Draw-off nozzle hydraulics

I imagine that many readers might skip this chapter. After all, a nozzle is simply a hole in a vessel, flanged up to a pipe (see Fig. 14.1). Why a whole chapter Well, it is not that simple. Lots of process problems occur due to improperly designed draw-off nozzles. 

The pressure drop of a fluid flowing through a nozzle is equal to 

V = velocity of the fluid, as it flows through the nozzle, in feet per second 

This equation assumes that before the fluid enters the nozzle, its velocity is small, compared to its velocity in the nozzle. The increase in the velocity, or the kinetic energy, of the fluid in the nozzle comes from the pressure of the fluid. This is Bernoulli s equation in action. The energy to accelerate the fluid in the draw-off nozzle comes from the potential energy of the fluid. This is Newton s second law of motion. 

The coefficient used in the equation above (0.34) assumes the process fluid has a low viscosity. For most process nozzles, this is a 

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Bottom Draw-off. At horizontal reboilers, whether the drawoff nozzle is elevated or located in the bottom of the tower, the hydraulic conditions are the same. For available energy, the AP equation and Figure 7-74 can be used. 

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