(296i) Multiscale Analysis of a Two-Phase Flow in a Heat Exchanger Using the Wavelet Technique

Biphasic heat exchangers are widely used in petroleum refining. In diesel hydroprocessing units where there is a large amount of hydrogen in contact with the diesel, there may be slugs flow inside it, causing undesirable pressure oscillations. In this study, the volume of fluid (VOF) approach was applied to predict the gas-liquid flow in an experimental unit, which is a scaled-down model of the heat exchanger used in diesel hydrotreatment process of the oil refinery industry. To modelling the turbulence nature of this operation, the mathematical modeling considers the unsteady Reynolds averaged Navier-Stokes equations (URANS) with Transition Shear Stress Turbulence model (TSST) as turbulence closure equation, and the gas phase is considered compressible ideal gas, for spatial discretization of volume fraction was used Geo-Reconstruction Model. The typical operational conditions were simulated using a commercial CFD code by at least 100s in which the first 40s were discarded for the properties calculations. The time-series of data were decomposed from wavelet transform. Multi-resolution analysis (MRA) of pressure fluctuation were applied to reorder the frequency in three groups according to the macro, meso and micro-scale phenomena (multiscale analysis).The sum of energy of each scales was calculated, and the influence of the energy on the flow pattern was verified over of operating conditions and the geometry influence. In addition, the positioning of pressure transducers was numerically tested, with 31 points of monitoring pressure to available the better position to install them. The position which means more difference and characteristic of the flow pattern, was choised to verify in a experimental unit. These results are now being used to design experiment based on CFD to carry out physical experiments to be used in future studies of verification and validation in CFD (V&VinCFD). Results indicate that the wavelet technique is a useful to evaluate multiphase flow patterns of different scales/frequency in heat exchangers.