Nielsen P V, Hoff L, et al
Bibliographic info:
9th AIVC Conference "Effective ventilation" Gent, Belgium, 12-15 September 1988

The paper describes measuring results of the air movement from three different types of diffusers for displacement ventilation. Two of the diffusers are lowlevel wall mounted diffusers, one with a low and one with a high initial entrainment. The third diffuser is of the floor mounted type. The air flow close to the diffusers and in the rest of the room is analysed. Velocity decay in the flow from the low-level diffusers is given as a function of the Archimeaes number, and the paper suggests a general equation for this part of the flow. The velocity level and velocity decay in the flow are dependent on the room geometry. The flow is not influenced by the Reynolds number for supply flow above a certain level. Measurements of the turbulence intensity show a level in the cold flow along the floor which is rather equivalent to the level in an isothermal wall jet. The floor mounted diffuser generates a circular jet with swirl along a vertical line in the room. The velocity decay in the flow from this jet is high compared to the decay in a conventional, free circular jet. The ventilation efficiency based on temperatures and vertical temperature profiles are given for the diffusers for different levels of air exchange rates and thermal loads. The ventilation efficiency varies between 1.5 and 2.3 for all diffusers and it is rather unaffected by the type of diffuser.