Development of a new onset of nucleate boiling model for helical tubes

The flow inside a helical tube is influenced by the combined effects of centrifugal force and gravitational buoyancy, resulting in uneven circumferential heat transfer characteristics. This circumferential non-uniformity leads to a significant difference in the onset of nucleate boiling (ONB) compared to straight tubes. Currently, there are few studies on the ONB in helical tubes. This lack of high-precision prediction models significantly restricts the accuracy of heat transfer predictions for the helical tubes. The present study investigated the effects of circumferential non-uniform heat transfer characteristics on the ONB. It was found that the relative circumferential wall temperature in a helical tube during single-phase flow follows a trigonometric function distribution for the circumferential angle. A new empirical correlation was proposed to predict the circumferential wall temperature distribution in helical tubes in single-phase flow. Based on the new wall temperature distribution correlation, a new theoretical model for the ONB in helical tubes was proposed. The prediction error of the new ONB model is within ±10 %, which is superior to existing models.