Flow patterns analysis using experimental PIV technique inside scraped surface heat exchanger in continuous flow condition

摘要

This study is focused on experimental analysis of the flow patterns inside scraped surface heat exchanger (SSHE) under isothermal and continuous flow conditions. Experimental flow pattern analyses are the basis for further experimental explorations of mixing and heat exchange mechanism. The 2D particle image velocimetry (PIV) is used to characterize the flow structure. Synchronization between the laser sheet and blades rotation was achieved in order to allow a statistical analysis of the obtained velocity vectors. Axial, radial and tangential velocity components have been examined. Newtonian and non-Newtonian shear thinning fluids are examined. The statistical results based on the calculation of the relative standard deviation show that the error made in the experiments is less than 2%. The analysis of the axial velocity inside SSHE shows the presence of very large axial heterogeneities. At the entrance and exit of shearing region, axial velocity can reach 10 times the velocity corresponding to the imposed inlet mass flow. These results illustrate the importance and extent of flow reversal for two used fluids and for N > 4-5 rev/s. Tangential velocity dominates around blades, and the maximum is reached near the tip of the blade. In most cases, the obtained velocities resulting near the walls show a violating no-slip condition, which is due to the high velocity gradient near to the wall, and not captured by PIV. The radial velocity revealed a poor radial mixture near the rotor wall and the best mixing is localised on both sides of the blades. The results showed that under certain experimental flow conditions of rotating velocity and axial flow rate, a more effective flow can be obtained, which is characterized by low axial velocity dispersion. The obtained results in this work will be used to validate a 3D numerical model.