• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.75-86
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• 2013

The effects of acoustic resonance and volute geometry on phase resonance are studied theoretically and experimentally using a centrifugal fan. One dimensional theoretical model is developed taking account of the reflection from the discharge pipe end. It was found that the phase resonance occurs, even with the effects of acoustic resonance, when the rotational speed of rotor-stator interaction pattern agrees with the sound velocity. This was confirmed by experiments with and without a silencer at the discharge pipe exit. The pressure wave measurements showed that there are certain effects of the cross-sectional area change of the volute which is neglected in the one dimensional model. To clarify the effects of area change, experiments were carried out by using a ring volute with a constant area. It was demonstrated that the phase resonance occurs for both interaction modes travelling towards/away from the volute. The amplitude of travelling wave grows towards the volute exit for the modes rotating towards the volute exit, in the same direction as the impeller. However, a standing wave is developed in the volute for the modes rotating away from the volute exit in the opposite direction as the impeller, as a result of the interaction of a growing wave while travelling towards the tongue and a reflected wave away from the tongue.

• 한국가시화정보학회지
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• 제15권3호
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• pp.20-26
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• 2017

The two-fluid equations are widely used to simulate two-phase flows in a nuclear reactor. For the two-fluid momentum equation, the wall and interfacial drag terms play an important role in predicting a two-phase flow behavior. Since the bubble density is much smaller than the water density, the bubble accelerates faster than the liquid in a nozzle. As a result, the bubble phase becomes faster than the liquid phase in the nozzle. In contrast, the opposite phenomena occur in the diffuser. The purpose of our study is to experimentally show these behaviors in an area-varying channel such as nozzle and diffuser. Experiments were made of turbulent bubbly flows in an area-varying horizontal channel. The velocities of the bubble and liquid phases were measured by the PIV technique. It was shown that the two-phase velocities were no longer close to each other in the area-varying regions. The bubble was faster than the liquid in the nozzle; in contrast, the bubble was slower than the liquid in the diffuser. Code simulations were also performed using the MARS code. By replacing the original wall drag model in the MARS code with Kim (1)'s wall drag partition model, we obtained the simulation results being consistent with experimental observations.

• Journal of Animal Science and Technology
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• 제56권6호
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• pp.22.1-22.7
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• 2014

The present study was performed to investigate the effects of two groups of sires with 'medium' and 'high' weight gain potentials (M-sires and H-sires, respectively) on growth of their progenies on varying planes of nutrition during the growing-finishing period. The ADG of the M-sires' progeny was greater (P < 0.05) than that of the H-sires' progeny (0.51 vs. 0.47 kg) during a 26- to 29-d early grower phase beginning from 55 d of age, but the opposite was true (0.66 vs. 0.72 kg) during the latter grower phase. Overall grower-phase ADG was greatest on the high plane of nutrition (H plane) followed by the medium (M) and low (L) planes (0.65, 0.61, and 0.51 kg, respectively; P < 0.05) in the M-sires' progeny, whereas in the H-sires' progeny, ADG was greater on the H and M planes vs. L plane (0.63, 0.62, and 0.54 kg, respectively). The ADG of pigs on the M or H plane during the grower phase and switched to the H plane thereafter (M-to-H or H-to-H planes) was greater than that of pigs on the L-to-L planes (0.99 vs. 0.78 kg) during the early finisher phase in the M-sires' progeny (P < 0.01). However, in the H-sires' progeny, ADG of pigs on the L-to-L planes did not differ from that of pigs on the M-to-M or H-to-M planes (0.94 vs. 0.96 kg). Results suggest that the H-to-H or H-to-M planes and M-to-M or M-to-L planes are optimal for maximal growth of the M- and H-sires' progenies, respectively.

• 한국지구과학회지
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• 제32권5호
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• pp.514-520
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• 2011

As homework, a total of 32 seventh grade science-gifted students were asked to observe the moon at daily intervals for one month duration. They were also asked to take the photos and to record relevant variables in a given format. The purpose of the task was to investigate what students thought, as they observed the moon. The results show that students paid attention mainly to the position of the moon relative to other variables such as the date in the lunar calendar, the observer's position on the earth, and the position of the sun. Overall students' response implied that students did not observe the lunar phase in relation with relevant variables. Some reponses from students show common misconceptions such as the cause of the lunar phase to reflect the shadow of the earth. However, some responses reveal students' idea that has been rarely reported in the previous researches. For example, some students drew the moon to revolve in the opposite direction. Significant number of students drew the sun's position to be due west before the full moon and due east after the full moon. Few students recognized the relation between the time of observation and observer's position on the earth. The results of current research suggest that not only the education but also the research needs to be expanded to consider informal environment such as the actual field conditions.

• 대한기계학회논문집B
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• 제26권12호
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• pp.1646-1654
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• 2002

A two-phase closed thermosyphon was one of the most effective devices in the removing heat because of its simple structure, thermal diode characteristics, wide operating temperature range and so on. In this study, a two-phase closed thermosyphon(working fluid PFC(C6F14), container copper(inner grooved surface)) was fabricated with a reservoir which can change the fill charge ratio. The experiments were performed in the range of 50~600W heat flow rate and 10~70% fill charge ratio. The results were compared with some correlations that were presented by Rohsenow and Immura et al. in the evaporator, by Nusselt, Gross and Uehara et al. in the condenser and by Cohen and Bayley, Wallis, Kutateladze and Faghri et al. in heat transfer limitation etc.. The heat transfer coefficient at the evaporator increased with the input power. However the effect of the fill charge ratio was nearly negligible. At the condenser, it showed an opposite trend to the evaporator and with increase of the fill charge ratio, showed some enhancement of heat transfer. The heat transport limitation was occurred by the dry-out limitation for small fill charge ratio(10%) and presented about 100W. For the case of large fill charge ratio(Ψ$\geq$40%), it was occurred by the flooding limitation at about 500W.

• Biotechnology and Bioprocess Engineering:BBE
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• 제7권1호
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• pp.1-5
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• 2002

A fusion protein, consisting of a human epidermal growth factor (hEGF) as the recognition domain and human angiogenin as the toxin domain, can be used as a targeted therapeutic against breast cancer cells among others. The fusion protein was expressed as inclusion body in recombinant E. coli, and when the conventional, solution-phase refolding process was used the refolding yield was very low due to severe aggregation. It was probably because of the opposite electric charge at a neutral pH resulting from the vastly different pI values of each domain. The solid-phase refolding process that exploited the ionic interactions between ionic exchanger surface and the fusion protein was tried, but the adsorption yield was also very low, below $ 30\%$, regardless of the resins and pH conditions used. Therefore, to provide a higher ionic affinity toward the solid matrix, six lysine residues were tagged to the N-terminus of the hEGF domain. When heparin-Sepharose was used as the matrix, the adsorption capacity increased 2.5-3 times to about $88\%$. Besides the intrinsic affinity of angiogenin to heparin, the poly-lysine tag provided additional ionic affinity. And the subsequent refolding yield increased nearly 13-fold, from ca. $4.8\%$ in the conventional refolding of the untagged fusion protein to $63.6\%$. The process was highly reproducible. The refolded protein in the column eluate retained RNase bioactivity of angiogenin.

• 대한화학회지
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• 제39권11호
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• pp.848-855
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• 1995

평판형 열장흐름분획법에서 중력효과에 의한 polystyrene(PS)와 polymethylmethacrylate(PMMA)의 머무름 거동에 관하여 연구하였다. 하향 이동상 흐름의 경우 이동상 흐름 방향과 같은 방향으로 작용하는 중력 효과는 수평면 으로부터 장치각도가 0.deg.에서 60.deg.까지 변화함에 따라 증가하였다. 이 효과는 PS와 PMMA의 머무름 시간을 작게 하였고, 무차원 변수 .lambda.의 값을 증가시켰다. 그리고 분자량이 다른 두개의 고분자 머무름 시간차를 감소시켜 분리기능 저하시켰다. 상향 이동상 흐름의 경우 이동상 흐름의 반재 방향으로 작용하는 중력 효과는 수평면으로부터 장치의 각도가 0.deg.에서 60.deg.까지 증가함에 따라 증가하였다. 이 효과는 PS와 PMMA의 머무름 시간을 크게 하였고, 무차원 변수.lambda.의 값을 감소 시켰다. 그리고 분자량이 다른 두 개의 고분자 머무름 시간 차를 증가시켜 분리능을 향상시켰다.

• 한국산학기술학회논문지
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• 제1권1호
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• pp.15-22
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• 2000

다상유체의 작동에 의해서 그 기능을 수행하는 산업기계는 매우 광범위하게 이용된다. 이들 중 일부는 서로 분리된 2상 유체가 반대방향으로 흐르는 특성을 이용하고 있다. 서로 반대방향으로 흐르는 액체상과 기체상의 최대 유량은 역류유동제한 현상으로 제한된다. 이상유동의 질량 및 운동량 보존 방정식을 세우고 쌍곡선형 방정식이 시스템의 특성방정식으로부터 역류유동제한 현상을 예측할 수 있는 모델을 개발하였다. 현재의 모델은 액체상 유입부의 기하학적 모양이 수직이거나 이와 유사한 형태로 되어 있어서 주변에 비등류가 형성되는 경우에 적용된다. 이 모델은 액체와 기체 사이의 질량전달을 일으키는 기계에 대한 유체역학적 운전제한 조건으로 이용될 수 있다.

• 폴리머
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• 제24권3호
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• pp.342-349
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• 2000

아이소탁틱 폴리프로필렌과 대두유 시스템으로부터 열유도 상분리 및 연신공정에 의하여 중공사막을 제조하였다. 막의 구조와 성능에 관계되는 각종 조업변수들의 영향을 조사하였고 이들을 최적화하였다. 폴리프로필렌/대두유의 용융점도가 microfibril 형성에 영향을 미침을 확인하였고 기핵제를 첨가함에 따라 핵생성 밀도가 증가하여 연신에 의한 구정 간의 기공형성이 향상되었다. 막을 열처리함으로써 연신 시 유도되었던 stress를 이완시켜 막의 수축현상을 방지하여 다공도를 유지할 수 있었다. 기핵제를 첨가한 경우 고-액 상분리에 의하여 구조가 형성되며 응고조의 온도 변화에 따라 핵 생성 밀도가 변화하게 되고 이에 따라 연신에 의한 기공 형성이 영향을 받게 되었다. 기핵제를 첨가하지 않은 경우 핵 생성이 활발하지 않아서 주로 액-액 상분리 거동이 구조 형성에 영향을 미치게 되며 응고조 온도 변화에 따른 효과가 기핵제를 넣은 경우와는 반대의 경향을 나타내었다.

• 한국전기전자재료학회논문지
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• 제35권6호
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• pp.523-546
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• 2022

Morphotropic phase boundary (MPB), which is a special boundary that separates two or multiple different phases in the phase diagram of some ferroelectric ceramics, is an important concept in identifying physics that includes piezoelectric responses. MPB, which had not been discovered in organic materials until recently, was discovered in poly(vinylidene fluoride-co-trifluoroethylene (P(VDF-TrFE)), resulting from a molecular approach. The piezoelectric coefficient of P(VDF-TrFE) in this MPB region was achieved up to -63.5 pC N^-1, which is about two times as large as the conventional value of -30 pC N^-1 of P(VDF-TrFE). An order-disorder arrangement greatly affects the rise of the piezoelectric effect and the ferroelectric, paraelectric and relaxor ferroelectric of P(VDF-TrFE), so the arrangement and shape of the polymer chain is important. In this review, we investigate the origin of negative longitudinal piezoelectric coefficients of piezoelectric polymers, which is definitely opposite to those of common piezoelectric ceramics. In addition to the mainly discussed issue about MPB behaviors of ferroelectric polymers, we also introduce the consideration about polymer chirality resulting in relaxor ferroelectric properties. When the physics of ferroelectric polymers is unveiled, we can improve the piezoelectric and pyroelectric properties of ferroelectric polymers and contribute to the development of next-generation sensor, energy, transducer and actuator applications.