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An air spray is composed mainly from two tubes, one through supplied with compressed air having speed v and one supplied with a liquid from a reservoir (see the figure below). It works on the Bernoulli principle which is: the sum of the static pressure `P` , dynamic pressure `rho*v^2/2` and position pressure `rho*g*h` is the same in all points of a fluid tube.
At the base of the vertical tube the pressure is only `P0` (atmospheric pressure) . At the top of the vertical tube the pressure is `P1 +ro_("liquid")*g*h +ro_("air")*v^2/2` . As Bernoulli law states
`P0 = P1 +ro_("liquid")*g*h + ro_("air")*v^2/2`
which means `P1 <P0` .
Explained a bit different, because the air is blowing at the top of the vertical tube, the dynamic pressure increases, and in turn, the static pressure decreases. This causes the liquid to raise into the tube and be sprayed by the compressed air.
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