Experimental and numerical study of the laminar flow in helically coiled pipes

The problem of steady incompressible laminar flow in helically coiled pipes is addressed from an experimental and numerical point of view. At first a brief review of published works on the subject presents some of the main steps made toward the comprehension of the considered phenomenon. An experimental campaign performed in a facility simulating a helical tube of the Steam Generator of a Small-medium Modular Reactor (SMR) is presented and discussed. In particular, the measured values of the Darcy friction factor are analyzed and then compared with numerous empirical correlations for laminar flow in helical pipes available in literature, in order to compare their predictions of friction pressure losses. Moreover, different numerical codes are applied. In particular the hydraulic problem of laminar flow in helical ducts is solved making use of commercial software, namely FLUENT, OpenFOAM fluid dynamic codes and COMSOL Multiphysics. The numerical simulation allows to describe the effect of geometry on the flow through the onset of a secondary motion and the deformation of the axial velocity profile, which affects in turn the friction factor. The prediction capabilities of the adopted codes are assessed comparing numerical friction factor values with experimental data and literature correlations. Maximum deviations result of the order of few percent.