Numerical Simulation of Airborne Salt Particle Behavior in Dry Gauze Method Using Porous Media Model

Airborne salt accelerates the corrosion of steel materials and, thus, must be quantitatively evaluated for the management of steel structures. In Japan, the dry gauze method, which uses a gauze embedded in a wooden frame, is often used to evaluate the amount of airborne salt. However, its collection efficiency for salt particles has not been verified owing to the complex airflows around the device. Therefore, as a first step to clarify the collection efficiency, the authors simulated the flow field around the collection device using computational fluid dynamics. In this study, the gauze was modeled as a porous medium to reduce the computational costs. Wind tunnel tests were performed to obtain the pressure loss coefficients of the gauze, which is necessary for the porous media method. Subsequently, particle tracking was performed in the calculated flow field, and the collection efficiency was evaluated under the condition of a filtration efficiency of 100%. The flow fields around the device were accurately reproduced using the porous media model, which considered both the tangential and normal resistances of the gauze. This result suggests that the tangential resistance must be considered in the porous media model when the porosity of an object is small, even if the thickness is small. The dependence of collection efficiency on wind speed and direction was quantitatively evaluated. The results showed that the collection efficiency was greatly affected by the complicated flow field around the device due to the combination of the gauze and wooden frame.

Optical and magnetic properties of particles containing guanine in strong basic solution

Guanine based particle is one of very efficient material to control light especially near the surface of animal body. Past studies reported that platelets of anhydrous guanin crystal are utilized by living creatures, and they can change their colour and light reflection intensity when the arrangement of platelets. Guanine has relatively high reflective index and its particle can exhibit a unique optical property. Under higher pH which can be provided by a high concentration of NaOH aqueous solution, guanine molecules formed a sodium salt particle which contain guanine. Here this work presents that particles containing guanine in basic aqueous solution with NaOH exhibited very strong shining and light reflection switching by magnetic fields. In addition, adding an extracted solution of a fish iridophore enhanced the formation of intensively light reflecting guanine particles floating in a strong basic solution.

Analysis and Comparison of Different Dewatering Methods On Salt Quality

The salt quality was studied by dewatering methods such as centrifugal hydro extraction, fixed bed dryer, and rotary drum dryer. The effect of different salt particle sizes was also analyzed. The centrifugal hydro extractor is found to be effective when reducing the high-water content of salt and suitable for reducing water content after the salt wash stage. Fixed bed dryers produce lower water content than rotary drum dryers. A water content lower than 1% can be achieved using fixed bed dryers. Finally, all dewatering methods such as centrifugal hydro extractors, fixed bed dryers, and rotary bed dryers are suitable for salt production methods. Reduced salt particle size from 30 to 60 mesh also improved the drying performance.

The Effects of Dry and Wet Grinding Processes on The Salt Quality

Studies were conducted on the salt quality, such as NaCl percent and whiteness achieved by dry and wet grinding methods. Crude solar salt is carefully collected from traditional solar salt ponds to ensure the uniformity of the sample. Several salt processing methods were applied in this research, such as washing, grinding, and dewatering by centrifuge hydro extractor and drying. The effect of reducing salt particle size to 0.6 and 0.25 mm was also studied. The dry grinding method is conducted before the washing stage, while the wet grinding method is applied after the washing stage. Both dry and wet grinding methods provide high-quality salt products, indicating high NaCl percent and whiteness. The dry grinding method produces higher NaCl percent and whiteness than the wet grinding method. However, the wet grinding method was better in water management and equipment durability with loss of salt losses during the washing stage. Finally, both grinding methods have advantages and disadvantages, so for developing the salt processing industry, both methods should be correctly chosen and match product output requirements.

Under-oil superhydrophilic salt particle filter for the efficient separation of water-in-oil emulsions

In this study, a surfactant stabilized water-in-oil emulsion has been successfully separated by using only NaCl particles as a filter.

CFD Study for the Particle Transport and Deposition in Secondary Air Systems

The recent expansion of civil aviation industry into the new market demands modern aero-engines to operate in hot, harsh and polluted environments. Moreover there is a significant increase in the flight paths across the sea leading to large amount of micro salt particle ingestion into the engines. These contaminants can cause severe damage to the turbine parts through hot corrosion fatigue. The mechanism of the very small particle transport in the secondary air system and their deposition on turbine parts is less reported and not well understood. This study explores the physics of the particle transport (< 0.5–10 micron) and their deposition characteristics in the secondary air paths. Specifically, a three-dimensional computational fluid dynamics (CFD) model is developed for an engine representative turbine cavity with blade shank utilizing commercial finite volume-based software incorporating the SST k-ω turbulence model. The particle transport is captured using discrete random walk model and their wall interaction (bounce and stick) is simulated using the critical velocity model. A comprehensive parametric study is conducted using 2 and 6 micron CaSO4 particles covering a wide range of operating and design variables. From the parametric study it has been observed that rotor speed, swirl and the radial location of the feed holes strongly influence the flow structure in the shank cavity and particle deposition.

A thermodynamic description for the hygroscopic growth of atmospheric aerosol particles

The phase state of atmospheric particulate is important to atmospheric processes, and aerosol radiative forcing remains a large uncertainty in climate predictions. That said, precise atmospheric phase behavior is difficult to quantify and observations have shown that “precondensation” of water below predicted saturation values can occur. We propose a revised approach to understanding the transition from solid soluble particles to liquid droplets, typically described as cloud condensation nucleation – a process that is traditionally captured by Köhler theory, which describes a modified equilibrium saturation vapor pressure due to (i) mixing entropy (Raoult's law) and (ii) droplet geometry (Kelvin effect). Given that observations of precondensation are not predicted by Köhler theory, we devise a more complete model that includes interfacial forces giving rise to predeliquescence, i.e., the formation of a brine layer wetting a salt particle at relative humidities well below the deliquescence point.

Internal Flow Analysis in a Two-Channel Pump Used for Salt Transportation

Two-channel pumps usually have very complicated flow field due to the special impeller geometry. The present paper treats the internal flow analysis based on numerical simulation so as to investigate the pumping performance and passage erosion for a two-channel centrifugal pump used for transporting salt particles. The static state flows are calculated by applying RANS method and k-omega SST turbulence model. The numerical results indicate that there are strong circulation flows near the impeller inlet and blade pressure side, and zones with high turbulent kinetic energy near impeller exit when the pump is operated under the designed flow rate i.e. Qd. Pressure decay is also found at the rear part of blade pressure side. At the operation condition of 1.3Qd, the internal flow becomes better. Further, the numerical analysis based on Eulerian-Lagrangian method shows the trajectory of salt particle, salt particle concentration and erosion rate in the pump. It is noted that the salt particles go smoothly in the flow passage due to the large section size of the pump, and there is severe erosion at the blade leading edge and the wall of volute casing due to strong impingement and high particle concentration. Thus, these areas such as blade leading edge and the wall of volute casing are the zones with high erosion risk in the two-channel pump.