Two-phase flow frictional pressure drop prediction in helical coiled tubes

Abstract

Based on the construction of different experimental databases, the frictional pressure drop in helical tubes for single-phase and water-steam two-phase flow was analyzed empirically. The aim of the present study is to provide the scientific community with a reliable and simple to use predictive tool for estimating frictional pressure drop in helical tubes covering operating conditions of interest for the design and operation of coiled tube once-through steam generators, as those used in small modular advanced nuclear reactors. The single-phase database contains around 2000 data points from 14 different sources, including data measured with air and water as working fluids, covering Reynolds numbers ranging from 40 to 145,000 and curvatures between 0.0027 and 0.3. The prediction capability of some existing correlations for simple phase flow was analyzed, concluding that Ito correlations for laminar and turbulent regime (1959) are the best ones fitting the experimental data. The average difference between experimental data and Ito correlations was 3.75% for laminar regime and 2.11% for turbulent regime. The two-phase flow database was built with data available from open literature works. Due to the fact no existing correlation was found to successfully predict the available data, a new prediction tool based on the homogeneous equilibrium model was developed for water-steam flows at conditions of interest. The proposed tool, so-called FEMA correlation, converges to the Ito correlations for single phase flow, i.e. for thermodynamic qualities equal to 0 and 1. In addition, the correlation successfully fits the experimental data with an average error of 7.4% which is smaller than any other existing correlation. In addition, the new correlation is recommended for water-steam flow in vertical helical tubes with liquid only Reynolds numbers ranging from 20000 and 124000, pressures between 1 and 8 MPa, curvatures between 0.01 and 0.08, and thermodynamic qualities ranging from 0 to 1.