• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3276-3286
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• 1994

In most direct contact liquid-liquid heat exchangers, oil or hydrocarbon with a density less than water is normally used as dispersed working fluid. The main difficulty that arises with this arrangement lies in the control of the interface at the top of the column. When it is connected with a solar collector which uses water as its working fluid, the main difficulties arise from the fact that the water can be frozen during winter time. In order to solve these problems and to demonstrate the technical feasibility of a direct contact liquid-liquid heat exchanger, liquids heavier than water with low freezing temperature has been utilized as dispersed phase liquids in a small laboratory scale model made of pyrex glass. In the present investigation, dimethyl phthalate(C/sub 6/H/sub 4/)COOCH/sub 3/)/sub 2/) and diethyl phthalate (C/sub 6/H/sub 4/(CO/sub 2/C/sub 2/H/sub 5/)/sub 2/) are utilized as heavy dispersed phase working fluids. The results of the present investigation the technical in the utilization of heavier dispersed working liquid in the spray-column liquid-liquid heat exchanger for a solar system. The overall average temperature difference along the column is found to be almost half of the initial temperature difference between the dispersed and the continuous phase. Despite the fact that the two phthalates tested in the experiment differ significantly in some of their physical properties, the volumetric heat transfer coefficients in terms of dispersed fluid superficial velocities were found to be similar for both phthalates tested.

• Journal of Powder Materials
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• v.28 no.4
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• pp.331-335
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• 2021

The effects of drying temperature on the microstructure of porous W fabricated by the freeze-casting process of tert-butyl alcohol slurry with WO₃ powder was investigated. Green bodies were hydrogen-reduced at 800℃ for 1 h and sintered at 1000℃ for 6 h. X-ray diffraction analysis revealed that WO₃ powders were completely converted to W without any reaction phases by hydrogen reduction. The sintered body showed pores aligned in the direction of tert-butyl alcohol growth, and the porosity and pore size decreased as the amount of WO₃ increased from 5 to 10vol%. As the drying temperature of the frozen body increased from -25℃ to -10℃, the pore size and thickness of the struts increased. The change in microstructural characteristics based on the amount of powder added and the drying temperature was explained by the growth behavior of the freezing agent and the degree of rearrangement of the solid powder during the solidification of the slurry.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.59-67
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• 2016

The strength of frozen soils is affected by size and shape of particles, and the amount of ice and unfrozen water. The objective of this study is to characterize the unfrozen water content and the unconfined compressive strength of the frozen soils according to the degree of saturations and silt fractions. The specimens are mixtures of sand, silt, and water. The silt fractions (SF), which are the ratio of the silt weight ($W_{silt}$) to the sand weight ($W_{sand}$), are 10% and 30%. In addition, the degrees of the saturation are 5%, 10%, 15%, and 20%. The specimens are frozen under the temperature of $-10^{\circ}C$ conditions. The uniaxial compression tests are conducted for 24 hours, 48 hours, and 72 hours after freezing to determine proper freezing time. The freezing time of 24 hours is chosen because the unconfined compressive strengths of specimens after 24 hours freezing times are similar to each other. Furthermore, the unfrozen water content is monitored during freezing using the TDR system. The unfrozen water content increases with the increase of the silt fraction and degree of saturation. The unconfined compressive strength of the frozen soils exponentially increases with increasing the degree of saturation. This study shows that the amount of ice has more influence on the strength of the frozen soils than the amount of unfrozen water.

• Preventive Nutrition and Food Science
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• v.18 no.1
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• pp.67-75
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• 2013

Descriptive analysis and consumer acceptance tests were conducted with frozen (FCR), homemade (HCR), and aseptic-packaged (ACR) cooked rice products from two cultivars-IM and SD. FCR was prepared using a rapid freezing process, which may provide consumers with a quality similar to that of HCR. The intensity of the flavors of roasted, glutinous rice, rice cake, and rice starch and the textures of glutinousness, moistness, chunkiness, adhesiveness, and squishiness were all greater in the FCR as compared to the HCR and ACR (p<0.05) in IM and SD cultivars. The differences in sensory characteristics between the FCR and ACR were larger than the equivalent differences between the FCR and HCR. Overall consumer acceptance ratings for FCR in overall aspect, appearance, aroma, and texture were not significantly different compared to those for HCR (p>0.05); however, in most cases these factors showed significant differences when compared with ACR (p<0.05). From partial least square regression analysis, cooked rice was positively related to sweet, transparency, glossiness, roasted, glutinousness, chunkiness, moistness, glutinous rice, adhesiveness, rice shape, rice starch, and squishiness attributes but negatively related to raw rice, old rice, old rice aroma, a particle feeling, off-aroma, white color, scatteredness, slickness, size of cooked rice, and firmness attributes.

• Journal of the Korean Electrochemical Society
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• v.8 no.4
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• pp.149-154
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• 2005

Fuel cell performance evaluation logic was developed using G-language (LabVIEW) to measure performance stability. Degree of stability and reliability of performance data were improved with averaged value and standard deviation method. Water injection system was introduced and the performance using this method was comparable to that of conventional humidification method. Water injection system has advantage of lowering operation energy consumption, reducing the number of parts needed in humidification, therefore increasing efficiency of fuel cell system. Fuel cell performance was decreased in case of low temperature operation such as sub freezing condition. Air purge method was tested to reduce the water content in cell fixture before sub freezing condition. The performance degradation due to low temperature operation was minimized by air purge method in medium size cell fixture ($25cm^2$) case.

• Journal of Powder Materials
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• v.28 no.3
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• pp.216-220
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• 2021

The effect of tert-butyl alcohol (TBA) as a freezing solvent on the pore structure of a porous tungsten body prepared by freeze-drying is analyzed. TBA slurries with a WO3 content of 10 vol% are prepared by mixing with a small amount of dispersant and binder at 30℃. The slurries are frozen at -25℃, and pores are formed in the frozen specimens by the sublimation of TBA during drying in air. After hydrogen reduction at 800℃ and sintering at 1000℃, the green body of WO₃ is completely converted to porous W with various pore structures. Directional pores from the center of the specimen to the outside are observed in the sintered bodies because of the columnar growth of TBA. A decrease in pore directionality and porosity is observed in the specimens prepared by long-duration drying and sintering. The change in pore structure is explained by the growth of the freezing solvent and densification.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.617-620
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• 2008

When fresh concrete is exposed to the cold weather, the concrete may happen frost damage because of freezing at early ages and the strength development may be go down. Therefore, this paper is intend to investigate the properties and availabilities of cold weather concrete using anti-freeze based formate-acetate for ensure of excellent concrete quality on cold temperature. According to test result for concrete in anti-freeze agent, strength properties in sub-zero temperature increases in comparison with concrete of non anti-freeze agent without decline of strength until later age. When anti-freezing agent is added by 3.0% to binder, it gives good effects on the performance of the fresh and harden concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.124-131
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• 2017

The purpose of this study is to evaluate the basic performance of cement mortar for repair using alumina cement and nitrite can be cured in low temperature environment. For this purpose, the repair mortar used in the domestic construction site was selected and the experimental evaluation was carried out by adjusting the mixing amount by substituting alumina cement and nitrite for the blending ratio. The experimental test results confirmed that alumina cement and nitrite were replaced with the repair mortar, the initial strength was improved. Also, the chemical resistance was improved, the shrinkage behavior was decreased, and the resistance to freezing and thawing was increased. As a result, applying alumina cement and nitrite at a ratio of 2:1 at 7.5%, the surface condition was maintained for 5 months or longer and it was judged to be excellent in practical use for external structures.

• Korean Journal of Materials Research
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• v.23 no.1
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• pp.67-71
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• 2013

Porous $Al_2O_3$ dispersed with nano-sized Cu was fabricated by freeze-drying process and solution chemistry method using Cu-nitrate. To prepare porous $Al_2O_3$, camphene was used as the sublimable vehicle. Camphene slurries with $Al_2O_3$ content of 10 vol% were prepared by milling at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing of the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled to $-25^{\circ}C$ while unidirectionally controlling the growth direction of the camphene. Pores were subsequently generated by sublimation of the camphene during drying in air for 48 h. The green body was sintered in a furnace at $1400^{\circ}C$ for 1 h. Cu particles were dispersed in porous $Al_2O_3$ by calcination and hydrogen reduction of Cu-nitrate. The sintered samples showed large pores with sizes of about $150{\mu}m$; these pores were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores due to the traces of camphene left between the concentrated $Al_2O_3$ particles on the internal wall. EDS analysis revealed that the Cu particles were mainly dispersed on the surfaces of the large pores. These results strongly suggest that porous $Al_2O_3$ with Cu dispersion can be successfully fabricated by freeze-drying and solution chemistry routes.

• Korean Journal of Environmental Agriculture
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• v.33 no.4
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• pp.327-333
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• 2014

BACKGROUND: Rabbiteye blueberry(Vaccinium ashei) is one of the most widely grown blueberry types in the world, together with Northern and Southern highbush blueberry(Vaccinium corymbosum). Rabbiteye blueberry have higher soil adaptability and fruit productivity but less cold tolerance to low temperature than highbush blueberry. The objective of this study is to investigate freezing tolerance of floral buds and establish a cultivation zone for rabbiteye blueberry cultivars. METHODS AND RESULTS: Bearing branches which have similar thickness and same number of floral buds were collected in the early January at the blueberry germplasm preservation plot located in Namhae Sub-station, National Institute of Horticultural and Herbal Science in Gyeongsangnamdo. Cold response of bearing branches were investigated by electrolyte leakage and freezing tolerance of floral buds were determined by ovary browning ratio of 50%($LT_{50}$). Cultivation zone was established based on mean annual extreme minimum temperature for 30 years, from 1981 to 2010. The electrolyte leakage of bearing branches in rabbiteye blueberry increased as temperature decreased and was lowest in 'Brightwell' but highest in 'Bluegem' when they were kept in $-5^{\circ}C$. Besides, the electrolyte leakage increased in 'Brightblue', 'Brightwell', 'Climax', 'Delite', 'Gardenblue', 'Southland' and 'Woodard' in $-20^{\circ}C$. Freezing tolerance($LT_{50}$) was lowest in 'Bluegem' and 'Homebell'($-13.3^{\circ}C$), and highest in 'Tifblue'($-25^{\circ}C$) among different rabbiteye blueberry cultivars. $LT_{50}$ of 'Southland' was from -15.0 to $-16.7^{\circ}C$, that of 'Delite', 'Brightwell',' Austin' and 'Climax' was $-18.3^{\circ}C$, and that of 'Bluebelle', 'Woodard' and 'Powderblue' was $-20^{\circ}C$. CONCLUSION: This study indicate that The hardiness zones of rabbiteye blueberry were classified into Six cultivation zones and cultivation zones of most cultivars were the south of Jeollanam-do and Gyeongdangnam-do, except for 'Tifblue.'