Observation of natural convection flow over a heated flat plate at inclined and horizontal positions

The characteristics of thermals and instability of natural convection flow over a flat plate at different orientations were investigated. With water as the working fluid, an electrochemical method using thymol blue as a pH indicator was used to visualize the flow patterns. When the plate was turned from vertical towards the horizontal, instability of the flow was observed first in the form of two dimensional waves and later three dimensional vortices. This change of instability occurred in a transition zone, ranging from 15 to 23 deg when the temperature difference between the plate and the surrounding water was 6.67 C. With the plate horizontal, the flow consisted of thermals which were periodic, fixed at regular intervals along the span of the plate and mushroom-like in appearance. Interactions between thermals were detected.