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In the present study, the characteristics of gas-liquid Taylor flow in a fractal microchannel network were investigated by numerical modeling and experiments. With perpendicular gas intake, the fractal design methodology resulted in uniform flow distribution. Unstable Taylor flow and saddle-shaped velocity profile were observed in a high-level branch with 0.3 mm width. The liquid slug exhibited different flow fields during splitting in the bifurcations of different levels. The significant size effects were further investigated in four channels representing different sizes (0.3, 0.6, 1.2, and 2.4 mm) via a μ-PIV and high-speed camera. The normalized slug length (LS/W) increased with the increasing gas-liquid flow rate ratio (jG/jL), while the bubble length (LB/W) followed an opposite trend. The stability of the gas-liquid Taylor flow pattern became worse when the gas velocity increased beyond a certain value (Reynolds number Re > 220) under the microscale effect. Two typical counter rotating vortices were observed in the liquid slug, and the swirling strength increased exponentially with the jG/jL. It was found that both the velocity profile in the 0.3 mm channel deviated from the laminar flow. Particularly, a flow field similar to turbulence was observed in the 0.3 mm channel when the jG/jL reached 4. This work quantified the significant size effect in micro- and millichannels, providing theoretical basis for the effective scale-up of the microreactor.

A mathematical model for the operation of a thermal lance is developed and validated, with the focus on its heat transfer and kinetics behavior. It has been found that there is a "window"of combustion rates in which the thermal lance can operate, which is mainly dictated by the oxygen partial pressure. The particular value of the combustion rate can be set by adjusting the flow rate of the oxygen supply, which is practically done by manipulating the oxygen supply pressure. An open issue is the lack of experimental kinetics data for thermal lance combustion.

Double-layered microbubbles, microdroplets, and a mixture of microproducts were fabricated by a novel device of the geometric combination of a Y-junction and a flow-focusing junction in this study. An air-in-oil-in-water microbubble was used as a template for the preparation of double-layered microbubbles. The oil-in-water microdroplets and multiple microproducts could be generated in this system at the same time. To observe the evolution of the multiphase flow in a microchannel, high-speed microscopy and digital imaging technologies were applied. The fluidic mechanisms of generating specific microproducts under different operating conditions were investigated through the analysis of the flow patterns. The analysis of the microproduct generation process showed that operating conditions such as the air pressure and oil- and aqueous-phase flow rates had a significant impact on the size, generation frequency, and monodispersity of the microproducts. Dimensional analysis was applied to predict the diameters of the microproducts and showed a good agreement. Finally, the method to promote the emulsion stability was obtained.

The gas–liquid two-phase flow is widely encountered in many industrial applications, and its online and nonseparation flow rate measurement has plagued the industry for many years. Based on the the...

The effect of relatively low concentrations of Br2(g) in the Cl2(g) feedstock for phosgene synthesis catalysis via the reaction of CO(g) and Cl2(g) over activated carbon (Donau Supersorbon K40) is explored. Under the stated reaction conditions and in the absence of a catalyst, BrCl(g) forms from the reaction of Cl2(g) and Br2(g). Phosgene synthesis over the catalyst at 323 K is investigated for Br2(g):Cl2(g) molar flow ratios in the range 0–1.52% (0–15,190 ppm) and shows enhanced rates of phosgene production. Maximum phosgene production is observed at a Br2(g):Cl2(g) molar flow ratio of 1.52% (15,190 ppm), which corresponds to an enhancement in the rate of phosgene production of ∼227% with respect to the phosgene flow rate observed in the absence of an incident bromine co-feed. A reaction model is proposed to account for the experimental observables, where BrCl(g) is highlighted as a significant intermediate. Specifically, enhanced rates of phosgene production are associated with the dissociative adsorption of BrCl(g) that indirectly increases the pool of Cl(ad) available for reaction.

The investigation of pressure drop characteristics along the microchannels with surface texturing is crucial to arrive at a desired structural size and performance of a microchannel. This study presents the comparison of flow friction and pumping power for two different Reynolds numbers (Re = 1.01 and 50.31) for rarefied gas flows in textured microchannels. The three-dimensional microchannel is computationally modeled with ratios of the height of texture to the height of the microchannel taken as 20, 40, and 60 and texture shapes as rectangular, circular, and triangular. All simulations are conducted in the slip flow regime for the Knudsen number ranging from 1.10 A� 10-3 to 2.07 A� 10-2 and tangential momentum accommodation coefficient (TMAC) ranging from 0.1 to 0.9. The time- and cost-effective Taguchi statistical analysis of the L18 orthogonal array is carried out to find the efficiency of the textured microchannels in terms of Poiseuille number and pumping power per unit mass flow rate. It is found that the height of texture is the most important control factor for efficiency, while the shape is the least important factor for both Reynolds numbers. The second most significant factor for Re = 50.31 is the Knudsen number and that for Re = 1.01 is the TMAC. The present numerical work can be applied for designing micropiping systems and diffusers with lower pumping power, lower frictional resistance, and higher efficiency. ©

We systematically investigate the plugging performance and oil-displacement efficiency of the novel bilayer-coating microspheres (BCMS) designed for in-depth conformance control within heterogeneous hydrocarbon reservoirs. Visualization experiments on various glass models, as well as one- and two-phase core floods have been carried out at reservoir temperature and fluid salinity. Our results demonstrate that the rigid outer layer of BCMS can successfully protect its adhesive inner coating, enabling BCMS to transport deeply into porous media. Increasing particle concentration yields higher collision probability, leading to the formation of particle assembly that could effectively block pore throats in high-permeability channels and achieve more oil recovery in the low-permeability zones. It is also shown that as the BCMS slug size increases, the oil recovery asymptotically reaches a maximum value. A larger slug size cannot highly enhance the plugging performance yet significantly increase the resistance factor. A smaller permeability ratio of parallel cores leads to a narrower difference between the fractional flow rates. When the permeability ratio is two or lower, the fractional flow rates of parallel cores are both around 50%, yielding the best oil-displacement efficiency. BCMS exhibits promising application potential in production enhancement under reservoir conditions.

Autothermal operation (AO) has several advantages for carrying out highly exothermic catalytic partial oxidation (CPO) and/or oxidative dehydrogenation (ODH) reactions compared to traditional cooled multitubular reactors. In steady-state autothermal operation (AO), there is no heat addition to the reactor or intentional heat removal by cooling through reactor walls; the heat of reaction is removed mainly by convective flow of the cold feed. The existence of an ignited high temperature (and conversion) state at the lowest possible feed temperature and/or space time is essential. This work examines the impact of various design and operating variables on the feasibility and economic scale-up of shallow packed-bed catalytic reactors for autothermal operation. Specifically, we present scaling relations that can be used to examine the impact of effective bed thermal conductivity, bed length, particle size, catalyst activity, reaction kinetics, and operating pressure on the extinction (blow-out) flow rate or feed temperature for large scale autothermal CPO and ODH reactors operated close to the adiabatic limit. The scale-up relations derived for a single-step CPO/ODH reaction are verified by numerical simulations. They are also validated using the highly complex oxidative coupling of methane (OCM) as an example.

In this work, an energy-efficient extractive dividing-wall column process with heat integration (E-DWC-HI) is proposed for the first time to separate the dichloromethane (DCM)–methanol (MeOH) azeotrope, which is a widely existing waste effluent in the pharmaceutical industry. The result of economic evaluation shows that the E-DWC-HI process is a preferred choice for the separation of DCM–MeOH mixture. Designing a robust control strategy is essential for the E-DWC-HI process. Thus, four control structures are proposed and tested under the disturbances of ±20% feed flow rate and ±5% feed composition. The basic control structure (CS1) and the double temperature difference control structure (CS2) both have a fixed vapor split. The dynamic response shows that the required purity cannot be met due to the loss of an important control degree of freedom. In CS3, variable vapor split is carried out by adjusting the pressures on the two sides of the dividing wall, and all product purities are held close to their set points except for MeOH product purity with an obvious offset. The dynamic performance of CS4 has been significantly improved by integrating pressure swing and pressure compensation. The offset of MeOH product purity is significantly reduced from 2.05 to 0.03%.

This work focuses on the fabrication and organic dye adsorption capacity of pill-shaped polyimide aerogel microparticles of diameter approximately 200 μm and length approximately 1000 μm. First, spherical polyimide sol droplets suspended in silicone oil are generated in a microfluidic droplet generator. Second, these droplets are guided into a contraction flow channel to deform them into pill-shaped droplets. Third, the pill-shaped droplets undergo sol–gel transition in a heated section of the flow channel and turn into particles. Finally, the pill-shaped aerogel microparticles are recovered via solvent exchange and supercritical drying and characterized. The data indicate that the flow rates of polyimide sol and silicone oil strongly influence the length of the microparticles while surfactants, although not necessary to obtain pill-shaped particles, exert strong influence on the aspect ratio of the particles. The aspect ratio of particles and the internal morphology are discussed using hydrodynamic and interfacial forces. The ionic dye adsorption capacity of these pill-shaped particles is determined and compared with that of spherical gel microparticles.

The intensification of the reverse water gas shift (RWGS) reaction by water-permeable packed-bed membrane reactors (PBMRs) is studied to produce syngas using a CuO/ZnO/Al₂O₃ catalyst at 250 °C and 5 bar. Using experimental data from the literature, a modified kinetic model is developed for the RWGS reaction rate of the catalyst at low temperatures. The effects of gas hourly space velocity, H₂ to CO₂ ratio, H₂O/H₂ perm-selectivity, and sweep to reactor pressure and flow rate ratios are studied on the performance of the RWGS PBMRs for co- and counter-current flow configurations. The RWGS PBMRs are proven to be effective in overcoming equilibrium limitations of the RWGS reaction under different operating conditions. An optimization is performed to minimize the volume of the RWGS PBMRs to produce syngas for methanol synthesis. The optimization results show that the membranes are effective to produce the desired syngas under different operating conditions and flow configurations.

Multiwall carbon nanotubes (MWCNTs) were generated from recycled low-density polyethylene (LDPE). The polymer was pyrolyzed at 800 °C in inert atmospheres, and the gaseous pyrolyzates—light hydroca...

Transport properties in a nanoparticle-laden flow are of great importance for their practical use, such as in tubular reactor-based photocatalytic technologies. In our study, an experimental setup based on photocatalytic application was employed to investigate the nanoparticle transport characteristics in a flow reactor. An interesting periodical attenuated oscillation of the particle volume fraction and mean particle size with time was found in the nanoparticle-laden flow. We further analyzed the period of the attenuated oscillation curve by conducting a linear fitting, which shows that the period can be expressed as T = f(Q,L) in which the period is proportional to the length of the test section and inversely proportional to the flow rate. We found that the time 5T is a very important criterion for determining whether the particle suspension has reached the quasi-steady state and whether the nanoparticle has been well suspended. Our work is believed to be valuable, efficient, and effective in the study of transportation of nanoparticles in laminar flow with low energy consumption.

The flow distribution and mass transfer for gas-liquid flow in two parallel microchannels with different tree-shaped distributor are studied. Two parallel microchannels, both consist of four parallel branches, operated in the slug flow and with Reynolds number in the range of 0.2-10. The operating range in the halving-width microchannel (Tree-1) is significantly narrower than the constant-width microchannel (Tree-2). As the ratio of gas-liquid flow rate increases, the flow distribution in the Tree-1 gradually deteriorates. While in the Tree-2, there exists a critical ratio of gas-liquid flow rate to attain ideal flow distribution. Meanwhile, the volumetric mass transfer coefficient in the Tree-1 is lower, while in the Tree-2, the opposite is true. However, the high mass transfer coefficient is always accompanied by the high pressure drop. The pressure drop in the Tree-2 is higher than the Tree-1. Furthermore, the performance ratio is adopted to evaluate the mass transfer performance.

The importance of incorporating a vacuum pump performance curve into a mathematical model that describes the regeneration steps in a vacuum swing adsorption (VSA) cycle was assessed. This was accomplished by evaluating the relationship between pressure and flow rate at the exit of a 13X zeolite bed, initially and uniformly saturated with 70 vol% CO2 in N2 at 333.15 K and 1 atm, which then underwent just countercurrent depressurization (CnD) and light reflux (LR) steps, i.e., the regeneration steps in a VSA cycle. Overall, this study revealed it is imperative to use a realistic vacuum pump model in cyclic adsorption process simulation, especially for estimating the ideal isentropic energy consumed during the regeneration steps in a VSA cycle, and it revealed the possible inaccurate performance predictions that might result when using a valve equation alone to describe these steps. The study on the effect of valve size (cv) without the vacuum pump present to mimic the behavior of the vacuum pump performance...

In the present study, a double flow-focusing platform is applied to evaluate the application of microfluidic devices for the synthesis of liposomes with a uniform size distribution. The size, polydispersity index (PDI), and size distribution of liposomes are measured by varying different factors such as flow rate ratio (FRR), total flow rate (TFR), total lipid concentration, lipid/cholesterol molar ratio, and various lipid formulations. A comparison is made between the performance of double flow-focusing and single flow-focusing devices. The liposomes in the size range of 50–200 nm are produced with low PDIs of 0.1–0.37. The results show that the smallest particles are synthesized at the highest FRR and TFR, the lowest total concentration, a lipid/cholesterol molar ratio of 60:40, and single-lipid formulation. Also, the double flow-focusing device has the ability to apply higher TFR values than the single flow-focusing device, which leads to a higher productivity rate and smaller liposomes.

Removal of iron (III) and aluminum ions from phosphoric acid-nitric acid (PA-NA) solutions including their batch adsorption kinetics on sulfonic/monophosphonic acid chelation resin (S957) and the dynamic adsorption-elution process at the different operating parameters is studied. The results reveal that Fe(III) ion and Al(III) ion in PA-NA solutions on S957 resin present the slow batch adsorption rate. Their adsorption equilibriums are reached at 60 min and 40 min contact time, respectively. The dynamic adsorption process of Fe(III) ion and Al(III) ion is dependent on the feed flow rate through the fixed bed column, and at the 0.5 mLmin-1 flow rate, Fe(III) ion and Al(III) ion can be greatly removed from PA-NA solutions. In the dynamic elution process, the flow rate shows little effect on the elution process of Fe(III) and Al(III) ions. The better regeneration solution for the dynamic elution process is HCl solution, and the optimized concentration of HCl solution is 8 mol•L-1.

A novel pore-array intensified tube-in-tube microchannel (PA) with high throughput was developed to couple with a high-shear mixer (PAHSM) for improving its mixing performance. Effects of structural and operating parameters were intensively investigated with the Villermaux/Dushman system. The results indicated that the mixing performance in PAHSM was significantly impacted by the structural parameters, and it increased with both the rotor speed and flow rate but not with the flow ratio. The micromixing time estimated with the incorporation model could reach 10–4 s. Compared with other mixing devices, the PA liquid distributor can significantly enhance the mixing performance of HSM with high throughput but low pressure drop. An artificial neural network (ANN) was applied to correlate the micromixing time with the investigated parameters, and the comparison between the model and experimental data indicated that it was an efficient method to fit experimental data in the PAHSM.

Thermal stability is a crucial issue for fluidized-bed ethylene-polymerization reactors, especially when the particle-aggregation probability increases as a result of the high reaction temperature or operation under condensed mode. To determine the mean particle size, a population-balance model (PBM) considering particle growth and particle aggregation was implemented in the present study. Then, an integrated model including the two-phase model (TPM), the PBM, and an evaporation model was proposed to describe polymerization of ethylene in liquid-containing fluidized-bed reactors. The results demonstrate that the particle-growth rate and catalyst particle size dominate the particle size of the final product. Thermal stability of fluidized-bed reactors is mainly affected by the catalyst activation energy, the superficial-gas velocity, and the condensed-liquid flow rate.

Oxidative dehydrogenation (ODH) of ethane and propane feeds has been examined under a variety of temperatures, flow rates, and gas compositions in a fixed bed reactor using boron nitride-based cata...

We propose mixed-integer linear programming models for utility targeting and heat exchanger network synthesis that account for variable stream temperatures and flow rates as well as unclassified streams and thus can be integrated with process synthesis optimization models. By projecting temperature information onto a fixed discrete temperature grid, the model remains linear even under variable temperatures and flow rates, leading to a more tractable optimization model. The proposed model is well suited to address problems in the area of process intensification where the close interaction between different phenomena naturally leads to process synthesis problems with unclassified process streams. Several extensions are presented, including nonisothermal mixing as well as phase changes. Furthermore, we show how a nonuniform grid can be adopted to reduce the complexity of the model for medium and large-size problems.

In this study, two different approaches for investigating micromixing in a rotating packed bed (RPB) with a Villermaux-Dushman protocol are presented and detailed information on the operation, design, and power consumption of the RPB is given. First, a novel nozzle liquid distribution design is investigated for micromixing. A structured approach for experimental investigations is introduced, and the influence of different liquid distribution parameters on the micromixing results is presented. It is shown that the outlet velocity from the nozzles and the liquid hold-up at the inner rim of the packing play a crucial role in the mixing process. Second, micromixing in RPBs with equal flow rates is investigated. A comparison with other continuous mixing devices is conducted based on flow rates, pressure drop, and the micromixing time parameter tm. It is demonstrated that RPBs show a large potential for fast mixing at high flow rates and low pressure drop.

For offshore natural gas liquefaction operation, the single mixed refrigerant process is considered as one of the best and most suitable processes. However, multivariable nonlinear thermodynamic interactions among operating conditions and flow rates of mixed refrigerant ingredients lead to energy losses, which ultimately contributes to high energy consumption for liquefied natural gas production. The present work investigates the energy saving opportunities in the single mixed refrigerant liquefaction process through “krill-herd” strategy which is based on the biological flocking (herding) behavior of individual krill. To find the energy saving opportunities, the krill-herd approach effectively reduced the exergy losses of the compression units and cryogenic heat exchanger up to 18.6 and 41.1%, respectively, as compared to the published liquefaction process. The figure of merit was found as 27.0% in the krill-herd-optimized single mixed refrigerant process, whereas it was 22.2% in the base case.

Foam fractionation is extensively used for the separation and purification of surface active solutes from a low concentration mixture at room temperature. In this work we present the design of a novel microfluidic device to concentrate a solute by adsorbing it on a gas–liquid interface. The device is integrated with a downstream separator where the foam is separated from the residual liquid. Both gas and liquid streams flow continuously into the device. The device has a diverging and converging cross section to facilitate the formation of a foam-like structure. The device is demonstrated on the enrichment of bovine serum albumin (BSA) using cetyltrimethylammonium bromide (CTAB) as a surfactant. The effect of various parameters, i.e., gas flow rate, aqueous phase flow rate, and salt concentration, on the enrichment of the solute is investigated. We show how we can infer diffusiophoresis in the system at low gas flow rates by measuring macroscopic parameters like mean residence time.

A series of statistically designed experiments were conducted using two different Geldart Group B particles in a 0.3 m diameter circulating fluidized bed (CFB) cold model to evaluate the nonmechanical L-valve for controlling the solids flow rate. The objective of this study was to investigate the effects of standpipe aeration, L-valve aeration, solids inventory, and superficial gas velocity through the riser on the solids flow rate. A stochastic correlation was developed for calculating the solid flow rate as a function of these variables. It was found that the solid flow rate increased directly proportional to each of these variables. Dimensional analysis was used to generate an expression for the solids turnover ratio. The model developed in the present study is intended to simulate flow in the present CFB loop. It is not intended for scale-up and will probably not apply for alternative CFB loops with different geometries/pressure balance conditions.

In this work, process control is studied in an optimal Extractive Distillation (ED) system to dehydrate ethanol using a glycerol-ethylene glycol mixture as separating agent. ED system simulation and optimization with respect to the total annual cost (TAC) was made using the software platform Aspen Plus. The control structure of the optimized system was evaluated in Aspen Dynamics. Two control strategies were studied: a conventional control and a modified control scheme. The conventional control structure uses the distillate and bottoms flow rates to control the top and bottom levels, respectively. The second strategy uses the entrainer makeup flow rate to control the sump level in the recovery column and the recovery column bottoms flow rate to control the entrainer feed flow rate to the extractive column. Dynamic simulations show the control strategy that allows obtaining a soft-regulating control while at the same time ethanol purity is above 0.995 mole fraction. In addition, the use of solvents mixture...

Simulations of a 3-bed 9-step pressure swing adsorption (PSA) cycle were carried out to study the enrichment and recovery of 0.4 vol % CO2 from dry air using 13X zeolite with the feed pressure and flow rate fixed at 1 atm and 570 SLPM. The goal was to produce 97 vol % CO2 at greater than 62% CO2 recovery, less than 1 kW vacuum pump power, and small volume. The PSA cycle step sequence consisted of feed (F), idle (I), heavy reflux (HR), cocurrent equalization down (EqD), forced cocurrent depressurization (CoD), countercurrent depressurization (CnD), light reflux (LR), countercurrent equalization up (EqU), and light product pressurization (LPP). A parametric study revealed the following effects on the PSA process performance. Increases in the HR = LR = F step time (thus cycle time) caused significant increases in the CO2 purity and vacuum pump power, while the CO2 recovery exhibited a modest maximum. Increases in the LR ratio caused significant increases in both the CO2 recovery and power but only a modest i...

To investigate the separation performance of a novel liquid–liquid dynamic hydrocyclone (LLDH), a series of experiments and numerical simulations were conducted. Algebraic slip mixture model was used to simulate the multiphase flow in the LLDH, in which the turbulence was modeled using Reynolds stress model and the rotation of the walls was modeled by multiple reference frame model. The numerical results showed a good agreement with the observations and measurements in experiments. The results showed that the increase of rotation speed would strengthen the swirling intensity in LLDH and thereby separation efficiency was raised. However, increase of flow rate would decrease the residence time of oil droplets, causing reduction in efficiency. By comparison, flow split ratio had slight influence on the flow field, and the efficiency rose a little as flow split ratio increased. The efficiency of the LLDH could remain high when the nondimensional rotation rate was large enough.

Oil-in-water (O/W) emulsion is an effective plugging agent for improving fluid mobility conformance. Most studies to date have attributed the plugging mechanism solely to the “Jamin effect”. In this work, we investigate the influence of oil phase viscosity on the plugging performance of O/W emulsions in porous media. Sandpack flow tests were conducted to quantitatively evaluate such effects. Systematic data of pressure drop versus oil viscosity under varied sandpack permeabilities and flow rates were reported. The oil viscosities of emulsions used in this study ranged from 9.4 to 496.0 cP. During flow tests, potential interference from interfacial tension (IFT) and droplet size was eliminated. The results show that oil viscosity of O/W emulsion considerably affects pressure drop across the sandpack. Frictional resistance increases as oil viscosity increases, but the rate of increment tapers down significantly. The plugging effect due to oil viscosity is dependent on sandpack permeability and emulsion inje...

The water–phosphorus nexus problem for wet-process phosphoric acid production is first addressed in this article. A systematic methodology for water system optimization and water–phosphorus nexus analysis is proposed. On the basis of the preliminary process flowsheet and water flow rate balance, the potential water sources and sinks as well as the key component can be extracted. The mathematical model for the water system optimization integrated with water flow rate balance is presented. The process flowsheet can be improved according to the optimized water system. The flow rate of fresh water is reduced from 1803.98 t/h (preliminary design) to 160.98 t/h (improved design). The utilization efficiencies of the phosphorus element (calculated as P2O5) are calculated for the preliminary and improved designs. Because the process for wet-process phosphoric acid production is mostly in the aqueous phase, the utilization efficiency of the phosphorus element is increased from 94.22% (preliminary design) to 98.76% ...

High-level moisture removal is often encountered in the pressure swing adsorption (PSA) for air prepurification. The effects of high-concentration water vapor adsorption on the heat and mass transport characteristics of PSA should be described in detail for further design and optimization of air prepurification processes. In this work, a mathematical model of an alumina/13X-layered two-bed Skarstrom-type PSA cycle for the removal of high-level moisture along with CO2 from air is established to study the heat and mass transport characteristics during the process. The maximum increase and decrease in temperature are related to the water vapor concentration in the feed air, and two simplified formulas are proposed to estimate their magnitudes. The mass transport characteristics, especially the penetration depths of the two impurities, are examined under different inlet temperatures, adsorption pressures, purge-to-adsorption flow rate ratios, inlet flow rates, and cycle times. A relation between the penetrati...

Electrical discharges in gases or plasmas allow dissociation and conversion of molecular precursors, such as methane, at relatively low temperature. In a steady-state reactor geometry, the reaction conversion has been suggested to be dependent on basic process parameters, such as residence time, which, in turn, is a function of reactor volume and gas flow rate, and power. Here, we show, through a combined experimental and modeling study, that, for a plasma-based steady-state reactor, conversion is dependent on gas flow rate and power, but essentially independent of volume. A critical part of the experiments was to confine the plasma volume so that the power and volume could be controlled separately, and a critical part of the modeling was to segment the reactor into a volume containing filamentary discharges and a volume containing an afterglow to capture the spatial heterogeneity of our dielectric barrier discharge. The resulting similarity law for the conversion is consistent with the idea of energy den...

We propose a mixed-integer nonlinear programming (MINLP) model for simultaneous chemical process and heat exchanger network synthesis. The model allows process stream inlet/outlet temperatures and flow rates to vary and can be extended to handle unclassified streams, thereby facilitating integration with a process synthesis model. The proposed model is based on a generalized transshipment approach in which the heat cascade is built upon a “dynamic” temperature grid. Both hot and cold streams can cascade heat so that exchanger inlet and outlet temperature, heat duty, and area can be calculated at each temperature interval. We develop mixed-integer constraints to model the number of heat exchangers in the network. Finally, we present several solution strategies tailored to improve the computation performance of the proposed models.

An induction heating fluidized bed with liquid injection was designed to mimic the exothermic process of particles in industrial olefin polymerization fluidized beds. The effects of liquid injection flow rate on agglomeration behaviors were investigated through the characterization of agglomerate size and mass. Agglomeration mechanisms were proposed based on the experimental data of bed pressure drop, axial temperature distribution, and microscale visualization. Results have revealed that, with the increase of liquid injection flow rate, the agglomeration mechanism was controlled by the solid bridge force, the liquid bridge force, and the cooperative action of them, respectively. Wet agglomerates caused by the liquid bridge force induced local dead zones and provided a good environment for the occurrence of a hot spot and growth of solid bridge, and thus the formation of solid agglomerates. Besides, elevating the liquid injection position and increasing the induction heating power can widen the operation ...

In this work, the gas-side mass transfer was investigated in a rotating packed bed (RPB) with structured nickel foam packings, with different surface properties, either a nonmodified nickel foam packing (NNP) or a hydrophobic surface-modified nickel foam packing (SNP). Effects on gas-side volumetric mass-transfer coefficient (kGae) of rotational speed, liquid flow rate, and gas flow rate were experimentally studied in the RPB with NNP and SNP. It can be found that the RPB loaded with SNP has a higher mass-transfer efficiency, compared with that loaded with NNP. Based on the experimental data, correlation of kGae in a RPB with structured nickel foam packing was proposed, which can hence provide a fast calculation of mass-transfer coefficients for the RPB design with structured nickel foam packing.

This paper presented a novel technology for the desorption of SO2 in the basic aluminum sulfate solution (BASS) by falling film evaporator with spring tube. The liquid film falling along the internal surface of the evaporation tube was heated by the steam outside. The desorption performances of the vertical single falling film evaporators with spring tube and smooth tube were comparatively investigated. The film distribution on the inner surface of the two tubes were also analyzed through visualization experiments. Compared with the smooth tube, the spring tube was found to be much better in heat transfer and mass transfer. Thus, analysis on the operating parameters for the desorption of SO2 was performed only in the spring tube. The results showed that the flow rate of BASS rich in SO2, heating steam temperature, vacuum of the system, and initial concentration of SO32– played important roles in the desorption performance.

This work presents a novel process of nano-Ni preparation by liquid reduction method without surfactant in a combined reactor of a rotating packed bed (RPB) and a stirred tank reactor (STR). The reaction mechanism of this process was studied, and the effects of different operating conditions including rotation speed, NaBH4 concentration, liquid volumetric flow rate, and liquid circulation time on the characteristics of the nano-Ni were systematically investigated in the RPB to control the morphology and average particle size of the prepared nano-Ni. The average particle size of the prepared nano-Ni can be adjusted from 42 to 130 nm by changing operating conditions, and the prepared nano-Ni with a face centered cubic (FCC) structure, an average particle size of 42 nm, and a particle size distribution of 30–60 nm was obtained under the optimal operating conditions. This research provides a novel pathway and theoretical basis for controllable preparation production of nano-Ni.

Hollow Au/CeO2 as a highly efficient and stable heterogeneous catalyst is successfully used for a continuous-flow reaction. The hollow CeO2 microspheres with thicknesses of 21 nm as functional supports can greatly improve the catalytic activity and stability of the Au nanoparticles. The catalytic activity of hollow Au/CeO2 catalysts is 4.5 times higher than the Au catalysts without the hollow structure under the same reaction conditions for the reduction of 4-nitrophenol. Meanwhile, the hollow structure also accelerates the mass transfer of reactant for the continuous-flow system. A high turnover number of 65.7 mol h–1 molAu–1 is yielded for hollow Au/CeO2 catalysts at a flow rate of 250 mL h–1 with remarkable stability for a continuous-flow 4-nitrophenol reduction reaction. The present continuous-flow system exhibits a huge potential for the automation treatment of pollutant 4-nitrophenol.

Hydrogen is becoming a more and more crucial resource for chemical industries. Hydrogen network integration is an effective tool in hydrogen resource conservation. Hydrogen sources flow in and flow out from different processing units where consumption, generation, mixing, and separation occur. Consequently, there is a dependence on both hydrogen and contaminant species among those streams, especially when throughputs of processing units fluctuate. Hydrogen network integration should account for such a dependence so that real properties including the flow rate and concentration can be obtained to perform reliable network integration. This article proposes the processing unit mass balance to describe the dependence of hydrogen streams and establishes a corresponding superstructure as problem illustration. A mixed integer nonlinear programing (MINLP) model is built to synthesize hydrogen networks for fresh hydrogen minimization. This method considers the tolerable disturbance of the processing unit and thus ...

A continuous flow synthesis of tryptophol is developed in a tubular reactor at different temperatures and flow rates, by Fischer indole synthesis route using phenyl hydrazine hydrochloride (PHH) and 2,3-dihydrofuran (DHF) as starting materials. The maximum conversion of PHH was 93%, and the yield of tryptophol was 72% in 6 min. A kinetic model is proposed for the process by taking into account the formation of intermediate species. The reactor was simulated in COMSOL platform for temperature profiles in the reactor, which were subsequently used to estimate the kinetic parameters of the reaction. The reaction was further intensified by executing the reaction in a continuous microwave reactor (CMWR), at different flow rates and at different power. The maximum conversion of PHH was obtained to be 91%, and the yield of tryptophol was 95% in 5 min using CMWR.

Ag/AgCl/ZnO composites were successfully synthesized in a continuous microfluidic system under visible light irradiation, which was employed in situ to reduce a portion of AgCl to metallic Ag. The formation of Ag/AgCl/ZnO composites was confined in small aqueous plugs, which were dispersed by octane as the continuous phase. In this way, enhanced mixing, low risk of channel clogging, and uniform light distribution were achieved. The characterization results revealed that the as-prepared Ag/AgCl/ZnO composites were composed of flowerlike ZnO with Ag/AgCl nanospheres anchored to them. It was found that the synthesis parameters such as water/oil volume flow ratio, total volume flow rate, temperature, and the molar ratio of Zn2+ to Ag+ had effects on the synthesis of Ag/AgCl/ZnO composites. Furthermore, the as-prepared Ag/AgCl/ZnO composites outperformed Ag/ZnO composites and AgCl/ZnO composites in the visible-light-driven degradation of methyl orange.

Dehydration of used solvents in the printing and packaging industry is required in order to reuse or increase the commercial value of the solvents. In this study, a pervaporation–liquid-phase adsorption hybrid process for dehydration of a low-value byproduct solution obtained from a real operation was examined. The byproduct solution contained water varying in the range of 1–11.5 wt %, and the majority of the rest is ethanol and isopropanol with minor components such as ethyl acetate and methoxy propanol. We measured the flux and separation factor of two commercial membranes as a function of process parameters such as feed and membrane module temperature, feed flow rate, and permeate side pressure in addition to the feedwater and ethyl acetate concentration. We observed higher flux and separation factors at high temperatures and low permeate side pressures. PERVAP 2201 membranes showed higher flux with a reasonable separation factor toward water. PERVAP 2211 showed higher water separation factor but lower...

Microfluidic fuel cells are a group of miniaturized fuel cells without membranes for operation. Their unique flow of the steams in a microchannel allows a parallel laminar flow without mixing with each other. We investigated the cell performance with different iron-based soluble salts as oxidants. The best performance was achieved by FeCl3 as the oxidant, achieving the highest power density of 192.71 mW cm–3 and the largest limiting current density of 883.33 mA cm–3 (normalized to the active electrode volume). And we optimized the performance of the FeCl3-based microfluidic fuel cell by adjusting the flow rates, HCl concentrations, and FeCl3 concentrations. The optimal flow rate was 20 mL h–1. Although the maximum power density of the cell with 4 M HCl and 0.5 M FeCl3 solution reached high values of 212.21 mW cm–3 and 250.42 mW cm–3, respectively, both cell performances were under mass transfer control at high current densities.

Reactor corrosion and plugging problems severely hinder commercial application of supercritical water oxidation. A transpiring wall reactor can overcome these two problems by forming a protective water film on the inner surface of a porous transpiring wall to isolate corrosive substances and inorganic salt. This work proposed water film coverage rate and inorganic salt concentration in water film as evaluation indexes of water film characteristics. A computational fluid dynamics model of a new transpiring wall reactor was built to explore the characteristics of water film under key operating parameter conditions by numerical simulation together with experiment validations. The results show that water film coverage rate raised either with transpiration intensity and transpiration water temperature increasing or with feedstock flow rate and feedstock preheating temperature decreasing. Inorganic salt concentration in water film declined as transpiration intensity and transpiration length increased. Two equat...

This article describes a microfluidic method for fabricating anisotropic polymer microfibers. Janus colaminar flows were realized in a microfluidic device. Microfibers with a noncircular cross-section were fabricated by an in situ photopolymerization method. The microflows experienced different evolutionary states in the microchannel. Simple control of the curing time resulted in the microfibers forming different shapes. The morphology of the cross-section could be readily manipulated by the interfacial tensions and flow rates of the fluids. Theoretical analysis and computational fluid dynamics simulation were used to predict the effect of these factors on the fiber morphology. The theoretical and simulation results were in good agreement with the experimental results. Microfibers with nonuniform surface properties could also be produced by adding modification reagents into the different fluids. The selective coating of micro/nanoparticles on the convex or concave surfaces of the microfibers was realized.

Chemical absorption of CO2 with aqueous NH3 was numerically analyzed in an Eulerian manner for steady 1D spray towers in which gas velocity and liquid flow were uniform, and the results were formulated into a universal correlation. The capture efficiency η predicted by the proposed correlation is a sort of upper bound, and can be used as a base to evaluate the optimality of each design. Drop-size poly dispersity was considered; a spray of poly dispersed droplets was found to be equivalent in η to a spray of monodispersed droplets of an equivalent diameter, and a general formula for the equivalent size was attained in terms of mean size and geometric standard deviation. Total mass transfer coefficient was linearly proportional to the gas–liquid flow rate ratio, and the efficiency correlation agreed well with published results.

The rotating packed bed (RPB) has drawn wide attention owing to its outstanding advantage in process intensification. In the present study, gas flow characteristics in RPB were investigated by particle image velocimetry (PIV) measurement. The velocity and turbulent kinetic energy (TKE) in the packing zone were obtained and the effects of various parameters were analyzed. During rotation, gas rapidly acquired tangential velocity, which was dominant in resultant velocity. Mean gas velocity increased with the increase of rotational speed, but was almost independent of gas flow rate and packing size at lower rotational speed. Moreover, mean radial and tangential slip velocities were overall positively affected by gas flow rate and rotational speed, respectively. Higher TKE near the inner packing than those in the bulk zone revealed the existence of a gas end-effect zone in RPB. The results could provide a theoretical basis for further study on gas–solid catalytic reaction or the gas–liquid mass transfer proce...

Product yield optimization in bimodal reaction sequences including degradation has been performed considering three-phase reactors such as the jet loop and trickle bed reactors. The considered reaction network comprises two consecutive homogeneous reaction steps toward intermediates which are converted to the corresponding final products by heterogeneously catalyzed reactions, while the reactant and these intermediates are susceptible to irreversible degradation. In the jet loop reactor, the so-called “homogeneous product” is the main product; hence, the remaining challenge is the reduction of degradation. For the trickle bed reactor, gas−liquid mass phase transfer plays a very pronounced role in its ultimate performance. Higher gas flow rates may be employed in the trickle bed reactor to overcome potential mass-transfer limitations and selectively form the “heterogeneous product”. Lower gas flow rates result in a less effective gas dissolution, and product selectivities change toward the homogeneous product, rendering avoiding degradation difficult.

Continuous gravity settlers are widely used for liquid-liquid separation in solvent extraction processes. In the present work, effects of settler design (geometry, settling area (A), location of inlet/outlet) and internals (baffles, picket fence, end-plate) on the separation performance are investigated. An experimentally validated Eulerian CFD model implemented in OpenFOAM is used. For fixed flow rate of dispersion (Qt), an increase in settler length led to a reduction in the dispersion band thickness. For settlers with L/W < 1.5, the settler performance was found to be improved by combined use of baffle and picket fence. The organic to aqueous phase ratio (αorg/αaq), end-plate height and aqueous outlet location were found to influence the phase separation significantly. An empirical correlation is developed to predict the dispersion band thickness as a function of Qt, A, ρorg/ρaq, inlet baffle opening slot position and αorg/αaq. The present work will be useful for design of optimal settler configuration.

The turbulence characteristics in the presence of bubbles is very important for multiphase processes such as froth flotation. The turbulence characteristics in an aerated Denver flotation cell were investigated using a high speed stereoscopic particle image velocimetry technique at single-phase (water) and two-phase (water and air) systems to provide insight into the change in liquid phase hydrodynamics. The effect of the gas flow rate (0.043–0.125 cms–1) and Reynolds number (107 000–154 000) on the fluid flow properties were investigated. The results showed that the flow pattern at the both systems was the radial-type flow. The presence of air bubbles changed the local turbulence characteristics (mean velocity, the root-mean-square velocity, turbulence kinetic energy dissipation, and turbulence kinetic energy). The results obtained may be useful for deeper investigation about the effect of the turbulence properties on the hydrodynamic characteristics and subprocesses in the mechanical flotation cells.