• Journal of Advanced Marine Engineering and Technology
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• v.34 no.1
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• pp.30-36
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• 2010

The heat flowrate and pressure drop of $CO_2$ in a multi-tube-in-tube helical coil type gas cooler were investigated experimentally. The mass flowrate of $CO_2$ and coolant were varied from 0.06 to 0.075 [kg/s], respectively and the cooling pressure of gas cooler were from 8 to 10 [MPa]. The heat flowrate of $CO_2$ in the test section is increased with the increase in mass flowrate of coolant, the cooling pressure and mass flowrate of $CO_2$. The pressure drop of $CO_2$ is decreased with the decrease in mass flowrate of coolant and $CO_2$, but decreased with increase in cooling pressure of $CO_2$. The heat flowrate of $CO_2$ in the multi-tube-in-tube helical coil type gas cooler is greatly higher than that of $CO_2$ in the double pipe type gas cooler, while the pressure drop of $CO_2$ in the multi-tube-in-tube helical coil type gas cooler is greatly lower than that of $CO_2$ in the double pipe type gas cooler. Therefore, in case of the application of $CO_2$ at the multi-tube-in-tube helical coil type gas cooler, it is expected to carry out the high-efficiency, high-performance and compactness of gas cooler.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.259-266
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• 2010

The heat flowrate and pressure dorp of $CO_2$ in a multi-tube-in-tube helical coil type gas cooler were predicted using LMTD method and compared with the experimental data. The mass flowrate of $CO_2$ and coolant were varied from 0.06 to 0.075 [kg/s], and the cooling pressure of gas cooler were from 8 to 10 [MPa], respectively. The LMTD method is used to predict the heat flowrate and pressure drop of supercritical $CO_2$ during in-tube cooling. The equations used by LMTD method were Gnielinski correlation for $CO_2$ and Dittus-Boelter correlation for coolant, respectively. The equation used to predict the pressure drop of $CO_2$ and coolant is Blasius correlation. In comparison of heat flowrate and pressure drop of $CO_2$ measured by experiment to that predicted by LMTD method, the experimental heat flowrate and pressure drop of $CO_2$ in the multi-tube-in-tube helical coil type gas cooler shows a relatively good agreement with that predicted by LMTD method.

• Journal of the Korean Institute of Gas
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• v.11 no.3
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• pp.44-48
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• 2007

The cooling heat transfer characteristics of supercritical $CO_2$ in a helical coil gas cooler on the change of coil diameters are experimentally investigated. The main components of the refrigerant loop are a receiver, a variable speed pump, a mass flow-meter, a pre-heater and a helical coil gas cooler (test section). The test sections are made of a copper tube which the inner diameter is 4.55 mm and the helical coil diameters are done of 26.75 mm and 41.35 mm. The mass fluxes of refrigerant are varied from 200 to 800 [$kg/m^2s$] and the inlet pressures of gas cooler are 7.5 to 10.0 (MPa). A gas cooler with helical coil diameter of 26.75 mm has larger heat transfer coefficient than that of 41.35 mm. Also, when compared with experimental data and published correlations avaliable, most of correlations are under-predicted, but Pitla published correlations avaliable, most of correlations are under-predicted, but Pitla et al.'s correlation shows a relatively good coincidence with the experimental data except the region of pseudo critical temperature.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.5
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• pp.439-444
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• 2008

The heat capacity and pressure drop of $CO_2$ and coolant in a multi-tube type gas cooler were investigated experimentally. The main components of the refrigerant loop are a receiver, a $CO_2$ compressor, a mass flow meter, an evaporator and a multi-tube type gas cooler as a test section. The mass flowrate of $CO_2$ and coolant were varied from 0.06 to 0.075 [kg/s], respectively and the cooling pressure of gas cooler were from 8 to 10 [MPa]. The heat capacity of $CO_2$ in the test section is increased with the increment in mass flowrate of coolant, the cooling pressure and mass flowrate of $CO_2$. The pressure drop of $CO_2$ is decreased with the decrease in mass flowrate of coolant and $CO_2$, but decreased with increase in cooling pressure of $CO_2$. The heat capacity of $CO_2$ per unit heat transfer area of gas cooler is greatly high. Therefore, in case of the application of $CO_2$ at the multi-tube type gas cooler, it is expected to carry out the high-efficiency, high-performance and compactness of gas cooler.

• Journal of the Korean Institute of Gas
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• v.11 no.3
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• pp.1-6
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• 2007

The heat transfer coefficient and pressure drop during gas cooling process of $CO_2$ (R-744) in inclined helical coil copper tubes were investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and a inclined helical coil type gas cooler (test section). The test section consists of a smooth copper tube, which is specified as the inner diameter of 4.55 mm. The refrigerant mass fluxes were varied from 200 to $600kg/m^2s$ and the inlet pressures of gas cooler were done 7.5 to 10.0 (MPa). The heat transfer coefficients of $CO_2$ in the inclined helical coil tubes increase with the increase of mass flux and gas cooling pressure of $CO_2$. The pressure drop of $CO_2$ in the gas cooler shows relatively good coincidence with those predicted by Ito's correlation developed for single-phase in a helical coil tube. The local heat transfer coefficient of $CO_2$ is well coincident with the correlation by Pitla et al. However, at the region near pseudo-critical temperature, the experiments indicate higher values than the Pitla et al. correlation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.9
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• pp.640-646
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• 2007

The cooling heat transfer coefficient of $CO_2$ (R-744) for tube and coil diameter (CD), inclined angle of tube and coil pitch of inclined helical coil type copper tubes were investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and a inclined helical coil type gas cooler (test section). The test section consists of a smooth copper tube of 2.45 and 4.55 mm inner diameter (ID). The refrigerant mass flukes were varied from 200 to 800 [$kg/m^2s$] and the inlet pressures of gas cooler were 7.5 to 10.0 [MPa]. The heat transfer coefficients of $CO_2$ in inclined helical coil tube with 2.45 mm ID are $5{\sim}10.3%$ higher than those of 4.55 mm. The heat transfer coefficients of 41.35 mm CD are $8{\sim}32.4%$ higher than those of 26.75 mm CD. Comparison between $45^{\circ}\;and\;90^{\circ}$ of coil angle, the heat transfer coefficients of $45^{\circ}$ are higher than those of $90^{\circ}$. For coil pitch of gas cooler, the heat transfer coefficients of inclined helical coil gas cooler with coil pitch of 5 mm are similar to those of 10 and 15 mm.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.699-706
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• 2007

The cooling heat transfer coefficient and pressure drop of $CO_2$(R-744) in helical coil copper tubes were investigated experimentally The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter. a pre-heater and a inclined helical coil type gas cooler (test section). The test section consists of a smooth copper tube of 2.45 and 4.55mm inner diameter The refrigerant mass fluxes were varied from 200 to $600 [kg/m^2s]$ and the inlet pressures of 9as cooler were 7.5 to 10.0 [MPa]. The heat transfer coefficients of $CO_2$ in helical coil tubes increase with the increase of mass flux and gas cooling pressure of $CO_2$. The pressure drop of $CO_2$ in the gas cooler shows a relatively food agreement with those Predicted by Ito's correlation developed for single-phase in helical coil tubes. Though a few correlation available with the data. the local heat transfer coefficient of $CO_2$ agrees well with those presented by Pitla et al. among the predictions. However at the region near pseudo-critical temperature. the experiment data indicate higher values than the Pitla et al. correlation.

• Proceedings of the SAREK Conference
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• 2006.11a
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• pp.38-38
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• 2006

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.1
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• pp.32-38
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• 2009

In this paper, cycle performance analysis for cooling capacity, compression work and COP of R744($CO_2$) transcritical vapor compression refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, outlet temperature of gas cooler and evaporating temperature in the R744 vapor compression cycle. The main results were summarized as follows : The cooling capacity of R744 increases with superheating degree, but decreases with the increasing evaporating temperature and outlet temperature of gas cooler. The compression work increases with superheating degree and cooling pressure of R744, but decreases with the increasing evaporating temperature. And, The COP increases with outlet temperature and evaporating temperature of R744 gas cooler, but decreases with the increasing superheating degree. Therefore, superheating degree, outlet temperature and evaporating temperature of R744 vapor compression refrigeration system have an effect on the cooling capacity, compression work and COP of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle using R744.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.277-277
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• 2011

본 논문은 $CO_2$ 히트펌프용 모세관의 기초 설계자료를 제공하기 위해서 모세관 길이 예측에 대해서 이론 및 실험적으로 조사하였다. 본 연구에서 고려된 작동변수로는 증발온도, 가스냉각기 냉각압력, 냉매유량, 모세관의 관경 등이다. 몇몇연구자들의 자료를 바탕으로 $CO_2$ 모세관 길이를 예측할 수 있는 수학적 모델식을 작성하였다. 그리고 단열 모세관 팽창장치내 $CO_2$의 증발온도, 냉매유량, 냉각압력 등에 대해서 실험한 결과, Fig. 1에 나타낸 것처럼, 모세관 길이가 증가할수록 증발온도는 감소하는 것을 알 수 있다. 그리고 증발온도에 대한 실험값과 예측값의 비교 결과, 실험값이 예측값보다 약간 높게 나타났다. $CO_2$냉매가 모세관내를 통과할 때 플래쉬 가스(flash gas)의 발생으로 인해 액상의 양보다 기상의 양이 많아지고 액상의 압력강하보다 기상의 압력강하가 휠씬 더 크기 때문이다. 또한 증발온도에 대한 실험값과 예측값은 6.5~9.9% 이내에서 좋은 일치를 보였다. Fig. 2에 나타낸 것처럼, 모세관 길이가 증가할수록 냉매유량은 감소하는 것을 알 수 있다. 이는 전술한 바와 같이 모세관 길이가 증가할수록 냉매 압력강하가 더욱더 증가하기 때문이다. 그리고 냉매유량에 대한 실험값과 예측값의 비교 결과, 실험값이 예측값보다 약간 높게 나타났다. 이는 전술한 증발온도와 동일한 이유로 실제 $CO_2$냉매가 모세관내를 통과할 때 플래쉬 가스의 발생량이 많아지기 때문이다. 또한 냉매유량에 대한 실험값과 예측값은 0.64~10.9% 이내에서 좋은 일치를 보였다. Fig. 3에 나타낸 것처럼, 모세관 길이가 증가할수록 냉각압력은 증가하는 것을 알 수 있다. 이는 증발온도가 일정한 경우 모세관 길이가 증가할수록 냉매유량이 감소하여 압축기 토출측 온도(압력)가 상승하기 때문이다. 그리고 냉각압력에 대한 실험값과 예측값의 비교 결과, 실험값이 예측값보다 약간 낮게 나타났으며 실험값과 예측값은 1.04~3.7% 이내에서 좋은 일치를 보였다. 따라서 본 연구에서는 수송기계용 $CO_2$ 열펌프 단열 모세관에 대한 기초설계 자료로서, 냉각압력, 증발온도, 모세관 직경, 냉매유량 등의 조건으로부터 모세관 길이를 계산해낼 수 있는 예측 상관식을 제안하였다.