Optimal Flow Rate Ratio Research Articles

Preconditioning Operation of Membraneless Vanadium Micro Redox Flow Batteries

AbstractDevelopment of a Membraneless Vanadium Micro Redox Flow Battery (MVMRFB) with an automated closed‐loop control, using micro actuators and micro sensors, is presented for the first‐time during electrolyte preconditioning operation in recirculation mode. The progress of preconditioning is tracked with UV‐vis spectroscopy by 3D printed micro flow cuvettes. Influence of flow rate, reactor internal resistance, and presence of side reactions in the preconditioning process are studied. Optimal flow rate ratio between negative and positive electrolytes is determined and significant performance improvements achieved by operating at lower flow rates are obtained. Influence of reactor internal resistance, which is directly related with the maximum power density, is evaluated demonstrating that operating at a high‐power density can be a source of inefficiency due to the presence of side reactions. Finally, presence of side reactions is evaluated through a dual measurement of electrolytes concentrations in both negative and positive side, and it is demonstrated to be a cause for charge imbalance between the two half‐cells. This work lays a solid foundation for the successful implementation of a charge‐discharge cycle in MVMRFBs operating in recirculation mode.

Simultaneous reduction of nitrogen oxides and sulfur dioxide in circulating fluidized bed combustor during oxy-coal combustion

For stable carbon capture utilization and storage, highly-pure CO2 content and low pollutant emissions must be maintained throughout oxy-coal firing operation; however, studies on combining absorbent addition and oxidant staging combustion to eliminate simultaneous nitrogen oxides (NO, N2O) and sulfur dioxide (SO2) have not been reported. Accordingly, the purpose of this study was to investigate the effects of oxidant staging and limestone addition on the reductions of NO, N2O, and SO2 emissions in an oxy-circulating fluidized bed combustor at 25% and 31% input oxygen. The operating parameters considered in this study were: oxidant compositions; corresponding flow rate ratios; primary, secondary, and tertiary oxidants (PO, SO, and TO, respectively); TO supply heights; and limestone addition. The results revealed that compared to the TO supply heights, increasing TO flow rate was more effective at reducing the nitrogen oxide emissions. Under an optimal flow rate ratio (PO:SO:TO = 70:10:20) and TO height (6.4 m), NO, N2O, and SO2 emissions were ≈7.4, 4.2 and 4.1 mg MJ−1, respectively. The increase in SO2 emission caused by the application of oxidant staging could be effectively decreased by 60.6% without impacting combustion performance via limestone injection into the combustor; effectively facilitating the production of >86 vol% CO2. These findings can serve as valuable references for future designs, and the efficient operation of oxy-coal combustion plants constructed at larger scales, thereby ensuring highly-pure CO2 content and low pollutant emissions.

A needle tip CCEA microfluidic device based on enhanced Dean flow for cell washing

Particle/cell washing is an essential technique in biological and clinical manipulations. Herein, we propose a novel circular contraction–expansion array (CCEA) microdevice. It can be directly connected to a needle tip without connection tubes. Its small size and centrosymmetric structure are beneficial to low sample consumption, high connection stability, and a wide application range. Computational fluid dynamics (CFD) simulation results show that the CCEA structure can produce a stronger Dean flow and lead to faster particle/cell focusing than the circle structure and CEA structure with the same length. Experimentally, an optimal flow rate ratio of 1:3 and an optimal total flow rate of 120 μL/min were found to ensure a stable fluid distribution. Under these conditions, rapid focusing of 10–20 μm particles with high efficiencies was achieved. Compared with a normal CEA device using tubes, the particle loss rate could be reduced from 64 to 7% when washing 500 μL of a rare sample. Cell suspensions with concentrations from 3 × 105/mL to 1 × 103/mL were tested. The high cell collection efficiency (>85% for three cell lines) and stable waste removal efficiency (>80%) reflected the universality of the CCEA microfluidic device. After the washing, the cell activities of H1299 cells and MCF-7 cells were calculated to be 93.8 and 97.5%, respectively. This needle-tip CCEA microfluidic device showed potential in basic medical research and clinical diagnosis.

Simulation of water recovery in membrane condenser dehumidification process

Abstract The high humidity gas dehumidification process and water recovery characteristics in the membrane condenser (MC) were investigated with numerical simulation method in this paper. Different from the traditional condensation process, the hydrophobic porous membrane was utilized for water gases separation. The transmembrane pressure difference was considered as a supplement to the driving force of temperature difference. Results indicate that the porous surface has a positive effect on the high humidity gas dehumidification. It is important to note that water recovery tends to increase and then decrease with inlet feed flow rate increasing from 0.12 L/min to 0.6 L/min. The sweep flow rate ranging from 0.094 L/min to 0.885 L/min were considered. The optimal flow rate ratio between sweep side and feed side is 0.281 for the single-pipe model. It is found that increasing the inlet feed flow temperature from 315 K to 335 K can improve the water recovery over 20%. Additionally, water recovery reduces significantly with the increase of transmembrane flux, for the transmembrane gas reduces the transmembrane temperature difference while increasing the perturbation. These findings would provide important references in using hollow fiber MC for water recovery from high humidity gas.

Separation of exfoliated tumor cells from viscoelastic pleural effusion using a microfluidic sandwich structure.

A microfluidic device with a sandwich structure is proposed to achieve label-free and size-selective separation of tumor cells from pleural effusion. The sandwich structure is a co-flow system incorporating an initial sample layer, an isolation layer and the target sample layer. The isolation layer is used to provide a size-selective interface between the initial sample layer and the isolation layer. The relative magnitude of the inertial lift force and the interfacial lift force at the interface only allows exfoliated tumor cells to migrate out of the sample layer. The high interfacial elastic lift force of the isolation layer also enables the device to be used for pleural effusion samples, whose properties usually vary across a wide range. The target sample layer is used for large migration distances of exfoliated tumor cells in the contraction-expansion array (CEA) channel and high separation efficiency. Cell washing is also achieved with the target sample layer, demonstrating the integration of our device. Experimentally, an optimal flow rate ratio of 1:1:6 was obtained to ensure the stability of the sandwich structure, and the collected fluid was all from the target sample layer. A critical polyethylene oxide (PEO) concentration of the isolation layer (500ppm, η0 = 1.37mPa·s) was then obtained by particle tests. Twenty-micrometer particles were efficiently separated from different viscoelastic samples (PEO concentration changes from 0 to 400ppm) at this concentration. For the cell test, exfoliated tumor cells from different pleural effusion samples were successfully separated and washed. The separation efficiency of exfoliated tumor cells and blood cells was about 100% and over 90%, respectively. Compared with a conventional co-flow system of two fluids, this device has great advantages in 1) wide applicability for pleural effusion samples of various viscoelasticity and 2) focusing performance. It shows potential for use in medical research and clinical diagnosis of cancer.

Energy efficiency of membrane distillation: Simplified analysis, heat recovery, and the use of waste-heat

Membrane distillation (MD) is a thermal desalination process that is advantageous due to its ability to harness low-grade waste heat to separate highly saline feedstock. However, like any thermal desalination process, the energy efficiency depends on the ability to recover latent heat from condensation in the distillate. In direct contact MD (DCMD), this can be achieved by integrating a heat exchanger (HX) to recover latent heat stored in the distillate stream to preheat the incoming feed stream. Based on the principle of equal heat capacity flows, we derive a simple and intuitive expression for the optimal flow rate ratio between the feed and distillate streams to best recover this latent. Following the principle of energy balance, we derive simple expressions for the specific thermal energy consumption (SECth) and gained output ratio (GOR) of DCMD with and without a coupled HX for latent heat recovery, revealing an intuitive critical condition that indicates whether DCMD should or should not be coupled with HX. As MD is attractive for its ability to use low-grade waste heat as a heat source, we also evaluate the energy efficiency of DCMD powered by a waste heat stream. A waste heat stream differs fundamentally from a conventional constant-temperature heat source in that the temperature of the waste heat stream decreases as heat is extracted from it. We discuss the implication of this fundamental difference on energy efficiency and how we should analyze the energy efficiency of DCMD powered by waste heat streams. A new metric, namely specific yield, is proposed to quantify the performance of DCMD powered by waste heat stream. Our analysis suggests that, for a single-stage DCMD powered by a waste heat stream, whether implementing latent heat recovery or not only affects conventional metrics for energy efficiency (e.g. SECth and GOR) but not the specific yield. Overall, this analysis presents an intuitive and important framework for evaluating and optimizing energy efficiency in DCMD.

A Method for Optimizing Jet-Mill-Bit Hydraulics in Horizontal Drilling

Summary Efficient cuttings transport is a major challenge in horizontal drilling; one can use a new type of jet-mill bit to overcome the challenge fundamentally. However, currently, there is no available method for optimizing jet-mill-bit hydraulics, which restricts the jet-mill bit from being widely used. In this paper, on the basis of the high-pressure water-jet comminution and jet-pump theory, a basic performance model of the jet-mill bit is developed. Then, the optimal parameter model for the jet-mill bit is presented according to the multivariable limitation theory; meanwhile, a method for optimizing jet-mill-bit hydraulics is also developed. With the method, one can determine the optimal jet-mill-bit hydraulics. Theoretical analysis and discussion show that the impact angle and the friction-loss coefficient are the key factors affecting the efficiency of the jet-mill bit; the impact angle is suggested to be set at approximately 70 ° and the optimal flow-rate ratio at appoximately 1.0; and the effect of rate of penetration (ROP, m/h) is not obvious, and one can ignore it. The optimal area ratio is almost not related to friction-loss coefficient and ROP, but it is related to the impact angle significantly. It provides drilling engineers a practical tool for determining the optimal jet-mill-bit hydraulics in horizontal drilling and promotes the jet-mill bit to be widely used.

The recovery of sulphuric acid from the waste anodic aluminum oxidation solution by diffusion dialysis

The recovery of H 2SO 4 from waste anodic aluminum oxidation solution using diffusion dialysis process was investigated by a series of batch, dynamic and pilot-scale tests. Experimental results from batch tests indicated that to some extent agitation could reduce concentration polarization phenomenon and CuSO 4 could enhance proton permeability throughout the DF120 anion exchange membrane. Dynamic experimental results showed that both acid recovery and H + concentration in recovered acid decreased with flow rate increase when the flow rate ratio of water to feed was kept at 1.0, and the optimal flow rate range of 3.0 × 10 −4 m 3/h to 5.0 × 10 −4 m 3/h (corresponding to the membrane flux of 9.4 × 10 −5 m 3/h m 2 to 1.56 × 10 −4 m 3/h m 2) was obtained. Although acid recovery efficiency could be improved by increasing the flow rate ratio, the recovered acid concentration decreased and metal leakage increased. And it is confirmed that the optimal flow rate ratio of water to feed should be controlled at 1.0–1.2. Pilot-scale tests performed very well when using the wastewater from a real anodic aluminum oxidation plant. H 2SO 4 recovery, recovered acid concentration and Al 3+ leakage in steady-state condition were 85.25%, 4.08 mol/L and 4.98%, respectively, suggesting that diffusion dialysis is a cost-effective technique for acid recovery from waste anodic aluminum oxidation solution.

Optimization and design considerations of two-phase continuous protein separation

Aqueous two-phase systems (ATPS) have begun to be used industrially for the isolation and separation of recombinant enzyme proteins. However, until now most studies have concentrated on investigating factors affecting the partition coefficients of molecules and even the pilot plant and scale-up developments have lacked engineering, optimization and design considerations. This paper investigates such considerations in the process of protein separation and purification in ATPS. A cost function for the process of protein extraction that takes into account the effect of variables in ATPS has been developed to study the influence of this extraction stage over the rest of the stages in the process (production, concentration and purification). The effect of the flow rate ratios, the relative sizes of the PEG and Phosphate phases and the NaCl concentration have been analysed. An extended mathematical model was used to describe the continuous, steady state operation of an aqueous two-phase system for protein extraction. The basic model is based on steady state mass balances of the main components and phase equilibrium data. Experimental data on the separation of α-amylase from Bacillus subtilis supernatant in a PEG/salt system was used. Simulations were carried out to study the effect of flow rate ratio as a function of NaCI concentration in the feed. At a flow rate ratio above 2.4 the extraction process was very sensitive to NaCl concentration. A rigorous optimization was carried out using the Sequential Quadratic Programming Method (SQP) with a fixed initial NaCI concentration of 8.8%. An optimal Flow Rate Ratio of 2.27 was obtained. Thus, the optimization strategy developed in this paper was mathematically implementable and successful. The optimal steady state process conditions corresponded to conditions of a large and continuous bottom phase in both the forward and back extractions. This is very favourable for phase separation as it results in fast settling rates which are also virtually independent of phase volume ratio, which are extremely favourable conditions for the design of appropriate settlers.