• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1275-1283
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• 2006

Condensation heat transfer coefficients in a 7.92 mm inside diameter copper smooth tube were obtained experimentally for R22, R134a, and R410A. Working conditions were in the range of $30-40^{\circ}C$ condensation temperature, $95-410 kg/m^2s$ mass flux, and 0.15-0.85 vapor quality. The experimental data were compared with the eight existing correlations for an annular flow regime. Based on the heat-momentum analogy, a condensation heat transfer coefficients correlation for the annular flow regime was developed. The Breber et al. flow regime map was used to discern flow pattern and the Muller-Steinhagen & Heck pressure drop correlation was used for the term of the proposed correlation. The proposed correlation provided the best predicted performance compared to the eight existing correlations and its root mean square deviation was less than 8.7%.

• Journal of Energy Engineering
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• v.26 no.3
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• pp.105-112
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• 2017

A lot of piping systems have been used from nuclear power systems to water supply systems. The maintenance of the piping systems is needed to ensure proper operation of the piping systems. Failure of the large pipe systems especially such as KDHC(Korea District Heating Corporation) can be a matter directly related to the enterprise productivity and profitability. It can also lead to very important issues in promoting public safety and convenience. Therefore a method of quick and safety repairs have been emerged as the most important problem. In this study, freezing seal isolation method using liquid nitrogen cryogenic refrigerant was developed for the maintenance of a pre insulated heat transport pipe of KDHC with a diameter of 300 mm. In this study, by employing computational analysis techniques we performed the flow and heat transfer analysis for the targeted pre insulated heat transfer pipe and freezing seal jacket(ice-Plug) and have selected for optimal system. The detailed design model based on the results of the computational analysis finally was produced. A laboratory-scale test apparatus were designed and the freezing seal isolation self-test carried out. Also the performance assessment tests in the test bed of KDHC were carried out for on-site application.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2008.04a
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• pp.193-198
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• 2008

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2010.04a
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• pp.104-107
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• 2010

• Proceedings of the SAREK Conference
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• 2004.06a
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• pp.93-93
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• 2004

• Journal of Climate Change Research
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• v.2 no.3
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• pp.175-189
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• 2011

In this research, we describe the methodology and the quantification about GHG reduction effects, expected by optimization of operation mode according to establishing additional heat storage system of Bundang Combined Cycle Power Plant. As an intermediate form of General Combined Cycle Power Plant and Heat supply only district heating plant, Bundang Combined Cycle Power Plant(and Ilsan, Anyang, Bucheon) is possible to satisfy demand for the electrical load and thermal load capacity at the same time through changes to the operation mode itself. Therefore, through the operating transition of high-efficiency mode that the condenser cooling water is recovered and supplied to district heat and cooling, establishing additional heat storage system have flexible supply ability at the power and heat market. In this research, We calculated using the operating performance for the last three years(2008~2010) and efficiency of each mode-specific values. As a result, GHG reduction effects were calculated as $97.95kg_{-}CO_2/Gcal$ per heat energy 1 Gcal supplied at the heat storage system and we expected emmision reduction effect about $13,500Ton_{-}CO_2/yr$.

• Journal of Korean Society for Geospatial Information Science
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• v.21 no.1
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• pp.3-9
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• 2013

Development of housing, industrial and public lands has been a cause to increase a temperature of a city higher than that of a rural area. Knowing that, the research analyzed temperature changes in a riverside district and a coastal area depending on the land usage and climate change in the areas. Add to this, the study examined a correlation between topographic characteristics and temperature changes. According to the results, the temperature was increased by $1.80^{\circ}C$ in 2007 comparing to 2003 while the wind velocity was reduced by 0.24m/s. In addition, a more number of areas were designated as build-up areas which, in return, decreased the forested land. The analysis on the correlation reported that the riverside district has more of grassland and bare land while the coastal area has more of wooded land and grassland. The study is expected to be used as fundamental data for research on heat island effect which would be different by each regional characteristic as it proposes measures to solve the heat island effect.

• Corrosion Science and Technology
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• v.20 no.4
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• pp.204-209
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• 2021

Corrosion failure analysis of the flow plate, which is one of the accessories of the plate heat exchanger in a district heating system, was performed. The flow plate is made of 316 stainless steel, and water at different temperatures in the flow plate exchanges heat in a non-contact manner. The flow plate samples in which water mixing issues occurred were collected. Corrosion-induced pits, oxides, and contaminants were observed at locations where two plates are regularly in contact. The EDS analysis of the surface oxides and contaminants revealed that they were composed of carbon, silicon, and magnesium, which came from chemical adhesives. The IC/ICP analyses showed that the concentration of chloride ions was 30 ~ 40 ppm, which was not sufficient to cause corrosion of stainless steel. In the crevice, a local decrease in dissolved oxygen occurs along with an increase in chloride ions, thus forming an acidic environment. These environments destroyed the passive film of stainless steel, resulting in pits. Moreover, contaminants formed a narrower gap between the two metal plates and inhibited the diffusion of ions, thereby accelerating crevice corrosion.

• Journal of Environmental Science International
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• v.12 no.7
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• pp.705-713
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• 2003

In mid-August 2002, under clear summer pressure patterns, we carried out an intensive meteorological observation to examine the warming effects due to artificial constructions in a large housing complex. We set an automatic weather system(AWS) at two places in a bare soil surface within a limited development district and an asphalt surface within a large apartment residence area, respectively. As a result of observation, it became clear that the difference of the surface air(ground) temperature between the bare soil surface and its peripheral asphalt area reached about 4$^{\circ}C$(13$^{\circ}C$) at the maximum from diurnal variation of surface temperatures on AWS data. Through the heat balance analysis using measurement data, it became clear that the thermal conditions at two places are dependent on the properties of surface material. The latent heat flux over the bare soil surface reached to about 300 W/㎡, which is more than a half of net radiation during the daytime. On the other hand, it was nearly zero over the asphalt surface. Hence, the sensible heat flux over the asphalt surface was far more than that of the bare soil surface. The sensible heat flux over the asphalt surface showed about 20∼30 W/㎡ during the night. It was released from asphalt surface which have far more heat capacity than that of bare soil surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.5
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• pp.334-341
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• 2011

In the present study, optimal heat supply algorithm which minimize the heat loss through the distribution pipe line in group energy apartment was developed. Variation of heating load of group energy apartment building in accord with the outdoor air temperature was predicted by the heating load-outdoor temperature correlation. Supply water temperature and mass flow rate were controlled to minimize the heat loss through distribution pipe line. District heating apartment building located in Hwaseong city, which has 1,473 households, was selected as the object building for testing the present heat supply a1gorithm. Compared to the previous heat supply system, 10.4% heat loss reduction can be accomplished by employing the present method.