Jo Jul 12, 2024
Foam glass has been used as insulation material since 1930s. The most important properties of foam glass are light weight, mechanical stability, low thermal conductivity, freeze-thaw cycle resistance, nonflammability and chemical inertness.
There are two methods of producing foam glass according to the kinds of raw materials. One uses glass while the other uses waste glass as raw material. The second method is very simple and consumes less electricity and fuel.
Anthracite fine, graphite powder, soot, calcite, calcium carbide and silicon carbide can be used as a foaming agent. The quantity of foaming agent is 1~7% of finished products.
Previous papers considered thermo-physical properties of foamed glass using a single-system foaming agent.
Pae Kyong Ho, a researcher at the Faculty of Metal Engineering, conducted experiments under different conditions by using a mixture of calcite and hard coal in order to produce low density foam glass with both closed and open porosities and compressive strength of up to 1.8MPa.
The results show that addition of 5wt.% of calcite powder and 2wt.% of anthracite powder ensures the density of foam glass of below 240kg/m3, the compression strength of over 1.8MPa and the heat conductivity of below 0.21W/(m·K).
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Jo Jul 9, 2024
Superhydrophobic materials find their applications in self-cleaning, resistance reduction, corrosion protection, and anti-fogging due to their unique hydrophobicity. Lotus, a natural superhydrophobic material (SHP), has a contact angle (CA) of 162° because it has teat-like microstructures with a diameter of 5-9㎛ and nanostructures with a diameter of 124nm. One of the interesting applications of SHP materials is their self-cleaning ability to prevent and remove contamination of material surface by itself.
Superhydrophobic materials can be prepared by various methods, such as physical and chemical decomposition, chemical etching, anode oxidation, laser etching, chemical vapor deposition, sol-gel method, etc. The sol-gel method is a promising method for large-scale applications (metal, glass, ceramics and plastics), which can improve the mechanical durability of superhydrophobic materials and reduce fabrication cost.
Hollow ash is 10-20% in fly ash, a waste produced by coal-fired power plants. Hollow ash has excellent thermal insulation properties due to its porosity in the particles, so it is widely used as an insulating material.
Kim Jong Ho, a researcher at the Faculty of Chemistry, has formed a thermal barrier layer by using a composite solution of MMA-BA co-polymers and hollow ash, and investigated the functional coatings with high thermal insulation efficiency, self-cleaning ability and anticontamination performance. Based on the literature, he prepared mixed solutions of MMA-BA co-polymers and silica sol by using methyl methacrylate, butyl acrylate, methacrylate-β-hydroxyethyl ester and o-xylene. To maximize the thermal barrier properties and superhydrophobicity of the coatings, he carefully studied the effects of various factors such as the ratio of raw materials, coating thickness, and morphology.
Thermal characterization of the prepared films showed that the thermal insulation effect of the films was enhanced when hollow ash was added to the MMA-BA co-polymers solution.
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Jo Jul 5, 2024
Flexibility is a key concept in the management of modern manufacturing systems. The principal motivation is to achieve rapid response to manager’s demands by improving the efficiency of a job-shop while retaining its flexibility. To achieve this goal, the term flexible manufacturing system (FMS) is defined. FMS is an integrated computer controlled complex of automated material handling devices and numerically controlled machine tools that can process medium-sized volumes of a variety of part types. Flexible manufacturing systems have many potential advantages including high flexibility and high machine utilization rate.
As scheduling is the core of this control system, it plays a decisive role in achieving a goal. FMS scheduling problems are more difficult than those of conventional production systems because of a number of reasons such as machine setup times, part routing and operations scheduling. Flexible manufacturing system scheduling problems are very difficult, so mathematical modeling methods need to be improved to solve them.
Pak Myong Chol, a researcher at the Robotics Institute, designed a scheduler based on a self-adaptive genetic algorithm and obtained the optimal solution for the job-shop schedule. Then, he constructed a flexible production simulation system with the scheduling module and Flexsim and conducted a simulation based on the optimized part scheduling.
The simulation results verified that it is possible to reduce the total machining completion time, increase machine utilization and realize process optimization.
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Jo Jul 2, 2024
ASPEN PLUS, a chemical process design system, is widely used for solving scientific and technological problems arising in the process, device design and process operation, for production of chemicals.
Process simulation techniques have been widely used in the development of new processes because of their high economic effectiveness and scientific accuracy. So far, many researchers have used ASPEN PLUS to simulate gasification processes.
Choe Hyon Il, a researcher at the Faculty of Metal Engineering, has developed an entrained-flow gasification compartment model, which consists of sub-models of pyrolysis, combustion and gasification, by combining the modules provided by Aspen Plus, and analyzed the effects of operating conditions, i.e., oxygen to coal ratio, steam to coal ratio and pressure, on the composition of coal gas.
The results are as follows.
As the oxygen to coal ratio increases from 0.7 to 0.9, the CO content increases by 16% in the outlet gas and the H2 content decreases by about 20%. The CO2 content starts to increase when the oxygen to coal ratio is greater than 0.85. When the steam to coal ratio varies from 0.12 to 0.6, the CO content in the outlet coal gas is reduced by 50% and the H2 content by 29%. As the pressure increases, the effective content in the outlet coal gas decreases, but it is not very large, and especially the effect becomes weaker above 300kPa.
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Jo Jun 30, 2024
The transient electromagnetic method (TEM) is an efficient geophysical prospecting method widely used in mineral exploration, groundwater detection, etc.
When working by TEM, firstly, the transmitter injects the current into the transmitter loop, which will excite the primary magnetic field in the ground. When the transmitter current is abruptly turned off, then the receiver measures the changing rate of the secondary magnetic field using the receiver loop. Ideally, the primary field is therefore absent while measuring. The transmitter loop of TEM system has large inductance and small resistance. Its power supply utilizes rechargeable batteries and the H-bridge inverter is used to generate bipolar pulse current. In most TEM systems, the typical waveform of transmitter current is referred to as a bipolar square pulse. However, in practice, the real current waveform is often distorted and different from an ideal square pulse because of the dynamic characteristics resulting from the inductive load (the transmitter loop), the energy-storage components and the parasitic parameters of circuit elements. The waveform quality of the transmitter current affects the measuring accuracy.
Therefore, there has been a lot of research to further shorten the fall time of current pulse and improve the linearity of falling-edge.
Jang Chol Jin, a researcher at the Nano Physics Engineering Institute, has proposed a TEM transmitter topology using the passive voltage clamp circuit and the divided transmitter loop. The proposed scheme can greatly shorten the fall time of current pulse and improve the linearity of falling-edge, which is of great significance in mine TEM surveys or shallow TEM detections. Besides, it has simple circuit structure.
The details are found in his paper “Fast Turn-off of Pulse Current using the Clamping Circuit and Divided Loop in TEM Transmitter” in “Informatica” (SCI).
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Jo Jun 29, 2024
Accurate evaluation of ozone saturation property in bulk grains is very important for evaluating the effectiveness of ozone treatment on them.
Kim Su Gil, a researcher at the Nano Physics Engineering Institute, has proposed a model of ozone deposition during ozone treatment on bulk grains and evaluated ozone saturation property with the saturation time determined by the model.
First, he built a model of ozone deposition on bulk grains based on a material balance of ozone.
Second, he applied the model to calculate the time-dependent deposition velocities of ozone at various flow rates and depths in columns of wheat grains.
Third, he analyzed the saturation property of ozone in bulk grains based on the deposition velocities and compared it with previous works.
Finally, he determined the surface reaction probability of wheat grains.
You can find the details in his paper “Modeling ozone deposition on bulk grains and ozone deposition in columns of wheat grains” in “Journal of Stored Products Research” (SCI).
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