Features of metastable superheated water atomization when being discharged through convergent-divergent nozzles at different superheat values

Experiments with the metastable superheated water atomization proved the significant increase of the submicron droplets mass fraction at the outlet of convergent-divergent nozzle from 0.45-0.55 to 0.75-0.9 with an increase of the inlet water temperature from170to255°C. Two different approaches to dimensionless treatment of the atomization processdata and determining the boundary of the zone of flashing predominance are compared. The analysis of two approaches to dimensionless treatment of experimental and calculating results concerning transition to predominating role of nucleation in the process of superheated liquid atomization in convergent-divergent nozzles is done.

Risk Exposure during Showering and Water-Saving Showers

Eco-friendly showers aim to lower energy and water consumption by generating smaller water droplets than those produced by traditional systems. To evaluate the risk of users inhaling the contaminants associated with such water droplets—namely, chemical components or opportunistic bacterial pathogens such as Legionella—we modeled the behavior of water droplets aerosolized by water-atomization technology at a flow rate of 2.2 L/min and compared the results obtained using this model with those determined experimentally in a typical shower stall. Additionally, we monitored the number and mass of inhalable water droplets emitted by twelve showerheads—eight using water-atomization technology and four using continuous-flow technology—which have distinct characteristics in terms of water flow rate, water pressure, spray angle, and number of and diameter of nozzles. The water-atomizing showers tested not only had lower flow rates, but also larger spray angles, less nozzles, and larger nozzle diameters than those of the continuous-flow showerheads. We observed a difference in the behavior of inhalable water droplets between the two technologies, both unobstructed and with the presence of a mannequin. The evaporation of inhalable water droplets emitted by the water-atomization showers favored a homogenous distribution in the shower stall. In the presence of the mannequin, the number and mass of inhalable droplets increased for the continuous-flow showerheads and decreased for the water-atomization showerheads. The water-atomization showerheads emitted less inhalable water mass than the continuous-flow showerheads did per unit of time; however, they generally emitted a slightly higher number of inhalable droplets (1.6 times more), including those large enough to carry a bacterium each—only one model performed as well as the continuous-flow showerheads in this regard. Further experiments are needed to assess whether this slight increase in the number of inhalable water droplets increases the biological risk.

The Masteralloy Concept for Sintered Steels - New Impetus for a Classical Approach

Among the various alloying techniques used in powder metallurgy, the masteralloy concept has been known for a long time. However, its use for production of ferrous precision parts has been hampered by several obstacles such as poor output of the useful fine fractions, high tool wear and slow homogenization kinetics of the alloy elements in the matrix. On the other hand, the masteralloy concept is particularly interesting for introducing cost-effective alloy elements such as Cr, Mn and Si since the masteralloy approach at least alleviates the problems caused by the high oxygen affinity of these elements. In the present study it is shown that recent developments have given a boost to this classical concept, one of these developments being powder manufacturing by high pressure water atomization which dramatically increases the yield of fine masteralloy fractions. The other progress is availability of thermodynamic software that enables defining masteralloy compositions with low melting range and thus fast homogenization also at moderate sintering temperatures. Combined, these new developments open the door for implementation of the masteralloy route in large scale PM parts production.

Development of High-Performance Thermoelectric Materials by Microstructure Control of P-Type BiSbTe Based Alloys Fabricated by Water Atomization

Developing inexpensive and rapid fabrication methods for high efficiency thermoelectric alloys is a crucial challenge for the thermoelectric industry, especially for energy conversion applications. Here, we fabricated large amounts of p-type Cu0.07Bi0.5Sb1.5Te3 alloys, using water atomization to control its microstructure and improve thermoelectric performance by optimizing its initial powder size. All the water atomized powders were sieved with different aperture sizes, of 32–75 μm, 75–125 μm, 125–200 μm, and <200 μm, and subsequently consolidated using hot pressing at 490 °C. The grain sizes were found to increase with increasing powder particle size, which also increased carrier mobility due to improved carrier transport. The maximum electrical conductivity of 1457.33 Ω−1 cm−1 was obtained for the 125–200 μm samples due to their large grain sizes and subsequent high mobility. The Seebeck coefficient slightly increased with decreasing particle size due to scattering of carriers at fine grain boundaries. The higher power factor values of 4.20, 4.22 × 10−3 W/mk2 were, respectively, obtained for large powder specimens, such as 125–200 μm and 75–125 μm, due to their higher electrical conductivity. In addition, thermal conductivity increased with increasing particle size due to the improvement in carriers and phonons transport. The 75–125 μm powder specimen exhibited a relatively high thermoelectric figure of merit, ZT of 1.257 due to this higher electric conductivity.

Effect of Powder Heat Treatment on Chemical Composition and Thermoelectric Properties of Bismuth Antimony Telluride Alloys Fabricated by Combining Water Atomization and Spark Plasma Sintering

In this work, Bi0.5Sb1.5Te3 materials were produced by an economically viable and time efficient water atomization process. The powder samples were heat treated at different temperatures (673 K, 723 K, 743 K, 773 K, 803 K, and 823 K) followed by spark plasma sintering (SPS). It was found that the Te evaporated slightly at 723 K and 743 K and became dominated at 773 K, 803 K, and 823 K, which severely influences the thermoelectric properties. The electrical conductivity was significantly improved for over 803 K heat treated samples due to the remarkable improvement in hole concentration. The power factor values for the 803 K and 823 K samples were significantly larger at T > 350 K compared to other samples. Consequently, the peak ZT of 0.92 at 350 K was obtained for the 803 K sample, which could be useful in commercial thermoelectric power generation.