spray impact:
de-scaling

In de-scaling, the most effective droplets are those that have sufficient mass and velocity to directly dislodge the highest frequency scale size.

above: count mapping of droplets meeting momentum threshold

 Droplets with momentum below this threshold act on the scale indirectly, removing material by erosion. Since erosion is a relatively slow process characterized by a latent "incubation" period during which mass removal is minimal, de-scaling effectiveness is significantly degraded if the spray contains large populations of droplets below the momentum threshold.

The plot shown above is of the same de-scaling nozzle whose gross impact force was mapped on the previous page. This plot shows the impact frequency [in impacts per square centimeter-sec] of droplets which met or exceeded the momentum threshold necessary to effect direct removal of 0.1" scale particles. The contour scale is logarithmic [i.e. - red = 100,000 counts, blue = 10,0000, cyan = 1,000 etc.].

Although the gross impact mapping appears to suggest that this particular de-scaling nozzle would perform well across most of the spray width, the momentum threshold mapping shows a much more erratic and highly localized de-scaling effectiveness.