• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.401-412
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• 2016

It is extremely difficult to apply conventional grouting methods to subsea tunnelling construction in the high water pressure condition. In such a condition, the rapid artificial freezing method can be an alternative to grouting to form a watertight zone around freezing pipes. For a proper design of the artificial freezing method, the influence of salinity on the freezing process has to be considered. However, there are few domestic tunnel construction that adopted the artificial freezing method, and influential factors on the freezing of the soil are not clearly identified. In this paper, a series of laboratory experiments were performed to identify the physical characteristics of frozen soil. Thermal conductivity of the frozen and unfrozen soil samples was measured through the thermal sensor adopting transient hot-wire method. Moreover, a lab-scale freezing chamber was devised to simulate freezing process of silica sand with consideration of the salinity of pore-water. The temperature in the silica sand sample was measured during the freezing process to evaluate the effect of pore-water salinity on the frozen rate that is one of the key parameters in designing the artificial freezing method in subsea tunnelling. In case of unfrozen soil, the soil samples saturated with fresh water (salinity of 0%) and brine water (salinity of 3.5%) showed a similar value of thermal conductivity. However, the frozen soil sample saturated with brine water led to the thermal conductivity notably higher than that of fresh water, which corresponds to the fact that the freezing rate of brine water was greater than that of fresh water in the freezing chamber test.

• Applied Microscopy
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• v.37 no.1
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• pp.35-42
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• 2007

The late pupal stage of Drosophila melanogaster occurs immediately before the completion of retinal development, during which the rhabdomere rapidly forms. In this period, the photoreceptor cells were fixed and dehydrated using a high-pressure freezer (HPF) and freeze substitution (FS) technique, which is the most effective in preserving the cell structures, and observed using high-voltage electron microscopy (HVEM) at 1000 KV. The rhabdomere was classified structurally into three types of formation patterns using stereo-tiling image of thick sections. Initially, hexagonal arrays of rhabdomere existed in different angles. In addition, small pieces of rhabdomere could be observed in the cytoplasm of the photoreceptor rolls, which were visible during the profess of rhabdomere formation. In addition, multiple layers of rhabdomere strings were observed. We observed there are at least three types of vesicles related to rhabdomere formation in photoreceptor cells. In addition, it was found that these vesicles initiate the formation of the rhabdomeres during the pupal stage. Collectively, these data suggest that rhabdomeres were mainly formed through vesicles, and that parts of the rhabdomere formed first and then gathered and formed rhabdomeres in the late pupal stage.

• Journal of the Korea Safety Management & Science
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• v.16 no.2
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• pp.211-216
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• 2014

Using a high-rise building water piping after hydrostatic test of the reliability of the leak to be completed if the pressure is maintained until the leak is not commercially available considered. Due to the nature of high-rise buildings and the construction period will take several years from the lower levels of use of the water supply and fire fighting water pipe construction is in progress, the order of which I do most of the first pipe to the construction and more than three years. So kind of riser pipe is complete, install the valve in the basement by installing an automatic pump to maintain a constant pressure after hydrostatic test and after each floor plumbing piping is complete, the progress of the hydrostatic test without undergoing a separate branch pipe the valve is opened automatically when the number of the pressing pressure of the structure. I kind of do and keep working pressure of pipe until the completion of the construction work to keep the damage to human error when it is intended to prepare. In winter, the frost protection and an alternative to drainage water pipe is damaged or deformed, even if unaware of the finishing work to the building, the use of the damage caused by a leak in a after construction of finish work to be expected. Alternative to reduce this damage if the pressure test without fear of freezing to help maintain long-term commercial pressures may be considered.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.65-74
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• 2003

Most of land reclamation projects are being implemented along the south and west coastal lines of the Korean Peninsula. The earth structures and in-ground LNG tank, and buildings can be constructed using artificial freezing method on the reclaimed land to control the uplift pressure caused by capillary forces. In this study, upon freezing a saturated soil in a closed-system from the top, a considerable frost heaving pressure was developed. Decomposed granite soils, silty soil, and sandy soil were used in the laboratory freeze test which is sometimes subjected to thermal gradients under closed-systems. A major concern has been the ability to predict the frost heaving pressure over the results of relatively short-term laboratory tests. The frost heaving pressure arising within the soil samples and the temperature of the samples inside were monitored with time elapse. The degree of saturation versus heaving pressure curve is presented for each soil sample and the maximum pressure is closely related to this curve. TDR apparatus was used to measure the volumetric water content by the measurement of unfrozen water contents of frozen soils. Unfrozen water increased in soils containing a high percentage of fine-grained particles. In fine-grained soils with strong attractive farces between soil grains and water molecules, additional water is attracted into the pores leading to further volume changes and ice segregation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.12 s.243
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• pp.1299-1306
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• 2005

The suitable pressure regulator modeling at each opening ratio and pressure ratio is very important to obtain reliable results, especially in small scale pipeline network analysis such as a pressure regulator system. And it is needed to confirm both whether temperature recovery is achieved after passing by the pressure regulator's narrow neck and how much amount of low temperature area that can cause condensate accumulation is distributed by various PCV models and driving conditions. In this research, the numerical model resembling P company pressure regulator that is used widely for high pressure range in commercial, is adopted as the base model of CFD analysis to investigate pressure regulator's flow characteristics at each pressure ratio and opening ratio. And it is also introduced to examine pressure regulator's critical flow characteristics and possibility of condensation or freezing at each pressure ratio and opening ratio. Additionally, the comparison between the results of CFD analysis and the results of analytic solution obtained by compressible fluid-dynamics theory is attempted to validate the results of CFD modeling in this study and to estimate the accuracy of theoretical approach at each pressure ratio and opening ratio too.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.181-182
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• 2016

We developed eco-friendly lightweight concrete in order to apply eco-friendly lightweight concrete into structural wall or slab of shallow depth urban railway system. However, since lightweight aggregate has different structural feature of porous and it has been overvalued at current KS standard when applied, we did compare the characteristics of freezing and thawing of normal weight aggregate concrete by comparative test method(KS, ASTM). According to test method, there was a big difference of dynamic elastic modulus in lightweight concrete rather than in normal weight aggregate concrete. The big absorption factor in lightweight aggregate is main reason for that. For more detail, in KS law in which only 14 days water curing is carried out, the big amount of moisture in lightweight aggregate is frozen and high heaving pressure occurs and finally that lead to destruction of lightweight concrete. Therefore, it is considered that in case of lightweight concrete, resistibility against freezing and thawing has been undervalued in domestic KS law compared to ASTM law, which is overseas standard. So, a variety of examination about testing criteria and rule would be necessary for exact assessment of lightweight concrete.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.5
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• pp.347-355
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• 2021

This paper is a study on the thermal design of printed circuit heat exchanger (PCHE) to supply cryogenic high pressure liquid hydrogen stored from hydrogen liquefaction process by using computational fluid dynamics (CFD). This PCHE should be thermally designed to raise the temperature of cryogenic liquid hydrogen to a desired temperature and also to be anti-icing to avoid any local freezing in hot channel. This research presents the effect of inlet velocity and inlet temperature of hydrogen, and the effect of flow configurations of co/counter-flow on thermal design of PCHE heat exchanger based on various CFD simulation analysis.

• Journal of Food Hygiene and Safety
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• v.31 no.1
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• pp.42-50
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• 2016

The effects of freezing and thawing conditions on microbiological quality and microstructure change of inoculated (Listeria monocytogenes and Campylobacter jejuni) and non-inoculated chicken breasts were investigated. Chicken breasts were frozen with air blast freezing (-20, -70, and $-150^{\circ}C$), ethanol ($-70^{\circ}C$) and liquid nitrogen ($-196^{\circ}C$) immersion freezing. There were no significant differences on the populations of L. monocytogenes inoculated with chicken breasts under different freezing conditions. However, air blast freezing ($-20^{\circ}C$) resulted in significant reductions for total aerobic bacteria and C. jejuni compared to the control and other freezing treatments. The frozen samples were thawed with (hot or cold) air blast, water immersion, and high pressure thawing at $4^{\circ}C$ and $25^{\circ}C$. the populations of total aerobic bacteria, and yeast and mold in the frozen chicken breast increased by 5.78 and 4.05 log CFU/g after water immersion thawing ($25^{\circ}C$) treatment. After five freeze-thaw cycles, the populations of total aerobic bacteria, yeast and mold, and C. jejuni were reduced by 0.29~1.40 log cycles, while there were no significant differences (P > 0.05) in the populations of L. monocytogenes depending on the freeze-thaw cycles. In addition, the histological examination of chicken breasts showed an increase in spacing between the muscle fiber and torn muscle fiber bundles as the number of freeze-thaw cycles increased. These results indicate that freezing and thawing processes could affect in the levels of microbial contamination and the histological change of chicken breasts.

• Food Engineering Progress
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• v.22 no.4
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• pp.328-336
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• 2018

The aim of this study was to investigate the effect of pretreatments on quality of frozen peach. Pretreatments including steam blanching, water blanching, high pressure, and osmotic dehydration were applied to two varieties (Daeokgye and Hwangdo). Pretreated peaches were frozen and thawed at $-20^{\circ}C$ and $5^{\circ}C$, respectively. Steam blanching and osmotic dehydration with ascorbic acid reduced ${\Delta}E$ values without change of pH and acidity. Osmotic dehydration with sucrose decreased drip loss and increased brix. Freezing/thawing resulted in an increase of maximum force, while maximum force decreased with increasing time of steam and water blanching. Furthermore, osmotic dehydration with calcium chloride increased maximum force. High pressure decreased maximum force of Daeokgye and increased that of Hwangdo compared with non-treatment. Total polyphenol content, DPPH radical scavenging activity, and ABTS radical scavenging activity were improved by pretreatment including steam blanching, blanching, and osmotic dehydration with ascorbic acid.

• Proceedings of the Microbiological Society of Korea Conference
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• 2001.11a
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• pp.39-45
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• 2001

Extremophiles are unique microorganisms that are adapted to survive in ecological niches such as high or low temperatures, extremes of pH, high salt concentrations and high pressure. These unusual microorganisms have unique biochemical features which can be exploited for use in the biotechnological industries. Due to the high biodiversity of extremophilic archaea and bacteria and their existence in various biotopes a variety of biocatalysts with different physicochemical properties have been discovered. The extreme molecular stability of their enzymes, membranes and the synthesis of unique organic compounds and polymers make extremophiles interesting candidates for basic and applied research. Some of the enzymes from extremophiles, especially hyperthermophilic marine microorganisms (growth above $85^{\circ}C$), have already been purified in our laboratory. These include the enzyme systems from Pyrococcus, Pyrodictium, Thermococcus and Thermotoga sp. that are involved in polysacharide modification and protein bioconversion. Only recently, the genome of the thermoalkaliphilic strain. Anaerobranca gottschalkii has been completely sequenced providing a unique resource of novel biocatalysts that are active at high temperature and pH. The gene encoding the branching enzyme from this organism was cloned and expressed in a mesophilic host and finally characterized. A novel glucoamylase was purified from an aerobic archaeon which shows optimal activity at $90^{\circ}C$ and pH 2.0. This thermoacidophilic archaeon Picrophilus oshimae grows optimally at pH 0.7 and $60^{\circ}C$. Furthermore, we were able to detect thermoactive proteases from two anaerobic isolates which are able to hydrolyze feather keratin completely at $80^{\circ}C$ forming amino acids and peptides. In addition, new marine psychrophilic isolates will be presented that are able to secrete enzymes such as lipases, proteases and amylases possessing high activity below the freezing point of water.