• Journal of the Korean Magnetics Society
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• v.15 no.5
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• pp.270-275
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• 2005

Dust cores (compressed powder cores) of $Fe-6.0wt\%Si$ alloy with a size of $35\~180\;{\mu}m$ in diameter have been prepared by phosphate coatings and annealings at $600\~900^{\circ}C$ for 1 h in nitrogen atmosphere. Further the magnetic and mechanical properties of the powder cores were investigated. As a general trends, the compressive strength and core loss decreased with the increase in annealing temperature. When annealed at $800^{\circ}C$, the compressive strength was 15 kgf, the permeability and quality factor were 74 and 26, respectively. Moreover the core loss at 50 kHz and 0.1 T induction was $750\;mW/cm^3$, and the percent permeability under the static field of 50 Oe was estimated to be about 78. In addition, the cut-off frequency in the cure representing the frequency dependence of effective permeability was measured to be around 200 kHz. These properties of the $Fe-6.0wt\%Si$ alloy dust cores could be considered to be due to the good insulation effect of iron-phosphate coats, the decrease in magnetocrystalline anisotropy and saturation magnetostriction and the increase in electric resistivity.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.102-106
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• 1997

Micro gas sensors including thin film catal) tic type require stress-free memhrancs for etch stop of Si anisotropic etching and sublayer of sensing elements hecause stress is one of the main factors affecting breakdown of thin membranes. This paper reports the effects of deposition conditions on stress and refractive index of $SiN_{x}/SiO_{x}/(NON)$ films deposited by low pressure c11ernic;rl vapor deposition(L, t'CVI)) 2nd reactve sputtering. In the case of I.PCVI1, the stresses of $SiN_{x}$ and NON films arc $7.6{\times}10^{8}dyne/cm^2$ and $3.3{\times}10^{8}dyne/cm^2$, respectibely, and the refractive indices are 3.05 and 152, respectively. In the cxse oi the sputtered SiN, , compressi\e stress decreased in magnitude and then turned to tensility as increasing proc, ess pressure by lmtorr to 30mtorr and cicreasmg applied power density by $2.74W/cm^2$ to $1.10W/cm^2$. The hest value of film stress obt;~ined under condition of lOmtorr and $1.37W/cm^2$ in this' experiment was $1.2{\times}10^{9}dyne/cm^2$ cnnipressive. The refr~ict~ve index decreased from 2 05 to 1 89 as decreasing applied power density by lnitorr to 3Orntorr and increasing process pressure hy $2.74W/cm^2$ to $1.10W/cm^2$. Stresses of films deposited by both LPCVL) and sputtering decreased as incre;lsing temperature and showed plastic behavior as decreasing temperature.

• Transactions of the KSME C: Technology and Education
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• v.3 no.4
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• pp.241-248
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• 2015

Most of the Stirling cryocoolers used for infrared detector cooling in domestic is imported. Because the cooler has a high price, short life and poor durability, demand for the coolers continues steadily. However, the cooler is highly related to defense and space technology, technology transfer or co-development with the countries having experties in cooler design is very limited. The pulse tube cooler to be developed in this study is such that the mechanical piston in low temperature actuating part is replaced by the gas piston and linear compressor is adopted, which results in low vibration, long life and better durability. It is expected that development of the pulse tube cooler will not only improve our technology to the level of advanced countries, but also enhance the skills in designing and manufacturing of the infrared detector.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.1
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• pp.33-39
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• 2020

Lightweight geopolymers were fabricated by using fused slag from integrated gasification combined cycle as a law material and Si sludge from silicon wafer process as a bloating material for the purpose of replacing autoclaved lightweight concrete (ALC). Density and compressive strength of geopolymers were measured and compared with the properties of ALC according to the variation of mol concentration of alkaline activator, W/S ratio, addition of fibers, and addition of polystyrene and the possibility of replacing ALC panel was estimated through the comparisons. Although the geopolymer satisfying the standard of ALC panel was not made by controlling mol concentration and W/S ratio, addition of inserts such as fibers and polystyrene insert was tried to overcome the obstacle of enhancing properties. Geopolymers cannot satisfying the standard of ALC panel by adding carbon or glass fibers; however, adding fibers can be suggested as one of the methods enhancing compressive strength because the compressive strength of the specimen containing 0.3 wt.% glass fibers was increased by 3 times. The maximum addition of polystyrene insert was turned out to be 50 vol.% and the properties of geopolymers varied by the method of insertion. When using single polystyrene insert, compressive strength was 17.8 MPa and density was 0.996 g/㎤ which were similar values to the standard of ALC panel. If the difficulties of reproductivity of production and insertion method of inserts were overcome through the future research, the geopolymers containing polystyrene inserts could possibly replace ALC panel.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.5
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• pp.1-14
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• 2015

In case of a gas turbine engine for supersonic operation, the engine have a wide range of operating inlet mass flow rate and required high performance such as thrust and fuel consumption. Therefore, variable system and its optimal control logic are essentially needed. In this work, a method for performance prediction of a gas turbine engine with variable system compressor and its control scheme were developed. Conceptual design of compact acuation system for the operation of the variable system was also conducted. The performance of a low-bypass ratio mixed flow turbofan engine was analyzed, and it was observed that the surge margin of the engine is improved at off-design condition by applying the control scheme.

• Food Science and Preservation
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• v.11 no.2
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• pp.250-256
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• 2004

The objectives of this study were to develop a new commercial grain cooler suited to domestic weather and post-harvesting conditions for paddy, and to evaluate the performance. A prototype grain cooler capable of cooling paddy of 200 tons within 24 hours was developed. The grain cooler was designed to control the refrigeration capacity from 0 to 100% by controlling the capacity of compressor with unloading solenoid valve and by changing the flow rates of hot refrigerant gas flowing into reheater and evaporator from compressor. And a controller with one chip microprocessor was developed to control temperature and relative humidity of cooling air. The maximum cooling capacity of the grain cooler was 35,284㎉/hr at condensing/evaporating pressure of 16.5/3.6 kgf/$\textrm{cm}^2$. Maximum flow rate of cooling air was 120 ㎥/min at static pressure of 279 mmAq. The total maximum required power was 22.8㎾, and total required energy was saved from 26.7 to 33.3% of maximum power depending on operating conditions. The coefficient of performance of refrigeration devices and total coefficient of performance of the grain cooler were 4.71 and 1.8, respectively.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.363-370
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• 2016

Lightweight geopolymers are more readily produced and give higher fire resistant performance than foam cement concrete. Lowering the density of solid geopolymers can be achieved by inducing chemical reactions that entrain gases to foam the geopolymer structure. This paper reports on the effects of adding different concentrations of aluminum powder on the properties of cellular structured geopolymers. The apparent density of lightweight geopolymers has a range from 0.7 to $1.2g/m^3$ with 0.025, 0.05 and 0.10 wt% of a foaming agent concentration, which corresponds to about 37~60 % of the apparent density, $1.96g/cm^3$, of solid geopolymers. The compressive strength of cellular structured geopolymers decreased to 6~18 % of the compressive strength, 45 MPa of solid geopolymers. The microstructure of geopolymers gel was equivalent for both solid and cellular structured geopolymers. The workability of geopolymers with polyprophylene fibers needs to be improved as in fiber-reinforced cement concrete. The lightweight geopolymers could be used as indoor wall tile or board due to fire resistance and incombustibility of geopolymers.

• Journal of the Korean GEO-environmental Society
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• v.20 no.5
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• pp.31-38
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• 2019

Recently, there has been an increasing number of ground subsidence (sink-hole) in the downtown areas, and in such a case, it is important to minimize accidents and passages through prompt recovery. With respect to the present recovery method for ground subsidence, the methods of applying the back filling after excavating the ground subsidence or using the grouting injected materials to restore the ground are mostly used, but there has been few studies on materials used for recovering the ground subsidence. Therefore, in order to clarify the characteristics of back filling materials used in the ground subsidence, this study uses the environment-friendly hardening agent to improve the dredged clay, and then, the mixture ratio of hardening agent and mixture ratio of decomposed granite soil is changed to cure for 3, 7, 14 and 28 days to analyze the intensity characteristics of the unconfined compression, and it was compared with the unconfined compression intensity for the previously used cement, a hardening agent. In order to evaluate the characteristics of intensity on the back filling materials, the C.B.R test was carried out, and for the review on whether the back filling materials influence on corrosion of water and sewer pipes and others, the soil non-resistance test was carried out. As a result of the test, for the case of the recovery work of the ground subsidence that requires urgency, it is considered as prudent if the hardening agents of 12% are integrated to cure for 3 days or longer, and for not having the influence on the corrosion of the gas tube or water pipes, it is proposed to mix for 30% or more of the decomposed granite soil. Door model test were conducted To confirm the bearing capacity characteristics of the solidified layer.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.43-52
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• 2021

As port development in soft ground is actively promoted for international logistics and transportation, the Deep Mixing Method (DMM) is continuously applied to form an improved column body directly in the ground by mixing cement with soil to secure the stability of the structure. However, in the case of cement, there is a problem of emitting a lot of greenhouse gases during the production process, so the development and use of new alternative materials are socially required to achieve the national goal of carbon neutrality. Accordingly, in this study, CMD-SOIL, developed to induce a hardening reaction similar to cement by recycling recycled resources, was used as a ground improvement material for the DMM. In addition, it was attempted to determine the possibility of replacing cement by conducting on-site test construction and evaluating applicability. As a result of the study, the compressive strength of CMD-SOIL compared to the design reference strength was 1.46 to 2.64 times higher in the field mixing test and 1.2 to 5.03 times higher than in the confirmed boring. In addition, the ratio (λ) of the compressive strength in the field to the design reference strength was 0.63 to 1.14, which was similar to the previous research results. Therefore, in the case of CMD-SOIL, it is possible to express the compressive strength necessary to secure stability, and there is no difference in applicability compared to existing materials such as ordinary portland cement and blast furnace slag cement, so it was analyzed that it could be used as a ground improvement material for the DMM.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.27-32
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• 2003

Diesel-Fueled HCCI(Homogeneous Charge Compression Ignition) Engine is an advanced combustion process explained as a premixed charge of diesel fuel and air is admitted into the cylinder and compression ignited. It has possibility to reduce NOx by spontaneous auto-ignition at multiple points that allows very lean combustion resulting in low combustion temperatures. Also PM could be reduced by the premixed combustion and no fuel-rich zones. But HCCI couldn't be realized because of the difficulties in vaporizing the diesel, control of combustion phase directly. To solve these problems, new fuel injection strategy, explained as the pilot fuel injection to promote ignition near TDC following the main fuel injection at the extremely advanced timing, is applied during the compression ratio is varied from 18.9:1 to 27.7:1 This is not a pilot fuel to promote the ignition but also the direct control method of the combustion phase. Experimental result shows the pilot fuel injection promote the ignition and the compression ignition of the HCCI engine is achieved as compression ratio becomes higher. Also there is an optimal pilot fuel injection timing for the HCCI combustion. NOx is reduced more than 90% compared to DI-Diesel case but PM and THC emission needs more investigation.