Design for Uniform Airflow Distribution in a New Waste Heat Dryer by CFD Modeling

Waste heat in flue gas of an internal combustion (IC) engine could be recovered to generate electricity or provide heat in some processes. In this study, a new tray dryer was designed to recover the waste heat. However, a common drawback of a tray dryer is poor airflow distribution in the drying chamber, which results in non-uniform moisture contents in final products. Therefore, this waste heat dryer was designed for uniform airflow distribution by the Computational Fluid Dynamics (CFD) modeling. A finned tube heat exchanger was chosen to recover waste heat from IC engine exhaust into hot air. Several designs of drying chambers and waste heat exchangers were assessed in order to achieve the design with good airflow distribution. The CFD simulation results showed that the installation of the outlet plenum chamber and the exit funnel with the proper dimensions at the tray outlet could provide the uniform airflow distribution in the drying chamber. In the best design of the drying chamber, the standard deviation of average velocities among all trays was 0.0047 m/s. Likewise, the CFD modeling was also applied in the design of the finned-tube exchanger section. The uniform airflow distribution at the exchanger outlet could be achieved by installing some baffles, an exit plenum chamber, and a wire mesh air distributor. In the best design of the exchanger, the average velocity at the exchanger outlet was 0.7002 m/s, which was in accordance with the specified inlet velocity in the drying chamber simulation.