• 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.

• Nuclear Engineering and Technology
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• v.31 no.5
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• pp.486-497
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• 1999

The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate, A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side has a shape of annulus around vertical tube and the lost heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 11 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348∼3.282kg/hr, of inlet air mass fraction 11.8∼55.0%. The investigation of the flooding is preceded to find the upper limit of the reflux condensation. Onset of flooding is lower than that of Wallis' correlation. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the increase of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed by 165 data of the local heat transfer. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7% between the results by the experiment and by the correlation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.1022-1027
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• 2005

An experimental study is conducted to investigate the characteristics of the ion wind generated by the electric field between a needle electrode and the parallel plate electrodes. The ion wind enhances heat and mass transfer between the surface and the surrounding gas. Moreover such enhancement makes no noise or vibration. This study is conducted to develop the electronic cooling device. The measured gas velocities and heat transfer coefficients are proportional to the applied voltage. The heat transfer coefficient can be increased as compared with a natural convection. The maximum enhancement of heat transfer obtained in this system is $47\%$ for 3 W in heat transfer rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.713-723
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• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• Journal of the Korean Society of Combustion
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• v.20 no.2
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• pp.14-27
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• 2015

Calcination, which represents thermal decomposition of $CaCO_3$, is the key reaction in a cement process. Some reactions including heating-up also take place simultaneously in the calcination reactors. Basic thermal performance and dimensions of the reactors in two cases, which are a rotary kiln wih a four-stage cyclone pre-heater and a simple single rotary kiln, were compared. To employ the heat transfer, mass transfer and reaction rate as well as calcination, one-dimensional modeling was conducted in each case. Some simplification about the reactors was described, however, the reliable Nusselt number and heat transfer coefficients on the reactors were used to make results reliable.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.7
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• pp.681-687
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• 2005

Experimental results for heat transfer characteristic and pressure gradients of HCs refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 during evaporating inside horizontal double pipe heat exchangers are presented. The test sections which has one tube diameter of 12.70 m with 0.86 mm wall thickness, another tube diameter of 9.52 mm with 0.76 mm wall thickness are used for this investigation. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were higher than that of R-22. The average evaporating heat transfer coefficient increased with the increase of the mass flux. It showed the higher values in hydrocarbon refrigerants than R-22. Hydrocarbon refrigerants have higher pressure drop than R-22 in 12.7 mm and 9.52 mm. This results form the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air- conditioning systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.6
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• pp.530-537
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• 2004

In recent years, carbon dioxide among natural refrigerants has gained consider-able attention as an alternative refrigerant due to its excellent thermophysical properties. However, few investigations have been performed to develop useful correlations of heat trans-fer coefficients and pressure drop during evaporation of carbon dioxide. This study is aiming at providing the characteristics of heat transfer and pressure drop during the evaporation process of carbon dioxide. Heat is provided by a direct heating method to the test section, which was made of a seamless stainless steel tube with an inner diameter of 7.53 mm, and a length of 5.0 m. Experiments were conducted at saturation temperatures of -4 to 2$0^{\circ}C$, heat fluxes of 12 to 20 ㎾/$m^2$ and mass fluxes of 200 to 530 kg/$m^2$s. A comparison of different heat transfer correlations applicable to evaporation of carbon dioxide has been made. Based on the experiments for evaporation heat transfer and pressure drop, new correlations were developed. The newly developed empirical correlations for the heat transfer and pressure drop show average absolute deviations of 15.3% and 16.2%, respectively.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.28-35
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• 2001

The heat transfer and pressure drop characteristics of R718 flowing in smooth horizontal copper tubes with inner diameter of 3.36 mm, 5.35 mm, 6.54 mm and 8.12 mm were investigated. The test section is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. Experiments were peformed for the flowing range of variables : Reynolds number (1000 to 20000), mass flow rate of brine (450 kg/h) and refrigerant temperature (5$0^{\circ}C$). The main results were summarized as follows : (1) The heat transfer coefficient of 3.36 mm ID was about 10% to 30% higher than that of 5.35 mm, 6.54 mm and 8.12 mm ID, and the heat transfer coefficients for small diameter. tubes are about 20% to 27% higher than these predicted by Gnielinski. The new correlation is proposed to predict the experimental data. (2) As a result of comparison with correlation prosed by Blasius. the deviation of the experimental data slightly increased as the tube diameter decreased. (3) The ratio of heat transfer to friction factor (j/f) correlated by all experimental data increased as the tube diameter decreased.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.1143-1148
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• 2005

Experimental results for heat transfer characteristic and pressure gradient of HCs refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 during condensing inside horizontal double pipe heat exchangers are presented. The test sections which have one tube diameter of 12.70 mm with 0.86 mm wall thickness, another tube diameter of 9.52 mm with 0.76 mm wall thickness are used for this investigation. The local condensing heat transfer coefficients of hydrocarbon refrigerants were higher than those of R-22. The average condensing heat transfer coefficient increased with the increase of the mass flux. It showed the higher values in hydrocarbon refrigerants than R-22. Hydrocarbon refrigerants have higher pressure drop than those of R-22 in 12.7 mm and 9.52 mm. This results from the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.12
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• pp.977-983
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• 2006

Experimental results for heat transfer characteristic and pressure gradient of hydrocarbon refrigerants (R-290, R-600a, R-1270) and HCFC refrigerant (R-22) during condensation inside horizontal double pipe heat exchangers are presented. The test sections which have one tube diameter of 12.70 mm with 0.89 mm, 9.52 mm with 0.76 mm, 6.35 mm with 0.13 mm wall thickness are used for this investigation, respectively. The local condensing heat transfer coefficients of hydrocarbon refrigerants were higher than those of R-22. The average condensing heat transfer coefficient increased with the increase of the mass flux. It showed the higher values in hydrocarbon refrigerants than R-22. Hydrocarbon refrigerants have higher pressure drop than R-22 in 10.92 mm, 8 mm and 6.1 mm inner diameters. These results from the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.