• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.12
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• pp.495-501
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• 2016

Condensation heat transfer and pressure drop of R245fa were investigated experimentally in a plate-shell heat exchanger which consisted of thirty seven counter flow channels formed by thirty-eight plates with a chevron angle of $50^{\circ}$. The upflow of the water in one channel receives heat from the downflow of R245fa in the other. The effects of refrigerant mass flux, imposed heat flux, refrigerant saturation pressure, and mean vapor quality on the heat transfer characteristics were explored in detail. Experimental correlations were proposed to predict the condensation heat transfer coefficient and friction factor in terms of the Boiling number, Reynolds number, and Prandtl number. In the experiments, the mean vapor quality in the refrigerant channel was varied from .22 to .82, mass flux from 3 to $5kg/m^2$, imposed heat flux from 1 to $3kW/m^2$, and system pressure from .61 to .81 MPa.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.247-251
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• 2007

Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical micro-fin tube have been investigated by experiment. Before a test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. The micro-fin tube with outer diameter of 5 mm and length of 1.44 m was selected as the test section. The test was conducted at mass fluxes of 318 to $530\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat fluxes of 15 to $30\;kW/m^2$. As the vapor quality increases, the heat transfer coefficients of carbon dioxide are increased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase, and there was not much of influence of mass flux on the heat transfer coefficients.

• Journal of the Korean Wood Science and Technology
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• v.22 no.2
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• pp.61-70
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• 1994

This study was executed to find the applicability of press drying of tree disk by investigating the shrinkage and drying defect and to form appropriate model by comparing the actual moisture content(MC) and internal temperature in respect of drying time with calculated values based computer simulation to which was applied finite difference method. In press drying disk, heating period, constant drying rate period maintained plateau temperature at 100$^{\circ}C$ and falling drying rate period were significantly distinguished. Actual MC and internal temperature were analogous to those calculated at comparing points. Heat transfer model formed by Fourier's law using specific heat of moist wood and conduction coefficient considering fractional volume of each element of wood cell wall, bound water, free water and air showed applicability as basic data to developing heat expansion, shrinkage and drying stress during press drying. Also mass transfer model formed by Fick's diffusion law using water vapor diffusion coefficient showed applicability. Longitudinal shrinkage was developed by pressure of hot press and tangential shrinkage was restrained by hygrothermal recovery. The heart check, surface check and ring failure were occurred differently in species, but V-shaped crack didn't develop.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.542-550
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• 1998

A direct contact heat exchanger using particle-suspended gas as a heat transfer medium is analyzed with an extended emphasis on the radiation, i. e., considering the radiation by both gas and particles. While the Runge-Kutta method is used for a numerical analysis of the momentum and energy equations, the finite volume method is utilized to solve the radiative transfer equation. Present study shows a notable effect by the gas radiation in addition to the particle radiation, especially when changing the chamber length as well as the gas and particle mass flow rate. When the gas and particle mass flow rate is raised, the gas temperature in the particle heater still increases as the gas absorption coefficient increases, which is different from the results for the small scale heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.73-80
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• 1995

The object of the present study is to develop a high performance evaporator for automotive air conditioner. The experiment has been conducted on evaporative heat transfer coefficient inside a plate type heat exchanger with a sharp 180-degree turn flow. The test plates have different formed surface, cross-ribbed channel and elliptical-ribbed channel. Also experimental study has been performed to determine optimal design in elliptical-ribbed plate heat exchanger with different turn clearance. In addition to the above experiments, refrigerant behavior and surface temperature distribution in the plate heat exchanger were observed using color thermoviewer(infrared thermometer). In this experiment, working fluid was used R-12 and test conditions were as follows : (1) saturation pressure of $2.116kg/cm^2$, (2) mass fluxes of 40 to $70kg/m^2s$, (3) heat fluxes of 4,500 to $7,300W/m^2$, (4) inlet quality of 0.1 to 0.7. The results indicated that the evaporative heat transfer coefficient of an elliptical-ribbed plate heat exchanger was higher than that of cross-ribbed plate heat exchanger. Also optimal turn clearance in an elliptical-ribbed plate heat exchanger was determined.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.535-544
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• 2004

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s : 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s : 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.187-192
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• 2003

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s = 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s = 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.210-217
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• 1999

This paper reports the experimental results on heat transfer characteristics of R-22 and R-407C(HFC-32/125/134a 23/25/52 wt%) condensing inside horizontal smooth and finned tubes. The test condensers used In the study are double pipe heat exchangers of 7.5 mm ID, 9.5 mm OD smooth tube, and 60 finned micro-fin tube with 8.53 mm ID, 9.53 mm OD. Each of these tubes was 4 000 mm long tubes connected with an U-bend. These U type two-path test tubes are divided In 8 local test sections for the identification of the local condensing heat transfer characterisitcs and pressure drop, U-bend effects on condensing flows. Inlet quality is maintained 1.0, and refrigerant mass velocity is varied from 102.0 to $301.0kg/m^2{\cdot}s$. From the results, it was found that the pressure drop of the R-407C Increased, and heat transfer coefficient decreased compared to those of R-22. In comparison condensing heat transfer characteristics of micro-fm tube with those of smooth tube, increasing of condensing heat transfer coefficient was found outstanding compared to the increasing ratio of pressure drop. Furthermore, pressure drop In U-bend showed at most a 30 % compared to the total pressure drop in the test section.

• 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.