hydraulic diameter

Longitudinal ventilation is a common technique for smoke management during a fire accident within tunnels. In this paper, fire and smoke movement behaviour in longitudinally ventilated tunnels is investigated focusing on critical ventilation velocity. Firstly, critical velocity (VC) is evaluated for different heat release rates and results are compared and verified with model scale experimental data. Secondly, two fire scenarios inside tunnels with different cross sections are arranged and the reliability of some existing correlations for VC is explored.

Investigations were carried out into the airflow in a non-unidirectional airflow cleanroom and its affect on the local airborne particle cleanliness. The main influence was the method of air supply. A supply inlet with no diffuser gave a pronounced downward jet flow and low levels of contamination below it, but poorer than average conditions in much of the rest of the room. A 4-way diffuser gave much better air mixing and a more even airborne particle concentration throughout the cleanroom.