COMPARING THE MOJET® How does the MoJet® compare with conventional jet fans?

Conventional jet fans are the standard means of providing longitudinal ventilation in tunnels.  However, they suffer from the following significant disadvantage compared to the MoJet®:

Thrust is lost due to friction between the jet and the tunnel surfaces

The discharged jet tends to stick to tunnel soffit and walls, due to the Coanda effect and swirl. Typically, 25% to 30% of thrust is thereby lost. In addition, the blades of conventional jet fan tend to unload due to ingestion of an upstream jet, which leads to a further reduction in in-tunnel thrust.

Certain correlations of the jet fan installation factor, such as those based on Kempf’s model-scale measurements from 1965 and the South Bank University tests from 1997, significantly over-estimate the in-tunnel thrust. This is because they do not account for differences in Reynolds number between model-scale and real tunnel dimensions, and nor do they account for the unloading effect.

TechnologyDeflect jetCompactNo jet throw extensionNo noise regenerationNo deflector metal fatigue riskNo additional power
No loss of bench thrustNo risk of bearing damage



Slanted silencers

None of these drawbacks are present with the MoJet®, which is the most modern jet fan technology available for enhancing in-tunnel thrust.

Read our technical paper on the performance of deflection vanes

Discover the benefits of the MoJet®

The reversible MoJet® tunnel ventilation system can increase the in-tunnel aerodynamic thrust by up to 100%