Numerical design of efficient slit fin surfaces with strips in different directions

In this article, 3D numerical simulations are performed to study the heat transfer performances of different fin surfaces for a one-row fin-and-tube heat exchanger. Five fin surfaces are evaluated: the first is the plain fin surface for comparison purposes, and the other four are slit fin surfaces, named Slit 1, Slit 2, Slit 3, and Slit 4. The global geometry parameters of the five fin surfaces are all the same. The Slit 1 and Slit 2 fin surfaces have parallel strips normal to the incoming airflow, the difference is Slit 1 has five strips, and Slit 2 has six strips. The Slit 3 and Slit 4 fin surfaces also have six strips, whereas the slits of Slit 3 are along with the radial direction of the tubes, and the slits of Slit 4 are arranged in the quasi-radial direction of the tubes. The heights of the strips for the four slit fin surfaces are kept the same. The grid-independent check and the comparison with experimental data are conducted in advance to make sure the numerical results are reliable. Under identical pumping power, the heat transfer improvement is from 5.3% to 37.3% for the Slit 1 fin surface, 5.3%–41.3% for the Slit 2 fin surface, 6.5%–42.3% for the Slit 3 fin surface, and 8.9%–47.3% for the Slit 4 fin surface compared to the plain fin surface within the studied Reynolds number range (226–1805). To reveal the heat transfer enhancement mechanisms, the effects of slits on the heat transfer coefficient and the fin efficiency are analyzed in detail.