In the present work, a technique based on the laser attenuation is experimented with to quantify the properties of suspended particles and droplets. The scope of the study includes research, improvement, modification, testing and calibration as well as analysis.
Sources of Attenuation
Photoelectric effect (PE)
Absorption of x-rays occurs when the photon of x-rays is absorbed, resulting in the ejection of electrons from the outer shell of the atom and thus ionization of the atom. The ionized atom then returns to its neutral state by emitting an x-ray characteristic of the atom.
Compton scattering (C)
Pair production (PP)
Basically, light scattering has been used to measure the thermal properties of liquids and solids since Einstein showed that the intensity of light scattered by density fluctuations is proportional to the isothermal compressibility of the liquid. This theory provides the connection between the spectrum of scattered light and various thermodynamic and transport properties of the fluid (Mountain, 1966).
Types of light scattering
Rayleigh scattering
It is produced when light penetrates the gaseous, liquid or solid phase of matter, and its intensity is highly dependent on the size of the particles. This type of scattering is therefore responsible for the blue color of the sky during the day and the orange colors at sunrise and sunset.
Mie scattering
Phase Doppler Anemometry
9 shows the spray flow visualization and figure 2.10 optical setup for PDA system based on the Aerometrics Phase Doppler Particles Anemometry. Laser wavelength Laser beam diameter (1/e) Focal length of collimating lens Focal length of transmitting lens Beam separation. Nominal edge count Maximum velocity Off-axis receive' any)e Focal length of the receiving lens Theoretical droplet size ranges (min).
Helium Neon laser
Experiments are done from either side of the first power meter; right and left. The tension value of fresh water and sea water is different due to different properties of the water. Next, the mole of seawater Nseawater is calculated by dividing mseawater by the molecular weight M. The concentration, C is then obtained by dividing N8ea water by volume of seawater VSeawater·.
Compared to the absorbance of fresh water, which achieves 0.073 or 7.3%, the absorbance of seawater is higher. In the figure, the second power meter was located 30° to the right of the first power meter. Based on the results of the second power meter, there was a significant difference in the average voltage between the right side and the left side of the power meter.
The increasing voltage reading at certain angles means that the LDR has detected part of the laser beam. The experiments were conducted in the laboratory due to the needs of pump use. When the laser beam strikes the diesel spray, reflections and transmission of the beam through the particles to the environment will occur.
Laser principal
Properties of green laser
Methodology
In the meantime, both information and research about the project will be collected and understood. A laboratory introductory briefing of Laser Doppler Anemometry and Particle Dynamics Analysis (LDA/PDA) will then be attended. The reassembly of the laser attenuation measurement system could improve the current meter circuit by replacing the current standard circuit with a printed circuit board (PCB).
For this project, laser beam will be sent through the water and the average voltage will then be recorded by the power meter. Two power meters are used in this experiment with one power meter being the reference for the second one.
Construction of a laser system
Additionally, a small hole was drilled in the front layer to allow the laser beam to pass through. For the electrical part, a small piece of platinum was used in the construction of the laser system. The platinum is first connected to the wire before it is placed between the batteries and connected to the toggle switch.
Batteries are still being used due to the lack of significant differences when using the power supply unit.
Power meter printed circuit board
Constructing power meter circuit
Power meter circuit is designed using easily applicable graphical layout editor, or EAGLE software. The process of designing the circuit is quite difficult, so it causes several times of change to the circuit and it causes longer time consumption.
Testing of power meter circuit
Components of the System
Laser Source
Light Intensity Power Meter
Two aluminum U-channels from the previous FYP are used as the platforms for the measurement system. These two platforms can be attached and detached to suit the different conditions of testing and also for the flexibility. There are two aluminum plates which are milled using Computer Numerical Control (CNC) into a square plate of 60 rnm x 60 mm with 15 mm thickness.
Figures 3.14 and 3.15 show the milled plates with two different diameters and a completed lens holder, while Figure 3.16 shows the plano-convex lenses with a diameter of 5 cm with a focal length of 15 em.
Data Acquisition System
Measurement of droplet size using PDA system
Based on the results, there were distinct differences of the first and second power voltage readings within 60 seconds. Longer wires mean higher resistance, so this factor can also contribute to the slight deviation of the voltage reading. Lowering the voltage means reducing the intensity of the laser beam due to the obstruction in the path of the laser beam.
Based on the results of the second power meter, the highest average voltage recorded for the right side of the first power meter is 4.117 V at the angles of 70°, while for the left side it is 3.634 V at the angles of !0°. The first experiment was to compare the warm-up period of the laser, where the new laser has higher voltage value.
RESULTS AND DISCUSSION
Functionality of power meters
- Experiment to determine warm-up period oflaser source
- Experiment using the first and second power meter
- Experiments of comparing covered LDR with uncovered LDR. 37
Then, when the laser source was turned on, an average voltage reading of 4.780 V was displayed with a standard deviation of 0.702 V. For the second power meter, when the laser source was turned off, the light intensity meter gave an average voltage reading of 2.438 V with a standard deviation of 0.204 V. Then, when the laser source was turned on, the average displayed voltage was 4.204 V with a standard deviation of 0.017 V.
From the graph, when the laser source was turned off without cover, the light intensity power meter gave the average voltage reading of 3.477 V with a standard deviation of 1.1 02E-4 V. Next, when the laser source was turned on without cover, the average voltage reading displayed is, was 4.646 V with a standard deviation of 0.559 V.
Experiment with sea water
The average voltage continued to decrease when seawater was poured into the container, with the average value of the voltage being 3.879. The tension continues to decrease as the fresh water is replaced by the sea water. The mass of sea water (msea water) is obtained by multiplying its density (psea water).
Based on the calculation above, absorption of sea water is 0.160 which means that 16% of the laser beam was absorbed by the sea water. From the experiments, seawater obtains 0.792 cm2/mol molar absorptivity while fresh water obtains 0.188 cm2/mol.
Experiment with fog
The higher absorbance means that a larger part of the laser beam will be absorbed by the particles, resulting in lower intensity of the beam that will be recorded by the power meter. Basically, the second wattmeter was moved 10° relative to the first wattmeter and the displayed voltage reading was recorded. The magnitude of the observed broadening has been shown to exhibit a strong dependence on the receiver parameters.
In this experiment, a quantity of the incident current is reflected at the entrance and exit surfaces of the fog glass, and another quantity is absorbed and the rest is transmitted. The highest average voltage is recorded by the second power meter on the left side at angles of 60° and 70°.
Experiment with diesel spray
Based on the calculation, the number density recorded at 50 kPa is 0.79 drops/cm3, while the number density for I OOkPa is 2.08 drops/cm3•. This is due to the increasing spray angle as the pressure increases, leading to more particles absorbing the laser beam and resulting in higher number density recorded. Last but not least was the experiment with diesel spray, where the diesel atomization was introduced into the measurement system to quantify the number density.
Choi, Measurement of the mass-specific extinction coefficient of acetylene and ethylene fumes using the Agglomerate Optics Facility, Department of Mechanical Engineering, University of Illinois at Chicago, Chicago. 34; Scattering Effects in Laser Attenuation System for Measuring Droplet Density", Conference Paper, Department of Mechanical Engineering, Universiti Tekno1ogi PETRONAS, Tronoh, Perak.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
This was followed by a comparison of both power meters with a new modified circuit, which later proved to be reliable due to the increased voltage value. The highest extinction coefficient was reached at 2 minutes, which is the fastest the beam was attenuated as it passed through the medium. The laser beam fell on a Perspex container containing seawater and fresh water for the third experiment related to the absorbance value.
Seawater had greater absorption compared to fresh water as the voltage recorded was much lower. As the oil pressure increased, more particles would absorb the laser beam due to the higher spray angle.
Recommendations
The wood dust may vary due to different types of wood or different sizes of wood dust. The experiment with radiation fog could be done in such a way that the result could be compared with the existing result of advection fog. 20 1 0) Scattering Effects in Laser Damping System for Droplet Density Measurement, Final Year Project (FYP) Dissertation, Dept.
Ahmed, Zaliman Sauli, Uda Hashim, Yarub Al-Douri, Investigation of the absorption coefficient, refractive index, energy band gap and film thickness for Al0.11Ga0.89N, Al0.03Ga0.97N and GaN by optical transmission method, School of Microelectronic Engineering, Universiti Malaysia Pedis,. Phase Doppler Anemometry, 3'd August 2008, Department of Energy and Process Engineering, Tampere University of Technology, retrieved 22 September 2010, from.
