Algal biomass harvesting using low-grade waste heat: the effect of waste heat temperature and air speed on dewatering algal suspension

This study investigated the feasibility of evaporating water from heated algal biomass in an evaporation tank. Computational fluid dynamic (CFD) analysis was performed with Ansys Fluent, and the results were verified with experiments. The results of CFD analysis showed a positive effect on the evaporation rate. As the speed of the air stream increased from 0 to 3 m/s, the evaporation rate increased from 9 to 200 mL/h. It was also observed that the temperature of the mixture of air and water vapor decreases more rapidly, but the temperature of the liquid decreases more slowly, as the speed of the air stream increases. The liquid flow is more disturbed as the speed of the air stream increases while the air streamlines are more parallel at higher speeds. Finally, as the speed of the air stream increased from 0 to 3 m/s, the liquid pressure at the bottom of the tank decreased from 270 to 140 pa. The experimental results were compared with the calculation based on the stagnant film theory and showed excellent agreement. The CFD results underestimated the evaporation rate by 10% compared with the experimental results.