• 한국식품과학회지
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• 제21권6호
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• pp.735-741
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• 1989

For the accurate prediction of freezing time, probably the most difficult factor to measure and major error source is the surface heat transfer coefficient. In this work, surface heat transfer coefficient were determined for still air freezing and immersion freezing methods by theory of the transient temperature method and confirmed by using a modification of plank's equation to predict the freezing time of ground lean beef. The results showed the cooling rate of immersion freezing was about 11 times faster than that of still air freezing method. A comparison of surface heat transfer coefficient of copper plate and ground lean beef resulted an difference of 25-30% because the food sample surface is not smooth as copper plate. Also, when h-values measured by ground lean beef were applicated to modified model, the accuracy of its results is very high as difference of about 8%.

• 대기
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• 제25권1호
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• pp.31-49
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• 2015

From the hourly data of 75 Korean weather stations over a 12-year period (2001~2012), this study has chosen three cases (January 12, 2006; January 11, 2008; and February 22, 2009) of multiple freezing rains and investigated the atmospheric circulations that seemed to cause the events. As a result, the receding high pressure type (2006), prevailing high pressure type (2008), and warm front type (2009) are confirmed as synoptic patterns. In all three cases, freezing rain was found in regions with a strong ascending current near the end point of a low-level jet that carried the warm humid air from low latitudes. The strong ascending current resulted from lower-level convergence and upper-level divergence. In 2006 and 2009, the melting process was confirmed. In 2008, the supercooled warm rain process (SWRP) was confirmed. In contrast to existing SWRP theory, it was found that the cool air produced at the middle atmosphere and near the earth's surface led to the formation of freezing rain. The sources of this cool air were supposed to be the evaporative latent heat and the cold advection coming from the northeast. On the other hand, a special case was detected, in which the freezing rain occurred when both the soil surface temperature and surface air temperature were above $0^{\circ}C$. The thickness distributions related to freezing rain in Korea were found to be similar to those in North America. A P-type nomogram was considered for freezing rain forecasting; however, it was not relevant enough to Korea, and few modifications were needed.

• 설비공학논문집
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• 제23권3호
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• pp.173-178
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• 2011

Gas diffusion layer(GDL) in PEMFC performs the discharge of water vapor smoothly. When GDL is revealed to cold environment, the freezing of the water droplet or water net in GDL occurs. The purpose of this work is to observe the cooling and freezing behavior of the water droplet which meets to the microporous surface and air under the various low temperature conditions. GDL was coated with waterproof material, which has three types of coating rate, 0, 40 and 60%. Water droplets in series of sizes on GDL were supercooled, frozen and crystalized orderly by circulating low temperature brine. The process of cooling was investigated with the temperature and the snapshot of the water droplet.

• 설비공학논문집
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• 제17권7호
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• pp.629-634
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• 2005

This paper performed to predict vertical temperature distribution and air flow near cold heat source in the mass merchandising store. At the height of 150 cm, the vertical air temperature difference between the results of CFD and of measurement field showed $10\%$ near the refrigeration zone and $8.8\%$ near the freezing zone. Therefore, it regarded as appropriate for the using CFD to investigate airflow near the heat sources. The 3 kinds of CFD model were divided by the disposition of diffuser/exhaust and diffuser air temperature. At the refrigeration and freezing zone in the Model 2 and 3, the temperature difference between the front and the back of human model were showed $6.8^{\circ}C\;and\;3.9^{\circ}C$ with diffuser air temperature $17^{\circ}C$ and were showed $6.8^{\circ}C$ and $4^{\circ}C$ with diffuser air temperature $19^{\circ}C$.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.530-533
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• 2008

Refrigerators have some frost related problems in a freezing compartment. The frost formation in the refrigerator gives customers a bad impression concerning quality problems. Therefore, many engineers have been studying the optimum solution to avoid frost formation. But the problem of frost formation is very complex and hard to approach to the answer. The frost generation of a household refrigerator have been widely known that is closely related to the distribution of temperature inside the compartment. The distribution depends on the cold air circulation inside the refrigerator. So frost problem can be reduced and energy consumption efficiency also improved through optimization of air flow fields inside the freezing compartment. In this paper, numerical simulation has been carried out to check fluid flow. The variation of temperature at the walls was measured and quantitative analysis of frost generated from the freezing compartment was carried out. Through comparison between simulation and experiment, some correlation revealed.

• 한국환경과학회지
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• 제11권9호
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• pp.857-863
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• 2002

The meteorological elements were measured to investigate cause of summertime ice formation at Unchiri, Gangwon Province. The cause of freezing at valley was conformed as adiabatic expansion theory, latent heat of evaporation, natural convective theory, cold air remain theory, and convective freezing theory according to former study. However nither theory produced a satisfactory explanation. This studying area is not valley but ridge, and underground water surface exists at below than freezing height. wintertime temperature drop and summertime cold air spouting were explain as natural convective theory, generation of water drop on the rock was explained as cooling theory by air expansion, and ice formation on the rock was explained as adiabatic expansion theory. In conclusion, formation of ice valley at Unchiri was formed by natural convective theory, adiabatic expansion theory, and latent heat of evaporation successively.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.48-53
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• 2003

The steel slag, a by-product which is produced on the process of manufacturing steel by refining pig iron is mainly used as road materials after aging it. It is necessary to age steel slag for long time in air because the reaction with water and free-CaO in steel slag could make the volume expanded. Due to this reason it prevents steel slag from being used as aggregate of concrete. But steel slag used in this study is controled by a air-jet method which rapidly cools substance melted at a high temperature. Rapid cooling prevents from generating of free-CaO in steel slag. In this study, it was investigated that steel slag manufactured by air-jet method affects on concrete in the freezing and thawing. As results of this study, concrete mixed with steel slag was worse in the freezing and thawing than concrete mixed with sand in spite of using air entraining agent. To obtain durability of concrete in the freezing and thawing, it is desirable to mix 50% of steel slag in concrete per unit weight of volume.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.593-598
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• 2018

본 연구는 혹한기 결빙 방지를 위한 열회수형 환기장치의 개발에 관한 연구로써, 개발에 필요한 내부 리턴 댐퍼를 최적화하여 적용하기 위하여 전산유체해석(Computational Fluid Dynamics)을 수행하였고 이를 바탕으로 실험을 위한 시제품을 만들어 혹한기 결로 및 결빙실험을 수행하였다. 배기 재순환 비율이 최대가 되는 최적의 내부 리턴 댐퍼를 설계하기 위하여 총 16 model의 전산유체해석을 수행하였다. 전산유체해석 결과 외기에 대한 배기 재순환 비율은 59.9% ~ 62.3%로 나타났다. 외기온도(Outdoor Air Temperature)가 $-15^{\circ}C$ 이상에서는 배기 재순환 운전과 통상 운전 모두 결로와 결빙이 발생하지 않았다. 그러나 외기온도가 $-20^{\circ}C$에서는 내부 리턴 댐퍼를 $45^{\circ}$ 열어 배기 재순환 운전을 하여야 결로와 결빙이 발생하지 않았다. 혹한기 결빙 방지를 위한 열회수형 환기장치는 외기온도에 따라 통상 운전 모드와 배기 재순환 운전 모드의 두 가지 운전모드로 운전하여야 한다. 외기온도가 $-15^{\circ}C$보다 높을 경우에는 통상 운전 모드로 작동하고 외기온도가 $-15^{\circ}C$보다 낮을 경우에는 재순환 운전 모드로 작동하는 열회수형 환기장치의 운전 알고리즘을 개발하여 적용하였다.

• 한국식품과학회지
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• 제34권3호
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• pp.413-418
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• 2002

제빵에 이용 할 반죽을 발효하거나 발효하지 않은 상태로 다섯 가지의 다른 냉동 및 저장 환경에서 냉동하고 일주일간 저장하여 해동 한 후 제조된 빵의 품질을 비교하였다. 냉동속도가 빠르더라도 발효한 후 냉동된 반죽은 빵의 부피가 감소하였으며 이러한 문제점은 침지식 냉동 방식에서도 해결되지 않았다. $-70^{\circ}C$의 초저온 냉동은 $-20^{\circ}C$ 침지식 냉동고에 비하여 냉동 온도가 매우 낮으나, 냉동 속도도 느리고 해동 후 재 발효하여도 빵의 부피가 작아서 효과적인 냉동 방법이 되지 못하였다. 반면 냉동 속도는 느리지만 $-20^{\circ}C$ 공기 송풍식 냉동고가 $-70^{\circ}C$ 공시 송풍식 냉동고보다 냉동에 따른 장해가 적어서 반죽의 발효가 잘되었다. 동일한 온도일 때는 침지식 냉동이 더욱 효과적이었으며 침지식 가운데도 온도가 더 높은 $-10^{\circ}C$ 냉동이 가장 효과적이어서 발효하지 않고 냉동하여 재 발효 할 경우 대조구보다도 오히려 반죽의 발효가 잘되어 빵의 부피가 더 컸다. 따라서 본 연구에 이용한 방법 가운데 $-70^{\circ}C$ 공기 송풍식 냉동고에서 냉동, 저장하는 것이 가장 비효율적이며 침지식 냉동방법들이 냉동 온도가 높더라도 오히려 해동 후 발효 장해가 적어서 효율적이었다. 위의 실험 결과를 종합하였을 때, 냉동 전에 반죽을 발효하지 않고 $-10^{\circ}C$ 침지식 냉동고에서 냉동하여 저장하거나, $-20^{\circ}C$ 침지식 냉동고에서 초기에 냉동을 하고, $-20^{\circ}C$ air freezer에 저장하는 방법이 가장 효과적이었다.

• 한국축산식품학회지
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• 제38권5호
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• pp.959-969
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• 2018

This study investigated the effects of deep freezing and storage temperature ($-50^{\circ}C$, $-60^{\circ}C$, and $-80^{\circ}C$) on the quality and freshness of lamb. To compare the qualities of deep frozen and stored lamb, fresh control and normal freezing conditions ($-18^{\circ}C$) were adopted. As quality and freshness parameters, drip loss (thawing loss and cooking loss), water-holding capacity (WHC), texture profile analysis (TPA), thiobarbituric acid reactive substances (TBARS), and total volatile basic nitrogen (TVBN) were evaluated during 5 months of storage. Temperature influenced the drip loss and WHC, and deep freezing minimized the moisture loss during frozen storage compared to the normal freezing condition. Lamb frozen and stored at deep freezing temperature showed better tenderness than that stored in normal freezing conditions. In particular, lamb frozen at lower than $-60^{\circ}C$ exhibited fresh lamb-like tenderness. Regardless of temperature, evidence of lipid oxidation was not found in any frozen lamb after 5 months, while TVBN was dependent on the applied temperature. Therefore, this study demonstrated that deep freezing could potentially be used to maintain freshness of lamb for 5 months. From the quality and economic aspects, the freezing and storage condition of $-60^{\circ}C$ is estimated as the optimum condition for frozen lamb.