Jo May 24, 2023
A research team led by Choe Hyon Chol, a researcher at the Faculty of Mechanical Science and Technology, has proposed a reactor of a new type which ensures smooth ignition of pulverized anthracite coal and determined the most reasonable parameters.
More precise analysis of flow in a non-oil ignition reactor considering the effect of plasma is very important for several purposes such as raising the efficiency of a reactor, lengthening its service life, etc.
First, he proposed a conical air plasma reactor based on the cyclone principle as the most reasonable reactor for the ignition of anthracite coal.
Next, he created a geometrical model of the conical air plasma reactor and meshing and performed a CFD simulation by ANSYS Fluent using an RNG κ-ε turbulence model.
Through the numerical simulation of the joule heating process inside the reactor on an MHD model, he verified that the average temperature on the central axis increases with the cone angle and decreases with the increase in the inlet velocity, and it decreases as the inside diameter of the electrode increases.
The simulation on the electrochemical reaction and combustion process of plasma arc and pulverized coal-air mixture showed that as the cone angle increases, CO quantity increases and then decreases, and as the inlet velocity and the inside diameter of the electrode increase, CO quantity increases.
The reactor is regarded as essential for all kinds of furnaces for high temperature as well as boilers as it uses no heavy oil but pulverized anthracite coal, natural solid fuel.
It is simple in structure, easy to build and environmentally-friendly.
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Jo May 22, 2023
Clustering analysis is being applied to many fields of engineering and social science. One of the most important problems in clustering is to determine the number of clusters properly. The K-means clustering algorithm is widely used due to its simplicity. However, application of this algorithm is restricted by the fact that K must be chosen at the start. Thus, correct selection of K is essential, especially in this algorithm.
Many approaches to infer K and estimate the significance of the clustering result have been proposed. In those approaches, the first thing to be done beforehand is determination of the range of K. And, clustering is performed for every possible value of K, and then the value of the cluster number is determined. This is at a disadvantage of high complexity in the case of a great number of data points or high dimension. This would seem to become more serious when clustering big datasets is required and when it comes to density functions.
Ri Yong Ae, a lecturer at the Faculty of Applied Mathematics, has proposed a new method to determine the cluster number without clustering for every K in K-means.
First, introducing a new statistics RVR (ratio of variance to range), she proposed an algorithm to determine the cluster number K and perform clustering.
Then, to evaluate the effectiveness, she performed a simulation test with different types of datasets.
She has concluded that the proposed method has observed a significant improvement in speed and quality of determination of the cluster number and clustering, and the proposed algorithm would be used efficiently and widely for clustering of multi-dimensional data.
If further information is needed, please refer to her paper “A New Method to Determine Cluster Number without Clustering for Every K based on Ratio of Variance to Range (RVR) in K-Means” in “Mathematical Problems in Engineering” (SCI).
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Jo May 19, 2023
The amount of free chlorine generated by disinfection is one of the core parameters that should be monitored for seawater aquariums.
Ko Kye Hak, a researcher at the Faculty of Chemistry, has proposed a novel analytical method by which the amount of free chlorine in ozonized seawater can be determined by the conventional cyclic voltammetry (CV) with a bare platinum disk electrode without developing any new sensing material.
He determined the amounts of both free chlorine and ozone in ozonized seawater samples by spectrophotometry, which showed that most of ozone was converted to free chlorine.
CV experiments with a bare platinum electrode were carried out for the samples and attention was paid to the fact that the peak current of hydrogen oxidation generated by water electrolysis, which was ignored in the previous studies, depends on the amount of free chlorine in the sample.
The CVs exhibited a well–defined oxidation peak for hydrogen molecules and the linear range of free chlorine amounts in the ozonized seawater samples spanned from 0.02 to 0.4 mg•L–1 with a correlation coefficient of 0.998 2(n=5), a detection limit of 1.2×10–2mg•L–1 at 3σ and a high sensitivity of 4 063μA•cm–2•mg–1•L.
The reproducibility of this technique had a relative standard deviation of 4.41%(n=10).
For more information, please refer to his paper “A novel cyclic voltammetric determination of free chlorine generated by ozone disinfection in seawater aquarium” in “Chinese Journal of Analytical Chemistry” (SCI).
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Jo May 18, 2023
Up to now, a total table has been made manually. BOM (Bill of Materials) of the overall assembly drawing had to be stored as an Excel workbook file after design on SolidWorks before it was processed by various arrays and calculation functions in Excel. This method is laborious and has a high probability of error, thus making it difficult to guarantee the accuracy of calculation results.
A research team led by Kim Kuk Jin, a researcher at the Faculty of Mechanical Science and Technology, has developed a program for automatic generation of total tables, thus saving time and labor for making total tables and increasing the accuracy of calculation.
The program works in the following steps.
First, using the SolidWorks API function, the program reads the data of all parts, standards and subassemblies from the general assembly BOM.
Next, based on the tree root structure and the identity evaluation criteria of the data, the actual number of parts, purchases and standards used in equipment is calculated.
Then, calculation on parts material is performed.
A total table is generated by filling corresponding contents in existing template files.
Some of the problems arising during the generation of a total table are handled in real time and others are displayed in the form of report.
The program can reduce the time for generating a total table from 4~8 hours to 1~2 minutes and guarantee the accuracy of calculation.
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Jo May 16, 2023
The maximum operation temperature of a heater is a very important factor for conserving the quality and performance of the heater. Experimentally, it is difficult, expensive and time-consuming to measure the temperature field distribution of materials, but numerical simulation can easily solve such problems.
Kim Yong Il, a researcher at the Nano Physics Engineering Institute, has found through a simulation that the maximum operation temperature of a laser-induced graphene (LIG) heater with a 1.0cm2 heated area which is written directly on a polyimide film is about 225℃ at an electrical power density of 1.4W/cm2 and a response time of 8s.
The numerical simulation was computed on COMSOL Multiphysics 5.3. He produced a 3D finite element model and boundary conditions of a heat conduction equation in order to simulate the temperature field distribution of an LIG heater by electrical power.
The simulation results were in agreement with the experimental results of previous researches.
The simulation showed that the maximum operation temperature of an LIG heater which is written directly on exposed polyimide substrate can be predicted at any power density and response time without any experiments.
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