• Journal of Energy Engineering
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• v.15 no.3 s.47
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• pp.166-173
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• 2006

R134a is considered as an alternative refrigerant to R22 for air conditioners. An experimental investigation was made to study the characteristics of the heat transfer and pressure drop for R134a flowing in a fin-and-tube heat exchanger used for commercial air-conditioning units. Experiments were carried out under the conditions of inlet refrigerant temperature of $60^{\circ}C$ and refrigerant mass fluxes of $150,\;200,\;and\;250\;kg/m^{2}s$. The inlet air has dry bulb temperature or $35^{\circ}C$, relative humidity of 40% and air velocity varying from 0.68 to 1.6 m/s. Experiments show that air velocity decreased by 5.9% is needed for R134a than that of R22 while pressure drop for R134a was $18.1{\sim}20.4%$ higher than that of R22 for the degree of subcooling $5^{\circ}C$. The results are useful in designing more compact and effective condensers for various refrigeration and air conditioning systems using refrigerant R134a.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.339-344
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• 2005

A PEMFC system model for FCEV was constructed and simulated numerically to examine the heat/water flow of the system and air/fuel humidification process for various operation conditions (ambient pressure /temperature/humidity, operating temperature, power load). We modeled PEMFC stack which can generate maximum electricity of about 80 kW. This stack consists of 400 unit cells and each unit cell has $250cm^2$ reacting area. Uniform current density and uniform operating voltage per each cell was assumed. The results show the flow characteristics of heat and water at each component of PEMFC system in macro-scale. The capacity shortage of the radiator occurred when the ambient was hot $(over\;40^{\circ}C)$ and power level was high (over 50 kW). In spite of some heat release by evaporation of water in stack, heat unbalance reached to 20kW approximately in such a severe operating condition. This heat unbalance could be recovered by auxiliary radiators or high speed cooling fan with additional cost. In cold environment, the capacity of radiator exceeded the net heat generation to be released, which may cause a problem to drop the operating temperature of stack. We dealt with this problem by regulating mass flow rate of coolant and radiator fan speed. Finally, water balance was not easily broken when we retrieved condensed and/or unused water.

• Tribology and Lubricants
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• v.22 no.5
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• pp.237-242
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• 2006

Surfaces found in nature, including biological surfaces have been providing inspiration to modify/fabricate artificial surfaces as solutions for tribological applications. As an example, the concept of 'lotus-effect' has motivated tribologists world wide to modify/fabricate surfaces for enhanced tribological performance. These was done by creating nano/micro-scale asperities on various surfaces using ion beam milling and ion-beam assisted roughening. In order to understand the attributes of natural surfaces, which are inspirational to tribologists, we characterized the surface of two natural surfaces-Nelumbo nucifera (lotus) and Colocasia esculenta leaves. Further, we evaluated their micro-scale friction property, both in their fresh and dried conditions. The characterization of surfaces was conducted using a confocal microscope and SEM, which involved the evaluation of size and distribution of protuberances. The micro-scale friction property was evaluated using a ball-on-flat type micro-tribo tester, under reciprocating motion. A soda lime glass ball (2 mm diameter) was used in these tests. Tests were conducted at the applied normal load of $3000{\mu}N$, at a sliding speed of 1 mm/sec for a scan length of 3 mm. All experiments were conducted at ambient temperature ($24{\pm}1^{\circ}C}$) and relative humidity ($45{\pm}5%$). It was observed that the friction behaviour of the natural surfaces was influenced by their surface characteristics (morphology and distribution of protuberances) and also by the condition (fresh or dried) in which they were tested.

• Membrane Journal
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• v.19 no.1
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• pp.25-33
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• 2009

PES (polyethersulfone) membranes with highly enhanced their asymmetry were prepared by phase inversion process. The membranes were prepared by using PES/DMF (N,N-dimethylformamide)/TSA (p-toluenesulfonic acid)/PVP (polyvinylpyrrolidone) casting solution and water coagulant. The pre-coagulation of membrane surface which was induced by an addition of TSA as a demixing agent and PVP as a swelling polymer in the PES solution and humid exposure time, played a crucial role in determining morphological properties and the PWP (pure water permeation) performance. The PES solution was coated on polyester film under condition of 80% humidity for a while ($72{\sim}144$ sec) before immersing in a coagulation bath. The characterization of membranes was carried out by a capillary flow porometer, a FE-SEM and a permeation test apparatus. As the thickness of the smallest pore size layer (SPL) decreased, the asymmetry of membrane increased under conditions of 20 wt% of TSA and 10 wt% of PVP in 11 wt% of PES solution during longer humid contact time. As a result, the membranes showed a remarkable increase of PWP.

• 보존과학연구
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• s.26
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• pp.141-164
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• 2005

Most of the stone cultural properties is exposed to the weathering factor(rain, windetc.), so the shelter is constructed for reduction of its direct effect. But the shelter is indicated some problems that inharmoniousness of the surroundings, in section disturbance for insufficiency of light, the loss about the value of cultural properties and so on. So we have investigated on environmental condition (temperature, relative humidity, wind etc.) at the Standing Stone Buddhist Triad in Bae-ri, Gyeongju and Rock-carved Triad Buddha in Seosan because check the effect of the shelter. As the result, the Standing Stone Buddhist Triad in Bae-ri, Gyeongju is located a pine wood and a lot of bamboo grow naturally in nearing. Environmental difference on inside and outside of the shelter is not found because opened on all sides. But there is so dim for the direction of the sunlight that can't see the Standing Stone Buddhist. The base rock of Rock-carved Triad Buddha in Seosan well develop with crack and break, and the vegetation(trees, moss, lichen etc.) grow naturally in surroundings. Environmental difference on inside and outside of the shelter is found because closed on all sides and opened the front gate only inspection time. Inside of the shelter was too calm(air-velocity not detected) and humid(over 75%RH). Also the surface is occurred the dew(at 2-4 pm) and the efflorescence for effect of the water(rain, dew etc.). Besides the head of the central Buddhist is so dangerous for crack.

• 보존과학연구
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• s.31
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• pp.103-120
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• 2010

Most of the important stone cultural heritage (National treasures and Treasures) in Korea are mainly located outdoor and considerably affected by the changes of the temperature, humidity and rainfalls. 541 of the stone cultural heritage are preserved as National treasure and Treasure. The pagodas occupy 187 remains and next 127 Buddha statues, 68 monuments, 60 stupas, and the others 74 stone cultural heritages. The shelter has been installed for one pagoda, 60 Buddha statues, 36 monuments and two stupas. The shelters are categorized in three shapes as traditional shape, modern shape, and others (tradition+modern). Approximately 100 of shelters that have constructed in traditional ways, and about nine of shelters have modern ways, and the only one has the combination shape of tradition and modern, which has been constructed since mid 1900s and repaired from the 1980s~2000s. Many researchers are studying for improvement of manners such as repairing, remodeling or removing of the shelter because problems have occured on shelters. Architectural form of traditional style of Korean timber building is respected, but it has problems on importing natural sunlight to the inside as well as ventilation and spacial problems. However, it needs to supplement policies to improve the positive roles of shelters such as prevention of artificial damage, blocking acid rain, and so on. For instance, the rock-carved Buddha Triad in Seosan, it had problems with viewing, contamination, and dew condensation on the surface. These problems decreased after dismantling the shelter, the space was made for improvement of viewing and dew condensation, and moisture problems were in better conditions. The velocity wind is an important factor in drying conditions on the surface of the rock, therefore the condition has improved after dismantling the shelter.

• The Korean Journal of Ecology
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• v.14 no.4
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• pp.449-455
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• 1991

The water striders, gerris paludum insularis larvae which were fed with the drosophila melanogaster cultured on the appli diet and artificial diet, were reared in the growth cabinet controlled as the two constant temperature regimes of 25 c and 30 c under the condition of photoperiod 16l : 8d, light intensity 510 240 lux, relative humidity 65 3%, and in the natural state. The effects of temperature and diet on the devolopment of g. paludum insularis were analyzed and the results were summarized as follows. 1. The total developmental period of the water strider larvae fed with the d. melanogaster reared on the apple diet at the natural stste was the longest 40 days, and the total devopmental periods at 25 c and 30 c were 35 days and 27 days respectively. The tolal developmental period of larvae fed with d. melanogaster reared on the artifical diet at 25 c was the longest 42 dats, and the total developmental periods at natural stste and 30 c were 32 days and 27 days, respectively. 2. In the larval developmental stages, the fifth stage was longer than that of any stage. The duration of egg stage which was not influenced by diet at 25 c was the longest. 3. The water strider larvae fed which the d. melanogaster reared on the artificial diet at 25 c did not complete their devolopment. 4. No significant difference was odserved in the developmentperiod for diet at 30 c. but, there were significant differences in developmental periods for diet at 25 c and natural state. 5. The rate of adult emergence on the apple diet was higher than that of the artificial diet was higher than of the artificial diet. 6. The shapes of the survivorship curve were convex-curve. 7. The development periods of the larval stages of water striders might be affected to temperature and diet dependently.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.892-897
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• 2020

Previous plastic heat exchangers are expensive because the mold must be newly manufactured depending on the air conditioning space. On the other hand, danpla is so thin that the heat exchange performance is excellent. Moreover, danpla can be used easily in ventilation systems in view of fabrication. This study proposes correlations for the cooling performance of an indirect evaporative cooling system. The experimental apparatus consisted of a heat exchanger, spray nozzle, fan, thermostat, pump, and measuring sensors for temperature, humidity, and airflow rate. The results showed that the effectiveness decreased gradually as the airflow rate increased. In addition, there was an optimal condition in terms of effectiveness. The performance prediction correlations were determined using the experimental data from various conditions. The proposed correlations showed performance accuracies within 4 % error.

• Journal of the Korean Society of Safety
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• v.32 no.6
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• pp.150-156
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• 2017

A frozen road surface increases traffic accidents during the winter season. Hence, information on easily-frozen road sections and their specificities are required to prevent traffic accidents. Frozen road surfaces are determined by equipment measuring road surface temperatures. However, there are limitations in investigating the entire road network. Therefore, it is imperative to develop new methods that effectively determine road surface freezing risks. Meteorologically, road surfaces are frozen when the actual temperature cools down to the dew point temperature. Under this condition, there is likely to be frost if relative humidity reaches 100% and frozen road surfaces as the temperature gets lower. Meteorological characteristics give us an alternative to a direct measurement road surface temperature to estimate risks of road surface freezing. Based on the clues, the relationship between severity of traffic accidents and temperature changes is empirically investigated using Paju weather data. The results reveal that as the temperature gets lower and changes in current temperature are relatively small, the severity of traffic accidents become higher. In addition, the same is true when the difference between current temperature and the dew point temperature is relatively small, as it increases possibilities of road surface freezing. Future studies must investigate how current temperature and the dew point temperature affect road surface freezing and thereby establish a time-space scope to estimate possible road surface freezing sections using only weather and road material type data. This would provide invaluable information for predicting and preventing frozen road accidents based on weather patterns.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.6
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• pp.1283-1288
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• 2011

In this paper we collect data concerning sleep environments in a bedroom and analyze the relationship between the collected condition data and sleep. In addition, this paper detects scene changes from the subjects in a sleeping state and presents the physical conditions, reactions during sleep, and physical sensations and stimuli. To detect scene changes in image sequences, we used color histogram for the difference between the preceding frame and the current frame. In addition, to extract the tossing and turning for different situations, the subjects were instructed to enter the level of fatigue, the level of drinking, and the level of stomach emptiness. For the sleep experiment system, we used the H-MOTE2420 Sensor composed of temperature, humidity, and light sensors. This paper is intended to provide the best sleep environment that enhances sleep quality, thus inducing people today to get regular and comfortable sleep.