Closed-circuit Configuration Research Articles

Effect of electron acceptors on electricity production and desalination of caspian sea water using microbial desalination cells

ABSTRACT The Microbial Desalination Cell (MDC) stands out as an innovative and a sustainable technology for both renewable energy generation and water treatment. The choice of electron acceptor significantly influences the efficiency of electricity flow. This study focuses on exploring the MDC performance under different conditions, including variations in cathode electron acceptors, initial pH levels, and hydraulic retention time (HRT). The investigation assesses simultaneous reduction of TDS and power generation from Caspian Sea water, a prominent saline water source in northern Iran, in both open-circuit (OC) and closed-circuit (CC) modes. The findings reveal that sodium hypochlorite, potassium permanganate, and potassium bromate as catholyte achieved TDS reduction rates of 84%, 77%, and 72%, respectively, under CC conditions at pH 5. Furthermore, it was observed that increasing HRT and pH levels lead to a decrease in desalination efficiency and power generation. Notably, the study highlights that the maximum power density was attained using permanganate, hypochlorite, and bromate as catholyte in both OC and CC configurations. By showcasing the adaptability of MDC performance with different cathode electron acceptors under varying conditions, this research offers valuable insights for optimizing MDC efficiency when treating real saline water sources.

Surface tension effect on flexoelectric energy harvesting based on extended isogeometric analysis

This study presents a numerical framework to model the effect of surface tension on a flexoelectric energy harvesting system with liquid inclusions. The equivalent Young’s modulus and Poisson’s ratio of the liquid inclusions embedded in flexoelectric composites considering the surface tension are derived for the first time. An extended isogeometric analysis (XIGA) based on non-uniform rational B-splines (NURBS) is developed to model and solve the electromechanical response of weak discontinuities in flexoelectric composites. The interface between liquid and solid materials is implicitly represented by the level set method. Several numerical examples are presented as linear dielectric solids embedded with liquid inclusions under mechanical compression and different electric circuit configurations, including square matrixes and truncated pyramids. The simulation results indicate that a significant enhancement in the electromechanical coupling coefficient can be obtained by considering the effect of surface tension in open- and closed-circuit configurations. The maximum electric potential and energy conversion are higher in the open-circuit configuration. In addition, the XIGA simulation shows that the energy conversion of the flexoelectric devices increases as the size of the structural system and Young’s modulus of the flexoelectric material decrease. The maximum energy conversion capability of the flexoelectric composite, including the effect of surface tension, is enhanced by 32.4% with a central inclusion and 57% or higher with random inclusions. Finally, the influence of the length scale on the flexoelectricity is analyzed.

Evaluation of the nanofiltration of brines from seawater desalination plants as pre-treatment in a multimineral brine extraction process

Many materials essential to the European Union's (EU) economy lack primary resources, and the major suppliers of these materials are non-EU nations. It has been determined that seawater reverse osmosis (SWRO) desalination brines are a circular answer for the supply of critical elements. SWRO desalination brines, however, are distinguished by high concentrations of elements with negligible economic worth. (e.g., Na, Cl) compared to critical elements present in very low concentrations (e.g. Mg, B, Sc, V, In, Ga, Li, Mo, Rb). Therefore, an efficient separation pre-treatment is necessary to maximize the recovery efficiency in a brine extraction process. Nanofiltration (NF) was proposed as pre-treatment stage to separate monovalent from divalent ions and it was investigated if a Ca(II) removal stage was necessary before the NF to avoid scaling. The performances of three polyamide commercial membranes (NF270, Fortilife XC-N and PRO-XS2) treating SWRO brine (brine 1) and Ca(II)-free SWRO brine (after Ca(II) removal with sodium bicarbonate - brine 2) were evaluated in a closed circuit configuration as a function of the applied pressure from 6 to 30 bar.Results showed that NF was an efficient process to separate target elements present in seawater desalination brine into two different streams. Moreover, removal of Ca(II) before the NF step (brine 2) increased the selectivity between multivalent and monovalent species (higher rejection of multivalent and lower rejection of monovalent species compared to brine 1) for all the membranes tested, reaching the highest selectivity at 20 bar. At 20 bar, the polyamide membrane PRO-XS2 presented rejections of 71% for Ca(II) and 89% for Mg(II) and the highest selectivity in experiments with brine 2, being recommended for this application. In addition, the transport of species was characterized by membrane permeances by using the Solution-Electro-Diffusion-Film model. The scaling assessment at the membrane surface showed a lower scaling potential if Ca(II) was removed before the NF stage.

Charge carrier transport and electrical response by driving band gap modulation in semiconductors

Electrical responses and carrier transport dynamics in intrinsic bulk semiconductors are found when a variable gradient in a physical property or field causes a gradient in the band gap and, in turn, in the carrier concentrations. A variable carrier concentration profile leads to a dynamic carrier diffusion flow. The electrical responses depend on temperature and the difference between electron and hole mobilities. This novel effect is evaluated for both open-circuit and closed-circuit configurations. One example is a variable carrier concentration created by acoustically stimulated band gap modulation. A standing acoustic wave in the lattice produces a dynamic pressure-induced variable band gap modulation. Responses from an indium antimonide crystal in acoustic resonance with amplitude of 2.23 MPa (rms) are found to be in the ranges of 30–40 mA and 0.1–0.3 mV for closed and open circuit cases, respectively. At room temperature, quantum effects do not contribute significantly to the description of carrier behavior and transport, except for scattering. The effect can also be produced by perturbations other than pressure if the band gap depends on those perturbations. The electrical responses characteristic of these semiconductors can be used for developing new sensors or transducers to measure gradients, such as pressure gradient transducers.

Energy Comparison between a Load Sensing System and Electro-Hydraulic Solutions Applied to a 9-Ton Excavator

With the increasingly stringent regulations on air quality and the consequent emission limits for internal combustion engines, researchers are concentrating on studying new solutions for improving efficiency and energy saving even in off-road mobile machines. To achieve this task, pump-controlled or displacement-controlled systems have inspired interest for applications in off-road working machines. Generally, these systems are derived from the union of a hydraulic machine coupled to an electric one to create compact components that could be installed near the actuator. The object of study of this work is a 9-ton excavator, whose hydraulic circuit is grounded on load sensing logic. The validated mathematical model, created previously in the Simcenter Amesim© environment, represents the starting point for developing electro-hydraulic solutions. Electric components have been inserted to create different architectures, both with open- and closed-circuit layouts, in order to compare the energy efficiency of the different configurations with respect to the traditional load sensing system. The simulations of a typical working cycle show the energy benefits of electro-hydraulic solutions that allow for drastically reducing the mechanical energy required by the diesel engine and, consequently, the fuel consumption. This is mainly possible because of the elimination of directional valves and pressure compensators, which are necessary in a load sensing circuit, but are also a source of great energy dissipations. The results show that closed-circuit solutions produce the greatest benefits, with higher energy efficiencies than the open-circuit solution. Furthermore, closed-circuit configurations require fewer components, allowing for more compact and lighter solutions, as well as being cheaper.

On-chip 3D confocal optical study of an InGaN/GaN microrod LED in the low excitation regime

In this work, we studied p-i-n InGaN/GaN core-shell microrod (μrod) LEDs using confocal microscopy with a spatial resolution below 500 nm in all three dimensions. At low excitation conditions, the devices emit in the red spectral range, while green and blue emissions become more prominent with increasing driving current. 3D photoluminescence (PL) maps demonstrate that the red emission originates from the apex of the tip area, while the green emission stems from the corners between m- and r-planes and the dominant blue emission from the m-plane. Analyzing individual μrods of the LED chip in a closed circuit configuration, a pronounced photocurrent is found for quasi-resonant laser excitation, indicating charge carrier tunneling losses out of the quantum well. This hypothesis is confirmed by applying an external voltage in the forward direction, where a characteristic blueshift of the single μrod PL signal is observed due to a modified band alignment, and a nonlinear increase in the PL intensity proves suppressed tunneling losses.

Modeling of demagnetization processes in permanent magnets measured in closed-circuit geometry

The hysteresis loops of nucleation-type magnets made of exchange-decoupled grains (i.e., sintered Nd–Fe–B magnets) reflect the discrete character of magnetization switching in such materials. Due to this discrete character, the experimental determination of coercivity depends on the measurement protocol. Finite element modeling allows us to investigate how the pattern of reversed grains develops during sample demagnetization performed under closed-circuit conditions, provided that the basic features of the hysteresigraph are known. Numerical modeling provides a quantitative understanding of the collective effects that are very pronounced in the closed-circuit configuration and shows how they affect both the slope of the demagnetizing curve and the sample coercivity. With a grain coercive field standard deviation adjusted to 0.1 T, it is numerically found that the difference in coercivity between closed- and open-circuit configurations is 40 kA/m, in good agreement with previous experimental data.

Computational Fluid Dynamics Analysis of Gerotor Lubricating Pumps at High-Speed: Geometric Features Influencing the Filling Capability

The paper presents an extensive analysis of the influence on the suction capacity of the main geometric parameters of gerotor lubricating pumps. The study was carried out using a computational fluid dynamics (CFD) model developed with the commercial software PumpLinx®. The model of a reference gerotor unit was validated experimentally in terms of delivered flow rate in different operating conditions, in open and closed circuit configuration. In the former case, different geometries of the inlet pipe were tested. In the latter, the influence of the suction pressure at constant speed was analyzed. After the model validation, several geometric features were changed to assess their influence on the volumetric efficiency in conditions of incomplete filling, such as the thickness and the diameter of the gears, the position of the inlet pipe with respect to the rotors (radial, axial, and tangential), and the shape of the port plate.

Ferromagnetic-Insulator-Based Superconducting Junctions as Sensitive Electron Thermometers

We present an exhaustive theoretical analysis of charge and thermoelectric transport in a normal metal-ferromagnetic insulator-superconductor (NFIS) junction, and explore the possibility of its use as a sensitive thermometer. We investigated the transfer functions and the intrinsic noise performance for different measurement configurations. A common feature of all configurations is that the best temperature noise performance is obtained in the non-linear temperature regime for a structure based on an europium chalcogenide ferromagnetic insulator in contact with a superconducting Al film structure. For an open-circuit configuration, although the maximal intrinsic temperature sensitivity can achieve $10$nKHz$^{-1/2}$, a realistic amplifying chain will reduce the sensitivity up to $10$$\mu$KHz$^{-1/2}$. To overcome this limitation we propose a measurement scheme in a closed-circuit configuration based on state-of-art SQUID detection technology in an inductive setup. In such a case we show that temperature noise can be as low as $35$nKHz$^{-1/2}$. We also discuss a temperature-to-frequency converter where the obtained thermo-voltage developed over a Josephson junction operated in the dissipative regime is converted into a high-frequency signal. We predict that the structure can generate frequencies up to $\sim 120$GHz, and transfer functions up to $200$GHz/K at around $\sim 1$K. If operated as electron thermometer, the device may provide temperature noise lower than $35$nKHz$^{-1/2}$ thereby being potentially attractive for radiation sensing applications.

Staged reverse osmosis operation: Configurations, energy efficiency, and application potential

Reverse osmosis (RO), currently the most energy efficient desalination process, is inherently more energy intensive compared to conventional fresh water treatment technologies, as it is constrained by the thermodynamics of separation of saline solutions. Therefore, pushing the energy consumption towards the thermodynamic limit of separation would lead to significant long-term savings in energy cost. In this work, we quantitatively demonstrate the potential of energy reduction for RO desalination using staged operations with both multi-stage direct pass and closed-circuit configurations. We relate the minimum specific energy of desalination (i.e., the minimum energy required to generate a unit volume of permeate water) to the number of stages in each configuration, and elucidate the fundamental difference between the two configurations. Our analysis suggests that although it is theoretically impossible to reach the thermodynamic minimum energy of separation with closed-circuit RO, this configuration is robust and much more practical to implement than the multi-stage direct pass RO.

Performance of direct and reverse Samarco grinding circuits

This paper compares the performance associated with both direct and reverse ball mill closed circuit configurations. Survey campaigns were carried out in both Samarco Mineração industrial plants, i.e., Concentrator I and Concentrator II. The former is equipped with a reverse-configured ball mill closed grinding circuit, while the latter is equipped with ball mills under a direct closed circuit. The study consisted of laboratory jar tests, as well as comparisons between historical data obtained for both industrial plants. Comparisons based on historical data indicated that Concentrator II, configured in a direct mode, exhibited a better performance than that of Concentrator I. Such a conclusion is in contrast with the results obtained from survey campaigns, which indicated a better performance for the reverse configuration. Such a difference was determined by the performance of the classification stage, carried out in cyclones, as demonstrated by simulations conducted on the basis of previously calibrated models.

Performance of a Yeast-mediated Biological Fuel Cell

Saccharomyces cerevisiae present in common Baker’s yeast was used in a microbial fuel cell in which glucose was the carbon source. Methylene blue was used as the electronophore in the anode compartment, while potassium ferricyanide and methylene blue were tested as electron acceptors in the cathode compartment. Microbes in a mediator-free environment were used as the control. The experiment was performed in both open and closed circuit configurations under different loads ranging from 100 kΩ to 400Ω. The eukaryotic S. cerevisiae-based fuel cell showed improved performance when methylene blue and ferricyanide were used as electron mediators, rendering a maximum power generation of 146.71±7.7 mW/m3. The fuel cell generated a maximum open circuit voltage of 383.6±1.5 mV and recorded a maximum efficiency of 28±1.8 % under 100 kΩ of external load.

PUMP MODE PREDICTION FOR FOUR-QUADRANT VELOCITY CONTROL OF VALUELESS HYDRAULIC ACTUATORS

Displacement-controlled actuation offers energy savings by eliminating the metering losses associated with hydraulic valves and allowing energy recovery. In a closed-circuit configuration, four-quadrant pump operation can be achieved. This paper considers displacement-controlled boom lift cylinders on a skid-steer loader. Undesirable pump mode oscillation is observed while rapidly lowering small loads. Avoiding this oscillation requires actuator pressure control, which cannot be directly achieved due to insufficient pump dynamic response. The authors propose a predictive observer to provide sufficient lead time for feedforward control of actuator pressure. Design and analysis are presented for a discrete time linear observer which predicts future system states by delaying the input signal. Successful state prediction is demonstrated through simulation and experiment.

Magnetic Saturation in Perpendicular Recording

Results of investigations involving calculations using the finite element method and experiments to determine the magnetic saturation during writing for both closed-circuit configuration single-sided heads and open-circuit configuration separated type heads are reported. The single-sided head reaches the same magnetic flux density as the separated-type head at approximately 1/3 the recording current, and the single-sided head has almost three times the recording efficiency of the separated-type head. In the single-sided head magnetic flux density within the media is restricted by magnetic saturation within the closed magnetic circuit.

Balloon Counterpulsation Together with Bio-Medicus Pump Closed Circuit Membrane Oxygenation for Left Ventricular Assist: A Case Report

A 23-year old male was admitted at 1,093 days post cardiac transplantation in cardiac failure. Despite inotropic support and later intra-aortic balloon pumping there was a slow continued fall in cardiac output, renal function and a worsening metabolic state. The patient was then placed on extracorporeal membrane oxygenation (ECMO), consisting of a Bio-Medicus pump and Kolobow membrane oxygenator in a closed circuit configuration (without reservoir). Vascular access was by femoral artery and vein using a non-obstructive technique. Anticoagulation management consisted of a heparin infusion of 2,000 Iu/hour into a peripheral line to an ACT of 170 seconds and a prostacyclin infusion of 3ng/Kg/min. into the venous line. Induction of ECMO was followed by a rapid hemodynamic and metabolic improvement allowing the patient to sit up, talk and eat normally. One hundred and one hours later a new donor organ was located and transplanted. This system has much to recommend it. The equipment forms a compact module. The device functions safely with minimal perfusionist supervision. The system produces excellent offers effective short and medium term support for a range of cardiac and pulmonary disorders. hemodynamic function and offers effective short and medium term support for a range of cardiac and pulmonary disorders.

A generalized transfer parameter treatment of crushing and grinding circuit simulation

A generalized transfer parameter treatment for simulation models of crushing and grinding devices is presented. The treatment is illustrated for existing models of batch and continuous ball mills, air-swept ball mills, vertical (ball-and-race) mills, and double-roll crushers. An extension of the treatment to size reduction devices in closed circuit is given and a single algorithm for simulating open and three common closed circuit configurations is described.

Closed form analytical solutions for models of closed circuit roll crushers

An existing model for the size distributions produced by roll crushers has been put into more convenient form and extended to various closed circuit configurations.

A versatile compact wind tunnel for industrial aerodynamics

A wind tunnel of compact closed circuit configuration designed specifically for industrial aerodynamics is described and its performance discussed. It has a working section 2 m wide × 1 m high × 6.5 m long with a maximum windspeed of 18 m s −1 under typical operating conditions, and a secondary high speed working section 0.5 m wide × 1 m high × 1.75 m long. A feature of the tunnel is a flow processing region upstream of the main working section, where apparatus to simulate various conditions of the atmosphere can be easily and quickly installed and interchanged. The uniformity of velocity and level of turbulence in the main working section are compromised somewhat by the compact design, but are good enough for many industrial aerodynamic problems where simulated natural wind conditions are required rather than an aerodynamically smooth flow. The tunnel is powered by a 60-kW hydraulic drive system, employs contra-rotating fans and a multi-cell rapid diffuser. It is mainly of very simple design and construction. The current cost in Britain (late 1970) would be of the order of £8500, assuming all construction work were contracted out.