Study on Spinnability of Arabinoxylan Extracted From Barley Husks

Valorisation of bio-based materials derived from agricultural and industrial side-streams or waste-streams is a basis of circular economy. However, the success of it depends on the full understanding of materials and finding their optimal way of processing. Barley husk is a side-stream waste material derived from the starch and ethanol production. This study is focused on the processability of the arabinoxylan extracted from barley husk using the electrospinning technique to produce thin xylan-poly(vinyl alcohol) fibers. As a comparison, lignin-free xylan of beech wood was used. The properties of spinning solutions and resulting nanofibrous mats were assessed by using rheological measurements, FTIR spectroscopy, scanning electron microscopy and contact angle measurements. It was found that solubility plays a crucial role in the spinnability of xylan extracts. Decrease in viscosity of arabinoxylan achieved by decreasing its concentration was found to improve the jet stability but at the same time, to reduce the diameter of spun fibre. Hydrophilicity of nanofibrous mats were strongly affected by the type of xylan and solvent used.

Zn22Al4Ag ALLOY MICROWIRES CASTING TO RAPID SOLIDIFICATION PROCESS BY ROTATING DRUM

In this work, the Zn22Al4Ag alloy was synthesized by melting in a muffle furnace.The alloy obtained was characterized by Scanning Electron Microscopy Energy Dispersive Spectroscopy and was analyzed by the X-Ray Diffraction technique, where the crystallinity of the material was verified before and after being processed. Likewise, the Differential Scanning Calorimetry technique was used to obtain the temperatures where phase transformations occurin the alloy. These results were fed to the Termocalc®, software to numerically obtain the phase diagram of the alloy. Subsequently, a section of the ingot was taken to the rapid solidification process by rotating drum. The process variables were manipulated: jet stability, nozzle diameter, distance from the nozzle surface to the cooling medium, the delay time of the molten material in the crucible, speed of the rotating drum and jet angle, until obtaining a microwire with a diameter of ~ 160µm. Finally, it was determined that inadequate control of these parameters can result in powders, flakes or blockage of the crucible outlet. Potentially uses within the micro and nanoworld as an analogy to structural elements and electrical conductors, in addition to its current use as a coating anti-corrosive. Key Words: ZnAlAg alloy, Melt spinning process, Microwire, DSC analysis, Thermodynamic simulation

Stability of a Viscous Liquid Jet in a Coaxial Twisting Compressible Airflow

Based on the linear stability analysis, a mathematical model for the stability of a viscous liquid jet in a coaxial twisting compressible airflow has been developed. It takes into account the twist and compressibility of the surrounding airflow, the viscosity of the liquid jet, and the cavitation bubbles within the liquid jet. Then, the effects of aerodynamics caused by the gas–liquid velocity difference on the jet stability are analyzed. The results show that under the airflow ejecting effect, the jet instability decreases first and then increases with the increase of the airflow axial velocity. When the gas–liquid velocity ratio A = 1, the jet is the most stable. When the gas–liquid velocity ratio A > 2, this is meaningful for the jet breakup compared with A = 0 (no air axial velocity). When the surrounding airflow swirls, the airflow rotation strength E will change the jet dominant mode. E has a stabilizing effect on the liquid jet under the axisymmetric mode, while E is conducive to jet instability under the asymmetry mode. The maximum disturbance growth rate of the liquid jet also decreases first and then increases with the increase of E. The liquid jet is the most stable when E = 0.65, and the jet starts to become more easier to breakup when E = 0.8425 compared with E = 0 (no swirling air). When the surrounding airflow twists (air moves in both axial and circumferential directions), given the axial velocity to change the circumferential velocity of the surrounding airflow, it is not conducive to the jet breakup, regardless of the axisymmetric disturbance or asymmetry disturbance.

On the thermal instability of supercavitating liquid jet surrounded by coaxial rotary gas

Based on the jet stability theory, under the conditions of gas rotation, fluid compressibility and supercavitation, this paper gives the mathematical model describing the thermal instability of supercavitating liquid jet surrounded by a coaxial rotary gas, and the corresponding numerical method for solving the mathematical model is proposed and verified by the data in reference. Then, this paper analyzes the effects of gas–liquid temperature differences and temperature gradients on jet instability, and studies the thermal stability of supercavitating jet. The results show that the maximum disturbance growth rate, the dominant frequency and the maximum disturbance wave numbers increase linearly with the increase of gas–liquid temperature differences. The existence of temperature gradient inside the jet makes the effects of temperature differences on jet instability more obvious. The temperature gradient will inhibit the effect of supercavitation on jet instability, while gas–liquid temperature difference will promote the effect of supercavitation on jet instability.

Turbulent jet stability increased by ribs inside the nozzle – Stereo PIV measurement one diameter past the nozzle

We observe that decreasing the inner nozzle surface by adding longitudinal ribs increases the jet stability in terms of the amount of turbulent kinetic energy in the near shear layer. We try to explain our observation as a stabilization effect of secondary flow vortices emerging in the corners of the ribs. These stream-wise vortices damage the development of larger-scale structures in the near shear layer. This explanation is supported by autocorrelation function of the stream-wise velocity component, which displays slightly smaller integral length-scale in the case with ribs than in the case of smooth nozzle. The experiment is performed at Reynolds number 2.2 × 105 (based on the nozzle diameter 50 mm); the Stereo-PIV (Particle Image Velocimetry) measurement takes place at the plane perpendicular to the jet axis one diameter past the nozzle exit. Optical 3D scanner controls the real nozzle geometry. This article presents preliminary measurement at single position and single velocity only; further exploration of this problem is needed.

Dope-Dyeing of Polyvinyl Alcohol (PVA) Nanofibres with Remazol Yellow FG

The lack of aesthetic properties of electrospun nanofibres in terms of colour appearance is the drive in this preliminary study. This research is conducted to study the dyeing behaviour and colorimetric properties of electrospun nanofibres blended with Remazol Yellow FG reactive dye using dope-dyeing method via electrospinning process. This paper reports the colorimetric properties of dyed poly vinyl alcohol (PVA) nanofibres within the range of 2.5 wt.% to 12.5 wt.% dye content. The electrospinning parameters were fixed at the electrospinning distance of 10 cm, constant feed rate of 0.5 mL/h and applied voltage of 15 kV. The resulting impregnated dye of 10 wt.% exhibits acceptable colour difference of dyed PVA nanofibres, with a mean fibre diameter of 177.1 ± 11.5 nm. The SEM micrographs show the effect of dye content on morphology and fibre diameter upon the increment of dye used. Further increase of dye content adversely affects the jet stability during the electrospinning, resulting in macroscopic dropping phenomenon. The presence of all prominent peaks of Remazol dye in the PVA nanofibers was supported with FTIR analysis. The addition of dye into the nanofibres has resulted in the enhancement of thermal stability of the PVA as demonstrated by TGA analysis.

Brane-jet stability of non-supersymmetric AdS vacua

We classify the non-supersymmetric, and perturbatively stable within D = 4, AdS vacua of maximal D = 4 supergravity with a dyonic ISO(7) gauging in a large sector of the supergravity. Seven such vacua are established within this sector, all of them giving rise to non-supersymmetric AdS4× S6 type IIA backgrounds with and without non-trivial warpings and with internal fluxes. Then, we analyse the dynamics of various probe Dp- branes in these backgrounds searching for potential brane-jet instabilities. In all these cases, such instabilities are absent. Finally, an alternative decay channel through tunnelling is investigated, focusing on one of the seven backgrounds. We do not find instabilities either, but the analysis remains inconclusive.