• Biomolecules & Therapeutics
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• 제26권2호
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• pp.182-190
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• 2018

The objective of this work is to evaluate the effect of polyamidoamine (PAMAM) dendrimers on electroosmotic flow (EOF) through skin. The effect of size and concentration of dendrimer was studied, using generation 1, 4 and 7 dendrimer (G1, G4 and G7, respectively). As a marker molecule for the direction and magnitude of EOF, a neutral molecule, acetoaminophen (AAP) was used. The visualization of dendrimer permeation into the current conducting pore (CCP) of skin was made using G4-fluorescein isothiocyanate (FITC) conjugate and confocal microscopy. Without dendrimer, anodal flux of AAP was much higher than cathodal or passive flux. When G1 dendrimer was added, anodal flux decreased, presumably due to the decrease in EOF by the association of G1 dendrimer with net negative charge in CCP. As the generation increased, larger decrease in anodal flux was observed, and the direction of EOF was reversed. Small amount of methanol used for the preparation of dendrimer solution also contributed to the decrease in anodal flux of AAP. Cross-sectional view perpendicular to the skin surface by confocal laser scanning microscope (CLSM) study showed that G4 dendrimer-FITC conjugate (G4-FITC) can penetrate into the viable epidermis and dermis under anodal current. The permeation route seemed to be localized on hair follicle region. These results suggest that PAMAM dendrimers can permeate into CCP and change the magnitude and direction of EOF. Overall, we obtained a better understanding on the mechanistic insights into the electroosmosis phenomena and its role on flux during iontophoresis.

• 설비공학논문집
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• 제6권4호
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• pp.325-336
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• 1994

A numerical simulation of velocity and temperature fields and Nusselt number distributions is performed by using the algebraic stress model (ASM) for the velocity profiles and low Reynolds number ${\kappa}-{\varepsilon}$ model and the algebraic heat flux model(AHFM) for turbulent heat transfer in a $180^{\circ}$ bend with a constant wall heat flux. In the low Reynolds number ${\kappa}-{\varepsilon}$ model, turbulent Prandtl number is modified by considering the streamline curvature effect and the non-equilibrium effect between turbulent kinetic energy production and dissipation rate. Every heat flux term presented in the transport equation of turbulent heat flux is reduced to algebraic expressions in a way similar to algebraic stress model. Also. in the wall region, low Reynods number algebraic heat flux model(AHFM) is applied.

• Nuclear Engineering and Technology
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• 제37권5호
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• pp.457-468
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• 2005

An experimental study on post-CHF heat transfer has been performed with a $3\times3$ rod bundle using a vertical steam-water two-phase flow at low flow conditions. The effects of various parameters on the post-CHF heat transfer are investigated and the reasons for the parametric effects are discussed. As the heat transfer regime changes from CHF to post-CHF, the radial wall temperature distribution is changed depending on the pressure and the mass flux conditions. The superheat of the fluid increases considerably with an increase of the wall temperature (or heat flux) and with a decrease of the mass flux. This implies, indirectly, a strong thermal non-equilibrium at high wall temperature and low mass flux conditions. In order to improve the prediction accuracy of the existing post-CHF correlations, it is necessary to perform more experiments, particularly direct measurement of the vapor superheat, and to modify the correlation by considering a strong thermal non-equilibrium at low flow and low pressure conditions.

• 해양환경안전학회지
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• 제17권1호
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• pp.23-28
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• 2011

조류자원을 평가하기 위해 양쪽이 무한한 바다에 연결되어 있고, 수평한 바닥을 갖고 있는 수로를 가정하고, 수위의 시간변화에 따른 동적효과를 무시한 개수로 유동에서 양 끝단의 수두 차에 의해 구동되는 단순 수로에 대해 에너지 추출 모델을 제안하였다. 조류에너지는 그 단면을 지나는 유속의 3승에 비례하며, 수로 내에서의 에너지 추출은 반드시 유속의 감소를 초래하였다. 교란되지 않는 흐름의 수로에서 10%의 에너지 추출은 약 5.7%의 유속 감속을 초래하며, 20%가 추출되면 유속은 약 11.3%로 감소되었다. 또한, 수로 내에서 더 유속 감소가 가능하다면 이용 가능한 에너지의 추출은 보다 높을 수 있음을 보였다.

• 멤브레인
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• 제8권2호
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• pp.102-108
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• 1998

본 연구는 Si 미립자를 함유한 반도체 세정폐수의 평판막을 이용한 한외여과특성을 검토하였다. 평판막의 투과유속은 시간이 경과함에 따라 점차 감소하는 경향을 나타냈으며, 이현상은 막표면에 형성된 케익층의 증가 및 기공막힘에 기인한다. 흐름형태에 따른 투과유속은 cross flow가 dead-end flow의 약 1.4배 높았다. Si 미립자에 의한 막오염을 제거하는데는 역세법이 sweeping법 보다 우수하였다. 막오염으로 인한 투과유속의 감소는 질소가스로 역세척하여 초기투과유속의 약 85% 정도 회복되었다. 평판막을 이용한 cross flow 공정의 용질배제율은 약 90%였으며, 투과수증의 Si 미립자의 크기는 평균 70 nm였다.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1432-1439
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• 2004

By using unique experimental techniques and careful construction of the experimental apparatus, the characteristics of the local heat transfer were investigated using the condensing R134a two-phase flow, in horizontal single mini-channels. The circular channels (D$_{h}$=0.493, 0.691, and 1.067 mm) and rectangular channels (Aspect Ratio=1.0, D$_{h}$=0.494, 0.658, and 0.972 mm) were tested and compared. Tests were performed for a mass flux of 100, 200, 400, and 600 kg/$m^2$s, a heat flux of 5 to 20 ㎾/$m^2$, and a saturation temperature of 4$0^{\circ}C$. In this study, effect of heat flux, mass flux, vapor qualities, hydraulic diameter, and channel geometry on flow condensation are investigated and the experimental local condensation heat transfer coefficients are shown. The experimental data of condensation Nusselt number are compared with existing correlations.ons.

• Nuclear Engineering and Technology
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• 제51권8호
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• pp.1897-1904
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• 2019

Three-layer back propagation network (BPN) and genetic neural network (GNN) were developed in this study to predict the flow boiling heat transfer coefficient (HTC) in conventional and small-diameter channels. The GNN has higher precision than BPN (with root mean square errors of 17.16% and 20.50%, respectively) and other correlations. The inputs include vapor quality x, mass flux G, heat flux q, diameter D and physical parameter φ, and the predicted flow boiling HTC is set as the outputs. Influences of input parameters on the flow boiling HTC are discussed based on the trained GNN: nucleate boiling promoted by a larger saturated pressure, a larger heat flux and a smaller diameter is dominant in small channels; convective boiling improved by a larger mass flux and a larger vapor quality is more significant in conventional channels. The HTC increases with pressure both in conventional and small channels. The HTC in conventional channels rises when mass flux increases but remains almost unaffected in small channels. A larger heat flux leads to the HTC growth in small channels and an increase of HTC was observed in conventional channels at a higher vapor quality. HTC increases inversely with diameter before dry out.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.21-24
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• 2014

In the entrained-flow coal gasifier, coal ash turns into a molten slag most of which deposits onto the wall to form liquid and solid layers. Critical viscosity refers to the viscosity at the interface of the two layers. The slag layers play an important role in protecting the wall from physical/chemical attack from the hot syngas and in continuously discharging the ash to the slag tap at the bottom of the gasifier. For coal with high ash melting point and slag viscosity, CaO-based flux is added to coal to lower the viscosity. This study evaulates the effect of critical viscosity temperature and ash/flux ratio on the slag behavior using numerical modelling in a commercial gasifier. The changes in the slag layer thickness, heat transfer rate, surface temperature and velocity profiles were analyzed to understand the underlying mechanism of slag flow and heat transfer.

• 수산해양교육연구
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• 제27권5호
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• pp.1310-1317
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• 2015

Two-phase flow boiling heat transfer in micro-channels was experimently investigated. The test section consisted of 15 rectangular micro-channels with a depth of 0.45mm, width of 0.20mm. The experiments were performed for heat fluxes ranging from 5.6 to 46.1kW/m2 and mass fluxes from 150 to 450kg/m2s using FC-72 as the working fluid. According to the results, at the low heat flux region, heat transfer coefficient strongly depends on the heat flux, while heat transfer coefficient at the high heat flux region was independent on the heat flux. Four correlations were used to predict the heat transfer coefficient. The measured heat transfer coefficient was compared with four correlations. It was found that Kaew-On and Wongwises's correlation well predicted the measured data, within the MAE of 40.3%.

• 수산해양교육연구
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• 제28권5호
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• pp.1388-1394
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• 2016

This paper presents a experimental study of two-phase flow boiling of FC-72 in multi channels. Flow boiling heat transfer coefficients are obtained with mass flux ranging from 152.9 to $353.9kg/m^2s$ and heat flux from 5.6 to $46.1kW/m^2$. The experimental results show that the heat transfer is governed by nucleate boiling mechanism in the low heat flux region. However, it is found that the effects of nucleate boiling and forced convection boiling are combined as the heat flux increases. A new correlation to predict the heat transfer coefficient is developed by using the dimensionless number such as Reynolds number, Weber number, boiling number. This correlation shows good predictive accuracy against the measured data.