Jo Jan 20, 2025
With the rapid development of science and technology, the production of a large number of high-efficiency heat pumps has led to the active use of shallow geothermal energy with lower development cost than deep geothermal heat in many countries.
U-type GSHE (ground source heat exchanger) is a system used for shallow geothermal energy development where the heat exchanger is embedded in the ground and the geothermal energy is extracted from the heat exchange between the ground and the water flowing through the pipe.
Heat transfer models for mathematically modeling U-type GSHE and several experimental and numerical simulation methods have been proposed.
Previous studies used laboratory and field experimental data for comparative analysis, focusing on simulation calculations to enhance the performance and heat exchange efficiency of single well modes such as U-type ground source heat pump (GSHP) system, standing column well (SCW) geothermal heat pump system, and forced external circulation single well (FECSW) geothermal heat pump system. In addition, the simulation calculations and experimental results were compared, limited to individual modes, and three modes have never been studied in relation to one another.
In order to study and introduce these modes to realistic conditions, the heat exchange characteristics of individual modes under different environmental conditions should be studied and the heat extraction efficiency of each mode should be compared.
Choe Tok Gi, an institute head at the Faculty of Earth Science and Technology, has designed a 1:20 scaled model and made 10 experimental scenarios considering different experimental conditions such as soil moisture, groundwater convection, heat conduction, abstraction and injection interval selection. Then, he has conducted heat extraction experiments according to the scenarios and compared the effectiveness.
The results show that in the U-type mode it is reasonable to use porous casing or gravel-filled materials because there is no possibility of groundwater contamination in the case of water without antifreeze, in the standing column well mode the convective heat exchange between the circulating water and surrounding ground should be increased as much as possible to increase the geothermal extraction, and in the forced external circulation single well (FECSW) mode it is effective to inject water into the top of the borehole during heating and into the bottom during cooling to generate convection.
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Jo Jan 19, 2025
Manganese is a very important alloying element for steel production. So far, in blast furnaces or submerge arc furnaces, ferromanganese has been made from manganese ore for producing alloy steel. Although alloying steel with ferromanganese is advantageous for steel production with high manganese content and it is easy to accurately control the manganese content, the requirement level for raw materials is very high.
Recently, there is a growing interest in direct alloying of steels by manganese ore as high-grade manganese ore needed for ferromanganese is gradually depleted and the price of ferromanganese is increasing. Direct alloying by manganese ore is a way of producing steels by smelting reduction and alloying manganese ores, coke (or anthracite), lime, etc. added to the liquid steel in steel furnaces or ladle refining furnaces.
Previous researchers found that direct alloying of steel by manganese ore in the steelmaking process of an electric arc furnace is feasible, but they all used high-grade ores with approximately 40% of Mn content for test melting.
Jang Sung Ryong, a researcher at the Faculty of Metal Engineering, has analyzed the reduction thermodynamic characteristics of manganese oxide in an electric arc furnace and the effect of several factors such as liquid steel temperature, slag basicity, manganese ore grade on the direct alloying process by low-grade manganese ore using the material thermodynamic calculation program “Factsage”.
The comparison of the theoretical analysis of Factsage and the results of the test melting for direct alloying in a five-tonne electric arc furnace shows a relatively good agreement in the contents of carbon, manganese and sulfur in the liquid steel as well as the MnO content in the slag near the end of the reduction period.
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Jo Jan 17, 2025
Nowadays, main facilities used in heavy industry, including metallurgical, chemical and power generation industries, all use a large amount of heat energy, and they usually have water-cooling systems. A water cooling system has many advantages including its simple structure and low maintenance cost, but on the other hand, the use of low-temperature natural water as an input increases water consumption from the water source, which increases the overall operating cost of production process.
To reduce the operating cost, water consumption has to be reduced by introducing more effective water-cooling methods. But there are technical limitations to the minimum water consumption. Besides, as even the minimum water consumption contains a certain amount of potential energy, recycling of hot cooling water is very important to reduce the energy consumption level of the whole production process.
Since long ago, natural cooling ponds such as rivers and lakes or artificial cooling ponds have been widely used to recycle the hot water from the output of a water-cooling system. However, due to the low cooling effect of traditional cooling ponds and the limited ratio of land occupation, extra cooling facilities are needed.
Introducing high-efficiency cooling ponds to further raise the cooling effect is a good way of reducing the surface area of cooling ponds and energy consumption for urban and other businesses on the limited surface area. Introduction of high-efficiency cooling ponds needs a methodolgy to uniquely design the structure and determine reasonable structural parameters that could satisfy the local climatic and geologic conditions.
Sin Sok Chol, a researcher at the Faculty of Metal Engineering, has proposed a concept of sectional cooling pond (SCP) of simple sectional region structure to raise the hot water-cooling effect without any extra cooling facilities and energy consumption.
In addition, he has conducted a mathematical modeling and CFD analysis of the recycling process of cooling water in the SCPs, thus proving their cooling effects and providing a way of determining reasonable structural parameters for them.
Introduction of SCPs enables recycling of cooling water required by production processes without the need for additional surface area and cooling equipment and energy consumption.
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Jo Jan 15, 2025
Forward neural networks are the most common neural networks in a neural network structure, for transmitting signals from input layers to output layers in one direction. In the feedforward neural network, there is no recursive coupling in the hidden layer. This feedforward neural network can simulate complex nonlinear relationships based on training data sets and it has a wide range of applications. In recent years, the feedforward neural network has been applied to many fields such as pattern recognition, decision making, future prediction and inaccessible object simulation. Currently, there is a growing interest in improving convergence and generalization ability in the application of feedforward neural networks.
With increasing researches on convolutional neural networks, the image recognition performance has been greatly improved. Convolutional neural networks have a structure for extracting the features of data by combining multiple convolutional layers with local filtering characteristics. Convolutional neural networks have been used to solve many problems such as satellite image analysis, object detection in natural images, face recognition, object recognition, etc.
Recently, sparse representations have attracted a lot of attention in the field of pattern recognition. The study of sparse representations has been carried out for nearly a century and they have been applied to various fields. In particular, the signal processing sector has aroused interest in sparse representations for compression and interpretation of speech, images and animations in the last decade.
Previous works presented a sparse matrix generation method by singular value decomposition, i.e, k-SVD algorithm. This algorithm increases the order of the dictionary matrix by no less than that of the measurement matrix, which leads to a higher number of iterations and a lower computational efficiency. Thus, it is not suitable for high-dimensional measurement signal processing.
Hwang Chol Hyon, a section head at the Faculty of Information Science and Technology, has studied a sparse representation computation method by singular value decomposition that updates several column data at a time, and proposed an improved k-SVD algorithm. In addition, he has constructed a three-layer BP neural network using the sparse representation calculation procedure of multiple measurement vectors, and implemented the feature extraction of multiple measurement vectors.
The feature extraction method with sparse representation can improve the coupling characteristics of neural network, thus greatly improving the learning speed.
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Jo Jan 14, 2025
Water is an important basic material in the chemical industry and indispensable for human life. The world has witnessed a lot of progress in the research on the disinfection of water, which is closely related to the human life.
Generally, sterilizers used for water disinfection and wastewater treatment contain chlorine, hydrogen chloride, chlorine dioxide, ozone, hydrogen peroxide and ferrate. These sterilizers have been degraded due to the high cost and the release of substances harmful to the human body. In addition, their low disinfection effectiveness and short duration restrict their usage.
At present, there is a worldwide research to develop new chemical water treatment reagents with a strong disinfection effect and no harm to the human body, especially with a focus on potassium ferrate, one of the green multifunctional water treatment reagents.
Currently, commonly accepted methods for producing potassium ferrate include melting, electrolysis and wet methods. Among them, the wet methods are most widely used since the electrolytic and melting methods have some disadvantages such as high production cost, high power consumption and explosion risk.
One of the most important problems arising in the production of potassium ferrate is that it is stable in dry air but very unstable in aqueous or humid environments and it is easily decomposed. It is rapidly decomposed to release oxygen in acidic solutions and slowly decomposed in neutral or weak basic solutions. The rate of decomposition decreases as the salinity of the solution increases.
The main focus of the research on the production of potassium ferrate is to maximize its stability.
Ri Su Ryon, a researcher at the Faculty of Chemical Engineering, has examined the stability of the production of potassium ferrate widely used for water disinfection by using KI, K2SiO3 and K3PO4 as stabilizers. The experimental results show that the production of potassium ferrate is stabilized most when the amounts of KI, K2SiO3 and K3PO4 are 0.1%, 0.4%, and 0.4% of the total amount of reactants, respectively. She has also found that having dimethyl sulfoxide, methanol, diethyl ether as a detergent, it is effective to dehydrate first by using dimethyl sulfoxide and, subsequently remove the impurities such as KCl and KOH by using methanol before finally removing the remaining water and methanol by using diethyl ether. It has also been proved that when the washing temperature is lower than 20℃ and the number of washing is three, the potassium ferrate can be kept for a long time.
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Jo Jan 10, 2025
Time delay is one of the common cases in industrial processes such as chemical and metallurgical industries. The controlled value cannot reflect the dynamic change of systems under disturbances because of the existence of time delay. It also results in significant overshoot, longer settling time and even instability of the system. Therefore, the time-delay system (TDS) is more difficult to control.
A lot of control methods have been proposed to overcome the impact of time delay. The complexity of time-delay systems such as long time delay, nonlinearity, stochastic uncertainty and multivariable coupling characteristics limit the application of the existing control theories and methods to actual systems.
ADRC (active disturbance rejection control) is an effective method to solve the control problem of complex structure (nonlinearity, uncertainty, coupling, etc.) systems. The core idea of ADRC regards the integral form as a standard form of feedback system. System dynamics different from the standard form are treated as total disturbance including internal disturbance and external disturbance. A complex system with full disturbance, uncertainty and nonlinearity can be reduced to a linear, canonical form.
Several control strategies based on ADRC have been proposed to handle time delay. According to those strategies, it can be concluded that time delay parameter τ is of vital importance. However,τ may be a time-varying parameter changing with working conditions in real industrial processes.
Kim Ha Su, a researcher at the Faculty of Metal Engineering, has proposed a predictive active disturbance rejection control with adaptability (AD-PADRC) to solve the control problem of a time-varying delay system.
The proposed method is based on the integration of a PADRC and an estimation module for adaptive delay. First, a time-delay system is controlled by PADRC. Then, the time-varying delay is estimated via correlation technique. The minimum variance principle is used as a benchmark to monitor the control performance of a time-varying delay system under AD-PADRC.
The simulation results have proved the efficiency of AD-PADRC when the time delay changes on a large scale.
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