• Korean Journal of Materials Research
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• v.16 no.2
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• pp.111-115
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• 2006

High-finned tubes have good thermal conductivity and have better cooling efficiency than plain tubes or low-fined tubes due to bigger air contact area. During high-fined tubes are manufactured by roll forming, the main technique is illustrated to optimizing primary material(copper pipe), optimized die matrix designing technique for roll forming, control manufacturing speed to develop productivity etc. In this study, a roll forming system was developed in oder to produce high-finned tube. Also a multi-step roll forming die was designed & built to produce high-finned tube that has over 10 mm fin height. And then, roll forming test using copper pipe was performed to produce high-finned tube. Roll forming process for producing highfinned tube was optimized by analyzing and adjusting misrostructure, hardness, and surface roughness of roll formed high-fined tube.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.96-103
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• 2000

In this study, evaporation heat transfer tests were conducted in flat aluminum multi-channel tubes using R-22. Two internal geometries were tested ; one with smooth inner surface and the other with micro-fins. Data are presented for the following range of variables ; vapor quality $(0.1{\sim}0.9)$, mass flux$(100{\sim}600kg/m^2s)$ and heat flux$(5{\sim}15kW/m^2)$. The micro-tin tube showed higher heat transfer coefficients compared with those of the smooth tube. Results showed that, for the smooth tube, the effects of mass flux, quality and heat flux were not prominent, and existing correlations overpredicted the data. For the micro-fin tube at low quality, the heat transfer coefficient increased as heat flux increased. However, the trend was reversed at high quality Kandlikar's correlation predicted the low mass flux data, and Shah's correlation predicted the high mass flux data. The heat transfer coefficient of the micro fin tube was approximately two times larger than that of the plain tube. New correlation was developed based on present data.

• Proceedings of the SAREK Conference
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• 2004.06a
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• pp.21-21
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• 2004

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2415-2423
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• 2015

Experiments were conducted on sine wave fin-and-tube heat exchangers having oval tubes under wet condition. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. Results showed that, for oval tube samples, the effect of fin pitch on j and f factor was not significant. As for the effect of tube row, the lowest j factor was obtained for one row configuration(81% of two row configuration), which is clear contrast to round tube samples, where the highest j factor was obtained for one row configuration. Possible reasoning is provided considering the flow and heat transfer characteristics of sine wave channel combined with connecting oval tubes. Comparison of $j/f^{1/3}$ with plain fin-and-tube heat exchanger having 15.9mm O.D. round tube reveals that present oval fin-and-tube heat exchanger shows superior thermal performance except for one row configuration. In other words, $j/f^{1/3}$ of the two row oval tube heat exchanger was 1.6~2.5 times larger than those of round tube heat exchanger, 1.4~2.4 times larger for three row configuration and 1.2~2.8 times for four row configuration.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.343-352
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• 2013

In this study, a smooth flat surface, low fin, Turbo-B, and Thermoexcel-E surfaces are used to examine the effect of the flow velocity on the pool boiling heat transfer coefficients (HTCs) and critical heat fluxes (CHFs). HTCs and CHFs are measured on a smooth square heater of $9.53{\times}9.53mm^2$ at $60^{\circ}C$ in a pool of pure water at various fluid velocities of 0, 0.1, 0.15, and 0.2 m/s. Test results show that for all surfaces, CHFs obtained with flow are higher than those obtained without flow. CHFs of the low fin surface are higher than those of the Turbo-B and Thermoexcel-E surfaces due largely to the increase in surface area and sufficient fin spaces for the easy removal of bubbles. CHFs of the low fin surface show even 5 times higher CHFs as compared to the plain surface. On the other hand, both Turbo-B and Thermoexcel-E surfaces do not show satisfactory results because their pore sizes are too small and water bubbles easily cover them. At low heat fluxes of less than $50kW/m^2$, HTCs increase as the flow velocity increases for all surfaces. In conclusion, a low fin geometry is good for application to steam generators in nuclear power plants.

• Applied Chemistry for Engineering
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• v.17 no.5
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• pp.476-482
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• 2006

An experimental study has been performed to investigate the characteristics of air-side heat transfer and friction of a fined tube heat exchanger under heating conditions. Air enthalpy calorimeter was used to obtain the performance evaluation and analysis of the fined tube heat exchanger. Eight finned tube heat exchangers with slit fin, louver fin, and plain fin were used. The air-side heat transfer coefficient was calculated by the log-mean-temperature-difference. Air-side heat transfer and friction were presented in terms of j factor and friction factor on Reynolds number. From the experimental result, it was found that the variations of air-side heat transfer and friction of fined tube heat exchanger with the change of the fin configuration, row number, fin pitch, and tube circuit were obtained. j factor and friction factor decreased with Reynolds number increased. The tube circuit affected the air-side heat transfer and friction. In the case of slit and louver fin, j factor of 1st row was higher than that of 2nd row. But, with increasing Re, j factor was reversed. The characteristics of j factor and friction factor of 2nd row heat exchanger were different according to the kind of fins.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1137-1143
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• 2009

Experiments were conducted to evaluate pool boiling heat transfer performance between plain and micro finned surfaces with FC-72, which is chemically and electrically stable. Three kinds of micro fins with the dimension of $100{\mu}m\;{\times}\;10{\mu}m$, $150{\mu}m\;{\times}\;10{\mu}m$ and $200{\mu}m\;{\times}\;10{\mu}m$ (width $\times$ height) were fabricated on the surface of a silicon chip. The experiments were carried out on the liquid subcooling of 5, 10 and 15 K under the atmospheric condition. The micro finned surface with a larger fin width of $200{\mu}m$ provided a better pool boiling heat transfer performance. Also, the micro finned surfaces showed a sharp increase in heat flux with increasing wall superheat and a larger heat transfer enhancement compared to a plain surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.292-301
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• 2000

This study experimentally investigates an air-side performance of oval tube heat exchanger against round tube heat exchanger using scaled-up model experiment for home air conditioners. A plain fin and round tube heat exchanger with 21 FPI(fins per inch) was used as a reference heat exchanger, and these were applied equally to 4 oval tube heat exchangers. Oval tube samples were designed with the same perimeter as 7.5mm diameter round tube, and their aspect ratios were 1:2, 1:3, respectively. In this study, the heat transfer and pressure drop characteristics of oval tube heat exchangers against round tube heat exchanger were also compared to one another, and an optimal samples for home air conditioners was recommended. And, general performance characteristics for an optimum oval tube samples chosen in this work was compared with round tube heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.7
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• pp.315-321
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• 2014

In this study, external condensation heat transfer coefficients (HTCs) of two non-azeotropic refrigerant mixtures of HFC32/HFC152a at various compositions were measured on both 26 fpi low-fin and Turbo-C enhanced tubes, of 19.0 mm outside diameter. All data were taken at the vapor temperature of $39^{\circ}C$, with a wall subcooling of 3~8 K. Test results showed that the HTCs of the tested mixtures on the enhanced tubes were much lower than the ideal values calculated by mass fraction weighting of the pure component HTCs. Also, the reduction of HTCs due to the diffusion vapor film was much larger than that of a plain tube. Unlike HTCs of pure fluids, HTCs of the mixtures measured on enhanced tubes increased, as the wall subcooling increased, which was due to the sudden break-up of the vapor diffusion film with an increase in wall subcooling. Finally, the heat transfer enhancement ratios for mixtures were found to be much lower, than those of pure fluids.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.9
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• pp.685-692
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• 2012

In this work, nucleate pool boiling heat transfer coefficients(HTCs) of 5 refrigerants of different vapor pressure are measured on horizontal Thermoexcel-E square surface of 9.53 mm length. Tested refrigerants are R32, R22, R134a, R152a and R245fa. HTCs are taken from 10 $kW/m^2$ to critical heat fluxes for all refrigerant at $7^{\circ}C$. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and in the liquid pool. Test results show that critical heat fluxes(CHFs) of Thermoexcel-E enhanced surface are greatly improved as compared to that of a plain surface in all tested refrigerants. CHFs of all refrigerants on the Thermoexcel-E surface are increased up to 100% as compared to that of the plain surface. The improvement of Thermoexcel-E surface in CHF, however, is lower than that of the low fin surface. HTCs on Thermoexcel-E surface increase with heat flux. But after certain heat flux, HTCs began to decrease due to the difficulty in bubble removal caused by the inherent complex nature of this surface. Therefore, at heat fluxes close to the critical one, sudden decrease in HTCs needs to be considered in thermal design with Thermoexcel-E surface.