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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Korean Journal of Air-Conditioning and Refrigeration Engineering
Journal Basic Information
Journal DOI :
The Society of Air-Conditioning and Refrigerating Engineers of Korea
Editor in Chief :
Volume & Issues
Volume 12, Issue 12 - Dec 2000
Volume 12, Issue 11 - Nov 2000
Volume 12, Issue 10 - Oct 2000
Volume 12, Issue 9 - Sep 2000
Volume 12, Issue 8 - Aug 2000
Volume 12, Issue 7 - Jul 2000
Volume 12, Issue 6 - Jun 2000
Volume 12, Issue 5 - May 2000
Volume 12, Issue 4 - Apr 2000
Volume 12, Issue 3 - Mar 2000
Volume 12, Issue 2 - Feb 2000
Volume 12, Issue 1 - Jan 2000
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The Effects of Oil on Refrigerant Flow through Capillary Tubes
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 791~801
An experimental study was conducted to analyze the effects of oil on refrigerant flow through adiabatic capillary tubes, and to develop a model for mass flow rates of refrigerant/oil mixture at various capillary tubes and flow conditions. Mass flow rates and the profiles of the pressures and temperatures along the capillary tubes was obtained with the oil concentration of R-22/SUNISO 4GS oil mixture at various test conditions. The flow trends as a function of geometry and flow conditions for pure refrigerant and refrigerant/oil mixture were similar in adiabatic capillary tubes. Mass flow rate of the refrigerant/oil mixture was less than that of pure refrigerant at the same test conditions.
Thermal and Flow Analysis inside the Header of a Parallel Flow Heat Exchanger
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 802~809
This study numerically analyzes the thermal and flow characteristics inside the header in PFHE(parallel-flow heat exchanger) by employing a three-dimensional turbulence modeling. The following quantities are examined by varying the injection angle of the working fluid, the location of entrance and the shape of entrance: flow nonuniformity, heat transfer rate, and flow distribution in each passage. The result shows that the degree of significance among the parameters affecting the header part is in the order of the injection angle, the shape of entrance, and the location of entrance. The result also indicates that heat transfer rates compared to the reference model are increased by about 152% for the angle of injection of -
, by about 127% for the shape of entrance with right and left long rectangular form, and by about 108% for the location of entrance located at the lowest Position.
Experimental Analysis of Thermal Comfort of an Office Space for Ceiling and Floor Supply Air Conditioning Systems
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 810~816
Thermal comfort plays an important role in modern office buildings. Four major factors affecting thermal comfort are air temperature, velocity, humidity and radiation temperature. Distribution of these thermal factors in indoor space depends largely on the air flow which is related to the method of supplying and extracting air. In this study, an experimental analysis on indoor thermal comfort is conducted to study the difference between a ceiling supply cooling system and a floor supply one. The two cooling systems are applied to an office space during summer season and the distributions of temperature, velocity, radiation temperature and PMV are measured. Results show that the floor supply cooling system is superior in terms of thermal comfort and energy saving. Studies need to be done, however, to reduce the vertical temperature difference of a floor supply air conditioning system.
Measurement of Heat Transfer Rates and Pressure Drops in a Solid Particle Circulating Fluidized Heat Exchanger
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 817~824
The fluidized solid particles not only increase heat transfer rates but have a cleaning function eliminating contaiminated substances caused from condensate water. An experiment was performed to measure heat transfer rates and pressure drops in a fluidized heat exchanger with circulating solid particle for constant heat transfer rate. As a results, the heat transfer rate increased by 26.9~2.6%, heat transfer coefficient by 11.9~2.7%, and pressure drop by 79.1~10.9% at the gas velocity of 6.1 ~12.1 m/s and solid particle flow rate of 100~50 kg/h with the heat exchanger of H: 50 mm,
Analysis of a Cryogenic Nitrogen-Ambient Air Heat Exchanger Including Frost Formation
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 825~834
A heat exchanger analysis is performed to investigate the heating characteristics of cryogenic nitrogen by ambient air for the purpose of cryogenic automotive propulsion. The heat exchanger is a concentric triple-passage for supercritical nitrogen, and the radial fins are attached on the outermost tube for the crossflow of ambient air. The temperature distribution is calculated for the nitrogen along the passage, including the real gas properties of nitrogen, the fluid convections and the conductions through the tube walls and the fins. Since the wall temperature of the outer (ambient side) tube is very low in most cases, a heavy frost can be formed on the surface, affecting the heat exchange performance. By the method of the similarity between the heat and the mass transfer of moist air, the frost growth and the time-dependent effectiveness of the heat exchanger are calculated for various operating conditions. It is concluded that the frost formation can augment the heating of nitrogen during the initial period because of the latent heat, then gradually degrades the heat exchange because of the increased thermal resistance. Practical design issues are discussed for the flow rate of nitrogen, the velocity and humidity of ambient air, and the sizes of the fin.
Study on Film-Boiling Heat Transfer of Subcooled Turbulent Liquid Film Flow on Horizontal Plate
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 835~842
Film boiling heat transfer of the subcooled turbulent liquid film flow on a horizontal plate was investigated by theoretical and experimental studies. In the theoretical analysis, by solving the integral energy and momentum equations analytically, some generalized expressions for Nusselt number was deduced. Next, by comparing the deduced equations with the experimental data on the turbulent film boiling heat transfer of the subcooled thin liquid film flow, the semi-empirical relation between the Nusselt number based on the modified heat transfer coefficient and the Reynolds number was obtained. The correlating equation was very similar to that of the turbulent heat transfer in a single phase flow, and it was found that the heat transfer was dissipated to increase the liquid temperature.
An Experimental Study on the Effect of Fluid Flow and Heat Transfer Characteristics by the Longitudinal Vortices
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 843~852
The flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices were studied experimentally. The test facility consisted of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta winglet protruding from the surface. In order to control the strength of the longitudinal vortices, the angles of attack of the vortex generators were varied from
degree, but spacings between the vortex generators were fixed to 4 cm. The 3-dimensional mean velocity measurements were made using a five-hole pressure probe. Heat transfer measurements were made using the thermochromatic liquid to provide the local distribution of the heat transfer coefficient. By using the method mentioned above, the following conclusions were obtained from the present experiment. The boundary layer was thinned in the regions where the secondary flow was directed toward the wall and thickened where it was directed away from the wall. The peak augmentation of the local heat transfer coefficient occurred in the downwash region near the point of minimum boundary-layer thickness.
Performance Test of Low Temperature Waste Heat Recovery Heat Exchanger Using Self-excited Oscillating Heat Pipe
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 853~859
In this study, low temperature waste heat recovery heat exchanger was developed using a principle of self-excited oscillating heat pipe. The heat exchanger of serpentine type was composed of extruded flat aluminum tube with 6 channels (3 nm
2.75nm) and louvered fin. The heat transfer area density of heat exchanger was
. Working fluid is R141b and charge ratio was 40% by volume. Heat transfer rate and the effectiveness of heat exchanger was primary concern of this study. As a result, the effectiveness of heat exchanger was about 0.4-0.67, and recovered waste heat rate was about 4.5 kW per one unit of heat exchanger.
Physical Properties of Microencapsulated Phase Change Material Slurries
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 860~869
The thermal conductivity and density of slurries entrained with the particles of Micro-PCM are measured with respect to its temperatures as well as concentrations. For the thermal conductivity of slurries, a device made from P.A. Hilton (Model No. H470) is adopted. There is a well-scaled 0.3 mm gap between shells into which the slurry is injected. The temperatures of the slurry are changed to
, for which it is controled by the supplied voltage and cooling water circulated around the outer shell. The concentrations of Micro-PCM slurries are varied from 5 wt% to 50 wt%. Some general equations such as Maxwell's equation, are evaluated for their applicability with Micro-PCM slurry. As a result, it happens to be some 20% discrepancy between the experiment and the applied equations. The density measurements of Micro-PCM slurry to its temperature and concentration are peformed by hydrometer. For the experiment, tetradecane encapsulated slurry ((
) and a mixed wax (
) are tested. The temperature changes of tetradecane are applied for
and a mixed wax for
and its concentrations are changed from 5 wt% to 30 wt%. The results are compared with a general equation and the referenced data. For the conclusion, the experimental result and a general equation are well agreed.
Analysis of Pressure Drop for Combining Junctions in Gas-Liquid Two-Phase Flows
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 9, 2000, Pages 870~878
An experimental study and a modeling are peformed to investigate the pressure drop of combining junctions in two-phase flows. Experiments on tripod geometry used in a condenser or an evaporator, are conducted with inlet mass fluxes from 200 to$ 400 kg/m^2$s, and pipe diameters of 7 m and 9.52 m. The working fluid is R22. The result shows that the pressure drop increases as the quality does, but the effect of the increase of the pressure decreases when the diameter of a pipe increases. When the mass flux increases, the pressure drop linearly does. Furthermore, when the pipe diameter decreases, the pressure drop has a quadratic increase.