Particle Deposition in Drying Porous Media

The drying of porous media is a ubiquitous phenomenon in soils and building materials. The fluid often contains suspended particles. Particle deposition may modify significantly the final material, as it could be pollutants or clogging the pores, decreasing the porosity, such as in salt, in which particles and drying kinetics are coupled. Here, we used SEM and X-ray microtomography to investigate the dried porous media initially saturated by nanoparticle suspensions. As the suspensions were dried, nanoparticles formed a solid deposit, which added to the initial solid matrix and decreased the porosity. We demonstrate that since the drying occurred through the top surface, the deposit is not uniform as a function of depth. Indeed, the particles were advected by the liquid flow toward the evaporative surface; the deposit was significant over a depth that depended on the initial volume fraction, but the pore size was affected over a very narrow length. These findings were interpreted in the frame of a physical model. This study may help to design better porous media and take into account particle influence in drying processes.

Essential Oil Composition From Cryptomeria japonica D.Don Grown in Azores: Biomass Valorization From Forest Management

Cryptomeria japonica biomass was obtained monthly from forest lumbering operations at São Miguel, Terceira and Pico (Azores), between May 2018 and June 2020. C japonica stands with different ages (2 to ±50 years), grown in different soil types (lithosol and andosol) and at different altitudes (200 to >800 m) were used. The chemical composition of 118 C japonica essential oil (EO) samples, plus 1 sample from an EO solid deposit, were analyzed by gas chromatography and gas chromatography–mass spectrometry. Chemical composition cluster analysis showed 2 clusters, cluster I and II, with no chemical correlation. Cluster I grouped all 117 EO samples that resulted from extraction of branches and foliage with, or without, strobili, from strobili, and from the solid deposit sample. Cluster II grouped the 2 samples of EO isolated from wood, with a markedly different composition. Cluster I showed 5 subclusters (Ia-Ie). The degree of chemical correlation between the samples in these subclusters varied between moderate (subclusters Id and Ie), high (subclusters Ib and Ic), and very high (subcluster Ia). Of the 119 samples, 94 (79% of the total) were included in subcluster Ia, with 66 samples from São Miguel, 2 from Terceira, and 26 from Pico, showing a yield range from 0.1% to 0.4% (v/w). All these samples, with a high chemical correlation, were obtained by steam distillation from branches and foliage with, or without, female or male strobili, or both. This subcluster did not show any grouping pattern regarding the collection month, the altitude (200 to >800 m), the soil type (lithosol, andosol, or its subtypes), or the wood age (±30 to ±50 years). Subcluster Ia was characterized by the dominance of α-pinene (13%-43%), sabinene (5%-25%), phyllocladene (2%-22%), limonene (2%-16%), kaurene (traces-13%), elemol (1%-11%), and terpinen-4-ol (1%-7%). The determination of the concentration limits of the EOs representative components confirmed the homogeneity of C japonica EO, obtained from plant material collected in the 3 Azores islands, despite the variability in the range of some diterpenes that deserves further study. This study allowed for the determination of the concentration limits of the EOs representative components, with the purpose of adding value to C japonica EO, obtained from forest lumbering.

Crack morphologies in drying suspension drops

Drops of aqueous suspensions of nanoparticles placed on a substrate form a solid deposit as they dry. The initial concentration of particles governs both the shape of the deposit and the complex crack morphology.

Evolution of mechanical properties of Ti6242S alloy after oxidation in air at 560°C: influence of solid salts deposits

Titanium alloys are widely used in aerospace applications due to their good ratio of weight versus mechanical properties. When exposed to air at 560°C, Ti6242S titanium alloy presents very good oxidation resistance: a very thin oxide layer forms at its surface and oxygen dissolution inside the metallic material is rather limited. However, in real functioning conditions of the plane, near seas or oceans, the atmosphere contains NaCl, that can crystallise at the surface of hot parts. An active corrosion mechanism is established in these conditions, with catastrophic effect on the material behaviour at high temperature: very thick and brittle oxide scales and very important damaging of the metal outer part. Another issue is the formation of Na2SO4 specie by reaction of NaCl with kerosene combustion gases (SO2/SO3), leading to mixed NaCl/Na2SO4 deposits. The effect of exposure conditions on the mechanical properties of titanium alloy Ti6242S was evaluated through tensile tests performed on the raw alloy and after oxidation in air at 560°C of the specimens: without any deposit, with NaCl solid deposit, with NaCl/Na2SO4 solid deposit. The evolution of mechanical properties was interpreted in connexion with the microstructural modifications that occur during the high temperature ageing.

A Study on Urea-Water Solution Spray-Wall Impingement Process and Solid Deposit Formation in Urea-SCR de-NOx System

Selective catalytic reduction (SCR) has been exhibited as a promising method of NOx abatement from diesel engine emissions. Long-term durability is one of the key requirements for the automotive SCR system. A high NOx conversion, droplet distribution and mixing, and fluid film and solid deposit formation are the major challenges to the successful implementation of the SCR system. The current study is therefore three-fold. Firstly, high-speed images disclose detailed information of the spray impingement on the heated impingement surface. The spray impingement investigation took place in a specially-designed optically-accessible visualization chamber where the Z-type shadowgraph technique was used to capture the high-speed images. Wall temperature has a great influence on the film formation and wall wetting. A higher wall temperature can significantly increase the droplet evaporation, and consequently, wall wetting decreases. The numerical analysis was performed based on the Eulerian-Lagrangian approach using STAR CCM+ CFD code. Secondly, the resultant phenomena due to spray-wall impingement such as fluid film generation and transport, solid deposit formation, and thermal decomposition were recorded using a high-speed camera operating at a low frame rate. Infrared thermal imaging was used to observe the spray cooling effect after impingement. Spray impingement caused local cooling, which led to wall film formation, which introduced urea crystallization. Finally, solid deposits were analyzed and characterized using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). FTIR analysis revealed that urea decomposition products vary based on the temperature, and undecomposed urea, biuret, cyanuric acid, ammeline, and melamine can be formed at different temperatures. TGA analysis showed that accumulated deposits were hard to remove. Moreover, complete thermal decomposition of deposits is not possible at the regular exhaust temperature, as it requires a comparatively long time span.

Modelling of hydrochemical and hydromechanical parameters’ synergism in the process of solid deposit creation in geothermal and other hard waters

This paper presents the experimental research results, regarding the effect of hydromechanical parameters and based on the relative reduction of the starting hardness of geothermal water of Sijarinska Banja and Niska Banja as well as the water from the Medijana spring in Nis. The measurements were conducted on a laboratory pilot plant/ facility with glass pipes of diameter 2, 4, 6, 8 and 10 mm and with water flow controlled by a digital peristaltic pump with a flow interval from 2 to 5000 ml min-1. The effect of the hydrodynamic parameters on the change of input hardness of geothermal and other hard waters and the process of solid deposit creation were modelled by an empirical model based on simple linear regression analysis, multiple linear regression model and the neural network. The high accuracy of all applied models unequivocally proves that a synergism of hydrochemical and hydrodynamic parameters exists in the process of creation of solid deposit ? limescale, thanks to which the starting hypothesis is confirmed.