Ultrasonic nozzle

Both a pneumatic heated nozzle system [487] and an ultrasonic nozzle/vacuum system [699] have been described for removing the troublesome solvent in order to simplify IR analysis. The former system (LC Transform ) has been commercialised [700], and allows full use of the mid-IR spectral range by providing analyte films free from solvent interference. The evaporative... 

Solvent-elimination approaches include evaporative spray deposition onto infrared-transparent surfaces (141) or reflective surfaces and powders (142, 143). Other approaches include partial evaporation of the mobile phase before spray deposition (144, 145), and continuous liquid-liquid extraction systems that transfer solutes from LC mobile phases to solvents possessing an infrared window (146). Spray systems include both pneumatic and ultrasonic nozzles (147). 

While possible to obtain satisfactory products with the pneumatic nebuliser, the experimental difficulties due to clogging and the strong dependence on many interrelated variables indicated that another type of atomiser should be investigated. An ultrasonic nozzle, in which high frequency electrical energy is converted into vibratory mechanical motion at the same frequency, was therefore examined. The ultrasonic nozzle was chosen because the average droplet size was small, about 25 microns, and... 

Figure 5 X-ray diffraction pattern for hydrolysis reaction products obtained with the ultrasonic nozzle...

Scanning electron micrographs for particles of Cu2OCl2 obtained with the ultrasonic nozzle with an optimised power setting had an estimated size of 100 nanometers to 30 microns. 

Solid Cu2OCl2 products formed by the ultrasonic nozzle were subsequently heated from room temperature to 700°C to investigate its decomposition behavior as a function of temperature. While several mass numbers were monitored as a function of time and reaction temperature, the oxygen peak at mass number 32 is shown in Figure 6. The peak area was determined and converted to an amount of oxygen via a calibration curve. As can be seen the oxygen signal started near 400°C and ended near 550°C. The calibration showed that the peak area corresponded to 100% of the theoretical amount. 

The spray reactor with the ultrasonic nozzle provided sufficient heat and mass transfer in the laboratory tests as essentially all of the CuCl2 was converted to Cu2OCl2. The ultrasonic nozzle provided droplets with an estimated size of 25 microns. Mass and heat transfer was achieved by injecting these small droplets/dehydrated particles into an atmosphere of superheated, humidified Ar. These results provide... 

The test results with the ultrasonic nozzle were obtained with an estimated steam to copper (S/Cu) ratio of 23 and the humidified Ar was injected co-currently with the CuCl2 solution. Several variables remain to be investigated, i.e. lower S/Cu ratios, counter-current instead of co-current operation, and subatmospheric pressures. LeChatelier s Principle predicts that reducing the pressure in the hydrolysis reactor should reduce the S/Cu ratio. The effect of a reduced pressure was quantified by the results of a sensitivity study using Aspen. Aspen predicts that a S/Cu ratio of 17 is needed for essentially complete conversion at 375°C and atmospheric pressure while a S/Cu ratio of 13 is required at 0.5 bar. The conceptual process design specifies that the hydrolysis reactor be run at 0.25 bar. The pressure drop in the reactor is achieved by adding a low temperature steam ejector after the condenser at the exit of the hydrolysis reactor in the conceptual design. 

One of the most important characteristics of this cycle is the relatively low maximum process temperature required, about 550°C. Early tests showed that a temperature of 530-550°C was required for complete decomposition (Serban, 2004). The results of the decomposition studies with the Cu2OCl2 produced with the ultrasonic nozzle also showed that the maximum temperature is near 550°C. 

Figure 7. Importance of fuel nitrogen content. All data taken in AR/O2/CCL, tunnel furnace, ultrasonic nozzle, 5% excess 02 (Reproduced with permission from Ref. 16. Copyright 1979, The Combustion Institute.)...

Fig. 1a. Ultrasonic nozzle Fig. 1b. A conventional nozzle spraying a fluid...

Spray nozzles are used for dust control, water aeration, dispersing a particular pattern of drops, coating, paintings, cleaning surfaces of tanks and vats, and numerous other applications. They develop a large interface between a gas and liquid, and can provide uniform round drops of liquid. Atomization occurs by a combination of gas and liquid pressure differences. The Figure below (courtesy of Misonix Inc.) compares the particle sizes from the ultrasonic nozzle with those from the conventional nozzle. 

The Dekmezian solvent-evaporative interface design consists of an ultrasonic nozzle installed in a heated vacuum chamber. The mobile phase is spray-dried over discs that are sequentially placed below the nozzle in a... 

The Effect of Evaporation Conditions on Film Morphology. Two extreme modes of operation were examined evaporation sufficiently rapid to avoid any accumulation of solution on the surface of the KBr disc during the run, and evaporation so mild that liquid accumulated on the disc surface and then evaporated completely. Evaporation control variables included ultrasonic nozzle power, spray temperature, gas flow rate around the disc, oven temperature, and pressure. With accumulation... 

In 1933 Lim and Debenedetti (107) patented the formation of protein microparticles by antisolvent precipitation. Since that date, other patents dealing with the formation of protein by the same processes have been filed. Recently, Niu (100) patented the formation of insulin and albumin using an ultrasonic nozzle. 

Both LaMer s and the falling film aerosol generators yield only small quantities of products. Much larger amounts of aerosols can be produced by dispersing liquids with the help of various mechanical devices, e.g. rotating disks or ultrasonic nozzles [6]. These techniques, however, usually yield aerosols with broad distribution of droplet sizes and thus lead to polydisperse systems. The dispersion aerosol generators can, consequently, be used... 

Ultrasonic nozzles use a metal horn geometry to amplify a small peizoelectric vibration. These vibrations drive surface instabilities along a thin film and generate droplets of very uniform size, but at low flow rates. 

FIGURE 8.5 In situ mixing/ultrasonic nozzle-spray/microwave (INM) method. 

Ultrasonic nozzles are designed to specifically operate from a vibration energy source. In ultrasonic atomization, a liquid is subjected to a sufficiently high intensity of ultrasonic field that splits it into droplets, which are then ejected from the liquid-ultrasonic source interface into the surrounding air as a fine spray (Rajan and Pandit 2001). A number of basic ultrasonic atomizer types, like capillary wave, standing wave, bending wave, fountain, vibrating orifice, and whistle, etc., exist. 

Rajan and Pandit (2001) assessed the impact of various physicochemical properties of liquid, its flow rate, the amplitude and frequency of ultrasonic, and the area and geometry of the vibrating surface on the droplet size distribution. A correlation was proposed to predict the droplet size formed using an ultrasonic atomizer taking into consideration the effect of liquid flow rate and viscosity. The droplet size distribution from an ultrasonic nozzle follows a log-normal distribution (Berger 1998). 

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