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Argon bottom stirring is commonly practiced in secondary steelmaking processes due to its positive effects on achieving uniform temperatures and chemical compositions throughout a steel melt. It can also be used to facilitate slag metal refining reactions. The inter-mixing phenomena associated with argon gas injection through porous plugs set in the bottom and its stirring efficiency can be summarized by evaluations of 95% mixing times. This study focuses on investigating the impact of different plug positions and ratios of argon flow rates from two plugs on mixing behavior within a 110-tonne, elliptical-shaped industrial ladle. A quasi-single-phase modeling technique was employed for this purpose. The CFD findings revealed that the optimal position of the second plug is to be placed diametrically opposite the existing one at an equal mid-radius distance (R/2). An equal distribution of argon flow rates yielded the best results in terms of refractory erosion. A comparative study was conducted between single- and dual-plug-configured ladles based on flow behavior and wall shear stresses using this method. Furthermore, a transient multiphase model was developed to examine the formation of slag open eyes (SOE) for both single- and dual-plug configurations using a volume of fluid (VOF) model. The results indicated that the dual-plug configuration outperformed the current single-plug configuration. [ABSTRACT FROM AUTHOR]

The cleanness of steel has always been a big problem for secondary refining. In this work, a new method, which is coupled with slot and porous plugs, is proposed to improve the cleanness in steel. Water experiments and numerical simulations were performed to study this effect. Results revealed that when using slot-porous plugs, the flow field was obviously asymmetrical, and the circulation flow was pushed towards the porous side. Then, the removement of inclusions was increased to about 22.7% percent, comparing with traditional two-slot bottom stirring and reducing the dead zone area near the bottom of the ladle; however, the mixing time delay was 16%, comparing with traditional plugs. Then, in order to explain the reason for these phenomena, we established a mathematical model through large eddy simulation and discrete particle modeling (DPM). Results shows that the asymmetry flow field awoke the recirculation flow downwards after using slot-porous plugs, which would homogenize the flow at the bottom, promoting floating in steel. What is more, the velocity near the free surface was lowered; therefore, it could also stabilize the surface velocity as well, which is also beneficial for removing inclusions as well.

In secondary refining operations, injection of inert gases into the metal bath is required to generate stirring in order to produce cleaner steels with low sulfur, ultra-low contents of nitrogen and hydrogen gases as well as improving both temperature and composition homogenization of the steel and control the inclusions and floating of them. To demonstrate the viability and competitiveness of the non-consumable lance versus porous plugs, a series of experiments in a model of secondary refining ladle were carried out in previous research (Liu et al. in ISIJ Int 57:1971, 2017). Simulation of gas injection was carried out to test the two methods: porous plug and non-consumable lance. It was found that the porous plug injection involves shorter mixing times (10–12 s) when it is positioned in an intermediate point between the center and edge of the ladle and with the increase in the airflow injected, as compared to the lance. However, one problem with this technique in the actual plant is the metal oxidation because the liquid metal is exposed to air as a result of excessive agitation. In this work, gas injection through porous plug and non-consumable lance into secondary refining ladle was simulated by the addition of oils of different densities, to simulate the behavior of the slag of different viscosities. The results show that the non-consumable lance exhibits less water surface area exposed compared with the porous plug. This means less metal is exposed to the environment and less oxidation of it, under the same agitation conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with (i) fabrication of microfluidic devices using living radical photo-polymerization method with various polymers (aromatic urethane diacrylate, photo-initiator, and photo-iniferter), and placement of porous plug using salt-leaching technique in microfluidic channel, (ii) determination of the pore size of the porous plug using flow field-flow fractionation, and (iii) investigation of separation of various particles including latex micro-particles and bacteria. It was demonstrated that the microfluidic device with porous plug could be used as a new and simple tool for particles (including microorganisms) separation based on their sizes and a miniaturized filter for water sample analyses. [Copyright &y& Elsevier]

The Low Temperature Micro-gravity Physics Facility (LTMPF) designed by Ball Aerospace & Technologies Corp. contains a 180-l superfluid helium dewar for conducting fundamental physics experiments. The dewar and ancillary experiment electronics will be located on the Japanese experiment module-exposed facility (JEM-EF), a module of the International Space Station. The helium is expected to deplete over approximately 5 months, after which the facility will be returned for new experiments, refurbished, refilled and relaunched on a projected 22-month cycle time. Because of the JEM-EF envelope constraints, the dewar has a unique ob-round cross section. The strut-mounted helium tank has provisions to accommodate two separate experiments, one at each end of the tank. Until the cryostat is constructed and tested, assessments of cryostat performance must be accomplished with analytic models. This paper documents the predicted thermal/thermodynamic performance of the cryostat from final launch top-off operations, through post-launch transients, to steady-state on-orbit performance. [Copyright &y& Elsevier]

SIRTF is the last of NASA''s great observatories. The thermal function of the CTA is critical to the success of the SIRTF mission. The CTA cryogenic and thermal system will provide the low temperature environment that the telescope and science instruments require to conduct infrared observations. A key issue with the early flight data is the peak helium bath temperature, which depends upon cryostat isolation, the helium vent path, and pre-launch cryostat operations. This paper includes a general description of the CTA thermal/cryogenic system, followed by an update on the cryostat status and a discussion of the analysis and performance testing of the porous plug and helium vent path. The pre-launch cryostat preparations have been demonstrated, and those results are presented. There is also summary of performance from the observatory thermal balance test, which completes the verification of the CTA external thermal system. All of the pieces are in place for a successful SIRTF launch and mission. [Copyright &y& Elsevier]

In the last decades, the interest of many scientists has been focused on the atypical electrokinetic behavior of charged colloidal systems since several studies have shown, in most cases; it is not so ideal as expected. Particularly, two interesting phenomena have not been clearly explained yet. First, the zeta potential magnitude does not decrease monotonically with increasing ionic strength, as expected according to the Gouy–Chapmann model predicts. Second, the zeta potential obtained from different techniques shows discrepancies. More specifically, the ζ potential obtained from streaming potential is lower (in absolute value) than that measured through electrophoretic mobility. However, a recent work has pointed out that these discrepancies seem to disappear if certain conditions (related with the surface charge density) are satisfied. This work also revealed that unexpected results are found when the electric conductivity was used. Spherical polystyrene particles of appropriate particle size and charge density are employed as polymeric colloidal model in the present work. Common and adequate models are used to make clear and easy our theoretical analysis and its interpretation. To test the surface conductance and ionic mobility effects at the solid–liquid interface, both water medium and alcohol–water mixtures are used. [Copyright &y& Elsevier]

The zeta potential of mixed nickel–iron oxide particles is evaluated by a new laboratory instrument. This latter allows the measurement of streaming potential together with the electrical resistance of porous plugs. The conductivity of electrolyte inside plug (pore conductivity) is deduced from electrical resistance measurements and is used together with streaming potential to evaluate the zeta potential by accounting for the surface conduction phenomenon. It is shown that neglecting the surface conduction phenomenon leads to a substantial underestimation of the zeta potential. The coupled measurements of streaming potential and plug electrical resistance yield zeta potential values that are in very good agreement with those obtained by electrophoresis. The densification of the porous plug with increasing pressure increments is put in evidence by the decrease in measured streaming potentials. Electrical resistance measurements make it possible to account for the increase in surface conductivity resulting from the more compacted structure of the plug. By doing so, the calculated zeta potential is found to be virtually independent of the pressure difference involved in streaming potential experiments, whereas the negligence of surface conduction phenomenon leads to a decrease in the apparent zeta potential with increasing pressure level. [Copyright &y& Elsevier]

The cleanness of steel has always been a big problem for secondary refining. In this work, a new method, which is coupled with slot and porous plugs, is proposed to improve the cleanness in steel. Water experiments and numerical simulations were performed to study this effect. Results revealed that when using slot-porous plugs, the flow field was obviously asymmetrical, and the circulation flow was pushed towards the porous side. Then, the removement of inclusions was increased to about 22.7% percent, comparing with traditional two-slot bottom stirring and reducing the dead zone area near the bottom of the ladle; however, the mixing time delay was 16%, comparing with traditional plugs. Then, in order to explain the reason for these phenomena, we established a mathematical model through large eddy simulation and discrete particle modeling (DPM). Results shows that the asymmetry flow field awoke the recirculation flow downwards after using slot-porous plugs, which would homogenize the flow at the bottom, promoting floating in steel. What is more, the velocity near the free surface was lowered; therefore, it could also stabilize the surface velocity as well, which is also beneficial for removing inclusions as well. [ABSTRACT FROM AUTHOR]