Development of a Photothermal Deflection Analyzer for Measurement of Thermophysical and Thermo-Optical Properties of Fluids
Photothermal deflection techniques are non-contact methods for optical and thermal properties characterization of solids, liquids and gases. The main focus in this project was to design, construct and test reliability of an instrument based on the principle of photothermal deflection technique. I...
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| Format: | Thesis |
| Language: | English |
| Published: |
2008
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/5117/1/FS_2008_16%20IR.pdf |
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| Summary: | Photothermal deflection techniques are non-contact methods for optical and thermal
properties characterization of solids, liquids and gases. The main focus in this project
was to design, construct and test reliability of an instrument based on the principle of
photothermal deflection technique. In this technique, the heating source is a NiCr
resistance wire and the probe beam is a CW HeNe. The instrument is intended for the
characterization of thermal properties of liquids and it is named Photothermal
Deflection Analyzer (PTDA).
The PTDA setup consists mainly of a CW HeNe probe laser beam, a NiCr resistance
wire, a position sensitive detector and a personal computer with an installed data
acquisition card. The PTDA measured the deflection of a probe beam passing near a
heating source immersed in a liquid sample. The beam deflection is caused by the
refractive index gradient induced by the temperature change in the liquid. The
deflection angle of the probe laser beam is measured by the position sensitive detector. Short electrical pulses from a data acquisition card generated across the
resistance wire cause a heating gradient in the liquid. The duration and temporal
shape of the electrical pulses can be change in a wide range.
The temperature distribution of the heating wire and liquid is simulated by solving
numerically a coupled transient heat conduction equations for wire and liquid. The
effect of different temporal profiles and pulse durations of the heating source to the
temperature distribution in the liquid is discussed. Using obtained temperature profile
it is possible to calculate the probe beam displacement. Thermal properties of the
liquid can be determined by comparing the numerical and experimental probe beam
displacement.
In order to test the reliability of the PTDA, thermal properties of selected liquid
samples: distilled water, alcohol, sodium chloride liquid solution and coconut oil
were determined. The thermal properties for distilled water and alcohol show a good
agreement with the literature. For sodium chloride liquid solution, the PTDA is
sensitive enough to sense the changes of thermal properties due to the variation of the
solution concentration. The thermal diffusivity of coconut oil was dependent to the
moisture content whereas the thermal conductivity and thermo-optical properties was
not affected by the moisture content. Presently to the best of our knowledge, there is
no literature data on thermal properties of coconut oil versus moisture content. |
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