• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.339-345
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• 2002

When a flow passes a series of parallel ones, vortexes will be formed in the wake after the cylinder. This paper treats the problems of vibration and noise in tube bank of gas flow duct of heat exchanger thermal suppling boiler in combine cycle thermal power plants. The boiler burner type has recently been changed to low Nox burner and begun commercial operation. After more load up operation then 70%, high level noise and vibration were generated at gas flow duct of heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.525-531
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• 2002

The effects of different surface hydrophilicity on frosting and defrosting characteristic were experimentally investigated. Mass of frost and water hold-up was measured. Results showed that no significant difference in the frost mass was found between the two different surfaces while the water hold-up of heat exchanger court be reduced by the enhancement of surface hydrophilicity. Also, the defrosting efficiency m hydrophilic surface was improved by 76%. It was expected that hydrophilic heat exchanger could provide the improvements in both thermal-hydraulic performances and system reliability during frost/defrost operating in refrigeration systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.488-500
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• 1995

An air-cooled ammonia/water GAX(Generator-Absorber heat eXchange) absorption cooling cycle is proposed and its performance is numerically evaluated. It is shown that the performance of the system is greatly dependent on the quality of the refrigerant leaving the evaporator. For any refrigerant concentration in the investigated range(99.1~99.9% ammonia), the cycle COP(coefficient of performance) reaches the highest value, when some amount(about 7%) of refrigerant evaporates in the refrigerant heat exchanger. Among temperature differences in various heat exchangers, the temperature difference between GAX-absorber and the GAX-generator shows the greatest effect on the system performance, whereas pressure losses cause no significant decrease in COP. The system COP increases almost linearly with increasing evaporator temperature, decreasing absorber temperature or decreasing condenser temperature. If both absorber and condenser temperature increase simultaneously, the decrease in the COP becomes larger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.6
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• pp.505-513
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• 2001

A revised VX cycle using ammonia/water as the working fluid is a cycle which is suitable to produce cooling utilizing low temperature hat sources. The cycle was analyzed numerically to investigate the effects of the design and operating conditions on the performance. It was shown that both COP and cooling capacity were significantly influenced by the performance of he rectifier. Insufficient UA of the rectifier reduced both ammonia mass fraction and mass flow rate of the vapor entering the condenser, which produced cooling effect in the evaporator. As the temperature and the mass flow rate of the heat source increased, both COP and exergetic efficiency decreased due to the irreversibilities produced in heat exchangers, but cooling capacity did not vary much. Cooling capacity increased significantly as the coolant temperature decreased, although COP and exergetic efficiency remained nearly constant.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.16 no.3
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• pp.1-7
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• 2020

To provide a design direction for high efficiency thermoelectric module(TEM) dehumidifiers, the effects of design factors of TEM dehumidifiers on dehumidification energy efficiency and performance were numerically investigated. The design factors considered in this study are the TEM capacity, the performance of heat exchangers on the heating and cooling surfaces of the TEM. The higher capacity of the TEM results the higher dehumidification energy efficiency and performance at some operating voltage. The enhanced performance of the heat exchanger on heating surface increased the dehumidification energy efficiency and performance at all the operating voltage. The enhanced performance of the heat exchanger on cooling surface decreased the dehumidification energy efficiency and performance at all operating voltage.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2106-2109
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• 2008

Nanofluids have been studied as possible alternatives for heat transfer fluids to improve the efficiency of heat exchangers. There are deviations of measured effective thermal conductivities between research-groups, and the mechanisms of the effective thermal conductivity enhancement of nanofluids are not confirmed yet. In this study, the effects of particle shape on the effective thermal conductivity enhancement are discussed and presented as a possible explanation of the deviations. The particle motion effect is found to be negligible for nanofluids of high aspect ratio cylindrical particles, which is believed to be important for nanofluids of spherical particles, while the percolation network formation and contact resistance play dominant roles in determining the effective thermal conductivity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.3
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• pp.183-190
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• 1992

The Collins cryocooler is numerically analysed with the optimization technique, and the optimum operating and design conditions are searched. This paper shows that liquefied helium quantity has an external maximum w.r.t. the total mass flow rate, the mass flow rates through expander and the capacities of heat exchangers. The liquefied helium quantity increases as the compressor exit pressure of the cryocooler does. The maximum quantity of liquefied helium and the maximum coefficient of performance have been found to exist in extremum, depending on the ratios of each heat exchanger capicities to the total one. At the optimum condition, the capacity of heat exchanger in high temperature region is larger than that in low temperature region.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.429-433
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• 2007

Cement mortar and concrete can be used as grouts but problems regarding shrinkage and the discord of coefficients of thermal expansion between grouts and HDPE pipes has to be solved. Thermal conductivities of wet condition two times larger than those of dry condition, except for pure cement mortar. The addition of sand into the cement grouts greatly increases the thermal conductivity. The addition of bentonite into the cement grouts reduces thermal conductivity thus reducing the density. Bentonite grouting must be used only below the groundwater table since bentonite grouts possesses high shrinkage property in dry condition. The addition of sand prevents the shrinkage of bentonite grouts. Bentonite manufactured in Korea can be used since they possess similar thermal conductivities with imported products. The addition of sand into the bentonite grouts greatly increases the thermal conductivity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.9
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• pp.671-678
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• 2012

The objective of this study is to analyze theoretically the performance of an open air-cycle refrigeration system in which environmental concerns increase. The pressure ratio of the external compressor and efficiencies of the components that compose of the system are selected as important parameters. As the pressure ratio of the external compressor increases, the pressure ratio of the ACM compressor is determined high, the refrigerating temperature and capacity increase, the COP decreases, and the total entropy production rate increases. The effect of heat exchanger effectiveness and turbine efficiency on the performance are greater than that of the ACM compressor efficiency. Also the performance of the air-cycle refrigeration system with two heat exchangers has been enhanced like high COP and low total entropy production rate, compared to the system with one heat exchanger.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.4
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• pp.156-162
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• 2007

Flow visualization experiments were conducted for two louver arrays having large louver pitch ratio ($L_p/F_p=1.0$ and 1.4). Flow efficiencies and critical Reynolds numbers were obtained from the data, and were compared with existing correlations. The correlations failed to predict the present flow efficiency data adequately; some correlation overpredicted the data, while others underpredicted the data. Large louver pitch ratio of the present model, which is outside of the applicable range of the correlations may partly be responsible. The critical Reynolds numbers obtained from the present flow visualization data were in close agreement with those obtained from the heat transfer tests on actual flat tube heat exchangers. Existing correlations on the critical Reynolds number generally overpredicted the present data.