Analysis of effect caused by fitting in the measurements of flow in air conditioning system

This work presents the results of a 3D numerical analysis, particularly the effect at the volumetric flow measurements due to a perturbation generated downstream by fitting used in ducts of the air conditioning systems. The numerical simulations were developed using commercial software based on Computational Fluid Dynamics (CFD), where the Reynolds Averaged Navier–Stokes equations (RANS), through an approach of finite volume method (FVM) using several turbulence models, are solved. The turbulence models used are the one-equation Spalart–Allmaras, the two-equation eddy viscosity (EVMs) and Reynolds stress (RSM). The numerical results were compared with velocity profiles obtained from technical literature, where the Spalart–Allmaras turbulence model offers the best numerical predictions, according to measurements taken near and far from the perturbations in the case of 90° elbow with single thickness vanes. Also, the behavior of the mass flow rate measurements taken downstream of the fitting is presented; identifying the zones where the largest deviations are located with respect to the real mass flow rate supplied to the system, which are about 1.61% in the case of 90° elbow CR3-9, 2.6% and 4.6% in the cases of rectangular transition piece ER4-1 with θ = 60° and θ = 180°, respectively. As well as the effect on the flow measurement due of the number of points used in the measurement plane. This study allows knowing the flow behavior downstream of fitting.