Thermal stratification in air over a hot flat plate: an experimental approach to assess the consequent flow field

This article presents an experimental analysis of the dynamic effects of thermal stratification in air over a heated horizontal and flat surface. A suitable tracer was utilised to put in evidence how the temperature gradient can affect the natural air flow directed upwards. The tracer, made of aluminium, has the shape of a coil and is free to rotate around a vertical rod. Its angular velocity is the target variable as it is dependent on the geometrical and thermal analysis parameters. The idea of using a coil–shaped tracer to investigate the air flow field over a hot horizontal plate was also the object of previous researches quoted within this paper: thanks to those results it was understood how to modify the experimental setup to study more completely the phenomenon. By means of the modified setup the study allowed to observe how, diminishing the weight or increasing the number of turns, maintaining constant one of the two parameters, tracer increased its angular velocity. That situation, clearly evidenced in this paper for a particular range of value, depend to a lessening of the friction between the coil and the tip of the rod in the first case and to an increase of the influence of the thermal gradient on coils tracer in the second.