• 한국가시화정보학회지
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• 제19권3호
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• pp.84-91
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• 2021

Effervescent tablets generate gas bubbles when chemical reaction occurs between water and tablets. Most of previous studies have been focused on pharmaceutical characteristics of tablets. However, for their applications in disinfectants, cleaners, and pesticides, physical characteristics of bubbles released from the effervescent tablets when they are in water are important. In this study, we experimentally investigated the characteristics of microbubbles generated by an effervescent tablet made of sodium bicarbonate and tartaric acid using PDPA and high-speed camera. Microbubbles were generated using different weights of effervescent tablet as well as in different water temperature. The experimental study shows increase in reaction time, bubble concentration and rise velocity as the weight of effervescent tablet increases from 1 to 20 g. The decrease in average bubble diameter was observed when the temperature of water increased from 25 to 45 ℃. Further, reaction time varies inversely with increase in water temperature, while bubble rise velocity is directly proportional to increase in water temperature. Effervescent table continuously generates the bubble with approximately constant diameter (235 ㎛) in the water. However, bubble concentration and bubble rise velocity decreased over time.

• Journal of Biosystems Engineering
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• 제39권4호
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• pp.336-344
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• 2014

Purpose: In this study, the effect of milling on paddy rice stored at low temperature, the changes in grain temperature of bulk storage bags exposed at room temperature, the post-milling water content of paddy rice, the whiteness of rice, and the rate of pest incidence were investigated and data were analyzed. Methods: Changes in temperature inside the bulk storage bags kept at low temperature and grain temperature after exposure to room temperature were measured. Experiments were conducted for identifying the reasons of post-milling quality changes in paddy rice stored at low temperature. Results: It was determined that a short-term increase of water content in paddy rice was directly related to surface condensation, and that rice should be milled at least 72 h after removal from low-temperature storage, in order to completely eliminate surface condensation of paddy rice kept in bulk storage bags. It was observed that post-milling quality of rice changed, but water content was maintained at high levels for more than 18 d in rice that was milled when condensation occurred, regardless of paper or vinyl packaging. Rice whiteness rapidly decreased in rice that was milled when condensation occurred, regardless of packaging, while rice that was milled 72 h or more after removal from low temperature storage did not show any significant changes in whiteness. No pest incidence was observed up to 12 d after removal from low temperature storage, regardless of packaging. Starting at 18 d, after removal from low temperature storage, rice that was milled when condensation occurred, was affected by pests, while 24 d after removal from low temperature storage, all portions of rice were affected by pests. Conclusions: Our results suggest that changes in post-milling quality of rice could be significantly reduced by exposing paddy rice to room temperature for at least 72 h before milling, in order to allow the increase of grain temperature and prevent surface condensation.

• 한국습지학회지
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• 제19권4호
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• pp.409-422
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• 2017

월동수조류의 군집에 영향을 미치는 환경요인을 파악하기 위하여 원주천을 6구간으로 나누어 조류의 군집 및 하천의 크기, 기온, 수질, 저서성무척추동물, 어류를 조사하였다. 원주천에서 수조류의 군집에 영향을 미치는 요인은 하천의 구조 및 기온, 수질이었다. 하천의 구조 중 월동수조류의 군집에 가장 큰 영향을 미치는 요인은 저수로의 폭과 흐르는 물의 넓이인 유폭으로 그 넓이가 넓을수록 월동수조류의 종수와 개체수가 많았으며, 둔치의 폭이 넓어서 저수로의 폭과 유폭이 좁아질수록 개체수는 적었다. 월동기의 기온 변화는 하천의 결빙으로 이어지므로 수조류의 군집에 영향을 미쳤으며 결빙되지 않는 구간은 기온의 하강과 상승에 뚜렷한 증가와 감소를 보였다. 수질조사 항목 중 pH, 수온, COD, BOD, T-N, T-P, 총대장균의 수치는 하류로 갈수록 증가하여 월동수조류의 개체수 증가와 높은 상관성을 보였는데 하류에 위치한 하수처리장의 영향으로 S6의 수질검사 항목의 수치가 높게 나타났으며 월동수조류의 개체수 또한 가장 많이 관찰되었다. 하수처리장 배출수는 수질에 상당한 영향을 미치는 것으로 보이는데 T-N을 비롯하여 여러 항목 수치의 증가는 하천의 영양화를 촉진시키고 이로 인해 유기물질의 축적과 수서생물의 증식을 가져옴으로 이를 먹이원으로 하는 월동수조류의 증가 원인이 될 수 있을 것으로도 여겨진다. 저서성 대형무척추동물의 군집과 어류의 군집은 원주천 모든 구간에서 대체적으로 양호한 것으로 나타났으나 월동수조류의 군집과의 상관성을 보이지 않았다.

• 콘크리트학회논문집
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• 제16권5호
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• pp.597-604
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• 2004

본 연구는 실리카퓸을 사용한 고강도 콘크리트의 고온하의 압축강도의 저하 및 공극률 변화를 통하여 강도 감소와 공극구조와의 연관성을 검토하였다. 또한, 실리카퓸 혼입의 유무와 각 가열온도에서의 시멘트 수화물의 탈수에 의한 공극특성의 변화에 관한 기초 데이터를 제공하고자 하였다. 연구결과, 실리카퓸의 혼입에 따른 필러효과 및 물-결합재비의 차로 인해 공극률 및 공극분포는 다르게 나타났다. 가열온도가 상승함에 따라 공극률도 점진적으로 증가하는 경향을 보였다. 또한, $600^{\circ}C$ 이상의 고온에서의 경향성은 더욱 현저하였다. 가열온도의 상승에 따라 $0.1{\~}0.5{\mu}m$공극의 증가는 현저하였으며 이는 모세관 공극의 수분의 증발 및 C-S-H계 수화물 및 수산화칼슘이 분해되어 결합수가 탈수한 결과이다. 고열에 의한 신축도 콘크리트 내부의 미세균열을 발생시켜 공극률 증가를 유발한다. 이러한 공극률 증가는 가열온도에 따라 일정한 경향성을 띠므로 화해를 입은 콘크리트의 수열온도 및 국부적인 성능저하를 예측할 수 있을 것으로 기대된다.

• Applied Biological Chemistry
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• 제31권1호
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• pp.46-51
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• 1988

대두를 tap water와 0.5% $NaHCO_3$ 용액에 침지시켜 수화속도에 미치는 침지온도의 영향에 대하여 실험하였다. 그 결과 침지온도가 높아 질수록 수화속도는 빠르고 세품종중 크기가 가장 작은 단엽이 tap water에 침지 할때나 0.5% $NaHCO_3$ 용액에 침지 할때도 모두 빨랐다. Arrhenius식을 사용하여 수화에 따르는 활성화 에너지를 계산하였고 일정 수분 함량에 도달하는데 필요한 시간과 침지온도와의 관계를 z값으로 나타내었을때 대두의 수화도가 증가 할수록 tap water에 침지할때나 0.5% $NaHCO_3$ 용액에 침지 할때도 z값이 감소하는 경향을 보였다.

• 한국지반공학회논문집
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• 제33권11호
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• pp.45-57
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• 2017

연약지반의 압밀거동은 온도변화에 의하여 영향을 받는다. 연약 점토지반 내에 온도가 증가하면 간극수압이 증가하고 간극수압의 소산은 부피와 간극비를 감소시킨다. 또한 높은 온도는 간극유체의 점성을 감소시키므로 압밀속도가 빨라진다. 본 연구에서는 온도가 압밀침하량, 압밀시간, 간극수압과 같은 압밀거동에 미치는 영향을 분석하였으며, 이를 위하여 수리역학적(HM) 및 열수리역학적(THM) 거동에 대한 수치해석을 수행하였다. 열주입과 샌드드레인을 동시에 고려하였으며, 온도 변화 및 샌드드레인 직경 변화를 고려하여 해석을 수행하였다. 해석결과, 시료내부의 온도는 열원의 온도와 샌드드레인의 직경 증가에 따라 증가하는 것으로 나타났다. 또한 열주입은 과잉간극수압을 증가시키고 그에 따라 과압밀 영역에서는 추가적인 침하량을 유발하고 정규압밀 영역에서는 압밀시간을 감소시키는 것으로 나타났다.

• Membrane and Water Treatment
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• 제10권5호
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• pp.387-394
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• 2019

Membrane distillation (MD) is one of the water treatment processes which involves the momentum, heat and mass transfer through channels and membrane. In this study, CFD modeling has been used to simulate the heat and mass transfer in the direct contact membrane distillation (DCMD). Also, the effect of operating parameters on the water flux is investigated. The result shows a good agreement with the experimental result. Results indicated that, while feed temperature is increasing in the feed side, water flux improves in the permeate side. Since higher velocity leads to the higher mixing and turbulence in the feed channel, water flux rises due to this increase in the feed velocity. Moreover, results revealed that temperature polarization coefficient is rising as flow rate (velocity) increases and it is decreasing while the feed temperature increases. Lastly, the thermal efficiency of direct contact membrane distillation is defined, and results confirm that thermal efficiency improves while feed temperature increases. Also, flow rate increment results in enhancement of thermal efficiency.

• 한국농공학회지
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• 제32권E호
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• pp.74-79
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• 1990

Important factors in evaluating solar collcetor efficiency are solar radiation, temperature and flow rate of the working fluid. The effects of these factors on the energy and the exergy gained by water, the working fluid, from the collector were analyzed. The results indicated that the collector efficiency and the energy and the exergy gained by the water from the collcetor increased with the increase of solar radiation. According to the exergy analysis, as the water temperature at the inlet of the collector increased, the exergy gained by the water increased while the energy gained by the water decreased. The water temperature at the outlet of the collector could be calculated with a mean error of 2.8%, and the energy and the exergy could be calculated theoretically with mean errors of 16.8% and 19.1%, respcetively.

• 설비공학논문집
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• 제15권8호
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• pp.690-696
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• 2003

This paper presents the heat recovery performance of water fluidized-bed heat exchanger. Temperature and humidity ratio of waste gas are considered as important parameters in this study. Therefore, the heat recovery rate through water fluidized-bed heat exchanger for exhaust gases with various temperatures and humidity ratios can be estimated from the results of this study. Mass flow ratio (the ratio of mass flow rate of water to that of gas) and temperature of inlet water are also considered as important operating variables. Increase of heat recovery rate can be obtained through either high mass flow ratio or low temperature of inlet water with resultant low recovered temperature. The heat recovery performance with the mass flow ratio of about up to 10 has been investigated. The effect of number of stages of water fluidized-bed on the heat recovery performance has been also examined in this study.

• 오토저널
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• 제4권3호
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• pp.24-39
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• 1982

It has already been known that quenching effect is influenced greatly by stirring and changing coolant's temperature on quenching. But according to the past investigations its effect has not been taken into consideration quantitatively in the cooling process. The purpose of this study is that the influence of flow rate and temperature on the quenching effect of cooling water as quenching medium is quantitatively examined by using the open channel. The stream of water in this study is turbulent flow. The temperature of the specimen made of pure copper is measured by CA thermocouple in the vicinity of the surface and recorded by an automatic recorder during the quenching process in city water. The results obtained are as follows; 1. The quenching effect of cooling water generally increases with Reynolds Number(characteristic length; specimen diameter)as shown in the experimental formula; but at the realm of Reynolds Number from 1.2 * 10$^{4}$ to 9.2 * 10$^{4}$, the increasing rate of quenching effect shows little increase. 2. The increasing rate of quenching effect was increased under the flow rate of 221 cm/sec. On the other hand, it was decreased below this flow rate. 3. The quenching effect was influenced by the water temperature and the flow rate. But it was rather dependent upon the former than the latter. 4. Although the quenching effect appeared loosely in the water temperature of 50.deg. C, it was shown that the quenching effect increased in the low flow rate of 31 cm/sec. comparing with the still water. 5. It is desirable to design the quenching system to be over 1.2 * 10$^{4}$ in Reynolds Number or over, 3000$cm^{-1}$ / in V/v in order to increase the quenching effect of the system using open channel.annel.