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In order to investigate the solute distribution and freckles formation during directional solidification of superalloy ingots, a mathematical model with coupled solution of flow field, solute and temperature distribution was developed. Mean-while, the reliability of this model was verified by the experimental and simulation results in relevant literatures. The 3-D directional solidification process of Ni-5.8 wt.% Al-15.2 wt.% Ta superalloy ingot was simulated, and then the dynamic growth of solute enrichment channels was demonstrated inside the ingot. Freckles formation under different cooling rates was studied, and the local segregation degree inside the ingot was obtained innovatively after solidification. The results show that the number of freckles formed at the top gradually decreases, and so do the degree of solute enrichment at these freckles with the increase of cooling rate. Moreover, the relative and volume-averaged segregation ratio is defined to describe the segregation degree inside the ingot. The span of relative segregation ratio for positive segregation is wider than that for negative segregation, but it accounts for less of total volume. As the cooling rate increases from 0.1 K/s to 1.0 K/s, the proportion of weak segregation (?20%~20%) increases significantly from 26% to 41%, so that the segregation degree is weakened in general. By analyzing the freckles formation and segregation degree inside the ingot, the numerical simulation results can provide a theoretical basis for optimizing the actual production process to suppress the freckle defects.

A three-dimensional transient multi-physical field model with comprehensive reduction reaction consideration has been developed to capture the complex processes of a three-phase submerged arc furnace. The multi-physics model integrates electromagnetic, fluid flow, reduction reaction, and thermodynamics phenomenon in unison computational framework. The furnace internal structure consists of arc and furnace charge, for which the physical properties include temperature dependence. Aiming to search the optimum design for more efficient industrial operation, the electrode insertion depth is investigated. The predicted temperature distribution of high temperature is in agreement with the measurement and simulation results. The result shows that the temperature of arc zone is maximum, which is 5897.17 K. The high-temperature area of furnace charge is near the arc zone. The temperature distribution is similar with current density. With the increase of electrode insertion depth, the average voltage drop of three arc zones is 11.43, 11.12, 10.83, and 10.35 V, respectively. When the electrode insertion depth is 1.99 and 1.79 m, the maximum magnetic field intensity around the electrode bottom is of 0.068 and 0.063 T. Cr2O3 mainly reacts under the arc bottom, while iron oxides are reduced less in the same location. An optimum electrode insertion depth exists according to the simulation results.

Ammonia appears to be a potential alternative fuel that can be used as a hydrogen vector and fuel for gas turbines and internal combustion engines. Chemical mechanisms of ammonia combustion are important for the development of ammonia combustion systems, but also as a mean of investigation of harmful NOx emissions, so they can be minimized. Despite of large body of experimental and modelling work on the topic of ammonia combustion, there is still need for additional investigation of combustion kinetics. The object of this work is further numerical study of ammonia combustion chemistry under conditions resembling industrial ones. After literature review, three mechanisms of ammonia combustion that also include carbon chemistry are used for simulation of experimental premixed swirl burner with the aim of evaluating their performance. San Diego mechanism, that was also the most detailed one, proved to be the best in terms of emissions, but neither one of the models was able to accurately reproduce CO emission after equivalence ratio went beyond 0.81. It was also observed that oxygen is excessively consumed. This study contributes to the current knowledge by providing new insights in ammonia burning conditions closely resembling those in industrial applications, and consequently is expected that insights obtained will help in the design of real industrial burning systems.

A walking beam type reheating furnace with advanced control technology has been evaluated by combined energy and exergy analysis. In order to gain insight into the performance of the present furnace, the results of energy analysis are compared with those in published papers and the irreversibility of the furnace is analyzed via exergy destruction calculation. The results show that slabs preheated before charged into the furnace can save fuel and improve energy utilization. The structure and material of the wall and roof show good thermal insulation. However, the oxidized scale is a little more and the temperature of flue gas is high in the present reheating furnace. The energy efficiency of the furnace is 71.01%, while exergy efficiency is 51.41%, indicating a potential for energy-saving improvements of the present furnace. The exergy destruction of the furnace accounts for 28.36% of total exergy input which is mainly caused by heat transfer through a finite temperature difference (14.71%), fuel combustion (11.66%) and scale formation (1.99%).

Size-induced particle segregation in rotating drums has been investigated using an Eulerian continuum approach (ECA). The mixing process of a binary mixture were respectively predicted in an unbaffled drum, a drum with a “+” shaped central baffle and a drum with a “-” shaped central baffle. Qualitative comparisons with DEM results showed that ECA works well for describing the mixing process of binary mixtures. A mixing index based on sampling information from the computational grids was developed and used for quantitative analysis. Compared with a base case which uses equal-sized particles, the results showed that ECA can separate the effects of mixing from the effects of segregation. However, the rate of mixing were over-estimated and the improvement effects of “+” shaped baffle and “-” shaped baffle were hard to distinguish quantitatively in the ECA. The drag model was modified for improving the ECA. The final segregation was found independent on the initial particle distribution using ECA.

The fully passive solar energy utilization system of Chinese solar greenhouse is efficient for ensuring year-round cultivation of vegetables, owing to the high amount of heat charge and discharge characteristic of the north wall enclosure. In the present research, the thermal performance is investigated using CFD. A 3-D mathematical model has been established to evaluate the wall thickness, layered configuration and material property. The predicted thermal environments are in good agreement with the experimental measurements, indicating the reliability of the established numerical model. The results showed that the increase of north wall thickness could cause the waste of resources due to the thermal masses mainly concentrate in the superficial layer. Constructing layered configuration is rec-ommended for the north wall which uses Styrofoam in the outer layer to reduce heat loss. Nevertheless, the property of north wall material has little effect on the thermal environment. The research results, thus obtained, will give good guidance for completing the Chinese solar greenhouse engineering database and optimizing the solar energy utilization.

Ladle baking technology is a widely adopted method in the iron and steel industry. For reducing defects such as centre segregation of billet, it is crucial to minimize the heat loss of molten steel; maintaining a high drawing speed and low superheat during the continuous casting process. Nevertheless, it is well known that the traditional air combustion ladle baking technology suffers from high energy consumption and severe pollution problems. On the other hand, the oxy-fuel combustion technology where fuel combustion is supported by pure oxygen offers many attractive advantages, including high theoretical combustion temperature, low flue gas emission, and enhanced heat transfer of gas radiation. Unfortunately, up to date, limited researches have been carried to understand the potential of the technology. In the present study, a 3-D mathematical model has been established considering the details of turbulent combustion behaviour and its coupling effects on the heat transfer phenomenon during ladle baking process. Considering the difference between gas radiation in oxygen-enriched combustion and the traditional air-assisted combustion, a modified weighted sum of gray gases model were introduced and compared with the conventional model. Based on the established mathematical model, the operation efficiency of the oxy-fuel combustion and air combustion technologies were studied in details. Numerical results show that the oxy-fuel combustion is more efficient and achieves a potential fuel savings of 41.6%.

The manganese-silicon is mainly used as deoxidizer in the steel production and intermediate material of alloying agent. It is obtained by smelting in a submerged arc furnace, which the main furnace materials are manganese ore and coke. Two significant aspects affect ore smelting. One is the power supply, which a three-phase alternating electric energy is transferred to the furnace through electrodes. The other is the furnace smelting state, which encompasses the ore, slag, alloy, and gas phases. In the present paper, a systematic furnace melting model has been developed for ore smelting, which is dominated jointly by electrical control and metallurgical control. The 36 MW furnace for manganese-silicon production has been investigated during the production period. The reduction reactions and associated magneto-hydrodynamic flow are also considered in the three-dimensional transient model. The arc plasma and furnace lining sub-models are simulated. The arc heat and Joule heat by electrothermal conversion raise the temperature in the furnace. The temperature distribution has a great influence on the electrode current and the alloy yield. The output of alloy can be obtained in real time. The numerical results provide valuable insights for the interactions between multi-physics field in the submerged arc furnace. A better understanding of ore smelting process will improve the smelting efficiency and furnace control.

This work presents multi-objective optimization of an aspirating smoke detection system which uses the pipeline to transport air sample from the sampling points to the analysing module. On the basis of 3D computational fluid dynamics simulation it has been shown that the smoke transport will not always take place in the centre of the pipe and that one dimensional analysis is not able to provide information in which layer smoke transport will take place. Consequently, velocity from the layer at the distance of 0.95R from the pipe centreline was taken as an input for calculation of the transport time to bind the calculation on the safe side. By employing the multi-objective optimization approach, balancing of specific transport time and volume flow at the sampling points’ location was achieved through pipeline configuration variation with respect to pipe diameters and the position of branches along the main pipe. Objective function was assembled from the flow rate function and transport time function using the weighted sum method. Results for five different values of weight factor have been discussed. After reaching weight factor value of 0.75, configuration reached requested sensitivity, and further increase of weight factor enabled more uniform flow across the network without deterioration of transport time.

In order to study the effect of refractory graphite content and heating temperature on carbon pick-up of ultra-low-carbon steel from magnesia-carbon refractory, a transient axisymmetric mathematical model has been established. The momentum, heat and mass transfer between the refractory and the molten steel was modeled by using porous medium. Arrhenius law was employed to define the rate of the carbothermic reduction reaction of the magnesia. Besides, a series of experiments were carried out to verify the model. The results indicate that the carbon content of the molten steel rapidly rises when the refractory graphite content ranges from 3 mass% to 10 mass%, and the carbon pick-up induced by direct dissolution is significantly promoted. The influence of the heating temperature on the carbon content in the molten steel however is negligibly small, and the proportions of the carbon pick-up caused by the direct dissolution and the chemical reaction basically remain the same although the heating temperature increases by 100 K. The effect of the refractory graphite content on the carbon pick-up of the molten steel far outweighs that of the heating temperature.

Thermoelectric generator has been considered as a promising device to recover industrial waste heat for electricity generating. To figure out the heat transfer and electric conduction processes in thermoelectric generator, a three-dimensional numerical model has been built up which consists of 127 thermocouples. The open-circuit voltage, internal resistance, and output power have been studied by numerical simulation. All calculation results are in good agreement with the experimental results, and the maximum deviation is less than 6%. Due to the influence of Peltier effect, both heat flow and equivalent thermal conductivity increases by 30.2% when temperature difference between the hot and cold side is 170 °C and the thermoelectric generator reaches its maximum power output. In addition, the Peltier effect has been investigated when the convective heat transfer boundary conditions are applied. The results showed that the effective temperature difference was raised to 13.6 °C (a 10.2% increase) and maximum output power was raised to 0.59 W (a 14.8% increase) for the thermoelectric generator model with a fin height of 100 mm when compared with that without fins. Besides that, the radio of load resistance to internal resistance decreased from 1.31 to 1.14.

The integrated flow fields of multiple interacting jets and oblique impinging flow have been investigated. The flow structure and heat transfer characteristics on the impinged surface are predicted through a comprehensive numerical transient simulation as well as an experimental oil flow visualization. The complicated multi-jet impinging flow is simulated by solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations with compressibility correction. The near-wall resolution is accomplished by employing an improved analytic wall function (AWF) approach. The oil flow testing is conducted to reveal the flow patterns of parallel multiple impinging jets, using a practical scarfing unit. The deformable oil trace has successfully reproduced the impinging grooves on the flat plate. The results indicated that the generated grooves on the impinged surface are mainly triggered by the multi-jet attraction and combination mechanism caused by the Coanda effect. The defined merging point (MP) location and impinging groove degree are employed to examine the multi-jet flow evolution and the corresponding impinging performance. The heat transfer characteristic on the impinged surface is highly dependent on Reynolds number, jet-to-jet spacing and jet-to-plate spacing. While the flow structure presents insensitive to Reynolds number.

Energy consumption of fuel-fired industrial furnace accounts for about 23% of the national total energy consumption every year in China. Meanwhile, the reduction of combustion-generated pollutants in furnace has become very important due to the stringent environment laws and policy introduced in the recent years. It is therefore a great challenge for the researchers to simultaneously enhance the fuel efficiency of the furnace while controlling the pollution emission. In this study, a transient 3-D mathematical combustion model coupled with heat transfer and pollution formation model of a walking-beam-type reheating furnace has been developed to simulate the essential combustion, and pollution distribution in the furnace. Based on this model, considering nitrogen oxides formation mechanism, sensitivity study has been carried out to investigate the influence of fuel flow rate, air-fuel ratio on the resultant concentration of nitrogen oxides in the flue gas. The results of present study provide valuable information for improving the thermal efficiency and pollutant control of reheating furnace.

The main objective of this paper is to assess the thermal performance of the RKEF process based on the actual operational data by using exergy analysis method. To identify the factors affecting exergy efficiency loss, exergy destruction caused by the main chemical reactions (fuel combustion, reduction reaction, decomposition reaction and slagging reaction) is investigated in detail. The results show that the energy efficiency of the RKEF process is 53.3% whereas the exergy efficiency is 15.7%, indicating a great potential for energy-saving. The overall exergy destruction accounts for 46.4% of the total exergy input, in which 24.8% is caused by chemical reactions. Moreover, the exergy destruction due to chemical reactions of rotary dryer, rotary kiln and electric furnace is 20.4%, 27.1% and 5.1%, respectively. It is also found that combustion is the dominant factor for the efficiency loss of rotary dryer and rotary kiln and slag with high temperature contributes most for the efficiency loss of electric furnace. Several suggestions for improving the thermal performance of RKEF system are proposed. The present work should do helpful effort for further improvement of the RKEF process.

A new methodology of average bubble number density (ABND) model for handling the evolution of polydispersed bubbly flow in the slab continuous casting mold is presented and evaluated. The average bubble number density transport equation coupled with the Eulerian-Eulerian two-fluid model is employed to describe size distribution of bubbles. Various interfacial forces including drag force, lift force, virtual mass force, and turbulent dispersion force are incorporated in this model. SST turbulence model is used with extra source terms introduced to account for the interaction between the bubbles and the liquid. The coalescence of bubbles is formulated according to the random collision driven by turbulence and wake entrainment, and the breakage of bubbles is formulated through considering the impact of turbulent eddies. The intermediate peak and core peak behaviors of void fraction inside the submersed entry nozzle (SEN) are captured very well. Comparisons of gas void fraction, liquid flow pattern, and local bubble size distribution profiles with experimental measurements are provided, showing the applicability and accuracy of the ABND approach in modeling the polydispersed bubbly flow in the slab continuous casting mold.

Annular shaft kilns with opposite burners (OBASK) has been widely adopted due to the advantages of cost saving and easy controlling. Nonetheless, compared with the traditional annular shaft kiln, the OBASK is not favorable in terms of thermal performance and energy efficiency. Aiming to improve the thermal performance, a comprehensive energy and exergy analysis of an OBASK has been conducted based on the actual operational data obtained from on-site measurements. For making a thorough thermal analysis of the OBASK, special attentions have been focused in considering magnesium decomposition reaction and moisture in limestone in the methodology. The energy and exergy efficiencies are determined to be 63.6% and 35.7%, respectively. The exergy destruction is 44.0% of total exergy input of which fuel combustion causes 56.6% of the exergy destruction. Furthermore, the effects of CaO and moisture contents in limestone on energy and exergy efficiencies are analyzed. The results have demonstrated the potential energy saving of the OBASK and identified three proposed energy conservation measures. Improvement and effect of the three proposed measures on the thermal performance are verified via further analysis.

The megawatt high-power permanent magnet direct-drive generator is the main trend of wind power development. The temperature rise of the generator is an important indicator of the reliability of the permanent magnet generator. According to the problems of high loss density, large generator volume, cooling difficulty and permanent magnet being easy to occur irreversible demagnetization at high temperatures in high-power permanent magnet direct-drive generator, the cooling system of 3.2MW split-type permanent magnet direct-drive wind turbine generator is designed and analyzed. In this paper, a stator pipeline-circulating watercooling system was designed, and the temperature calculation model was established based on the fluid-solid coupling method. In order to study the design law of the cooling system, it was compared with the traditional shell-type water-cooling scheme and the stator-slot air-cooling scheme. The calculation results show that the air gap is not conducive to the radial heat dissipation of the generator. The air-cooling scheme will cause the larger axial temperature difference of the generator. As the generator power becomes larger, the above effect will also increase. The greater flow rate of the water in the cooling pipeline, the lower the temperature rise of the generator will be obtained, but the speed of reduction will slow down and the cost will increase. It has guiding significance for the design of the cooling system of the subsequent 10 MW high-power permanent magnet direct-drive generator.

With the demand of high-quality steel and miniaturization of the special steel production, single snorkel vacuum refining process has been widely concerned in China recently, because of its simple structure and good performance of degassing and decarburization. In this study, a water model experimental system and a three-dimensional mathematical model based on two-fluid multiphase flow model have been built to analyze the refining efficiency limitation of the single snorkel vacuum refining furnace from the flow pattern and gas distribution. The results showed that there is a limited gas flow rate, and beyond this flow rate the gas column deviates to the wall and the redundant bubbles escape from the free surface, which will not further improve the refining efficiency and will lead to the erosion of the snorkel. In this case, the limited flow rate is 900 NL/h. Furthermore, the fluctuation of the free surface and the different structural parameters have significant effects on the flow field in single-snorkel vacuum refining furnace (SSF).

A transient 3D integrated model has been developed to investigate the role of a rotating electrode on the improvement of productivity and refining ability in the electroslag remelting process. All essential considerations of the fluid flow, heat transfer, and inclusion removal are incorporated in the model. The electrode melting rate is predicted based on the heat flux from the slag to the electrode. The motion of inclusions is considered and resolved by the Lagrangian approach. The reliability of the model is thoroughly validated against a scale experimental data. Numerical results show that metal droplets tend to separate at the centre of the static electrode tip. With the rotating electrode, metal droplets are however detached by centrifugal force at the outer side of the electrode tip. The highest temperature area also migrates from the outer mold region to the mold centre as the rotating speed increases from 0 to 60 rpm. The averaged electrode melting rates for the four rotating speeds (i.e. 0, 20, 40, and 60 rpm) are 0.02292, 0.02410, 0.02795, and 0.02506 kg/s, respectively. The maximum improvement of productivity with a value of 21.95% is achieved when the rotating speed is 40 rpm. The removal ratio of inclusions is also enhanced by increasing the rotating speed. The impact of the rotating electrode and the enhanced removal mechanism are discussed in detail.

Electroslag remelting (ESR) furnace with triple-electrode is always used to produce large ingots and the process complexity makes the application not widely spread. Thus, a transient three-dimensional coupled model in industrial scale has been developed to investigate the coupled magneto-hydrodynamics two-phase flow and heat transfer in system. Different from the previous studies with multi-electrode, the current work reveals the triple-electrode ESR with the formation of metal droplets and the solidification of liquid metal. Compared with single-electrode system with the same fill ratio, the heat source in the slag pool with triple-electrode is much more dispersive, and the U-shape metal pool in the ESR furnace with triple-electrode is much shallower and flatter than the V-shaped one in the single-electrode system. A shorter distance from each electrode to the center of system brings a higher heat efficiency, as well as a deeper and narrower metal pool.

Population balance equations combined with Eulerian–Eulerian two-phase model are employed to predict the polydispersed bubbly flow inside the slab continuous-casting mold. The class method, realized by the MUltiple-SIze- Group (MUSIG) model, alongside with suitable bubble breakage and coalescence kernels is adopted. A two-way momentum transfer mechanism model combines the bubble induced turbulence model and various interfacial forces including drag, lift, virtual mass, wall lubrication, and turbulent dispersion are incorporated in the model. A 1/4th scaled water model of the slab continuous-casting mold was built to measure and investigate the bubble behavior and size distribution. A high speed video system was used to visualize the bubble behavior, and a digital image processing technique was used to measure the mean bubble diameter along the width of the mold. Predictions by previous mono-size model and MUSIG model are compared and validated against experimental data obtained from the water model. Effects of the water flow rate and gas flow rate on the mean bubble size were also investigated. Close agreements by MUSIG model were achieved for the gas volume fraction, liquid flow pattern, bubble breakage and coalescence, and local bubble Sauter mean diameter against observations and measurements of water model experiments.

The evolution of bubble size distribution is an important consideration in vertical gas-liquid flow, especially in determining the appropriate mass, momentum, and heat transfer between two phases. In order to adequately capture the distribution and to account for its effect on the local hydrodynamics, which generally represents the dominant flow characteristic in such a practical system, a numerical assessment has been performed to understand the six widely adopted different bubble coalescence and bubble breakage kernels. Three different breakage kernels have been selected where each kernel considers a different shape of the daughter size distribution of the bubbles, such as the U-shape, bell-shape, and M-shape. These are combined with different coalescence kernels. The bubble size distribution, void fraction, interfacial area concentration, and gas velocity profiles are compared against the experimental data. Numerical results reveal that the effect on the two-phase flow structure is mainly due to the application of the different breakage kernels. Moreover, the predicted results also show that the bell-shape daughter size distribution favours equal breakage of bubbles, which could lead to the over-prediction of large bubbles. A more sophisticated model for handling bubble induced turbulence should nonetheless be applied in future investigations of vertical gas-liquid flow.

An inhomogeneous Multiple Size Group (MUSIG) model based on the Eulerian–Eulerian approach has been developed to describe the polydispersed bubbly flow inside the continuous-casting mold. A laboratory scale mold has been simulated using four different turbulence closure models (modified k − ɛ, RNG k − ɛ, k − ω, and SST) with the purpose of critically comparing their predictions of bubble Sauter mean diameter distribution with previous experimental data. Furthermore, the influences of all the interfacial momentum transfer terms including drag force, lift force, virtual mass force, wall lubrication force, and turbulent dispersion force are investigated. The breakup and coalescence effects of the bubbles are modeled according to the bubble breakup by the impact of turbulent eddies while for bubble coalescence by the random collisions driven by turbulence and wake entrainment. It has been found that the modified k − ɛ model shows better agreement than other models in predicting the bubble Sauter mean diameter profiles. Further, simulations have also been performed to understand the sensitivity of different interfacial forces. The appropriate drag force coefficient, lift force coefficient, virtual mass force coefficient, and turbulent dispersion force coefficient are chosen in accordance with measurements of water model experiments. However, the wall lubrication force does not have much effect on the current polydispersed bubbly flow system. Finally, the MUSIG model is then used to estimate the argon bubble diameter in the molten steel of the mold. The argon bubble Sauter mean diameter generated in molten steel is predicted to be larger than air bubbles in water for the similar conditions.

A population balance model based on the multiple-size-group (MUSIG) approach has been developed to investigate the polydispersed bubbly flow inside the slab continuous-casting mold and bubble behavior including volume fraction, breakup, coalescence, and size distribution. The Eulerian–Eulerian approach is used to describe the equations of motion of the two-phase flow. All the non-drag forces (lift force, virtual mass force, wall lubrication force, and turbulent dispersion force) and drag force are incorporated in this model. Sato and Sekiguchi model is used to account for the bubble-induced turbulence. Luo and Svendsen model and Prince and Blanch model are used to describe the bubbles breakup and coalescence behavior, respectively. A 1/4th water model of the slab continuous-casting mold was applied to investigate the distribution and size of bubbles by injecting air through a circumferential inlet chamber which was made of the specially-coated samples of mullite porous brick, which is used for the actual upper nozzle. Against experimental data, numerical results showed good agreement for the gas volume fraction and local bubble Sauter mean diameter. The bubble Sauter mean diameter in the upper recirculation zone decreases with increasing water flow rate and increases with increasing gas flow rate. The distribution of bubble Sauter mean diameter along the width direction of the upper mold increases first, and then gradually decreases from the SEN to the narrow wall. Close agreements between the predictions and measurements demonstrate the capability of the MUSIG model in modeling bubbly flow inside the continuous-casting mold.

A finite element model has been developed to examine the electromagnetic field and interface wave of electrolyte/aluminum melt in aluminum reduction cell with the novel cathode structure. The edge-based method is used to solve the Maxwell equations. The results show that the current density distribution in the novel cathode structure aluminum reduction cell becomes more uniform than the traditional cells, weak horizontal current appears on the convex surface, and weakened the longitudinal waves of molten aluminum. The voltage drop of the whole novel aluminum reduction cell has reduced. The result shows that the movement of molten aluminum affected by the electromagnetic force dominates and two reverse eddies in horizontal plane arise in aluminum reduction cell. The velocity and amplitude of molten aluminum wave reduce in the novel cathode structure aluminum reduction cell.