Mixing in the NETmix Reactor

NETmix is a static mixing reactor composed of a network of mixing chambers interconnected by channels. The repetitive mixing pattern inside the reactor enables the use of reduced geometries to represent the NETmix network, such as the ExtendedNUB model, used in this work. Mixing in NETmix is based on the impingement of jets, issuing from channels. Inside the chambers, the jets are engulfed by dynamic vortices which can be quantified using Lagrangian techniques. Batch Lagrangian Mixing Simulation (BLMS) is based on successive injections of particles to measure the fraction of the fluids at the outlet of the mixing chambers. The distribution of the outlet fraction of particles indicates that it is possible to have nearly perfect mixing inside the NETmix chambers, depending on the dimensions of the channels and chambers. The NETmix design is here optimized in relation to the chamber diameter to channel width ratio, D/d. Results from BLMS show that best performance in NETmix occurs for 6.65≤D/d≤6.85.

On the spacing of meandering jets in the strong-stair limit

Based on an assumption of strongly inhomogeneous potential vorticity mixing in quasi-geostrophic $\beta$ -plane turbulence, a relation is obtained between the mean spacing of latitudinally meandering zonal jets and the total kinetic energy of the flow. The relation applies to cases where the Rossby deformation length is much smaller than the Rhines scale, in which kinetic energy is concentrated within the jet cores. The relation can be theoretically achieved in the case of perfect mixing between regularly spaced jets with simple meanders, and of negligible kinetic energy in flow structures other than in jets. Incomplete mixing or unevenly spaced jets will result in jets being more widely separated than the estimate, while significant kinetic energy outside the jets will result in jets closer than the estimate. An additional relation, valid under the same assumptions, is obtained between the total kinetic and potential energies. In flows with large-scale dissipation, the two relations provide a means to predict the jet spacing based only on knowledge of the energy input rate of the forcing and dissipation rate, regardless of whether the latter takes the form of frictional or thermal damping. Comparison with direct numerical integrations of the forced system shows broad support for the relations, but differences between the actual and predicted jet spacings arise both from the complex structure of jet meanders and the non-negligible kinetic energy contained in the turbulent background and in coherent vortices lying between the jets.

The dependence between the structural-morphological features mixes 0.8SiO2/0.2Al2O3 from the time of mechanicall treatment

This paper highlights the relationship between changes in structural and morphological features, electronic structure and exanging of time mechanical treatment at microbraker (MBT). Scaning electron microscopy revealed a change in the morphological features of nanoscale powders. From the comparison of SEM images of 0.8SiO2/0.2Al2О3 mixture before and after MBT, it is established that due to MBT, the agglomerates of the initial components are simultaneously crushed with perfect mixing particles of oxides between each other and the formation of new agglomerates with a denser structure. The increase in processing time leads to an increase in the density of the nanocomposite. The effect of time of mechanical treatment on the structural parameters and phase composition of mixtures of silicon dioxide and titanium were studied using the method of X-ray structural analysis. The established agglomeration is accompanied by a change in the lattice parameter c with a change in the regions of coherent scattering of crystalline Al2О3. Ultra-soft X-ray emission spectroscopy was used to study the distribution of Op-, Sisd- and Alsd- valence electrons in 0.8SiO2/0.2Al2О3 powder mixtures after the different time of mechanicall treatment. An increase in atomic charges has been measured and can be explained by the transfer of electrons from Si and Al to O atoms in split Opπ-binding states.

A simulation study of nonideal mixing effect on the dynamic response of an exothermic CSTR with Cholette’s model

The study of nonideal mixing effect on the dynamic behaviors of CSTRs has very rarely been published in the literature. In this work, Cholette’s model is employed to explore the nonideal mixing effect on the dynamic response of a nonisothermal CSTR. The analysis shows that the mixing parameter n (the fraction of the feed entering the zone of perfect mixing) and m (the fraction of the total volume of the reactor), indeed affect the characteristic roots of transfer function of a real CSTR, which determine the system stability. On the other hand, the inverse response and overshoot response are also affected by the nonideal mixing in a nonisothemal CSTR. These results are of much help for the design and control of a real CSTR.

INFLUENCE OF FLUE GAS PATTERN FLOW IN BOILER RADIANT SECTION ON HEAT TRANSFER

During the sizing of the radiant zone in boilers and furnaces, the most often used method is the Lobo-Evans model. This method is based on the perfect mixing model for flue gas flow inside the fire box, which represents a conservative or pessimistic flow pattern. This paper presents a different, optimistic model which is based on the plug flow for flue gas flow which results in the largest possible heat duty. The proposed model is given in two distinct forms – integral and numerical. As shown in the paper, the integral model results in small deviations with respect to the numerical model and, as such, is well suited for the engineering practice. Paper also presents an engineering approach to the calculation of the conductive heat transfer through the membrane wall, which is shown to be sufficiently accurate and simple for engineering calculations.

Influence of geometry on eruptive behaviour of magma reservoirs

<p>All active polygenetic volcanoes erupt magma sourced from a shallow crustal reservoir.  Those chambers are complex entities that act as a collector of magma originating from deeper crustal sources. The geometry of those active storage systems depends on the rheology of the magma and on the rock properties of the host. Studying how the geometry influences the eruptive behaviour of a magma chamber has implications for our understanding of volcanic hazard.<br>We introduced a simple model where a magma reservoir is cooled by an overlying geothermal system and recharged by a deeper magma source. The geometry of the chamber is defined by its volume and aspect ratio. The model tracked changes in pressure, mixture enthalpy and composition, and implemented parameterisations of eruption, hydrothermal cooling, viscoelastic relaxation, and volatile leakage. The thermodynamic properties of the melt, crystals and water were computed using rhyolite-MELTS.<br>A large number of simulations sweeping our parameter space gave us insight into how the different magmatic processes trade off with respect to the geometry of the inclusion. An example of the complex control of geometry on the eruptive behaviour can be made regarding cooling and the effective compressibility of an ellipsoidal inclusion. On the one hand, a larger aspect ratio will favor eruptibility by offering a larger area for cooling therefore increasing the exsolution of water and pressure build up. On the other hand, a larger aspect ratio will work against eruptibility by decreasing the compressibility making it harder to build overpressures within the chamber. We found that a specific geometry is required in order for a chamber to erupt without any external stimuli (such as a large recharge event).<br>A limiting factor of our model is the assumption of a perfect mixing. Whereas, in reality, we would expect recharge, cooling and leakage to occur within specific regions of the chamber. In a model where mixing is not considered perfect, those processes would be a source of heterogeneity. We could conjecture that under the right conditions, eruptible regions would appear within the chamber. A model focusing more on the flows within the chamber might be able to give additional insights on the eruptive behaviour of magma chambers.</p>

Application of Cholette’s model in non-ideal mixing CSTR: a simulation study on dynamic behavior

Non-ideal mixing phenomena are widely found in industrial chemical reactors. In this work we derived the bifurcation formulas for a non-adiabatic CSTR with an irreversible exothermic first order reaction with the non-ideal mixing effect. This is investigated via dynamic behavior simulations based on Chollete’s model. The results show that the non-ideal mixing parameter n (the fraction of the feed entering the perfect mixing zone) determines the variation between six classified regions and dominates the dynamic behavior patterns in the steady-state response diagram. On the other hand, the phase portraits of examples verify the formulas derived in this work. We note that the non-ideal mixing effect has significant importance in CSTR design and control steps. For example, in the safe operating region for an ideal mixing CSTR, non-linear dynamics are obtained by the system under non-ideal mixing conditions (n ≠ 1). The present study has significance and help for chemical reactor design and CSTR control.

Gastroenterology Procedures Generate Aerosols: An Air Quality Turnover Solution to Mitigate COVID-19’s Propagation Risk

The growing fear of virus transmission during the 2019 coronavirus disease (COVID-19) pandemic has called for many scientists to look into the various vehicles of infection, including the potential to travel through aerosols. Few have looked into the issue that gastrointestinal (GI) procedures may produce an abundance of aerosols. The current process of risk management for clinics is to follow a clinic-specific HVAC formula, which is typically calculated once a year and assumes perfect mixing of the air within the space, to determine how many minutes each procedural room refreshes 99% of its air between procedures when doors are closed. This formula is not designed to fit the complex dynamic of small airborne particle transport and deposition that can potentially carry the virus in clinical conditions. It results in reduced procedure throughput as well as an excess of idle time in clinics that process a large number of short procedures such as outpatient GI centers. We present and tested a new cyber-physical system that continuously monitors airborne particle counts in procedural rooms and also at the same time automatically monitors the procedural rooms’ state and flexible endoscope status without interfering with the clinic’s workflow. We use our data gathered from over 1500 GI cases in one clinical suite to understand the correlation between air quality and standard procedure types as well as identify the risks involved with any HVAC system in a clinical suite environment. Thanks to this system, we demonstrate that standard GI procedures generate large quantities of aerosols, which can potentially promote viral airborne transmission among patients and healthcare staff. We provide a solution for the clinic to improve procedure turnover times and throughput, as well as to mitigate the risk of airborne transmission of the virus.

Reactor engineering calculations with a detailed reaction mechanism for the oxidative coupling of methane

The oxidative coupling of methane (OCM) is a potential option for conversion of excess natural gas to higher value products or useful feedstocks. The preferred or ideal OCM stoichiometry is: 2CH4 + O2 → C2H4 + 2H2O, but real OCM produces a variety of species. Using a detailed mechanism from the literature for OCM over a La2O3/CeO2 catalyst that combines coupled elementary gas phase and surface reactions, a reactor engineering study has been done. Adiabatic packed bed reactor (PBR, modeled as plug flow) and continuous stirred tank reactor (CSTR, perfect mixing) simulations using this mechanism are presented. Each reactor simulation used the same total number of catalyst sites. Process variables included CH4/O2 feed ratio (7, 11), feed temperature (843–1243 K), and feed rate. All runs were conducted at 1.01E5 Pa pressure. The results show the CSTR produces high conversions at much lower feed temperatures than those required by the PBR. Once full PBR “light off” occurs, however, its CH4 conversions exceed CSTR. The simulations reveal OCM over this catalyst at these conditions gives a mixture of synthesis gas (CO, H2) and C2Hx (primarily C2H4 plus small quantities of C2H6 and C2H2). The CSTR favors the production of synthesis gas, while the PBR favors C2Hx. Within the suite of CSTR cases, C2Hx is favored at the lowest feed temperature and highest CH4/O2 feed ratio.