• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.6
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• pp.532-540
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• 2001

The objectives of this study are to analyze the control variables according to condensation occurrence, to find the range in floor surface temperature and frequency of condensation, and to evaluate the control methods through simulations when the radiant heating system is used for cooling. Through the simulation analysis the control methods such as on/off control, variable flow control and outdoor reset with indoor temperature feedback control are evaluated and compared. The results show that the lowest floor surface temperature is around $23^{\circ}C$, the surface condensation can be prevented by controlling indoor humidity within 20g/kg(DA0, and that outdoor reset with indoor temperature feedback control is more appropriate than on/off control and variable flow control with regard to prevention of the condensation and thermal comfort.

• Journal of the Korean housing association
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• v.15 no.3
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• pp.73-82
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• 2004

The objective of this study is to demonstrate the potential of radiant cooling systems using Ondol as an alternative cooling system in residential buildings. For this purpose, computer simulation and model experiments have been performed for the system performance analysis regarding comfort, floor surface condensation, and supply water temperature. The results of this study is the following: In radiant floor cooling system, room air temperatures were maintained within the set temperature range of $\pm$1$^{\circ}C$ without any discomfort condition. And taking into account only the condensation occurrence, it was possible to achieve radiant floor cooling for a period of about 77% of the total cooling period in weather condition of Seoul. The minimum supply water temperature is about 15$^{\circ}C$, so renewable energy system such as ground heat exchange system can be used as an alternative in cooling source. Also, floor surface condensation can be prevented by integrating with the dehumidification system.

• Journal of The Korean Association For Science Education
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• v.14 no.3
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• pp.272-284
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• 1994

The aim of this research was to compare and analyze the children's ideas on evaporation and condensation between pre- and post-intervention. Forty-eight children from six elementary schools in Seoul and Kyung Ki provinces were sampled by stratified random sampling. A set of structured activities was then provided which allow children to explore evaporation and condensation phenomena. All of these activities had a preliminary phase which required the child to predict or speculate on evaporation and condensation using their existing knowledge. These structured activities on evaporation and condensation were reviewed by three professors and eigth primary school teachers. Their comments were used to revise the original contents of the structured activities. The data analysed were gathered by the questionaire and the interview. Pre- and post-intervention data related to evaporation and condensation were collected by the same teacher, and analysed into the same category scheme. Data coding was carried out several times by the researcher to ensure reliablity. Data collected were then classified and analyzed according to the types of children's ideas. The findings of this study were as follows: Results of this study showed that the the vocabulary used to describe the evaporation phenomena varied according to the context, and the scientific term "evaporated" was more frequently used by the older children after post-intervention. But everyday terms such as"dried up","disappered", "gone up" were also used by children as much as the level of pre-intervention. Scientific conception on the location of evaporated water, the factor of evaporation, the ideas about getting the water back and assumption about the physical state of the missing water has been increased for the most of the children after intervention. It was found that the intervention using was effective SPACE strategies regardless of the grade level of the children.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.813-820
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• 2001

The Safety depressurization System(SDS) of KNGR prevents RCS from overpressurization by discharging high pressure and temperature coolant through the I-sparger into the IRWST during an accident. If IRWST water temperature rise locally, around the sparger, beyond $200_{\circ}$2000 F by the discharged coolant, unstable steam condensation can cause large pressure load on the IRWST wall. To investigate whether this condition can be avoided for the design basis event IOPOSRV(Inadvertent Opening of one Pilot Operated Safety Relief Valve), the flow and temperature distribution of water in the IRWST is calculated by using CFX 4.3 computational fluid dynamic code. According to the results, since pool water temperature does not exceeds temperature limit within 50 seconds after the opening of one POSRV, it can be assured that the integrity of IRWST wall is maintained.

• Nuclear Engineering and Technology
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• v.24 no.2
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• pp.130-140
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• 1992

The physical benchmark problem on the direct-contact condensation under the horizontal occurrent stratified flow was analyzed using the RELAP5/MOD2 and /MOD3 one-dimensional model. Analysis was peformed for the Northwestern experiments, which involved condensing steam/water flow in a rectangular channel. The study showed that the RELAP5 interfacial heat transfer model, under the horizontal stratified flow regime, predicted the condensation rate well though the interfacial heat transfer area was underpredicted. However, some discrepancies in water layer thickness and local heat transfer coefficient with experimental results were found especially when there is a wavy interface, and those were satisfied only within the range.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.2
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• pp.159-165
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• 2004

Fuel cell makes electricity through chemical reaction. Bipolar-plate distribute hydrogen, oxidation using channel geometry condensation of water vapor inside channels of bipolar-plates lowers efficiency of fuel cell. Usually high pressured gas supply is used to solve the water condensation problem with serpentine type channel geometry. In this study, a new channel geometry shows feasible to minimize lowering efficiency due to water condensation through numerical and experimental analysis.

• Journal of the Korean Solar Energy Society
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• v.31 no.1
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• pp.44-50
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• 2011

The solar radiation, inner temperature of the tilted box and the amount of condensed water were measured to find the most effective purified water production system. The inner temperature of the tilted box was related with solar radiation that was affected by sunshine and cloud. With analyzing those relationships of the solar radiation, inner box temperature, the angle of tilted boxes and amounts of water condensation optimal collecting system area could be calculated.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.68-78
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• 1999

Heat transfer performance is studied for boiling and condensation of R-11 on integral-fin tubes. Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64 mm height respectively are tested. in case of condensation CFC-11 condensates at saturation stat of 32$^{\circ}C$ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1 bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube,. The tube having fin transfer coefficient concerns fin tubes with caves show higher valve than low fin tube having find density of 1299fpm and 30grooves. The overall heat transfer coefficient of fin tube with caves is about 5155 W/mK at 2.8m/s of water velocity, The value is abuot 2.7 times higher than plain tube and 1.3 times higher than low fin tube having fin density of 1299fpm and 30 grooves.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.65-65
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• 1999

Heat transfer performance is studied for boiling and condensation of R-11 on integral-fin tubes. Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64 mm height respectively are tested. in case of condensation CFC-11 condensates at saturation stat of 32℃ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1 bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube,. The tube having fin transfer coefficient concerns fin tubes with caves show higher valve than low fin tube having find density of 1299fpm and 30grooves. The overall heat transfer coefficient of fin tube with caves is about 5155 W/mK at 2.8m/s of water velocity, The value is abuot 2.7 times higher than plain tube and 1.3 times higher than low fin tube having fin density of 1299fpm and 30 grooves.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.5
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• pp.444-451
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• 2004

Flow condensation heat transfer coefficients (HTCs) of R22, R134a, R407C, and R410A were measured on horizontal plain and microfin tubes. The experimental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water/glycol loop. The test section in the refrigerant loop was made of both a plain and a microfin copper tube of 6.0∼6.16 mm inside diameter and 1.0 m length. Refrigerants were cooled by passing cold water through an annulus surrounding the test section. Tests were performed at a fixed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, and 300 kg/m2s. Test results showed that at similar mass flux the flow condensation HTCs of R134a were similar to those of R22 for both plain and microfin tubes. On the other hand, HTCs of R407C were lower than those of R22 by 4∼16% and 16∼42% for plain and microfin tubes respectively. And HTCs of R410A were similar to those of R22 for a plain tube but lower than those of R22 by 3∼9% for a microfin tube. Heat transfer enhancement factors of a microfin tube were 1.3∼1.9.