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Abstract: The results of an experimental study of micro-jets produced with a gas dynamic virtual nozzle (GDVN) under the influence of an electric field are provided and discussed for the first time. The experimental study is performed with a 50% volume mixture of water and ethanol, and nitrogen focusing gas. The liquid sample and gas Reynolds numbers range from 0.09–5.4 and 0–190, respectively. The external electrode was positioned 400–500 μm downstream of the nozzle tip and an effect of electric potential between the electrode and the sample liquid from 0–7 kV was investigated. The jetting parametric space is examined as a function of operating gas and liquid flow rates, outlet chamber pressure, and an external electric field. The experimentally observed jet diameter, length and velocity ranged from 1–25 μm, 50–500 μm and 0.5–10 m/s, respectively. The jetting shape snapshots were processed automatically using purposely developed computer vision software. The velocity of the jet was calculated from the measured jet diameter and the sample flow rate. It is found that micro-jets accelerate in the direction of the applied electric field in the downstream direction at a constant acceleration as opposed to the standard GDVNs. New jetting modes were observed, where either the focusing gas or the electric forces dominate, encouraging further theoretical and numerical studies towards optimized system design. The study shows the potential to unlock a new generation of low background sample delivery for serial diffraction measurements of weakly scattering objects.
Keywords: micro jet, electric field, experimental study, flow focusing, Taylor cone, gas dynamic virtual nozzles
Published in DiRROS: 07.02.2024; Views: 185; Downloads: 81
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Abstract: Alkali activated foams have been extensively studied in recent years, due to their high performance and low environmental footprint compared to foams produced via other methods. Three types of fly ash differing in chemical and mineralogical composition and specific surface were used to synthesize alkali activated foams. Sodium perborate monohydrate was added as a foaming agent and sodium dodecyl sulphate as a stabilizing agent. Foams were characterized at room temperature and after exposure to an elevated temperature (1,000 °C). Densities from 1.2 down to 0.3 g/cm 3 were obtained, depending on the type of fly ash and quantity of foaming agent added. Correspondingly, compressive strength ranged from 1 to 6 MPa. Comparing all three fly ashes the most favorable results, in terms of density and corresponding compressive strength, were achieved from the fly ash with the highest amounts of SiO 2 and Al2 O 3 , as well as the highest amorphous phase content i.e., RI fly ash. Furthermore, after firing to 1,000 °C, the density of samples prepared using fly ash RI remained approximately the same, while the compressive strength increased on average by 50%. In the other two types of fly ash the density increased slightly after firing, due to significant shrinkage, and compressive strength increased by as much as 800%. X-ray powder diffraction analysis confirmed the occurrence of a crystallization process after firing to 1,000 ° C, which resulted in newly formed crystal phases, including nepheline, sodalite, tridymite, and gehlenite.
Keywords: foamed alkali activated materials, geopolymers, properties, micro-CT
Published in DiRROS: 22.08.2023; Views: 253; Downloads: 164
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Keywords: CO2 reduction to methanol, multisite micro-kinetic model, structure-activity relationship, copper-zinc-alumina, heterogeneous catalysis materials
Published in DiRROS: 21.05.2021; Views: 1071; Downloads: 991
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