와이어붙이관의 핵비등 열전달촉진

김내현,김정식,남기일 대한기계학회 1994 대한기계학회논문집 Vol.18 No.5

In this study, experimental results of the nucleate boling of wire-wrapped tubes are provided. Both water and R-113 were boiled. Solid stainless steel wires, stranded copper wires and stranded nylon wires were tested. Solid stainless wire is effective to enhance the boiling of water. The performance is approximately the same(or slightly better at certain conditions) as that of GEWA-T tubes. For the test range of wire diameter 0.6 $mm{\le}d{\le}2.6 mm$, the optimum gap width increases as the wire diameter increases. The maximum heat transfer coefficient was obtained for the 1.0 mm diameter wire, and it is 1.6 times larger than that of the GEWA-T at the heat flux of 20 $kW/m^{2}.$ Solid stainless wire is also effective to enhance the boling of R-113 at low heat fluxes. The performance of the wire-wrapped tube approaches that of GEWA-T. At high heat fluxes, however, the enhancement decreases. The reason may be attributed to the cavity shape and the high wettability of the refrigerants. Stranded copper or nylon wire is effective to enhance the boiling of R-113. The performance is approximately the same(or slightly better) as that of GEWA-T tubes. Maximum heat transfer was obtained for the stranded nylon wire, and it is approximately 1.4 times larger than that for the GEWA-T at the heat flux of 20 $kW/m^{2}.$ The reason may be atrributed to the favorable thermal environment in the restricted regions formed by twisted wires.

An Experimental Study on Laminar Heat Transfer in Flat Aluminum Extruded Tubes Having Small Hydraulic Diameter

김내현,Jung Ho Ham,Do Young Kim 대한설비공학회 2007 International Journal Of Air-Conditioning and Refr Vol.15 No.2

Effect of Inlet Direction on the Refrigerant Distribution in an Alu-minum Flat-Tube Heat Exchanger

김내현,김도영,변호원,최영민 대한설비공학회 2008 International Journal Of Air-Conditioning and Refr Vol.16 No.4

The refrigerant R-134a flow distributions are experimentally studied for a round header/ten flat tube test section si-mulating a brazed aluminum heat exchanger. Three different inlet orientations (parallel, normal, vertical) were investi-gated. Tests were conducted with downward flow for the mass flux from 70 to 130 kg/m²s and quality from 0.2 to 0.6. In the test section, tubes were flush-mounted with no protrusion into the header. It is shown that normal and vertical inlet yielded approximately similar flow distribution. At high mass fluxes or high qualities, however, slightly better results were obtained for normal inlet configuration. The flow distribution was worst for the parallel inlet configuration. Possible explanation is provided based on flow visualization results.

Heat Transfer and Pressure Drop Characteristics of Plain Fin-and-Tube Heat Exchangers Having 5.0 mm Tubes Under Dehumidifying Condition

김내현 대한설비공학회 2015 International Journal Of Air-Conditioning and Refr Vol.23 No.2

In this study, wet surface pressure drop and heat transfer characteristics of plain finned heat exchangers having 5.0 mm diameter (5.3 mm after tube expansion) tubes were investigated. Nine samples having different fin pitches (1.1 to 1.3 mm) and tube rows (1 to 3 rows) were tested. The fin pitch had a negligible effect on j and f factors. Both j and f factors decreased as the number of tube row increased. When compared the j and f factors of the samples having 5.3 mm diameter tubes with those of 7.3 mm diameter tubes, 5.3 mm samples yielded higher j factors and lower f factors. The j/f ratios of 5.3 mm samples are larger than those of 7.3 mm samples which implies that 5.3 mm geometry is more beneficial than 7.3 mm geometry.

An Experimental Investigation on the Airside Performance of Fin-and-Tube Heat Exchangers Having Nonsymmetrical Slit Fins

김내현,Mi-Hye Kwon,Min-Geon Go 대한설비공학회 2015 International Journal Of Air-Conditioning and Refr Vol.23 No.2

In this study, the heat transfer and friction characteristics of nonsymmetric slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on j and f factors is negligible. Considering the small variation of the fin pitch (from 1.3 mm to 1.5 mm), the foregoing argument should hold true for the present samples. Louver fin samples yield higher j and f factors than slit fin samples. Both j and f factors increase as the number of tube rows decreases. The row effect is true for both slit and louver fin samples. For one-row configuration, j/f ratios of louver fin samples are larger than those of slit fin samples. The trend is, however, reversed for three-row configuration. Data are compared with available correlations.

THERMAL PERFORMANCE OF SINE WAVE FIN-AND-OVAL TUBE HEAT EXCHANGERS

김내현,이강종,JI-CHAO HAN,BYUNG-NAM CHOI 대한설비공학회 2013 International Journal Of Air-Conditioning and Refr Vol.21 No.1

Experiments were conducted on sine wave ¯n-and-tube heat exchangers having oval tubes of 0.6aspect ratio. Twelve samples having di®erent ¯n pitches and tube rows were tested. Eight herringbone wave ¯n-and-tube heat exchangers having round tubes were also tested. For round tube samples, the e®ect of tube row on j factor is not prominent. For oval tube samples, however, the highest j factor is observed for two row con¯guration, whereas the lowest one is observed for one row con¯guration. Possible reasoning is provided considering the °ow and heat transfer characteristics of sine wave channel combined with connecting oval tubes. The friction factor decreases as number of tube row increases. Comparison with round tube samples reveals that airside performance of oval ¯n-and-tube heat exchangers is generally superior except for one-row configuration.

An experimental investigation on the airside performance of fin-and-tube heat exchangers having slit fins under wet condition

김내현,김태현 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.11

In this study, the heat transfer and friction characteristics of the 5.3 mm O.D. slit-finned heat exchangers under wet condition havebeen experimentally investigated. Plain-finned heat exchangers having the same 5.3 mm O.D. tubes are also tested for comparison purpose. The effect of fin pitch on j and f factor is negligible. Slit fin samples yield higher j and f factors than plain fin samples. For one rowconfiguration, the average f factor ratio between slit fin sample and plain fin sample is 2.18. The ratio increases to 2.41 for two row configuration,and to 2.65 for three row configuration. As for the j factor, the ratios are approximately the same (1.61, 1.70 and 1.71 for one,two and three row configuration). Both j and f factor increase as the number of tube row decreases. The same trend is observed for theplain fin samples. At high Reynolds numbers, the j/f ratios of the slit fin are approximately the same as those of the plain fin. At lowReynolds numbers, the j/f ratios of the slit fin are smaller than those of plain fin. Data are compared with existing correlations.

Effect of corrugation geometry on the moisture transfer and pressure drop for humidifying element made of cellulose and PET

김내현 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.12

New humidifying element samples were made and the moisture transfer and pressure drop characteristics were investigated. Resultsshow that the new sample (cellulose 50% and PET 50%) yielded superior moisture transfer and pressure drop performance than currentlywidely used Glasdek (Glasswool). The jm factors of the new sample are 33% ~ 39% larger than those of Glasdek. On the other hand, the ffactors of Glasdek are 0% ~ 51% larger. In general, the jm or f factor increases as corrugation angle increases or corrugation height decreases. The moisture transfer capacity index (hDA/ΔP) was the largest for 30°/30° sample, followed by 15°/15°, 45°/45° and 60°/60°sample. Correlations were developed to predict jm and f factors of the new samples.

Airside performance of fin-and-tube heat exchangers having sine wave fins under wet condition

김내현 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.9

In this study, experiments are conducted on sine wave heat exchangers under wet condition, and the results are compared with those ofherringbone wave heat exchangers having same wave height. Sine wave samples yield higher j and f factors than herringbone wave samples. The reason may be attributed to the reduced recirculation zone in the valleys of the sine wave channel. The effect of fin pitch on jand f factor is not pronounced both for sine and herringbone wave heat exchangers. The j factor decreases as number of tube row increases. However, the effect of number of tube row on f factor is dependent on the fin configuration. For herringbone wave samples, ffactor decreases as the number of tube row increases. For sine wave samples, on the other hand, f factor is independent of the number of tuberow. Ratios of j/f 1/3 between sine wave and herringbone wave samples are between 0.95 and 1.0, which decrease with theincrease of finpitch. A new correlation was developed based on the present data.

Evaporation heat transfer and pressure drop of R-410A in three 7.0 mm O.D. microfin tubes having different inside geometries

김내현 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.8

R-410A evaporation heat transfer and pressure drop data are provided for three 7.0 mm O.D. microfin tubes. The microfin tubes haddifferent helix angle, fin height and fin apex angle. Tests were conducted for a range of quality (0.2 ~ 0.8), mass flux (216 ~ 390 kg/m2s),heat flux (9 ~ 17 kW/m2) and saturation temperature (8 ~ 12oC). It was found that three microfin tubes yielded approximately the sameheat transfer coefficients. Microfin tube with larger inter-fin spacing or smaller helix angle yielded lager pressure drop. Both heat transfercoefficient and pressure drop increased as mass flux or quality increased. However, they decreased as saturation temperature increased. The range of heat transfer enhancement factor (1.37 ~ 1.97) was comparable with that of pressure drop penalty factor (1.22 ~ 1.77). Dataare compared with available heat transfer and pressure drop correlations.