• Journal of Hydrogen and New Energy
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• v.20 no.3
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• pp.224-231
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• 2009

The improvement of cold start capability is one of the most challenging tasks to be solved for commercialization of fuel cell vehicle. In this study, cold start test and ice blocking test(IBT) of fuel cell stack were carried out under various operating conditions. This fuel cell stack can be thawed from -20$^{\circ}$C within 25s and the voltage change was found to be comprised of 4 steps; the first step is the voltage decrease by overpotential, the second step is the voltage increase by the cell temperature increase, the third step is the voltage decrease by ice blocking, and the last step is the voltage increase by thawing. Bootstrap startup was failed after shutdown at temperature under 40$^{\circ}$C because of much condensed water in the fuel cell. Quantitative estimation of cold start capability have been demonstrated by ice blocking test(IBT). In the results, it was found that cold start capability was improved double every 10$^{\circ}$C from 30$^{\circ}$C to 65$^{\circ}$C and enhanced by 30% at the condition of SR 3/4 compared to SR 1.5/2.0 and enhanced by 20% with dry purge condition compared to with RH 50% purge condition.

• International Journal of Highway Engineering
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• v.7 no.2 s.24
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• pp.87-95
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• 2005

To prevent the lowering of structural capability due to freezing and thawing in cold winter, numerous researches on frost heaving have been performed. As the result, the freezing index contour map of the Korea peninsula has been made for the design of the anti-freezing layer of pavements. However, the validity of the anti-freezing layer needs to be evaluated because systematic investigations on the variation of freezing depth with the thickness and material types of pavement layers and the configuration of the ground have been rarely performed. The freezing index of the Korea Highway Corporation test road site was calculated and the freezing depths of the concrete and asphalt pavements of the test road were investigated using the ambient and pavement temperature and water content. In addition, the investigated freezing depths were compared to the values estimated by existing freezing depth models. This is the preliminary study on the freezing-related data measured at the test road. The results with higher reliability will be produced by the long-term accumulation of the data and the analysis on it.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.177-183
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• 2011

VES-LMC(very-early strength latex modified concrete) has been widely used as repair material for bridge deck overlay or rehabilitation, because it could be opened to the traffic after 3 hours of curing. However, the bright color of VES-LMC disturb driver's sigh. A black VES-LMC, matching to asphalt concrete, was developed and applied at a filed for driver's comfort and safety. The black VES-LMC included 2% carbon black in cement weight ratio. A series of performance evaluation for black VES-LMC was done in terms of field applicability, pavement color and temperature change. The field applicability test result showed that there were no change of workability, slump and air void, and the compressive strengthen developed more than 20MPa after 4 hours of placement. The thermal stress of black VES-LMC was smaller than that of OPC and asphalt concrete, which means the stability of black VES-LMC. The performance evaluation result showed that the black VES-LMC could prevent road icing at below zero temperatures and promote thawing at melting temperature.

• Applied Chemistry for Engineering
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• v.1 no.1
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• pp.23-29
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• 1990

The effect of a rapid freeze pretreatment of organic ion exchange resins on their grinding properties was studied. It was found that the structure of ion exchange resins was defected by freezing pressure formed in the process of rapid freezing. The defected resins didn't recover their own structure after thawing and those could be easy to be broken at room temperature by small force. Therefore, organic ion exchange resins could be ground readily at room temperature after rapid-freezing the fully swelled resins using by solid carbon dioxide, or liquid nitrogen. The rapid freeze pretreatment of cation exchange resins was very effective on grinding in particular. However, the effect of the pretreatment of anion exchange resins on grinding was less than that of cation exchange resins. In case of anion exchange resins, the ionic form of affected the grindability remarkably.

• Journal of the Korean Geotechnical Society
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• v.30 no.8
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• pp.39-47
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• 2014

Frost heaving and thawing settlement cause unexpected stress around buried pipelines, which results in deformation and permanent demage. A large scale laboratory test has been performed to observe deformation, stress, and temperature of a buried pipe during atmospheric temperature changes. From the experimental results, the stress concentrated around the buried pipe is inevitable and deformation is caused by the frost heaving. Even though backfill materials are sandy soils which are normally assumed to be non frost susceptible, it is revealed that frost demage can happen due to drainage condition, the level of ground water table, and water content.

• Korean Journal of Agricultural Science
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• v.45 no.2
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• pp.177-184
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• 2018

The frost heave process from repeated freezing and thawing actions in winter on forest road cut-slopes is important for forest road maintenance and management. This study investigated the damages of the forest heave process on forest road cut-slopes by measuring the changes in the road-cut surface elevation and sediment production and by conducting vegetation surveys which were aimed at providing information for forest road maintenance plans. The temperature and humidity differences were determined between the north and south cut-slopes. T-test showed that the north slope had a lower temperature and humidity than that of the south slope. Field observations also confirmed frozen soils on the north slopes, indicating that the north slopes are susceptible to frost heave. Sediment was converted to dry weight per unit area ($g/m^2$). T-test showed that the north slope produced more sediment than that of the south slope. The study confirmed that more frost heave occurred on the north cut-slopes than on the south cut-slopes. Vegetation surveys were conducted on five cut-slope plots. Considering the dominant species found above the cut-slopes, vegetations in all the plots are expected to succeed to pine and oak in the future. The dominant species appearing on the cut-slopes of the study area were exotic species because the elapsed time of the site was only 2 - 4 years.

• Journal of Embryo Transfer
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• v.9 no.1
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• pp.65-71
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• 1994

This study were carried out to investigate the effective concentration of cryoprotectant agents and sucrose by one-step straw method, and to determine the optimum thawing temperature and equilibration time of frozen bovine embryos. The bovine embryos following dehydration by cryoprotective agents and a various concentration of sucrose were directly plunged into liquid nitrogen and thawed in 3O$^{\circ}C$ water. Survival rate was defined by FDA test. The results are summarized as follows : 1. The survival rate of bovine embryos thawed after rapid freezing in the freezing medium containing a various kinds of cryoprotective agents added 0.25M and O.50M sucrose were 28.6% and 25.0%, 35.1% and 31.6%, 32.4% and 24.4%, 34.2% and 28.2%, 18.9% and 17.6%, 14.7.% and 21.6%, respectively. 2. The survival rate of bovine embryos thawed after rapid freezing in the freezing medium containing a various concentration of sucrose added 1.5M and 2.OM glycerol, i.5M and 2.OM DMSO and 1.5M and 2.OM propanediol were 22.9~37.8%, 2O.7~31. 3%, 19.2~30.0% and 17.2~25.0%, respectively. 3. The temperature thawed at 2$0^{\circ}C$ after rapid freezing of bovine embryos resulted in a significantly higher embryos survival rate than did at 3$0^{\circ}C$ and 35$^{\circ}C$. 4. The equilibration time on the survival rate of bovine embryos was attained after short period of time(2.5~5 min.) in the freezing medium higher than long period of time (1O~20 min.).

• Korean Journal of Animal Reproduction
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• v.20 no.3
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• pp.233-238
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• 1996

This study was conducted to investigate the effects of cryoprotective agents and thawing temperature on the survival rate of the bisected embryos of mouse. The results of this study were summairzed as follows: 1. In in vitro culture after frozen with DMSO, glycerol, ethylene glycol or propanediol and thawed, the rates of normally developed bisected morula which was denuded were 31.7, 39.1, 28.0 and 23.1%, respectively. 2. The survival rates of bisected morula encased into the zona pellucida in in vitro culture after frozen with DMSO, glycerol, ethylene glycol or propanediol and thawed were 72.4, 68.7, 64.0 and 59.5%, respectively. 3. The survival rates of bisected denuded blastura in in vitro culture after frozen with DMSO, glycerol, ethylene glycol or propanediol and thawed were 48.3, 44.8, 32.1 and 28.6%, respectively. 4. The survival rates of bisected blasturae encased into the zona pellucida in in vitro culture after frozen with DMSO, glycerol, ethylene glycol or propanediol and thawed were 73.6, 67.4, 53.0 and 49.1%, respectively. 5. In in vitro culture after frozen with DMSO, glycerol, ethylene glycol or propanediol and thawed at room temperature, the rates of the normally developed bisected morula which was encased into the zona pellucida were 67.1, 62.3, 57.7 and 53.0%, respectively, and those of the bisected blasturae encased into the zona pellucida were 70.8, 65.4, 56.6 and 52.1%, respectively. 6. The survival rates of bisected morula which was encased into the zona pellucida in in vitro culture after forzen with DMSO, glycerol, ethylene glycerol or propanediol and thawed at 37$^{\circ}C$ were 74.3, 71.3, 63.9 and 57.4%, respectively, and those of bisected blastura encased into zona pellucida were 76.0, 69.1, 61.1 and 56.1%, respectively.

• Korean journal of food and cookery science
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• v.2 no.2
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• pp.21-31
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• 1986

Here is a research on hospital foodservice system, when korea traditional food of pyeon yuk and bin dae deok were used by ready-prepared foodservice system, it was estimated the preservations of microbiological quality and sensory quality. All data collection was replicated three times. The results were as following; 1. In time and temperature data, two menu items were needed internal temperature below $7^{\circ}C$ in a cooling stage, and in the case of cook/chill storage, the days were shortened within weeks, and the holding time must be possiblely minimized. Finally foods were served sanitary. 2. In view of microbiological safety, in the case of cook/chill storage as $0{\sim}4^{\circ}C$ the days must be shortened within 2 weeks and its was possible to store until 6 weeks in $-20{\sim}-23.3^{\circ}C$. So to preserve pre-cooked food longly, it was effective to freeze them quickly by using vacuum package and to reheat them by a microwave oven before serving and to serve lastly in microbiological quality. 3. Hospital ready-prepared foodservice system with food storage in plastic bags, biochemical test of C. Perfingens C. botulinum and Salmonella were not detected. 4. By using of a microwave oven, it had effects of thawing, reheating and sterilizing of chilled and frozen foods in a short time. 5. Sensory evaluations were made by a 10-member panel using five scoring tests. Because sensory of quality was lowered in the case of chilled storage, it was possible to serve foods within 2 weeks. Texture and aroma were preserved by cook/frozen system and usually there was no significance from 4 weeks until 6 weeks, but considering of the objects, it was good to store until 4 weeks in sensory quality.

• Food Science of Animal Resources
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• v.41 no.6
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• pp.1012-1021
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• 2021

This study evaluated the effect of freezing rate on the quality characteristics of pork loin to establish an objective standard for rapid freezing. To generate various freezing rates, three air flow rates (0, 1.5, and 3.0 m/s) were applied under three freezing temperatures (-20℃, -30℃, and -40℃). Based on the results, freezing rates ranged from 0.26-1.42 cm/h and were graded by three categories, i.e, slow (category I, >0.4 cm/h), intermediate (category II, 0.6-0.7 cm/h) and rapid freezing (category III, >0.96 cm/h). Both temperature and the air flow rate influenced the freezing rate, and the freezing rate affected the ice crystal size and shear force in pork loin. However, the air flow rate did not affect thawing loss, drip loss or the color of pork loins. In the comparison of freezing rates, pork belonging to category II did not show a clear difference in quality parameters from pork in category I. Furthermore, pork in category III showed fresh meat-like qualities, and the quality characteristics were clearly distinct from those of category I. Although the current standard for rapid freezing rate is 0.5 cm/h, this study suggested that 0.96 cm/h is the lowest freezing rate for achieving meat quality distinguishable from that achieved with conventional freezing, and further increasing the freezing rate did not provide advantages from an energy consumption perspective.