MSP Corporation Announces a New Breakthrough in Monodisperse Droplet Generation

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MSP's newly developed Model 1530 Monodisperse Droplet Generator (MDG) produces uniform monodisperse droplets as small as 15 microns in diameter. The 1530's small high precision droplets are very useful for evaluating the performance of laboratory laser phase Doppler systems.

Model 1530 Calibration System

Model 1530 MDG used for calibration of a Laser Doppler Instrument

The MDG produces small droplets without the clogging problems that a VOAG device typically has with very small orifices.

The Vibrating Orifice Aerosol Generator (VOAG) was developed in the 1970s and has been a key device for generating monodisperse droplets of known diameters for research applications such as for calibrating droplet measuring instruments, for studying droplet processes and for generating monodisperse solid particles by drying monodisperse droplets.

The VOAG requires forcing liquid out of an orifice about half the diameter of the desired droplets. Liquid jet emerging from the orifice is broken down uniformly using narrow-bandwidth ultrasonic excitations, so a single drop is formed during each cycle of ultrasonic perturbation. Diameters of the droplets thus produced are determined with a high accuracy as they carry the liquid volume forced out of the orifice in a single cycle of ultrasonic perturbation.

However, this excellent process of generating monodisperse droplets of known diameters becomes unreliable and difficult to implement with decreasing orifice diameters, as small orifices are prone to clogging and wear out under liquid pressure, thus making it difficult to generate small droplets. Over years, there has been a growing need for sub-50-micron droplets that cannot be easily produced using the VOAG device. MSP has recently solved this problem by using the ‘flow-focusing’ technique in combination with ultrasonic liquid jet breakup (patent pending). The newly developed Model 1530 Monodisperse Droplet Generator (MDG) uses a robust nozzle with a 100-micron diameter opening that is neither prone to wear nor clogging under normal operating conditions. The liquid jet issuing from the nozzle is attenuated to the desired diameter using flow-focusing air, which flows concentric to the liquid jet and accelerates it, thus reducing the jet diameter. The amount of energy in the flow-focusing air, controlled by its initial pressure, determines the final jet diameter, which can be as small as 10 microns.

The Model 1530 MDG has been extensively tested with ultrapure water and organic solvents (e.g. methanol and ethyl alcohol) and shown to generate a wide-range of droplet diameters from nearly 15 microns up to 100 microns. Unlike the VOAG, the MDG does not require hardware reconfiguration to cover this wide droplet size range. Tables and graphs are provided to choose operating conditions for generating the desired droplet diameters.

Using a touchscreen menu and a flow metering valve, Model 1530 provides convenient and user-friendly means to set three key parameters: liquid flow rate, ultrasonic frequency and flow-focusing air pressure. Proper choice of these parameters ensures stable output of monodisperse droplets of the desired size with a geometric standard deviation of 1.01-1.03. The droplet generating head is connected to the main body of the instrument via flexible tubing and an electrical signal cable, so it can be positioned with an arbitrary orientation at the desired location in an experimental setup, such as a setup involving characterization of sprays using the phase Doppler technique.

MSP is a privately-held division of TSI Inc. For over 30 years MSP has created micro- and nano-particle instrument and equipment technologies for scientific research and industrial applications. MSP is known world-wide for particle technology expertise in helping researchers and manufacturers solve tough problems with creative equipment designs. Contact MSP at sales(at)mspcorp(dot)com to discuss micro- and nano-particle application or research needs.

Contact: Francisco J. Romay, Product Manager, Aerosol Instruments

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Francisco Romay
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