Page 85 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

60 Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Lense
Light source
High-pass filter
CCD sensor

(A) H2O+RhB Optics
1.2
1
Normalized Intensity 0.6
0.8

0.4
0.2
0
20 25 30 35 40 45 50 55 60
(B) Temperature (°C)
Fig. 3.1.4 LIF principle.

detected by the CCD sensor of Fig. 3.1.4A.The equation governing this phenomena is
(Tropea et al., 2007)

E 1
(3.1.20)
I f ¼ CI L χ ðP,TÞe K B T ξ ΓðP,TÞΦ 21 ðP,TÞ,
0
12
where I f is the fluorescent intensity emitted by a dye solution excited with intensity I L .
The correlations account for the density of dye molecules at the thermodynamic state 0
χ ðÞ, population of dye molecules at the energy level 1 E 1 Þ described through
ð
0
Boltzmann distribution, Einstein probability of absorption and transition from state
1 to state 2 ξ ð 12 Þ, absorption and emission spectrum overlap Γ ðÞ, emission probability
expressed as the ratio between spontaneous emission and alternative energy dissipation
mechanisms(fluorescencequantumyieldΦ 21 )andopticalsetup(C).Themeasurement
is performed when the fluorescent signal I f , detected by the CCD sensor, is related to a
temperature value through a calibration. The calibration curve of Fig. 3.1.4B describes
the relationship between the fluorescence intensity and the temperature.

3.1.2.4.4 Refractive index matching techniques

One of the disadvantages of optical techniques, such as LDA and PIV, is the require-
ment of optical access to the measurement region of interest. The use of transparent,
solid walls, having a refractive index, which is different from the fluid around them,
poses problems due to the refraction of light. The refraction is described by the well-
known law of Snell:
n 1 sinðθ 1 Þ¼ n 2 sinðθ 2 Þ: