Nozzle pressure

Spray Drying and Agglomeration. Most instant coffee products are spray-dried. Stainless steel towers with a concurrent flow of hot ak and atomized extract droplets are utilized for this purpose. Atomization, through pressure nozzles, is controUed based on selection of the nozzles, properties of the extract, pressures used, bulk density, and capacity requkements. Low inlet ak temperatures (200—280°C) are preferred for best flavor quaHty. The spray towers must be provided with adequate dust coUection systems such as cyclones or bag filters. The dried particles are coUected from the conical bottom of the spray drier through a rotary valve and conveyed to bulk storage bins or packaging lines. Processors may screen the dry product to... 

Spray characteristics of pressure nozzles depend on the pressure and nozzle-orifice size. Pressure affects not only the spray characteristics but also the capacity. If it is desired to reduce the amount of liquid sprayed by lowering the pressure, then the spray may become coarser. To correct this, a smaller orifice would be inserted, which might then require a higher pressure to produce the desired capacity, and a spray that would be finer than desired might result. Multiple nozzles tend to overcome this inflexible charac teristic of pressure atomization, although several nozzles on a diyer complicate the chamber design and air-flow pattern and risk collision of particles, resulting in nonuniformity of spray and particle size. 

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 (Pressure) Nozzles Manufacturers data such as shown by Fig. 14-88 are available for most nozzles for the air-water system. In Fig. 14-88, note the much coarser solid-cone spray. The coarseness results from the less uniform discharge. 

Two-fluid (see Fig. 14-87h). Gas impinges coaxially and supplies energy for breakup. High velocities can he achieved at lower pressures because the gas is the high-velocity stream. Liquid-flow passages can he large, and hence plugging can he minimized. Because gas is also accelerated, efficiency is inherently lower than pressure nozzles. 

At some low flow, pressure nozzles do not develop their normal pattern but tend to approach solid streams. The required flow to achieve the normal pattern increases with viscosity. 

Direct inlet fogging, is a type of evaporative cooling method, where de-mineralized water is converted into a fog by means of high-pressure nozzles operating at 1000-3000 psi. (67-200 Bar) This fog then provides cooling... 

The cluster reactor is attached to the pulsed cluster source s condensation channel, as shown in Figure 6. (16) To it is attached a high-pressure nozzle from which a helium/hydrocarbon mixture is pulsed into the reactor at a time selected with respect to the production and arrival of the clusters. The effect of turbulent mixing with the reactant pulse perturbs the beam, but clusters and reaction products which survive the travel from the source to the photoionization regime ( 600y sec) and the photoionization process are easily detected. 

Various correlations for mean droplet sizes generated by air-assist atomizers are given in Table 4.6. In these correlations, mA is the mass flow rate of air, h is the height of air annulus, tf0 is the initial film thickness defined as tj ) = dQw/dan, d0 is the outer diameter of pressure nozzle, dan is the diameter of annular gas nozzle, w is the slot width of pressure nozzle, C is a constant related to nozzle design, UA is the velocity of air, and MMDC is the modified mean droplet diameter for the conditions of droplet coalescence. Distinguishing air-assist and air-blast atomizers is often difficult. Moreover, many... 

With this atomiser, the drop size is effectively independent of viscosity, and the size spectrum is narrower than with other types of pressure nozzle. 

Pressure nozzles are somewhat inflexible since large ranges of flowrate require excessive variations in differential pressure. For example, for an atomiser operating satisfactorily at 275 kN/m2, a pressure differential of 17.25 MN/m2 is required to increase the flowrate to ten times its initial value. These limitations, inherent in all pressure-type nozzles, have been overcome in swirl spray nozzles by the development of spill, duplex, multi-orifice, and variable port atomisers, in which ratios of maximum to minimum outputs in excess of 50 can be easily achieved(34). 

Break-up of the jet occurs as follows. Ligaments of liquid are tom off, which collapse to form drops. These may be subsequently blown out into films, which in turn further collapse to give a fine spray. Generally, this spray has a small cone angle and is capable of penetrating far greater distances than the pressure nozzle. Small atomisers of this type have been used in spray-drying units of low capacities. 

Pressure nozzles are most suited to low viscosity liquids and, where possible, viscous liquids should be preheated to ensure the minimum viscosity at the nozzle. Because of their simplicity, pressure nozzles are also employed to atomise viscous liquids with a kinematic viscosity up to 0.01 m2/s, depending upon the nozzle capacity. Under these conditions, injection pressures of up to 50 MN/m2 may be required to produce the required particle size. With slurries, the resulting high liquid velocities may cause severe erosion of the orifice and thus necessitate frequent replacement. 

A spray-dryer eonsists of a feed tank, a rotary or nozzle atomizer, an air heater, a drying ehamber, and a eyelone to separate the powder from the air. A rotary atomizer uses eentrifugal energy to form the droplet. Pressure-nozzle atomizers feed solution to a nozzle under pressure, whieh forms the droplet. Two-fluid nozzles feed solutions separately into a nozzle head, whieh produces high-speed atomizing air that breaks the solution into tiny droplets. Both the feed solution and the drying air are fed into the drying ehamber in a standard eoeurrent flow [27]. 

Fig. 18. (a) End effector collecting substances that can cause scratches, (b) If a high-pressure nozzle or a clean brush is used, the end effector is clean [16],... 

Pump Pressure = Nozzle Pressure -i- Friction Loss + Appliance Loss -i- Elevation Loss or Gain. 

Specific impulse, calculated by this technique, represents a 100% conversion of chemical energy to mechanical energy, and, therefore, is an upper limit to the performance available from a real rocket engine. However, regardless of the technique utilized, the theoretical Is of each of the systems are compared on a common basis (e.g.y at the same combustion chamber pressure, nozzle geometry, exit pressure, etc.) with the desired performance level dictated by the mission and engine system rquirements. 

The liquid jet formed by a pressure nozzle is inherently unstable. The breakup of the laminar jet occurs by symmetrical oscillation, sinusoidal oscillation, and atomization. 

Pressure nozzle the fluid under pressure is broken up by its inherent instability and its impact on the atmosphere, on another jet, or on a fixed plate. 

In order then to determine what influences flavor retention during drying, one must focus attention on the very early stages of dehydration. In fact, it has been shown that the major fraction of total volatiles lost during nozzle-atomized spray drying occurs within ten centimeters of the pressure nozzle (17, 33, 35). 

Proper atomization of feed is the key to successful spray drying. The three devices of commercial value are pressure nozzles, pneumatic nozzles, and rotating wheels of various designs. Usual pressures employed in nozzles range from 300 to 4000 psi, and... 

The main variables in the operation of atomizers are feed pressure, orifice diameter, flow rate and motive pressure for nozzles and geometry and rotation speed of wheels. Enough is known about these factors to enable prediction of size distribution and throw of droplets in specific equipment. Effects of some atomizer characteristics and other operating variables on spray dryer performance are summarized in Table 9.18. A detailed survey of theory, design and performance of atomizers is made by Masters (1976), but the conclusion is that experience and pilot plant work still are essential guides to selection of atomizers. A clear choice between nozzles and spray wheels is rarely possible and may be arbitrary. Milk dryers in the United States, for example, are equipped with nozzles, but those in Europe usually with spray wheels. Pneumatic nozzles may be favored for polymeric solutions, although data for PVC emulsions in Table 9.16(a) show that spray wheels and pressure nozzles also are used. Both pressure nozzles and spray wheels are shown to be in use for several of the applications of Table 9.16(a). 

Pressurizer. The pressurizer is a cylindrical pressure vessel, vertically mounted and bottom supported. Energy to the water is supplied by replaceable direct-immersion electric heaters, which are inserted from the bottom head of the pressurizer. Nozzles are provided for spray, surge,... 

---