This article discusses the numerical prediction of performance of a wire mesh and a C-shaped vane type mist eliminator using principles of computational fluid dynamics (CFD). These type of mist eliminators or demisters are commonly used in thermal desalination processes like multi effect distillation, multi stage flash evaporation etc. In the Low Temperature Thermal Desalination (LTTD) plant, a demister is placed in the upper part of flash chamber. A proper selection of demister is essential as the vapour is required to be completely freed of entrained brine droplets before it enters the condenser. The study under consideration was aimed at determining the pressure drop across wire mesh and C-shaped vane type mist eliminators for inlet vapour velocity of 4-12 m/s. The wire mesh demister used for the study is of overall size 1 m × 1 m × 0.1 m and packing density of 144 kg/m³ with wire diameter 0.15 mm. The C-shaped vane type demister is 10 cm long and has a pitch of 20 mm. The numerical solutions were arrived at using commercial CFD code ANSYS FLUENT 14.0. It is found that the wire mesh demister shows higher pressure drop compared to C type. It is also observed from the simulation that for the given range of vapour velocities the C type vane demister efficiently filters out particles of higher size whereas it has very limited filtering capacity for particle sizes of smaller range. In contrast the wire mesh mist eliminator effectively captures particles of smaller sizes. The study helps in predicting the threshold droplet diameter below which only a wire mesh demister filters the droplet effectively.

Keywords: Computational fluid dynamics, Demister, Discrete phase modeling, Particle size distribution, Rosin-Ramler distribution, Desalination.