• Title/Summary/Keyword: Freezing characteristics

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Fatigue Characteristics of Asphalt Concrete Based on compacted Density (아스팔트 콘크리트의 다짐도에 따른 피로 특성)

  • 김광우;이병덕;박용철
    • Proceedings of the Korea Concrete Institute Conference
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    • 1994.10a
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    • pp.205-210
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    • 1994
  • This study was conducted to evaluate performance of asphalt concretes under various densities, using Marshall specimens before and after freezing-and-thawing treatment. Six different compaction blows per side (20, 30, 40, 50, 60, 70 blows) were applied to specimens to produce different densities. Test results showed that the lower density specimens had the weaker resistance to freezing-and-thawing treatment. The density was an index of retaining fatigue life and displacement after freezing-and-thawing. Therefore, poor compaction in pavement was considered to be a major cause of early distress mechanisms such as rutting, ravelling and cracking, which were resulted in a reduced service life.

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The Frost Heaving Characteristics of Subgrade Soils Using Laboratory Freezing System (실내동결시스템을 이용한 노상토의 동상 특성)

  • Shin, Eun-Chul;Ryu, Byung-Hyun;Park, Jeong-Jun
    • International Journal of Highway Engineering
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    • v.12 no.2
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    • pp.71-79
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    • 2010
  • The influence of fines of the frost susceptibility of subgrade soils were established by laboratory freezing system test simulating closely the thermal conditions in the field. During the winter season, the climate is heavily influenced by the cold and dry continental high pressure. Because of siberian air mass, the temperature of January is $-6{\sim}-7^{\circ}C$ on average. This chilly weather generate the frost heaving by freezing the moisture of soil and damage potential of the road structure. In the freezing soil, the ice lenses increase the freeze portion of soil by absorbing the ground water with capillary action. However, the capillary characteristics differ from the sort of soil on the state of freezing condition. In the current design codes for anti-freezing layer, the thickness of anti freezing layer is calculated by freezing depth against the temperature condition. Therefore, they have a tendency of over-design and uniform thickness without the considerations of thermal stability, bearing capacity and frost susceptibility of materials. So, it is essential for studying the appropriateness and bearing capacity besides the seasonal and mechanical properties of pavement materials to take a appropriate and reasonable design of the road structure. In this Paper, the evaluation of frost susceptibility was conducted by means of the mechanical property test and laboratory freezing system apparatus. The temperature, heaving amount, heaving pressure and unfrozen water contents of soil samples, the subgrade soils of highway construction site, were measured to determine the frost susceptibility.

Characteristics of Elastic Waves in Sand-Silt Mixtures due to Freezing (동결에 따른 모래-실트 혼합토의 탄성파 특성)

  • Park, Junghee;Hong, Seungseo;Kim, Youngseok;Lee, Jongsub
    • Journal of the Korean GEO-environmental Society
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    • v.13 no.4
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    • pp.27-36
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    • 2012
  • The water in surface of the earth is frozen under freezing point. The freezing phenomenon, which causes the volume change of soils, affects on the behavior of soils and causes the significant damage on the geotechnical structures. The purpose of this study is to investigate the characteristics of elastic waves in sand-silt mixtures using small size freezing cells, which reflect the frozen ground condition due to temperature change. Experiments are carried out in a nylon cell designed to freeze soils from top to bottom. Bender elements and piezo disk elements are used as the shear and compressional wave transducers. Three pairs of bender elements and piezo disk elements are placed on three locations along the depth. The specimen, which is prepared by mixing sand and silt, is frozen in the refrigerator. The temperature of soils changes from $20^{\circ}C$ to $-10^{\circ}C$. The velocities, resonant frequencies and amplitudes of the shear and compressional waves are continuously measured. Experimental results show that the shear and compressional wave velocities and resonant frequencies increase dramatically near the freezing points. The amplitudes of shear and compressional waves show the different tendency. The dominant factors that affect on the shear wave velocity change from the effective stress to the ice bonding due to freezing. This study provides basic information about the characteristics of elastic waves due to the soil freezing.

Ideal Freezing Curve Can Avoid the Damage by Latent Heat of Fusion During Freezing (냉동 시 잠재용융열에 의한 피해를 최소화할 수 있는 이상냉동 곡선)

  • 박한기;박영환;윤웅섭;김택수;윤치순;김시호;임상현;김종훈;곽영태
    • Journal of Chest Surgery
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    • v.36 no.4
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    • pp.219-228
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    • 2003
  • Background:Liquid nitrogen freezing techniques have already met with widespread success in biology and medicine as a means of long-term storage for cells and tissues. The use of cryoprotectants such as glycerol and dimethylsulphoxide to prevent ice crystal formation, with carefully controlled rates of freezing and thawing, allows both structure and viability to be retained almost indefinitely. Cryopreservation of various tissues has various con-trolled rates of freezing. Material and Method: To find the optimal freezing curve and the chamber temperature, we approached the thermodynamic calculation of tissues in two ways. One is the direct calculation method. We should know the thermophysical characteristics of all components, latent heat of fusion, area, density and volume, etc. This kind of calculation is so sophisticated and some variables may not be determined. The other is the indirect calculation method. We performed the tissue freezing with already used freezing curve and we observed the actual freezing curve of that tissue. And we modified the freezing curve with several steps of calculation, polynomial regression analysis, time constant calculation, thermal response calculation and inverse calculation of chamber temperature. Result: We applied that freezing program on mesenchymal stem cell, chondrocyte, and osteoblast. The tissue temperature decreased according to the ideal freezing curve without temperature rising. We did not find any differences in survival. The reason is postulated to be that freezing material is too small and contains cellular components. We expect the significant difference in cellular viability if the freezing curve is applied on a large scale of tissues. Conclusion: This program would be helpful in finding the chamber temperature for the ideal freezing curie easily.

An Experimental Study on the Freezing Protection Valve Using Phase Change Material(PCM) for the Heat Exchanger (상변화물질(PCM)을 이용한 열교환기용 동파방지밸브에 관한 실험적 연구)

  • Yun, Jea-Ho;Kim, Joung-Ha;Jeong, Soon-Young;Yang, Yoon-Sub;Kim, Seong-Hyun;Song, Duk-Yong
    • Journal of the Korean Solar Energy Society
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    • v.32 no.6
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    • pp.127-133
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    • 2012
  • This paper is an experimental study on the freezing protection valve used for solar water heating, air-conditioning systems, and plumbing systems. When the phase change occurs from liquid to solid, most of the substances except water volumetrically shrink. And referred to as PCM(Phase Change Material) a substance with such properties, the phase change temperature varies depending on the material. To prevent the freezing of the plumbing system, such as air-conditioning system in the winter season, we developed a several types of freezing protection valve using PCM whose freezing temperature are $2-4^{\circ}C$. The working principle of the freezing protection valve is that the fluid inside the pipe is released to prevent the system-collapse when fluid temperature reaches the freezing temperature of the PCM. And then the valve is closed and returned to the original position automatically when the temperature of the operating fluid rises. In this paper, the operating temperatures, discharge flow rate and the response characteristics of the valve during the operation are tested and investigated. From the results of this research the freezing protection valves employing PCM are expected to be commercialized in the near future.

A Thermodynamic Study on Freezing Characteristics of Weathered Tuff Soil- Freezing Point Depression with the Variation of Overburden Pressure - (응회암 풍화토의 동결특성에 관한 열역학적 연구-상재하중과 동결점 저하를 중심으로-)

  • 서상열
    • Journal of the Korean Geotechnical Society
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    • v.15 no.6
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    • pp.297-306
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    • 1999
  • In this research, the frost heave mechanism of the weathered tuff soil sampled from the area tying between Ulanbator and Beijing was studied. The frost heave tests were carried maintaining the constant temperature at both upper$(+5^{\circ}C)\; and\; lower(-5^{\circ}C)$ ends of the sample. Here, main emphasis is given on variation of the freezing point depression with the variation of applied overburden pressure. The expansion of ice lens and migration of the pore water towards freezing front were observed in the test. It was found that with the increase in overburden pressure there is decrease in heave rate and increase in the absolute value of a segregation-freezing temperature. Hence the equation between segregation-freezing temperature and overburden pressure could be suggested. Also the water content of the samples at the frozen side was shown to be higher than those at the unfrozen side. Similarly, the water at warmer part of the frozen tuff was found much higher than that of the cooler part.

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Numerical Investigation into Behavior of Retaining Wall Subject to Cycles of Freezing and Thawing (동결-융해 반복작용에 노출되는 옹벽의 거동에 관한 수치해석 연구)

  • Yoo, Chung-Sik
    • Journal of the Korean Geotechnical Society
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    • v.29 no.1
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    • pp.81-92
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    • 2013
  • This paper presents the results of a numerical investigation into the behavior of retaining wall subject to cycles of freezing and thawing due to seasonal temperature change. The thermo-hydro-mechanical coupled finite element modeling strategy was first established to simulate the wall behavior. A series of finite element analyses were then performed on a range of conditions representing seasonal temperature change characteristics. The results indicated that the average freezing temperature and the number of cycles of freezing and thawing were the primary influencing factors for the wall behavior. Also revealed was that the duration of freezing period does not significantly affect the wall displacement and the lateral earth pressure, and that the earth pressure on the wall does not significantly change due to the freezing and thawing action suggesting that the increase in the wall displacement during the freezing and thawing action may be attributed to degradation of backfill due to the freezing and thawing action.

A Study on the Engineering Characteristics of PVA (Polyvinyl Alcohol) Fiber-Cement-Soil Mixtures (PVA 시멘트 혼합토의 공학적 특성 연구)

  • Kim, Young-Ik;Yeon, Kyu-Seok;Kim, Ki-Sung;Yoo, Kyeong-Wan;Kim, Yong-Seong
    • Journal of The Korean Society of Agricultural Engineers
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    • v.53 no.2
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    • pp.35-43
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    • 2011
  • This study aimed to investigate the engineering characteristics of PVA fiber-cement-soil mixture used to prevent or reduce brittle failure of cement-soil mixtures due to the tensile strength increase from the addition of a synthetic fiber. The engineering characteristics of PVA fiber-cement-soil mixtures composed of PVA fiber, soil, and a small amount of cement was analysed on the basis of the compaction test, the unconfined compression test, the tensile strength test, the freezing and thawing test, and the wetting and drying test. The specimens were manufactured with soil, cement and PVA fiber. The cement contents was 2, 4, 6, 8, and 10%, and the fiber contents was 0.4, 0.6, 0.8, and 1.0% by the weight of total dry soil. To investigate the strength characteristics depending on age, each specimen was manufactured after curing at constant temperature and humidity room for 3, 7 and 28 days, after which the engineering characteristics of PVA fiber-cement-soil mixtures were investigated using the unconfined compression test, the tensile strength test, the freezing and thawing test, and the wetting and drying test. The basic data were presented for the application of PVA fiber-cement-soil mixtures as construction materials.

Effects of Freezing and Microwave Heating on the Textural Characteristics of Nonwaxy Rice Flour Gels and Rice Cake(Injolmi) (동결 및 마이크로파 가열이 멥쌀가루겔 및 인절미의 조직 특성에 미치는 영향)

  • 고하영
    • Food Science and Preservation
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    • v.6 no.1
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    • pp.81-86
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    • 1999
  • The textural characteristics of nonxaxy rice flour gels and rice cake(Injolmi) with different water contents and additives were evaluated after freezing and microwave heating. As moisture content of rice flour gels increased from 45% to 55%, its hardness and gumminess decreased, but adhesive and cohesiveness had no significant difference. Microwave heating did not markedly affect the texture but frozen storage was very effective to prevent the hardening of products. Hardness of reheated rice gels increased more rapidly in non-packaged sample than in PE wrap film and affected by storage time of 24hrs at 20$^{\circ}C$. As sugar content of rice flour gels increased from 0% to 10%, its hardness, adhesiveness, and gumminess decreased, while cohesiveness did not change.

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Freezing Characteristics in a Horizontal Rectangular Channel with the Two-Dimensional Protuberances (2차원 직사각형 덕트 내부에 돌기부를 갖는 흐름의 동결특성에 관한 연구)

  • Oh, Cheol
    • Journal of Advanced Marine Engineering and Technology
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    • v.27 no.6
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    • pp.721-727
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    • 2003
  • Freezing of turbulent water flow between two horizontal cooled parallel plates with the separated region has been investigated experimentally. The flow separation was induced by vertical plates (two-dimensional plates) situated at the inlet of the rectangular channel. The degree of flow separation was varied by employing vertical thin plates with various heights. Three kinds of the vertical plates with 8.0, 9.8 and 12.5 mm in height were utilized. The Reynolds number and cooling temperature ratio were ranged from $3.45\times10^3 to 1.73\times10^4$ and 7.0 to 20.0 respectively, The measurements show that the flow separation influenced remarkably on the local ice formation characteristics. The location of the first ice layer and the average heat transfer at the ice surface were found be correlated as a function of the Reynolds number, the cooling temperature ratio, and the orifice height ratio.