• Proceedings of the KSME Conference
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• 2001.06d
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• pp.440-446
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• 2001

The pressure drop and heat transfer of the spirally indented tubes were measured and analyzed. Eight sample tubes of indentation depth 0.4, 0.7mm and indentation pitch 10, 14, 20, 26mm were used in this experimental tests. And all the tubes have same outer diameter of 16mm, and same indentation start number of I. Air was used as the internal fluid from 10000 to 50000 for Reynolds Number. The friction factors and heat transfer coefficients have increased when indentation depths increase and indentation pitches decrease. Finally, the correlations were made between the effect of the tube geometry and characteristics of tubes for the pressure drop and heat transfer.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3006-3013
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• 2015

Flat tube heat exchangers can improve the thermal performance significantly compared with round tube heat exchangers. For proper design of flat tube heat exchangers, one should know the tubeside heat transfer coefficients. In this study, convective boiling heat transfer coefficients of R-410A were obtained in a flat extruded aluminum tube with $D_h=1.41mm$. The test range covered mass flux from 200 to $600kg/m^2s$, heat flux from 5 to $15kW/m^2$ and saturation temperature from $5^{\circ}C$ to $15^{\circ}C$. The heat transfer coefficient curve shows a decreasing trend after a certain quality(critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kaew-On et al. correlations reasonably predicted the present data.