給湯用コルゲート管内単相流の流動様相

抄録

In this study, the flow pattern of a single–phase flow in a tube to simulate that inside corrugated tubes was investigated. The objective was to elucidate the flow pattern in corrugated tubes via observation. The flow pattern is closely related to the characteristics obtained in single–phase heat transfer and pressure drop experiments. The experiment was carried out in a Reynolds number range of 500 to 3500. For visualization, we used an acrylic tube with an inner diameter of 11.0 mm, in which wires with diameters of 0.5 mm and 0.9 mm were coiled and inserted at varying pitches in close contact with the inner tube wall.
The generally accepted transition conditions inside a smooth tube and the results observed in this study are consistent. From these results, we confirmed the soundness of the experimental equipment. The observation results of the flow pattern inside the simulated corrugated tubes were mostly in agreement with the authors’ previous experimental results. The previously proposed prediction for the transition Reynolds number had a maximum error of +20% when the wire diameter was 0.9 mm. When the wire diameter was 0.5 mm, the prediction accuracy decreased, and a maximum error of –37% was observed. The conventional prediction was not able to adequately organize the transition conditions according to corrugated groove geometries. Therefore, a conditional expression for the transition from laminar to turbulent flow in a single–phase flow for a corrugated tube was proposed via the expansion of the applicable range of the inner diameter and groove geometries.