Study of Suspended Droplets by Laser Attenuation Method

This study investigates the properties of suspended particles by usmg laser
attenuation measurement system with reference to the Beer-Lambert's Law. These
suspended particles either solid particles or liquid droplets are not visible in the air due to
their fine sizes (smaller than 2.5 pm ). Fundamentally, laser attenuation is defined as a
technique in measuring reduction or attenuation of light intensity of a laser beam due to
its passage through a body. The portion of incident flux is reflected at the entrance and
exit surfaces and another portion is absorbed while the remainder is transmitted.
Quantification of the properties of particles and droplets is important due to various
applications; for instance, to measure size and velocity of droplets of spray painting to
reduce the environmental effects, to study flows inside engines and obtaining important
data on the fuel injection to improve the fuel efficiency. A system that applies laser
attenuation was developed in a past research work and was proved as a reliable
measurement system but to deepen the understanding in suspended particles, several
experiments have been added and some modification has been done to improve the
measurement system. The objectives of this project are to study experimentally the
properties of various specimens by using laser attenuation method and to improve power
meter system as well as laser system. For the methodology, it includes gathering
information, planning the experiments, modification of the existing measurement system
and conducting experiments of smoke, sea water, fog and diesel spray. First experiment
which is comparison of both power meters with new modified circuit that afterwards was
proved reliable due to increment of voltage value. It will be continued by experiment
with smoke. This experiment was conducted to quantifY the extinction coefficient of
smoke. The laser beam was incident to a Perspex container containing sea water and
fresh water for third experiment which concern with absorbance value. The sea water has
greater absorbance compared to fresh water as the voltage recorded is much lower. Next
was experiment to study the scattering effect of fog. Last but not least was the experiment
with diesel spray where the diesel atomization was introduced within the measurement
system in order to quantifY the number density. As the pressure of diesel was increased,
more particles will absorb the laser beam due to higher angle of spray.