Nebulizers baffles

The aerosol then passes along the plastic expansion chamber. Large droplets collect on the walls of the chamber and, to ensure that only the smallest particles reach the flame, spoilers or baffles may be placed in the path of the gases. The chamber also allows for mixing of the gases and tends to damp fluctuations in nebulization efficiency. Some loss of solvent by evaporation will also occur. The chamber requires a drain tube which must be sealed to provide a back-pressure for the flame. This is usually... 

Nebulizers are specialized atomizers which permit recycling of the liquid. They have in-built baffles to ensure that large primary drops are returned to the reservoir and thus the aerosol emitted from the device has a size distribution which will aid airway penetration. 

The jet nebulizer is driven by air pressurized typically at 20-40 psi. The compressed air accelerates through an arrow orifice to break the bulk liquid into sheets, jets, films, or streams. Those ligaments are accelerated to a velocity sufficient to impact on baffles or on the nebulizer wall. The outgoing air becomes saturated with water vapors derived from the liquid retained in the nebulizer, and this has two important consequences ... 

Fig. 2 Schematic diagram of a typical ultrasonic nebulizer. (A) Face mask or mouthpiece (B) baffles (C) geyser of respiratory solution or suspension (D) piezoelectric crystal (E) internal fan (F) battery or electrical source. (From Ref. l)...

Patient compliance with prescribed nebulization regimes is primarily determined by the duration of the therapy. Nebulizer fluids may be atomized for a set period, or more usually, a measured volume of therapeutic liquid is nebulized to dryness. The time taken to achieve this is directly related to the volume to be delivered. However, not all the fluid in the nebulizer can be atomized, and some fluid remains associated with the baffles, internal structures, and walls of the nebulizer as the dead or residual volume. The proportion of fluid remaining as the residual volume and thus unavailable to patients is higher for smaller fill volumes. 

Nebulizers and atomizers used in aerosol research produce a polydisperse aerosol consisting of particles under 10 pm in diameter. Most nebulizers use compressed air for atomization, whereas some use ultrasonics. Many models of compressed-air nebulizers have been developed, but they basically use the principle of air blast atomization of liquids issuing through a small orifice. Impaction plates or baffles are used to remove the larger droplets. Mass median diameters normally range from 2 to 5 pm, with a compressed-air pressure of 20-30psig. A detailed discussion of nebulizers can be found in Raabe [5]. Most nebulizers or atomizers tend to have a small liquid reservoir and cannot be used for long duration unless the reservoir is refilled continuously. 

The aerosol produced by an air-jet nebulizer (Fig. 3) is generated by a completely different principle. When compressed air is forced through an orifice, an area of low pressure is formed where the air jet exists. A liquid may be withdrawn from a perpendicular nozzle (the Bernoulli effect) to mix with the air jet to form droplets. A baffle (or baffles) within the nebulizer is often used to facilitate the formation of the aerosol cloud. Carrier air (oxygen) can be used to generate the air jet. Alternatively, compressors may be used to generate the airstream. 

Most aerosol delivery systems have surfaces that are designed to collect or disperse particles. Jet nebulizers have spheres, as shown in Fig. 4, or plates placed immediately in front of the jet to collector break up large droplets. Metered-dose inhalers do not traditionally have baffles however, the surface of the actuator collects aerosol particles as they pass through the mouthpiece. Dry powder... 

The burners used in flame spectroscopy are most often premixed, laminar flow burners. Figure 28-11 is a diagram of a typical commercial laminar-flow burner for atomic absorption spectroscopy that employs a concentric tube nebulizer. The aerosol flows into a spray chamber, where it encounters a series of baffles that remove all but the finest droplets. As a result, most of the sample collects in the bottom of the spray chamber, where it is drained to a waste container. Typical solution flow rates are 2 to 5 mL/min. The sample spray is also mixed with fuel and oxidant gas in the spray chamber. The aerosol, oxidant, and fuel are then burned in a slotted burner, which provides a flame that is usually 5 or 10 cm in length. 

With the use of a standard nebulizer, significant variation may occur in the amount of aerosol delivered per inhalation, even if inspiratory flow rate is controlled (as discussed earlier). A second important determinant of nebulizer output is related to the actual structure of the nebulizer. In the De Vilbiss 646 model, for example, the straw and baffle assembly is a detachable component of the nebulizer that is removed for washing. When this component is reattached, variable distances may result the straw and baffle assembly and the jet orifice, which is the source of pressurized air (see Fig. 2 in Dicpinigaitis 2005). This variation in distance, albeit minute, may result in variable nebulizer output. Thus, to optimize reproducibility, the author uses a nebulizer with an inspiratory flow regulator valve, as described earlier, and, with the straw and baffle assembly welded in place, thereby eliminating the variations in nebulizer output that may result when this component is detached and reattached, resulting in variable distances between the jet orifice and straw. 

In 1946, electrical pumps providing a continuous flow of air were advocated. The Collison nebulizer (25), made of ebonite with a plate baffle to fil-... 

Once formed, the aerosol passes into the burner or spray chamber (sometimes also called the cloud chamber). The role of the spray chamber is to homogenize both the aerosol and gases that tend to dampen fluctuations in nebulizer efficiency, and to remove any large droplets before they reach the flame. Large droplets (diameter > 10 pm) collect on the sides of the chamber and then drain to waste. Spoilers and baffles placed at the end of the spray chamber aid this process. Because the spray chamber will fill with flammable gas, modern instruments will also incorporate some form of antiflashback protection from the flame. 

The turbo ISP interface has been developed for conventional LC systems with high flow rates. Relatively high gas temperatures must be applied to achieve sufficient heat transfer to the evaporating droplets. The Z-spray interface is another variant where the ESP nebulization is performed with concurrent desolvation gas. Ions are extracted orthogonally from the spray into the sampling cone, while large droplets and non-volatile material are collected onto a baffle plate. From the expansion area behind the sampling... 

Most flame spectrometers use a premix burner, such as that in Figure 20-4, in which the sample, oxidant, and fuel are mixed before being introduced into the flame. Sample solution is drawn in by rapid flow of oxidant and breaks into a fine mist when it leaves the tip of the nebulizer and strikes a glass bead. The formation of small droplets is termed nebulization. The mist flows past a series of baffles, which promote further mixing and block large droplets of liquid (which flow out to the drain). A fine mist containing about 5% of the initial sample reaches the flame. The remainder flows out the drain. 

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