membrane reactors to substitute the conventional gas turbine combustors is a promising technology for the applications of ZEPP. An ITM monolith structure reactor design is introduced in this study for substituting a conventional gas turbine combustor. Due to reactor symmetry, only 3D four quarters of four adjacent channels sharing one common edge are considered in all simulations using LSCF1991 membranes. Effect of feed and sweep flow rates have been considered and it was calculated in order to meet the power required for the reactor and keeping the reactor size as compact as possible. Effects of flow configurations, channel width and percentage of CH4 in the permeate side flow are introduced under constant inlet gas temperature of 1173K and fixed operating pressure of 1000000 Pa. The reactor geometry has been calculated based on the calculations of the minimum possible channel width. Counter-current flow configuration design resulted in improved oxygen permeation flux and improved heat transfer characteristics. However, this flow configuration resulted in unacceptable increase in the membrane temperature. It was found that any reduction in the channel width below 15mm results in large increase in the viscous pressure drop. Also, increasing the amount of CH4 in the permeate side over 5% was found to be non-applicable because of oxygen permeation flux limitation. The reactor length was fixed to 0.9m to be similar to that of real gas turbine combustors with 25,000 channels for each stream. The present reactor design resulted in a reactor height of 3.35m and overall volume and membrane surface area of 10m3 and 2700m2, respectively. The reactor is capable of delivering power ranging from 5 to 8MWe based on cycle first law efficiency.

Modelling Tomato Dehydration in a Tunnel Dryer Using Geothermal Energy

Low-temperature geothermal waters can be used efficiently in drying various vegetables and fruits, replacing sun-drying or drying using conventional fuels. A “geothermal” tomato dehydration plant has been operating since 2001 in Neo Erasmio, northern Greece, producing high-quality, “sun-dried” tomatoes. The unit uses low-cost geothermal water to heat atmospheric air to 56–58°C, which is introduced in a specially designed tunnel-type dryer. The scope of this work is to model the aforementioned tomato-drying process that uses low-enthalpy geothermal energy. The modelling procedure consists of two stages: the first stage focuses on the modelling of a single tomato piece, whereas the second stage is concerned with the modelling of air drying of tomatoes in a tunnel with trays moving in batches. The influence of air velocity, air temperature, and tomato tray loading on the drying process was investigated. The effect of flow configuration, i.e., co-current or counter-current operation, on the drying characteristics was also explored. The model can be used for the design and optimization of the continuous drying process existing in Neo Erasmio and can be easily extended and modified to deal with other agricultural products and tunnel designs.

The effect of flow configuration on hydrodynamic stresses and dispersion of low density rigid aggregates

The effect of flow configuration on the distribution of internal stresses in rigid colloidal aggregates was investigated numerically for cluster–cluster aggregates with fractal dimensions ranging from 1.7 to 2.3. Stokesian dynamics was used to evaluate the hydrodynamic force on each monomer, while the internal intermonomer interactions were calculated by applying force and torque balances on each primary particle. The examined two-dimensional flows were characterised by a mixing index λ, that ranged from 0 (rotation) to 1 (elongation), with pure shear flow at λ=0.5. Two regimes of motion were identified: for λ≲0.6 aggregates rotate continuously, whereas at higher values (λ≳0.7) they reach a stationary orientation with respect to the flow field. A transition region, in which only some of the aggregates reach the stationary condition, separates the two regimes. The stationary regime appeared more favourable to induce breakage or restructuring, because in this case the generated internal stresses are sustained in time, while in the rotational regime they vary cyclically. We showed that the greater effectiveness of elongation with respect to shear can be explained by relating the condition of breakage to the time-averaged value of the internal stress rather than to the instantaneous value. By exploiting this relationship, the information on the viscous stress required to break or restructure an aggregate in a particular flow configuration can be easily extended to a different flow type.

Thermal and hydraulic characteristics of nanofluid flow in a helically coiled tube heat exchanger

The effects of using different geometrical parameters with the combination of nanofluid on heat transfer and fluid flow characteristics in a helically coiled tube heat exchanger (HCTHE) are numerically investigated. A CuO nanoparticle with a diameter of 25nm dispersed in water with a particle concentration of 4% was used as the working fluid. The three dimensional governing equations (continuity, momentum and energy) along with the boundary conditions are solved using the finite volume method (FVM). The mass flow rate of water in the annulus was kept constant and the nanofluid flow rate in the inner tube was varied. The effect of flow configuration (parallel and counter) was also examined in this study. The performance of the HCTHE was evaluated in terms of Nusselt number, heat transfer rate, pressure drop, effectiveness and performance index. The results reveal that certain geometrical parameters such as the helix radius and inner tube diameter do affect the performance of the HCTHE under laminar flow conditions. It is also found that counter-flow configuration produced better results as compared to parallel-flow configuration.

Effect of Flow Configuration on the Performance of Gas–liquid Membrane Contactor

Effect of Flow Configuration on the Performance of Gas–liquid Membrane Contactor

Effect of flow configuration on the behavior of a membrane reactor operating without sweep gas

A simulation study of a multitubular membrane reactor for the water gas shift reaction is presented. No sweep gas is considered. Two alternative flow configurations between the retentate and permeate streams are compared: cocurrent and countercurrent. The influence of the flow scheme on the ignition temperatures, CO conversions and axial temperature profiles is analyzed. Simple algebraic equations are derived to predict the temperature rise along the reactor length. The cocurrent scheme enables the attenuation of the thermal effects in the membrane reactor, by minimizing the temperature rise in the catalyst bed. Conversely, the temperature rise corresponding to the countercurrent scheme is considerably higher than that of the cocurrent configuration. Both thermal increases exceed the temperature rise of a conventional adiabatic fixed-bed reactor. Under countercurrent flow, the membrane reactor could exhibit steady-state multiplicity because of the heat feedback introduced by the permeate stream.

High Resolution Neutron Radiography Imaging of Operating PEM Fuel Cells: Effect of Flow Configuration and Gravity on Water Distribution

High resolution neutron radiography was used to image polymer electrolyte membrane fuel cells (PEMFCs) during operation under a variety of conditions. The effect of specific operating conditions, including flow direction (co-flow or counter-flow), orientation of the PEMFC with respect to gravity, and simulated anode recycle loop, were examined. Counter-flow operation was found to result in higher water content than co-flow operation, with more uniformly distributed water. Orientation with respect to gravity was also significant, with net water transport observed from the higher side of the cell to the lower side. The higher anode flow rate resulting from the simulated recycle loop facilitated convective removal of liquid water from the anode flow field, leading to lower overall levels of water in the PEMFC.

High Resolution Neutron Radiography Imaging of Operating PEM Fuel Cells: Effect of Flow Configuration and Gravity on Water Distribution

not Available.

Effect of flow configuration on the operation of coupled combustor/reformer microdevices for hydrogen production

The effect of flow configuration, namely co- vs. counter-current flow, on the operation of multifunctional microdevices for hydrogen production is analyzed using two-dimensional computational fluid dynamics simulations. Stoichiometric propane/air gaseous combustion and ammonia reforming on Ru occur in alternate parallel channels (600 and 300 μ m wide, respectively) separated by a thermally conducting wall ( 300 μ m thick). It is shown that complete conversion of ammonia can be achieved at millisecond residence times in both flow configurations. The power generated, based on 100% utilization of the hydrogen produced, is in the range of 8–60 W per cm height of the device depending on flow rates. A proper balance of the flow rates of the combustion and reforming streams is, however, crucial in achieving this. For either configuration, the maximum power generated is determined by extinction at large reforming stream flow rates. Materials stability, resulting from high temperatures generated at low reforming stream flow rates, determines the lower power limit for a given flow rate of combustible mixture. The two flow configurations are contrasted based on multiple performance criteria, such as device temperature, power exchanged, conversions, and net hydrogen production by constructing operation maps. They are found to be practically equivalent for highly conductive materials. Using properly balanced flow rates, the co-current configuration expands the operation window to medium as well as low thermal conductivity materials as compared to the counter-current configuration that shows a slightly superior performance but in a rather narrow regime of high ammonia flow rates and high thermal conductivity materials.