• Membrane Journal
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• v.17 no.4
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• pp.302-310
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• 2007

The effects of various system parameter on the absorption of sulfur dioxide into the absorbent liquid were investigated in a circulatory porous polymer membrane contactor. A feed gas and an absorbent used in the study were the gas mixture of air and $SO_2$ and the $Na_2SO_3$ aqueous solution, respectively. The separation of sulfur dioxide was measured in terms of the concentration of $Na_2SO_3$ absorbent, the concentration of sulfur dioxide, the feed flow rate, the absorbent velocity and the different membrane material. As the concentration of absorbent increased from 0.05 to 0.2 M, the removal efficiency increased from 74 to 100%. By increasing the concentration of sulfur dioxide from 700 to 2,500 ppm, the removal efficiency decreased from 100 to 75%. Also as the absorbent velocity increased from 2.5 to 15 mL/min, the removal efficiency increased from 85 to 100%. As the porosity of the membrane increased, the removal efficiency increased.

• Korean Journal of Ichthyology
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• v.27 no.4
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• pp.275-283
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• 2015

Habitat characteristics and feeding ecology of Iksookimia pacifica were investigated in this study to provide baseline data for its ecological characteristics in Bukcheon (stream), Goseong-gun, Gangwon-do, Korea. The main inhabit of I. pacifica was found to be sand bottoms of Bb or Bc river type with slow water flow. Based on studies of their habitat preferences according to age, their preference for sand bed was the same. However, their preference for depth and velocity was different. When their age was increased, their depth preference was also increased ($24.9{\pm}17.61cm$ for 0+ year, $69.6{\pm}30.32cm$ for 1+ year, $82.4{\pm}33.30cm$ for 2+ years, and $90.0{\pm}31.55cm$ for $3+{\leq}$ years). The water velocity was found to be 3.8 ~ 4.0 cm/sec for ages between 0+ and 1+ and 6.0 ~ 7.3 cm/sec for ages between 2+ and $3+{\leq}$. They were active on sand from March to November. They would hibernate in sand during the winter season. During the day from 12 pm to 24 am, they were highly active with high food consumption. Their main food sources analyzed with index of relative importance (IRI) include Chironomidae (76.7%), Simuliidae (10.3%), Rotatoria (7.3%), and Arcellidae (2.2%). Their juveniles (total length 20~40 mm) would feed on small-sized preys such as Rotatoria, Copepoda, and Arcellidae. Older I. pacifica would feed on big-sized preys such as Chironomidae and Simuliidae.

• Membrane Journal
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• v.15 no.1
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• pp.52-61
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• 2005

Permeate flux decline in a microfiltration was analyzed by measuring the permeability of bentonite colloidal solution through polyethylene capillary membranes. The flux decline with time was due to the growth of cake layer on the membrane surface and to the pore blocking by particles. As the time approaches to steady state, the permeate flux is almost controlled by the cake filtration model. Faster flux decline at high trans-membrane pressure was attributed to the formation of denser packed cake layer and pore blocking. The ratio of permeate flux to the initial permeate flux, J/J₁, decreased with increasing the trans-membrane pressure, from 45% for 0.5 kg/sub f//㎠ to 38% for 2.0 kg/sub f//㎠. In comparing the ratio of each fouling component to the total fouling for the 0.5 kg/sub f//㎠ TMP condition, complete blocking was 23.4%, standard blocking was about 14.6% and cake filtration was 62.0%, respectively. Permeate flux through the membrane increases with cross flow velocity, and the effect of the variation of velocity is more significant at 1.0 kg/sub f//㎠ rather than at 2.0 kg/sub f//㎠ of the operation pressure. Permeate flux for the membrane having the average pore diameter of 0.34 ㎛ was higher than that for the membrane of 0.24 ㎛ pore size, with the higher flux with the low concentration of feed. On the operation using the membrane of 0.34 ㎛ pore, the pore blocking in the low concentration of 200 ppm is negligible relative to the pore blocking in the 1000 ppm feed.

• The Korean Journal of Ecology
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• v.17 no.4
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• pp.523-531
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• 1994

Optimal conditions for the seed germination and growth of Hedyotis diffusa were studied. As photoperiod was increased from 12 hr to 24hr, the germination rate of Hedyotis diffusa was gradually increased. The photoperiod and temperature inflenced on the fermination synergistically. After the growth of 20 weeks under the natural condition (June~Oct.), the length of H. diffusa was $38.9{\pm}4.2cm$ (15.5~52.5cm), and total dry weight per $3.3m^2$ was $316.7{\pm}10.3g$. It is considered that H. diffusa could be cultivated in a part of inland. The anticancer effect of H. diffusa extract was examined. F-344 rats aged 6 weeks were divided into 3 groups and were given an I.P. of diethylnitrosamine at 200mg/kg body weight as a promoter, initially. And in two weeks after the beginnign of the experiment, group 1 was supplied iwth feed containing 0.02% 2-AAG as a promoter for 6 weeks. Group 2 was supplied with feed containing extracts of H.diffusa (0.02%) for two weeks. Group3 was supplied with only basal diet. All rats were sacrificed for partial hepatectomu, and the antipromoting effect was examined by the number 문 area per $cm^2$ of foci in river. In group 1, the number of hyperplastic nodule was $18.5{\pm}7.7$, but in group2, it was drastically reduced to $10.3{\pm}1.8$ rather thn those of group1. The total area of nodules $(mm^2)$ /whole liver $(cm^2)$ of group 1 and group2 were $19.2{\pm}7.7$ and $5.0{\pm}3.2$, respectively. These results indicate that extract of H.diffusa act as an anticancer agent at statistically significant level (p<0.001).

• Membrane Journal
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• v.20 no.4
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• pp.342-350
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• 2010

Membrane distillation (MD) is a separation process which higher vapor pressure components are evaporated in mixed liquid solution through hydrophobic membrane with 0.1 or $0.5{\mu}m$ pore size. In this study, direct contact membrane distillation process for hollow fiber module were interpreted numerically using the "COMSOL Multiphysics" software. The variables for the system were temperatures and flow rates of lumen and shell side solutions. The permeate flux increased from 1.0 to $3.8L/m^2{\cdot}hr$ as temperature of the feed solution for lumen increased from 30 to $50^{\circ}C$. However the effect of shell solution temperature on permeate flux was relatively low. Also, the optimum velocity of lumen feed was obtained at 0.15 m/s ($Re_L=135$) by considering MD permeate flux as well as operating pressure loss.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.691-698
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• 2017

In this study, the injector transfer function (ITF) of a gas-gas coaxial jet-swirl injector is measured by applying excitation to jet or swirl flow using a loudspeaker. As a result of measuring the ITF according to the variation of feed system length, the ITF peak occurs at the resonance frequency of the space where the perturbed flow passes. When applying the excitation to the jet flow, as the jet flow increases up to 56 slpm, the magnitude of ITF decreases, and ITF increases thereafter. Therefore the larger the velocity difference between the jet and the swirl flow, the larger the ITF. In the case of the swirl excitation, the ITF decreases as the jet flow increases because of the decrease of the energy with respect to the constant flow at the downstream. This difference is caused by the location of the hot wire anemometer on the downstream of the injector center axis.

• Membrane and Water Treatment
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• v.8 no.2
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• pp.113-123
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• 2017

This study investigated effects of physical and chemical cleaning methods on the initial flux recovery of fouled membrane in membrane distillation process. A laboratory scale direct contact membrane distillation (DCMD) experiment was performed to treat digested livestock wastewater with 3.89 mg/L suspended solids, 874.7 mg/L COD, 543.7 mg/L nitrogen, 15.6 mg/L total phosphorus, and pH of 8.6. A hydrophobic PVDF membrane with an average pore size of $0.22{\mu}m$ and a porosity of 75 % was installed inside a direct contact type membrane distillation module. The temperature difference between feed and permeate side was maintained at $40^{\circ}C$ with the feed and permeate stream velocity of 0.18 m/s. The results showed that the permeate flux decreased from $22.1L{\cdot}m^{-2}{\cdot}hr^{-1}$ to $19.0L{\cdot}m^{-2}{\cdot}hr^{-1}$ after 75 hours of distillation. The fouled membrane was cleaned first by physical flushing and consecutively by chemicals with NaOCl and citric acid. After the physical cleaning the flux was recovered to 92 % as compared with the initial clean water flux of the virgin membrane. Then 94 % of the flux was recovered after cleaning by 2,000 ppm NaOCl for 90 minutes and finally 97 % of flux recovered after 3 % citric acid for 90 minutes. SEM-EDS and FT-IR analysis results presented that the foulants on the membrane surface were removed effectively after each cleaning step. The contact angle measurement showed that the hydrophobicity of the membrane surface was also restored gradually after each cleaning step to reach nearly the same hydrophobicity level as the virgin membrane.

• Clean Technology
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• v.29 no.1
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• pp.39-45
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• 2023

To investigate the effects of Mg addition at different aging times and temperatures, Cu/MgO/Al₂O₃ catalysts were synthesized for the low-temperature water gas shift (LT-WGS) reaction. The co-precipitation method was employed to prepare the catalysts with a fixed Cu amount of 30 mol% and varied amounts of Mg/Al. Synthesized catalysts were characterized using XRD, BET, and H₂-TPR analysis. Among the prepared catalysts, the highest CO conversion was achieved by the Cu/MgO/Al₂O₃ catalyst (30/40/30 mol%) with a 60 ℃ aging temperature and a 24 h aging time under a CO₂-rich feed gas. Due to it having the lowest reduction temperature and a good dispersion of CuO, the catalyst exhibited around 65% CO conversion with a gas hourly space velocity (GHSV) of 14,089 h-1 at 300 ℃. However, it has been noted that aging temperatures greater or less than 60 ℃ and aging times longer than 24 h had an adverse impact, resulting in a lower surface area and a higher reduction temperature bulk-CuO phase, leading to lower catalytic activity. The main findings of this study confirmed that one of the main factors determining catalytic activity is the ease of reducibility in the absence of bulk-like CuO species. Finally, the long-term test revealed that the catalytic activity and stability remained constant under a high concentration of CO₂ in the feed gas for 19 h with an average CO conversion of 61.83%.

• Journal of Energy Engineering
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• v.8 no.2
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• pp.248-255
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• 1999

Catalytic cracking of pyrolysed waste lubricating oil over solid acid catalysts (HY zeolite, ${\beta}$-zeolite, HZSM-5) has been carried out in a micro-fixed bed system. The feed oil for catalytic activity tests has been prepared by thermal cracking of waste lubricating oil under the reaction conditions of 480$^{\circ}C$, 60 min. Optimum reaction conditions for the maximum light oil yields($\_$21/) were WHSV(weight hourly space velocity)=1 at 375$^{\circ}C$. The amounts of total and strong acid sites appeared to be the largest in ${\beta}$-zeolite as determined by NH$_3$, TPD. It is seen that the catalytic activity order, in terms of the light fuel oil ($\_$21/) production, were HY zeolite)${\beta}$-zeolite>HZSM-5. Also, coke formation followed the same order. The highest activity in HY zeolite may be attributed from the fact that it has supercages facilitating the easy diffusion of larger molecules and also the effectiveness of the acid sites for cracking within the pore. This fact could be confirmed by the coke formation characteristics.

• Korean Journal of Ecology and Environment
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• v.34 no.4 s.96
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• pp.342-348
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• 2001

The present work is to introduce the preliminary experimental results for a primary hydrocyclones process in lake sediment thickening. A few cyclones based on the Rietema standard geometry were prepared. The test particles were sediments from a local lake and waste coal fly ash for a reference test. As a result of the chemical analysis, organic contaminants were abundantly found in smaller particles in overflow. Experimental results showed that the physical characteristics of particles, configuration of the cyclone and operating variables including feed solids concentration and volumetric flow rate could affect the separation efficiency. The limiting feeding velocity for the separation and enrichment of particles was 1.5 m/s, higher separation efficiency, in general, was obtained under the high velocity with the small cyclones.