Two antagonistic effects of flow/mixing on reactive polymer blending

Reactive polymer blending is basically a flow/mixing-driven process of interfacial generation, interfacial reaction for copolymer formation and morphology development. This work shows two antagonistic effects of mixing on this process: while mixing promotes copolymer formation by creating interfaces and enhancing collisions between reactive groups at the interfaces, excessive mixing may pull the in-situ formed copolymer out of the interfaces to one of the two polymer components of the blend, especially when the copolymer becomes highly asymmetrical. As such, the copolymer may loss its compatibilization efficiency. The mixing-driven copolymer pull-out from the interfaces is a catastrophic process (less than a minute), despite the high viscosity of the polymer blend. It depends on the molecular architecture of the reactive compatibilizer, polymer blend composition, mixing intensity and annealing. These findings are obtained using the concept of reactive tracer-compatibilizer and a model reactive polymer blend.

Designing 3D Membrane Modules for Gas Separation Based on Hollow Fibers from Poly(4-methyl-1-pentene)

Designing hollow fiber (HF) membrane modules occupies one of the key positions in the development of efficient membrane processes for various purposes. In developing HF membrane modules, it is very important to have a uniform HF distribution and flow mixing in the shell side to significantly improve mass transfer and efficiency. This work suggests the application of different textile 3D HF structures (braided hoses and woven tape fabrics). The 3D structures consist of melt-spun, dense HFs based on poly(4-methyl-1-pentene) (PMP). Since the textile processing of HFs can damage the wall of the fiber or close the fiber bore, the membrane properties of the obtained structures are tested with a CO2/CH4 mixture in the temperature range of 0 to 40 °C. It is shown that HFs within the textile structure keep the same transport and separation characteristics compared to initial HFs. The mechanical properties of the PMP-based HFs allow their use in typical textile processes for the production of various membrane structures, even at a larger scale. PMP-based membranes can find application in separation processes, where other polymeric membranes are not stable. For example, they can be used for the separation of hydrocarbons or gas mixtures with volatile organic compounds.

Influence of Magnetic Fields with Induction of 7 T on Physical and Chemical Properties of Aqueous NaCl Solutions

The physicochemical properties of NaCl aqueous solutions in a wide range of concentrations were studied. We determined that constant magnetic fields with an induction of up to 7 T had a significant effect on the physicochemical properties of these solutions. First, we detected a decrease in pH that was dependent on the magnetic field strength both in water and in NaCl solutions. This effect was not associated with the presence of sodium cations or chlorine anions in water. Secondly, with an increase in magnetic field induction the redox potential of aqueous solutions also increased. Magnetic fields did not cause any changes in the concentration of dissolved molecular oxygen in deionized water. In this case, in aqueous solutions of NaCl under the action of a magnetic field, a concentration-dependent tendency to a decrease in the concentration of dissolved molecular oxygen is observed. Third, it was shown that under the action of a magnetic field on a NaCl solution, the rate of hydrogen peroxide generation increased with increasing NaCl concentration. Fourth, the essential role of the primary state of aqueous solutions in relation to the gas composition and gas equilibrium under magnetic influence was established. The work also evaluated the contribution of flow-mixing during sample preparation on the physicochemical properties of the solutions.

Predictive Numerical Analysis to Optimize Ventilation Performance in a Hydropower Surge Chamber for H2S Removal

The role of a hydropower plant surge chamber as a pressure buffer to compensate excessive pressure fluctuations as a result of load demand variations contributes to the degassing phenomenon of hydrogen sulfide (H2S). Recent data collected from the surge chamber of a hydropower plant reveals that the H2S extraction designs are not effective in controlling the H2S concentration levels especially during surge events. To manage a safe working environment in the presence of H2S requires a systematic evaluation and prediction of the influence of critical flow control conditions in relation to suction optimization and exhaust ducting location. A numerical study was carried out to analyze the flow dynamics and the subsequent response of H2S concentrations to cases involving the following flow mixing and suction scenarios: C1 - absence of suction fans, C2 - absence of fresh air supply, C3 - enhanced suction capability, C4 - reduction in the amount of fresh air supply and C5 - presence of additional ducting. The CFD model was able to provide a reliable assessment of the case scenarios as justified by the validation carried out with in-situ measurements (within 10 % of the actual measured data). The cases where the H2S presence was found to be acceptable with concentrations less than 5 ppm at the upper region of the surge chamber, are C3, C4 and C5. A major finding from the flow studies in the surge chamber is that a combination of negative pressure at the suction locations and the absence of the forced fresh air resulted in significant amount of air drawn in from the outdoors. It was also found that the existing forced fresh air inlet locations are inappropriate as they generate vortex flows which displaces the H2S adjacent to the water level upwards and would later fill the entire chamber. All in all, the validated CFD model of the hydropower plant surge chamber was helpful in providing an understanding of the flow conditions in relation to the management of H2S concentrations.

Vane induced two phase flow mixing

Micromixers are used for mixing of multiphase fluids in microchannels. Passive micromixers help in mixing of fluids by having a designed periphery in their structure. In the current study, a Y micro-channel section of 25 mm length with an inlet diameter of 2 mm is considered. Vane shaped micromixers are placed inside the channel to mix fluids of two different concentrations. The vanes are positioned at specific places inside the channel to enhance mixing in the stratified flow stream. The presence of vanes during the flow induces mixing of the stratified fluids without requiring additional components. The study is carried out using COMSOL Multiphysics. The mixing index increases with increase in the number of vanes and no considerable change in velocity is observed downstream of the last vane. Further, when the thickness of the vane is increased, it is found that the mixing index also increases.

How to Control the Microfluidic Flow and Separate the Magnetic and Non-Magnetic Particles in the Runner of a Disc

Biochips play an important role in both medical and food industry safety testing. Moreover, magnetic activated cell sorting is a well-established technology for biochip development. However, biochips need to be manufactured by precision instruments, resulting in the high cost of biochips. Therefore, this study used magnetic-activation and mechanics theories to create a novel disc that could manipulate the microfluidic flow, mixing, reaction, and separation on the runner of the disc. The goal of the research was to apply in the field of biomedical detection systems to reduce the cost of biochips and simplify the operation process. The simulation and experimental investigation showed that the pattern of the reaction chamber was stomach-shaped and the reservoir chamber was rectangular-shaped on the disc. The microfluid could be controlled to flow to the reaction chamber from the buffer and sample chamber when the disc spun at 175~200 rpm within three minutes. This was defined as the first setting mode. The microfluid could then be controlled to flow to the reservoir chamber from the reaction chamber when the disc spun at 225 rpm within five to ten minutes. This was defined as the second setting mode. This verified that the pattern design of the disc was optimized for control of the microfluid flow, mixing, reaction, and separation in the runner of the disc by different setting modes.

Numerical analysis of hydrodynamics influenced by deformed bed due to near-bank vegetation patch

This study with a 2D hydro-morphological model analyzes hydrodynamics over flat and deformed beds with a near-bank vegetation patch. By varying the patch density, the generalized results show that the hydrodynamics over deformed beds differs a lot from those over flat beds. It is found that the deformed bed topography leads to an apparent decrease in longitudinal velocity and bed shear stress in the open region and longitudinal surface gradient for the entire vegetated reach. However, the transverse flow motion and transverse surface gradient in the region of the leading edge and trailing edge is enhanced or maintained, suggesting the strengthening of secondary flow motion. Interestingly, the deformed bed topography tends to alleviate the horizontal shear caused by the junction-interface horizontal coherent vortices, indicating that the turbulence-induced flow mixing is highly inhibited as the bed is deformed. The interior flow adjustment through the patch for the deformed bed requires a shorter distance, La, which is related to the vegetative drag length, (Cda)−1, with a logarithmic formula (La = 0.4ln[(Cda)−1] + b, with b = 3.83 and 4.03 for the deformed and flat beds). The tilting bed topographic effect in the open region accelerating the flow may account for the quick flow adjustment.

On-grid and in-flow mixing for time-resolved cryo-EM

Time-resolved cryo-electron microscopy (TrEM) allows the study of proteins under non-equilibrium conditions on the millisecond timescale, permitting the analysis of large-scale conformational changes or assembly and disassembly processes. However, the technique is developing and there have been few comparisons with other biochemical kinetic studies. Using current methods, the shortest time delay is on the millisecond timescale (∼5–10 ms), given by the delay between sample application and vitrification, and generating longer time points requires additional approaches such as using a longer delay line between the mixing element and nozzle, or an incubation step on the grid. To compare approaches, the reaction of ATP with the skeletal actomyosin S1 complex was followed on grids prepared with a 7–700 ms delay between mixing and vitrification. Classification of the cryo-EM data allows kinetic information to be derived which agrees with previous biochemical measurements, showing fast dissociation, low occupancy during steady-state hydrolysis and rebinding once ATP has been hydrolysed. However, this rebinding effect is much less pronounced when on-grid mixing is used and may be influenced by interactions with the air–water interface. Moreover, in-flow mixing results in a broader distribution of reaction times due to the range of velocities in a laminar flow profile (temporal spread), especially for longer time delays. This work shows the potential of TrEM, but also highlights challenges and opportunities for further development.