Question

Many entrainment devices have a constriction, called a Venturi, such as shown in Figure 12.24. How does this bolster entrainment?

Short answer

The venturi forces the fluid to pass through its constricted area creating lower pressure inside and higher pressure outside.

Step-by-step solution

Entrainment

The fluid with higher velocity forces other fluid into the stream when pressure is higher outside.

Design of a venturi

The venturi is designed in such a way that it creates a low pressure inside the fluid by forcing it to pass through the constricted area. In the middle of the constricted part of the venturi, there is an open tube through which entrained fluid can be sucked inside.

Fig.: 12.24

How does aventuri boost entrainment?

Bernoulli's principle says when incompressible fluid passes through a constricted area, its kinetic energy increases which in turn reduces the fluid pressure to maintain a constant flow rate. Venturi has a smaller cross-sectional area which helps to reduce the pressure of the fluid. This creates lower pressure inside and higher pressure outside. The fluid which is inside the open tube can easily be pulled inside because of pressure differences. Thus, venturi bolster entrainment by creating low pressure inside.