• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2004.05a
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• pp.201-212
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• 2004

An experimental study of the absorption process of water vapor into a lithium bromide solution was performed. For the purpose of developing high performance absorption chiller/hater utilizing lithium bromide solution as working fluid, it is important to improve the performance of absorber with the larger heat transfer area of the four heat exchangers. The experimental apparatus was composed of a plate type absorber which could increase the heat exchange area per unit volume to investigate more detail characteristics instead of the conventional type, that is, horizontal tube bundle type. The size of plate absorbers were made for 0.4m$\times$0.6m and the design objective of a refrigeration capacity was 1RT. In this experiment, three kinds of plate absorbers namely flat plate, dimple plate and groove plate were used. The obtained results were less than the design objective values, that is, the refrigeration capacity was about 0.3 ～0.4RT and the overall heat transfer coefficient was 500～600 kcal/$m^2$h$^{\circ}C$ at the standard conditions.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.6
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• pp.1-8
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• 2017

The purpose of this study was to provide basic data for development of environmental design technology for greenhouses constructed in reclaimed lands. We analyzed the climatic conditions around seven major reclaimed land areas in Korea, which have a plan to install advanced horticultural complexes. The characteristics of heating load through the thermal environment measurement of the greenhouse in Saemangeum were analyzed. The part to be applied to the environmental design of the greenhouses in reclaimed lands were reviewed. The overall heat transfer coefficient of the experimental greenhouse with the aluminum screen and multi-layer thermal curtain averaged $3.79W/m^2^{\circ}C$. It represents a 44 % heat savings rate compared with plastic greenhouses with a single covering, which was significantly lower than that of the common greenhouses with 2-layer thermal curtains. This is because the experimental greenhouse was installed on reclaimed land and wind was stronger than the inland area. Among the total heating load, the transmission heat loss accounted for 96.4~99.9 %, and the infiltration loss and the ground heat exchange were low. Therefore, it is necessary to take countermeasures to minimize the transmission heat loss for greenhouses constructed in reclaimed lands. As the reclaimed land is located on the seaside, the wind is stronger than the inland area, and the fog is frequent. Especially, Saemangeum area has 2.6 times stronger wind speed and 3.4 times longer fog duration than the inland area. In designing the heating systems for greenhouses in reclaimed lands, it is considered that the maximum heating load should be calculated by applying the wind coefficient larger than the inland area. It is reasonable to estimate the operation cost of the heating system by applying the adjustment factor 10 % larger than the average in calculating the seasonal heating load.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.213-219
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• 2015

A thermal storage tank with internal heat exchange coils is commonly used in solar thermal systems with a collector area below $100m^2$. The coils are installed in the lower part of the tank because the temperature of the upper part of the tank can drop if the outlet temperature of the collector becomes lower than the upper temperature of the tank, which is a kind of temperature reversal. As an alternative to the well-mixed storage tank with lower coil only, we have proposed a tank with lower and upper coils and have achieved superior thermal stratification in the tank, which results in increased collector efficiency and solar fraction. But, the phenomenon of temperature reversal was often observed in the tank when the load or solar radiation changed rapidly. In the present work, revised control was successfully applied, i.e., to heat only the lower coil using a three way valve if temperature reversal occurs and to operate the collector at a low flow rate when the quality of solar radiation is not good.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.101-108
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• 2011

Understanding the exhaust gas recirculation (EGR) cooler fouling in diesel engine is important factor in the durability characteristic of a EGR system. We develope a test rig and PM feeder using carbon black to examine the effect of fouling on EGR cooler devices those were consisted of flat and shell & tube type. The EGR cooler fouling process is a complex interaction involving heat exchanger shape, boundary condition, constitutes, chemistry and operating mode. As the soot deposited to EGR cooler, these formed a thin deposit layer that was less heat exchange than the fresh status of tube enclosing the exhaust gas, resulting in lower heat exchange effectiveness in both type coolers. But these deposits caused different results in pressure drop, it is increased in flat type, but decreased in Shell & tube type of EGR cooler. A cause was estimated from a change of the flow structure and a decrease of contact area as the EGR cooler fouling.

• Journal of the Korean Solar Energy Society
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• v.38 no.5
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• pp.75-84
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• 2018

The most crucial point of reducing building energy is application of high performance envelope. The amount of heat exchange through window is highest in comparison of other envelopes so that heat exchange through window influence directly with building energy consumption. The window energy performance can be define with thermal, leakage and optical performance. In previous study we can confirmed that not only thermal performance but also optical performance are considered, 11% to 15% of building energy consumption can be reduced. Smart window system has potential of energy saving so that many industry field use smart window system including architectural area and these aspect causes smart window market continuous growth year by year. In this study, building energy consumption has been analyzed which consist of smart window that dynamically control optical states. The consideration of standard commercial building model for research, the reference medium size commercial building model of DOE (Department Of Energy, USA) has been used. The building energy simulation result of 4 axis in 8 regions in Korea shows 8% to 22% reduction of building energy consumption by application of smart window system.

• Journal of Welding and Joining
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• v.28 no.1
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• pp.66-71
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• 2010

With large specific strength and outstanding corrosion resistance and erosion resistance in sea water, titanium and titanium alloy are widely used in heat exchanger production. In particular, pure titanium demonstrates outstanding molding performance and may be considered optimal for production of heat exchanger. Since titanium is very vulnerable to oxidation and embrittlement during welding, processes with less heat input are widely used, and laser welding is widely applied by considering production performance and shield etc in atmosphere. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through oxygen and nitrogen quantitative analysis and hardness measurement, and evaluated welding performance and mechanical properties of butt welding. This study evaluated field applicability of lap welding to heat exchange plate of LPG re-liquefaction device for ships through tensile stress test, hardness test and internal pressure test etc after deducing optimal weding condition and applying to actual heat exchange plate. In bead overlap area, the experiment produced sound welds with no porosity or defect by increasing and decreasing laser power, and tensile-shear test results indicated virtually the same tension and yield strength as base metal. As a result of measuring hardness at lateral cross section and bead overlap zone of actual heat exchanger welds, hardness difference within 20Hv was produced at base metal, HAZ and weldment, and as a result of pneumatic and hydraulic pressure test, no leakage occurred.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.359-366
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• 2008

A two-dimensional thermal model of proton exchange membrane fuel cell with large active area is developed to investigate the performance of fuel cell with large active area over various thermal management conditions. The core sub-models of the two-dimensional thermal model are one-dimensional agglomerate structure electrochemical reaction model, one-dimensional water transport model, and a two-dimensional heat transfer model. Prior to carrying out the simulation, this study is contributed to set up the operating temperature of the fuel cell with large active area which is a maximum temperature inside the fuel cell considering durability of membrane electrolyte. The simulation results show that the operating temperature of the fuel cell and temperature distribution inside the fuel cell can affect significantly the total net power at extreme conditions. Results also show that the parasitic losses of balance of plant component should be precisely controlled to produce the maximum system power with minimum parasitic loss of thermal management system.

• KIEAE Journal
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• v.17 no.4
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• pp.33-39
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• 2017

Purpose: The use of renewable energy system is essential for building energy independence and saving energy consumption in the building sector. Among renewable energy technologies, ground source heat pump(GSHP) system is more energy-efficient and environmental-friendly than other heat source systems due to utilize stable ground heat source. However, the GSHP system requires a high initial installation cost and installation space in limited urban area, so it is difficult to have superiority in the market of heat source system. Therefore, it is necessary to develop the installation method of low-cost and improve system performance. This paper aims to evaluate the performance of double u-tube ground heat exchanger(GHX) and verify system feasibility through real-scale experiment. Method: In this study, the real-scale experiment of vertical closed-type GSHP system was conducted using double u-tube GHX and high-efficiency grout. Through the verification experiment, heat source temperature, heat exchange rate(HER) and seasonal performance factor(SPF) were measured according to the long-term operation. In addition, the feasibility analysis was conducted comparing to the single u-tube system. Result: In the results of experiment, average HER was 136.27 W/m and average SPF was 5.41. Furthermore, compared to the single u-tube, the installation cost of the developed system could be reduced about 70% in the same heating load condition.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.1083-1090
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• 2005

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue is tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall have a 45$^{\circ}$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increase with increasing the number of rough walls.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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• pp.340-348
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• 2005

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue is tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall have a $45{\circ}C$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increase with increasing the number of rough walls.