Experimental and numerical studies on two-phase flow instability behavior of a parallel helically coiled system

This paper reports on the experimental and numerical studies on two-phase flow instability behavior of a parallel helically coiled system. The experiment employs two vertically parallel helical tubes both with 9 mm hydraulic diameter (350 mm coil diameter, 4790 mm length, 10 degrees helix angle) connected by a lower and an upper header. The experiment is carried out in a matrix of conditions: pressures (2 MPa, 4 MPa, 6 MPa), mass fluxes (120-500 kg/m(2)s), inlet subcooling (from 20% up to 0) and inlet throttling (35-245 entrance resistance coefficient). Within the experiment range, parametric effects of thermal power, mass flow rate and inlet throttling are consistent with classical two-phase flow instability theory in straight tubes, however some characteristics on pressure and inlet subcooling are highlighted for helical tubes. The period of oscillations and stability maps of the experimental facility are also discussed in this paper. In the end, the experimental data are compared with the numerical simulation results of a modified RELAP5 code. (C) 2020 Elsevier Ltd. All rights reserved.