To do this comparison, I will use the same velocity as the Super Air Knife. To equate this to a blower system, the size of the blower will determine the maximum velocity. A reasonable air pressure for the Super Air Knife is 80 PSIG, and the exit velocity is near 540 ft/sec (164 m/s). The blower type air knives can use a blower with a variable frequency drive (VFD) to change the exit velocity. The higher the air pressure, the higher the velocity. The exit velocity of the Super Air Knives can be changed by regulating the air pressure. If we compare for example a standard 12″ wide air knife, we can calculate the hydraulic diameter, Dh, by using Equation 2: Hydraulic Diameter Calculations Since both the Super Air Knives and blower-type air knives have rectangular cross sections, the Dh can be calculated as follows: The hydraulic diameter is an equivalent tube diameter from a non-circular flow area. From Equation 1 above, the gap opening helps determine the hydraulic diameter, Dh. The gap opening is typically 0.5″ (13mm). A blower does not generate a high force, so the opening of the blower-type air knife has to be larger to overcome any back pressure the opening creates. It uses the force of the compressed air to “push” it through the small opening to create a strong velocity. The Super Air Knife has a gap opening of 0.002″ (0.05mm). The main difference between the two products is the dimension of the slot opening. The EXAIR Super Air Knife is powered by compressed air, and the blower-type air knife is powered by an air blower. Both products are designed to clean and blow off wide areas like conveyor belts. Let’s do a comparison of Reynolds numbers between the EXAIR Super Air Knife and a blower-type air knife. When it comes to effective blowing, cleaning and lower noise levels, laminar flow is optimal. The area between these two numbers is the transitional area where you start to get small eddy currents and velocities in a non-linear direction. If Re is greater than 4000, then it is considered turbulent (chaotic and disarrayed). If the Reynolds number, Re, is below 2300, then it is considered laminar (streamline and predictable). The value of Re will determine the state in which the fluid (liquid or gas) will move. U – Kinematic Viscosity (Feet^2/sec or Meter^2/sec) The formula to determine the Reynolds number is as follows: If the inertial forces are dominant over the viscous forces, the fluid will act in a violent and chaotic manner. This number is the ratio of the inertial forces to the viscous forces. What is laminar flow and turbulent flow? Osborne Reynolds popularized this phenomenon with a dimensionless number, Re.

Turbulent flow vs laminar flow