|
|
PDF FEDSM2000-11043 Data sheet ( Hoja de datos )
| Número de pieza | FEDSM2000-11043 | |
| Descripción | DUAL EMISSION LASER INDUCED FLUORESCENCE TECHNIQUE | |
| Fabricantes | ETC | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de FEDSM2000-11043 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
|
No Preview Available !
Proceedings of ASME FEDSM’00
ASME 2000 Fluids Engineering Division Summer Meeting
June 11-15, 2000, Boston, Massachusetts
FEDSM2000-11043
DUAL EMISSION LASER INDUCED FLUORESCENCE TECHNIQUE (DELIF) FOR
OIL FILM THICKNESS AND TEMPERATURE MEASUREMENT
Carlos H. Hidrovo and Douglas P. Hart
Massachusetts Institute of Technology
Cambridge, MA 02139
ABSTRACT
This paper presents the development and implementation
of a Dual Emission Laser Induced Fluorescence (DELIF)
technique for the measurement of film thickness and
temperature of tribological flows. The technique is based on a
ratiometric principle that allows normalization of the
fluorescence emission of one dye against the fluorescence
emission of a second dye, eliminating undesirable effects of
illumination intensity fluctuations in both space and time.
Although oil film thickness and temperature measurements are
based on the same two-dye ratiometric principle, the required
spectral dye characteristics and optical conditions differ
significantly. The effects of emission reabsorption and optical
thickness are discussed for each technique. Finally, calibrations
of the system for both techniques are presented along with their
use in measuring the oil film thickness and two-dimensional
temperature profile on the lubricating film of a rotating shaft
seal.
INTRODUCTION
Laser Induced Fluorescence (LIF) is based on the use of a
light source to excite a fluorescence substance (fluorophore or
fluorescent dye) that subsequently emits light. The fluorescence
substance is used as a tracer to determine characteristics of
interest. LIF has gained popularity as a general purpose
visualization tool for numerous 1-D, 2-D, and 3-D applications.
It, however, has seen limited use as a quantitative tool. The
reason for this stems primarily from the difficulty in separating
variations in excitation illumination and vignetting effects from
tracer emission. Presented herein is a two-dye ratiometric
technique that allows measurement of temperature and film
thickness while minimizing variations in excitation illumination
and non-uniformities in optical imaging.
Fluorescence is the result of a three-stage process that
occurs in fluorophores or fluorescent dyes (Haugland, R. P.,
1999). The three processes are (Fig. 1):
1: Excitation
A photon of energy hvEX is supplied by an external source
such as an incandescent lamp or a laser and absorbed by the
fluorophore, creating an excited electronic singlet state (S1’).
2: Excited-State Lifetime
The excited state exists for a finite time (typically 1–10 x
10-9 seconds). During this time, the fluorophore undergoes
conformational changes and is also subject to a multitude of
possible interactions with its molecular environment. These
processes have two important consequences. First, the energy of
S1' is partially dissipated, yielding a relaxed singlet excited state
(S1) from which fluorescence emission originates. Second, not
all the molecules initially excited by absorption (Stage 1) return
to the ground state (S0) by fluorescence emission. Other
processes such as collisional quenching, fluorescence energy
transfer and intersystem crossing may also depopulate S1. The
fluorescence quantum yield, which is the ratio of the number of
fluorescence photons emitted (Stage 3) to the number of
photons absorbed (Stage 1), is a measure of the relative extent
to which these processes occur.
3: Fluorescence Emission
A photon of energy hvEM is emitted, returning the
fluorophore to its ground state S0. Due to energy dissipation
during the excited-state lifetime, the energy of this photon is
lower, and therefore of longer wavelength, than the excitation
photon hvEX. The difference in energy or wavelength
represented by (hvEX–hvEM) is called the Stokes shift. The
Stokes shift is fundamental to the sensitivity of fluorescence
techniques because it allows emission photons to be detected
against a low background, isolated from excitation photons.
1 Copyright © 2000 by ASME
1 page  
Consequently, film thickness cannot be inferred from
fluorescence intensity unless illumination intensity at a
particular location and time is known. The ratio of the
illumination intensity and the fluorescence intensity, however, is
independent of spatial and temporal variations in excitation
light intensity.
I f ≡ R = R(t,
Io
(16)
Obtaining illumination intensity is not trivial. A two-
dimensional instantaneous illumination map, however, can be
inferred from the fluorescence of a second dye. This is the
principle behind DELIF:
(1) the fluorescence of dye 1 in a two-dye system contains
the desired information (film thickness, temperature,
which will be discussed later), along with exciting light
intensity information.
(2) the fluorescence of dye 2 also contains the exciting
light intensity information but behaves differently than
dye 1 to the scalar of interest.
(3) By rationing the fluorescence of dye 1 with the
fluorescence of dye 2, the excitation light information
is canceled out, giving a ratio that contains only the
desired scalar information.
Oil Film Thickness
Oil film thickness measurements are achieved using an
optically thick system that takes advantage of reabsorption. The
film thickness information is contained in the reabsorption of
the fluorescence of dye 1 by dye 2. The excitation light
intensity information is contained both in the fluorescence of
dye 1 and dye 2. If two narrow-band interference filters are
used to capture the two distinctive fluorescence emissions, an
emission intensity defined by
I f,1’(t,
,filter1 y,
= I o(y, 1( laser )C1
laser )C+ 2(
( )1 1 filter1
)Cfilter1 2
( { [ ] })× 1−exp − laser )C+ 2( )Cfilter1 2 t (17)
I f,2(t,
,filter 2 y,
= Io(y,
2( laser )C2 2
laser )C
2(
)filter 2
[ ]( { })× 1−exp − laser )C t
(18)
R(t,
,filter1
filter 2
)=
I
I
f,1
’
=
f,2
1( laser )C1
2( laser )C2
( )1 1 filter1
( )2 2 filter 2
( { [ ] })× ( laser )C 1−exp − laser )C+ 2( )Cfilter1 2 t
[ ]( { [ ] }) laser )C+ 2( )Cfilter1 2 1−exp − laser )C t
(19) .
is obtained.
By taking the ratio of the emission of the two dyes, the
excitation light intensity dependence is cancelled leaving a ratio
that is only dependent on film thickness. As film thickness
information is contained in the reabsorption of the fluorescence
of dye 1 by dye 2, the system must be optically thick, in order
for the reabsorption to be substantial and measurable (Fig. 6).
Figure 6: Film thickness ratio
Temperature
It is possible to use LIF as a temperature indicator when
there is a dependence of either the molar absorption (extinction)
or quantum efficiency coefficients on temperature.
= 7
(20)
5 Copyright © 2000 by ASME
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet FEDSM2000-11043.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| FEDSM2000-11043 | DUAL EMISSION LASER INDUCED FLUORESCENCE TECHNIQUE | ETC |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |