• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.44.2-44.2
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• 2005

• 한국세라믹학회지
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• 제40권4호
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• pp.371-374
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• 2003

Various types of equation for mixing rule on permittivity of mixture have been proposed, but none of these is not perfect because of the inconsistency between the actual geometrical configuration and the basic model for calculation. Serial model and parallel model are lower and upper extremes of mixing manner, the apparent permittivity of any other type of mixture stay between these two extreme states. For the random mixture of the stumpy fine particles, customarily the logarithmic mixing rule has been applied. But, the logarithmic mixing rule does not give the proper value of permittivity in low or high mixing rate of constituent. The author proposed the new mixing rule that gives better consistency with measured value in whole mixing range compared to the logarithmic rule. In this paper, a desirable refinement on the equation proposed in the previous paper is made to adapt to thr configuration image of actual compound and then the equation has been expanded to the complex permittivity to apply the mixing rule on the dissipative materials cases.

• 대한기계학회논문집B
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• 제30권2호
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• pp.144-152
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• 2006

In order to consider the effect of Karman vortex for mixing, mixing indices are calculated for 4 models of micro channel flows driven from the combinations of a circular cylinder and a oscillating stirrer. And their results are compared to that of a simple straight micro channel flow(model I). The mixing rate is improved 5.5 times by Karman vortex (model II) and 11.0 times by the stirrer(model III) respectively. In case of successive mixing by the cylinder and the stirrer(model IV), $27\%$ of shortening the channel length for the complete mixing as well as 1.37 times improvement of mixing efficiency then model III. And then, variation of mixing indices are much stable comparing with the others. Thus, it is found that the Karman vortex plays a good role as a pre-mixing method. The D2Q9 Lattice Boltzmann methods are used.

• 에너지공학
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• 제11권4호
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• pp.306-316
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• 2002

본 연구에서는 공기청정기의 최적설계에 필요한 자료를 획득하기 위해 다양한 실내공간에서의 유동에 대한 연구를 수치해석적인 방법으로 수행하였다. 실내유동 해석을 위해서 사용된 공기청정기의 사용처로는 물류창고, 아파트 거실과 주방, 6인 병실을 선정하여 계산을 수행하였다 시간에 따른 평균농도 변화는 모든 실내공간에서 완전 혼합(perfect mixing)인 경우와 매우 흡사하게 나타나는 것을 볼 수 있었고, 공기청정기의 설치 위치가 시간에 따른 실내의 평균농도 변화에 미치는 영향은 미미한 것을 볼 수 있었다. 실내의 국부적인 농도를 살펴보면 사용처 별로 유동의 흐름이 원활하지 못해서 생기는 공기정화 취약구 역을 관찰할 수 있었으며, 이는 각 공간모델과 공기청정기의 설치위치에 따라 크게 달라지는 것을 볼 수 있었다.

• 상하수도학회지
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• 제23권6호
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• pp.799-810
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• 2009

With time, the stable management of turbidity is becoming more important in the water treatment process. So optimization of coagulation is important for the improvement of the sedimentation efficiency. we evaluated the mixing and hydrodynamic behavior in the coagulation basin using Computational Fluid Dynamics (CFD). The items for evaluation are a location and the speed of agitator and angle of an injection pipe. The results of the CFD simulation, the efficacy of mixing in the coagulation basin was not affected according to one or two injection pipe and angle of an injection pipe. If there is a agitator near outlet of coagulation basin, the efficacy of mixing don't improve even though the speed of agitator increase. So location of agitator is perfect when it locate center at the inlet stream. The coagulation basin at this study, the proper speed of agitator is form 20rpm to 30rpm.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.525-530
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• 2000

The effects of vortex generators, in the form of small tabs projecting into the flow at the axisymmetric supersonic nozzle exit and triangular thin tapes attached on the inner surface at the nozzle exit, on the characterixtics of supersonic mixing enhancements are experimentally investigated. Delta-shaped tabs as small as 1% of the nozzle exit area produce strong counter-rotating vortices, and is found to produce significant effects on the jet flowfield downstream of the nozzle. The effects is larger on the under-expanded cases than over- and perfect-expanded cases. Nozzle inner surface roughness also can do a role of centerline pressure decay for highly under-expanded jet cases. The effects of the angle of tabs with respect to flow direction are also investigated.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.320-329
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• 2008

The influence of thermodynamic transition associated with transcritical nitrogen injection upon the flow structure was investigated to explore numerical simulation of the injectant dynamics of oxygen/hydrogen coaxial jet in liquid rocket engines. Single and coaxial nitrogen jets were treated by comparing the transcritical and perfect-gaseous conditions, wherein the numerical model was accommodative to the real-fluid thermodynamics and transport properties at supercritical pressures. The model was in the first place validated by comparing the results of transcritical nitrogen injection between calculations and available experiments. For a single jet under the transcritical condition, the nitrogen kept a relatively high density up to its pseudo-critical temperature inside the mixing layer, since it remains less expanding until heated up to its pseudo-critical temperature. Numerical analysis revealed that cryogenic jets exhibit strong dependence of specific enthalpy profile upon the associated density profile that are both dominated by turbulent thermal diffusion. In the numerical model, therefore, exact evaluation of turbulent heat fluxes becomes very important for simulating turbulent cryogenic jets under supercritical pressures. Concerning the coaxial jets due to transcritical/gaseous nitrogen injections, the density profile inside the mixing layer was again affected by the thermodynamic transition of nitrogen. However, hydrodynamic instability modes of the inner jet did not show significant differences by this thermodynamic transition, so that further study is needed for the mixing process downstream of the near injection position.

• Journal of Biosystems Engineering
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• 제27권5호
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• pp.381-390
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• 2002

Direct seeding of rice-seed pellets is expected to be an alternative for solving problems in current direct seeding cultivation of rice. but mass production of rice-seed pellets is prerequisite for practical application. Design. construction and performance evaluation of an experimental rice seed pelleting machine were carried out for mass production of rice-seed pellets. The pelleting machine intended to make a ball type rice-seed pellet, which have 3∼5 rice seeds and diameter of which is 12 mm. Pellet materials ; rice seeds, soil, and binder were mixed and kneaded by the mixer. The designed rice seed pelleting machine fed pellet materials by screw conveyor to forming rolls and made rice-seed pellets. Capacity, ratio of perfect rice-seed pellets, seed and pellet material loss were investigated as mixing ratio of soil to rice seed and feeding rate of pellet materials. The pelleting machine showed up to 37,000 pellets/h of pelleting rate, 61∼71% of weight ratio of perfect rice-seed pellets to pellet materials supplied, 17∼48% of seed loss ratio. Average weight and average diameter of the pellets were 1.66 g and 12.0 mm. respectively. More than 3 rice seeds were included in most pellets at 6 : 1 of mixing ratio of soil to rice seed. And compression strength of the pellets was in the range of 88-130 N. To improve performance of the pelleting machine, improvements of the forming rolls, feeding mechanism, and discharging mechanism for reducing loss of pellet materials and seeds damage are needed.

• Journal of Biosystems Engineering
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• 제20권3호
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• pp.288-298
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• 1995

In greenhouse vegetable, the automatic control in cultivating environment has been projected as a national business ; especially a countermeasure against the settlement of UR negotiation. Because it makes possible to manage a large greenhouse with family-hands and to expect the betterment of quality and the increasement of harvest in crops. In the course of carrying the workout, however, there are many problems with the overall control system with computers as well as the individual systems for environment control because of hardware and software problems : especially the shortage of data for development of the system is most serious. Among the many problems for development of the automatic control system, the automations of irrigation, liquefied fertilizer and chemical solution, mixing and ventilation, etc and the development of the general automatic controller system for environment control in greenhouse are studied, which requires a lot of tabors. The results are summarized as follows ; 1. In moisture control by the soil moisture meter, the error was shown 10 % in the beginning irrigation point and 19 % in the stop irrigation point. 2. The supply of liquefied fertilizers with the irrigation system was excellent by setting the operating time and the mixing ratio. 3. The developed chemical spraying system was operated well, but not perfect in nozzle positions. 4. The cucumber was cultivated properly with the trickle irrigation system. 5. The developed controller for the automatic control system in greenhouse was remarkable in the part of hardware, but more researches are needed in the part of software.

• 한국분말재료학회지
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• 제28권4호
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• pp.287-292
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• 2021

In this study, the layered structures of immiscible Fe and Cu metals were employed to investigate the interface evolution through solid-state mixing. The pure Fe and Cu powders were cold-consolidated by high-pressure torsion (HPT) to fabricate a layered Cu-Fe-Cu structure. The microstructural evolutions and flow of immiscible Fe and Cu metals were investigated following different iterations of HPT processing. The results indicate that the HPT-processed sample following four iterations showed a sharp chemical boundary between the Fe and Cu layers. In addition, the Cu powders exhibited perfect consolidation through HPT processing. However, the Fe layer contained many microcracks. After 20 iterations of HPT, the shear strain generated by HPT produced interface instability, which caused the initial layered structure to disappear.