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Introduction
The measurement of a continuous stable spray is the simplest that can be made
with your instrument, requiring no essential extra accessories. Malvern offer an
Aerosol Mounting Unit which you may find useful for repeatably positioning the
nozzles and directing the spray.
Arrange for the spray to be extracted
Sprays are not contained within a cell and if there is nowhere for them to go after
they have passed through the beam they can back circulate and possibly deposit
out onto the optics. Remember therefore to consider where your spray goes after
measurement and ensure that nothing prevents it. Avoid operating against walls
or other equipment that prevent air circulation. Ideally arrange for an extraction
air flow. Also consider any health risks when spraying hazardous materials.
Use the correct optical configuration
Because all normal sprays will occupy a long illuminated beam length it is not
feasible to measure sprays using the 300RF lens and the Mastersizer S or the
45mm lens on the Mastersizer X. In addition, the short lens cut-off distance of
the 300mm range restricts the usefulness of this range for sprays. The most
suitable range is the 1000mm range (long bench users only) but the 300mm range
may also be used if you pay attention to the possibility of the large angle scattering
being cut-off (vignetting) by the lens aperture.
Positioning the spray nozzle
A spray invariably expands in extent as it travels away from the nozzle. If no
evaporation occurs then this means that the concentration of particles that will lie
at any time in the Mastersizer analyser beam will reduce as the distance from
beam to nozzle increases. Close to the nozzle there will be a limit caused by the
concentration being too high for accurate measurement. Downstream a limit will
also occur where the spray concentration has become so low as not to be reliably
detectable. Between these extremes an acceptable range of measurements can be
made.
In some types of spray the droplets do not reach a stable size until some distance
away from the nozzle. Close to the nozzle the liquid may be in the form of
A P P E N D I X E
G E T T I N G
S T A R T E D
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