More effective ventilator designs
Dr. Fathi Tarada is the founder and MD of Mosen Ltd. and a leading expert in fire safety engineering, tunnel ventilation, and computational fluid dynamics, with design, review and operations experience worldwide.
Impulse ventilation can be a cost effective solution for tunnels if we are able to reduce inefficiencies due to frictional drag on solid surfaces. There have been done calculations that indicates that by using conventional jet fans, discharged flow adheres to soffit due to Coanda effect. By using deflection vanes the discharged flow adheres to floor due to the same effect. A full scale test of these effect has not jet been done, but Dr. Fathi Tarada underline that such tests must be conducted under the same circumstances, installed in tunnel with the right distance to the soffit and to the floor.
By using so called banana shaped ventilators you might avoid the Coanda effect, but the jet fans are often more space consuming, and is often not considered the optimal solution due to more need for space.
Well established and also innovative devices are available, and the MoJet fan is an example of this, says Dr. Fathi Tarada. With the new upgraded 39° Blade Pitch Angle, the MoJet manage to avoid the Coanda effect, with the same space consume as a conventional fan. By reducing the coanda effect it is possible to reduce number of fans and/or reduce the effect on each fan.
As indicated, it is also important to do full scale tests of the different types of jet fans in proper conditions. This to confirm and improve calculation methods and in the end to reduce costs and improve safety in tunnels.
Tunntech News would like to follow this topic, and of course receive new information and maybe soon new updated reports from full scale tests.