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Despite the excellent specific energy of lithium-air batteries, their unclear discharge mechanism and product morphology remain great challenges for successfully replacing commercial lithium-ion ba...

A cellular automata-lattice Boltzmann coupled model was established to simulate the grain formation process of aluminum alloy under convection conditions. The influence of flow on crystal grain growth was simulated. Results show that the existence of convection prevents the crystal from growing symmetrically compared with the pure diffusion condition. Moreover, the growth of dendrite at the upstream side is promoted, whereas that at the downstream side is inhibited because of solute segregation. The greater the flow velocity is, the stronger the asymmetry of the grain is. The greater the undercooling is, the greater the dendritic growth driving force is, the faster the dendritic growth is, the dendrite arms coarsen, and the secondary dendrite arms become increasingly developed, thereby increasing the solute concentration at the solid-liquid interface at the tip of the dendrite and aggravating the solute segregation.

Air quenching refers to a common technique used for treating metallurgical molten slag, which generates a mass of high-temperature solid slag particles. In this research, we proposed a new technology to recover the waste heat from slag particles using a drum apparatus that uses cold steel balls as intermediate heat storage. This research focuses on the radial mixing of slag particles and steel balls in the rotating drum with baffles. Previous studies mainly focus on the mixing process of a single type of particles or two types of similar particles in the drum. However, the slag particle size of this research has a continuous distribution, and the slags are mixed with steel balls with greatly different parameters, such as size and density. Few similar studies have been conducted, and the corresponding mixing and segregation phenomena are also different from those of previous studies. In this research, numerical simulations with discrete element method (DEM) were carried out to understand and quantify the mixing and segregation processes of slags and balls in a horizontal drum. The slag size distribution includes two typical cases: normal diameter distribution and normal volume distribution. The corresponding control groups (e.g., uniform diameter and uniform volume) were set. According to the current research situation, several mixing criteria, including the whole process and subprocesses, were improved and used to evaluate the different aspects of the mixing processes under diverse cases. The influence of slag size distribution on the mixing process was mainly investigated. The time required for complete mixing in different aspects was compared to reveal the mixing mechanism efficiently. Results show that the mixing criteria of the whole process cannot reflect many details of the subprocesses. The use of the criteria of the subprocesses—a combination of the entry order index and number of contacts—is accurate in evaluating the mixing time of the granular bed.

Recent theoretical and experimental studies have shown that the formation of Li2O2, the main discharge product of nonaqueous Li-O2 batteries, is a complex multistep reaction process. The formation, nucleation, and adsorption of LixOy (x and y = 0, 1, and 2) and (Li2O2)n clusters with n = 1-4 on the surface of carbon nanotubes (CNTs) were investigated by periodic density functional theory calculation. The results showed that both Li2O2 and Li2O on CNT electrodes are preferentially generated by lithiation reaction rather than disproportionation reaction. The free energy profiles demonstrate that the discharge potentials of 2.54 and 1.29 V are the threshold values of spontaneous nucleation of (Li2O2)2 and (Li2O)2 on a CNT surface, respectively. The electronic structure indicates that Li2O2 is a p-type semiconductor, while Li2O exhibits the properties of an insulator. Interestingly, once Li2O2 molecules condense into large clusters, they will be repelled away from the CNT surface and continue to grow into large-sized Li2O2. Our results provide insights into the full understanding of the electrochemical reaction mechanism and product formation processes of lithium oxides in the cathodes of Li-O2 batteries.

In a continuous hot-dip galvanizing vertical furnace for strip steel, zinc vapor oxidizes in the snout of the furnace to form zinc ash. The zinc ash adheres and agglomerates on the inner walls of the snout. If the zinc ash falls off and adheres to the surface of the strip, zinc ash defects will be formed, thereby affecting the surface quality of the galvanized layer. Given that the snout connects the annealing furnace and the zinc pot, the zinc ash will be transported into the annealing furnace and form nodulation on the roller, affecting the normal operation of the equipment. To study the deposition pattern of zinc ash inside the snout, a model of particle movement and deposition is established in this work to predict the movement and deposition characteristics of zinc ash particles, and it is verified by literature. On this basis, the zinc ash deposition patterns of three improvement cases of snout structure are compared. Results show that all three improvement schemes can effectively reduce the deposition rate of the zinc ash particles in the annealing furnace. In the case of slotted-baffle-added-only, although adding slotted baffles reduces the deposition of zinc ash in the furnace, it also increases the deposition rate in the snout and entry sections. In the case of exhaust-duct-added-only, the addition of the exhaust duct not only reduces the overall deposition rate in the furnace, but also effectively reduces the deposition rate in the snout and the entry section. By contrast, the scheme with slotted baffles and exhaust ducts is the most effective in inhibiting the diffusion of zinc ash.

A series of experiments was performed to investigate the enhancement effect of micro fin, contact pressure, and interface temperature on thermal contact conductance. The specimens were made of 7075 aluminum alloy. The contact surfaces of specimens with micro fin were specially machined such that two specimens were coaxially inlayed together. Contact pressure ranged from 2 MPa to 4.2 MPa, and interface temperature ranged from 165 °C to 180 °C and 215 °C to 227 °C. Experimental results showed that the micro fin could enhance thermal contact conductance, and the contact heat transfer enhancement effects caused by the micro fin gradually increased with contact pressure. Thermal contact conductance was high under higher interface temperature. The loading process changed the enhancing effect of the micro fin, and enhancement of contact heat transfer was greater in the unloading process than in the loading process. A qualitative analysis on the enhancement effect was conducted to explain the contact heat transfer enhancement effect for different micro-finned surfaces.

Recent theoretical and experimental studies have shown that the formation of Li

A set of experimental devices was designed and built to investigate the effects of average temperature of lamination, contact pressure, and lamination number on the effective axial thermal conductivity of silicon steel multi-stacked material in the loading and unloading processes under atmospheric environment. Specimens are stacked by oriented silicon steel sheets, the content of silicon is approximately 3.3%, and thickness is 0.23 mm. Average temperature is in the range of 200–800 °C, and contact pressure is between 0.16 and 16.68 MPa. Experimental results indicated that: effective axial thermal conductivity presented an obvious relationship with the average temperature and contact pressure of lamination but showed independence from the lamination number. Effective axial thermal conductivity is more sensitive to contact pressure in the loading process than in the unloading process. The correlation equations of effective axial thermal conductivity have an accuracy of 15%.

A one-dimensional mathematical model is adopted to analyse influences of operational parameters on process performance during flue gas recirculation sintering (FGRS). Simulation results show that F...

TiC has attracted tremendous recent attention in lithium-oxygen batteries as a means of reducing the irreversible accumulation of by-products (i.e., Li2CO3) on the air cathode. However, TiC is intrinsically reactive to oxygen under ambient conditions, and its stability is completely determined by the surface overlayer. Herein, the catalytic effects of oxide overlayer (TiO) on adsorption mechanism, reaction path, and growth morphology of lithium oxides were comprehensively elucidated using periodic density functional theory calculations. The results indicate that the TiO overlayer on the surface of TiC(100)-TiO enhances the adsorption of lithium oxides. As compared to the disproportionation reaction, the lithiation reaction is the primary contributor to the formation of Li2O2 and Li2O on TiC(100) surface. Interestingly, the oxidized TiC(100)-TiO performs better in inhibiting the generation of undesirable Li2O. Analysis demonstrates that the discharge performance is not only related to the widely known morphology and size of product but also to the adsorption of (Li2O2)n clusters on the TiC(100) surface. The electronic structures of (Li2O2)n clusters on TiC(100)-TiC and TiC(100)-TiO surfaces have been examined to study the influence of TiO overlayer on the conductivity of accumulated products, which helps explain the innovative discovery of the experiment that TiC has excellent performance in improving the cycle ability of lithium-oxygen batteries. Our results promote the understanding of the ORR mechanism on TiC surface and provide theoretical guidance for the design of efficient and stable air cathodes for lithium-oxygen batteries.

Converter sludge is a by-product of converter steelmaking and a secondary resource of recovery; however, it needs to be dried before recovery. Obtaining the expected results using traditional sludge drying technologies is difficult due to the special properties of converter sludge. In this research, we proposed a new rotating-drum-drying technology using hot steel balls. Steel balls are heated by the waste heat of metallurgical slag. This technology has the advantages of low cost, high efficiency and thorough drying, and can overcome the shortcomings of traditional technologies. This research explored the converter sludge drying in a drum through experiments. The effect of four operating parameters on the drying process was investigated, and the suitable model for the drying process was discussed. The operating parameters include sludge treatment mass (3.0/4.0/5.0/6.7/9.0 kg), steel ball (initial) temperature (300/500 °C), steel ball diameter (20/30/40 mm) and drum rotating speed (1/3/5/7 rpm). Results show that this proposed technology is feasible and efficient. Sludge drying can be accelerated by appropriately reducing the sludge treatment mass, increasing the steel ball temperature, increasing the steel ball diameter, and selecting an appropriate drum rotating speed. The Weibull model can better predict the drying process by comparing multiple models. The operating parameters have obvious relationships with the fitting parameters of the Weibull model.

As calcium carbide (CaC2) production is an energy-intensive industry, a novel low rank coal to CaC2 (LRCtCC) process has been developed. This study is aimed to evaluate the techno-economic performance of the LRCtCC process. A model integrating particle swarm optimization and nonlinear programming (PSO-NLP) is developed to predict the behavior of coal pyrolysis. The techno-economic assessment of the LRCtCC process is analyzed. Results show that the power consumption of electric arc furnace is expected to drop to 2845 from 3169 kW·h/t with the hot material (HM) temperature increasing from 25 to 850 °C. The effect of increasing HM temperature is greater than that of adjusting the composition of fuel on system efficiency, cost of CaC2, and internal rate of return. In addition, the effects of typical economic factors on net present value (NPV) of the LRCtCC process are compared. Results show that variations of CaC2 price and power consumption pose a remarkable impact on NPV. The findings of this study suggest that the LRCtCC process would be an attractive method for the improvement of CaC2 production.

This paper examines the randomness of porous structure composed by cubes or spheres and particle size level in flow and heat transfer characteristics using the 3D lattice Boltzmann method. The simulation results show that randomness has significant effects on permeability and the Nusselt number when the number and size of spheres or cubes are fixed. As the particle size level increases, normalized permeability increases, but the Nusselt number decreases. When the particle size level increases to five, permeability and the Nusselt number cease to change. Furthermore, the effect of porosity for the porous structure with the least number of particle size level on the Nusselt number is the most significant.

The permeability of random porous media composed of multi-sized particles is calculated by using the lattice Boltzmann method. This paper studies the randomness of porous structure, particle size level and particle shape on flow characteristics. Results show that randomness has significant effects on permeability when the number and size of spheres or cubes are fixed, especially for the cubes. As the particle size level increases, the normalized permeability increases. When the size level increases to five, the permeability does not continue to increase. Furthermore, this paper studies the effect of particle shape on flow characteristics. The results show that the normalized permeability of sphere particle is larger than cube particle. In addition, our research results extend studies to a case where the cube length is smaller than the cube height.

Results from experimental and numerical studies of the transient heat-transfer characteristics of circular air-jet impingement are presented. The circular nozzle has an inner diameter of 6 mm. The Reynolds number is defined based on the nozzle diameter varied from 14,000 to 53,000. The nondimensional distance between the nozzle exit and the target plate is varied from 4 to 8. The local Nusselt number variation with the time obtained from the experimental and numerical studies are presented. The local Nusselt number rapidly increases when the air jet began its impingement. The increasing speed of Nuloc slows down as the jet impingement continues to cool down. At the 50–80 s region, the Nuloc at various radii R/Dn get the maximum point and remain almost constant from 80 s until the end of the experiment.

In this work, an improved comprehensive model was developed for large coal particles to predict temperature variation and volatile component yields. The kinetics model of volatile component yields, where the volatile matters were assumed to comprise nine species, was combined with heat transfer model. The interaction between volatile yield and heat transfer during pyrolysis of large Maltby coal particles was investigated. An apparent temperature difference has been observed between the surface and core of particles at the initial heating stage. The non-uniform temperature distribution inside coal particles causes non-simultaneous volatile yields release from the surface and core area. The volatile release occurs after the coal temperature rises higher than 350 &deg, C, and its yield steeply increases within the temperature range of 450&ndash, 520 &deg, C. The peak of volatile release rate corresponds to about 485 &deg, C due to the rapid release of tar and H2O. The tar is almost completely released at around 550 &deg, C. With the increasing particle size, the difference in temperature and volatile yield between the surface and core increases at the end of heating. The results are expected to provide insights into the interaction between heat transfer and volatile yields during pyrolysis of large coal particles.

This study analyzes the heat transfer characteristics of multi-slot nozzles air jets with velocity difference between the adjacent jets. The research content includes the influence of thermal uniformity analysis and heat transfer capacity owing to the existence of adjacent jets. The multi-slot nozzles experiment was carried out under the specified conditions. The heat transfer uniformity of multi-slot nozzles jet heat transfer was improved compared with that of a single-nozzle jet heat transfer. Moreover, the closer the Reynolds number of the adjacent jets, the better the heat transfer uniformity. The existence of adjacent jets would relatively inhibit the heat transfer capacity. Through a single-slot nozzle experiment, an empirical formula for heat transfer characteristics of a single-nozzle jet on this experimental platform is obtained. The empirical formula of multi-slot nozzles is obtained by extending the empirical formula of single nozzle. The accuracy of multi-slot nozzles empirical formula is verified through a multi-nozzle confirmatory experiment, and the application scope of the empirical formula is relatively widened.

Flow and heat transfer through a 2D random porous medium are studied by using the lattice Boltzmann method (LBM). For the random porous medium, the influence of disordered cylinder arrangement on permeability and Nusselt number are investigated. Results indicate that the permeability and Nusselt number for different cylinder locations are unequal even with the same number and size of cylinders. New correlations for the permeability and coefficient b ′ D en of the Forchheimer equation are proposed for random porous medium composed of Gaussian distributed circular cylinders. Furthermore, a general set of heat transfer correlations is proposed and compared with existing experimental data and empirical correlations. Our results show that the Nu number increases with the increase of the porosity, hence heat transfer is found to be accurate considering the effect of porosity.

Hot tearing susceptibility is commonly assessed using a pressure drop equation in the mushy zone that includes the effects of both tensile deformation perpendicular to the thermal gradient as well as shrinkage feeding. In this study, a Pore Fraction hot tearing model, recently developed by Monroe and Beckermann (JOM 66:1439–1445, 2014), is extended to additionally include the effect of strain rate parallel to the thermal gradient. The deformation and shrinkage pore fractions are obtained on the basis of the dimensionless Niyama criterion and a scaling variable method. First, the model is applied to the binary Al-Cu system under conditions of directional solidification. It is shown that for the same Niyama criterion, a decrease in the cooling rate increases both the deformation and shrinkage pore fractions because of an increase in the time spent in the brittle temperature region. Second, the model is applied to the industrial aluminum alloy AA5182 as part of a finite element simulation of the Direct Chill (DC) casting process. It is shown that an increase in the casting speed during DC casting increases the deformation and shrinkage pore fractions, causing the maximum point of pore fraction to move towards the base of the casting. These results demonstrate that including the strain rate parallel to the thermal gradient significantly improves the predictive quality of hot tearing criteria based on the pressure drop equation.

Flue gas recirculation sintering (FGRS) technology has been applied for two decades with the aim of reducing pollutant emissions. Compared with the conventional sintering (CS), the changes of input gas conditions may influence the bed combustion process greatly. Mathematical models have been developed to predict sintering behavior quantitatively, but few of the previous work focused on FGRS process. In this study, a multiphase theory-based mathematical model is established. This model considers nine kinds of major physicochemical reactions, in which six modes of gaseous reactions make it more comprehensive and accurate to model FGRS process. Heat transfer within/between different solid and gas phases are modeled in better manners. Geometric changes caused by reactive-factors are modeled in simple terms. Sub-models are available to simulate the effects of the temperature, gas supply, composition and content of recirculated gas on combustion characteristics in the sintering bed. Good agreements between simulated and measured results have been obtained from contrasting to six sinter pot tests based on FGRS technology. Four combustion parameters are selected to evaluate quantitatively the advantages and potential problems of FGRS technology. Results show that the flatter maximum temperature (MaxT) profile for FGRS compared with that for CS implies a stronger tumble strength of the sintered ore. The broader MaxT and combustion zone thickness (CZT) curve indicate a higher degree of melt fraction, together with a lower FFS and productivity. To better investigation, further parameter simulation and process optimization of FGRS technology is necessary.

A relatively more comprehensive 1D mathematical model, compared to previous models, is proposed for flue gas recirculation sintering (FGRS). The proposed model considers multiphase theory, eight major reactions significantly affected by the input gas conditions, and various heat transfer processes within/between different solid and gas phases. Characteristic size distributions of materials including coke, limestone and dolomite are used to correct the reaction rates of key sub-models, as well as specific kinetic parameters determined via thermogravimetric analysis instead of empirical values. Geometric changes caused by the reactive and melting factors are described in improved manners. This model is validated by contrasting the modeling results and the measured data from sinter pot tests. Parametric studies show FGRS technology can significantly enhance combustion characteristic within sinter bed, meaning to increase maximum temperature and melt fraction, improve the uneven distribution of heat. Therefore, the quality of sintered ore can be improved. However, the slightly reduced flame front speed deserves further attention. The velocity of input flue gas exerts the most significant effect, followed by O2 concentration, and then, temperature. The operating parameters of FGRS must be carefully determined. Three measures, which still require further investigations, can be proposed to optimize the process.

An experiment was performed to investigate the effects of interface temperature, specimen surface roughness, and contact pressure on thermal contact conductance (TCC). Specimens were prepared using SUS 304 stainless steel, the interface temperature was in the region of 360–640 °C, the contact pressure was between 2.39 and 15.17 MPa, and the surface roughness ranged from 0.25 μm to 2.00 μm. All experiments were conducted in ambient atmosphere. Results indicated that TCC presents a power law relationship with contact pressure and interface temperature. While the contact pressure exponent varied between 0.20 and 0.46 at different surface roughness, the interface temperature exponent showed a much wider range of 0.45–2.36. TCC increased more rapidly with temperature in specimens with higher surface roughness than in those with lower surface roughness. The correlation equations between thermal contact conductance, contact pressure, and interface temperature revealed a relative error of 20%.

A 2D axisymmetric inverse heat-conduction model based on the Levenber–Marquardt method was built. The equivalent Nusselt number Nu equ of air jet impinging on a stainless steel plate with finite thickness were obtained. Radiant heat transfer is significant when the temperature of the target plate is high, which induces the nonlinear feature of the inverse heat-conduction problem. The results of the experiments and the inverse analysis provide the following findings. First, the inverse heat-conduction model is accurate. Second, Nu equ maintains a relatively small value before the onset of the air jet. After the air jet starts, however, the values of Nu equ within the stagnation zone (dimensionless radius R / D n ≤ 1.0) increase dramatically, reach the peak points in the next 20 s, and then remain nearly constant until the end of the experiments. Third, the radial distribution of Nu equ shows that it decreases rapidly within the region of R / D n ≤ 8.0. When R / D n exceeds 10, Nu equ appears unaffected by the Reynolds number and R / D n . Lastly, Nu equ decreases slowly with the increase in time, which indicates that radiant heat-transfer flux decreases with target plate temperature.

Three-dimensional (3D) coil core is one kind of transformer iron core that is made of grain-oriented electrical steel. This material should be annealed before use because of the residual stress generated inside the silicon steel strip during production. The temperature evaluation of the 3D coil core is important to its annealing quality, but this temperature cannot be measured easily and the prediction method is seldom mentioned in the open literature. A numerical model, which considers the anisotropic heat conduction inside the 3D coil core and convection and radiation heat transfers inside the furnace, is built to link the temperature of furnace with the temperature of 3D coil core. Monte Carlo method is used to calculate the view factors between surfaces in the furnace. Thermal radiation resistance network method is used to obtain radiant heat flux. A computational fluid dynamics model is established to predict the convection heat transfer coefficient. The finite volume method is used to solve the anisotropic conduction inside the 3D coil core, wherein radiant heat flux and convection heat transfer coefficient serve as boundary conditions. The model considers the effects of size, position, location, orientation, and number of 3D coil cores on the temperature evolution. Onsite experiments verify that this digital model is precise in practical application, and the typical simulation error is less than ±2.5%. A straight forward optimization strategy is proposed on the basis of the digital model. The onsite experiments also show that the optimization method can effectively shorten the annealing time and increase the efficiency of the annealing process. Making a near real-time prediction and keeping 3D heat transfer features are the advantages of the present method.

Moving beds with staggered tubes are widely used in industrial applications to heat or cool solid particles. The heat transfer process is complicated and involves heat transfer amongst particles and between particles and tubes. Furthermore, the heat transfer mechanism is directly determined by the flow characteristics of particles across the outer surfaces of tubes because particles are the main heat carriers of particle flow. However, the particle flow across tubes is a kind of non-continuum flow, which is substantially different from Newtonian fluids, and the continuum theory is inappropriate for predicting particle flow in moving bed. In addition, little attention has been focused on this process. Thus, it is necessary to study the flow patterns of particles across tubes before studying the corresponding heat transfer mechanism. To describe this process, this work establishes a quasi-funnel flow (QFF) model, which can be used to calculate parameters, such as velocity field and residence time, by analyzing particle flow characteristics. The discrete element method (DEM) is used for a numerical simulation of three-dimensional particle flow across staggered tubes. The flow patterns, velocity field, typical particle trajectories and particle flow of local areas are obtained. Meanwhile, a moving bed experimental system is constructed, and the obtained results are used to verify the DEM numerical simulation results. Lastly, the results of the QFF model and that of the validated DEM numerical simulation are compared and found to be consistent. The ranges of the parameters required to describe the particle flow across tubes and the applicable range of the QFF model are also determined.