Research PaperLaminar natural convection heat transfer from a pair of attached horizontal cylinders set in a vertical array

- It is the first comprehensive study for the case of two vertically attached cylinders.
- For both cylinders, their heat transfer rates are degraded more than 87.5%.
- Three empirical equations for individual cylinder and for the whole array are provided.
- The heat transfer rate for S/D=1 is almost similar to the case of S/D=1.1.
- The average Nusselt number for S/D=1 is lowered by 16-53% than that at S/D=2.

The natural convection heat transfer from two attached cylinders set in a vertical array in air has been studied numerically for the Rayleigh number varying from 10 to 105. The comprehensive results consisted of streamlines and isothermal contours, temperature and velocity profiles, as well as local and average Nusselt number are presented with different Rayleigh numbers. They show that the heat transfer for both cylinders is degraded relative to that for a single cylinder owing to the interactions of their plumes. That trend mainly stems from the greater effects of the interaction on the upper part of the lower cylinder and the bottom surface of the upper cylinder. By contrast, it has little influence on the bottom surface of the lower cylinder and top region of the upper cylinder thereby leading to the similar results to that for a single cylinder there, but with a small noticeable difference. Also, their stronger interactions lead to the heat transfer rate of the upper cylinder reduced by 16-53% relative to that at S/D=2. What's more, the correlating equations for individual cylinder and the whole array have been proposed respectively, which provide an accurate prediction for the engineering calculations applying the present configuration.