• 설비공학논문집
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• 제7권3호
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• pp.501-511
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• 1995

A numerical model for predicting the performance of gas distrubutor type double inlet pulse tube refrigerators has been developed. The model was based on adiabatic analysis and the losses of heat exchangers and regenerator were considered. Thermodynamic behavior of working fluid within a double inlet pulse tube refrigerator was investigated and the effects of design parameters, such as valve and orifice openings, cold heat exchanger temperature, frequency and pulse tube length, on the cooling capacity and COP were shown.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2102-2107
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• 2007

GSHP systems are used for air-conditioning systems in commercial buildings, schools, and factories because of low operating and maintenance costs. These systems use the earth as a heat source in heating and a heat sink in cooling mode. Ground heat exchangers are classified by a horizontal and vertical type according to the installation method. Vertical type is usually constructed by placing small diameter high density polyethylene tube in a vertical borehole. Vertical tube sizes range from 20 to 40 mm nominal diameter. Borehole depth range between 100 and 200 m depending on local drilling conditions and available equipment. In this study, to evaluate the performance of single u-tube with bentonite grouting, single u-tube with broken stone grouting and double u-tube bentonite grouting of vertical ground heat exchangers, test sections are buried on the earth and experimental apparatus is installed. Therefore the heat transfer performance and pressure loss of these are estimated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.717-724
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• 2008

Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source for nuclear hydrogen generation, which can produce hydrogen from water or natural gas. A primary hot gas duct (HGD) as a coaxial double-tube type cross vessel is a key component connecting the reactor pressure vessel and the intermediate heat exchanger for the VHTR. In this study, structural sizing methodology for the primary HGD with a coaxial double-tube of the VHTR that produces heat at temperatures in the order of $950^{\circ}C$ was suggested and a structural pre-sizing of it was carried out as an example.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.657-662
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• 2006

The present paper dealt with an experimental study of condensation heat transfer coefficients with refrigerant R-22, R-407C and R-410A, and was focused on pressure gradient and heat transfer coefficient in horizontal tube-in-tube heat exchangers using inner diameter of 4 mm, 3 mm and 2 mm in a 16.91 mm tube and length of 3,000 mm. Experiments were performed at inlet saturation temperature of 35 to $45^{\circ}C$ and mass flux ranges from 200 to $600 kg/m^2s$. The pressure gradient with inner tube diameter of 4.0 mm is higher 2.5 times than that of 8.0 mm. In tube-in-tube HEX, the pressure gradient of R-410A were lower than those of R-22 and R-407C. The condensation heat transfer coefficients increased with mass flux increase, but they decreased with saturation temperature increased. Condensation heat transfer coefficients of R-410A were a little higher than those of R-22 and R-407C. The condensation heat transfer coefficients of tube-in-tube HEX were about 40% higher than those of double tube HEX.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.63-64
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• 2006

Chracteristics on evaporating pressure drop of HCs refrigerants inside a horizontal tube were studied experimentally. Experimental results were presented for pressure drops of hydrocarbon refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 inside a horizontal double pipe heat exchanger. Three tubes with a tube diameter of 12.70mm, 9.52mm and 6.35mm were used for this study. Hydrocarbon refrigerants showed higher evaporating pressure drop than that of R-22 in all tubes. The highest pressure drop was founded in R-600a. The highest evaporating perssure drop of all refrigerants was shown in a tube diameter of 6.35mm with same mass flux. The results can be used as the basic data for the design of heat exchanger using hydrocarbon refrigerants as an alternatives.

• 설비공학논문집
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• 제2권2호
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• pp.127-136
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• 1990

Air-solid bed has been known to be an effective heat transfer augmentation device which could be applied to heat exchangers. In this study, pressure drop and heat transfer characteristics of vertical annular fluidized bed heat exchanger with air flowing through were studied experimentally. The experiments was conducted to calculate overall heat transfer coefficient on fluidized bed heat exchangers immersed single vertical tube and investigate minimum fluidized velocity in fluidized bed of alumina beads and steel balls. The influence of flow direction, particle diameter, the heights of static bed and air mass fluidizing velocity has been examined. The experimental results showed the optimum operating condition and effective static bed height for fluidized bed heat exchangers. For the same power loss, comparisions of heat transfer effect between the fluidized bed heat exchanger and the single phase forced convetion heat exchanger indicate that both miniaturization of heat exchanger and heat transfer augmentation at low flow velocity are possible by application of the air-solid to heat exchangers.

• 대한기계학회논문집 C: 기술과 교육
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• 제3권1호
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• pp.23-28
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• 2015

본 논문은 GHP 에 사용되고 있는 이중 쉘-튜브형 배기가스 열교환기의 설계 변수의 변화에 따라 열전달 및 마찰특성 변화를 알아보기 위해 CFD 와 RSM 을 이용하여 최적화를 수행하였다. CFD 해석은 복잡한 형상의 열교환기 해석에 유용한 도구이나, 해석결과를 얻기까지 많은 시간이 소요된다. 이러한 해석시간을 줄이고, 유용한 결과를 얻기 위해 RSM 과 병행하여 최적화 설계를 진행하였다. 시뮬레이션 결과를 이용한 RSM 해석결과, 배플 6 개, 튜브 25 개에서 최적화되었으며, 기존 보다 차압 및 열전달 성능이 약 12.2% 개선되었다. 이러한 CFD 와 RSM 을 이용한 최적화 기법은 다양하고 복잡한 형상의 열교환기 해석에 유용함을 확인하였다.

• 한국압력기기공학회 논문집
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• 제4권2호
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• pp.1-6
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• 2008

Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source for nuclear hydrogen generation. The VHTR can produce hydrogen from heat and water by using a thermo-chemical process or from heat, water, and natural gas by steam reformer technology. A co-axial double-tube primary hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger (IHX) for the VHTR. In this study, a preliminary design analysis for the primary HGD of the nuclear hydrogen system was carried out. These preliminary design activities include a determination of the size, a strength evaluation and an appropriate material selection. The determination of the size was undertaken based on various engineering concepts, such as a constant flow velocity model, a constant flow rate model, a constant hydraulic head model, and finally a heat balanced model.

• 설비공학논문집
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• 제21권5호
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• pp.297-304
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• 2009

The aim of this study is to investigate the cooling performance of ground source multi-heat pump systems with a vertical single U-tube GLHX(U-tube system) and a vertical double tube GLHX(double tube system), which were installed in a school building located in Cheonan. All systems were operated in a part load conditions for all day, and the maximum COP of the single U-tube system and the double tube system were 6.2 and 5.2 at cooling mode, respectively. The double tube GLHX designed by the GLHEPRO, commercial program, was estimated to have the same performance as the U-tube GLHX, because the inlet temperatures of each outdoor unit heat exchanger for the former was similar to the latter. However, it is needed to prove the long tenn performance. It is suggested that the new algorithms to control the flow rate of secondary fluid for GLHX according to load variation have to be developed in order to enhance the performance of the system.

• Journal of Advanced Marine Engineering and Technology
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• 제20권3호
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• pp.91-100
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• 1996

Experimental results for forced convection condensation of non-azeotropic refrigerant mixtures inside a horizontal smooth tube are presented. The mixtures of R-22+R-134a and pure refrigerants R-22 and R-134a are used as the test fluids and a double pipe heat exchanger of 7.5mm ID and 4800mm long inside tube is used. The range of parameters are 100-300kg/h of mass flow rate, 0-1.0 of quality, and 0, 33, 50, 67, and 100 weight percent of R-22 mass fraction in the mixtures. The heat flux, vapor pressure, vapor temperature and tube wall temperature were measured. Using the data, the local and average heat transfer coefficients for the condensation have been obtained. In the same given experimental conditions, the liquid heat transfer coefficients for NARMs were considerally lower than that of the pure refrigerant of R-22 and R-134a. Local heat transfer characteristics for NARMs were different from pure refrigerant R-22 and R-134a. In some regions, local heat transfer coefficients for NARMs were increased in the following order ; Bottom$\rightarrow$Top$\rightarrow$Side. The condensation heat transfer coefficients for NARMs increased with mass velocity, heat flux, and quality, but were considerably lower than that of pure refigerant R-22 and R-134a.