Search Results (12)

The viscoelasticity of fluids have a significant impact on the process of heat and mass transfer, which directly affects the efficiency and quality, especially for highly viscous functional polymer materials. In this work, the effect of elasticity on hydrodynamic behavior of pipe flow for highly viscous non-Newtonian fluids was studied using viscoelastic polyolefin elastomer (POE). Two constitutive rheological equations, the Cross model and Wagner model, were applied to describe the rheological behavior of typical POE melts, which have been embedded with computational fluid dynamics (CFD) simulation of the laminar pipe flow through the user-defined function (UDF) method. The influence of both viscosity and elasticity of a polymer melt on the flow mixing and heat transfer behavior has been systematically studied. The results show that the elastic effect makes a relative larger velocity gradient in the radial direction and the thicker boundary layer near pipe wall under the same feed flow rate. That leads to the higher pressure drop and more complex residence time distribution with the longer residence time near the wall but shorter residence time in the center. Under the same conditionals, the pipeline pressure drop of the viscoelastic fluid is several times or even tens of times greater than that of the viscous fluid. When the inlet velocity increases from 0.0001 m/s to 0.01 m/s, the difference in boundary layer thickness between the viscoelastic fluid and viscous fluid increases from 3% to 12%. Similarly, the radial temperature gradient of viscoelastic fluids is also relatively high. When the inlet velocity is 0.0001 m/s, the radial temperature difference of the viscoelastic fluid is about 40% higher than that of viscous fluid. Besides that, the influence of elasticity deteriorates the mixing effect of the SK type static mixer on the laminar pipe flow of highly viscous non-Newtonian fluids. Correspondingly, the accuracy of the simulation results was verified by comparing the pressure drop data from pipeline hydrodynamic experiments. Full article

Resonance Acoustic Mixing (RAM) is an efficient mixing technique and holds significant application value in many fields, especially in the mixing of high-viscosity materials. Due to the one-time loading feature, different material structures formed during the feeding process may cause undesired irregularities in the mixing process, which is not conducive to maintaining the mixing consistency between different batches. However, in the analysis of multi-component mixtures, previous studies have often overlooked the impact of the initial material structure. This study delved into the mixing mechanism of RAM in viscous solid–liquid mixtures. By constructing a numerical model based on the Mixture model, simulations of gas–solid–liquid multiphase flows under different initial structures were conducted, and the reliability of the model was verified through experiments. The research results indicate that the mixing processes with different initial structures share similar temporal characteristics of being intense at first and then moderating, but their development trends vary. The mixing time of the structure with the solid on the upper part is shortened by about 10% compared with that of the structure with the solid on the lower part. The double-interface structure exhibits a significantly higher mixing efficiency than the single-interface structure, with the mixing time reduced by up to 41%. This study offers a theoretical basis for optimizing the parameters of resonant acoustic mixing and holds significant reference value for the refined operation of resonant acoustic mixing in the future. Full article

Ramie is a valuable natural fiber resource. The fabric made of ramie fiber has distinctive natural characteristics, and its products are widely favored in the international market. Because the cellulose fiber in ramie is closely adhered by a viscous material composed of pectin, hemicellulose, and lignin, mechanical stripping and processing is needed to obtain primary ramie fiber for downstream use. To address the production challenges posed by high labor intensity and the scarcity of small, direct-feeding ramie decorticators in hilly and mountainous regions, this study designed and optimized a spiral ramie decortication component that integrated functions of ramie stalk crushing, xylem removal, outer shell scraping, and phloem separating and throwing. The three-dimensional model of the ramie stripping component was crafted with SolidWorks software, and subsequent modal analysis and dynamic simulation studies were conducted using Abaqus software. The Box–Behnken experimental design method was used to construct a mathematical model describing the effects of the decorticating drum rotation speed and the decorticating gap on the fiber percentage of fresh stalk, and the optimal operating parameters were determined accordingly. The research findings indicated that the component’s initial ten natural frequencies span from 234.41 to 431.70 Hz, which do not overlap with the external excitation frequencies, thus ensuring that no resonance phenomenon occurs during the operation process, meeting the design requirements for the ramie decortication operation. Under dynamic load conditions, the ramie decorticator can efficiently perform the task of ramie fiber decortication, and the stress and strain experienced by the device meet the established design specifications; by optimizing operating parameters, the optimal operating conditions were determined to be the speed of feeding and crushing parts (SFCP) of 100 r/min, the speed of separating and throwing parts (SSTP) of 400 r/min, the gap of feeding and crushing parts (GFCP) of 8 mm, and the gap of separating and throwing parts (GSTP) of 0 mm. Experimental results indicated that under this optimal parameter combination, the fiber percentage of fresh stalk of the spiral ramie decorticator can reach 5.03%, with a relative error of less than 3% compared to the theoretical model prediction value, thus confirming the accuracy of the model prediction. This study establishes a robust technical basis for the development of a convenient decortication technology for ramie fibers. However, this technique is more suitable for small growers, especially in hilly areas, to achieve large-scale applications, schemes must be reevaluated based on production efficiency. Full article

Friction is the dominant factor restricting tracking accuracy and machining surface quality in mechanical systems such as machine tool feed-drive. Hence, friction modeling and compensation is an important method in accurate tracking control of CNC machine tools used for welding, 3D printing, and milling, etc. Many static and dynamic friction models have been proposed to compensate for frictional effects to reduce the tracking error in the desired trajectory and to improve the surface quality. However, most of them focus on the friction characteristics of the pre-sliding zone and low-speed sliding regions. These models do not fully describe friction in the case of insufficient lubrication or high acceleration and deceleration in machine tool systems. This paper presents a new nonlinear friction model that includes the typical Coulomb-Viscous friction, a nonlinear periodic harmonic friction term for describing the lead screw property in insufficient lubrication, and a functional component of acceleration for describing the friction lag caused by the acceleration and deceleration of the system. Experiments were conducted to compare the friction compensation performance between the proposed and the conventional friction models. Experimental results indicate that the root mean square and maximum absolute tracking error can be significantly reduced after applying the proposed friction model. Full article

Fast pyrolysis of biomass is a well-known opportunity for sustainable alternative fuel production for transport and energy. However, bio-oils from biomass pyrolysis are viscous, acidic bio-crudes that need further steps of upgrading before being used either as fuels or chemicals. A process that is complementary to bio-oil hydrotreatment or co-processing consists of optimizing and tuning the upstream condensation steps of fast pyrolysis to separate and concentrate selected classes of compounds. This can be implemented by varying the condensation temperatures in a multi-step condensation unit. In this study, fractional condensation of fast pyrolysis vapors from pinewood has been applied to a bubbling fluidized bed reactor of 1 kg h⁻¹ feed. The reactor was operated at 500 °C and connected to a downstream interchangeable condensation unit. Tests were performed using two different condensing layouts: (1) a series of two spray condensers and a tube-in-tube water-jacketed condenser, referred to as an intensive cooler; (2) an electrostatic precipitator and the intensive cooler. Using the first configuration, which is the focus of this study, high boiling point compounds—such as sugars and lignin-derived oligomers—were condensed at higher temperatures in the first stage (100–170 °C), while water-soluble lighter compounds and most of the water was condensed at lower temperatures and thus largely removed from the bio-oil. In the first two condensing stages, the bio-oil water content remained below 7% in mass (and therefore, the oil’s high calorific content reached 22 MJ kg⁻¹) while achieving about 43% liquid yield, compared to 55% from the single-step condensation runs. Results were finally elaborated to perform a preliminary energy assessment of the whole system toward the potential upscaling of this fractional condensation approach. The proposed layout showed a significant potential for the upstream condensation step, simplifying the downstream upgrading stages for alternative fuel production from fast pyrolysis bio-oil. Full article

Obesity is rapidly becoming an emerging disease in developing countries due to the Westernization of societies and lifestyle changes. This study evaluated the ameliorative effect of acidic heteropolysaccharides derived from Tremella fuciformis (TFPS) on high-fat diet (HFD; 34.9% fat)-induced obesity in mice. The TFPS exhibited high uronic acid content and high viscosity in water. The structural characteristics of TFPS showed that average molecular weight was 679 kDa, and the monosaccharide composition was galactose, glucose, fructose, xylose, fucose, and mannose at a ratio of 1.0:6.5:10.0:18.5:30.5:67.5. In an in vivo study, HFD-induced obese C57BL/6 mice were orally given a TFPS treatment at 1 and 2 g/kg of body weight for 8 weeks. The TFPS treatment significantly reduced features of obesity in the mice, namely weight gain, feed efficiency, body fat percentage, and serum cholesterol level and increased fecal lipid content, compared with mice fed an HFD with water. In addition, TFPS exhibited the inhibition of cholesterol micelles in vitro in a concentration-dependent manner. In conclusion, the TFPS treatment ameliorated the diet-induced obesity in the mice, presumably reducing fat absorption in the intestine by interfering with viscous TFPS. Full article

The bran accounts for approximately 25% of the wheat kernel but is currently only a by-product, used as animal feed. However, due to its high arabinoxylan content it could be a valuable raw material for food production. Arabinoxylans cannot be digested in the human intestine but are intensely studied for their health-beneficial properties. These include glycemic control by formation of a highly viscous gel in the intestine, and hence delaying starch digestion, alongside an increase in short chain fatty acids. To apply sufficient amounts of arabinoxylan for health-beneficial effects, extraction and concentration is required. Alkaline/oxidative conditions are commonly used, but for potential food applications more cost-efficient methods, without hazardous chemicals, are required. Therefore, this study aimed to optimize the conditions for hydrothermal extraction (extraction time and temperature) at laboratory-scale and to compare the results to an established alkaline/oxidative method. The resulting extracts were characterized for yield, purity, arabinoxylan molecular mass, arabinose/xylose ratio, and viscosity to evaluate the quality of the method. For the hydrothermal extraction, an extraction time of 1 h at 160 °C and 6.5 bar gave the best results. However, even these optimized conditions resulted in lower extract purity and severely degraded arabinoxylans. Although further optimization of the hydrothermal process is required, the present work builds an important foundation for the development of an industrial hydrothermal extraction method. Full article

Bio-oil is a promising fuel as one of the main products from biomass fast pyrolysis for improving energy density and reducing transportation cost, but high acidity and low calorific value limit its direct application. It can be used to prepare coal bio-oil slurry as partial green fuels for potential feeds for synthesis gas production via gasification with the advantages over traditional coal-water slurries of calorific values and being additives-free. In the present work, three bio-oils were blended with lignite to prepare slurry fuels for the investigation of the effect of bio-oil species on rheological behaviors and gasification characteristics of coal bio-oil slurry fuels. Results show that slurry prepared with bio-oil from fruit tree pyrolysis is highly viscous and has higher activation energy in gasification. Slurries prepared with bio-oils from straw pyrolysis and pyroligneous acid from wood pyrolysis exhibited an acceptably lower viscosity, and the gasification temperatures were lower than for coal. The activation energy decreased by 15.98 KJ/mol and 2.77 KJ/mol, respectively, which indicates these bio-oils are more suitable with lignite for slurries preparation. Full article

The selective agglomeration of a fine coal tailings stream using a high internal phase emulsion binder was investigated using a continuous steady-state plug flow through a high shear constriction. The emulsion binder effectively switches off the viscous resistance to particle–binder collision and adhesion, revealing the remarkable underlying speed of hydrophobic interactions. The emulsion binder is permeable, meaning the lubrication force between the particle and binder vanishes. The binder comprised a 95% aqueous solution dispersed within a 5% organic liquid (including the emulsifier). The agglomeration occurred within a high shear zone formed using a flow constriction within a 25 mm diameter pipe. The performance of the process was investigated at different flowrates in the range of 20–128 L/min, equating to extraordinarily high superficial flow velocities of up to 4.2 m/s and pressure drops in the range of 20–220 kPa. This rate greatly exceeds the nominal superficial feed velocity in flotation of order 0.01 m/s. Provided there was sufficient shear within the flow constriction, it was possible to process fine coal tailings with a feed ash of 50.1%, and generate a product ash of 8% at a combustible recovery of ~78%. Full article

Air-core–liquid-ring (ACLR) atomization presents a specific type of internal mixing pneumatic atomization. It can be used for disintegration of high viscous feed liquids into small droplets at relatively low gas consumptions. However, the specific principle of ACLR atomization is still under research and no guidelines for process and atomizer design are available. Regarding literature on pre-filming atomizers, it can be hypothesized for ACLR atomization that the liquid film thickness inside the exit orifice of the atomizer, as well as the resulting spray droplet sizes decrease with increasing air-to-liquid ratio (ALR) and decreasing feed viscosity. In this study, the time dependent liquid film thickness inside the exit orifice of the atomizer was predicted by means of computational fluid dynamics (CFD) analysis. Results were compared to high speed video images and correlated to measured spray droplet sizes. In conclusion, the hypothesis could be validated by simulation and experimental data, however, at high viscosity and low ALR, periodic gas core breakups were detected in optical measurements. These breakups could not be predicted in CFD simulations, as the simplification of an incompressible gas phase was applied in order to reduce computational costs and time. Nevertheless, the presented methods show good potential for improvement of atomizer geometry and process design as well as for further investigation of the ACLR atomization principle. Full article

Air-core-liquid-ring (ACLR) atomizers present a specific type of internal mixing pneumatic atomizers, which can be used for efficient atomization of high viscous liquids. Generally, atomization efficiency is considered as a correlation between energy input and resulting droplet size. In pneumatic atomization, air-to-liquid ratio by mass (ALR) is commonly used as reference parameter of energy input. However, the pressure energy of the atomization gas is not considered in the calculation of ALR. In internal mixing ACLR atomizers, it can be assumed that this energy contributes to liquid disintegration by expansion of the gas core after exiting the atomizer. This leads to the hypothesis that droplet sizes decrease with increasing gas pressure at constant ALR. Therefore, the use of volumetric energy density (E_V) as a reference parameter of energy input was investigated at different gas pressures between 0.4 and 0.8 MPa. Furthermore, scale up-related influences on the atomization efficiency of ACLR atomization were investigated by use of an atomizer with enlarged exit orifice diameter. We can conclude that E_V can be applied as a reference parameter of ACLR atomization processes with different gas pressures. However, within the range investigated no clear influence of gas pressure on atomization efficiency was found. Up-scaling of ACLR atomizers allows production of similar droplet sizes, but atomization efficiency decreases with increasing exit orifice diameter. Full article

Purpose: to design, assemble and test a prototype of a novel production plant, suitable for producing microparticles (MPs) by processing highly viscous feed solutions (FSs). Methods: the prototype has been built using a commercial air compressor, a piston pump, an airless spray-gun, a customized air-treatment section, a timer, a rotating base, and a filtration section. Preliminary prototype parameter setting was carried out to individuate the best performing nozzle’s dimension, the nebulization timing, and the CaCl₂ concentration in the gelation fluid. In addition, prototype throughput (1 L to 5 L) and the range of practicable feed solution (FS) viscosities were assayed. A set of four batches was prepared in order to characterize the MPs, in terms of mean particle size and distribution, flow properties, swelling, encapsulation efficiency and release. Results: according to a qualitative scoring, the large nozzle was suitable to nebulize FSs at a higher alginate concentration. Conversely, the small nozzle performed better in the processing of FSs with an alginate concentration up to 2% w/v. Only at the highest degree of viscosity, corresponding to 5% w/v of alginate, the FS processing was not technically possible. Among the CaCl₂ concentrations considered, 15% w/v was recognized as the most versatile. The prototype appears to be convenient and suitable to grant a high yield starting from 2 L of FS. The flow behavior of the FSs assayed can be satisfactorily described with the Carreau-Yasuda equation and the throughput begins to slightly decrease for FSs at alginate concentrations exceeding 3% w/v. MP morphology was irregular with crumpled shape. The angle of repose indicates a good flowability and the release studies showed gastro-resistance and potential prolonged release applications. Conclusions: the novel prototype of production plant is suitable to process large amounts (2 L or more) of FSs, characterized by a high viscosity, to produce MPs suitable for bioactive principle delivery. Full article