Impact of Coil Curvature, Pitch, and Orientation on Vapor Hydrodynamics over Helically Coiled Tubes during Saturated Pool Boiling near Critical Pressure

Temporal tracking of the interface with mass transfer phenomena is very complex during the boiling process. In this paper, the physics of two-phase boiling phenomena of water around the heated surface of a helically coiled tube at a critical pressure (P-sat = 21.9 MPa) has been predicted numerically. Such high-pressure systems are usually observed in boiling water reactors (BWRs). The boiling heat transfer characteristics were studied on eight different helically coiled heated surfaces with varying curvature ratios (delta) from 0 to 7.16 and coiled tube orientations (vertical and horizontal) at a degree of superheat (Delta T) of 10 K. The vapor bubble dynamics, i.e., bubble merging, sliding over the surface, and departure, have been studied over the heated helical surface. Although having vapor blanketing over the surface, the coil having zero curvature (straight tube) possesses a higher velocity and generation of vapor phase among all considered cases. The orthogonality of the surface normal and gravitation force makes the vapor move faster. Thus, the H1 (horizontally oriented tube) configuration possesses 3.79 times higher average velocity than the H4 coiled tube configuration. Vertical configuration, i.e., a helically coiled tube (V4) with a curvature ratio (delta = 0) produced 4.4 times higher vapor than that produced by a horizontally oriented helically coiled (H4) configuration. Thus, curvature and orientation play a critical role in fluid dynamics, heat transfer, and vapor volume production.

Automated summary

This paper numerically predicts the two-phase boiling phenomenon of water around the heated surface of a helically coiled tube at a critical pressure (P-sat = 21.9 MPa). Results show that curvature and orientation play a critical role in fluid dynamics, heat transfer, and vapor volume production.