The plate fin heat exchanger is a compact heat exchanger applied in many industries because of its high thermal performance. To enhance the heat transfer of plate fin heat exchanger further, three new kinds of wavy plate fins, namely perforated wavy fin, staggered wavy fin and discontinuous wavy fin, are proposed and investigated by computational fluid dynamics (CFD) simulations. The effects of key design parameters, including that of waviness aspect ratios, perforation diameters, staggered ratios and breaking distance are investigated, respectively, with Reynolds number changes from 500 to 4500. It is found that due to the swirl flow and efficient mixing of the fluid, the proposed heat transfer enhancement techniques all have advantages over the traditional wavy fin. At the same time, serration is beneficial to reduce the friction factor, and the breaking technique can reduce heat transfer area. Through the performance evaluation criteria, the staggered wavy fin has an advantage over the small waviness aspect ratio; with increasing waviness aspect ratio, this predominance is gradually surpassed by the perforated wavy fin, and the advantage of the discontinuous fin is the smallest and almost invariable. A maximum performance evaluation criteria (PEC) as high as 1.24 can be obtained for the perforated wavy fin at the waviness aspect ratio γ = 0.45.

Air cleaner is one of the viable options for particle removal in the indoor environment. Therefore, it is vital to understand the performances of air cleaners under various working conditions. In this work, the models for airflow pattern and particle transport in a room with an air cleaner were developed by combining the Lagrangian discrete trajectory model with the Eulerian fluid method. The effects of the operating conditions of the air cleaner on the particle transport characteristics were numerically investigated, including the volumetric flow rate and positioning of the air cleaner as well as the ejection orientation of the outlet air. The results show that the volumetric flow rate of the air cleaner is a key parameter affecting the particle concentration in the indoor environment. At low volumetric flow rates, the location of the air cleaner plays a significant role in the air cleaner performance. There is little difference in the removal processes of airborne particles between the horizontal and upward ejections of the air cleaner, but they are both superior to that with the downward ejection.