PERFORMANCE OF HEAT-TRANSFER AND PRESSURE-DROP IN A SPIRALLY INDENTEDTUBE

In an effort to develop a heat transfer enhancement technique for low temperature applications such as utilization of LNG cold energy, an ex periment was carried out to evaluate the heat transfer and the pressur e drop performance for a spirally indented tube using ethylene-glycol and water solutions and pure water under horizontal single-phase condi tions. The test tube diameter was 14.86 mm and the tube length was 5.3 8 m. Heat transfer coefficients and friction factors for both inner an d outer surfaces of the test tube were calculated from measurements of temperatures, flowrates and pressure drops. Correlations of heat tran sfer coefficients in the spirally indented tube, which were applicable for laminar and turbulent regimes were proposed for inner and outer s urfaces. The correlations showed that heat transfer coefficients for t he spirally indented tube were much higher than those for smooth tubes , increased by more than 8 times depending upon the Reynolds number. T he correlations were compared with other correlations for various type s of surface roughness. The effect of the Prandtl number on the heat t ransfer characteristics was discussed. The critical Reynolds number fr om the laminar flow to the turbulent flow inside the spirally indented tube was found to be around Re = 1,000.