Reaction Cavity Research Articles

Improvement of microwave heating efficiency by parabolic concentrator

The conventional microwave heating reaction cavity has deficiency of low heating efficiency, which will waste energy and even burn the microwave source and equipment. Therefore, to improve the heating efficiency will save energy and protect the microwave device. In this article, without changing the original heating reaction cavity, a parabolic wave concentrator is proposed to improve the heating efficiency of the microwave heating system. The first part of the article introduces the design and principle of the microwave wave concentrator and describes the control equation of microwave heating and the input parameters of the cavity. In the second part, based on the finite element method calculation, four feeding modes (single, dual, side, and inclined feed port) are simulated to verify the heating efficiency improvement after adding the wave concentrator. Finally, a microwave heating reaction cavity with an inclined feed port is built and used to carry out experiments, which validate the simulation results. The simulation and experiment results show that adding the wave concentrator has greatly improved the heating efficiency.

Optimisation and numerical simulation of ultrasonic reactor in hydrometallurgical process

ABSTRACT In this paper, COMSOL Multiphysics software is used to carry out simulations to visualise the distribution of the acoustic field and sound pressure in the reaction cavity for different ultrasonic frequencies, powers, reaction cavity shapes, ultrasonic horn diameters and ultrasonic horn action depths. The results indicate the ultrasonic frequency affects the uniformity of the acoustic field distribution, and the ultrasonic power affects the magnitude of the sonic pressure. Taking into account that the sonic pressure is not less than the cavitation threshold, the sound field is evenly distributed, and it is energy-saving and environment-friendly. The optimal simulation conditions are obtained. In a 500 mL cylindrical reaction chamber, the ultrasonic frequency and power are 25 kHz and 130 W, respectively. The diameter of the ultrasonic horn is 34 mm, and the depth of action is 30 mm. Under these conditions, the maximum sound pressure reaches 1.08 × 106 Pa.

Characterization of the ubiquinone reaction cavity in mitochondrial respiratory complex I using artificial ligands

Characterization of the ubiquinone reaction cavity in mitochondrial respiratory complex I using artificial ligands

Crystal Engineering-Driven Sunlight Responsiveness and Flexible Waveguide Transmission.

Here, a barbituric acid derivative containing pyrene rings (DPPT) was successfully synthesized, and two types of crystals were prepared by using crystal engineering methods. Orange sheet-like crystals (DPPT-O, observed in visible light), prepared in a DCM/CH3OH solution, exhibited brittleness and weak fluorescence emission, along with sunlight-induced bending and fracturing. Red needle-like crystals (DPPT-R, also observed in visible light), synthesized in a DCM/CH3CN solution, demonstrated elastic properties, strong fluorescence emission, and excellent optical waveguide performance (with an optical loss coefficient of 0.23-0.30 dB mm-1). Single-crystal data analysis revealed that the stacking arrangement of molecules critically influenced the elasticity of the crystals, while the reaction cavity size regulated the photomechanical properties of the crystals. This study achieved effective control over sunlight responsiveness and flexible optical waveguide transmission for the first time, providing innovative insights for the application of homogeneous organic polycrystalline molecular crystals in this field.

Controlled near-field boundaries to improve microwave heating performances

In this paper, we show that controlled near-field boundaries (CNFBs) fabricated from height-shiftable plate arrays (HSPAs) exhibit significant influences on the electromagnetic field distribution, which largely determines the performances of microwave heating; the significant influences provide a possibility to further improve the performances of microwave heating. First, the near-field boundary is proved theoretically having more influences on electromagnetic fields than the far-field boundary. Then, the CNFBs are fabricated by respectively placing three HSPAs, 2 × 2, 3 × 3, and 4 × 4, in a microwave reaction cavity (MRC). Based on the HSPA-MRC, three heating strategies are proposed to achieve extreme heating efficiency, excellent heating uniformity, and the best comprehensive heating performance, respectively. Compared with the conventional MRC, the proposed HSPA-MRC raises 56.27% heating efficiency and 394.64% heating uniformity. To validate the simulation results, a corresponding experiment system is built and experiments are carried out; the results of the experiments agree very well with simulations. Finally, the sensitivity of the proposed heating strategies is analyzed by heating samples with different shapes, sizes and materials.

Theoretical insights into the formation of oxygen activation sites with the affection of protein microenvironment in Flavin-Dependent monooxygenases MsuD

Flavin-dependent monooxygenases are very famous for their capability to catalyze the oxidation of various substrates using oxygen and reduced flavin mononucleotide (FMNH-) or reduced flavin adenine dinucleotide (FADH-). When investigating the catalytic mechanism of flavin-dependent monooxygenase systems, a fundamental problem remains unsolved is that the O2 binding scheme within the reaction cavity is unclear. By applying molecular dynamics simulations, MDpocket simulations, residue mutation molecular dynamics simulation and energy decomposition analyses, this work identified the O2 binding pockets and discovered a possible oxygen migration channel within MsuD enzyme. Molecular dynamics simulations after residue mutation proved that residues Asn104 plays an important role in maintaining the O2 position within the reaction cavity. By analyzing the interaction between O2 and the surrounding protein microenvironment, we demonstrated that N5 is a more favored reaction site and speculated a reasonable O2 activation process. This work recovers the formation of oxygen activation sites in MsuD enzyme, which is of great significance to further investigations of the catalytic reaction mechanism. This work provides a feasible method to study the O2 binding in proteins and the role of the protein microenvironment around the reaction cavity.

Iron‐Catalyzed Stereoconvergent 1,4‐Hydrosilylation of Conjugated Dienes

AbstractStereoconvergent transformation of E/Z mixtures of olefins to products with a single steric configuration is of great practical importance but hard to achieve. Herein, we report an iron‐catalyzed stereoconvergent 1,4‐hydrosilylation reactions of E/Z mixtures of readily available conjugated dienes for the synthesis of Z‐allylsilanes with high regioselectivity and exclusive stereoselectivity. Mechanistic studies suggest that the reactions most likely proceed through a two‐electron redox mechanism. The stereoselectivity of the reactions is ultimately determined by the crowded reaction cavity of the α‐diimine ligand‐modified iron catalyst, which forces the conjugated diene to coordinate with the iron center in a cis conformation, which in turn results in generation of an anti‐π‐allyl iron intermediate. The mechanism of this stereoconvergent transformation differs from previously reported mechanisms of other related reactions involving radicals or metal‐hydride species.

Iron-Catalyzed Stereoconvergent 1,4-Hydrosilylation of Conjugated Dienes.

Stereoconvergent transformation of E/Z mixtures of olefins to products with a single steric configuration is of great practical importance but hard to achieve. Herein, we report an iron-catalyzed stereoconvergent 1,4-hydrosilylation reactions of E/Z mixtures of readily available conjugated dienes for the synthesis of Z-allylsilanes with high regioselectivity and exclusive stereoselectivity. Mechanistic studies suggest that the reactions most likely proceed through a two-electron redox mechanism. The stereoselectivity of the reactions is ultimately determined by the crowded reaction cavity of the α-diimine ligand-modified iron catalyst, which forces the conjugated diene to coordinate with the iron center in a cis conformation, which in turn results in generation of an anti-π-allyl iron intermediate. The mechanism of this stereoconvergent transformation differs from previously reported mechanisms of other related reactions involving radicals or metal-hydride species.

Improvement of Microwave Heating Efficiency and Uniformity by Controllable Rotary Columns Array

The electromagnetic boundary (EMB) will primarily determine the reflection and distribution of the electromagnetic field. Therefore, a controllable time-varying EMB of microwave reaction cavity (MRC) provides a possibility for improving heating efficiency and uniformity. In this article, a controllable time-varying EMB is fabricated by placing a controllable rotary column array (CRCA) in a conventional cylindrical MRC, where the CRCA consists of 20 circularly arranged controllable eccentric rotary copper columns. The influence of the eccentric distance and the rotating angle of CRCA on the heating efficiency and uniformity are studied by the finite element simulation software—COMSOL Multiphysics. Based on CRCA, angle selection and dynamic rotational heating processes are proposed. Furthermore, the heating uniformity of the angle selection heating process is optimized by using the minimum method of energy loss distribution coefficient of variation (COV). To validate the simulation result, the corresponding heating system is made and the experiments are carried out, and the experiment result agrees very well with the simulations. The simulation result also shows that the heating efficiency and uniformity are improved up to 31.52% and 220.62%, respectively. Finally, the effects of the two heating processes on objects of different shapes and materials are discussed.

Respiratory complex I in mitochondrial membrane catalyzes oversized ubiquinones

NADH-ubiquinone (UQ) oxidoreductase (complex I) couples electron transfer from NADH to UQ with proton translocation in its membrane part. The UQ reduction step is key to triggering proton translocation. Structural studies have identified a long, narrow, tunnel-like cavity within complex I, through which UQ may access a deep reaction site. To elucidate the physiological relevance of this UQ-accessing tunnel, we previously investigated whether a series of oversized UQs (OS-UQs), whose tail moiety is too large to enter and transit the narrow tunnel, can be catalytically reduced by complex I using the native enzyme in bovine heart submitochondrial particles (SMPs) and the isolated enzyme reconstituted into liposomes. Nevertheless, the physiological relevance remained unclear because some amphiphilic OS-UQs were reduced in SMPs but not in proteoliposomes, and investigation of extremely hydrophobic OS-UQs was not possible in SMPs. To uniformly assess the electron transfer activities of all OS-UQs with the native complex I, here we present a new assay system using SMPs, which were fused with liposomes incorporating OS-UQ and supplemented with a parasitic quinol oxidase to recycle reduced OS-UQ. In this system, all OS-UQs tested were reduced by the native enzyme, and the reduction was coupled with proton translocation. This finding does not support the canonical tunnel model. We propose that the UQ reaction cavity is flexibly open in the native enzyme to allow OS-UQs to access the reaction site, but their access is obstructed in the isolated enzyme as the cavity is altered by detergent-solubilizing from the mitochondrial membrane.

Design of large horizontal gallium nitride hydride vapor-phase epitaxy equipment and optimization of process parameters

Gallium nitride (GaN) has been extensively investigated in the last two decades owing to its excellent characteristics and massive commercialization potential. GaN substrates have been increasingly investigated to enhance the quality and efficiency of GaN-based optoelectronic devices. Hydride vapor-phase epitaxy (HVPE) method is generally employed for preparing GaN substrates. Herein, a six-inch horizontal HVPE equipment was designed using computational fluid dynamics (CFD) for depositing GaN epitaxial thin films. First, the original model was structurally designed, and baffles and other structures were set to achieve uniform outlet velocity. Second, single-factor variable method was used to analyze the influence of process parameters (flow rate, chamber pressure, and rotating speed) on deposition rate. An orthogonal design was used to optimize the main process parameters for uniform film deposition on six-inch substrates. Numerical simulation results provide a theoretical basis for optimizing a large-size HVPE reaction cavity and process conditions, paving the way for high-quality large-size GaN epitaxial thin films.

Influence of Ridge Groove Structure on Local Field Distribution in Microwave Reaction Cavity

Uneven energy distribution and “hotspot” phenomenon are bottlenecks restricting the development of the microwave heating industry. The formation of high-intensity electric field aggregation areas can be effectively repressed by optimizing the reaction cavity structures. With a box-type microwave reaction cavity as the study object and an external ridge groove as the induction device, the influences of the structural parameters of different devices on the microwave local field distribution were analytically explored through the simulation technology, and a “hotspot” early warning method was proposed. This study provides a reference for inhibiting the “hotspot” phenomenon on microwave fields and optimally designing microwave reactors.

Influence of convex spherical device on the local field distribution in the microwave reaction cavity

Uneven energy distribution and “hotspot” phenomenon are bottlenecks restricting the development of the microwave heating industry. The formation of high-intensity electric field aggregation areas can be effectively repressed by optimizing the reaction cavity structures. With a box-type microwave reaction cavity as the study object and a built-in convex spherical as the induction device, the influences of the structural parameters of different devices on the microwave local field distribution were analytically explored through the simulation technology, and a “hotspot” early warning method was proposed. This study provides a reference for inhibiting the “hotspot” phenomenon on microwave fields and optimally designing microwave reactors.

Supratough and stretchable hydrogels with time-space controllability for athletic rehabilitation

There is a higher risk of injury for athletes when the intensive competition occurs. Minimally invasive surgery is still the first choice for athletes because of its small wound surface and fast recovery. In addition, knowing whether athletes recover in real time at the first time is beneficial for the athletes to return to the competition as soon as possible and maintain their peak performance. We developed a medical hydrogel to meet the dual needs of minimally invasive therapy and wearable testing. A novel ε-PL/PVP/MXene (εPM) hydrogel with spatio-temporal control and in situ enhancement was prepared by the concept of microchemical reaction cavity. MXene was introduced as the microchemical reaction center, and the dual effects of heat transport and microcatalysis were utilized to make the gel network uniform and moldability after injection in vivo, so as to realize the filling and treatment of irregular wounds. The hydrogel tissue is not only adhesive, self-healing and soft, but also super tough, keeping its shape stable under repeated stretches, intense hammering, continuous trampling, and even the extremely catastrophic impact of being run over 50 times by a car. At the same time, the hydrogel has excellent ionic conductivity (4.12 S/m) and sensing ability, which can record athletes' movement characteristics in real time and transmit them to doctors through wireless Bluetooth, so as to make accurate judgment on the recovery of health. This is the first exploration of the combination of hydrogel in the field of minimally invasive therapy and wearable devices, which opens up a new avenue for efficient minimally invasive therapy and accurate rehabilitation monitoring.

Photochemistry in a capsule: controlling excited state dynamics via confinement.

Exerting control on excited state processes has been a long-held goal in photochemistry. One approach to achieve control has been to mimic biological systems in Nature (e.g., photosynthesis) that has perfected it over millions of years by performing the reactions in highly organized assemblies such as membranes and proteins by restricting the freedom of reactants and directing them to pursue a select pathway. The duplication of this concept at a smaller scale in the laboratory involves the use of highly confined and organized assemblies as reaction containers. This article summarizes the studies in the author's laboratory using a synthetic, well-defined reaction container known as octa acid (OA). OA, unlike most commonly known cavitands, forms a capsule in water and remains closed during the lifetime of the excited states of included molecules. Thus, the described excited state chemistry occurs in a small space with hydrophobic characteristics. Examples where the photophysical and photochemical properties are dramatically altered, compared to that in organic solvents wherein the molecules are freely soluble, are presented to illustrate the value of a restricted environment in controlling the dynamics of molecules on an excited state surface. While the ground state complexation of the guest and host is controlled by well-known concepts of tight-fit, lock and key, complementarity, etc., free space around the guest is necessary for it to be able to undergo structural transformations in the excited state, where the time is short. This article highlights the role of free space during the dynamics of molecules within a confined, inflexible reaction cavity.

Crystalline-State Photochromism of a Newly Synthesized Rhodium Dithionite Complex with Inflexible Cyclo-Pentyl Groups

Abstract A rhodium dinuclear complex having inflexible cyclo-pentyltetramethylcyclopentadienyl (CpCyPen = η5-C5Me4cyclo-C5H9) and photoresponsive dithionite (μ-O2SSO2) ligands, [(CpCyPenRh)2(μ-CH2)2(μ-O2SSO2)] (1CyPen), was newly synthesized. Crystalline-state photochromism between 1CyPen and the corresponding μ-O2SOSO complex (2CyPen) was successfully investigated by performing time-dependent X-ray diffraction experiments. Without any degradation of the crystal, type-T inverse photochromic reaction based on the μ-O2SSO2 ligand proceeded within the rigid reaction cavity formed by the inflexible CpCyPen ligands.

Enzyme-Catalyzed Hydrolysis of Lipids in Immiscible Microdroplets Studied by Contained-Electrospray Ionization.

Enzyme-catalyzed hydrolysis of lipids was monitored directly in immiscible microdroplet environments using contained-electrospray mass spectrometry. Aqueous solution of the lipase enzyme from Pseudomonas cepacia and the chloroform solution of the lipids were sprayed from separate capillaries, and the resultant droplets were merged within a reaction cavity that is included at the outlet of the contained-electrospray ionization source. By varying the length of the reaction cavity, the interaction time between the enzyme and its substrate was altered, enabling the quantification of reaction product as a function of time. Consequently, enhancement factors were estimated by comparing rate constants derived from the droplet experiment to rate constants calculated from solution-phase conditions. These experiments showed enhancement factors greater than 100 in favor of the droplet experiment. By using various lipid types, two possible mechanisms were identified to account for lipase reactivity in aerosols: in-droplet reactions for relatively highly soluble lipids and a droplet coalescence mechanism that allows interfacial reactions for the two immiscible systems.

Laser-induced graphene non-enzymatic glucose sensors for on-body measurements

Non-enzymatic glucose sensors outperform enzymatic ones in terms of cost, sensitivity, stability, and operating duration. Though highly sensitive, it is still desirable to further improve the sensitivity of non-enzymatic glucose sensors to detect a trace amount of glucose in sweat and other biofluids. Among the demonstrated effective approaches using bimetals or 3D porous structures, the porous laser-induced graphene (LIG) on flexible polymers showcases good conductivity and a simple fabrication process for the integration of sensing materials. The uniform electroless plating of the nickel and gold layer on LIG electrodes demonstrates significantly enhanced sensitivity and a large linear range for glucose sensing. The sensor with the porous LIG foam exhibits a high sensitivity of 1080 μA mM−1 cm−2, whereas a further increased sensitivity of 3500 μA mM−1 cm−2 is obtained with LIG fibers (LIGF). Impressively, a large linear range (0–30 mM) can be achieved by changing the bias voltage from 0.5 to 0.1 V due to the Au coating. Because the existing non-enzymatic glucose sensors are limited to use in basic solutions, their application in wearable electronics is elusive. In addition to the reduced requirement for the basic solution, this work integrates a porous encapsulating reaction cavity containing alkali solutions with a soft, skin-interfaced microfluidic component to provide integrated microfluidic non-enzymatic glucose sensors for sweat sampling and glucose sensing. The accurate glucose measurements from the human sweat and cell culture media showcase the practical utility, which opens up opportunities for the non-enzymatic glucose sensors in wearable electronics.

A high temperature tubular reactor with hybrid concentrated solar and electric heat supply for steam methane reforming

Solar-powered steam methane reforming could offer an efficient avenue for hydrogen generation, therefore reducing carbon dioxide emissions. However, the current solar thermochemical reactor (STR) is subjected to the mismatch between the continuous chemical process and the intermittent solar irradiance. In this work, we proposed a novel heat pipe tubular reactor based on the high-temperature heat pipe, i.e., a high-temperature heat pipe reactor (HTPR), achieving a highly effective heat transfer and a hybrid energy supply, i.e., concentrated solar energy and photovoltaic electricity. These two heating modes enable the HTPR to achieve a round-the-clock reforming process. Firstly, the HTPR start-up performance was measured by a concentrated solar simulator and a high-frequency induction device, and the start-up time for both heating modes was only 9 min. The methane conversion and the hydrogen purity were respectively 90% and 74%, approaching the thermodynamic equilibrium of SMR. Then, the continuous operation stability of the HTPR was conducted by a hybrid energy supply, i.e., solar and electricity. The methane conversion and hydrogen purity retained 91% and 72% for 24 h, respectively. Finally, the heat and mass transfer in the reaction cavity of the HTPR was simulated. The results show that the high thermal conductivity of the HTPR is capable of supplying energy to the strongly endothermic SMR, therefore promoting H2 yields. This work provides a new way, in the aspect of reactor design, for resolving the unstable hydrogen production by renewable energy.

Design and Process Optimization of a New Reaction Cavity for High-Temperature MOCVD AlGaN Growth

AlGaN offers new opportunities for the development of the solid-state ultraviolet (UV) luminescence, detectors and high-power electronic devices, however, problems such as low growth rate and poor crystallization quality are common in the growing process of AlGaN material. In this paper, a new reaction cavity for high-temperature MOCVD AlGaN growth was carried out through the research of resistance heated, and the thermal field of high-temperature MOCVD growth was numerically simulated. Based on the high-temperature MOCVD reaction cavity, an orthogonal experimental method was used to simulate the process parameters, and the range, variance and matrix analysis were conducted on the calculation results. The finite element analysis was conducted on the temperature field, pressure field, velocity field, and the high-temperature MOCVD AlGaN growth model was established.