• Journal of Bio-Environment Control
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• v.30 no.4
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• pp.278-286
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• 2021

In this study, based on the Computational Fluid Dynamics (CFD) simulation model developed through previous study, inner environmenct of the modified glass greenhouse was predicted. Also, suggested the optimal shape of the greenhouse and location of the heat exchangers for heat energy management of the greenhouse using the developed model. For efficient heating energy management, the glass greenhouse was modified by changing the cross-section design and the location of the heat exchanger. The optimal cross-section design was selected based on the cross-section design standard of Republic of Korea's glass greenhouse, and the Fan Coil Unit(FCU) and the radiating pipe were re-positioned based on "Standard of greenhouse environment design" to enhance energy saving efficiency. The simulation analysis was performed to predict the inner temperature distribution and heat transfer with the modified greenhouse structure using the developed inner environment prediction model. As a result of simulation, the mean temperature and uniformity of the modified greenhouse were 0.65℃, 0.75%p higher than those of the control greenhouse, respectively. Also, the maximum deviation decreased by an average of 0.25℃. And the mean age of air was 18 sec. lower than that of the control greenhouse. It was confirmed that efficient heating energy management was possible in the modified greenhouse, when considered the temperature uniformity and the ventilation performance.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.106-111
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• 2001

The performance characteristics of heat pump system using the new refrigerant subcooling system were investigated. The new heat pump system has the ice storage tank to accumulate the latent heat of the refrigerant during the night-time. The heat is released to subcool the saturated refrigerant liquid at the outlet of a condenser in the daytime. The experimental apparatus is a well-instrumented heat pump which consisted of a refrigerant loop and a coolant loop. The test sections(condenser and evaporator) were made of tube-in-tube heat exchanger with the horizontal copper tube of 12.7[mm] outer diameter and 9.5[mm] inner diameter. The evaporating temperatures ranged from $-5[^{\circ}C]$ to $0[^{\circ}C]$ and the subcooling degrees of the refrigerant varied from $15[^{\circ}C]$ to $25[^{\circ}C]$. The test of the ice storage was carried out at evaporating temperature of $-10[^{\circ}C]$ and the ice storage mode is an ice-on-coil type. The main results were summarized as follows ; The refrigerant mass flow rate and compressor shaft power of the heat pump system were independent of the subcooling degrees. The cooling capacity o the heat pump system increases as the evaporating temperature and subcooling degree increases. The cooling capacity of the heat pump system is about 25 to 30% higher than that of normal heat pump system. The COP of the heat pump system which subcooled the refrigerant liquid at the outlet of the condenser is about 28% higher than that of the normal heat pump system.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.5
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• pp.403-411
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• 2016

Usually shell and tube heat exchangers are employed to recover energy between fluids. Recently, numerous papers on these heat exchangers have been published; however, the velocity and temperature profiles or comparison of the features of the flow with or without inside tubes have rarely been described. In this research, experimental and numerical studies were carried out to investigate the characteristics of the flow around the spiral baffle plates without inside tubes in a horizontal circular tube using a particle image velocimetry method and ANSYS 14.0~15.0 version (Fluent). The results showed that swirling flow was produced between the spiral baffle plates. The tangential components were strong between the two spiral baffles; however, the axial or radial velocities components were indicating nearly zero. From the spiral motion in the space of the two baffles, it is considered that there were no dead zones between the spiral baffle.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.3
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• pp.297-305
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• 2005

The evaporation heat transfer coefficient of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver. a variable-speed pump. a mass flow meter. a pre-heater and evaporator (test section). The test section consists of a smooth. horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500\;kg/m^{2}s$. saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$. and heat flux of 10 to $40\;kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has greatly effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality. heat flux and saturation temperature. The evaporation heat transfer coefficient of $CO_2$ is very larger than that of R-22 and R-134a. In making a comparison between test results and existing correlations. the present experimental data are the best fit for the correlation of Jung et al. But it was failed to predict the evaporation heat transfer coefficient of $CO_2$ using by the existing correlation. Therefore. it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.4
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• pp.167-174
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• 2005

The evaporation heat transfer coefficient of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500kg/m^2s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$, and heat flux of 10 to $40kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has greater effect on nucleate boiling than convective boiling. The evaporation heat transfer coefficient of $CO_2$ is highly dependent on the vapor quality, heat flux and saturation temperature. The evaporation heat transfer coefficient of $CO_2$ is very larger than that of R-22 and R-134a. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But the existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.262-267
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• 2005

The evaporation heat transfer coefficient of $CO_2$ in a horizontal round tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section was made of a horizontal stainless steel tube with the inner diameter of 7.75 mm, and length of 5 m. The experiments were conducted at mass flux of 200 to 500 $kg/m^2s$, saturation temperature of $-5^{\circ}C$ to $5^{\circ}C$, and heat flux of 10 to 40 $kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has great effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. In comparison with teat results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.857-862
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• 2002

Compressor is a major noise source of air-conditioner. Especially, its low frequency band noise below 1000Hz is very important because it will not be attenuated by passing through the cover panel and heat exchanger in air-conditioner. The factors affecting the low frequency band noise are studied by geometric similarity along with several experiments, and the low frequency noise is closely related with the discharge holes of muffler as well as the cavity of lower shell. The low frequency band noise is significantly reduced by proposed designs.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.2
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• pp.1-6
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• 2013

In high-speed vehicle, selection of fuel, configuration of components and cooling system are required to solve the heating issue by aerodynamic heating and inner combustion process. This subsystem consists of fuel tank, supply pump, various control valve, heat exchanger, including reactor, connecting line, adiabatic structures and insulations. In this paper, applicable fuel property is considered at flight characteristic of hypersonic vehicles. In this regard, current state of fuel/cooling system technology is identified.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.3
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• pp.263-271
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• 2007

The heat transfer coefficient and pressure drop during 9as cooling process of $CO_2$ (R744) in a helically coiled copper tube with the inner diameter of 4.55 mm and outer diameter of 6.35 mm 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 helically coiled type gas cooler (test section). The refrigerant mass fluxes are varied from 200 to $800kg/m^2s$ and the inlet pressures of gas cooler are 7.5 to 10.0 MPa. The heat transfer coefficients of $CO_2$ in a helically coiled tube are higher than those in a horizontal tube. The Pressure drop of $CO_2$ in the gas cooler shows a relatively good agreement with those predicted by Ito's correlation developed for single-phase in a helically coiled tube. The local heat transfer coefficient of $CO_2$ agrees well 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. Therefore, various experiments in helically coiled tubes have to be conducted and it is necessary to develop the reliable and accurate prediction determining the heat transfer and pressure drop of $CO_2$ in a helically coiled tube.