• 상하수도학회지
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• 제26권6호
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• pp.807-813
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• 2012

Flocculation and flotation are used as pretreatment steps prior to the reverse osmosis (RO) process. During seawater treatment, high temperature can change the water chemistry of seawater during the process of coagulation. It also affects bubble volume concentration (BVC) and bubble characteristics. Coagulants such as alum and ferric salts at $40^{\circ}C$ can also change flux rates in the seawater reverse osmosis (SWRO) process. In this study, the bubble characteristics in dissolved air flotation (DAF), used as a SWRO pretreatment process, were studied in synthetic seawater at $20^{\circ}C$ and $40^{\circ}C$. The flux of an RO membrane was monitored after dosing the synthetic seawater with coagulants at different temperatures. Results showed that BVC increases as the operating pressure increases and as the salt concentration decreases. The bubble size released at $40^{\circ}C$ is far smaller than that at $20^{\circ}C$The addition of a ferric salt is effective for turbidity removal in synthetic seawater at $20^{\circ}C$; it is more effective than alum. When synthetic seawater was dosed with a ferric salt, the RO membrane flux increased by 27 % at $40^{\circ}C$.

• Corrosion Science and Technology
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• 제14권4호
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• pp.195-199
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• 2015

Materials of choice for offshore structures and the marine industry have been increasingly favoring materials that offer high strength-to-weight ratios. One of the most promising families of light-weight materials is titanium alloys, but these do have two potential Achilles' heels: (i) the passive film may not form or may be unstable in low oxygen environments, leading to rapid corrosion; and (ii) titanium is a strong hydride former, making it vulnerable to hydrogen embrittlement (cracking) at high temperatures in low oxygen environments. Unfortunately, such environments exist at deep sea well-heads; temperatures can exceed $120^{\circ}C$, and oxygen levels can drop below 1 ppm. The present study demonstrates the results of investigations into the corrosion behavior of a range of titanium alloys, including newly developed alloys containing rare earth additions for refined microstructure and added strength, in artificial seawater over the temperature range of $25^{\circ}C$ to $200^{\circ}C$. Tests include potentiodynamic polarization, crevice corrosion, and U-bend stress corrosion cracking.

• 한국해양공학회지
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• 제23권6호
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• pp.39-43
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• 2009

A flow and low temperature of deep seawater the biofouling properties in a seawater environment of different materials, such as a steel pipe, polyethylene pipe, and nylon net, used for ocean industries. Experiments in a real sea environment were performed to grasp the quantitative and qualitative biofouling from diatoms attached to materials by measuring the Chlorophyll-a density. Experimental samples were placed under five types of ocean environmental conditions and analyzed every month for five months. It is shown that the biofouling by diatoms was strongly affected by the seawater temperature for all of the experimental samples. It was found that diatoms mainly adhered to the nylon net, while crustaceans prefer polyethylene, under a high temperature condition. It is believed that the biofouling properties are strongly related to the surface roughness of a material. The biofouling under the low temperature condition of deep seawater was rare and stable for the experimental periods. The inside of a pipe conveying deep seawater can be presumed to remain clear without biofouling on the condition of a flow and low temperature of deep seawater.

• 자원환경지질
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• 제33권5호
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• pp.417-424
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• 2000

We applied SP monitoring and resistivity surveys using the pole-pole electrode array to seawater leakage problems in the Youngsan estuary dam and the Eoeun embankment to estimate and detect the zone of seawater leakage. The embankment is generally affected by tidal variation and has low resistivity characteristics due to the high saturation of seawater. For this reason, SP monitoring and the pole-pole array resistivity surveys, which are relatively more effective to the conductive media, were carried out to delineate the leakage zones of sea water through the embankment. We checked out electrical conductivity (EC) and temperature variations along the inner part of Youngsan estuary dam to detect the zone of seawater leakage and found that the measured EC value agreed to that of seawater in the leakage zone and the temperature was lower than that of the vicinity of leakage zone. SP monitoring results were coincided with tidal variations at each embankment. At the leakage zones in the Youngsan estuary dam and the Eoeun embankment, SP anomalies are in the range of -60~-85 mV and -20~-50 mV, respectively, and true resistivity values obtained by 2-D inversion are 3~15 ohm-m and below 0.3 ohm-m, respectively. Both SP monitoring and the pole-pole array resistivity method are found to be quite effective for investigation of seawater leakage zones in the embankment.

• Corrosion Science and Technology
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• 제11권6호
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• pp.263-269
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• 2012

Copper alloys are commonly applied to ship's propellers, pumps and valves which are serviced in seawater due to their good castability and corrosion resistance. In the environment of high flow velocity, however, erosion damage predominates over corrosion damage. In particular, the cavitation in seawater environment accelerates surface damage to copper alloys, resulting in degradation of products and economic losses and also threatening safety. The surface was coated with WC-27NiCr by high velocity oxygen fuel(HVOF) spraying technique to attain durability and cavitation resistance of copper alloys under high velocity/pressure flow. The cavitation test was performed for the WC-27NiCr coating deposited by HVOF in seawater at the amplitude of $30{\mu}m$ with seawater temperature. The cavitation at $15^{\circ}C$ caused exfoliation of the coating layer in 17.5 hours while that of $25^{\circ}C$ caused the exfoliation in 12.5 hours. When the temperature of seawater was elevated to $25^{\circ}C$ from $15^{\circ}C$, more damage was induced by over 160%. Although WC-27NiCr has good durability, corrosion resistance and eletrochemical stability, the cavitation damage rate of the coating layer could remarkably increase at the elevated temperatures under cavitation environments.

• 동력기계공학회지
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• 제14권5호
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• pp.76-82
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• 2010

This paper investigates the optimum operating conditions to construct total automatic control system with high energy efficiency of a newly developed seawater ice machine. The machine has an electronic expansion valve(EEV) and a variable speed rotating drum with an evaporator installed inside. The coefficient of performance(COP) was used as an index to evaluate energy efficiency of the machine. At first, the opening angle of EEV was adjusted to obtain COP of the machine at a constant speed of the drum. Then, we checked seawater ice product versus opening angles of the EEV. Finally, effect of drum's rotating speed in response to product of seawater ice and seawater ice temperature were considered.

• 한국양식학회지
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• 제21권1호
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• pp.41-46
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• 2008

본 연구의 목적은 rotifer Brachionus rotundiformis의 수온과 염분농도의 변화에 따른 이들의 소화효소 활성을 파악하고, 소화효소 활성을 기초로 적정 영양강화 조건을 찾는 것이다. 다른 온도에서 24시간 배양된 rotifer 밀도는 $32^{\circ}C$에서 1,453 개체/mL로 가장 높았다(P<0.05). 그리고 배양온도 $28^{\circ}C$에서 염분농도에 따른 rotifer 밀도는 15 에서 2,147 개체/mL로 가장 높게 나타났다(P<0.05). 배양환경에 따른 rotifer의 소화효소 활성에서 TAP 개체당 활성은 $24-32^{\circ}C$에서 유의적으로 높게 나타났으며(P<0.05), 단백질 비활성은 $32-36^{\circ}C$에서 높게 조사되었다(P<0.05). 그리고 TG-lipase 활성에서는 개체당 활성과 단백질 비활성 모두 $20^{\circ}C$에서 가장 높은 활성을 보였다(P<0.05). 또한 염분별 실험에서 TAP와 TG-lipase 활성은 32 psu에서 가장 높은 활성을 보였다(P<0.05). 32 psu에서 온도별 영양강화한 rotifer의 methionine 함량(% in protein), 지질 함량과 지방산 불포화도이 $20^{\circ}C$에서 유의적으로 높게 나타났다. 특히, DHA와 DHA/EPA 비가 $20^{\circ}C$ 실험구에서 12.6%와 12.5의 비로 각각 높았다(P<0.05). 따라서 rotifer B. rotundiformis의 지질 영양강화는 특히 TGlipase 활성을 높여 줄 수 있는 32 psu, $20^{\circ}C$에서 실시하는 것이 지방산 불포화도, DHA 및 DHA/EPA 비를 높여 줄 수 있는 효과적인 방법이라고 판단된다.

• 한국해양환경ㆍ에너지학회지
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• 제3권2호
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• pp.33-40
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• 2000

해상에 설치되는 담수화 공장의 가동에 따른 환경영향평가를 위하여 고온고염 배출수의 확산을 예측하였다. 진해만에 설치될 담수화 공장에서는 200ton/일의 해수를 유입하여 50ton은 담수화 하고 150ton은 고온고염수로서 배출한다. 배출되는 해수의 수온은 15℃ 상승되며, 염분은 약 1.33배 증가된다. 배출수의 확산예측에서는 2차원 조류모델로 이류를 계산하며, 몬테카르로 방법으로 난류확산을 재현한다. 배출수에 의한 수온상승의 예측에서는 대기를 통한 열량 방출을 감소요인으로 고려하였으며, 100일간의 계산을 통하여 평형상태의 확산분포를 재현하였다. 고염수에 의한 확산에서는 감쇠가 없는 것으로 간주하였으며, 약 1년간의 계산을 통하여 평형상태의 확산분포를 재현하였다. 평형상태에서 배출수에 의한 수은상승과 염분상승은 배수구 근처에 국한되어 나타났으며, 각각 약 0.01℃와 0.001‰의 상승폭을 보였다.

• ALGAE
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• 제18권2호
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• pp.129-134
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• 2003

In order to examine the effects of deep seawater (mesopelagic water in the broad sense) on the growth of macroalgae, the growth and nutrient uptake (nitrate and phosphate) of Ulva sp. (Ulvophyceae, Chlorophyta) were investigated by cultivation in deep seawater (taken from 687 m depth at Yaizu, central Japan, in August 2001), surface seawater (taken from 24 m depth), and a combination of the two. Culture experiments were carried out in a continuous water supply system and an intermittent water supply system, in which aerated 500-mL flasks with 4 discs of Ulva sp. (cut sections of ca. 2 $cm_2$) were cultured at 20$^{\circ}C$ water temperature, 100 $\mu$mol photons $m^{-2}{\cdot}s^{-1}$ light intensity, and a 14:10 light:dark cycle. Nutrient uptake by Ulva sp. was high in all seawater media in both culture systems. The frond area, dry weight, chlorophyll a content, dry weight per unit area, and chlorophyll a content per unit area of Ulva sp. at the end of the experimental period were the highest in deep seawater and the lowest in surface seawater in both culture systems. These values, except for dry weight per unit area and chlorophyll a content per unit area, for each seawater media in the intermittent water supply system were higher than those in the continuous water supply system. We conclude that not only deep seawater as the culture medium but also the seawater supply system is important for effective cultivation of macroalgae.

• 한국표면공학회지
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• 제45권6호
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• pp.264-271
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• 2012

Due to the good corrosion resistance and machinability, copper alloy is commonly employed for shipbuilding, hydroelectric power and tidal power industries. The Cu alloy, however, has poor durability, and the seawater application at fast flow condition becomes vulnerable to cavitation damage leading to economic loss and risking safety. The HVOF(High Velocity Oxygen Fuel) thermal spray coating with WC-10Co4Cr were therefore introduced as a replacement for chromium or ceramic to minimize the cavitation damage and secure durablility under high-velocity and high-pressure fluid flow. Cavitation test was conducted in seawater at $15^{\circ}C$ and $25^{\circ}C$ with an amplitude of $30{\mu}m$ on HVOF WC-10Co4Cr coatings produced by thermal spray. The cavitation at $15^{\circ}C$ and $25^{\circ}C$ exposed the substrate in 12.5 hours and in 10 hours, respectively. Starting from 5 hours of cavitation, the coating layer continued to show damage by higher than 160% over time when the temperature of seawater was elevated from $15^{\circ}C$ to $25^{\circ}C$. Under cavitation environment, although WC-10Co4Cr has good wear resistance and durability, increase in temperature may accelerate the damage rate of the coating layer mainly due to cavitation damage.