Jo Oct 24, 2024
There are many kinds of nitrogen oxide exhausted from vehicles using fuel, but most of them are changed into NO2 after a certain period of time in the natural world and a very small amount of them fatally affect the human body. The very good level of NO2 gas concentration for human body in the atmosphere is below 100μg/m3 and the bad level is over 400μg/m3.
Thus, accurate estimation of NO2 concentration is very important to protect human lives.
Kim Yong Hyok, a researcher at the Faculty of Electronics, designed the structure of a three electrodes system (3ES)-electrochemical NO2 gas sensor and analyzed the action principle based on Nafion membrane material by using qualitative analysis method. In addition, he established the manufacturing process of the sensor and experimentally analyzed the NO2 sensing property depending on the bias voltage properties.
He proved that the optimal bias voltage range is 0.9~1.2V and the sensitivity is 0.31μA/ppm, and that it can sense NO2 gas up to 100ppm linearly.
You can find more information in his paper “Design of Three Electrodes - Electrochemical Nitrogen Oxide Gas Sensors and its Bias Characteristics” in “Journal of Analog and Digital Devices” (EI).
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Jo Oct 22, 2024
IH technology finds its wide application to melting, welding, hardening, cooking and other fields. IH applications use high current passing through an induction coil to produce a sufficient magnetic field and Eddy current within work pieces. Operating frequency is selected by heating application. Resonant circuits are commonly used in IH application to produce powerful current and high voltage to provide maximum output power to the heating load. Recently, the L-LC resonant topology has been widely introduced for its many advantages.
It is widely known that switching devices can be damaged from NON-ZVS operation and spike current generated during the phase shift angle adjustment with fixed frequency to vary the output power and that when the load parameter is changed due to the workpiece, the temperature is close to the Curie temperature. Therefore, the switching frequency must be controlled when the phase shift angle and load parameters are varied to maintain the ZVS operation and prevent the switching device from spike current.
Ri Nam Jin, a researcher at the Faculty of Automation Engineering, proposed a variable frequency phase shift control (VFPSC) to guarantee the ZVS operation and protect the switch from spike current during the heating process.
The proposed technique achieved more efficient performances than conventional fixed frequency control strategies by eliminating NON-ZVS operation and spike current caused by the change of output power and load and guaranteeing zero voltage switching (ZVS) during output power regulation. The theoretical results were verified experimentally on L-LC resonant inverter.
The experiments to validate the proposed control method were conducted on an induction melting of a 3kg Nickel work piece from room temperature to the melting point of 1 600℃.
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Jo Oct 20, 2024
Electrohydraulic servovalves are compact, accurate, broad-bandwidth modulating valves, which are widely used in several industrial applications that need high power and rapid response. Electrohydraulic servovalves can proportionally transform electric analog or digital input signals into stepless hydraulic output signals and they can be single-stage or two-stage servovalves. The first stage (pre-stage) of such servovalves may assume a variety of forms, such as a sliding spool, a nozzle-flapper, a jet-pipe and a deflector-jet.
The present designs of pilot operated servovalves are either of a nozzle-flapper type or of a jet pipe type, and the design aspects and various configurations of servovalves, particularly of a nozzle-flapper type, are available in many references.
However, there have been few studies on the deflector-jet type servovalves. Furthermore, no detailed design approaches and modeling of a deflector-jet type servovalve have been reported so far. Conventional design methods for structural parameters of the fluidic amplifier in the deflector-jet servovalve (DJSV) are confined in their applications due to the lower resolution and narrower working bandwidth of the deflector-jet type servovalve.
Hence, it is very important to develop a new type of electro hydraulic servovalve that has more ideal characteristics. To improve the characteristics of resolution and working bandwidth of DJSV, the most reasonable flow amplification coefficient and pressure amplification coefficient of a fluidic amplifier should be obtained, by properly determining the structural parameters of fluidic amplifiers in the pre-stage.
In order to obtain the most ideal coefficients (pressure amplification coefficient and flow rate amplification coefficient) of fluidic amplifier in the DJSV, Pang In Ho, a researcher at the Robotics Institute, conducted a computer simulation of the effects of the geometric parameters of a fluidic amplifier on the two coefficients.
First, he decided that the important geometric parameters which give the greatest effect on the characteristics of fluidic amplifier are the area and shape of the returning channel of receive ports. Then, he studied the characteristics of the fluidic amplifier, while changing the area of the discharging channel by changing its height.
He built 3D and fluid models for the fluidic amplifier in the DJSV using SolidWorks. He used ANSYS CFD 15.0 to solve the 3D continuity and momentum equations for incompressible flows. The results showed that the pressure amplification coefficient was Kp≈25MPa/mm and the flow rate amplification coefficient was KQ≈0.127L/s·mm-1, which means better sensitivity and better linearity.
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Jo Oct 18, 2024
Silicon carbide powder, complexed in metal matrix, has been widely used to manufacture various tool steels by casting and powder metallurgy as it has excellent hardness, abrasion resistance and heat resistance. However, silicon carbide powder, whose phase is like a kind of ceramic, has low wettability with metal, so when it is complexed in metal matrix, the microstructure of complex material around the particles of silicon carbide is changed, leading to the significant fall in the life of tool steels.
To overcome these disadvantages, there have been some researches to prolong the life of tool steels and to manufacture various functional complex materials by coating the surface of silicon carbide powder with metals such as nickel or copper by electroless plating based on the chemical reaction of oxidation and reduction.
However, there are no reports on the quantitative observation of nickel plating rate and the control of plating thickness on the basis of the reactions taking place during electroless plating on the surface of silicon carbide powder.
Jang Ryong, a researcher at the Faculty of Chemistry, experimentally studied the effects of amount of nickel salt and reducing agent on nickel-plating rate and thickness during the electroless nickel plating on the surface of silicon carbide powder.
He found that during electroless nickel plating on the surface of SiC powder with particle size of 42㎛ the amount of nickel salt should be as small as possible (mass of NiCl2·6H2O is 16.14g in 800mL solution) and the amount of reducing agent NaH2PO2·H2O should be more than 3 times that of nickel salt substance.
Laser Scanning Microscope (LSM) images of non-plated and plated SiC powders (0.5㎛ in thickness) showed that black metallic nickel was evenly coated on the surface of silicon carbide powders.
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Jo Oct 15, 2024
The environmental problems such as air pollution by exhaust gases and global warming are now growing worldwide, and the development of electric vehicles (EV) as a means to solve these problems is gaining attention. Recently, the development of low-volume, energy-density and high-power batteries and high-performance, low-cost rare-earth permanent magnets, and the rapid development of power electronics technology have made the development of electric vehicles more intensive and accelerating.
Vehicle acceleration, single-charging travel distance and maximum slope-climbing capability need to be increased to encourage wide use of electric vehicles like traditional fuel vehicles.
In many references, different driving modes to analyze the dynamic motion characteristics of an electric vehicle were considered and the effects of parameters on the performance of a vehicle and energy consumption were analyzed on MATLAB/SIMULINK.
Ri Tong Hyon, a researcher at the Faculty of Electrical Engineering, studied the mathematical model of an electric vehicle to analyze and simulate its static and dynamic motion. On this basis, he confirmed the technical specifications of a traction motor.
First, based on the simulation analysis of static and dynamic motion, he investigated the traction force characteristics, the driving resistance characteristics, the speed-torque characteristics of the traction motor and the distribution of the operation points of the traction motor in different driving modes. Then, he determined the technical indices including the power, torque and rotational speed of a traction motor with high acceleration performance.
The effectiveness of the proposed method was verified through the simulation.
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Jo Oct 14, 2024
Manganese and its compounds are widely used in various fields of the national economy such as ferrous and nonferrous metal industries, chemical and electrical industries, glass and ceramic industries and agriculture due to their unique physicochemical properties. This leads to the gradual depletion of high-grade manganese ores and, hence, growing concern is focused on the treatment of low grade manganese raw materials. Pyrometallurgy processing of low-grade manganese raw materials consumes a great amount of energy and produces huge waste volume and low yield. Therefore, it is suitable to process such raw materials by hydrometallurgy method.
Sulfuric acid is mainly used as a leaching solvent in the hydrometallurgy process of manganese raw materials. This leaching solution of sulfate contains different impurities such as Fe, Co, Ni, P and As. These impurities reduce the quality of manganese products and affect the technical and economic index of the production process. Hence, it is necessary to remove all the impurities in the liquid in order to obtain the desired product. The impurity which is found in largest quantities is iron. How to remove the iron in high concentration has a considerable effect on process yield, cost of production, working conditions and environments.
Jon Yong Nam, a researcher at the Faculty of Metal Engineering, has proposed a jarosite precipitation and an absorption method by manganese concentrate for removing iron from manganese sulfate leach, and comprehensively analyzed the basic experimental results for their applications.
In the synthesizing process of (NH4)2Fe6(SO4)4(OH)12 using MnSO4 solution, several factors including reaction temperature, reaction time, pH of reaction, seed addition, etc. have significant effects on the removal rate of Fe3+, among which the reaction temperature is the most prominent. The appropriate reaction conditions are 95℃ of reaction temperature, two hours of reaction time, 2.5 of pH of reaction and 15g/L of the addition amount of seed. After Fe in the solution is basically removed by the jarosite method, the remaining iron in the solution can be removed by Mn concentrate absorption. The absorption reaction condition is 65℃, 6.5~7 of pH, 6~8g/L of addition amount of Mn concentrate, and at this time, the Fe content in the solution can be ensured below 0.03g/L.
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