Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generat...Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.展开更多
A swimming pool can be considered as a chemical reactor with specific hydraulic and macro-mixing characteristics. The nature of flow into the pool depends on various characteristics, such as water inlets and outlets (...A swimming pool can be considered as a chemical reactor with specific hydraulic and macro-mixing characteristics. The nature of flow into the pool depends on various characteristics, such as water inlets and outlets (number and position), pool geometry, and flow rate. This study investigates how swimming pool design affects hydraulic behavior based on experimental and computational fluid dynamics studies (CFD). This paper does not describe the hydraulic behavior of all existing swimming pools, however the cases studied here are representative of pool designs widely used in Europe and the United States. The model developed, based on the principle of a stirred reactor, could be used as a first approach in describing the hydraulic behavior of regular pools. This model is suitable for the study of physical and chemical phenomena with long characteristic times. Other, more advanced, models were shown to be more suitable to the case of fast chemical processes.展开更多
In South Saharan countries, 85% of the population uses biomass as a primary energy source. Cameroon presents one of the highest biomass energy and sawmills produce important sawdust resources which are not used and ar...In South Saharan countries, 85% of the population uses biomass as a primary energy source. Cameroon presents one of the highest biomass energy and sawmills produce important sawdust resources which are not used and are burnt in piles leading to significant air toxic emissions. Therefore, we have to valorize industrially these available sawdusts. This study focuses on the physicochemical and thermochemical analysis of Ayous, Sapelli and Tali sawdust. The proximate and ultimate analysis, particle size, structural composition, as well as heavy metal content and calorific value were determined. In addition, the thermogravimetric mass losses were also estimated. The results showed that high water contents (24% - 41%) were recorded in the raw sawdust, and the thermal treatment reduced these contents from 78% to values in the range of 4% - 9%. The values for ash and volatile matter content were respectively between 0.25% - 0.74% and 68% - 76%. The LHV is higher in Ayous (17.5 MJ/kg) and Sapelli (16.8 MJ/kg) than that of Tali (15.7 MJ/kg). The concentration of heavy metals is very low in each species. Extractives are more present in Tali (16.06%) than in the other sawdusts. Pyrolysis of sawdust shows the typical decomposition of hemicellulose (270˚C - 325˚C), cellulose (325˚C - 400˚C) and lignin (200˚C - 550˚C) with a maximum loss of 75% at 370˚C and the melting point is 320˚C. The results of the sawdust parameters determined in the paper can be valorized to reduce pollutants emissions by developing the efficiency and effectiveness of biomass energy processes and promoting the use of biomass as a sustainable alternative to traditional fossil fuels.展开更多
Smart Materials are along with Innovation attributes and Artificial Intelligence among the most used “buzz” words in all media. Central to their practical occurrence, many talents are to be gathered within new conte...Smart Materials are along with Innovation attributes and Artificial Intelligence among the most used “buzz” words in all media. Central to their practical occurrence, many talents are to be gathered within new contextual data influxes. Has this, in the last 20 years, changed some of the essential fundamental dimensions and the required skills of the actors such as providers, users, insiders, etc.? This is a preliminary focus and prelude of this review. As an example, polysaccharide materials are the most abundant macromolecules present as an integral part of the natural system of our planet. They are renewable, biodegradable, carbon neutral with low environmental, health and safety risks and serve as structural materials in the cell walls of plants. Most of them are used, for many years, as engineering materials in many important industrial processes, such as pulp and papermaking and manufacture of synthetic textile fibres. They are also used in other domains such as conversion into biofuels and, more recently, in the design of processes using polysaccharide nanoparticles. The main properties of polysaccharides (e.g. low density, thermal stability, chemical resistance, high mechanical strength…), together with their biocompatibility, biodegradability, functionality, durability and uniformity, allow their use for manufacturing smart materials such as blends and composites, electroactive polymers and hydrogels which can be obtained 1) through direct utilization and/or 2) after chemical or physical modifications of the polysaccharides. This paper reviews recent works developed on polysaccharides, mainly on cellulose, hemicelluloses, chitin, chitosans, alginates, and their by-products (blends and composites), with the objectives of manufacturing smart materials. It is worth noting that, today, the fundamental understanding of the molecular level interactions that confer smartness to polysaccharides remains poor and one can predict that new experimental and theoretical tools will emerge to develop the necessary understanding of the structure-property-function relationships that will enable polysaccharide-smartness to be better understood and controlled, giving rise to the development of new and innovative applications such as nanotechnology, foods, cosmetics and medicine (e.g. controlled drug release and regenerative medicine) and so, opening up major commercial markets in the context of green chemistry.展开更多
The turbulence behavior of gas-liquid two-phase flow plays an important role in heat transfer and mass transfer in many chemical processes. In this work, a 2D particle image velocimetry (PIV) was used to investigate t...The turbulence behavior of gas-liquid two-phase flow plays an important role in heat transfer and mass transfer in many chemical processes. In this work, a 2D particle image velocimetry (PIV) was used to investigate the turbulent characteristic of fluid induced by a chain of bubbles rising in Newtonian and non-Newtonian fluids. The instantaneous flow field, turbulent kinetic energy (TKE) and TKE dissipation rate were measured. The results demonstrated that the TKE profiles were almost symmetrical along the column center and showed higher values in the central region of the column. The TKE was enhanced with the increase of gas flow and decrease of liquid viscosity. The maximum TKE dissipation rate appeared on both sides of the bubble chain, and increased with the increase of gas flow rate or liquid viscosity. These results provide an understanding for gas-liquid mass transfer in non-Newtonian fluids.展开更多
The design and preparation of hybrid mixed matrix membranes based on PVC （polyvinylchloride） were studied for the separation of toluene--n-heptane mixtures by pervaporation. PVC was chosen as the starting organic ma...The design and preparation of hybrid mixed matrix membranes based on PVC （polyvinylchloride） were studied for the separation of toluene--n-heptane mixtures by pervaporation. PVC was chosen as the starting organic matrix because it is an inexpensive polymer, possessing a very high selectivity for aromatics. This property is due to the polar macromolecular structure that can induce a specific transfer of aromatic species compared with aliphatic species. To improve the performance of the PVC glassy structure, lhe incorporation of several inorganic micro- and nanopartieles in the polymer matrix was performed to prepare mixed matrix membranes. The results reported were obtained using several types of clay, i.e., Maghnite, Wyoming, Kaolin and Nanocor, with the goal of improving membrane permeability due to the hybrid network. Our results show that the transport properties of the modified PVC network can be drastically modified by the type and amount of particles used,展开更多
Flexible photonic crystal(PC)materials possess exceptional optical properties.However,their structures often deteriorate under repeated mechanical responses,which may lead to structural impairments within the photonic...Flexible photonic crystal(PC)materials possess exceptional optical properties.However,their structures often deteriorate under repeated mechanical responses,which may lead to structural impairments within the photonic band gap.This poses a challenge to their sustainability.Herein,by introducing a self-healing thermoplastic polyurethane(STPU)material with inverse-opal PC structure,a self-healing discoloration skin with stress response is prepared,inspired by the structural coloration and self-healing mechanisms of natural organisms.Given the synergistic effects of dynamic covalent bonds(S-S bonds)and hydrogen bonds(H-bonds),STPU can be reversibly adjusted upon mechanical deformation,enabling it to coordinate with environmental changes and showing excellent mechanical strength(26.76 MPa)and elongation at break(2000%).At the same time,the inverse opal structure inside STPU gives composite reversible color transitions with sensitive optical responses to solvents(e.g.,water and ethanol)and mechanical stress(0%–70%strain)through the regulation of lattice spacing.Furthermore,the incorporation of an interpenetrating network composed of polyacrylamide hydrogel and carbon nanotubes enhances its strain sensitivity and structural color stability.More importantly,given its excellent self-healing properties,it exhibits broad application potential in flexible sensors,adaptive optical devices,bioinspired robotic skins,and dynamic anticounterfeiting encryption,overcoming the limitations of traditional PCs(e.g.,high fragility and single functionality).The proposed strategy paves the way for the development of durable intelligent sensing materials with enhanced environmental adaptability and multifunctional integration.展开更多
Elastomers play an irreplaceable role in our society due to their unique properties.Natural rubber is directly obtained from plants and is widely used in tires,shoes,etc.Recently,modified natural rubbers are proposed ...Elastomers play an irreplaceable role in our society due to their unique properties.Natural rubber is directly obtained from plants and is widely used in tires,shoes,etc.Recently,modified natural rubbers are proposed to expand the application of natural rubber.However,these natural rubbers have a limited variety of molecular structures and may not be able to meet ever-demanding applications.Traditional synthetic elastomers have a variety of molecular structures and their properties are used in various fields,but mainly originate from fossil resources.This review deals with bio-based elastomers,and more specifically natural rubber and bio-based synthetic elastomers.Based on reprocessability,bio-based elastomers can also be divided into bio-based chemically cross-linked ones and thermoplastic ones.Compared to traditional fossil-based elastomers,bio-based ones may alleviate environmental pollution and promote the sustainable development of the elastomer industry.展开更多
基金Supported by National Natural Science Foundation of China (No. 20876107)Open Project of State Key Laboratory of Chemical Engineering (No. SKL-ChE-08B06) Program of Introducing Talents of Discipline to Universities (No. B06006)
文摘Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.
文摘A swimming pool can be considered as a chemical reactor with specific hydraulic and macro-mixing characteristics. The nature of flow into the pool depends on various characteristics, such as water inlets and outlets (number and position), pool geometry, and flow rate. This study investigates how swimming pool design affects hydraulic behavior based on experimental and computational fluid dynamics studies (CFD). This paper does not describe the hydraulic behavior of all existing swimming pools, however the cases studied here are representative of pool designs widely used in Europe and the United States. The model developed, based on the principle of a stirred reactor, could be used as a first approach in describing the hydraulic behavior of regular pools. This model is suitable for the study of physical and chemical phenomena with long characteristic times. Other, more advanced, models were shown to be more suitable to the case of fast chemical processes.
文摘In South Saharan countries, 85% of the population uses biomass as a primary energy source. Cameroon presents one of the highest biomass energy and sawmills produce important sawdust resources which are not used and are burnt in piles leading to significant air toxic emissions. Therefore, we have to valorize industrially these available sawdusts. This study focuses on the physicochemical and thermochemical analysis of Ayous, Sapelli and Tali sawdust. The proximate and ultimate analysis, particle size, structural composition, as well as heavy metal content and calorific value were determined. In addition, the thermogravimetric mass losses were also estimated. The results showed that high water contents (24% - 41%) were recorded in the raw sawdust, and the thermal treatment reduced these contents from 78% to values in the range of 4% - 9%. The values for ash and volatile matter content were respectively between 0.25% - 0.74% and 68% - 76%. The LHV is higher in Ayous (17.5 MJ/kg) and Sapelli (16.8 MJ/kg) than that of Tali (15.7 MJ/kg). The concentration of heavy metals is very low in each species. Extractives are more present in Tali (16.06%) than in the other sawdusts. Pyrolysis of sawdust shows the typical decomposition of hemicellulose (270˚C - 325˚C), cellulose (325˚C - 400˚C) and lignin (200˚C - 550˚C) with a maximum loss of 75% at 370˚C and the melting point is 320˚C. The results of the sawdust parameters determined in the paper can be valorized to reduce pollutants emissions by developing the efficiency and effectiveness of biomass energy processes and promoting the use of biomass as a sustainable alternative to traditional fossil fuels.
文摘Smart Materials are along with Innovation attributes and Artificial Intelligence among the most used “buzz” words in all media. Central to their practical occurrence, many talents are to be gathered within new contextual data influxes. Has this, in the last 20 years, changed some of the essential fundamental dimensions and the required skills of the actors such as providers, users, insiders, etc.? This is a preliminary focus and prelude of this review. As an example, polysaccharide materials are the most abundant macromolecules present as an integral part of the natural system of our planet. They are renewable, biodegradable, carbon neutral with low environmental, health and safety risks and serve as structural materials in the cell walls of plants. Most of them are used, for many years, as engineering materials in many important industrial processes, such as pulp and papermaking and manufacture of synthetic textile fibres. They are also used in other domains such as conversion into biofuels and, more recently, in the design of processes using polysaccharide nanoparticles. The main properties of polysaccharides (e.g. low density, thermal stability, chemical resistance, high mechanical strength…), together with their biocompatibility, biodegradability, functionality, durability and uniformity, allow their use for manufacturing smart materials such as blends and composites, electroactive polymers and hydrogels which can be obtained 1) through direct utilization and/or 2) after chemical or physical modifications of the polysaccharides. This paper reviews recent works developed on polysaccharides, mainly on cellulose, hemicelluloses, chitin, chitosans, alginates, and their by-products (blends and composites), with the objectives of manufacturing smart materials. It is worth noting that, today, the fundamental understanding of the molecular level interactions that confer smartness to polysaccharides remains poor and one can predict that new experimental and theoretical tools will emerge to develop the necessary understanding of the structure-property-function relationships that will enable polysaccharide-smartness to be better understood and controlled, giving rise to the development of new and innovative applications such as nanotechnology, foods, cosmetics and medicine (e.g. controlled drug release and regenerative medicine) and so, opening up major commercial markets in the context of green chemistry.
基金Supported by the National Natural Science Foundation of China (21076139)the Opening Project of State Key Laboratory of Chemical Engineering (SKL-ChE-08B03)the Program of Introducing Talents of Discipline to Universities (B06006)
文摘The turbulence behavior of gas-liquid two-phase flow plays an important role in heat transfer and mass transfer in many chemical processes. In this work, a 2D particle image velocimetry (PIV) was used to investigate the turbulent characteristic of fluid induced by a chain of bubbles rising in Newtonian and non-Newtonian fluids. The instantaneous flow field, turbulent kinetic energy (TKE) and TKE dissipation rate were measured. The results demonstrated that the TKE profiles were almost symmetrical along the column center and showed higher values in the central region of the column. The TKE was enhanced with the increase of gas flow and decrease of liquid viscosity. The maximum TKE dissipation rate appeared on both sides of the bubble chain, and increased with the increase of gas flow rate or liquid viscosity. These results provide an understanding for gas-liquid mass transfer in non-Newtonian fluids.
文摘The design and preparation of hybrid mixed matrix membranes based on PVC （polyvinylchloride） were studied for the separation of toluene--n-heptane mixtures by pervaporation. PVC was chosen as the starting organic matrix because it is an inexpensive polymer, possessing a very high selectivity for aromatics. This property is due to the polar macromolecular structure that can induce a specific transfer of aromatic species compared with aliphatic species. To improve the performance of the PVC glassy structure, lhe incorporation of several inorganic micro- and nanopartieles in the polymer matrix was performed to prepare mixed matrix membranes. The results reported were obtained using several types of clay, i.e., Maghnite, Wyoming, Kaolin and Nanocor, with the goal of improving membrane permeability due to the hybrid network. Our results show that the transport properties of the modified PVC network can be drastically modified by the type and amount of particles used,
基金supported by the National Natural Science Foundation of China(22268009)the Guangxi Natural Science Foundation Program(GUIKEAB25069342 and 2025GXNSFFA069012)the Guangxi Science and Technology Major Program(AA24206037 and AA2420029)。
文摘Flexible photonic crystal(PC)materials possess exceptional optical properties.However,their structures often deteriorate under repeated mechanical responses,which may lead to structural impairments within the photonic band gap.This poses a challenge to their sustainability.Herein,by introducing a self-healing thermoplastic polyurethane(STPU)material with inverse-opal PC structure,a self-healing discoloration skin with stress response is prepared,inspired by the structural coloration and self-healing mechanisms of natural organisms.Given the synergistic effects of dynamic covalent bonds(S-S bonds)and hydrogen bonds(H-bonds),STPU can be reversibly adjusted upon mechanical deformation,enabling it to coordinate with environmental changes and showing excellent mechanical strength(26.76 MPa)and elongation at break(2000%).At the same time,the inverse opal structure inside STPU gives composite reversible color transitions with sensitive optical responses to solvents(e.g.,water and ethanol)and mechanical stress(0%–70%strain)through the regulation of lattice spacing.Furthermore,the incorporation of an interpenetrating network composed of polyacrylamide hydrogel and carbon nanotubes enhances its strain sensitivity and structural color stability.More importantly,given its excellent self-healing properties,it exhibits broad application potential in flexible sensors,adaptive optical devices,bioinspired robotic skins,and dynamic anticounterfeiting encryption,overcoming the limitations of traditional PCs(e.g.,high fragility and single functionality).The proposed strategy paves the way for the development of durable intelligent sensing materials with enhanced environmental adaptability and multifunctional integration.
基金National Natural Science Foundation of China,Basic Science Center Program,Grant/Award Number:51988102National Natural Science Foundation of China,Grant/Award Number:52073011Innovative Research Groups,Grant/Award Numbers:51221002,51521062。
文摘Elastomers play an irreplaceable role in our society due to their unique properties.Natural rubber is directly obtained from plants and is widely used in tires,shoes,etc.Recently,modified natural rubbers are proposed to expand the application of natural rubber.However,these natural rubbers have a limited variety of molecular structures and may not be able to meet ever-demanding applications.Traditional synthetic elastomers have a variety of molecular structures and their properties are used in various fields,but mainly originate from fossil resources.This review deals with bio-based elastomers,and more specifically natural rubber and bio-based synthetic elastomers.Based on reprocessability,bio-based elastomers can also be divided into bio-based chemically cross-linked ones and thermoplastic ones.Compared to traditional fossil-based elastomers,bio-based ones may alleviate environmental pollution and promote the sustainable development of the elastomer industry.
