ABSTRAKT

The study presented in this article aims at mapping experimentally the flow patterns in the annulus between an internally heated inner cylinder and a surrounding outer cylinder with an aspect ratio of length/diameter ~1. Both cylinders are stationary. The annulus is open axially to the ambient at both ends, and natural convection ensues when the inner cylinder is heated. The experiments are performed at temperatures of 32.2 °C (90 °F) and 65.6 °C (150 °F), corresponding to Rayleigh numbers (Ra_L = gβL³(T_i - T∞ /να) of 6.62 × 10³ and 1.58 × 10⁴ , respectively. This range encompasses the region in which stable laminar flow transitions to unstable laminar flow of higher intensity. The full flow field tracking (FFFT) method utilized in this study uses a coherent laser light sheet to illuminate sequential sections of the annulus, while a low-luminosity camera equipped with a long-distance microscope is coupled to a video recorder for recording the flow patterns.