Search

In this study, the performance of a stenter (ram machine) that enables the drying of textile products with hot air is theoretically modelled with a diffusion model derived from Fick's second law. The experimental study was conducted in a 10 chamber stenter with three different drying temperatures (110-130-150 degrees C) and three different fabric speeds (10-20-30 m per minute.) by using a fabric consisting of 95% cotton + 5% lycra. The drying behaviour of the dryer was determined by utilizing the data obtained from the studies. With the help of the utilized model, the values of diffusion coefficients and activation energies were obtained, the conformity of data between the model and the experimental studies were compared by using regression analysis, it was observed that the R-2 value varied between 0.9812 and 0.9961.

Liquid-liquid microfluidic systems rely on the intricate control over the fluid properties of either miscible or immiscible mixtures. Herein, we report on the use of partially miscible binary liquid mixtures that lend their microfluidic properties from a highly temperature-sensitive mixing and phase separation behaviour. For a blend composed of the thermotropic liquid crystal 4-Cyano-4'-pentylbiphenyl (5CB) and methanol, mixing at temperatures above the upper critical solution temperature (UCST; 24.4°C) leads to a uniform single phase while partial mixing can be achieved at temperatures below the UCST. Thermally-driven phase separation inside the microfluidic channels results in the spontaneous formation of very regular phase arrangements, namely in droplets, plug, slug and annular flow. We map different flow regimes and relate findings to the role of interfacial tension and viscosity and their temperature dependence. Importantly, different flow regimes can be achieved at constant channel architecture and flow rate by varying the temperature of the blend. A consistent behaviour is observed for a binary liquid mixture with lower critical solution temperature, namely 2,6-lutidine and water. This temperature-responsive approach to microfluidics is an interesting candidate for multi-stage processes, selective extraction and sensing applications.

A simple kinetic model for the standard NH3-SCR reaction by Cu-ZSM-5 catalysts has been developed by assuming three reaction steps: NH3 adsorption (desorption), reactions of adsorbed NH3 with O2 (NH3 oxidation) and NO (NH3-SCR). The model is based on Arrhenius parameters for NH3-SCR and NH3 oxidation by a powder catalyst, combined with models for heat and mass transport and parameters of monolithic catalysts. The model is validated with the experimental results, not included in the estimation of the model, for NH3-SCR by monolithic catalysts with different parameters (catalyst loading and cell density). NOx removal from diesel exhaust, generated by engine bench, was also carried out by using monolithic Cu-ZSM-5 and Cu-AFX catalysts. The results suggest the poisoning effect of hydrocarbons in the exhaust emissions on NOx conversion is more significant for Cu-ZSM-5 than Cu-AFX.

Droplet-based microfluidic extraction is a promising way for effective lanthanides extraction due to its outstanding mass transfer performance. The separation process can be greatly enhanced with the droplet-based microfluidic extraction technique. However, the interactions between mass transfer, microfluidic dynamics and extraction kinetics are still unclear, which has hindered further manipulation on microfluidic extraction to boost extraction performance. In this study, the mechanisms of microfluidic droplet-based extraction and separation intensification of lanthanides are for the first time unveiled by using a numerical simulation model. The limiting factors for the performance of droplet-based microfluidic extraction are identified through a model-based parametric analysis. The numerical analyses provide a comprehensive understanding of droplet-based microfluidic extraction systems and offer operation and optimization guidelines for future research in this area.

With the technological advances in 3D printing technology, which are associated with ever-increasing printing resolution, additive manufacturing is now increasingly being used for rapid manufacturing of complex devices including microsystems development for laboratory applications. Personalized experimental devices or entire bioreactors of high complexity can be manufactured within few hours from start to finish. This study presents a customized 3D-printed micro bubble column reactor (3D-µBCR), which can be used for the cultivation of microorganisms (e.g., Saccharomyces cerevisiae) and allows online-monitoring of process parameters through integrated microsensor technology. The modular 3D-µBCR achieves rapid homogenization in less than 1 s and high oxygen transfer with kLa values up to 788 h−1 and is able to monitor biomass, pH, and DOT in the fluid phase, as well as CO2 and O2 in the gas phase. By extensive comparison of different reactor designs, the influence of the geometry on the resulting hydrodynamics was investigated. In order to quantify local flow patterns in the fluid, a three-dimensional and transient multiphase Computational Fluid Dynamics model was successfully developed and applied. The presented 3D-µBCR shows enormous potential for experimental parallelization and enables a high level of flexibility in reactor design, which can support versatile process development.

Liquid-phase adsorption has hardly been established in micro-flow, although this constitutes an industrially vital method for product separation. A micro-flow UV-photo isomerization process converts cis-cyclooctene partly into trans-cyclooctene, leaving an isomeric mixture. Trans-cyclooctene adsorption and thus separation was achieved in a fixed-bed micro-flow reactor, packed with AgNO3/SiO2 powder, while the cis-isomer stays in the flow. The closed-loop recycling-flow has been presented as systemic approach to enrich the trans-cyclooctene from its cis-isomer. In-flow adsorption in recycling-mode has hardly been reported so that a full theoretical study has been conducted. This insight is used to evaluate three process design options to reach an optimum yield of trans-cyclooctene. These differ firstly in the variation of the individual residence times in the reactor and separator, the additional process option of refreshing the adsorption column under use, and the periodicity of the recycle flow. ispartof: AICHE JOURNAL vol:67 issue:1 ispartof: location:United States status: published

A new mathematical model is presented for the supercritical fluid extraction of lanoline from wool using near-critical ethanol-modified CO2, using our previous experimental data. The model is intended to account for the extraction of lanoline at conditions well above its melting point (60–80 °C) and pressures up to 150 bar. The model parameters are a Henry-type fluid-to-liquid partition coefficient for lanoline, K = Cg/CL, and a fluid-side mass-transfer coefficient, kG. For Re ∼1, K is independent of velocity and wool packing density, but increases with pressure (K = 4 − 15 × 10−4). kG is found to be independent of temperature; it increases with velocity, decreases with pressure, and increases with wool packing density. The values found are kG = 5.66 × 10-6 m/s (70 bar) and kG = 1.51 × 10-6 m/s (150 bar).

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was performed in perfluoroalkoxy alkane capillary microreactors packed with a carbon-supported ruthenium (Ru/C) catalyst with an average particle diameter of 0.3 or 0.45 mm. The reaction was executed under an upstream gas–liquid slug flow with 1,4-dioxane as the solvent and H2 as the hydrogen donor in the gas phase. Operating conditions (i.e., flow rate and gas to liquid flow ratio, pressure, temperature and catalyst particle size) were varied in the microreactor to determine the influence of mass transfer and kinetic characteristics on the reaction performance. At 130 °C, 12 bar H2 and a weight hourly space velocity of the liquid feed (WHSV) of 3.0 gfeed/(gcat·h), 100% LA conversion and 84% GVL yield were obtained. Under the conditions tested (70–130 °C and 9–15 bar) the reaction rate was affected by mass transfer, given the notable effect of the mixture flow rate and catalyst particle size on the LA conversion and GVL yield at a certain WHSV. A microreactor model was developed by considering gas–liquid–solid mass transfer therein and the reaction kinetics estimated from the literature correlations and data. This model well describes the measured LA conversion for varying operating conditions, provided that the internal diffusion and kinetic rates were not considered rate limiting. Liquid–solid mass transfer of hydrogen towards the external catalyst surface was thus found dominant in most experiments. The developed model can aid in the further optimization of the Ru/C catalyzed levulinic acid hydrogenation in packed bed microreactors.

ispartof: CHEMPHOTOCHEM vol:4 issue:10 pages:5193-5200 status: published

We reported experimental measurements of the diffusion coefficient of methane at effectively infinite dilution in methylbenzene and in heptane at temperatures ranging from (323 to 398) K and at pressures up to 65 MPa. The Taylor dispersion method was used and the overall combined standard relative uncertainty was 2.3%. The experimental diffusion coefficients were correlated with a simple empirical model as well as the Stokes–Einstein model with the effective hydrodynamic radius of methane depending linearly upon the solvent density. The new data address key gaps in the literature and may facilitate the development of an improved predictive model for the diffusion coefficients of dilute gaseous solutes in hydrocarbon liquids.

Maintaining chemical and physical stability of the product during freeze-drying is important but challenging. In addition, freeze-drying is typically associated with long process times. Therefore, mechanistic models have been developed to maximize drying efficiency without altering the chemical or physical stability of the product. Dried product mass transfer resistance ( R p ) is a critical input for these mechanistic models. Currently available techniques to determine R p only provide an estimation of the mean R p and do not allow measuring and determining essential local (i.e., intra-vial) R p differences. In this study, we present an analytical method, based on four-dimensional micro-computed tomography (4D- &mu, CT), which enables the possibility to determine intra-vial R p differences. Subsequently, these obtained R p values are used in a mechanistic model to predict the drying time distribution of a spin-frozen vial. Finally, this predicted primary drying time distribution is experimentally verified via thermal imaging during drying. It was further found during this study that 4D- &mu, CT uniquely allows measuring and determining other essential freeze-drying process parameters such as the moving direction(s) of the sublimation front and frozen product layer thickness, which allows gaining accurate process knowledge. To conclude, the study reveals that the variation in the end of primary drying time of a single vial could be predicted accurately using 4D- &mu, CT as similar results were found during the verification using thermal imaging.

A catalyst preparation method, consisting of slurry washcoating with γ-Al2O3 followed by impregnating platinum on the microreactor walls, has been investigated. The effect of various factors in the preparation procedures on the adhesion of the washcoated γ-Al2O3 was studied, including the slurry property (i.e., the binder type, concentration and molecular weight, γ-Al2O3 concentration and particle size, pH), and the (micro)reactor substrate and channel shape. The results show that the adhesion of γ-Al2O3 washcoat strongly depended on the slurry rheological characteristics. A good adhesion on FeCrAlloy substrates was obtained using the slurry with polyvinyl alcohol as the binder (typical concentration at 3–5 wt% and molecular weight of 57,000–186,000), 20 wt% γ-Al2O3 (particle size being around 3 µm) and pH = 3.5. FeCrAlloy as the substrate exhibited an excellent coating adhesion in rectangular or round channels, primarily due to the formation of alumina film over the surface during thermal pretreatment. The aluminum-free stainless steel as the substrate only showed a good adhesion in a round channel. Well-adhered Pt/γ-Al2O3 catalysts were then applied in a microreactor comprising parallelized microchannels made of FeCrAlloy under the optimized coating procedures, and investigated in terms of its performance in the catalytic methane combustion. It is shown that the reaction temperature has a greater influence on the methane conversion than the flow rate, and a favorable coverage of methane and oxygen on the catalyst surface is essential to obtain a good catalytic performance. These reaction results are in line with the temperature behavior measured along the microreactor.

Článek popisuje absorpční proces plynného amoniaku do kapalné vody v deskovém tepelném výměníku, který je považován za kritickou část absorpčního chladicího systému. Jsou aplikovány dva přístupy pro numerickou simulaci absorpce. První přístup spočívá v simulaci jak vlastního rozpouštění atomů plynného amoniaku v kapalné vodě, tak i jejich následné chemické reakci s molekulami vody za vzniku hydroxidu. Ve druhém, zjednodušeném, přístupu je simulována pouze první část absorpce, tedy jen rozpouštění molekul bez jejich následné reakce. This paper describes the absorption process of gaseous ammonia into liquid water in the plate heat exchanger, which is considered to be the crucial part of an absorption cooling system. Two approaches are utilized to numerically simulate this absorption process. In the first approach, the dissolution of gaseous ammonia into liquid water, as well as the following chemical reaction between the dissolved liquid ammonia and liquid water, are modeled. In the second approach, only the dissolution of ammonia into water is considered. The Henry’s Law with Van’t Hoff correlation is used for the simulation of the ammonia absorption process, namely the calculation of the concentration of ammonia in gas and in liquid. The Henry’s law is utilized since its line has the best correlation with the ammonia-water equilibrium line for the concentrations, which is taken into account in the numerical simulations. The ammonia mass flux from gas to liquid phase and its concentration at the outlet of the computational domain is determined as a result of the simulations.

Reducing the cost of redox flow batteries (RFBs) is critical to achieving broad commercial deployment of large-scale energy storage systems. This can be addressed in a variety of ways, such as reducing component costs or improving electrode design. The aim of this work is to better understand the relationship between electrode microstructure and performance. Four different commercially available carbon electrodes were examined – two cloths and two papers (from AvCarb® and Freudenberg Performance Materials) – and a comprehensive study of the different pore-scale and mass-transport processes is presented to elucidate their effect on the overall cell performance. Electrochemical measurements were carried out in a non-aqueous organic flow-through RFB with these different electrodes, using two supporting solvents (propylene carbonate and acetonitrile) and at a variety of flow rates. Electrode samples were scanned using X-ray computed tomography, and a customised segmentation technique was employed to extract several microstructural parameters. A pore network model was used to calculate the pressure drops and permeabilities, which were found to be within 1.26 × 10−11 and 1.65 × 10−11 m2 for the papers and between 8.61 × 10−11 and 10.6 × 10−11 m2 for the cloths. A one-dimensional model was developed and fit to polarisation measurements to obtain mass-transfer coefficients, km, which were found to be between 1.01 × 10−6 and 5.97 × 10−4 m s−1 with a subsequent discussion on Reynolds and Sherwood number correlations. This work suggests that, for these fibrous materials, permeability correlates best with electrochemical cell performance. Consequently, the carbon cloths with the highest permeability and highest mass-transfer coefficients, displayed better performances.

High throughput (HT) screening techniques for pressure-driven membrane processes allow simultaneous screening of multiple membrane samples under similar conditions, and are thus labour-, time- and consumables efficient. HT-modules have so far all been set-up in dead-end configuration. A new filtration set-up for cross-flow filtration has now been designed, allowing to simultaneously perform 16 pressure-driven separations with a membrane surface of 15 cm² each. The potential of the developed equipment and of the HT-screening concept in general was validated by demonstrating the reliability and reproducibility of the measurement of membrane performances, and by comparing flow simulations and experimental data. These data were obtained with 2 types of commercially available membrane: a nanofiltration membrane (NF 270, DowDuPont, USA) and a reverse osmosis membrane 73AC-UTC (Toray Industries Inc., Japan). Additionally, the flow-regime inside the cross-flow channel was studied by varying the hydrodynamic parameters and by applying feed spacers. The reproducibility of the data proved that this HT-approach can be a useful tool to rapidly screen a large array of operational parameters in membrane processes.

Mass transfer was studied at the external electrode of a cylindrical electrochemical reactor with decaying swirling flow using a single phase electrolyte and also a dispersion of a gas phase in the solution. The local mass-transfer coefficients were measured with a segmented cathode using the reduction of ferricyanide as test reaction. Two strategies were used to introduce the gas phase. In the first case the gas was fed by three holes symmetrically drilled at the bottom of the central anode tube and in the second one by means of a tee fitting at the reactor inlet. The best performance was obtained with the single phase electrolyte giving 0.78 as the exponent of the Reynolds number and the mass-transfer distribution along the reactor length is more uniform than that reported for a parallel plate electrochemical reactor under laminar flow conditions. The mass-transfer enhancement factor related to an annular duct with axial developing flow ranges from 8 to 11. This high value is the consequence of two factors: (i) the intensive forced convection produced by the swirling flow at the outer electrode and (ii) the sudden expansion of the flow at the entrance due to the small tangential inlet. The fed of a gas phase in the reactor has scarce influence on the mass-transfer performance. A comparison of mass-transfer results with previous studies is made. Fil: Contigiani, Camila Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina Fil: Gonzalez Perez, Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina Fil: Bisang, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina

An optimized design for a 210 kg alloy, Ti-Mn alloy based hydrogen storage system for stationary application is presented. A majority of the studies on metal hydride hydrogen systems reported in literature are based on system scale less than 10 kg, leaving questions on the design and performance of large-scale systems unanswered. On the basis of sensitivity to various design and operating parameters such as thermal conductivity, porosity, heat transfer coefficient etc., a comprehensive design methodology is suggested. Following a series of performance analyses, a multi-tubular shell and tube type storage system is selected for the present application which completes the absorption process in 900 s and the desorption process in 2000 s at a system gravimetric capacity of 0.7% which is a vast improvement over similar studies. The study also indicates that after fifty percent reaction completion, heat transfer ceases to be the major controlling factor in the reaction. This could help prevent over-designing systems on the basis of heat transfer, and ensure optimum system weight. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Liquid desiccant dehumidification provides a pathway to high-flow air pretreatment of air compressors for energy savings. However, high air-to-solution flow ratios (i.e., over 4.0) may result in an unacceptable decrease in dehumidification effectiveness, and few studies have managed to overcome this challenge. This study aims to experimentally demonstrate that the multi-stage internally-cooled liquid desiccant dehumidifier (MILDD) is capable of improving the effectiveness at extremely high air-to-solution flow ratios over 10.0. A laboratory bench of the MILDD is designed and tested in various operational conditions. Based on the finite difference model, the experimental results of dehumidification effectiveness are analyzed in terms of the heat and mass transfer process such as irreversible loss and driving forces. The specific cooling capacity associated with the energy efficiency is further studied by considering different desiccant regeneration efficiency. In addition, the experimental latent effectiveness from present and previous work is compared and correlated. Results show that the measured latent effectiveness of the MILDD exceeds 0.42 and goes even up to 1.02 at high air-to-solution flow ratios, i.e., 8.6–20.1, while existing liquid desiccant dehumidifiers maintain a comparable effectiveness only at much lower flow ratios, i.e., below 4.0. The proposed model and correlation also have been validated with a considerable accuracy for predicting the performance of internally-cooled dehumidifiers. This work has experimentally demonstrated the ability of the multi-stage internally-cooled liquid desiccant dehumidifier to overcome the low effectiveness at high gas–liquid flow ratios, which advances the potential application of liquid desiccant dehumidification in the air compression process.

Mass-transfer coefficients between an electrolyte solution and the wall of a hydrocyclone were experimentally determined by using the electrochemical technique. The local mass-transfer coefficients were measured as a function of the axial distance from the entrance changing the inlet volumetric flow rate and the underflow stream. An enhancement of mass-transfer was observed in comparison to that predicted for developing axial flow in an annular duct, being the cylindrical part more active than the conical one. The global mass-transfer coefficient in the cylindrical region depends on the Reynolds number raised to an exponent of 0.79, in accordance with the mass-transfer behavior of decaying annular swirl flow. The modified hydrocyclone was also examined for the removal of copper from dilute synthetic solutions. A diminution of copper concentration from 400 ppm to 40 ppm was achieved after 60 minutes of electrolysis in a recirculating system and the contaminant was recovered as a metal powder separated by the hydrocyclone. The space time yield and the specific energy consumption were 12.5 kg m-3 h-1 and 4.9 kWh kg-1, respectively, with a cumulative current efficiency of 54%, showing that the modified hydrocyclone is a suitable reactor for the electrochemical treatment of effluents. Fil: Resio, L. C.. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina Fil: Gonzalez Perez, Omar. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina Fil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina

openaire: EC/H2020/788489/EU//BioELCell The prediction of the morphology of wet-spun fibers has so far been only possible by complex and experimentally intensive approaches that include the construction of ternary phase diagrams. Ultimately, however, the available models give approximate information. Here we propose an alternative predictive approach that uses design principles based on the combination of (1) relative energy difference (RED) of Hansen solubility and (2) a kinetic parameter "T" that considers mass transfer effects. Such a model is applied and experimentally validated for a priori determination of the diameter and internal morphology of wet-spun fibers. Remarkably, only three. variables relevant to wet-spinning are needed, namely, the choice of polymer, solvent, and nonsolvent types. A combination of systems is tested, and the morphology of the obtained fibers is determined via electron microscopy. Aspects related to demixing, internal specific surface area (BET), and layer formation on the fibers are described qualitatively. The facile implementation of the design parameters is further confirmed through comparison with data published on the subject. Our proposed model is expected to accelerate future developments in nanomaterials, especially in the context of ongoing efforts related to fiber spinning with biopolymers.

The slag2PCC concept aims at transforming steelmaking slag into precipitated calcium carbonate (PCC) with market value. This paper reports on R&D work on two features that impact the overall performance and costs of slag2PCC as a carbon capture and utilisation (CCU) technology. Operating near ambient conditions, calcium is selectively leached from steelmaking slag using aqueous ammonium salt solvent, followed by carbonation using a CO2-containing stream. Separators for removing spent slag and PCC connect two reactors for extraction and carbonation, respectively, between which the solvent solution is cycling. One requirement is effective conversion of the CO2 fed to the system: while the dissolution of CO2 is the rate-liming step it is essential to minimise release of unreacted CO2. Mixing the solutions enhances mass transfer. High-speed video recordings were made around mixers located at various heights in a bubble column, analysing CO2 bubble swarm dissolution. A second feature studied are losses of ammonia (NH3) from the solution. An outlet for unreacted gas presents a risk of NH3 vapour release, which lowers solution alkalinity while adding costs. Multicomponent mixture mass transfer analysis showed that diffusion of NH3 into CO2 bubbles may be significant at least during initial stages of dissolution. Experimental findings were verified. (C) 2019 Elsevier Ltd. All rights reserved.

This study deals with the modeling of the extraction of solid lanoline from raw wool under near-critical conditions using 5% ethanol in CO2, using our previous experimental data. A mass-transfer model is developed to explain the extraction results at T¿=¿30¿°C, below the melting point of lanoline (36–42¿°C). Two variables are studied, the extraction pressure and the solvent mass flowrate. Our model depends on three parameters: the solubilities of the two lanoline fractions and the lanoline mass transfer coefficient. The model is a set of first-order partial differential equations, that is solved by orthogonal collocation in combination of optimization of the parameters. The fluid-side mass-transfer coefficient decreases with extraction pressure and is about 5¿×¿10-6 m/s for Re < 1 (at 70–150¿bar) and depends on fluid velocity. The solubilities of lanoline fractions, independent of flowrate, agree very well with those previously reported

Here, in this research article, we have investigated an incompressible viscoelastic fluid flow over a uniform stretching surface sheet along with slip boundary conditions in the presence of porous media. The partial differential equations which govern the fluid flow are changed into ordinary differential equations through suitable similarity transformation variables. Finally, the transformed ordinary differential equations are solved with the help of a seminumerical technique known as the homotopy analysis method (HAM). The uniqueness of our study is not only to analyze and carry out the effect of the elastic parameter but also to account for viscous dissipation which is important in the case of optically transparent flow. The novel effects for the parameters which affect the flow and heat transfer, such as the Eckert number, porous medium parameter, and the velocity slip parameter, are studied through graphs. Also, the convergence analysis for the proposed method is addressed. Additionally, for the sake of validation, the present work is also compared with the already published work and an outstanding agreement is found. This study was supported by King Saud University, Riyadh, Saudi Arabia (Project number RSP-2019/33).

This work investigates the effect of current density on the hydrogen gas bubble formation during electrolysis on a platinum electrode. Local detection of bubble evolution was performed electrochemically by using a hydrogen-collecting microelectrode placed in close proximity of a larger hydrogen-generating platinum electrode. The micro-electrode probe locally measured the concentration of dissolved molecular hydrogen produced during electrolysis. In acidic conditions, it was found that at low electrolysis currents the concentration of dissolved hydrogen could temporarily rise up to 50 times the saturation level, while once a large current was reached, the concentration dropped, increasing the concentration of hydrogen inside gas bubbles, and became independent of the current. Through laser reflectance, the onset of bubble formation was found (similar to-0.7 mA/cm(2)), which was lower than the first bubble observable by naked eye or detected by the microelectrode probe.

The conversion rate of the mass transfer controlled oxidation of CO over a Pt/?-alumina catalyst (d = 65 ?m) has been studied in a fluidized bed (internal diameter = 0.05 m) p operated close to and in the turbulent fluid bed regime. The objectives were to investigate the gas-solids contacting efficiency to evaluate the conversion data in terms of overall mass transfer coefficients and define the apparent contact efficiency. At high superficial gas velocities, the concept of formation of particle agglomerates and voids is more realistic than the two-phase model considering discrete bubbles and a dense phase. The two-phase model is not useless but has hardly any relation with the real flow pattern in the turbulent regime.

Results of unique heat transfer measurement in beds of fine, cracking catalyst particles, fluidized by air or helium gas, are compared with predictions from a theoretical model presented in the literature [1], and also with an earlier established empirical correlation [2]. Moreover, the results have been related to dense phase flow conditions around a silver heat transfer probe by a simple turbulence model. A maximum heat transfer coefficient of h = 2300 Wm-2K-1 has been measured in a bed of 14μm (average diameter) particles, fluidized by helium gas. The data collected, and the model developed, can be used for the design of heat transfer tubes in fluidized beds of fine particles as for instance in Fluid Catalytic Cracking of crude oil heavy residues. FCC is one of the most important conversion process in the petroleum refineries.

Oral lyophilizates also called orally disintegrating tablets (ODTs) are a patient friendly and convenient dosage form. They are manufactured by dosing a suspension in blister cups and subsequently freeze-drying these blisters to achieve porous tablets that disintegrate quickly (< 10 s) when placed upon the tongue. This paper proposes a mechanistic model of the primary drying phase of these oral lyophilizates processed in cold-form blisters. A heat transfer coefficient (Kv) and dried layer resistance (Rp) are regressed and applied in a dynamic optimization of the primary drying phase. The optimization exercise showed the possibility of ultra-short sublimation times for polyvinyl acetate (PVA) based formulations with a primary drying time of 3.68 h for a 500 mg acetaminophen tablet., Graphical abstract Image 1

A continuous-flow adsorption/desorption process for the recovery of phenolic compounds (PCs) from olive mill wastewaters (OMWs) was developed in a 0.53 m packed column, using a previously selected resin (Amberlite XAD16) and an actual OMW. The main goals of the study were (i) to evaluate the PC adsorption/desorption performances of XAD16 by means of adsorption isotherms and adsorption/desorption breakthrough tests, and (ii) to develop a reliable model of the process. A combination of centrifugation and microfiltration resulted necessary to attain a high suspended solid removal (98.5%) and thus avoid clogging of the packed bed. The quality of two packing procedures was evaluated by means of frontal analysis tests. XAD16 performed well in terms of both adsorption yield at 20% breakthrough (87–88%) and PC/COD selectivity (PC/COD adsorption constant = 7–9). The desorption solvent (acidified ethanol) was effectively regenerated by vacuum distillation. The adsorption breakthrough curves were successfully simulated with a 1-D convection/dispersion model with mass-transfer (R2 = 0.95–0.99; kLa = 0.8–2.5 · 10−3 1/s), whereas an equilibrium adsorption model with dispersion failed to predict the experimental data. In the perspective of a process scale-up, the simulation of the best-performing operational condition was used to evaluate the process performances for different column lengths (0.5–10 m). A precise and automated HPLC method for total PC measurement was developed and compared to the traditional Folin–Ciocalteu methodology. Further research is needed to optimize the desorption step, to scale up the process and to evaluate the long-term resin performances.

We report on detailed and systematic experiments of thin liquid films flowing as a result of the action of gravity under an inverted planar substrate. A measurement technique based on planar laser-induced fluorescence (PLIF) was developed and applied to a range of such flows in order to provide detailed space- and time-resolved film-height information. Specifically, the experimental campaign spanned three inclination angles (β=−15∘, −30∘, and −45∘, in all cases negative with respect to the vertical), two water-glycerol solutions (with Kapitza numbers of Ka=13.1 and 330), and flow Reynolds numbers covering the range Re=0.6–193. The collection optics were arranged so as to interrogate a spanwise section of the flow extending about 40mm symmetrically on either side the centerline of the film span (80mm in total), at a distance 330 mm downstream of the flow inlet. A range of flow regimes, typically characterized by strong three dimensionality and pronounced rivulet formation, were observed depending on the imposed inlet flow conditions. In the lower liquid Kapitza number Ka(=13.1) flows and depending on the flow Re, the free surface of the film was populated by smooth rivulets or regular sequences of solitary pulses that traveled over the rivulets. In the higher liquid Ka(=330) flows, rivulets were observed typically above Re≈30, depending also on the inclination angle, and grew in amplitude until quasi-two-dimensional fronts developed intermittently that were associated with distinct thin-film regions of varying length and frequency. These regions are of particular interest as they are expected to affect strongly the heat and mass transfer capabilities of these flows. The occurrence of the fronts was more pronounced, with higher wave frequencies, in film flows at smaller negative inclinations for the same flow Re. The rivulet amplitude was found to increase at larger inclinations for the same Re and showed a nonmonotonic trend with increasing Re, reaching a maximum that shifted to higher Re at larger inclinations. Furthermore, in flows that displayed pronounced rivulet formation [i.e., large (negative) β and higher Re], the local film-height standard deviation in regions corresponding to the rivulet crests and troughs was reduced compared to the film-height standard deviation calculated over the entire examined film region. The mean rivulet wavelength also increased at larger inclinations, peaking at 26 mm when Ka=330. Based on our experimental results and theoretical arguments, we hypothesize that the formation of rivulets can be attributed, at small β, to a secondary Rayleigh-Taylor instability mechanism that destabilizes the suspended two-dimensional wavefronts, and at larger β, to the primary Rayleigh-Taylor instability mechanism of a flat film coating the underside of the inclined plate.

Falling film reactors represent the actual technology to run sulfonation reaction at pilot and industrial scale. The reaction is characterized by high thermal tenor, thus realizing a liquid reactive film flowing directly downwards on the internal reactor wall, it benefits of high heat exchange to the external jacket. The scale-up of such reactors is straightforward as it consists mainly on increasing the pipe numbers, with heat exchanger shell/pipe architecture. The main problem of this reactor solution is its modelling. The fluid-dynamics is complex to be fully described and the few models proposed in the literature lacks in rigorousness. The aim of the present work is the realization of a detailed reactor model able to describe sulfonation reaction in a falling film reactor. The simulations were compared with data collected on a pilot-plant.

In this study, photoactive CuxO/TiO2 coatings were prepared using magnetron sputtering operated at different powers and modes (Direct-current magnetron sputtering and High Power Impulse magnetron sputtering). Indoor/outdoor air pollutions (Volatile Organic Compounds, VOCs) degradation have been dramatically reduced on sputtered CuxO/TiO2 on polyester (PES) cloth under low intensity visible light. The Low intensity visible light was used to irradiate the sputtered photocatalysts, which degraded various VOC molecules concomitant with a bacterial inactivation ability. The VOC removal kinetics were studied in the dark and under visible light as a function of the deposition time and applied peak currents during the coating by HiPIMS. High concentrations of chloroform and butyraldehyde were shown to be degraded (90% and 85%, respectively) on CuxO/TiO2-PES fabrics under daylight irradiation. The repetitive reuse of the sputtered coatings was also investigated showing the long operational lifetime of the prepared fabrics. The deposition rates of Ti and Cu atoms and their atomic distribution along the sputtered film have been investigated by Transmission Electronic Microscopy (TEM). Redox catalysis was shown to happen within the VOC degradation time as detected by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of the Cu2p3/2 peak in the CuxO/TiO2 on PES samples showed changes in the Cu2O and CuO within the VOCs degradation and the bacterial inactivation. The interfacial charge transfer (IFCT) between CuxO induced under light leading to VOCs oxidation path seemed to require a low photons energy and were able to oxidize the pollutants even at high concentrations. The mechanisms involving the VOCs degradation on CuxO/TiO2 catalysts are suggested in which the holes generated by Cu2O transfer to TiO2 in the TiO2 (n)/CuxO(p) in the hetero-junction. This transfer is favored by the electrostatic interaction between both semiconductors. The photo-generated ROS, mainly (OH)-O-center dot-radicals were determined by fluorescence method. The possible contribution of the (OH)-O-center dot-radicals in the bacterial inactivation on the sputtered CuxO/TiO2 catalysts was discussed. DRS, TEM, contact angle (CA) and XPS were used to characterize the catalyst optical and structural properties.

Reactive chromatography is a special topic in chemical reaction engineering, consisting of the combination of chemical reaction and chromatographic separation. The main idea is to avoid a further separation unit, by performing reaction and separation in one unique equipment, allowing process intensification. This technology is usually applied in hydrolysis (or esterification) reactions, that undergoes through the reaching of chemical equilibrium. The chromatographic reactor application would lead to complete conversion, by separating reactants and products as the reaction proceeds. Modelling is certainly a delicate issue for chromatographic reactor to optimize the operation conditions, thus different approaches were published. The aim of the present work is to show a novel chromatographic reactor model, were all the physical and chemical phenomena involved and described by a rigorous approach. The fluid-dynamics was treated by axial dispersion approach, and the Peclet number values were obtained from dedicated experiments. The external fluid-solid mass transfer was calculated from existing correlations, demonstrating to be negligible for the modelled chromatographic reactor. The intraparticle mass diffusion was assumed to be the sum of two parallel contributions, i.e. porous and surface diffusivity. The model was tested on literature data for methyl acetate hydrolysis experiments with satisfactory results, obtaining reliable values of the surface diffusivity. A sensitivity analysis was conducted highlighting that the model can predict complete ester conversion and product separation.

We present an experimental study of dissolution-driven convection in a three-dimensional porous medium formed from a dense random packing of glass beads. Measurements are conducted using the model fluid system MEG/water in the regime of Rayleigh numbers, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Ra=2000{-}5000$$\end{document}Ra=2000-5000. X-ray computed tomography is applied to image the spatial and temporal evolution of the solute plume non-invasively. The tomograms are used to compute macroscopic quantities including the rate of dissolution and horizontally averaged concentration profiles, and enable the visualisation of the flow patterns that arise upon mixing at a spatial resolution of about (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2\times 2\times 2)\,\hbox {mm}^3$$\end{document}2×2×2)mm3. The latter highlights that under this Ra regime convection becomes truly three-dimensional with the emergence of characteristic patterns that closely resemble the dynamical flow structures produced by high-resolution numerical simulations reported in the literature. We observe that the mixing process evolves systematically through three stages, starting from pure diffusion, followed by convection-dominated and shutdown. A modified diffusion equation is applied to model the convective process with an onset time of convection that compares favourably with the literature data and an effective diffusion coefficient that is almost two orders of magnitude larger than the molecular diffusivity of the solute. The comparison of the experimental observations of convective mixing against their numerical counterparts of the purely diffusive scenario enables the estimation of a non-dimensional convective mass flux in terms of the Sherwood number, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Sh=0.025Ra$$\end{document}Sh=0.025Ra. We observe that the latter scales linearly with Ra, in agreement with both experimental and numerical studies on thermal convection over the same Ra regime.

The dissolution of a gas bubble in a confined geometry is a problem of interest in technological applications such as microfluidics or carbon sequestration, as well as in many natural flows of interest in geophysics. While the dissolution of spherical or sessile bubbles has received considerable attention in the literature, the case of a two-dimensional bubble in a Hele-Shaw cell, which constitutes perhaps the simplest possible confined configuration, has been comparatively less studied. Here, we use planar laser-induced fluorescence to experimentally investigate the diffusion-driven transport of dissolved CO2 that propagates from a cylindrical mm-sized bubble in air-saturated water confined in a horizontal Hele-Shawcell. We observe that the radial trajectory of an isoconcentration front, r(f) (t), evolves in time as approximately r(f) - R-0 alpha root t, where R-0 denotes the initial bubble radius. We then characterize the unsteady CO2 concentration field via two simple analytical models, which are then validated against a numerical simulation. The first model treats the bubble as an instantaneous line source of CO2, whereas the second assumes a constant interfacial concentration. Finally, we provide an analogous Epstein-Plesset equation with the intent of predicting the dissolution rate of a cylindrical bubble. We acknowledge the support of the Spanish Ministry of Economy and Competitiveness through Grants No. DPI2014-59292-C3-1-P and No. DPI2015-71901-REDT, partly funded through European Funds.

A model for ionic and electronic grain boundary transport through thin films, scales or membranes with columnar grain structure is introduced. The grain structure is idealized as a lattice of identical hexagonal cells – a honeycomb pattern. Reactions with the environment constitute the boundary conditions and drive the transport between the surfaces. Time-dependent simulations solving the Poisson equation self-consistently with the Nernst-Planck flux equations for the mobile species are performed. In the resulting Poisson-Nernst-Planck system of equations, the electrostatic potential is obtained from the Poisson equation in its integral form by summation. The model is used to interpret alumina membrane oxygen permeation experiments, in which different oxygen gas pressures are applied at opposite membrane surfaces and the resulting flux of oxygen molecules through the membrane is measured. Simulation results involving four mobile species, charged aluminum and oxygen vacancies, electrons, and holes, provide a complete description of the measurements and insight into the microscopic processes underpinning the oxygen permeation of the membrane. Most notably, the hypothesized transition between p-type and n-type ionic conductivity of the alumina grain boundaries as a function of the applied oxygen gas pressure is observed in the simulations. The range of validity of a simple analytic model for the oxygen permeation rate, similar to the Wagner theory of metal oxidation, is quantified by comparison to the numeric simulations. The three-dimensional model we develop here is readily adaptable to problems such as transport in a solid state electrode, or corrosion scale growth.

In this paper we present a pore-scale model describing the multiphysics occurring during the rehydration of freeze-dried vegetables. This pore-scale model is part of a multiscale simulation model, which should explain the effect of microstructure and pre-treatments on the rehydration rate. Simulation results are compared to experimental data, obtained by MRI and XRT. Time scale estimates based on the pore-scale model formulation agree with the experimental observations. Furthermore, the pore-scale simulation model provides a plausible explanation for the strongly increased rehydration rate, induced by the blanching pre-treatment. Industrial relevance The increased insight in the physical processes governing the rehydration of porous or freeze-dried foods gives more rationale for optimizing all processing steps. Industry is seeking for means to give dried fruits and vegetables more convenience, but also higher quality concerning health and texture. This study shows that blanching pretreatment prior to freeze-drying strongly enhances the rehydration, while the loss of nutrients is hardly affected.

Feed spacers are used in spiral wound reverse osmosis (RO) membrane modules to keep the membrane sheets apart as well as to enhance mixing. They are beneficial to membrane performance but at the expense of additional pressure loss. In this study, four types of feed spacer configurations are investigated, with a total of 20 geometric variations based on commercially available spacers and selected filament angles. The impact of feed spacer design on membrane performance is investigated by means of three-dimensional (3D) computational fluid dynamics (CFD) simulations, where the solution-diffusion model is employed for water and solute transport through RO membranes. Numerical simulation results show that, for the operating and geometric conditions examined, fully woven spacers outperform other spacer configurations in mitigating concentration polarisation (CP). When designed with a mesh angle of 60°, fully woven spacers also deliver the highest water flux, although the associated pressure drops are slightly higher than their nonwoven counterparts. Middle layer geometries with a mesh angle of 30° produce the lowest water flux. On the other hand, spacers with a mesh angle of 90° show the lowest pressure drop among all the filament arrangements examined. Furthermore, the computational model presented here can also be used to predict membrane performance for a given feed spacer type and geometry.

Impinging air jets of various shapes, sizes and configurations are commonly used in heating, cooling and drying industrial processes. An analytical study has been carried out to optimise the thermal performance of single and multiple nozzle systems using impinging air jets. The optimisation of the nozzle array was given for practical purposes. The results show that within practical limits, a narrower nozzle size results in a greater heat and mass transfer coefficient. An economical analysis of the drying processes is also given for slot nozzles.

An experimental investigation on impingement heat transfer from a rib-roughened surface is performed. Single, double, and triple rib configurations are tested. The rib is also located at three different positions for a single rib case. The Reynolds number is varied from 10,000 to 50,000 whereas the dimensionless jet-to-surface distance (z/D) is kept constant as 8. Results show that, the Nusselt number decreases just before a rib. After the rib, however, the Nusselt number decreases by a larger amount. Since ribs cause a reincreasing in the Nusselt number after the stagnation point and since the stagnation point Nusselt number is not affected by ribs, they can be used to enhance heat transfer especially for spot cooling applications. It is also obtained that using ribs is more useful for low speed impinging jets, when heat transfer from the whole surface is considered.

The performances of well-known porous metal/metalloid oxide adsorbents (zeolite 13X, zeolite 4A and silica gel) and less explored Engelhard titanosilicate ETS-10 for water adsorption heating systems (AHSs) were compared with the aid of computational modelling and simulations. The developed model contemplated adsorption equilibrium, one-dimensional heat and mass transfer in the bed, external heat transfer limitations, and intraparticle mass transport. The pair zeolite 13X/water seemed most promising for the AHS partly due to a higher amount of heat generated per cycle, and favourable water-adsorption isotherm features. Based on sensitivity studies, for zeolite particle diameters in the range 0.2-0.6 mm, the coefficient of performance was 1.48 and the specific heating power was in the range 1141-1254 W Kg(s)(-1) Aiming at inferior computational and numerical efforts, the impact of considering some simplified postulations (e.g. constant thermal conductivity of the adsorbent; constant isosteric heat of adsorption; constant linear driving force coefficient), while ensuring comparable predictions of the performances of the AHSs, was successfully investigated. (C) 2016 Elsevier Ltd. All rights reserved.

In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime.

The advent of technology and development has led to a surge in energy demands by both developing and developed nations. Since 2000, the energy usage pattern in India has doubled. The majority of the power sector is dependent on the fossil fuel sources for energy generation. While energy generation is of prime concern the storage and retrieval with minimum losses is also significant. The packed beds system form a significant part of the solar power systems which are used to store energy during day time and retrieve it during the night. The present work investigates on the issues related to energy storage capability in packed beds. In the present work, volumetric heat transfer coefficient is measured using a transient technique in packed beds with uniformly sized spheres. The experiments are conducted for bed to particle diameter ratios of 5, 10 and 21. The temperatures inside the packed bed are measured at four axial locations with thermocouples placed inside the spheres and positioned 112 mm apart along the central axis. The temperatures are measured at four radial locations 5, 10, 15 and 20 mm apart from the solid wall along different axial planes from the entry of packing. The experimental results are compared with Schumann's curves and the volumetric heat transfer coefficient is estimated. It is found that the estimated volumetric heat transfer coefficient (h(v)) is higher for smaller particle diameter 2.38 mm as compared to larger diameter spheres with random packing. There is an increase in the volumetric heat transfer coefficient (h(v)) with the increase in the particle Reynolds number. (C) 2016 Elsevier Masson SAS. All rights reserved.

Emulsification using electric fields is an easy alternative to flow-induced drop breakup, and the former is reported to be more effective and economical than the latter, especially when the medium phase is poorly conducting and highly viscous. The emulsification of a coarse water-in-oil emulsion in a uniform electric field is studied. We perform a detailed experimental analysis of the effect of applied electric field strength and the duration of applied electric field on the drop size distribution. The average diameter as well as the time for emulsification decreases with an increase in the intensity of the electric field. Moreover, a narrow size distribution is observed. An average size of a few microns of the dispersed phase could be achieved. New breakup mechanisms at play in the emulsification process are discussed. Identified mechanisms involve charged lobe disintegration, charged drop breakup, chain formation in which several water droplets are interconnected by thin water bridges, electrospraying and charge transfer, and coalescence. The study shows that charged drop disintegration could be the key mechanism of fine emulsification of an initially electrically neutral coarse emulsion.

International audience; Mixed convection during evaporation of a water falling film in a vertical concentric annulus was studied numerically. The water thin film falls on the inner tube and is subjected to a constant heat flux density, whereas the outer cylinder is assumed to be insulated and dry. An imposed air flow circulates within the gap between the two concentric tubes. The objective of this work is to understand the evaporation phenomenon in order to improve the average evaporated mass flux density and heat and mass transfer. Conservative equations governing the gas phase are solved numerically using the finite volume method. In the liquid phase, a method based on local heat and mass balances on each level is used. Thus, the following liquid film parameters, feed water mass flow, feed temperature and heat flux density, are taken into account. The obtained results are analyzed to emphasize and evaluate the influence of the previous operating parameters and the annulus curvature on the effective evaporation surface and on the mass flux density of evaporated water.

Humidification of chicory root cold stores helps in maintaining the quality and extending the postharvest storage time of chicory roots. Low evaporation rate of the sprayed droplets at such sub-zero temperatures (-2 degrees C to -1 degrees C) favours surface deposition that could have an adverse effect on the efficiency of the storage room. A three-dimensional computational fluid dynamics (CFD) model was developed and used to predict the storage room air velocity, temperature and humidity distributions, and fate of the water droplets that were sprayed for humidifying the storage room. The humidification system in a chicory root cold store was then optimized. The efficiency of the humidification system was affected by length of cold air deflector, stack height, number of nozzles and duration of humidification. Elongating the air deflector, reducing the stack height, reducing the number of nozzles and shortening the humidification time increased the amount of droplet evaporated and decreased the amount of droplet deposited on the stack. The following combinations of room design and operating parameters could clearly give the best performance of the humidification system: deflector length of 0.8 m, two nozzles with an interval humidification of 1.5 min on and 2 min off cycle and stack height of 3.4 m. (C) 2009 Elsevier Ltd. All rights reserved. ispartof: Journal of food engineering vol:94 issue:1 pages:110-121 status: published

Steady two-dimensional flow of an incompressible and viscous fluid through a high-porosity medium in the presence of heat transfer and radiation is investigated when the thermal conductivity varies linearly with temperature and the porous medium is bounded by a stretching sheet in its. own plane with a velocity proportional to the distance from the origin of the sheet. The temperature distribution is found numerically for different parameters of the problem. Journal of Porous Media

In recent years, several publications on microfluidic devices have focused on the process of electroporation, which results in the poration of the biological cell membrane. The devices involved are designed for cell analysis, transfection or pasteurization. The high electric field strengths needed are induced by placing the electrodes in close proximity or by creating a constriction between the electrodes, which focuses the electric field. Detection is usually achieved through fluorescent labeling or by measuring impedance. So far, most of these devices have only concerned themselves solely with the electroporation process, but integration with separation and detection processes is expected in the near future. In particular, single-cell content analysis is expected to add further value to the concept of the microfluidic chip. Furthermore, if advanced pulse schemes are employed, such microdevices can also enhance research into intracellular electroporation. © Springer-Verlag 2006.

A single air jet or an array of air jets, impinging normally on a surface, may be used to achieve enhanced heat and mass transfer coefficients for convective heating, cooling and drying. To provide data for designers of industrial equipment, a programme of research has been implemented to study the heat and mass transfer processes. An original optimization of nozzle arrays under impinging air jets has been given for both academic and industrial users. Also optimum parameters presented here are simple and have a wide applicability.

Impinging air jets are widely used in industry, for heating, cooling, drying, etc., because of the high heat transfer rates which are developed in the impingement region. In this study, two methods of enhancing jet heat transfer have been investigated, namely, by using turbulence promoters to artificially raise the turbulence level, and by using a loudspeaker to excite the jet acoustically. In both these cases, the increases in heat transfer from enhancement were found to be modest. Some experimental hot-wire anemometry data obtained for free and impinging air jet flows are presented here. The existence of a relationship between turbulence intensity and heat transfer mechanism is also discussed.

Many microfluidic applications involve chemical reactions. Most often, the flow is predominantly laminar, and without active or passive mixing enhancement the reaction time can be extremely long compared to the residence time. In this work we demonstrate the merits of the combination of flow pulsation and geometrical characteristics in enhancing mixing efficiency in microchannels. Mixing was studied by introducing a mixing index based on the gray level observed in a heterogeneous flow of pure water and water colored by rhodamine B. The effects of the injection geometry at the microchannel inlet and the use of pulsed flows with average Reynolds numbers between 0.8 and 2 were studied experimentally and numerically. It appeared that the mixing index increases with the nondimensional residence time (τ), which is inversely proportional to the Reynolds number. In addition, we show that the mixing efficiency depends strongly on the geometry of the intersection between the two fluids. Better mixing was achieved with sharp corners (arrowhead and T intersections) in all cases investigated. In pulsed flow, the mixing efficiency is shown to depend strongly on the ratio (β) between the peak amplitude and the mean flow rate. Optimal conditions for mixing in the microchannels are summarized as a function of Reynolds number Re, the ratio β, and the geometries.