Thermal plumes in ventilated rooms: Measurements in stratified surroundings and analysis by use of an extrapolation method

The design of a displacement ventilation system involves determination of the flow rate in the thermal plumes. The flow rate in the plumes and the vertical temperature gradient influence each other, and they are influenced by many factors. This paper shows some descriptions of these effects. Free turbulent plumes from different heated bodies are investigated. The measurements have taken place in a full-scale test room where the vertical temperature gradient have been changed. The velocity and the temperature distribution in the plume are measured. Large scale plume axis wandering is taken into account and the temperature excess and the velocity distribution are calculated by use of an extrapolation method. In the case with a concentrated heat source (dia 50mm, 343W) and nearly uniform surroundings the model of a plume above a point heat source is verified. It represents a borderline case with the smallest entrainment factor and the smallest angle of spread.
Due to the measuring method and data processing the velocity and temperature excess profiles are observed more narrowly than those reported by previous authors. In the case with an extensive heat source (dia 400mm, lOOW) the model of a plume above a point heat source cannot be used. This is caused either by the way of generating the plume including a long intermediate region or by the environmental conditions where vertical temperature gradients are present. The flow has a larger angle of spread and the entrainment factor is
greather than for a point heat source.
The exact knowledge of the vertical temperature gradient is essential to predict the flow propagation due to its influence on the entrainment, e.g. in an integral method of plume calculation • Since the flow from different heated bodies is individual full-scale measurements seem to be the only possible approach to obtain the volume flow in: thermal plumes in ventilated rooms.