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| 型號： | FEDSM2000-11043 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | DUAL EMISSION LASER INDUCED FLUORESCENCE TECHNIQUE (DELIF) FOR OIL FILM THICKNESS AND TEMPERATURE MEASUREMENT |
| 中文描述： | 雙發(fā)射激光誘導(dǎo)熒光技術(shù)（DELIF）的油膜厚度和溫度測量 |
| 文件頁數(shù)： | 1/8頁 |
| 文件大小： | 190K |
| 代理商： | FEDSM2000-11043 |
1
Copyright 2000 by ASME
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 hv
EX
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 (S
1
’).
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
S
1
' is partially dissipated, yielding a relaxed singlet excited state
(S
1
) from which fluorescence emission originates. Second, not
all the molecules initially excited by absorption (Stage 1) return
to the ground state (S
0
) by fluorescence emission. Other
processes such as collisional quenching, fluorescence energy
transfer and intersystem crossing may also depopulate S
1
. 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 hv
EM
is emitted, returning the
fluorophore to its ground state S
0
. 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 hv
EX
. The difference in energy or wavelength
represented by (hv
EX
–hv
EM
) 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.
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