• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2256-2261
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• 2008

The electric snow melting and deicing system by electric heating cable which is adopted in this study is a part of road facilities to keep surface temperature of the road higher than freezing point of water for melting the snow or ice accumulated on it. The electric heating cables are buried under paved road at a certain depth and a certain pitch and operated automatically and manually. Design theory, amount of heating, and installation standard vary according to economic situation, weather condition, and installation place. A main purpose of this study is figuring out the appropriate range of required heat capacity and installation depth and pitches for solving snowdrifts and freezing problems with minimum electric power consumption. This study was performed under the ambient air temperature($-2^{\circ}C$, $-5^{\circ}C$), the pitches of the electric heating cables (200 mm, 300 mm), heating value ($250\;W/m^2$, $300\;W/m^2$, $350\;W/m^2$).

• 설비공학논문집
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• 제27권6호
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• pp.293-299
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• 2015

In Korea, it is the law that an apartment building which consists of over 100 households must have a ventilation system installed, either natural or mechanical. The heat recovery ventilator (HRV) is great way to reduce energy consumption. In this research we confirmed that based on site's construction plan and existing diffuser form, performed purpose CFD which simulates operation in temperatures below $-5^{\circ}C$ to circumstances of installation of an HRV in an apartment. As a result of this research we found that when the diffuser's aperture area was adjusted, the distribution of air temperature and residence time of air was more equally distributed and air temperature was higher, compared to when the diffuser has an identical aperture area. We also found that we are able to increase even more air temperature and air distribution of air temperature and residence time of air was even more equally distributed when run in parallel with a splitter damper.

• 한국지반환경공학회 논문집
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• 제17권5호
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• pp.37-46
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• 2016

해성 점토를 이용한 경량기포혼합토의 동결융해 및 수침조건에 따른 환경적 변화특성을 파악하기 위하여, 시멘트 사용량을 변화시키며 경량기포혼합토의 시료를 제작하여 동절기 저온양생, 지중양생 및 실내양생 조건에서 일축압축강도를 관찰하였다. 동결융해($-9.1^{\circ}C{\sim}17.2^{\circ}C$ 온도범위)를 받는 시료는 시멘트 사용량에 상관없이 강도발현이 안되었고 지표면 아래 30cm 깊이의 지중에서 양생한 경우 시멘트 사용량이 증가할수록 압축강도는 급격히 증가되었다. 따라서 동결융해를 받는 조건에서는 경량기포혼합토 타설 후 외기로부터 차단하는 보온층 설치가 필요하다. 장기간 수침상태를 유지한 시료는 단위중량의 증가가 매우 작게 발생하였고, 시료가 건조되어 함수비가 6%로 저하되었을 때 압축강도는 급격히 감소하는 경향이 있다. 그러나 건조를 방지하고 습윤상태를 유지할 경우 압축강도 및 단위중량의 변화는 매우 작았다. 지하수위 아래에 매설되거나 피복토를 갖는 경량기포혼합토는 장기적으로 안정적인 건설재료로 평가할 수 있다.

• 한국터널지하공간학회 논문집
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• 제13권4호
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• pp.319-345
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• 2011

한랭지에 건설된 터널의 경우 터널 주변지반 지하수의 동결은 동절기 터널 배수 장애의 원인이 되며 라이닝을 내공 측으로 압출시키는 원인으로 작용하기도 한다. 노르웨이 등 해외에서는 이미 한랭지에 건설되는 터널의 동해방지를 위한 단열기준을 가지고 있으나 국내에서는 아직까지 터널 라이닝 동해방지를 위한 단열설계가 도입되어 있지 않은 실정이다. 본 연구에서는 국내 도로터널의 동결 사례를 고찰하여 터널 라이닝 동해방지 대책이 필요함을 파악하였다. 또한 터널 주위의 온도분포를 파악하기 위해 화악터널에서 터널 종단길이에 따른 온도분포, 라이닝 내부의 온도, 포장면 하부지반의 온도 분포를 계측하였으며 이로부터 외기 온도변화에 따른 터널 내부 온도 분포 특성을 분석하였다. 화악터널의 온도분포 계측 결과를 바탕으로 단열재의 성능시험을 위해 인공기후실에서 단열재 설치 유무에 따른 암석시편의 열유동 실험을 수행하였다. 또한 터널 라이닝 동해를 방지할 수 있는 적정 단열재 두께를 제안하기 위해 3 차원 수치해석을 실시하였다. 수치해석 결과로부터 터널배면 지하수 동결기준으로 동결지수를 약 291$^{\circ}C{\cdot}$ Hr로 제안하였다.

• 설비공학논문집
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• 제22권8호
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• pp.567-572
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• 2010

Air shift type heat pump is combined heat recovery ventilator and refrigerator, and it is installed an air shifter changing air flow. And so it is an perfect AHU(Air Handling Unit) capable to cooling, heating, ventilation and heat recovery. Therefore, an experimental study has been carried out to investigate the operating performance in winter for this system. An experimental data are room temperature, inlet/outlet temperature of condenser, evaporator and heat exchanger. They have been measured as the variation of outdoor temperature. The results, in case of rising above freezing, the air shift type heat pump system is operated normally, and the heating COP is 3.0~4.2 by varying outdoor temperature from $-3^{\circ}C$ to $15^{\circ}C$.

• 한국초전도ㆍ저온공학회논문지
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• 제22권4호
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• pp.45-50
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• 2020

In this research, the variation of round-trip efficiency in a liquid air energy storage system (LAES) is calculated and an optimal configuration is found. The multiple stages of cold energy storage are simulated with several materials that process latent heat at different temperature ranges. The effectiveness in the charging and discharging processes of LAES is newly defined, and its relationship with the round-trip efficiency is examined. According to defined correlation, the effectiveness of the discharging process significantly affects the overall system performance. The round-trip efficiency is calculated for the combined cold energy storage materials of aqueous dimethyl sulfoxide (DMSO) solution, ethanol, and pentane theoretically. The performance of LAES varies depending on the freezing point of the cold storage materials. In particular, when the LAES uses several cold storage materials, those materials whose freezing points are close to room temperature and liquid air temperature should be included in the cold storage materials. In this paper, it is assumed that only latent heat is used for cold energy storage, but for more realistic analyzes, the additional consideration of the transient thermal situation to utilize sensible heat is required. In the case of such a dynamic system, since there is certainly more increased heat capacity of the entire storage system, the volume of the cold energy storage system will be greatly reduced.

• Journal of Advanced Marine Engineering and Technology
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• 제41권3호
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• pp.176-181
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• 2017

본 연구는 저온환경에서의 평판형 열교환기에 대해 제빙을 억제할 수 있는 방법을 살펴보았으며, 그 방법으로 초음파의 발생에 따른 제빙특성을 관찰하였다. 본 실험에서 최적의 조건을 찾아내기 위해 에틸렌글리콜을 브라인으로 사용하고, 온도는 $-8{\sim}-16^{\circ}C$로 순환시켰으며, 제빙에 사용된 물은 1~3mm 두께로 공급하여 데이터를 기록하였다. 또한 초음파의 발생정도에 따른 변화를 확인하기 위해 출력을 조절하여 실험을 진행하였다. 그 결과 제빙억제 효과는 브라인 온도, 제빙두께, 초음파 주파수의 영향을 받는 것을 알 수 있었다.

• International Journal of Industrial Entomology and Biomaterials
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• 제47권2호
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• pp.126-133
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• 2023

Genetic resources of mulberry trees are commonly preserved as trophosomes, which are vulnerable to environmental factors, such as natural disasters, diseases, and pests. This study establishes a basic protocol for ultra-low temperature cryopreservation of mulberry trees using a two-step freezing process. The procedure was established using the "Daeshim" variety and then tested on genetic resources from 24 other mulberry varieties. Samples were first dried to a moisture content of 33-43% in a low-temperature forced-air chamber at -5 ℃, then slowly frozen from -5 ℃ to -20 ℃, and preserved in liquid nitrogen (-196 ℃). To determine the regeneration rate, isolated dormant buds were inoculated into MS basal medium, and grown shoots were grafted onto 1-year-old rootstock via chip budding and then cultured. After freezing in liquid nitrogen, the "Daeshim" variety exhibited a survival and regeneration rate of more than 70% and 50%, respectively. Applying the two-step freezing process to genetic resources from 24 mulberry species yielded average survival and regeneration rates of 85.3% and 75.5%, respectively. Morus alba showed survival and regeneration rates of 100%, confirming the efficacy of the two-step freezing method. These results indicate the high feasibility of ultra-low-temperature cryopreservation through two-step freezing of dormant buds from mulberry genetic resources. Additional research is required into the variations in regeneration rates with freezing period in liquid nitrogen.

• 설비공학논문집
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• 제9권2호
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• pp.104-111
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• 1997

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.

• 대한설비공학회지:설비저널
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• 제13권4호
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• pp.223-229
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• 1984

Experiments were performed for freezing of an initially superheated or nonsuperheated liquid phase in a cooled vertical tube. The liquid was placed in a copper tube whose surface maintained a uniform temperature during the data run and the freezing occurred in a copper tube. The phase change medium was n-odtadecane, a paraffin which freezes at about $61^{\circ}C$. Measurements were made which yielded information about the time dependence of the freezing front, of the amount of frozen mass, and of the various energy components extracted from the tube. The time-wise decay of the initial liquid superheat was also measured. Initial superheat of the liquid tends to moderately diminish the rozen mass and associated latent energy extraction at small times but has lit tie effect on these quantities at large tiems. Natural convection in the liquid Plays a modest role only at small times and disappears when the superheat decay to zero. Although the latent energy constitutes the largest contributor to the total extracted energy, the sensible energy components can make a significant contribution, especially at large tube wall subcoolings, large initial liquid superheating and short freezing time.