• Journal of Power System Engineering
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• v.17 no.2
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• pp.95-102
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• 2013

For vessels operating in the cold climate regions, the ballast water inside or hopper tanks above the waterline may be frozen, starting at the top of the tank and at the side walls. Therefore, countermeasures against freeze-up of the ballast tank such as air-bubbling system, hot steam injecting system, heating coil system and water circulating system are taken to prevent freeze-up phenomenon; however, there are no rigorous investigations of anti-freezing to examine the effectiveness and validity of systems against freeze-up of the ballast tank, in which the temperatures are about $-25^{\circ}C$ (ambient air temperature) and $0^{\circ}C$ (sea water), respectively. In this paper, to ensure reasonable specifications for cold regions if the measures from the above-mentioned systems against freeze-up are effective, the phenomenon of ballast tank freeze-up is simulated and discussed in low temperature conditions. With the results using the commercial CFD code, CFX 14, the most cost-effective solution is conducted to prevent being frozen along the outer surface.

• Journal of Power System Engineering
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• v.17 no.5
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• pp.30-37
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• 2013

For vessels operating in the cold climate regions, the ballast water inside or hopper tanks above the waterline may be frozen, starting at the top of the tank and at the side walls. Therefore, countermeasures against freeze-up of the ballast tank such as air-bubbling system, hot steam injecting system, heating coil system and water circulating system are taken to prevent freeze-up phenomenon; however, there are no rigorous investigations of anti-freezing to examine the effectiveness and validity of systems against freeze-up of the ballast tank, in which the temperatures are about -$25^{\circ}C$ (ambient air temperature) and $0^{\circ}C$ (sea water), respectively. In this paper, to ensure reasonable specifications for cold regions if the measures from the above-mentioned systems against freeze-up are effective, the phenomenon of ballast tank freeze-up is simulated and discussed in low temperature conditions. With the results using the commercial CFD code, CFX 14, the most cost-effective solution is conducted to prevent being frozen along the outer surface.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.663-668
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• 2002

In this paper, insulating effects and strength development of concrete placed at mock up model structure are discussed using anti freezing agent and insulating forms. According to test results, concrete containing 8% of anti freezing agent shows lower freezing temperature, earlier setting time and higher strength development than plain concrete. As for the temperature history of mock up structures, when plain concrete is placed at euro form, the temperature drops to -4${\circ}$ before early 24 hours, and when concrete containing anti freeze agent at euro form, it to -3${\circ}$ before early 24 hours. Nevertheless, when concrete containing anti freeze agent is placed at insulating form, it does not go below zero, and the concrete containing anti freeze agent enhances higher strength development.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.13.2-17
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• 2003

When fresh concrete is exposed to low temperature, the concrete may suffer frost damage due to freezing at early ages and strength development may be delayed. One of the solution methods to resolve these problems is to lower freezing temperature of concrete by the use of chemical admixture called Accelerators for Freeze Protection. In this study, it was the results of appling cold weather concrete using Accelerator for Freeze Protection in the Daewoo Trump world field. Before the application of the cold weather concrete using accelerator for freeze protection, we executed the some test in the laboratory and mock-up test in the field. We examined the manifestation of compressive strength complying with the amount of Accelerators for Freeze Protection and curing conditions, and then made a selection of most suitable amount of Accelerators for Freeze Protection.

• Journal of the Korea Institute of Building Construction
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• v.3 no.4
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• pp.87-94
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• 2003

This study is to investigate the temperature hysteresis and development of compressive strength due to the curing conditions and to evaluate the optimum curing condition of test specimens showing the same development of strength to that of real structures in cold weather. The results of temperature curve with curing conditions in mock-up tests showed the trend of decrease plain concrete with insulation form, plain concrete with heating, concrete with accelerator for freeze protection, and control concrete in turn. The strength development of plain concrete of inside and outside of shelter showed the very slow strength gains due to early freezing, but that of concrete with accelerator for freeze protection showed the gradual increase of strength with time. From this, it is clear that accelerator for freeze protection has the effects of refusing the freezing temperature and accelerating the hardening under low temperature. Strength test results of small specimens embedded in members and located in insulation boxes at the site are similar to that of cores drilled from the members at the same ages, thus it is clear that these curing methods are effective for evaluating in-place concrete strength

• Food Science and Biotechnology
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• v.15 no.6
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• pp.844-850
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• 2006

This study was designed to compare various quality characteristics, such as nutrient composition and physicochemical and sensory properties of freeze-concentrated milk made by a newly developed continuous multi-stage process with those of evaporated milk. The freeze concentration process reduced the water content up to 73%. Most of the physicochemical properties of evaporated milk were different from raw milk; however the freeze-concentrated milk showed little difference from the raw milk. The thiobarbituric acid value and free fatty acid concentrations were significantly greater in the evaporated milk than in the freeze-concentrated milk. Several effects on sensory characteristics, such as off-taste, were significantly stronger in the evaporated milk. Overall, this study indicates that the newly developed freeze concentration technique results in improved physicochemical and sensory properties, and has little effect on most nutrient levels when compared with the evaporation process. Further research is necessary to further elucidate the chemical and sensory properties of freeze-concentrated milk.

• Biotechnology and Bioprocess Engineering:BBE
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• v.11 no.6
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• pp.489-495
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• 2006

In recent years, there has been an interest to use Moringa oleifera as the natural coagulant due to cost, associated health and environmental concerns of synthetic organic polymers and inorganic chemicals. However, it is known that M. oleifera as the natural coagulant is highly biodegradable and has a very short shelf life. This research was carried out to investigate the effects of storage temperature, packaging methods, and freeze-drying on the preservation of M. oleifera seeds powders. Non freeze-dried M. oleifera was prepared into different packaging namely open container, closed container and vacuum packing, whilst, freeze-dried M. oleifera was stored in closed container and vacuum packing. Each of the packaging was stored at room temperature ($30\;to\;32^{\circ}C$) and refrigerator ($4^{\circ}C$). The turbidity removal efficiencies of stored M. oleifera were examined using jar test at monthly interval for 12 months. The results indicated that non freeze-dried M. oleifera kept in the refrigerator ($4^{\circ}C$) would preserve its coagulation efficiency. In addition, closed container and vacuum packing were found to be more appropriate for the preservation of non freeze-dried M. oleifera, compared to open container. Freeze-dried M. oleifera retained its high coagulation efficiency regardless the storage temperature and packaging method for up to 11 months. Besides, higher increment in zeta potential values for water coagulated with freeze-dried M. oleifera indicated the higher frequency of charge neutralization and better coagulation efficiency of freeze-dried M. oleifera, compared to non freeze-dried seeds. As a coagulant, M. oleifera did not affect the pH of the water after treatment.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.96-98
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• 2006

Proper water management is vital to achieve high performance and durability of PEFC (Polymer Electrolyte Fuel Cell). The effects of the residual water from PEFC after purge in shut-down processes on GDL/MEAs were investigated with freeze/thaw cycles Freeze/thaw cycle tests were conducted with single cells which were designed from transparent acryl plates. Single cells which contain several amount of residual water were cycles from $80^{\circ}C$ to $-28^{\circ}C$. The resistance changes of the single cells which have various amount of residual water were evaluated by ac-impedance analysis with 24 times of freeze/thaw cycles. Also, after the freeze/thaw cycles, the property changes were characterized by visual methods such as SEM, EPMA. Though it was difficult to observe noticeable property changes in the visual characterizations, the resistance of cells dramatically increased with the amount of remained water.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.161-168
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• 2008

The freeze-thaw deterioration and chloride attack, which are the typical degradation factors for durability of marine concrete, are significantly affected by pore structures in terms of penetration and diffusion. These pore structures of concrete are closely related to the types and amount of AE agent, used to guarantee the resistance of freeze-thaw deterioration, and the elapsed time before concrete pouring. This paper evaluates the durability of concrete based on the results of tests on cylinder specimens and core specimens from mock-up members with different air content of 4~6% and 8~10%, respectively. According to the test results, the air content of hardened concrete is 2.5~5.2% at 7 days and 2.4~5.1% at 28 days. These air contents are about half of the initial values just after the concrete mixing. Judging from the amount of scale after the freeze-thaw test completed, air content of 8~10% is slightly more beneficial against the deterioration of concrete than air content of 4~6%. Meanwhile, the core specimens from mock-up members exhibit somewhat unfavorable freeze-thaw deterioration and chloride migration characteristic compared with the cylinder specimens tested in the laboratory under the same mixing condition, as to show 106% in freeze-thaw test and 160% in chloride diffusion coefficient test, respectively.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.281-283
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• 2005

Water management in polymer electrolyte membrane fuel cells(PEMFCs) is one of the most challenging issues. Freeze start-up in the automotive applications is also important research topic in the PEMFC field. Transportation of proton and separation of reactant gases are main roles of polymer electrolyte membranes. It has been known that water in the membrane conducts as a vehicle for the proton transportation. At sub-zero temperature, the frozen water blocks the access of reactant gases to the active sites of electrode as well as occurs the physical destruction of fuel cell structures. In this study, property changes of electrolyte membranes in the freeze conditions $(at\;-25^{\circ}C)$ were investigated. For the various amount of water contained membranes, the property changes, especially for the proton conductivity, were observed after several times of freeze/thaw$(-25\~80^{\circ}C)$ cycle.