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2.2.  BERNOULLI'S THEOREM

At any point in a tube through which a liquid is flowing, the sum of pressure energy, potential energy, and the energy of motion is constant. This theory was discovered by Daniel Bernoulli, a Swiss mathematician and physician. How the theory works is illustrated in figure 2.1. An American engineer, Clemens Herschel, invented the venturi tube and named it in honor of Giovanni Venturi. If the same amount of air that enters the airflow inlet is to leave the airflow outlet, then the velocity of the air must increase while passing the venturi throat. As the velocity increases, the air has less time to push against the sides of the tube, thereby exerting less pressure. Figure 2.1 shows the decrease in pressure gages. Because there is no change in the velocity of the air about the open end of the tube, there is no change in pressure. The differential pressure on the ends of the tubes attached to the venturi throat causes the fluid to move toward the end of the tube that has the least pressure.

Figure 2.1. Venturi Tube.

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