Outlet Chambers Research Articles

A new model for chloride ion diffusion in cracked concrete with consideration of damage and strain fields

In this paper, a new model for chloride diffusion in cracked concrete is presented. The model was developed within a standard continuum damage mechanics framework but newly considers both an irreversible damage variable and a strain field, gaps identified through a literature review, offering a more comprehensive description of the diffusion-like processes in concrete with small and moderate cracks than current models. The model utilizes a realistic dependence for the diffusion coefficient on the damage state and employs a bi-logistic mapping function or an S-curve mapping function to effectively describe the non-linear effects of cracks on diffusion in concrete. The dependence on the strain field introduced by this model not only allows examination of diffusion in opening cracks, it also enables the process of crack closing to be simulated, whatever the irreversible damage variable may be. This paper also proposes a novel calibration procedure for experimental testing involving the use of the Brazilian splitting test on samples enclosed in a steel ring. This innovative approach simplifies the process of creating a portfolio of cracks with varying widths. In the calibration tests described here, samples were subjected to natural diffusion while chloride content was monitored in inlet and outlet chambers attached to the samples, eliminating the need for laborious chloride profiling. Our in-depth examination of chloride diffusion in cracked concrete is applicable to analyses of corrosion in steel-reinforced concrete structures worldwide, with the new calibration procedure offering a straightforward method for populating the model with realistic material parameters, thus providing a valuable tool for accurately predicting chloride penetration in real-world scenarios.

Physicochemical characteristics of grease-trap wastewater with different potential mechanisms of FOG solid formation, separation, and accumulation inside grease traps

This work investigates the physicochemical characteristics of grease-trap wastewater discharged from a large community market. It proposes potential mechanisms of fat, oil, and grease (FOG) solid formation, separation, and accumulation inside grease traps. Sixty-four samples, i.e., the floated scum, suspended solid-liquid wastewater, and settled sludge, were collected from the grease-trap inlet and outlet chambers. A lower pH of 5-6 at 25-29 °C inside the grease trap than those reported under the sewer conditions (pH 6-7) was revealed. A significant difference in solid and dissolved constituents was also discovered between the inlet and outlet chambers, indicating that the baffle wall could affect the separation mechanism. The sludge samples had 1.5 times higher total solids (TS) than the scum samples, i.e., 0.225 vs. 0.149 g g−1 TS, revealing that the sludge amount impacted more significantly the grease trap capacity and operation and maintenance. In contrast, the scum samples had 1.4 times higher volatile solids (VS) than the sludge samples, i.e., 0.134 vs. 0.096 g g−1 VS, matching with the 64.2 vs. 29.7% of carbon content from CHN analysis. About 2/3 of the free fatty acids (FFAs) with palmitic acids were the primary saturated FFAs, while the remaining 1/3 of unsaturated FFAs were found in the solid and liquid samples. Although up to 0.511 g g−1 FOG can be extracted from the scum samples, none from the sludge samples. More diverse minerals/metals other than Na, Cl, and Ca were found in the sludge samples than in the scum samples. Grease-trap FOG solids and open drain samples exhibited similar physicochemical properties to those reported in the literature. Four potential mechanisms (crystallization, emulsification, saponification, and baffling) were presented. This work offers insights into the physicochemical properties of grease-trap wastewater that can help explore its FOG solid formation, separation, and accumulation mechanisms inside a grease trap.

Efficiency assessment of vortex tubular enameled coalescing devices for oil emulsion destabilization

The greatest intensity of the process of dispersion and subsequent coalescence of oil droplets in emulsified wastewater of oilfields takes place in the near-wall areas of tubular coalescing devices. Strengthening of the wall effect is possible by covering the surface of the flowing part of the coalescing device with silicate enamel, which provides the effect of sliding of the turbulent flow of waste water (emulsion) on a thin adhesive layer that appears directly on the surface of the enamel. Experimental studies to determine the effectiveness of treatment of oily wastewater in tubular vortex-type coalescing devices were carried out on an experimental unit consisting of three coalescing devices connected in series. Each coalescing device was a tubular shaft coaxially connected to the inlet and outlet chambers. Vortex tubular coalescing devices made of stainless steel (not coated with enamel) and vortex coalescing devices of similar design coated with silicate enamel were used in the experiments. The wastewater treated in the unit was sedimented, and the concentrations of oil and suspended particles were determined in the clarified water. Analysis of the data obtained showed that at the time of wastewater treatment from 1.1 to 6.3 s sedimentation effect on oil particles after coalescing devices coated with enamel on average by 1.5 to 1.8% was higher than the sedimentation effect obtained after the treatment of oil emulsion in coalescing devices not coated with enamel. The sedimentation effect on suspended solids in the second series of experiments was greater than the sedimentation effect observed in the first series by an average of 1.1-1.4 %.

Economic Analysis of Biogas Production via Biogas Digester Made from Composite Material

This study seeks to evaluate the economic implication of a biogas digester built from composite material to ascertain its cost effectiveness. The feasibility study conducted indicates that a brick made only of fixed dome digester costs between USD 3193.99 and USD 4471.59. This high cost is attributed to the construction material, thus prompting the need to use materials of lower cost for affordability and sustainability. Hence, the digester under study was made from composite material comprising high-density polyethylene (HDPE), bricks and cement. The inlet and outlet chambers were built using bricks and cement, while the digestion chamber was made from HDPE material. From the economic analysis conducted, the total initial investment cost of the biogas digester was reported to be USD 1623.41 with an internal rate of return (IRR) of 8.5%, discount payback period (DPP) of 2 years and net present value (NPV) of USD 1783.10. The findings equally revealed that the estimated quantity of biogas could replace 33.2% of liquefied petroleum gas (LPG) cooking gas. Moreover, the biogas daily yield of 1.57 m3 generates approximately 9.42 kWh of electricity, which costs about USD 1.54. Thus, the study recommends the use of composite material of plastics and bricks in constructing the biogas digester, as it is cost effective and sustainable.

Towards best practice recommendations for turbulence modelling of high-pressure homogenizer outlet chambers – Numerical validation using DNS data

• Accurate description of the flow inside emulsification devices is crucial. • This study compares LES and RANS predictions to DNS validation data for an HPH. • Both LES and RANS are able to predict the general outline of the flow. • LES shows slightly better performance than RANS in predicting dissipation rates. • Low computational cost of RANS keeps it an interesting supplementary tool. There is a large interest in predicting high-pressure homogenizer (HPH) valve hydrodynamics using CFD, in academic research and industrial R&D. Most of these studies still use two-equation RANS turbulence models, whereas only a few have used LES formulations. From a theoretical perspective, LES is known to be more accurate than RANS, especially in terms of estimating the dissipation rate of turbulent kinetic energy, which is the most important parameter needed for predicting efficiency using a population balance equation (PBE). However, LES also comes at a considerably higher computational cost. To choose the appropriate modelling approach, it is important to understand how much the accuracy and the computational cost increase between RANS and LES. This study provides the first validation of high-pressure homogenizer hydrodynamics, comparing RANS and a well-resolved LES to numerical experimental validation data of direct numerical simulation (DNS), on a model of the gap outlet jet. The LES does result in a higher accuracy throughout, but the differences are relatively small, when focusing on the flow inside the jet. When using the CFD results to predict maximum surviving drop diameter, the LES results in a relative error of 4.8% whereas the RANS leads to a relative error of 18%. Both errors are substantially smaller than those from a traditional scale-based equation instead of a CFD-PBE. When seen in the substantial reduction of computational time (a factor of 970), results illustrate how RANS could remain a viable supplementary technique for CFD modelling of HPHs, despite its many limitations. Best practice recommendations for obtaining this RANS performance is discussed.

Consecutive Flow Distributor Device for Mesostructured Reactors and Networks of Reactors

A manifold is introduced for homogeneous flow distribution to feed arrays of mesoreators or mesostructured networks of reactors. The flow distributor, hereafter the channelCOMB, consists of a main prismatic channel with an array of prismatic outlet channels. The configuration of channelCOMB enables the fabrication from both additive and subtractive manufacturing technologies. The flow distribution in channelCOMB is studied from Computational Fluid Dynamics (CFD) simulations. The parametric design of the device is made with CFD and addresses all the relevant dimensions. The best design of channelCOMB in terms of flow distribution is analysed for fabrication through Additive Manufacturing by stereolithography considering fabrication tolerance typically around ±50µm. A better flow distribution is reached for lower inlet velocity values, larger depth values, smaller expansion ratios from the inlet channel to the main chamber of ChannelCOMB, and narrower outlet chambers. An analytical mechanistic model was developed to calculate the pressure drop inside the device and to determine the outlet channels flow rate distribution. The model was implemented in an optimisation algorithm using Excel solver, and from the model analytical solution using Maple. These computer tools enable the fast design of channelCOMB distributors for multichannel devices and were validated from results of CFD simulations.

Design and Fabrication of a Plastic Biogas Digester for the Production of Biogas from Cow Dung

Biogas digester dimensions and materials of construction are important factors of consideration during the design and fabrication phase. The aim of this study is to provide a detailed analysis of the design and fabrication of a 2.15 m3 pilot plastic biogas digester for biogas generation. To establish this, a design equation covering the volume of the digester, inlet and outlet chambers, and digester cover plate were developed considering the shape of the digester. The digestion chamber of the biogas digester under study was fabricated using high-density polyethylene (HDPE) plastic, while the inlet and outlet chambers were constructed with bricks/cement. The study was motivated due to some limitations such as leakage associated with previous designs. In the present study, a ventilation test was conducted after the fabrication to ensure the digester is leak free. Results obtained showed a total volumetric methane gas yield of 2.18 m3 (54.50%) and carbon dioxide yield of 1.77 m3 (44.25%) making up a total biogas yield of 4.00 m3. In addition, the percentage concentration of methane and carbon dioxide were found to be 60% and 30%, respectively. The developed plastic biogas digester has been found to be appropriate for biogas production using cow dung as substrate.

Investigation of flow non-uniformities in the cross-flow heat exchanger with elliptical tubes

In heat exchangers, especially those with the cross-flow arrangement, it is nearly impossible to achieve the uniform distribution of the working fluid in the tubular space with the currently used inlet and outlet chambers (in some constructions as well). The improper inflow conditions to individual tubes, including those with an elliptical cross-section - often used because of their favorable features compared to round tubes, is the cause of improper heat transfer. In this respect, transitional flow is of particular importance. This flow regime is complex and challenging to model. Therefore, it is necessary to perform experimental verification. For this purpose, an appropriate stand was built, allowing to investigate the flow of the working fluid (water) to the elliptical tubes in the cross-current heat exchanger. The paper presents the results of measurements for manifold geometry, which are currently used in practice (for heat exchanger constructions). The analysis of the measurement data confirms the nonuniform flow distribution to individual tubes of the heat exchanger.

Two-Dimensional Microfluidic System for the Simultaneous Quantitative Analysis of Phototactic/Chemotactic Responses of Microalgae.

Microalgae have been spotlighted as a renewable energy source to produce biofuels from CO2 by photosynthesis. However, their innate inefficiency of CO2 conversion using light energy has been a challenge to the commercialization of algae-based biofuel production. Photosynthetic organisms have evolved behavioral responses, including phototaxis and chemotaxis, to find optimal conditions for capturing light energy and inorganic carbon (Ci) sources for photosynthesis. In this context, investigation of phototaxis and chemotaxis to HCO3-, the predominant form of Ci in neutral aqueous solutions, is necessary to understand the physiological role of tactic responses in photosynthesis. In this study, a two-dimensional microfluidic system enabled efficient analysis of phototactic and chemotactic responses by investigation of cell distribution in the outlet chambers. From statistical analysis (skewness and kurtosis) of tactic responses of different algal strains to external stimuli, the preferred concentrations of HCO3- for Chlamydomonas reinhardtii CC125 (wild type), PTS42 (random insertional mutant of C. reinhardtii, high photosynthetic activity), and CC2702 ( cia5 mutant of C. reinhardtii, unable to acclimate to low CO2 concentration) were determined to be 27.22, 43.23, and 36.95 mM, respectively. From the analysis of tactic responses of wild type and 14 mutant strains, it was found that the photosystem II (PSII) operating efficiency and CO2 fixation rate were strongly correlated with the phototactic ( R2 = 0.931) and chemotactic response ( R2 = 0.857), respectively. Finally, this system can be applied to high-throughput screening strategies for the rapid isolation of high photosynthetically productive microalgal strains based on their tactic responses.

Quantitative biological assays with on-chip calibration using versatile architecture and collapsible chambers

A new microfluidic device composed of pneumatically actuated multiple collapsible chambers arranged in an X-Y architecture has been developed. Elementary fluidic functions such as fluid transfer, volumes calibration, mixing, aliquoting and linear dilutions can be parallelized, achieving automatically and rapidly complex operations. The ultimate aim is to perform fully integrated quantitative assays such as complete enzymatic assays and Elisa assays by using existing kits and an on-chip calibration. Both objectives require to manipulate a high range of volumes (from 1 μL to 100 μL) while keeping an excellent accuracy. Furthermore, quantitative assays have to be highly repeatable to be relevant. This challenge has been successfully addressed by combining three original characteristics. First, a versatile architecture has been designed allowing to be adapted to any quantitative protocol. Then, a hyper elastic membrane with a high elongation rate and switching between two polymer solid layers has been used to control precisely the fluid volumes at each inlet and outlet chambers. Finally, repeatability was obtained by including linear dilutions to generate a standard curve and to calibrate the system.

Experience of commissioning the AES-2006 (V-392M) steam generator blowdown system

Structural features of the AES-2006 design (V-392M reactor plant) steam generator blowdown and drainage system have been considered. Design peculiarities of components and the system as the whole have been comprehensively analyzed, and the advantages and disadvantages of the circuitry and design solutions used are presented. An apparent advantage of the system's flowchart is the maximum blowdown rate increased to 140 t/h. At the same time, issues have been identified caused by insufficient elaboration of structural elements.Based on the earlier experience of the system commissioning, a modified flowchart has been proposed for the steam generator blowdown and drainage using multi-pass valves with an electric single-turn (EST) actuator drive in the system. The flowchart modification makes it possible to reduce the specific content of metal in the system and to provide an extra space for the maintenance of the system's regenerative heat exchanger in a pressurized shell, to use eight multi-pass valves for the steam generators instead of 36 electromagnetic valves, and to cut the operating and repair costs.Modifications have been proposed to the regenerative heat exchanger design to give it a better performance, including installation of circular partitions in the lower inlet (pressure) and the upper outlet chambers. As the result, this leads to a heat exchanger with three passes in the tube space which helps achieving the required flow rate.The above updates will improve the performance and reliability of the steam generator blowdown and drainage system as far as its design functions are concerned, this to result in the secondary circuit's water chemistry arranged so that to minimize the amount of deposits on the heat-exchange surface of the PGV-1000MKP steam generators.

Experimental stand for investigation of fluid flow in heat exchangers with cross-flow arrangement

The operation analysis of high-performance heat exchanger with tubes elliptical indicated that the heat exchangers can be subject to damage. The reason for this is probably improper distribution of working fluid in tubular space of heat exchanger. Therefore, a part of the tubes may be improperly cooled and subject to compressible stresses. The paper presents an experimental stand allowing to confirm the given assumption. The experimental investigation enables to examine the mass flow rate in heat exchanger tubes. Also, it is possible to assess the impact of the construction of inlet, intermediate and outlet chambers on the flow distribution within the heat exchanger tubes.

A simplified approach for the computation of steady two-phase flow in inverted siphons

Hydraulic, sanitary, and sulfide control conditions of inverted siphons, particularly in large wastewater systems, can be substantially improved by continuous air injection in the base of the inclined rising branch. This paper presents a simplified approach that was developed for the two-phase flow of the rising branch using the energy equation for a steady pipe flow, based on the average fluid fraction, observed slippage between phases, and isothermal assumption. As in a conventional siphon design, open channel steady uniform flow is assumed in inlet and outlet chambers, corresponding to the wastewater hydraulic characteristics in the upstream and downstream sewers, and the descending branch operates in steady uniform single-phase pipe flow. The proposed approach is tested and compared with data obtained in an experimental siphon setup with two plastic barrels of different diameters operating separately as in a single-barrel siphon. Although the formulations developed are very simple, the results show a good adjustment for the set of the parameters used and conditions tested and are promising mainly for sanitary siphons with relatively moderate heights of the ascending branch.

Unified Measurement System for the Gas Dispersion Coefficient, Air Permeability, and Gas Diffusion Coefficient in Variably Saturated Soil

The transport of gaseous compounds in soil takes place by gas diffusion, advection, and dispersion. Gas transport processes are influenced by the soil‐gas diffusion coefficient (Dp), air permeability (ka) and soil‐gas dispersion coefficient (DH), respectively. Of three gas transport parameters, DH is the least understood, especially how it is correlated to soil type, moisture conditions, and other transport parameters (i.e., Dp and ka). In this study, a unified measurement system (UMS) that enables sequential measurement of Dp, ka, and DH on the same soil core was developed. The experimental sequence is based on a two‐chamber measurement of DH and ka, followed by a one‐chamber measurement of Dp Gaseous oxygen concentration and air pressure sensors are located in inlet and outlet chambers as well as at multiple points along the soil column. Using different particle‐size fractions of non‐aggregated (Toyoura sand) and aggregated (Nishi‐Tokyo loam) soils, the effects of soil structure, particle (aggregate) size, and column scale (5‐cm i.d. and 30‐cm or 60‐cm length) on the three gas transport parameters were investigated. For both soils, DH linearly increased with increasing pore‐air velocity. For Toyoura sand, gas dispersivity (λ = DH/u0) decreased with increasing soil‐air content, while for Nishi‐Tokyo loam, gas dispersivity decreased with increasing soil‐air content to a minimum value when inter‐aggregate pores were drained and increased again when the pores inside the soil aggregates started to act as tortuous air‐filled pathways. In the arterial pore region (corresponding to the total pore volume for Narita sand and the inter‐aggregate pore volume for Nishi‐Tokyo loam), a linear relation between tortuosity of the air‐filled pore network (T, calculated from Dp) and the gas dispersivity (λ) was observed.

By-pass valve control to improve energy efficiency of pneumatic drive system

In order to improve the performance and energy efficiency of the pneumatic drive, the by-pass valve control scheme is designed and studied. For pneumatic positioning application, in the constant speed phase, the inlet and outlet chambers will be connected via by-pass valve to reduce the overshoot and allow some exhaust compressed air to be reused. Therefore, compared with the traditional control of the motion of the asymmetric cylinder, a 12–28% saving in energy use can be acquired and meanwhile the position accuracy is maintained. Preliminary results from the simulation and experiment studies will be reported.

Optimization of heat transfer characteristics, flow distribution, and reaction processing for a microstructured reactor/heat-exchanger for optimal performance in platinum catalyzed ammonia oxidation

The present work is focused on the demonstration of the advantages of miniaturized reactor systems which are essential for processes where potential for considerable heat transfer intensification exists as well as for kinetic studies of highly exothermic reactions at near-isothermal conditions. The heat transfer characteristics of four different cross-flow designs of a microstructured reactor/heat-exchanger (MRHE) were studied by CFD simulation using ammonia oxidation on a platinum catalyst as a model reaction. An appropriate distribution of the nitrogen flow used as a coolant can decrease drastically the axial temperature gradient in the reaction channels. In case of a microreactor made of a highly conductive material, the temperature non-uniformity in the reactor is strongly dependent on the distance between the reaction and cooling channels. Appropriate design of a single periodic reactor/heat-exchanger unit, combined with a non-uniform inlet coolant distribution, reduces the temperature gradients in the complete reactor to less than 4 °C, even at conditions corresponding to an adiabatic temperature rise of about 1400 °C, which are generally not accessible in conventional reactors because of the danger of runaway reactions. To obtain the required coolant flow distribution, an optimization study was performed to acquire the particular geometry of the inlet and outlet chambers in the microreactor/heat-exchanger. The predicted temperature profiles are in good agreement with experimental data from temperature sensors located along the reactant and coolant flows. The results demonstrate the clear potential of microstructured devices as reliable instruments for kinetic research as well as for proper heat management in the case of highly exothermic reactions.

A surface-tension driven micropump for low-voltage and low-power operations

In this paper, we first report a micropump actuated by surface tension based on continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in a microchannel filled with an electrolyte as actuation energy for the micropump. This allows low voltage operation as well as low-power consumption. The micropump is composed of a stack of three wafers bonded together. The microchannel is formed on a glass wafer using SU-8 and is filled with electrolyte where the mercury drop is inserted. The movement of the mercury pushes or drags the electrolyte, resulting in the deflection of a membrane that is formed on the second silicon wafer. Another silicon wafer, which has passive check valves and holes, is stacked on the membrane wafer, forming inlet and outlet chambers. Finally, these two chambers are connected through a silicone tube forming the complete micropump. The performance of the fabricated micropump has been tested for various operation voltages and frequencies. We have demonstrated actual liquid pumping up to 70 /spl mu/l/min with a driving voltage of 2.3 V and a power consumption of 170 /spl mu/W. The maximum pump pressure is about 800 Pa at the applied voltage of 2.3 V with an operation frequency of 25 Hz.

In vitro characterization of the occurrence of hemolysis during extracorporeal blood circulation using a mini hemodialyzer.

A minimodule dialyzer was made of polyacrylonitrile (PAN) hollow fibers and tested in an in vitro circuit under varying flow rates and blood volumes. Hemolysis occurred in the open circuit in the inlet and outlet chambers. The module was measured to investigate the hemolysis effect during dialysis. The results show that hemolysis ratio (HR) increased with blood flow rate. When the blood speed was increased from 27 to 70 cm/sec, the damaged fraction of red blood cells increased from 0.8% to 1.5%. Shearing in the hollow fiber contributed approximately 13% of the overall HR. Approximately 55% of the overall HR occurred at the inlet and outlet chambers. With increasing blood volume, the contacting surface area per unit blood volume (S/V) and the frequency of pump squeezing of red cells were decreased; hence the damage to the red blood cells and thus reduction of HR. When S/V was 2 cm(-1), the damaged fraction of red cells was approximately 0.7%. In addition, the tubing and connectors of the circuit caused further damage to the red blood cells. By referring to the linear velocity and blood volume, we can predict the HR in an actual protocol from the results of this experiment. This should improve the quality of hemodialysis and benefit the patient.

Plane wave analysis of side inlet/outlet chamber mufflers with mean flow

Integration of side inlet and/or side outlet expansion chambers into the rest of the muffler system for prediction of overall transmission loss (TL) or insertion loss requires knowledge of the four-pole parameters of these elements for propagation of plane waves in a moving medium. In this paper, transfer matrices have been derived for side inlet and side outlet elements for typically small mean flow Mach numbers. These are validated against the 3-D model existing in the literature for a stationary medium and for acoustically long chambers. The effect of mean flow on TL of the side inlet/ outlet chambers has been demonstrated. Incidentally, it has been shown that side inlets and side outlets behave more or less like extended inlets and extended outlets, respectively.

A comparative study of anaerobic digestion of acid cheese whey and dairy manure in a two-stage reactor

The performance of a two-stage, two-phase, unmixed anaerobic digester of 155 l working volume operating on acid cheese whey and dairy manure at various temperatures and hydraulic retention times was investigated. The effect of controlling the pH of the methanogonic stage of cheese whey digestion on the biogas production rate and pollution potential reduction was also investigated. The digester was designed to act as a liquid-solid separator, in order to maximize the microbial mass in the reactor, and was operated at three hydraulic retention times (10, 15 and 20 days) and two temperatures (25 and 35°C). It operated as a single-phase reactor under both the cheese whey and dairy manure feeding conditions when the pH was not controlled (similar pH values in the inlet and outlet chambers) and as a two-stage, two-phase reactor when the pH of the whey was controlled in the methanogenic stage (different pH values in the inlet and outlet chambers). The results indicated that production of biogas from cheese whey without pH control is not feasible as the digester experienced acid-phase digestion in both stages. However, controlling the pH of the methanogenic stage increased the biogas production rate and methane yield, as well as the reductions in COD and solids concentrations of the cheese whey by a factor of 2.7-3.0. Although the pH was maintained at 5.7-6.0, the results are comparable to those obtained with dairy manure of a similar solids concentration and a pH of 7 ± 0.2. A further increase in the pH (to 7.0 ± 0.2) would, therefore, increase the biogas production rate and methane yield from cheese whey.