• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.667-674
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• 2014

A ship's propulsion shafting system is subjected to varying magnitudes of intermittent loadings that pose great risks such as failure. Consequently, the dynamic characteristic of a propulsion shafting system must be designed to withstand the resonance that occurs during operation. This resonance results from hydrodynamic interaction between the propeller and fluid. For ice-class vessels, this interaction takes place between the propeller and ice. Producing load- and resonance-induced stresses, the propeller-ice interaction is the primary source of excitation, making it a major focus in the design requirements of propulsion shafting systems. This paper examines the transient torsional vibration response of the propulsion shafting system of an ice-class research vessel. The propulsion train is composed of an electric motor, flexible coupling, spherical gears, and a propeller configuration. In this paper, the theoretical analysis of transient torsional vibration and propeller-ice interaction loading is first discussed, followed by an explanation of the actual transient torsional vibration measurements. Measurement data for the analysis were compared with an applied estimation factor for the propulsion shafting design torque limit, and they were evaluated using an existing international standard. Addressing the transient torsional vibration of a propulsion shafting system with an electric motor, this paper also illustrates the influence of flexible coupling stiffness design on resulting resonance. Lastly, the paper concludes with a proposal to further study the existence of negative torque on a gear train and its overall effect on propulsion shafting systems.

• Journal of the Korean Wood Science and Technology
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• v.41 no.4
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• pp.346-357
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• 2013

In this study, it was conducted to produce wood pellets using domestic forest thinning residues and examine their quality according to Korean pellet quality standard. Raw materials were composed of larch and mixed broad leaves species. Based on the small-end diameter (6 cm), they were classified into four different types of raw materials such as LM (larch with middle diameter), LS (larch with small diameter), MM (mixed broadleaf with middle diameter), and MS (mixed broadleaf with small diameter). After crushing and drying process, wood pellets were produced by a ring-die type pelletizer using each raw material. Wood pellets made from four different types of raw materials were tested for their quality such as calorific value, moisture content, ash content, inorganic matters and so on. As results of quality analysis, the calorific values of all wood pellets were higher than 198 kcal/kg, and satisfied with the first grade of Korea wood pellet standard. The ash content was slightly increased after pelletizing. Mechanical durability of wood pellets was highly dependent on the types of raw materials. The quality differences among wood pellets were turned out due to different physical and chemical characteristics of raw materials even though the same pelletizing condition was applied.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.258-258
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• 2013

최근 건조 제품의 양질화, 고급화 및 편의화가 요구되어 이를 충족시키기 위한 새로운 건조방법이 계속 개발 되어 왔다. 이러한 방법들 중에서 저온과 진공하에서 건조가 이루어지는 진공 동결 건조는 가장 완벽한 건조 방법으로 최근 실용화 되고 있다. 진공동결건조란 건조의 한 종류로 수분을 함유한 시료를 동결시킨 후 진공펌프를 이용하여 수증기압을 3중점 이하로 낮추어 얼음을 직접 증기로 만드는 승화의 원리에 의해서 얻어진다. 분무진공동결건조의 특징은 (1) 물리적구조의 보존성, (2) 화학적인 안정성, (3) 생물학적인 활동의 보존성, (4) 제품의 높은 복원성 및 재생성이다. 따라서 분무진공동결건조 기술은 크게 진공, 분무, 동결, 건조, 멸균 등과 같은 요소기술의 복합기술이라 할 수 있다. 분말을 제조하기 위해서 진공동결건조 후 분쇄하는 방법을 사용하나 본 방법에서는 정밀화학품 제조를 위해서 분무진공동결건조 방식을 사용한다. 이를 통하여 적당한 크기인 5~10 um의 입경 제조가 가능하고, 공기동력학적인 입경이 기존 방식에 비해 작아서 허파까지의 운반효율이 1.5~2배 우수하다. 화학, 의학 분야에서의 분무동결 건조는 주로 민감한 제품, 즉 생물학적 고유성의 손상 없이 물을 제거하는데 사용되어 영구적으로 저장 가능한 상태로 보관할 수 있으며 물의 첨가로 원상태로 복구할 수 있어서 매우 각광을 받고 있다. 의약용 냉동건조 제품은 항생물질, 박테리아, 혈청, 백신, 검사 약물, 단백질을 포함하는 생물공학 제품들, 세포, 섬유, 화학제품 등이 있으며 주로 vial 또는 ampule 상태로 건조가 이루어진다.본 연구에서는 원료를 $-194^{\circ}C$의 액체질소에 분무시켜 동결된 미립자를 형성한 후 진공 및 저온상태에서얼음의 승화(sublimation)에 기반한 1차 건조와 수증기 탈착(desorption)에 기초한 2차 건조 과정으로 구성된 분무진공동결건조기를 개발하였다. 분무동결 과정의 해석을 통해 2유체식 노즐을 통해 분무된 미세 입경의 액적이 액체 질소 표면까지 도달하는 회수률, 분무 노즐의 위치, 운전 조건 및 용기의 설계의 최적화를 수행하였다. 초기 액적속도, 분무노즐의 높이, 흡입구 추가에 따른 액적 유동 및 회수의 특성을 제시하였으며 이를 통한 분사시스템 고도화 가능성을 제시하였다. 구형의 미세 입자가 적층된 제품의 동결건조 공정의 해석은 흡착승화 모델(sorption sublimation model)을 기반으로 다음과 같은 열전달, 물질전달, 상변화 모델을 고려하여 유도되었다. 분무노즐 및 냉동/진공 배기계 시작품을 개발하여, 표면의 고다공도를 갖춘 입경 3~20 m 정도의 시료를 얻을 수 있으며, 동역학적 입경 5 m 충족함을 확인하였다.

• Microbiology and Biotechnology Letters
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• v.44 no.4
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• pp.504-511
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• 2016

Lactulose, a synthetic disaccharide, has received increasing interest because of its role as a prebiotic that can increase the proliferation of Bifidobacterium and Lactobacillus spp. and enhance the absorption of calcium and magnesium. While the industrial production of lactulose is still mainly achieved by the chemical isomerization of lactose in alkaline media, this process has drawbacks including the need to remove catalysts and by-products, as well as high energy requirements. Recently, the use of cellobiose 2-epimerase (CE) has been considered an interesting alternative for industrial lactulose production. In this study, to develop a process for enzymatic lactulose production using CE, we screened improved mutant enzymes ($CS-H^RC^E$) from a library generated by an error-prone PCR technique. The thermostability of one mutant was enhanced, conferring stability up to $75^{\circ}C$, and its lactulose conversion yield was increased by 1.3-fold compared with that of wild-type CE. Using a recombinant Escherichia coli strain harboring a CS35 $H^RC^E$-expressing plasmid, we prepared cell beads immobilized on a Ca-alginate substrate and optimized their reaction conditions. In a batch reaction with 200 g/l lactose solution and the immobilized cell beads, lactose was converted into lactulose with a conversion yield of 43% in 2 h. In a repeated 38-plex batch reaction, the immobilized cell beads were relatively stable, and 80% of the original enzyme activity was retained after 4 cycles. In conclusion, we developed a reasonable method for lactulose production by immobilizing cells expressing thermostable CE. Further development is required to apply this approach at an industrial scale.

• Applied Biological Chemistry
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• v.37 no.4
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• pp.295-302
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• 1994

For the development of biological wastewater treatment process using photosynthetic bacteria (PSB), photosynthetic sludge process consisted of anaerobic digestion and PSB reactor were designed for the treatment of swine wastewater and the optimal operating conditions in flask-scale were examined. Photosynthetic bacteria from soil, pond, rice field, ditch etc. were isolated in synthetic medium containing high amount of organic acids and finally isolated one strain KK14 which showed the most degradating ability of organic acids was selected for the treatment of swine wastewater. It was identified as Rhodopseudomonas palustris. In the anaerobic digestion stage, the maximum organic acid productivity was obtained at pH 5.0, $37^{\circ}C$, HRT 2 day and under anaerobic standing condition. The optimal operating conditions of PSB reactor for the treatment of swine wastewater were pH 7.0, $30^{\circ}C$ under 4,000 lux illumination, and optimal initial COD loading (kg COD/kg D. C. W of PSB) was 2 (20% v/v seeding) in the main purification stage. Maximum removal rate of COD reached 92% under the above optimal conditions for 5 days.

• Journal of the Korea Organic Resources Recycling Association
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• v.23 no.2
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• pp.47-52
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• 2015

A microbial fuel cell (MFC) is a device that can be obtained electricity from a variety of organic through the catalytic reaction of the microorganism. The MFC can be applied to various fields, and research is required to promote the performance of the microbial fuel cell for commercialization. The lower performance of an MFC is due to oxygen reduction at the cathode and the longer time of microbial degradation at anode. The MFC amount of power is sufficient but, in consideration of many factors, as a renewable energy, now commonly power density as compared to Nafion117 it is an ion exchange membrane used is PP (Poly Propylene) from 80 to about 11 fold higher, while reducing the cost to process wastewater is changed to a microporous non-woven fabric of a low cost, it may be energy-friendly environment to generate electricity. All waste, in that it can act as a bait for microorganisms, sustainability of the microbial fuel cell is limitless. The latest research on the optimization and performance of the operating parameters are surveyed and through the SSaM-GG(Smart, Shared, and Mutual- Green Growth) or GG-SSaM(Green Growth - Smart, Shared, and Mutual) as the concept of sustainable development in MFC, the middle indices are developed in this study.

• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.700-704
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• 2009

A simulation study on SCR(steam carbon dioxide reforming) in gas-to-liquid(natural gas to Fischer-Tropsch synthetic fuel) process was carried out in order to find optimum reaction conditions for SCR experiment. Optimum operating conditions for SCR process were determined by changing reaction variables such as temperature and $CH_4/steam/CO_2$ feed ratio. Simulation was carried out by Aspen Plus. During the simulation, overall process was assumed to proceed under steady-state conditions. It was also assumed that physical properties of reaction medium were governed by RKS(Redlich-Kwong-Soave) equation. Optimum simulation variables such as temperature and feed ratio were determined by considering $H_2/CO$ ratio for FTS(Fischer-Tropsch synthesis), $CH_4$ conversion, and $CO_2$ conversion. Simulation results showed that optimum reaction temperature and $CH_4/steam/CO_2$ feed ratio in SCR process were $850^{\circ}C$ and 1.0/1.6/0.7, respectively. Under optimum temperature of $850^{\circ}C$, $CH_4$ conversion and $CO_2$ conversion were found to be 99% and 49%, respectively.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.412-418
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• 2020

Generally, the propeller shaft that constitutes the ship shaft system has different patterns of behavior due to the ef ects of engine power, propeller load and eccentric thrust, which increases the risk of bearing failure by causing local load variations. To prevent this, different studies of the propulsion shaft system have been conducted focused the relative inclination angle and oil film retention between the shaft and the support bearing, mainly with respect to the Rules for the Classification of Steel Ships. However, in order to secure the stability of the propulsion shaft via a more detailed evaluation, it is necessary to consider dynamic conditions, including the transient state due to sudden change in the stern wakefield. In this context, a 50,000 DWT vessel was analyzed using the strain gauge method, and the effects of propeller shaft movement were analyzed on the starboard rudder turn which is a typical transient state during normal continuous rate(NCR) operation in ballast draught condition. Analysis results confirm that the changed propeller eccentric thrust acts as a force that temporarily pushes down the shaft to increase the local load of the stern tube bearing and negatively affects the stability of the shaft system.

• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.952-959
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• 2012

The photocatalytic reactor was designed to have improved efficiency by enhancing a light intensity of photocatalytic reactor using a reflector coated on the surface at the outer radius of annular shaped photocatalytic reactor. The improved photocatalytic reactor performed to treat waste air containing malodor and VOC with the enhanced light intensity, of which the effect on their removal efficiency was investigated. The intensities of illumination of the improved photocatalytic reactor filled with porous silica-based media and nonporous glass bead media carrying photocatalyst were observed to increase by 28.5% and 30.1%, respectively, compared to those of photocatalytic reactor without any reflector. Using the improved photocatalytic reactor filled with porous silica-based media and nonporous glass bead media carrying photocatalyst, the removal efficiencies were enhanced by 2~3% and insignificantly, respectively. The removal efficiencies of the optimized photocatalytic reactor with reflectors, filled with porous silica-based media carrying photocatalyst, were observed to increase by 26% and 60%, compared to those of photocatalytic reactor (i.e., 19% and 53%), without any reflector, filled with nonporous glass bead media carrying photocatalyst, for hydrogen sulfide and toluene, respectively. The roughness of used reflector surface was measured to be ca. four times as big as that of a commercial mirror. However, their removal efficiencies are expected to be enhanced by increasing an light intensity resulting from lowering the roughness of used reflector coated on the improved photocatalytic reactor in the future.

• Membrane Journal
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• v.29 no.6
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• pp.339-347
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• 2019

Forward osmosis (FO) is operated at a lower pressure than reverse osmosis (RO), which has great advantages in terms of fouling control, maintenance, membrane cleaning, and potential energy reduction. In particular, since the membrane fouling layer of the forward osmosis process has a relatively loose and dispersed property, it is possible to control the membrane fouling by physical cleaning, unlike the reverse osmosis process. However, existing studies do not apply the proper cleaning flow rate for forward osmosis physical cleaning, and thus there is a limit that the optimal operation can not be performed. Therefore, this study aims to evaluate the justification of proper flow rate that can show high efficiency cleaning with economical energy amount. The membrane fouling experiments of the forward osmosis process were maintained at a circulating flow rate of 8.54 cm/s and the recovery rates were compared with the three cleaning flow rates. As a result of this experiment, it was confirmed that the 2 × speed cleaning showed the same efficiency as the water permeability recovery rate of the 3 × speed cleaning, and it was confirmed that the 2 × speed cleaning was an appropriate flow rate with high cleaning efficiency and economical SEC.