• Journal of the Korean Society of Food Science and Nutrition
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• v.14 no.4
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• pp.353-358
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• 1985

Three kinds of aqueous solution of tobacco extracts are used as a new experimental material. It is measured how the operating condition, freezing point, viscosity as fundamental properties have the relation to concentration and temperature of the solution. The results of this study are obtained as follows. 1) The freezing point of the solution $(t_m)$ is presented; $t_m=-{\frac{18.6X}{170-{\frac{X}{100}}(170+18)}}$ 2) The correlation of the viscosity, the temperature and the concentration of the solution is followed; $log_{10{\mu}}={\frac{1585}{T}}+2.11{\frac{X}{100-X}}-5.50$ 3) The ice crystals whose circumference is a toothed wheel are made from high concentrated solution, and the thick plate shaped ones are done from the low concentrated solution.

• Journal of the Korean Society of Food Culture
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• v.33 no.2
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• pp.125-132
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• 2018

This study was carried out to determine the optimal storage conditions by examining the effects of the storage conditions on the quality of red pepper powder during storage in households. Red pepper powder was stored at room temperature ($20^{\circ}C$), refrigeration (2 and $-1^{\circ}C$) and frozen (-5 and $-20^{\circ}C$) for 3, 6, 9 and 12 months. The ASTA color value, capsanthin content and redness ($a^{\ast}$) of the red pepper powders stored at -5 and $-20^{\circ}C$ were not decreased significantly depending on the storage temperatures until 9 months. The pH of red pepper powder stored at $20^{\circ}C$ decreased significantly until 9 months and increased at 12 months. The microbiological quality of the red pepper powder stored at -5 and $-20^{\circ}C$ was more stable during long-term storage. In the sensory evaluation of red pepper powder stored under all conditions, the overall freshness, redness, hot flavor, moisture release, and edibility decreased with increasing storage period from the control to 12 months. Moisture release increased from 3 months to 12 months. Overall, red pepper should be stored at low temperatures (2, $-1^{\circ}C$) for up to 6 months, and frozen (${\geq} -5^{\circ}C$) for 6 to 9 months. The optimal temperature for long-term storage (${\geq}9$ months) was $-20^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.9
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• pp.845-854
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• 2004

The evaporation heat transfer coefficient for R-l34a, R-407C (a mixture of 23wt% R-32, 25 wt% R-125, and 52 wt% R-l34a) and R-410A (a mixture of 50 wt% R-32 and 50 wt% R-125) flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study. Four vertical counterflow channels were formed in the exchanger by four plates of commercial geometry with a corrugated sinusoid shape of a chevron angle of 45 degree. The effects of the mean vapor quality, mass flux, heat flux, and saturation temperature of different refrigerants on the evaporation heat transfer were explored in detail. Similar to the case of a Plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. It is found that the evaporation heat transfer coefficient in the plates is much higher than that in circular pipes. The present data show that the evaporation heat transfer coefficients of all refrigerants increase with the vapor quality. At a higher mass flux h, is higher than for the entire range of the vapor quality. Raising the imposed wall heat flux was found to slightly improve h$_{r}$, while h$_{r}$ is found to be lower at a higher refrigerant saturation temperature. A comparison of the performance of the various refrigerants reveals that R-410A has the highest heat transfer performance followed by R-l34a, and R-407C had the lowest performance of the refrigerants tested. Based on the present data, empirical correlations of the evaporation heat transfer coefficient were proposed.sed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.4
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• pp.266-273
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• 2008

Natural gas hydrates are ice-like solid substances, which are composed of water and natural gas, mainly methane. They have three kinds of crystal structures of five polyhedra formed by hydrogen-bonded water molecules, and are stable at high pressures and low temperatures. They contain large amounts of organic carbon and widely occur in deep oceans and permafrost regions. Therefore, they are expected as a potential energy resource in the future. Especially, $1m^3$ natural gas hydrate contains up to $172Nm^3$ of methane gas, de pending on the pressure and temperature of production. Such large volumes make natural gas hydrates can be used to store and transport natural gas. In this study, three-phase equilibrium conditions for forming natural gas hydrate were numerically obtained in pure water and single electrolyte solution containing 3 wt% NaCl. The results show that the predictions match the previous experimental values very well, and it was found that NaCl acts as an inhibitor. Also, help gases such that ethane, propane, i-butane, and n-butane reduce the hydrate formation pressure at the same temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.4
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• pp.303-311
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• 2011

This study presents a new idea of liquid desiccant dehumidifier with extended surface to improve the compactness. Extended surface is inserted between vertical cooling tubes, and the liquid desiccant flows down along the tube walls and the extended surface as well. Though the extended surface contributes to the increase in the mass transfer area, the effect tends to be limited because less conductive non-metallic materials need to be applied due to the high corrosiveness of liquid desiccant. To analyze the effects of the extended surface insertion, mathematical modelling and numerical integration are performed for the heat and mass transfer in the liquid desiccant dehumidifier. The results show that, though the liquid desiccant on the extended surface is heated due to the moisture absorption, the temperature can be maintained by periodic mixing at the contact points between the tube and the extended surface with the liquid desiccant stream from the tube side at a relatively low temperature. This implies the absorption heat from the extended surface side can be removed effectively by mixing, which leads to a substantial improvement of the dehumidification in the liquid desiccant dehumidifier with extended surface. When the interval of the extended surface, $p_e/L$, is less than 0.1, the dehumidification is shown to increase by more than two times compared with that without extended surface.

• Journal of Biosystems Engineering
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• v.26 no.5
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• pp.449-460
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• 2001

This study was carried out to develop a simulation model with EES(Engineering equation solver) for analyzing the performance of a grain cooler. In order to validate the developed simulation model, several main factors which have affected on the performance of the gain cooler were investigated through experiments. A simulation model was developed in the standard vapor compression cycle, and then this model was modified considering irreversibe factors so that the developed alternate model could predict the actual cycle of a grain cooler. The compressor efficiency in vapor compression cycle considering irreversibility much affected on the coefficient of performance(COP). The COP in the standard vapor compression cycle model was greatly as high as about 6.50, but the COP in an alternative model considering irreversibility was as low as about 3.27. As a result of comparison between the actual cycle and the vapor compression cycle considering irreversibility, the difference of pressure at compressor outlet(inlet) was a little by about 48kPa (8.8kPa), the temperatures of refrigerant at main parts of the grain cooler were similar. and the temperature of chilled air was about 8$\^{C}$ in both. The model considering irreversibility could predict performance of the grain cooler. The theoretical period required to chill grain of 1,383kg from the initial temperature 24$\^{C}$ to below 11$\^{C}$ was about 55 hours 30 minutes, and the actual period required in a grain bin was about 58 hours. The difference between the predicted and an actual period was about 2 hours 30 minutes. The cooling performance predicted by the developed model could well estimate the cooling period required to chill the grain.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2323-2327
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• 2010

The experimental apparatus consists of dehumidifier with multi-layer type heat exchangers to remove the moisture from automatic equipments, semiconductors, and manufacturing processes under the low temperature environment, and chemical production lines which are likely to take moisture. The major components of this system are four evaporators with different fin pitch, two compressors, two condensers and an expansion valve. In this study, the performance characteristics of dehumidifier is analyzed by the variations of frontal air velocity in the first heat exchanger(evaporator). The cooling capacity of each heat exchanger is acquired by the enthalpy calculating from measuring point of temperature and relative humidity of the first heat exchanger from 1.0m/s to 4.0m/s with increasing interval 0.5m/s, and the front air velocity. As a result, it is found that cooling capacity of the first heat exchanger showed the best cooling capacity when its frontal air velocity is 2.0 m/s.

• Journal of the Korean Society of Food Science and Nutrition
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• v.33 no.5
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• pp.911-916
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• 2004

Widely used vegetables such as onion, soybean sprout, and carrot in Korean dishes were studied to reduce losses in firmness during cook/chill storage for food service system. Blanching at 7$0^{\circ}C$ affect positively on textural properties of the three vegetables while reheating at the food service practice. Firmness of the vegetables was improved and stabilized with addition of calcium ion in blanching solution during storage at refrigeration temperature. Calcium was effective to improve or sustain firmness during blanching. The effect of calcium on firmness of blanched and cooked soybean sprout was less significant than that of carrot and onion, especially at short period of storage under refrigerated condition. In conclusion, low temperature blanching with calcium ion was effective to maintain firmness of the three vegetables before cooking while refrigerated storage of the cooked vegetables and subsequent reheating for food service system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.6
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• pp.381-387
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• 2008

The presence of non-condensable gases as an additional thermal resistance inside a refrigerating circuit has been found for a general refrigerator, The effect of non-condensable gases was varied by controlling the injection amount of dry air into the refrigerating circuit to increase a thermal resistance. Energy consumption tests for the refrigerator were conducted under the various amounts of non-condensable gases. The tested refrigerating circuit was the household refrigerator. As the molar fraction of non-condensable gases was increased from 0% to 1.46%, the amount of energy consumption was found to increase up to 25%. The increase of the amount of non-condensable gases in refrigerating circuit was found to result in increasing the condensation temperature at the condenser and decreasing the evaporation temperature at the evaporator, which were presumably caused by the low specific heat and increased partial pressure of non-condensable gas.

• Korean Journal of Food Science and Technology
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• v.28 no.4
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• pp.632-637
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• 1996

Effects of refrigeration temperature and its fluctuation range on the growth of psychrotrophic microorganisms and the quality of refrigerated foods such as apple, fish and oyster were evaluated to find optimum storage conditions for a domestic refrigerator. Refrigeration temperature was $2^{\circ}C$ or $4^{\circ}C$, and fluctuation ranges were varied: ${\pm}0.3,\;{\pm}1.0,\;{\pm}1.2,\;or\;{\pm}4.0^{\circ}C$. Changes in hardness of apples stored at $2{\pm}0.3^{\circ}C$ were much slower than those of apples stored at $4{\pm}1.2^{\circ}C$. Freshness of fish and oyster also lasted much longer at low temperature such as $2{\pm}0.3^{\circ}C$. The growth of Listeria monocytogenes inoculated on sliced ham was inhibited for 1 month at $2{\pm}0.3^{\circ}C$, but the cells at $4{\pm}1.2^{\circ}C$ began to grows as time elapsed. Therefore, it was expected that shelf-life of certain food stored in a domestic refrigerator could be extended by lowering temperature to $2^{\circ}C$ and by reducing fluctuation range of refrigerator.