• Environmental Engineering Research
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• 제24권3호
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• pp.418-426
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• 2019

Current available commercial membranes are not robust and are therefore destroyed if left to dry out or handled roughly. Woven fibre microfiltration (WFMF) membranes have advantages over its competitors with respect to durability, thus, favourable for the developing economies and operation during rough conditions. Evaluation of the effects of aeration and brushing as a flux enhancement strategies for WFMF membrane was the purpose of this study. The WFMF membrane was found to be susceptible to pore plugging by colloidal material and adsorption/attachment by microbiological contaminants. This led to a 50% loss in flux. Aeration as a single flux enhancement strategy proved insufficient to maintain high flux successfully. Therefore combined flux enhancement strategies yielded the best results.

• Membrane and Water Treatment
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• 제1권4호
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• pp.253-271
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• 2010

A theoretical study for the flux enhancement by pulsation of transmembrane pressure is presented for osmotic pressure controlled ultrafiltration under laminar flow regime. The transient velocity profile is solved analytically using Green's function method. Time dependent convective diffusive equation is solved to quantify the membrane surface concentration and the permeate flux, numerically. The effects of the amplitude and frequency of pulsation on flux, surface concentration and observed retention are studied.

• Journal of Pharmaceutical Investigation
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• 제41권6호
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• pp.337-345
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• 2011

The objective of this work is to investigate the effect of chemical enhancer and current on the flux of donepezil hydrochloride (DH) through skin. Ethanol and N-methyl pyrrolidone (NMP) were used as chemical enhancers in combination with iontophoresis. We also have studied the effect of pH on flux and evaluated the role of electroosmosis. In vitro flux study was performed at $33^{\circ}C$, using side-by-side diffusion cell and full thickness hairless mouse skin. Passive flux of DH without enhancer was very small. As the concentration of enhancer increased, passive flux increased. After current application, flux increased markedly and the time to reach maximum decreased. Without enhancer, maximum flux was about 50 fold larger than that obtained without current. These results indicate that electromigration is playing a major role for the transport. As the enhancer concentration increased, flux also increased. NMP and ethanol increased not only the passive delivery, but also the iontophoretic delivery. Flux results indicate that ethanol has better ability than NMP in enhancing the transport of DH. The magnitudes of increase in flux by these enhancers indicate that there is a large synergistic effect in flux enhancement. Flux results from pH study showed that electroosmotic flow is reversed at low pH and the flux is hindered. These results provided some information on the flux enhancing ability of ethanol and NMP in combination with iontophoresis. The data also provided some mechanistic insights into the role of electromigration and electroosmosis on flux through skin.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1590-1596
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• 2003

The experiments of boiling heat transfer were performed to investigate the boiling enhancement in saturated water by using multi-stage electroplated surface. In order to optimize the boiling performance, current flux and duration in multi-stage electroplating were varied. Current flux, 2 $A/12cm^2$ and 0.33 $A/cm^2$, and duration ranging from 15 second to 50 second are considered. The results showed that multi-stage electro plated surfaces generate enhancement of boiling parameters such as boiling incipient superheat, boiling heat transfer coefficient, and critical heat flux compared to plain surface. The SEM images of the coated surfaces were captured to examine the structure of porous surface, which provides the enhancement of boiling heat transfer.

• Nuclear Engineering and Technology
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• 제42권3호
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• pp.297-304
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• 2010

In the design of advanced light water reactors (ALWRs) and in the safety assessment of currently operating nuclear power plants, it is necessary to evaluate the possibility of experiencing a degraded core accident and to develop innovative safety technologies in order to assure long-term debris cooling. The objective of this experimental study is to investigate the enhancement factors of dryout heat flux in debris beds by coolant injection from below. The experimental facility consists mainly of an induction heater, a double-wall quartz-tube test section containing a steel-particle bed and coolant injection and recovery condensing loop. A fairly uniform heating of the particle bed was achieved in the radial direction and the axial variation was within 20%. This paper reports the experimental data for 3.2 mm and 4.8 mm particle beds with a 300 mm bed height. The dryout heat density data were obtained for both the top-flooding and the forced coolant injection from below with an injection mass flux of up to $1.5\;kg/m^2s$. The dryout heat density increased as the rate of coolant injection increased. At a coolant injection mass flux of $1.0\;kg/m^2s$, the dryout heat density was ${\sim}6.5\;MW/m^3$ for the 4.8 mm particle bed and ${\sim}5.6\;MW/m^3$ for the 3.2 mm particle bed. The enhancement factors of the dryout heat density were 1.6-1.8.

• Korean Membrane Journal
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• 제1권1호
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• pp.43-49
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• 1999

Separation of soluble oil was investigated during filtration of cutting oil emulsion using various commercial ultrafiltration membranes. The surface properties of membranes used were hydrophilic hydrophobic and modified surfaces by various surfactant pretreatments. Conditions varied include stirring speed transmeembrane pressure membrane type and surfactant type for pretreatment. The results give some indication of mechanisms occurring at the membrane surface. Surfactant pretreatments significantly improved water flux and UF flux of hydrophilic regenerated cellulose(up to 2.4x for YM100) and hydrophobic polysulfone (up to 2.2x for PTHK) membranes depending on surfactant type and operating conditions. The UF flux enhancement was attributed to membrane swelling and reduction of interfacial surface tension between oil droplets and membrane surface. unexpectedly the hydrophilic membranes revealed greater flux enhancement than the hydrophobic membranes. The results also showed a greater improvement in UF flux at lower operating pressure.

• Nuclear Engineering and Technology
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• 제43권3호
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• pp.205-216
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• 2011

Recently, many research studies have investigated the enormous critical heat flux (CHF) enhancement caused by nanofluids during pool boiling and flow boiling. One of the main reasons for this enhancement is nanoparticle deposition on the heated surface. However, in real applications, nanofluids create many problems when used as working fluids because of sedimentation and aggregation. Therefore, artificial surfaces on silicon and metal have been developed to create an effect similar to that of nanoparticle deposition. These modified surfaces have proved capable of greatly increasing the CHF during pool boiling, and good results have also been observed during flow boiling. In this study, we demonstrate that the wetting ability of a surface, i.e., wettability, and the liquid spreading ability (hydrophilic surface property), are key parameters for increasing the CHF during both pool and flow boiling. We also demonstrate that when the fuel surface in nuclear power plants is modified in a similar manner, it has the same effect, producing a large CHF enhancement.

• 한국막학회:학술대회논문집
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• 한국막학회 2004년도 춘계 총회 및 학술발표회
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• pp.82-85
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• 2004

Flux-enhancement mechanism of thin-film-composite (TFC) membranes for the reverse comosis (RO) process was newly explained by positron annihilation lifetime spectroscopy (PALS) that has been found to be applied for detecting molecular vacancies or pores having sizes that are equivalent to salt or hydrate ions in RO membrane.(omitted)

• 대한기계학회논문집B
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• 제20권4호
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• pp.1481-1490
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• 1996

This study is intend to improve flow pattern within evaporator, which is low quality and low mass flux, by installing narrow horizontal annular crevice so that enhance heat transfer coefficient. The motive, which made to study heat transfer enhancement by using narrow annular crevice, came from capillary phenomena and pumping force of generating vapor on refrigerant boiling. Tests were run about 5 models of turbulence promoter with CFC-12, in the range of evaporating temperature (15.deg. C), mass flux (50 to 100 kg/m$\^$2/s), heat flux (3.4 to 6.7 kW/m$\^$2/), quality (0.1 to O.5). It is observed that flow pattern within evaporator is changed closely to semi-annular flow or annular flow, of which refrigerant liquid is reached to the upper side of tube by using narrow annular crevice. When the narrow annular crevice is installed in the evaporator tube, local heat transfer coefficient is generally more improved than that of smooth tube. That fact is according to observed result of flow pattern. It is learned that narrow annular crevice has more efficiency at a low mass flux. At the TP-5, enhancement of heat transfer rate is about 170% compare to that of smooth tube on a low mass flux (50 kg/m$\^$2/s), and it is about 134% on a high mass flux (100 kg/M$\^$2/S), so that we know that it is on a very high condition.

• 대한기계학회논문집B
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• 제40권5호
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• pp.275-281
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• 2016

본 연구에서는 비등표면 위에 다공판을 설치하여 풀비등을 촉진시키는 방안에 대하여 검토하였다. 실험은 대기압에서 R-123을 사용하여 수행되었다. 다공판은 풀비등을 현저히 촉진시켰다. 이는 다공판이 기포를 비등표면 위에 넓게 퍼뜨려 기포와 비등표면 사이 액막의 면적을 증가시키기 때문이다. 또한 높은 열유속에서는 다공도가 클수록, 낮은 열유속에서는 다공도가 작을수록 비등이 촉진되었다. 본 연구에서는 구멍 직경 2.0 mm, 구멍 간격 $2.5mm{\times}5.0mm$ 또는 $5.0mm{\times}5.0mm$, 비등 표면과의 간격 0.5 mm에서 최적 형상이 얻어졌고 이 형상들의 열전달계수는 상용 GEWA-T의 값에 근접하였다. R-123에서의 최적 다공도는 물이나 에탄올에서 보다 현저히 큰데 이는 R-123의 밀도비가 크고 증발잠열은 작기 때문이다. 한편 다공판의 비등이력은 평판보다 작았다.