과냉각 현상에 용액의 pH와 전해질이 미치는 영향

이종백(Ree, Jongbaik),김예린(Kim, Yae Rin),장소정(Chang, So Jeong),고경철(Ko, Kyoung Chul),이상권(Lee, Sang Kwon) 한국과학영재교육학회 2021 과학영재교육 Vol.13 No.1

이 연구는 광역시 소재 대학교 과학영재교육원 사사과정에서 진행하는 연구로 수행되었다. 물의 과냉각은 학생들 실험실에서 간단한 장치를 이용하여 쉽게 연구할 수 있다. 본 연구에서는 용액의 pH와 전해질이 물의 과냉각에 미치는 영향을 살펴보았다. 실험에서 온도 변화는 온도 센서와 MBL 장치를 이용하여 기록하였다. 또한 GAUSSIAN 프로그램을 이용하여 컴퓨터 시뮬레이션을 수행하고 실험 자료와 비교하였다. 물의 초기 온도가 높을수록 그리고 pH가 증가할수록 물의 과냉각이 더 잘 일어났다. pH가 낮을 때는 용액 중에 H3O+ 이온이 더 많이 존재하여 국소적으로 얼음 결정의 핵을 만들기가 더 쉽기 때문에 물의 과냉각이 잘 일어나지 않는다. 또한 시험관 내 물의 초기 온도가 80℃인 경우, pH가 7~13에서는 모든 물의 냉각 과정에서 물의 과냉각 현상이 나타나는 것을 알 수 있었다. 전해질이 첨가된 용액에는 전해질이 없는 경우에 비해 물의 과냉각이 훨씬 덜 일어나는 것을 알 수 있었다. 따라서 냉각 곡선에서 물의 과냉각 현상은 물이 국소적으로 결정핵을 더 쉽게 형성할 수 있는 환경과 관련이 있다는 것을 알 수 있다; 만일 결정핵을 쉽게 형성할 수 있다면 국소적으로 형성된 얼음 결정에 의해 물은 과냉각 없이 전체적으로 얼게 된다. 반면에 결정핵이 쉽게 형성될 수 없다면 결정핵의 형성은 지연되고 따라서 물은 과냉각된다. 컴퓨터 시뮬레이션 결과, H3O+ 이온에 의해 수소 결합의 형성이 더 촉진될 수 있다는 것이 예측되었다. This study is based on Research and Education (R&E) project in the University located in metropolitan city. Supercooling of water can be easily studied with a simple apparatus suitable for the student laboratory. We investigated the effects of the pH and electrolyte of the solution on the occurrence of supercooling of water. The temperature variations in the experiment were recorded using temperature sensor and MBL apparatus in the cooling the solution. The computer simulations were carried out using GAUSSIAN program and compared with the experimental data. As the initial temperature and pH of a solution become higher, supercooling of water occurs more easily. When the pH of a solution is low, supercooling of water does not occur easily because the presence of H3O+ ion accelerates the formation of ice crystals locally. Further, when the initial temperature of a solution is 80℃, supercooling of water occurs at all cooling experiments if the pH of a solution is between 7 to 13. When electrolytes are added in the solution, the occurrence of supercooling of water is not easy compared to the case of the absence of electrolytes. Therefore, we correlate the occurrence of supercooling of water with the circumstance of the solution to nucleate ice more easily; if it nucleates easily, the layer of ice crystals formed locally will initiate freezing of the bulk water without supercooling. On the other hand, If the circumstance is unable to nucleate ice easily, ice nucleation is delayed and the water is supercooled. As the result of the computer simulation, it is expected that the formation of the hydrogen bond can be accelerated by the presence of H3O+ ion.

수직 환형유로 내 과냉각비등 유동 가시화 및 국소 유동인자 측정 실험 연구

박일웅,강인엽,이연건 대한기계학회 2022 大韓機械學會論文集B Vol.46 No.10

A series of experiments were conducted to investigate flow structures and local temperatures in subcooled boiling in a vertical heated channel at a pressure approximately equal to atmospheric pressure. The test section was the internally heated annulus with an effective heated length of 2 m and hydraulic diameter of 20 mm; the heat flux, mass flux, inlet subcooling degree, and exit pressure were adjusted in the test. The boiling flow phenomena were recorded with a high-speed camera for three flow conditions. In addition, local void fraction profiles that had been measured by optical fiber probes were identified. Furthermore, the surface temperatures of the heater rod were obtained, and the radial distributions of fluid temperature were measured by traversing precisely the sensing tip of the thermocouples. 본 연구에서는 대기압 주변 조건에서 수직 가열채널 내 과냉각비등 유동장의 유동 구조를 분석하고, 국소 온도를 측정하기 위한 실험을 수행하였다. 유효 가열 길이 2 m, 수력 직경 20 mm의 내측 가열 환형유로를 갖는 비등 실험장치를 이용하여 열속, 질량속, 입구 과냉각도, 그리고 시험부 출구 압력을 제어하였다. 세 가지 유동 조건에 대해 시험부에 높이에 따라 세 군데에 설치된 가시창을 통해 과냉각비등 유동을 초고속 카메라로 촬영하였으며, 광섬유 프로브를 이용하여 측정된 국소 기포율 분포와 연계하여 유동 구조를 분석하였다. 또한, 온도 센서의 측온접점을 이송함으로써 유체 온도의 반경 방향 프로파일을 정밀 측정하였으며, 향후 벽면비등 모델의 검증에 유용하게 활용될 수 있는 가열봉의 외벽온도를 얻었다.

냉매 과냉각을 이용한 열펌프 시스템의 성능 특성

노건상,손창효 한국수소및신에너지학회 2007 한국수소 및 신에너지학회논문집 Vol.18 No.4

In this paper, the performance characteristics of heat pump system using a new refrigerant subcooling system designed for the study, are introduced. The new heat pump system have the ice storage tank at the outlet of condenser. The experimental apparatus is a well-instrumented water/water heat pump which consisted of working fluid loop, coolant loop, and ice storage tank. The experiment parameters of subcooling ranged as the evaporating temperature from -5℃ to 8℃, the condensing temperature from 30℃ to 35℃. The test of the ice storage was carried out at evaporating temperature of -10℃ and the ice storage mode is Ice-On-Coil type. The working fluid was R-22 and the storage materials were city-water. The test results obtained were as follows; The refrigerant mass flow rate and compressor shaft power were unchanged by the degrees of subcooling, that is, they were independent of degrees of subcooling. The cooling capacity of the new heat pump system increase as the evaporating temperature and subcooling degrees increase and is higher by 25~30%, compared to the normal heat pump system. The COP of the new heat pump system increases as the degrees of subcooling and evaporating temperature increase and is higher by 28% than that of the normal heat pump system.

빙축열시스템용 유화용액 축열재의 유동 및 온도특성

김재돌,윤정인 한국건축설비학회 1998 건축 설비 Vol.1 No.3

열에너지를 저장하는 축열 시스템은 공조설비 등에 이용되고 있는 유용한 방법의 하나이다. 이는 여름철 주간 전력의 피크컷(peak cut), 열원기기의 용량 축소, 열원기기 고장시의 대응 등을 목적으로 채용하는 경우가 많으며, 에너지 절약 및 유지비 절감 등의 가능성도 있다. 축열시스템은 크게 현열형(sensible heat type)과 잠열형(latent heat type)으로 나눌 수 있다. 전자는 온도차에 의한 방법으로 냉수, 온수, 건물 구조체, 암석 등이 있으며, 후자는 상변화를 이용한 것으로 얼음이나 잠열 축열재(유치화합물, 파라핀 등)가 여기에 해당된다. 물을 축열재로하는 시스템은 화학적으로 안정하고, 자원이 풍부한 등 여러가지 장점을 가지고 있지만 설비가 커지고, 축열조에서의 열손실이 큰 점 등의 결점이 있다. 한편 빙축열은 물이 얼음으로 상변화할때의 잠열을 이용한 것으로 이 잠열은 현열에 비해 약 80배 정도로 커 적은 체적으로도 효율적인 냉열저장이 가능하다. 또한 축열조의 소형화와 단열의 간편성 때문에 방열손실에 대해 유리하며, 일정온도의 열을 용이하게 이용할 수 있는 장점도 있다. 그러나, 빙축열시스템은 물을 냉각하여 얼음을 생성하는 축냉과정에서 과냉각이 발생하면 일정온도의 열에너지를 고효율로 축적할 수 있는 잠열 축열재로서의 장점을 잃게 된다. 따라서, 본 연구에서는 방축열시스템에 있어 최대의 결점인 과냉각에 의한 냉각온도의 저하로 소요전력의 증가와 얼음의 성장에 따른 열저항의 증대를 극복하기 위한 한 방법으로써 유동성을 가진 얼음의 이용을 고려하였다. 이 방법은 기름, 물, 계면활성제에 의한 다성분 혼합용액을 유화(乳化)냉각하는 것으로 과냉각이나 열저항에 의한 소요전력의 증대를 막을 뿐만 아니라, 혼합유체를 직접 유통시키기 때문에 고효율의 새로운 축열재 개발을 기대할 수 있다. 이와 같은 관점에서 다성분 혼합용액의 냉각에 의한 유동성이 있는 얼음의 생성 및 온도특성에 관한 실험을 통하여 빙축열시스템용 축열재 개발의 가능성을 제시하였다. A fundamental study on ice formation and its temperature characteristics in ice storage system was performed experimentally. In case of ice formation, failing of cooling temperature due to supercooling causes the inereasement of electricity consumption and thermal resistance which restrains the growth of ice. For these reasons, we took the ice with movement into consideration by using the mixture which contains oil, water, and surfactant. From the experimental results, it is possible to make use of the latent heat of mixture because the freezing phenomenon of mixture was almost alike in movement and solidification point maintenance time in comparison with water. Especially, the addition of ethyleneglycol brought the movement into the mixture. On the other hand, this made no use of the latent heat of mixture.

동결온도 조우 처리 및 방출열 현상에 의한 복숭아와 사과 과일의 동결점 해석

박윤문(Youn-Moon Park),홍윤표(Yoon-Pyo Hong) 한국원예학회 2009 원예과학기술지 Vol.27 No.4

열방출 현상을 통해 복숭아와 사과 과일의 동결점을 측정 하기위해 시장출하가 가능한 시점에서 수확한 과일을 동결 온도에 조우시킨 후 온도 데이타 저장장치를 사용하여 빙결이 진행과정에서의 과일 내부온도 변화를 측정하였다. 증류수 및 설탕용액을 이용한 예비조사에서 나타난 과냉각 및 열방출 현상은 이론적인 동결곡선과 일치하였다. 열방출 최고점을 기준으로 판단한 ‘미백도’ 복숭아와 ‘후지’ 사과 과일의 동결점은 각각 -0.7~-1.0℃와 -1.4~-1.7℃로 조사되었고 과냉각점은 -2.7~-3.1℃로 동일한 범위를 나타내었다. 열방출 곡선을 통해 추정한 동결점은 실증실험을 통해 확인한 동결온도와 일치함으로써 본 연구결과는 동결과정에서의 열방출 해석을 통해 신선 원예식품의 동결점을 손쉽게 조사할 수 있는 가능성을 보여주었고 과냉각점이 아닌 동결점을 기준으로 복숭아는 -0.7℃, 사과는 -1.4℃의 수확후 온도관리 한계점을 제시하였다. Freezing points of peach and apple fruits were investigated through exotherm study. Fruits were harvested at commercial maturity and exposed to freezing temperatures; changing patterns of fruit temperature were analyzed as related to ice formation using data logger devices. Preliminary time-course investigation on the temperature changes of water and sucrose solution during ice formation exhibited clear supercooling and exotherm curve, which were well in accordance with theoretical expectation. According to the exotherm peak, actual freezing points of ‘Mibaekdo’ peach and ‘Fuji’ apple fruit seemed to be in the range of -0.7~-1.0℃ and -1.4~-1.7℃, respectively. Supercooling points were the same for peach and apple in the range of -2.7~-3.1℃. The freezing points obtained through exotherm study were virtually identical to those confirmed by real storage experiment. The results of the present study suggest that freezing point of fruit and vegetable crops could be easily estimated through exotherm approach. Based on freezing point, not on the supercooling temperature, postharvest temperature management at above -0.7℃ and -1.4℃ is recommended as critical points for peach and apple fruit, respectively.

과냉각대형액적 충돌예측을 위한 오일러리안 기반 수치 모델링

정성기(Sung-Ki Jung),김지홍(Ji-Hong Kim) 한국항공우주학회 2012 韓國航空宇宙學會誌 Vol.40 No.8

외부 환경조건에 의한 항공기 위협인자로서 과냉각 대형 액적은 그 중요성이 지속적으로 보고되고 있다. 이러한 대형 액적의 거동은 상대적으로 작은 액적과 달리 그 형태가 변화하며 액적이 표면과 충돌시 파편이 발생하는 등 다양한 물리적 특성을 나타낸다. 이러한 대형 액적의 거동을 시뮬레이션 하기 위해 비정렬 격자계 기반 2차원 압축성 Navier-Stokes 코드와 액적 거동 시뮬레이션 코드를 개발하였다. 또한 대형 액적의 물리적 현상을 모사하기 위해 반경험적 기법에 기반한 액적항력모델과 액적-고체표면 충돌 모델을 기존 액적장 지배방정식의 액적항력계수 및 경계면의 수치적 경계조건으로 적용하였다. 그 결과 풍동 시험과 액적충돌 영역 및 최대 축적율은 매우 유사하게 나타난 반면 NACA23012 익형의 아랫면 주위 축적율의 경향은 풍동 시험보다 다소 크게 나타났다. Supercooled large droplet issues in aircraft icing have been continually reported due to the important safety considerations. In order to simulate the impingement behavior of large droplets, a two-dimensional and compressible Navier-Stokes code was developed to determine the flow field around the test model. Also, the Eulerian-based droplet impingement model including a semi-empirical approach for the droplet-wall interaction process and droplet break-up was developed. In particular, the droplet-wall interactions were considered as numerical boundary conditions for the droplet impingement simulation in the supercooled large droplet conditions. Finally, the present results were compared with the experimental test data and the LEWICE results. The droplet impingement area and maximum collection efficiency values between present results and wind tunnel data were in good agreements. Otherwise, the inclination of collection efficiency of the present result is over-predicted than the wind tunnel data around a lower surface of the NACA 23012 airfoil.

과냉각을 동반하는 물의 동결현상에 관한 실험

윤정인,김재돌,금종수,추미선,겸전가신,가등풍문,Yoon, J.I.,Kim, J.D.,Kum, J.S.,Chu, M.S.,Kamata, Y.,Kato, T. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.2

The freezing phenomenon of saturated water with the supercooled region in a horizontal circular cylinder has been studied experimentally by using the holographic real time interferometry technique. From the experiments, it was found that there were three types of freezing patterns. The first is the annular ice layer growing from the cylinder surface at a high cooling rate; the next is the asymmetric ice layer at a moderate cooling rate; and the last is the instantaneous ice layer growth over the full region at lower cooling rate. As the water was coolde from room temperature to the subfreezing point passing through the density inversion point, the freezing pattern was largely affected by the inversion phenomenon, which had much effected the free convection and was susceptible to influences from the cooling rate. When the cooling rate is high, supercooling energy is released before the water is sufficientry mixed by free convection. On the other hand, when the cooling rate is low, there is much time for the water to be mixed by free convection. This seems to be the reason why the different ice layer growths occur.

과냉각을 동반한 순수물의 냉각현상 해석

Chu, Mi-Seon,Yun, Jeong-In,Kim, Jae-Dol,Kamata, Yoshinobu,Kato, Toyofumi 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.7

Ice formation in a horizontal circular cylinder has been studied numerically. From the numerical analysis results, it was found that there were three types of freezing pattern and that freezing phenomenon was affected largely by density inversion and cooling rate. The type of freezing pattern largely depends on the secondary flow which is generated by density inversion. When supercooling energy is released before the development of the secondary flow, the annular ice layer grows. If the energy is released when the secondary flow is considerably developed and the supercooled region is removed to the upper half part of the cylinder, an asymmetric ice layer grows. And if the energy is released after perfect development of the secondary flow, instantaneous dendritic ice formation over the full region occurs. Furthermore, this secondary flow was found to have an effect on heat transfer characteristics. The heat transfer rate becomes small at the instant when the secondary flow is generated, but becomes large with the development of the flow. It's concluded that for the facilitation of heat transfer it is desirable to keep water in liquid phase until the secondary flow is perfectly developed. This study gave an instruction of performance improvement of capsule type ice storage tank.

과냉각을 동반한 동결과정의 수치해석

윤정인,김재돌,김성규,Yoon, J.I.,Kim, J.D.,Kim, S.G. 대한설비공학회 1996 설비공학 논문집 Vol.8 No.4

In this study, which focuses on ice storage, a fundamental study in cooling and solidification was performed, including the interesting phenomena of density inversion, supercooling and dendritic ice. A numerical study was performed for natural convection and ice formation considering existence of subcooling and dendritic ice were analyzed numerically by using finite difference method and boundary fixing method. In the mesh, the solid fraction was introduced with adding as a term to the energy conservation equation. A flow in the dendrite was modelled as a flow in a porous medium, and the momentum conservation equation was modified to incorporate resistance forces involved in flows through porous media. A numerical solution of the time dependencies of dendrite area and dense ice front was successfully obtained, and the numerical results were good agreement with experimental results. Based on this methodology, a discussion was made of phenomena and characteristics of cooling and freezing processes under various conditions.

압력 및 용존산소량이 증류수 과냉각 해소에 미치는 영향

박세창(SeChang Park),정수진(Su-Jin Jeong),박천완(ChunWan Park),이동규(DongGyu Lee),강채동(Chaedong Kang) 대한설비공학회 2013 대한설비공학회 학술발표대회논문집 Vol.2013 No.6

It is proposed that the dissolved air in pure water has been related to the release of supercooling. In this study, a supercooling experiment is performed to test tubes of pure water with three fixed initial dissolved oxygen(DO=4.1, 7.5, and 12.6 mg/L), i.e. dissolved air. The initial DO in each test tube is maintained to constant during supercooling, as possible. And the pressure effect on supercooling release of pure water is observed to supercooling degree and visualization of bubbles enclosed to the ice after full crystallization of the pure water. At results, the distribution and maximum of supercooling degree in each initial DO relate to the initial DO in pure water. Moreover, the supercooling degree of pure water relates to the pressure of the pure water. And the distribution of bubble in ice proves the effect of the initial DO and the pressure of supercooled water.