Numerical and physical study of transitions to unsteady modes of melt flow with the Prandtl number 16 in the Czochralski method

The evolution of the flow structure and heat transfer with an increase in the characteristic temperature drop in the ranges of Grashof and Marangoni numbers 3558 ≤ Gr ≤ 7116 and 2970 ≤ Ma ≤ 5939 are investigated numerically. The boundary of the transition to unsteady flow and heat transfer regimes has been determined.

Vanadium Extraction from Korean Vanadiferous Titanomagnetite Ore Using Alkali Roasting: Evaluation of Optimal Conditions and Leaching Rate

The extraction process of vanadium from vanadiferous titanomagnetite ore deposited in Korea was investigated by combining alkali roasting and water leaching processes. The effect of Na2CO3 addition on the efficiency with which the vanadium could be leached was investigated along with an X-ray diffraction analysis. When more than 30-wt% Na2CO3 was added at 1273 K, a vanadium leaching efficiency of approximately 70% was achieved. The minimum alkali-roasting temperature was determined to be 1273 K with the addition of 30-wt% Na2CO3. Thermodynamic calculations revealed that the formation of the liquidus phase of Na2CO3 enhanced the reaction between the vanadium in the concentrate and sodium, resulting in a higher leaching efficiency for vanadium being attained. The thermodynamic calculation results were indirectly supported by the characteristic temperature determination through hot-stage microscope analysis. After 30 min of thermal treatment, a leaching efficiency for vanadium of 75% was achieved, which remained constant as the thermal treatment time was increased. Finally, the effects of the leaching time and temperature on the efficiency with which vanadium and other impurities, namely, aluminum, silicon, and sodium, could be leached was analyzed by varying the leaching time. A higher leaching efficiency was attained at higher temperatures. The leaching rate of vanadium decreased considerably after 10–20 min and subsequently remained almost constant.

Resistivity saturation in Kondo insulators

Resistivities of heavy-fermion insulators typically saturate below a characteristic temperature T*. For some, metallic surface states, potentially from a non-trivial bulk topology, are a likely source of residual conduction. Here, we establish an alternative mechanism: at low temperature, in addition to the charge gap, the scattering rate turns into a relevant energy scale, invalidating the semi-classical Boltzmann picture. Then, finite lifetimes of intrinsic carriers drive residual conduction, impose the existence of a crossover T*, and control—now on par with the gap—the quantum regime emerging below it. Assisted by realistic many-body simulations, we showcase the mechanism for the Kondo insulator Ce3Bi4Pt3, for which residual conduction is a bulk property, and elucidate how its saturation regime evolves under external pressure and varying disorder. Deriving a phenomenological formula for the quantum regime, we also unriddle the ill-understood bulk conductivity of SmB6—demonstrating a wide applicability of our mechanism in correlated narrow-gap semiconductors.

Effects of organic sulfur on oxidation spontaneous combustion characteristics of coking coal

Research on the spontaneous combustion of coal caused by sulfur has always been focused on pyrite in coal but has rarely considered the influence of organic sulfur. In this paper, coal samples, rather than model compounds, were used to study the influence of organic sulfur content in coal on its spontaneous combustion process. The results of X-ray photoelectron spectroscopy and thermogravimetry, differential scanning calorimetry, and mass spectrometry indicate that organic sulfur in Shuiyu clean coal exists in forms of mercaptan, thioether, sulfone (sulfoxide), and thiophene. With the decrease of organic sulfur content, the characteristic temperature points and the peak values of the exothermic curves in the process of coal oxidation spontaneous combustion all shifted toward higher temperatures. The ignition activation energy of coal also increased, and the initial and peak gas evolution temperatures of the oxidation products shifted toward higher temperatures. These findings suggest that the reduction of organic sulfur content can inhibit the oxidation process and spontaneous combustion tendency of coal. This effectively reveals the mechanism of the spontaneous combustion of coal and is of great significance to future studies in this field.

Experimental investigation of a loop heat pipe with R245fa and R1234ze (E) as working fluids

Two kinds of new refrigerant-R1234ze (E) and R245fa were discussed as substitutes or supplements to traditional working fluids of loop heat pipes based on their favorable thermophysical properties and characteristics such as being safe and environmentally friendly. Thermal characteristics of a loop heat pipe with sintering copper wick at different charging ratios were experimentally investigated under variable heat loads. The results showed that the optimal charging ratio in the loop heat pipe range from 65% to 70%, and at this charging level, the R1234ze(E) system had better start-up response, while the R245fa system presented a stronger heat transfer capacity. The characteristic temperature of R1234ze(E) system was below 35 °C, and the corresponding thermal resistance was 0.08 K/W ~ 1.62 K/W under heat loads ranging from 5 W to 40 W. The thermal resistance of the R245fa system was 0.18 K/W ~ 0.91 K/W under heat loads of 10 W ~ 60 W, and the operating temperature was below 60 °C. The loop heat pipes charged with the proposed new refrigerants exhibit superb performance in room temperature applications, making them beneficial for enhancing the performance of electronics, and could provide a distinctive choice for the cooling of small-sized electronics especially.

The Metallogeny of the Tieling Cu-Mo Porphyry Deposit in Eastern Tianshan, NW China: New Insights from Zircon U-Pb, Fluid Inclusion, and H-O-S Stable Isotope Analyses

The eastern Tianshan metallogenic belt is an important molybdenum resource base in Xinjiang and is characterized by large-scale porphyry Mo deposits formed during the Triassic. The Tieling Cu-Mo porphyry deposit, which is situated in the western part of the eastern Tianshan metallogenic belt, was recently recognized as being related to Carboniferous granite porphyry. Three stages of hydrothermal mineralization were identified, including quartz+K-feldspar+pyrite±molybdenite±magnetite (stage I), quartz+molybdenite+pyrite+chalcopyrite (stage II), and quartz+pyrite±molybdenite±epidote (stage III). Fluid inclusion petrography and microthermometry analyses indicate the presence of gas-liquid inclusions with a H2O-NaCl composition. The ore-forming fluids have a characteristic temperature ranging from 157 to 262°C under stage II and 135 to 173°C under stage III, which correspond to salinities of 7.2-17.2 wt% NaCl equiv. and 5.9 to 9.6 wt% NaCl equiv., respectively. The hydrogen and oxygen isotope data indicate that the ore-forming fluids of the Tieling deposit were originally derived from magmatic hydrothermal fluids and then mixed with meteoric water. The sulfur isotope compositions indicate that the ore-forming materials were mainly derived from the Late Carboniferous felsic magma. Furthermore, zircon U-Pb analysis of ore-bearing granite porphyry yields a concordant age of 298.4 ± 0.7 Ma , indicating that the Tieling Cu-Mo deposit formed during the Late Carboniferous and differed from that processed under pre-Early Carboniferous and Triassic mineralization in the eastern Tianshan metallogenic belt. These results also indicate that the Tieling porphyry deposit was formed in the transition condition between subduction-related accretion and postcollisional orogeny, and it should be given more attention in prospect evaluations.

Research on the Damping Performance of Mining Highly Efficient Water-Retaining Colloidal Material Against the Spontaneous Combustion of Coal

In order to solve the shortcomings of the traditional mining anti-extinguishing gel material such as low strength and poor water retention, a high hydrocolloid anti-extinguishing material was developed with sodium alginate and light calcium carbonate as the base material and gluconolactone as the retarder, which was mixed and reacted. The base material ratio of highly efficient water-retaining colloidal material for coal void filling was determined as 2% SA + 0.5% PCC + 1% GDL with a moulding time of 4.5 min, while the base material ratio of highly efficient water-retaining colloidal material for extinguishing high temperature fires was 2.5% SA + 1% PCC + 1% GDL with a moulding time of 2.5 min. The highly efficient water-retaining colloidal material was found to reduce the concentration of signature gas and delay the characteristic temperature point and increase the activation energy of coal oxidation, which indicates that the highly efficient water-retaining colloidal material can effectively inhibit the spontaneous combustion process of coal at low temperature stage. Infrared spectroscopy experiments were conducted to investigate the microscopic resistance mechanism of the highly efficient water-retaining colloidal material, and the results showed that the highly efficient water-retaining colloidal material mainly reduce the activity of Ar-C-O-, -COO-, -CH3, -CH2 and -OH in coal to inhibit the spontaneous combustion of coal.

Composting as Sustainable Managing Option for Seaweed Blooms on Recreational Beaches

Purpose Seaweed blooms are an irregular but frequent phenomenon in many coastal areas and during the touristic season, can cause limitations for recreational use of beaches. Here, we propose composting of seaweed removed from the shoreline as alternative to current management practices (e.g. disposal in landfills or incineration). Methods A co-composting strategy with garden prune waste was chosen for the treatment of seaweed blooms removed from the beaches. Composting was performed in windrows of 10 m long, 1.5 m wide and 1 m high using different ratios of algae and garden prune residues (1:2; 1:1 and 2:1) at a composting facility in Rota (Cádiz, Spain). Results Characteristic temperature profiles consisting of a very brief mesophilic phase, a 15–20-day thermophilic phase (maximum of 50–70 °C) and a second mesophilic phase (40–35ºC) after 30–50 days were observed. After curing for more than 160 days, a stabilized non-phytotoxic composted material (50–70 g kg−1 C; 2–3 g kg−1 N; C/N ratio of 21–27 and electrical conductivity between 1.8–2.4 mS cm−1) was obtained. Composting worked best using a 2:1 ratio (prune waste:algae). The composted organic material showed larger presence of stabilized lignin-derived compounds as assessed via nuclear magnetic resonance. No odors were detected during the composting process suggesting that open-air treatment is feasible. Conclusion The co-composting strategy provides a safe, local and sustainable approach to deal with seaweed blooms during peaks of recreational use and in situations where algae have to be removed. Graphic Abstract

Influence of Air Supply on Coal Spontaneous Combustion During Support Withdrawal in Fully Mechanized Coal Mining and its Prevention

It is important to study the oxidation characteristics of coal samples under different air supply rates to prevent spontaneous combustion of coal, particularly when the air supply rate at the working face needs to be changed during support withdrawal. In this work a self-designed temperature-programmed experimental device was used to study the change laws of various index gases released during the spontaneous combustion of coal under various air supply conditions. The study focused on the analysis of the low-temperature (30–200 ℃) oxidation stage, the increase in air supply, and the concentration change process of four hydrocarbon gases (C2H6, C3H8, C2H4, and C2H2) generated by the coal sample. The change law of the CO generation rate under the combined effect of temperature and air supply was analyzed, and surface fitting was performed to determine the characteristics of phased changes. Based on the working face parameters of the Yangchangwan Coal Mine, this study predicted the CO concentration at the upper corner of the working face at the characteristic temperature of coal spontaneous combustion during the withdrawal period. The paper summarizes comprehensive safety measures that can help prevent spontaneous combustion during the withdrawal period.

Fundamental study of red mud based fluxes for desulphurization and dephosphorization of hot metal

Bauxite residue, also known as red mud, is generated during alumina production and is an abundant industrial waste material. Continuously increasing environmental concerns, together with scarcity of traditional mineral resources, have created a thrust to re-use the material. Red mud contains significant amounts of iron oxide and sodium hydroxide, hence a highly basic (pH > 10) slurry. In this research, the use of red mud as starting material for preparation of iron refining fluxes was evaluated. Red mud based fluxes and hot metal were equilibrated in graphite crucibles at the temperature range of 1300 ºC to 1400 °C and oxygen partial pressures range of 10-2 atm to 10-6 atm. It was found that the sulphide capacity increases with lime addition to a maximum 32 wt% CaO and decreases with increasing A12O3, TiO2 and SiO2 content in the fluxes saturated with lime. An iron foil equilibrium technique was employed to obtain precise measurements of phosphorus distribution between carbon saturated iron and red mud based fluxes. The measurements indicate that the equilibrium phosphorus distribution ratio initially increases with rise in FeO or CaO concentration of the fluxes and then drops. The melting behavior of the fluxes was also studied by visualizing the deformation of flux pellets as they were heated using a high temperature microscopy technique. Measurements of characteristic temperature for different fluxes indicated the melting property is a function of slag basicity. Therefore, optical basicity was used to establish a correlation between basicity of the red mud based fluxes and their melting properties.