Experimental Investigation on Flow Boiling and Dryout‐Induced Heat Transfer Deterioration in Helically Coiled Tubes

ABSTRACT Helically coiled tubes (HCTs) have found extensive applications in diverse engineering fields. This study experimentally explored the impact of the HCT orientation on the flow boiling heat transfer features of water at subcritical pressure. The circumferential distribution and calculation method of the dryout characteristics and critical quality were investigated. The operating conditions were set with a pressure range of 8–14 MPa, a mass velocity range of 375–1000 kg·m −2 ·s −1 , and a heat flux range of 50–200 kW·m −2 . The results revealed that both horizontal and vertical HCTs exhibit similar circumferential and axial heat transfer coefficient distributions. However, the vertical HCT consistently achieves significantly higher average heat transfer coefficients in the boiling two‐phase region, where the average ratio ranges from 1.07 to 1.21. At high vapor quality, the liquid film on the upper side of the vertical HCT was first torn, leading to dryout‐induced heat transfer deterioration, and thus, the critical quality here was at its minimum. Increasing pressure, mass velocity, or reducing heat flux could enhance the critical quality. A new correlation was proposed based on extensive data collection with ±8% error. The investigation imparts crucial perspectives and technical assistance to ensure the secure operation of HCT heat exchangers.