Practical review & application of CFD to condensing multiphase flows in geometries relevant to Plate Heat Exchangers
L.B. van den Hoek (TU Delft - Mechanical Engineering)
MAthieu Pourquié – Mentor
Joost Kirkenier – Mentor
J Westerweel – Graduation committee member
C.A. Infante Ferreira – Graduation committee member
Bas W. van Oudheusden – Graduation committee member
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Abstract
In the quest for renewable energy for tropical islands, Ocean Thermal Energy Conversion (OTEC) has revealed itself as one of the most promising technologies. OTEC stands or falls with the performance of the condenser. Plate Heat Exchangers (PHEs) have proven their selves as effective heat transfer
equipment for low enthalpy cycles such as OTEC. Nowadays, the design of PHEs mostly relies on models based on experimental data. This is deemed time-consuming and non-generic. Enormous successes in the application of Computational Fluid Dynamics to single-phase flows have raised the
interest to use CFD as a predictive and generic tool for the design of PHEs. Moreover, CFD yields a picture of the complete flow field, enabling the designer to better understand the fundamental flow structures that are relevant for the heat transfer and pressure drop performance of the PHE.
First, a comprehensive review of literature on condensation models is presented. Thereafter, the practicality of the phase change models in terms of real computation time needed is investigated. It is concluded that the stability issues associated with the vapor-liquid interface poses the biggest problem.
That is, for the simple Nusselt condensation problem, an extremely long computation time is needed for reasonable accuracy. Finally, the ability of the phase change models to cope with wave evolution,
flow circulation and flow separation is investigated. The multiphase model is found to properly predict the flow field. However, the heat and mass transfer predicted by the condensation models is estimated poorly.
In the end, until the stability issues of the current phase change models are solved, or a significant improvement in computational performance is made, the application of CFD to the design of condensation PHEs is questionable. Yet, using CFD only to find trends in heat transfer and pressure drop in PHEs might prove to be fruitful.