Dimples in corrugated channels to improve efficiency in plate heat exchangers

Sammanfattning: The development of new heat exchanger patterns is ever changing. Companies are constantly pushing innovation to satisfy costumer needs in terms of thermal efficiency, reliability and serviceability. In this thesis, the implementation of dimples in the corrugated pattern of a plate heat exchanger is investigated to increase the thermal efficiency. The thesis comprises three studies, moving from research of a dimpled surface to an implementation of dimples on a real-life heat exchanger model used by Alfa Laval. Computational fluid dynamics was applied to model heat transfer, pressure drop and thermal efficiency through three Reynolds Averaged Navier Stokes (RANS) models and one Large Eddy Simulation (LES). The RANS-models were shown to provide insufficient resolution which heavily affects mixing, vortex formation and flow distribution in the heat exchanger channel. The RANS-model suggested that the thermal efficiency decreases when dimples are added, but failed to accurately capture key phenomena such as vortex formation and mixing. In the more advanced LES model, dimples were shown to increase the thermal efficiency by 18 % compared to a flat channel. This study not only provides insight into the flow behavior in dimpled heat exchanger channels, but also shows the importance of using the correct turbulence model for a given problem. The flow dynamics in a dimpled plate heat exchanger is complex, and a RANS-model is not sufficient for an accurate description of the velocity field. In this regard, LES performs better and the result of the LES simulation is therefore more trustworthy than results from the RANS. As no experimental data exists, it is difficult to compare models to reality, laboratory trials are nessessary