Interaction d'un écoulement de thermosiphon avec un panache thermique à symétrie axiale: étude expérimentale

Abstract

The present work reports an experimental study of a thermosiphon effect on an axisymmetric thermal plume. An experimental apparatus composed of a circular disc heated at constant temperature was set up. The disc is placed at the entrance to an open-ended vertical cylinder of larger diameter. Thermal radiation emitted by the hot disc heats the cylinder wall. The heating of fluid to the cylinder-inlet is the cause of the thermosiphon effect around the thermal plume. First, we studied the flow generated by the thermal plume. The analysis of the average fields of velocity and temperature shows that the structure of a thermal plume generated by a hot obstacle is affected by the characteristics of the main flow around this obstacle. Furthermore, these results allowed us to rediscover the two classical zones which constitute a thermal plume. Secondly, we studied the thermosiphon effect on the thermal plume development. The average fields evolution of velocity and temperature as well as the flow visualization show the existence of three different zones. The first zone of the plume air feeding is characterized by the dynamic and thermal profiles in three extrema structures. These extrema disappear in the second zone where the profiles present only one maximum. In the last zone, the profiles are flattened and self-similar. Thus, the turbulence is fully developed. However, one observes an improvement in the amount of energy absorbed by the fluid and an increase in the flow rate inside the cylinder. A flow visualization with laser plan allowed us to show that the position of the vertical cylinder around the hot disc affects the flow structure plume and causes the appearance of a new zone at the entrance to the system. However, the analysis of the fluctuating fields related to two studied cases shows that the thermosiphon effect has an important influence on the turbulent intensity structure of the flow evolution.