Jo Jul 17, 2024
Spray nozzles are now used in various fields such as agriculture, chemical industry, etc., especially for cooling and dusting devices.
The most important aspect of the characteristics of spray nozzles is droplet size and spray volume distribution. In general, the purpose of almost all spraying is to spray uniformly over the area of spraying. However, it is important to ensure uniform distribution because the spray volume distribution radially from the spray center is not uniform and different distribution patterns are found depending on the flow rate.
Kim Song Won, a researcher at the Faculty of Mechanical Science and Technology, conducted an experimental study on the jet characteristics of a pressure swirling nozzle used for the design of a large cooling tower spraying system, and analyzed the effects of spray water flow rate and the structure of a nozzle outlet and a vortex vane on the spray characteristics.
The study confirmed the following.
First, the droplet size required for the large cooling tower can be achieved by a type X vortex vane in the range of 500 μm to 1000 μm, and the spray volume distribution becomes almost uniform when the vane angle is 120° and the spray flow rate is large.
Second, the smaller the flow rate is, the greater spray volume is concentrated in the spray center, and the larger the flow rate is, the lower the spray volume concentration peak gets and it moves radially.
Third, the length of the nozzle exit section does not significantly affect the spray characteristics in the pressure swirling atomization nozzle.
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Jo Jul 16, 2024
Cuprous oxide (Cu2O) possesses special optical, photoelectric and catalytic properties and it is widely used as a raw material in paints, glass and ceramics industries, and as a catalyst in agriculture and organic chemical industries. Specifically, it is used as a fungicide in orchards. Meanwhile, research works are under way to use it as a poison in the production of antifouling coatings against marine organisms such as mussels and scallops attached to marine structures like ships.
According to the literature, Cu2O is mainly prepared by wet chemistry, electrochemistry, radiation irradiation, polyol, etc. In these methods, operation is complicated and a number of wastes harmful to the environment are released during reactions. Hence, preparation of cuprous oxide by mechanochemical method, a simple and environmentally friendly preparation method, is being investigated.
Mechanochemistry studies physicochemical changes and reactions when energy by mechanoaction is given to the material. In other words, mechanical energy is converted to chemical energy that is needed to drive a thermodynamically impossible reaction with △G>0. Therefore, mechanochemical reactions have some features that are different from ordinary chemical reactions, and the reaction mechanism and thermodynamic and kinetic features are also significantly different from ordinary thermochemical reactions.
Several kinds of reducing agents including sodium sulfite, hydrazine, sodium hypophosphite, sodium borohydride, glucose, etc. are used to prepare cuprous oxide from copper compounds. All of them except glucose are environmentally harmful or hard to purchase. Meanwhile, few reports are related to the preparation of cuprous oxide from copper sulfate by mechanochemical method.
Kim Yong Chol, a researcher at the Faculty of Chemistry, investigated the possibility of preparing cuprous oxide ultrafine particles by the soft mechanochemical method in which copper sulfate and sodium hydroxide were mixed and glucose and sodium dodecyl sulfate (SDS) were added as a reducing agent and a dispersing agent, respectively, before undergoing milling. Then, he observed the effects of reaction time and molar ratio of sodium hydroxide and copper sulfate on the preparation of Cu2O by this method.
He found that cubic ultra-fine cuprous oxide with good dispersion property and initial particles of 36nm can be prepared when the additive amount of sodium hydroxide is 1.2 times as much as the theoretical value and the crushing time is 30 minutes.
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Jo Jul 14, 2024
The fracture occurring in many metallic structures made of steel is mainly fatigue fracture. Fatigue fracture is a dangerous one that decreases the safety of structures. Fatigue fracture occurring in metallic structures is predicted by fracture mechanics method.
Paris suggested a propagation equation for fatigue crack and many researchers found other crack propagation equations by correcting and supplementing Paris’s equation.
However, very few studies have focused on the prediction of the fatigue life of structures and components from the characteristic data of structures comprising metallic materials. For example, the relationship between the metallographic parameters of steel like hardness, volume ratio, grain size and distribution of non-metallic inclusion, etc., and its fatigue life was not quantified.
Kim Mun Chol, a researcher at the Faculty of Materials Science and Technology, simulated the fatigue procedure of a steel structure using a crack-tip sliding model based on continuous distribution dislocation theory and calculated the rest fatigue life of an inertia train structure.
Through the simulation, he found that the hardness of microstructure exerts decisive effects on the fatigue life of steel structures of ferrite-pearlite structure while the grain size and volume ratio hardly affect it, and slip-band crack sharply decreases as inclusion grain size decreases below 7㎛.
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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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