Assessment with computational fluid dynamics of the effects of baffle clearances on the shell side flow in a shell and tube heat exchanger

This work presents an analysis of the shell side flow in a shell and tube heat exchanger using Computational Fluid Dynamics (CFD). The heat exchanger has been designed with the software HTRI Xchanger Suite®, while CFD simulations have been performed with the computational package ANSYS Fluent 15.0. Both k-ε and SST turbulence models have been assessed and the SST model has shown to provide more accurate results for temperature prediction. Instead of using an uniform temperature on the tubes' walls, a linear temperature profile (provided by HTRI Xchanger Suite®) was used as boundary condition for the CFD simulations. Two single-segmental-baffle geometries have been considered: with and without baffle clearances. Simulations results with the SST turbulence model regarding mean velocity, temperature and pressure profiles in the shell side have been analysed and compared with those provided by HTRI Xchanger Suite®. The outlet temperature predicted with CFD for the geometry with clearances differed from that provided by HTRI Xchanger Suite® only by 0.12 K. Although leakage streams represent a loss in thermal performance, the results clearly showed smaller recirculation zones and lower temperature peaks on the geometry with baffle clearances, when compared to the same heat exchanger without them. Such peaks could reach values way beyond the specified outlet temperature, in the case where the cold fluid is in the shell side. In the present case, for instance, the highest temperature inside the heat exchanger overpasses the outlet temperature about 8 K. Moreover, pressure drop was about 40% smaller when clearances were considered. Therefore, the results highlight an important role of baffle clearances, not yet discussed, which might be crucial for processes with maximum temperature limits, such as those with crude oil.