Thin films, intriguing physics: understanding evaporating falling films

Abstrakt: We use multiphase direct numerical simulations of industrially relevant vertical falling-film evaporators to investigate how surface modifications influence both heat transfer enhancement and crystallisation fouling. The results show that surface structures can nearly double the heat transfer coefficient by inducing strong advective transport and film mixing through several synergetic flow mechanisms. We find that heat transfer performance depends strongly on surface geometry, linked to the recirculation zone length behind surface features. However, the same flow structures that enhance heat transfer also increase local supersaturation and scaling propensity by creating persistent near-wall concentration pockets. We show how surface topology governs the balance between improved thermal performance and fouling risk. We demonstrate how it is possible not only to maximise heat transfer but also to control crystallisation behaviour, reduce wall nucleation and promote bulk crystal formation.