• Journal of Advanced Marine Engineering and Technology
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• v.32 no.4
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• pp.542-549
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• 2008

The evaporation heat transfer coefficient and pressure drop of R-22 and R-407C in a horizontal copper tube were investigated experimentally. The main components of the refrigerant loop are a receiver, a compressor, a mass flow meter, a condenser and a double pipe type evaporator (test section). The test section consists of a smooth copper tube of 6.4 mm inner diameter. The refrigerant mass fluxes were varied from 100 to $300\;kg/m^2s$ and the saturation temperature of evaporator were $5^{\circ}C$. The evaporation heat transfer coefficients of R-22 and R-407C increase with the increase of mass flux and vapor quality. The evaporation heat transfer coefficients of R-22 is about $5.68{\times}46.6%$ higher than that of R-407C. The evaporation pressure drop of R-22 and R-407C increase with the increase of mass flux. The pressure drop of R-22 is similar to that of R-407C. In comparison with test results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient of R-22 and R-407C. therefore, it is necessary to develope reliable and accurate predictions determining the evaporation heat transfer coefficient of R-22 and R-407C in a horizontal tube.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.3
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• pp.30-37
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• 2008

The evaporation pressure drop of $CO_2$ (R-744) in horizontal tubes 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 and 4.57 mm inner diameter. The experiments were conducted at 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 pressure drop of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. The pressure drop measured during the evaporation process of $CO_2$ increases with increased mass flux, and decreases as the saturation temperature increased. The evaporation pressure drop of $CO_2$ is very lower than that of R-22. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Choi et al. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1007-1017
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• 2003

An experimental study on the air-side pressure drop and heat transfer coefficient of slit fin-tube heat exchanger has been carried out. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper focuses on new method of data reduction to obtain the air-side performance of fin-tube heat exchanger using R22 and recommends standard procedures for dry and wet surface heat transfer estimation in fin-tube heat exchanger having refrigerant on the tube-side. Results are presented as plots of friction f-factor and Colburn j -factor against Reynolds number based on the fin collar outside diameter and compared with previous studies. The data covers a range of refrigerant mass fluxes of 150∼250 kg/$m^2$s with air flows at velocity ranges from 0.3 m/s to 0.8 m/s.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.9
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• pp.557-567
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• 2016

In this study, the optimal design of heat exchangers, including the evaporator and condenser of a solar-heating ocean thermal energy conversion (SH-OTEC), is investigated. The power output of the SH-OTEC is assumed to be 100 kW, and the SH-OTEC uses the working fluid of R134a and high-performance commercial tubes. The surface heat transfer area and the pressure drop were strongly dependent on the number of tubes, as well as the number of tube passes. To solve the reciprocal tendency between the heat transfer area and pressure drop with respect to the number of tubes, as well as the number of tube passes, a genetic algorithm (GA) with two objective functions of the heat transfer area (the capital cost) and operating cost (pressure drop) was used. Optimal results delineated the feasible regions of heat transfer area and operating cost with respect to the pertinent number of tubes and tube passes. Pareto fronts of the evaporator and condenser obtained from multi-objective GA provides designers or investors with a wide range of optimal solutions so that they can select projects suitable for their financial resources. In addition, the surface heat transfer area of the condenser took up a much higher percentage of the total heat transfer area of the SH-OTEC than that of the evaporator.

• Proceedings of the SAREK Conference
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• 2003.07a
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• pp.24-24
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• 2003

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.8
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• pp.612-620
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• 2008

New alternative refrigerants have been developed due to the ozone layer depletion and global warming. For this reason, carbon dioxide is believed to be a promising refrigerant for use in air conditioners and heat pumps. Evaporative heat transfer characteristics and pressure drop of $CO_2$ with outer diameter of 5 mm in inclined ($45^{\circ}$) smooth and micro-fin tubes have been investigated by the experiments with respect to several test conditions such as mass fluxes, heat fluxes, evaporation temperatures in this study. The inclined ($45^{\circ}$) smooth and micro-fin tubes with length of 1.44 m were installed to measure the evaporative heat transfer coefficients of $CO_2$ and heat was supplied to the refrigerant by direct heating method where the test tube was uniformly heated by electricity. The tests were conducted at mass fluxes from 212 to $656\;kg/m^2s$, heat fluxes from 15 to $60\;kW/m^2$ and evaporation temperatures from -10 to $20^{\circ}C$. The heat transfer coefficients of $CO_2$ are slightly increased with increasing mass flux, and the heat transfer characteristics in the inclined ($45^{\circ}$) tubes are enhanced about $5{\sim}10%$ compared with those in horizontal or vertical tubes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.9
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• pp.615-621
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• 2007

Experimental study on the heat transfer characteristics of $CO_2$ in a horizontal smooth tube was carried out to investigate the heat transfer coefficient and pressure drop during evaporation of $CO_2$. The experiment apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiment was conducted for various mass fluxes ($200{\sim}1200kg/m^2s$), heat flukes ($10{\sim}100kW/m^2$) and saturation temperatures (-5, 0, $5^{\circ}C$). With increasing the heat flux, the evaporation heat transfer coefficient increased. But the variation of the heat transfer coefficient on the increase of the mass flux was not large. And the significantly drops of the heat transfer coefficient was observed at any heat flux and mass flux because of the change of the flow pattern in the tube. With increasing the saturation temperature, the heat transfer coefficient increased due to the promotion of a nucleate boiling. The measured pressure drop during evaporation increased with increasing the mass flux and decreasing the saturation temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.269-277
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• 2002

Experiments on the evaporation heat transfer and pressure drop in the brazed type plate heat exchangers were performed using refrigerants R410A and R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different 45$^{\circ}$, 35$^{\circ}$and 20$^{\circ}$chevron angles are used. Tests were conducted fur the ranges of the mass flux of refrigerant from 13 kg/m$^2$s to 34 kg/m$^2$s, the evaporation temperatures of 15$^{\circ}C$, 1$0^{\circ}C$ and 5$^{\circ}C$, vapor quality from 0.15 to 0.95 and the heat flux from 2.5 kW/m$^2$to 8.5 kW/m$^2$. The evaporation heat transfer coefficients and pressure drops were measured. Most of flow patterns are in the chum flow regime and become close to the annular flow for increasing the mass flux and the vapor quality. The heat transfer coefficient increases with increasing the evaporation temperature at a given mass flux in all plate heat exchangers. Also, the pressure drop increases with increasing the mass flux and the quality and decreasing the evaporation temperature and the chevron angle.

• Journal of Power System Engineering
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• v.14 no.4
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• pp.11-16
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• 2010

The evaporation heat transfer characteristics of propane(R-290) in horizontal small diameter tubes were investigated experimentally. The test tubes have inner diameters of 1 mm and 4 mm. Local heat transfer coefficients were measured at heat fluxes of 12, $24\;kW/m^2$, mass fluxes of 150, $300\;kg/m^2s$, and evaporation temperature of $15^{\circ}C$. The experimental results showed that the evaporation heat transfer coefficient of R-290 has an effect on heat flux, mass flux, tube diameter, and vapor quality. The evaporation heat transfer of R-290 has an influenced on nucleate boiling at low quality and convective boiling at high quality. The evaporation heat transfer coefficient of R-290 increases with decreasing inner tube diameter. And the evaporation heat transfer coefficient of R-290 is about 1~3 times higher than that of R-134a.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.852-859
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• 2003

R407C is considered as an alternative refrigerant of R22 for air conditioners. An experiment was carried out to investigate the characteristics of the evaporation heat transfer and pressure drop for refrigerant R407C flowing in a fin-and-tube heat exchanger used for commercial air-conditioning unit. The experimental data were useful in analyze the effects of the temperature glide and superheat for R407C. Test were conducted at the conditions of inlet refrigerant evaporation temperature of 7$^{\circ}C$, inlet air relative humidity of 50%, and refrigerant mass fluxes varying from 150 to 250 kg/m$^2$s. Representative results show that the heat exchanger performance for R407C evaporation is significantly affected by the change of the flow pattern from two-phase to super-heated vapor flow.