Stokes Number Analysis of the Moving Droplets in the Steam-Water Separator

The steam-water separator is vitally important equipment to remove the droplets entrained by the vapor stream to provide dry saturated steam for the steam turbine in the nuclear power station. With the development of the large nuclear power station and the vessel nuclear power plant, the steam-water separation performance should be more efficient under the condition of higher pressure, power load and circulating ratio. The droplet motion model, which is solved by typical four steps Runge-Kutta method and validated against the experimental results, is developed according to the physical phenomenon description and the mechanism comprehension of the vapor entrained droplets moving in the wave-type vanes separator. The Euler-Lagrange methodology is adopted to simulate the moving droplet entrained by the vapor stream in the wave-type vanes separator and the separation performance is investigated. The separation efficiency of the separator and motion trajectories of droplets with various sizes are presented. Stokes Number (St) of diverse droplets is obtained to analyze the influence of Stokes Number on the moving droplets trajectories and the separation efficiency. The results reveal that the values of Stokes Number for most of the moving droplets in the wave-type vanes separator are beyond 1, which indicates that most of droplets are likely to collide with the solid wall of the separator. Only when the droplet velocity is smaller than 1 m/s or the droplet radius is less than 2 μm, the Stokes Number may be below 1 and the moving droplets can be entrained by the stream flow until escaping from the separator. The analysis can forecast the maximum critical separation size of the droplets that cannot be removed, and the minimum critical separation size of the droplets that can be removed throughly by the separator and guide the design of the separator.

DAUGIAKANALIO CIKLONO PANAUDOJIMO DUJŲ SRAUTO DULKĖTUMUI MAŽINTI AGRESYVIOJE APLINKOJE TEORINIS VERTINIMAS

Contaminated gas cleaning from finely divided solids is carried out using a new generation of multi-channel design cyclones. The application of these devices are separated and precipitated particles with a minimum diameter up to 2 micrometers, reaching up to 95% cleaning efficiency. Cyclones of such constructions are usually used under usual conditions at elevated temperature and low humidity. Under aggressive conditions, these devices can be clogged, and their recovery is not possible. Further studies are research into the application of constructive solutions to adapt the cyclone gas cleaning of the particulate matter under aggressive conditions. This theoretical evaluation has described the characteristics change of gas flow and particulate matters at different aggressive environment. Such conditions were loudly describe the gas-flow high-temperature range of 50–200 °C and gas-vapor stream, the humidity reaches 70–100%. Estimated aggressive conditions on the gas flow dynamics forces – pressure, resistance and centrifugal, and particulate mechanical – gravitational and adhesion strength. All parameters are evaluated in comparison with the values under normal conditions. Naujos kartos daugiakanaliais ciklonais smulkiadispersės kietosios dalelės pašalinamos iš užterštų dujų. Naudojant šiuos įrenginius, yra atskiriamos ir nusodinamos kietosios dalelės, kurių minimalus skersmuo siekia 2 mikrometrus, taip gaunama iki 95 % valymo efektyvumo. Tokios konstrukcijos ciklonai dažniausiai yra naudojami įprastomis sąlygomis, esant padidintai temperatūrai ir nedideliam drėgniui. Esant agresyvioms aplinkos sąlygoms, šie įrenginiai užsikemša, o jų regeneruoti negalima. Tolesniuose ciklono veikimo parametrų tyrimuose numatoma analizuoti, kaip, taikant konstruktyvius sprendimus, pritaikyti cikloną ir šalinti kietąsias daleles iš dujų esant agresyvioms aplinkos sąlygoms. Šioje teorinėje analizėje yra aprašomas dujų srauto charakteristikų bei kietąsias daleles veikiančių jėgų pokytis esant skirtingai agresyviai aplinkai. Tokios sąlygos buvo apibrėžtos, nustačius 50–200 °C dujų srauto temperatūros intervalą ir tiriant dujų-garų srautą, kurio drėgnis siekė 70–100 %. Įvertinta agresyvių aplinkos sąlygų įtaka, daroma dujų srauto dinamikos jėgoms – slėgio, pasipriešinimo ir išcentrinei. – ir kietųjų dalelių mechaninėms jėgoms – gravitacijos ir adhezijos. Visi vertinami parametrai palyginti su vertėmis normaliomis sąlygomis.

An Arc Discharge by Closely Situated Electrodes for Synthesis of Nanostructures

Geometry of electrodes, distance between them, work atmosphere and ambient temperature are the important factors, which determine quantity and variety of structures synthesized via arc discharge. Usually, electrodes of different cross-section are placed away from each other, allowing a large vapor stream directed into the reactor inside to be obtained. Generally, the anode is thinner than the cathode; it heats up to a high temperature, sublimates and supplies the carbon vapor required for nanoparticle synthesis. In contrast to this commonly used approach, when electrode dimensions are appropriately chosen and electrodes placed closely together, temperature interaction between them becomes considerable, discharge area constrains and hot electrodes can be used as heaters for the evaporation of materials of high melting point.

Reduction of Nanometric Magnetite Powder

The investigated nanometric magnetite powders were synthesized electrochemically, and examined by XRD and SEM techniques. Their reduction was conducted through the isothermal heating in hydrogen in the temperature range from 600 to 860 K. Kinetics of the hydrogen recovery process during oxidation of freshly formed Fe powders in a water vapor stream was also studied. It was assumed that the solid-gas reaction is diffusion controlled, and Jander’s model was applied to describe it. The experimental data suggest that the reoxidation process proceeds in two stages, at various activation energies. By changing the conditions of the electrochemical (EC) process we were able to produce the iron oxide powders with optimal particle size and activity, for pure hydrogen production through appropriate reduction/oxidation processes.