Single-fluid pressurized nozzles

For single-fluid pressure nozzles, a rule of thumb is employed ... 

For proper use of the equations, the chamber shape must conform to the spray pattern. With cocurrent gas-spray flow, the angle of spread of single-fluid pressure nozzles and two-fluid pneumatic nozzles is such that wall impingement wiU occur at a distance approximately four chamber diameters below the nozzle therefore, chambers employing these atomizers should have vertical height-to-diameter ratios of at least 4 and, more usually, 5. The discharge cone below the vertical portion should have a slope of at least 60°, to minimize settling accumulations, and is used entirely to accelerate gas and solids for entty into the exit duct. 

Hydraulic or Pressure (Single Fluid) Spray Nozzles... 

The atomizing nozzle may be one of four basic types 1) dual-fluid 2) single-fluid pressurized 3) singlefluid disk or rotary and 4) single-fluid ultrasonic. 

Two-fluid nozzles share with pressure nozzles the lack of high feed capacity combined with fine atomization in one single unit. Many spray dryer applications with two-fluid nozzle atomization have a very high number of individual nozzles. The main advantage of two-fluid nozzles is the capability to achieve very fine atomization. 

Three general types of atomizers are available. The most conunonly used are the rotary wheel atomizers and the pressure nozzle single-fluid atomizers [8]. Pneumatic two-fluid nozzles are used only rarely in very special applications. 

A pressure nozzle, sometimes called a single-fluid nozzle, creates spray as a consequence of pressure to velocity energy conversion as the liquid passes through the nozzle under... 

Three general types of atomizers are available. The most commonly used are the rotary wheel atomizers and the pressure nozzle single-fluid atomizers [8]. Pneumatic two-fluid nozzles are used only rarely in very special applications. Existing spray drying systems provide various forms of the dry product—from fine powders to granules. The typical ranges of the disintegrated droplets and particle sizes of various products in a spray dryer are listed in Table 10.3. 

The phenomenon of critical flow is well known for the case of single-phase compressible flow through nozzles or orifices. When the differential pressure over the restriction is increased beyond a certain critical value, the mass flow rate ceases to increase. At that point it has reached its maximum possible value, called the critical flow rate, and the flow is characterized by the attainment of the critical state of the fluid at the throat of the restriction. This state is readily calculable for an isen-tropic expansion from gas dynamics. Since a two-phase gas-liquid mixture is a compressible fluid, a similar phenomenon may be expected to occur for such flows. In fact, two-phase critical flows have been observed, but they are more complicated than single-phase flows because of the liquid flashing as the pressure decreases along the flow path. The phase change may cause the flow pattern transition, and departure from phase equilibrium can be anticipated when the expansion is rapid. Interest in critical two-phase flow arises from the importance of predicting dis-... 

An alternative to spray drying of solids that are suspended in a liquid using high pressure single and two phase or rotary nozzles (see Section 7.4.3) is the break-up of a low pressure stream of slurry in gas dynamic atomization. In this process, the fluid is pumped to an orifice where it is released into a pulsating flow of hot gas (Fig. 7.81) and atomized. 

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