Jo Aug 5, 2022
Ri Yong Ho, a section head at the Faculty of Heat Engineering, has been working hard to make further achievements since he developed a speed control device of a turbo coupling which is widely used in the speed change coupling of a large rotating machine.
The device consists of a turbo coupling, a speed control instrument and a distributed control system.
The fluid coupling, a power transfer device of a rotating machine, can control speed, has a wide control range and has good control characteristics. With a good power transfer characteristic, it can raise energy efficiency.
To use the turbo coupling’s speed control function, we must get a correct understanding of the turbo coupling’s working principle before designing and making a speed control instrument based on it.
The oil system of a turbo coupling consists of a lubricating oil system and a hydraulic oil system. The lubricating oil system functions as a supplier to provide lubricating oil to the coupling’s gears and medals while the hydraulic oil system controls rotating speed. The deeper the coupling is submerged in the oil, the larger the viscosity of oil gets and the faster the output rotating speed gets. The depth of the oil depends on the height of the dipper pipe.
The flow control piston controls oil discharge which passes through the turbo coupling.
The depth of the dipper pipe piston controls the rotating speed; the flow control piston controls the amount of hydraulic oil discharge to allow the turbo coupling to work.
The speed control instrument consists of a rotating motor that converts the control system’s command into the rotation angle, and cam accessories. The rotating motor receives 4~20mA current signals from the control system and in proportion to it, rotates the axis in the range of 0~150°, feeds it back to the control system in proportion to the rotated angle.
Two cams are installed on the axis of the conversion device, and they press on the fluid control piston and the dipper pipe piston individually according to the rotated angle. The main components of the conversion device are the two cams.
Based on the piston’s working principle, the working cycle, the size and installation conditions of the speed control instrument, the cam’s curve radii are decided as follows.
The fluid control cam’s radius: min = 96mm, max =115mm.
The dipper pipe cam’s radius: min = 96mm, max =117mm.
If the above-mentioned turbo coupling is installed between the main feed pump and the motor of the 210MW boiler-turbine block, it controls the rotating speed of the feed pump, which enables to control the output water pressure and the drum level of the boiler.
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Jo Aug 3, 2022
A research group led by Choe Yong Chol, a researcher at the Faculty of Mining Engineering, has been employing his new method of reducing the amount of harmful explosion gas by using vermiculite and acidic deposits of mine water.
Introducing this technology, you can increase the power of explosion much higher than before thanks to the increase in the work ability resulted from the evaporation of combined water in vermiculite as well as the increase in brisance resulted from the increase in explosive density. At the same time, you can reduce the emission of harmful explosion gas such as CO and NOx by adsorption of expanded vermiculite, absorption of water separated from vermiculite and oxidation of metallic oxides in vermiculite at high temperature of explosion.
This method has two stages; manufacturing stage where vermiculite that passed through crushing, separating and distributing processes and acidic deposits of mine water are mixed, and application stage where they are admixed with explosives.
Explosive additives are made with vermiculite of 0.1mm~1.5mm in granulation size and acidic deposits of mine water less than 0.05mm in granulation size in the proportion 3:1. This mixture and Expanded Ammonium Nitrate Explosives are mixed evenly in a ratio of one to five and put into blasting cartridges before use.
Most of the acidic deposits of mine water consist of ferric hydroxide(Fe(OH)3) and basic ferric sulphate(Fe(OH)SO4). In vermiculite, some metallic oxides such as ferric oxide make up about 5.5%, which is less than those contained in acidic deposits of mine water. Trihydric ferric salt and ferric oxides serve as oxidizers that oxidize CO and NO in explosion gas to CO2 and NO2 respectively.
Vermiculite contains about 15% of interformational water which is not changed between micaceous layers at low temperatures but converted into water vapor at over hundreds of degrees. This interformational water removes harmful gases by absorbing soluble gases like NO2, N2O3, N2O4, etc. produced from explosive reactions and from oxidation by trihydric ferric constituents in the additives.
Vermiculite has a strong cation exchange ability. Its cation exchange capacity and base absorption capacity increases by 1.5 times at high temperatures. Thus, at high explosion temperatures vermiculites are expanded and the absorption ability for harmful explosion gas is further increased.
When explosives are mixed with vermiculites and acidic deposits of mine water that are heavier than constituents of explosives, the charge density of explosives increases. Consequently, the detonation velocity and pressure increase and the dynamic explosion power of explosives gets higher.
Vermiculite has a maximum of 18% of interformational and combined waters, which are changed into water vapour at the moment of explosion and expanded thousands of times in volume. It results in a considerable increase in the volume of explosion gas and in the explosion pressure of explosives, which leads to the increase in the static power and blast effects.
If this additive(vermiculit and acidic deposit of mine water) makes up 20% in explosives, removal rate for CO and NOx gases can be more than 93% and 85% respectively. The explosion power of explosives remains similar to or gets higher than before.
With the introduction of this method to all kinds of blasting operations such as driving, you can save a considerable amount of explosives and make a contribution to protecting the environment and improving working conditions by reducing the emission of harmful explosion gas.
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Jo Jul 26, 2022
Formal Concept Analysis (FCA) is considered to be a major formalism for knowledge extraction, reduction, representation and analysis. The core of the mathematical theory of FCA is formal concept lattice.
Determination and description problems on the formal concept lattice are basic ones of FCA. The determination problem is “How can one determine the concept lattice of a given context?” and the description problem is “How can one describe the concept lattice of a given context?”. The most communicative description of the concept lattice is known to be given by Hasse diagrams. However, it is difficult for any information retrieval software to autonomously understand the hierarchy of the concepts from Hasse diagrams. If the hierarchy of the concept lattice is described with a matrix corresponding to Hasse diagrams, any software will be able to autonomously understand the hierarchy of the concepts by the hierarchy-matrix.
In order to obtain such matrix, matrix-correspondence of finite topological spaces obtained by the introduction of Scott topology into the finite concept lattices must be employed and then a new hierarchy-matrix describing the hierarchy of the concept lattice be generated. This idea is based on the matrix-correspondence of finite topological spaces and the fact that Scott topology base is a collection of upper sets of every element. This hierarchy-matrix embodies all the information of the Hasse diagram and is well adapted for use to software.
Pak Chol Hong, a researcher at the Faculty of Applied Mathematics, has proposed a method for generating a new hierarchy-matrix, estimating the connectivity of concepts by the hierarchy-matrix, describing the Hasse diagram via a hierarchy-matrix and generating the hierarchy-matrix via the Hasse diagram in a given finite concept lattice.
The results can also be discussed in universal lattices. If the description of the concept lattices via the hierarchy-matrix is linked up with the determination of the concept lattices, then the formal concept analysis will be used more effectively in several areas of information retrieval, knowledge mining and database management.
Meanwhile, he has proposed that the finite concept lattice is an algebraic lattice and a topological lattice with respect to the Scott topology and the category of finite concept lattices as objects and monotonic mappings as morphisms. These results seem helpful to categorical research into FCA.
More information about this is in his paper “Describing hierarchy of concept lattice by using matrix” presented to SCI Journal “Information Sciences”.
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Jo Jul 24, 2022
Jang Ui Jun, a researcher at the Faculty of Earth Science and Technology, has developed a plasma water treatment device, an experimental device for education and research, which enables experiments for improving the quality of groundwater and surface water to be conducted in combination with laboratory conditions and field characteristics, and verified its utility.
In general, water treatment devices for improving the quality of groundwater or surface water include chlorine sterilizers, various kinds of filters such as activated carbon filters, UV disinfecters, ozone sterilizers and plasma sterilizers.
A plasma water treatment device, one of advanced water treatment devices, is able to overcome the limitations of the above-mentioned water treatment devices and conduct sterilization and water treatment comprehensively and efficiently by means of active chemical species as well as ultraviolet and ozone.
It consists of a power supply unit for geneartion of pulsed high voltage, a plasma reactor, a water sample tank and a water control valve and a tank for treated water.
Using this plasma water treatment device, we can do experiments the aim of which is to reduce the contents of various water quality indicators contained in contaminated surface water or groundwater, especially some elements such as Fe2+, to remove bacteria including Escherichia coli, and to improve water quality.
This device, compared to the aeration method, helps increase the rate of oxidation of Fe2+ ions in water by more than 2.5 times and raise recognition effect by providing visual effects.
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Jo Jul 21, 2022
In recent decades, temperature/pH dual responsive amphiphilic polymers have attracted the interest of researchers as they can perform certain functions by changing hydrophilic and hydrophobic balances corresponding to changes in the external environment. These types of amphiphilic polymers are very useful, especially for drug delivery, tissue engineering, biotechnology and other related fields.
However, most temperature/pH dual responsive polymers are prepared with petroleum chemical monomers as main raw material. This results in its limited applicability due to their toxicity and poor biocompatibility. In recent years, many researchers have focused their work on biomass derivatives to improve the temperature/pH dual responsiveness of polymers.
Jong Kwang Hyok, a section head at the Faculty of Applied Chemistry, has successfully synthesized a novel type of temperature/pH dual responsive polymer, PyHES (2-hydroxy-3-(2-propynyloxy) propyl hydroxyethyl starch)-DMAET (2-(dimethylamino) ethanethiol).
He prepared temperature-responsive polymer PyHES via hydrophobic modification of hydroxyl groups in hydroxyethyl starch (HES) with propynylglycidyl ether (PGE); subsequently, he connected a pH-responsive tertiary amine group to the propynyl group via a thiol-yne click reaction.
As PyHES-DMAET has pH-responsive amino groups and hydrophobic thioether groups, its aqueous solution exhibits excellent temperature/pH dual sensitivity, i.e., a good transference between hydrophobic (or self-assembly) and hydrophilic (or swelling) states resulting from changes in temperature/pH values. These properties can be exploited for hydrophobic drug release.
The experimental results showed that drug release reached 96% at 37℃ and a pH of 6.5, and that the drug-loading capacity of PyHES-DMAET increased with the degree of substitution (DS) of the hydrophobic propynyl groups in the PyHES, and the maximum drug-loading capacity for doxorubicin (DOX) achieved in the study was 33 wt%.
More information about this is in his paper “Temperature and pH dual responsive 2-(dimethylamino)ethanethiol modified starch derivatives via a thiol-yne reaction for drug delivery” presented to SCI Journal “Colloid and Polymer Science”.
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Jo Jul 19, 2022
Pak Song Chol, a researcher at the Faculty of Physical Engineering, has developed an air purifier by making use of the characteristics of non-equilibrium plasma.
The device employs non-thermal plasma, anti-bacterial nano material, ultra-violet ray(UV) and anion, which enables sterilization and air-purification in a pure physical mechanism without recourse to any chemical disinfectant harmful to human body.
The plasma air purifier consists of pre-filter, non-equilibrium plasma generator, activated carbon filter, nano photo-catalyst grid, ultraviolet ray sterilizer, anion generator, etc.
In the non-equilibrium plasma generator, high voltage of 10~15kV should be applied between the line or needle electrode and the plane electrode so that the nuclei of various microorganisms can be destroyed and burnt, and particles be ionized and absorbed. This ensures about 90% of sterilization and dust-collection efficiency for particles smaller than 0.1㎛ in size.
In the nano photo-catalyst grid, UV rays, electrons, excited molecules, oxygen radicals (O2.) collide with TiO2 on the nano-TiO2 grid and activate it. Various chemical reactions take place on the activated TiO2, resulting in formation of hydroxyl radicals(OH.) and activated oxygen atoms with strong organic destruction and sterilization ability.
The ultraviolet sterilizer uses a UV lamp emitting UV rays of 253.7nm in wavelength with high germicidal power.
The anion generator produces a great number of air anions that are good for human health and effective in purification of atmospheric wastes, nitrogen oxides and smoke, neutralizes charged particles and eliminates room odour in an effective way.
Compared with fiber-based filters (95% dust collection rate for particles larger than 0.5μm in diameter) in terms of sterilization property, the plasma air purifier can sterilize more than 95% of room air within an hour and over 98% within two hours.
With the introduction of this device to production processes of foodstuff, various electronic products such as IC and medical appliances, to the interiors of buildings of medical facilities like hospitals, and to large-scale cultural and welfare facilities crowded with people, you will purify the air and guarantee hygienic safety and quality of products.
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