U.S. patent number 5,273,359 [Application Number 07/976,018] was granted by the patent office on 1993-12-28 for remote high-temperature insulatorless heat-flux gauge.
This patent grant is currently assigned to The United States of America as represented by the United States. Invention is credited to Bruce W. Noel.
United States Patent |
5,273,359 |
Noel |
December 28, 1993 |
Remote high-temperature insulatorless heat-flux gauge
Abstract
A remote optical heat-flux gauge for use in extremely high
temperature environments is described. This application is possible
because of the use of thermographic phosphors as the sensing media,
and the omission of the need for an intervening layer of insulator
between phosphor layers. The gauge has no electrical leads, but is
interrogated with ultraviolet or laser light. The luminescence
emitted by the two phosphor layers, which is indicative of the
temperature of the layers, is collected and analyzed in order to
determine the heat flux incident on the surface being investigated.
The two layers of thermographic phosphor must be of different
materials to assure that the spectral lines collected will be
distinguishable. Spatial heat-flux measurements can be made by
scanning the light across the surface of the gauge.
Inventors: |
Noel; Bruce W. (Espanola,
NM) |
Assignee: |
The United States of America as
represented by the United States (Washington, DC)
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Family
ID: |
27127728 |
Appl.
No.: |
07/976,018 |
Filed: |
November 13, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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862886 |
Apr 3, 1992 |
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Current U.S.
Class: |
374/29; 374/30;
374/E11.017; 374/E17.015 |
Current CPC
Class: |
G01K
17/20 (20130101); G01K 11/3213 (20130101) |
Current International
Class: |
G01K
11/00 (20060101); G01K 11/32 (20060101); G01K
17/20 (20060101); G01K 17/00 (20060101); G01K
017/00 () |
Field of
Search: |
;374/29,30,31,43,161,44 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2758994 |
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Jul 1979 |
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DE |
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0587996 |
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May 1947 |
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GB |
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Other References
K A. Wickersheim et al., "Optical Temperature Measurement,"
Industrial Research/Development (Dec. 1979)..
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Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Gutierrez; Diego F. F.
Attorney, Agent or Firm: Wyrick; Milton D. Gaetjens; Paul D.
Moser; William R.
Government Interests
The invention is a result of a contract with the Department of
Energy (Contract No. W-7405-ENG-36).
Parent Case Text
This is a continuation-in-part application out of patent
application Ser. No. 07/862,886, filed Apr. 3, 1992, now abandoned.
Claims
What is claimed is:
1. An optically interrogated gauge for measuring heat flux incident
on a surface comprising:
a first thermographic phosphor in direct contact with said
surface;
a second thermographic phosphor overlying said first thermographic
phosphor;
light means incident on said first and second thermographic
phosphors, for producing first luminescence from said first
thermographic phosphor and second luminescence from said second
thermographic phosphor;
collecting means for collecting said first and second luminesces,
wherein said first luminescence and said second luminescence are
indicative of the temperatures of said first and second
thermographic phosphors; and
computing means connected to said collecting means for determining
heat flux on said surface using numerical differences between said
temperatures of said first and second thermographic phosphors.
2. The heat-flux gauge as described in claim 1, wherein said first
thermographic phosphor is embedded in a transparent matrix and said
second thermographic phosphor overlies said first thermographic
phosphor embedded in said transparent matrix.
3. The heat-flux gauge as described in claim 2, wherein said
transparent matrix comprises a glass or glass-like matrix.
4. The heat-flux gauge as described in claim 1, wherein said first
thermographic phosphor comprises YVO.sub.4 :Eu.
5. The heat-flux gauge as described in claim 1, wherein said second
thermographic phosphor comprises YVO.sub.4 :Dy.
6. The heat-flux gauge as described in claim 1, wherein said light
means comprises a mercury lamp.
7. The heat-flux gauge as described in claim 1, wherein said light
means comprises a laser.
8. The heat-flux gauge as described in claim 1, wherein said light
means is scanned across said second thermographic phosphor to
determine heat flux on a plurality of points on said surface.
9. A method of determining heat flux incident on a surface
comprising the steps of:
depositing a first thermographic phosphor on said surface;
depositing a second thermographic phosphor over said first
thermographic phosphor;
illuminating said second thermographic phosphor and said first
thermographic phosphor with light to produce first luminescence
from said first thermographic phosphor and second luminescence from
said second thermographic phosphor;
collecting said first and second luminescences; and
computing said heat flux incident on said surface from information
contained within said first and second luminescences.
10. The method as described in claim 9 wherein said step of
illuminating said second thermographic phosphor and said first
thermographic phosphor with light further comprises illuminating a
plurality of points on said second thermographic phosphor and said
first thermographic phosphor to allow spatial determination of said
heat flux on said surface.
Description
This invention relates generally to the measurement of heat flux,
that is the measurement of the amount of heat transferred across a
surface per unit area per unit time, and, more specifically, to the
measurement of heat flux at high temperatures, utilizing the
optical properties of thermographic phosphors without need for an
insulator.
The measurement of heat flux is important in many experimental
situations, such as those where heat transfer must be limited and
therefore monitored. For example, accurate measurement of
heat-transfer rates is considered critical to the design
improvements envisioned for high-pressure turbine engines. Improved
understanding of the effects that contribute to heat load can lead
to increased efficiency. Of particular interest is the heat
transferred from the free-stream gas to an engine component
surface. Examples include turbine blades and vanes.
Previous heat-flux gauges have principally involved some form of
resistance-thermometer temperature sensor applied on both sides of
an insulating medium. These sensors, which are conducting surfaces,
can also be made from pairs of materials in a thermocouple
configuration. Leads connected to these surfaces carry an
electrical current which is proportional to the surface temperature
detected by the sensor to an external instrument which would
measure the temperatures of the surfaces. A typical gauge is made
by depositing thin layers of an electrically and thermally
conductive material onto both sides of a thin sheet of insulating
material such as MYLAR.RTM., or KAPTON.RTM..
Heat flux, Q, incident on an ideal gauge made in this way is given
by the following equation
where k is the thermal conductivity of the insulator, L is the
thickness of the insulator, and .DELTA.T is the temperature
difference between the two conductive surfaces. This equation
assumes that the conductive surfaces are infinitely conducting and
infinitely thin.
Modern embodiments of this configuration are disclosed in U.S. Pat.
Nos. 4,779,994, 4,722,609, and 4,577,976.
U.S. Pat. No. 4,779,994 to Diller, et al. discloses a fairly
conventional heat-flux gauge which utilizes thin-film layers
applied to each side of a planar thermal-resistance element, with
its "cold" junctions applied to one surface and its "hot" junctions
applied to the other. The use of thin films allows the deposition
of a large number of junctions onto a small surface area which can
be interconnected in series. Of course, these junctions are of the
electrical-resistance type, and require electrical connections.
U.S. Pat. No. 4,722,609 to Epstein et al. discloses a double-sided,
high-frequency-response heat-flux gauge consisting of a metal film
approximately 1500 angstrom thick applied to both sides of a thin
(25 .mu.m) polyimide sheet. At low frequencies, the temperature
difference across the polyimide is a direct measure of the heat
flux. At higher frequencies, a quasi-one-dimensional assumption is
used to infer the heat flux. Numerous such gauges are arranged in a
serpentine pattern and applied to the surface of a turbine
blade.
Yet another thin-film heat-flux gauge is disclosed in U.S. Pat. No.
4,577,976 to Hayashi et al. wherein a pair of metallic thin films
are attached to opposite surfaces of a heat-resistive thin film.
The heat flux through the heat-resistive film is determined by
measuring the temperature gradient therein while using the metallic
thin films as resistance-thermometer elements.
The pervading problem plaguing the above heat-flux gauges, as well
as other similar prior art heat-flux gauges, is that they are
electrically based. Thus, they all require connecting wires of some
type in order to operate. This complicated their use, and limits
their application to rotating components, where wire connections
would have to be made through slip rings. This complicates such an
application, and detracts from its reliability.
Connecting leads or wires of the prior art also limit the spatial
resolution when multiple heat-flux gauges are needed to measure the
spatial distribution of heat flux. The degree of complication,
because of the inherent geometry of such electrically based gauges,
effectively precludes their use in measuring the spatial
distribution of heat flux with acceptable resolution and area
coverage. Wiring dozens of gauges is complicated and interferes
with the natural heat transfer to or from the surface under test.
Connecting wires also present problems when such gauges are used in
hostile environments.
The current invention solves the problems of the prior art by
providing a leadless heat-flux gauge that uses light instead of
electrical means as its interrogating medium. The sensing elements
of the gauges are thermographic phosphors, whose emission lines in
the luminescence spectrum are temperature dependent. This allows
accurate temperature determination when the phosphors are
interrogated by ultraviolet (uv) light, and the spectral lines of
the emitted light are analyzed. It also allows for a heat-flux
gauge requiring no electrical connections between the gauge and the
associated evaluation and display equipment.
Applicant is a co-inventor in three related U.S. Pat. No.
4,912,355, issued Mar. 27, 1990, U.S. Pat. No. 5,005,984, issued
Apr. 9, 1991, and U.S. Pat. No. 5,044,765, issued Sep. 3, 1991.
These patents deal with different configurations of optically
interrogated heat-flux gauges. As with the present invention, the
gauges are based on thermographic phosphors, arranged in a sandwich
fashion. These earlier gauges have a transparent plastic insulator
between adjacent phosphor layers. Although these gauges perform
properly in low to medium-temperature environments, the melting
point of the insulation makes them unsuitable for high-temperature
application.
It is therefore an object of the present invention to provide
apparatus for the accurate measurement of heat flux in
high-temperature environments.
It is another object of the present invention to provide a
heat-flux gauge which requires no plastic insulator between
adjacent thermographic-phosphor layers.
It is yet another object of the present invention to provide a
heat-flux gauge that does not require electrical connections.
It is still another object of the present invention to provide a
heat-flux gauge that will operate in a hostile environment.
It is still another object of the present invention to provide a
heat-flux gauge that is interrogated with light.
Additional objects, advantages and novel features of the invention
will be set forth in part in the description that follows, and in
part will become apparent to those skilled in the art upon
examination of the following, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects, and in accordance with
the purposes of the present invention, as embodied and broadly
described herein, the apparatus of this invention comprises an
optically interrogated gauge for measuring heat flux incident on a
surface comprising a first thermographic phosphor in direct contact
with the surface, with a second thermographic phosphor overlying
the first thermographic phosphor. Light means are incident on the
first and second thermographic phosphors, for producing first
luminescence from the first thermographic phosphor and second
luminescence from the second thermographic phosphor. Collecting
means collect the first and second luminescences, wherein the first
luminescence and the second luminescence are indicative of the
temperatures of the first and second thermographic phosphors.
Computing means are connected to the collecting means for
determining heat flux on the surface using numerical differences
between the temperatures of the first and second thermographic
phosphors.
In a still further aspect of the present invention, and in
accordance with its objects and purposes, a method of determining
heat flux incident on a surface comprises the steps of depositing a
first thermographic phosphor on said surface, and depositing a
second thermographic phosphor over the first thermographic
phosphor; illuminating the second thermographic phosphor and the
first thermographic phosphor with light to produce first
luminescence from the first thermographic phosphor and second
luminescence from the second thermographic phosphor; collecting the
first and second luminescences; and computing the heat flux
incident on the surface from information contained within the first
and second luminescences.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and from a
part of the specification, illustrate the embodiments of the
present invention and, together with the description, serve to
explain the principles of the invention. In the drawings:
FIG. 1 is a schematic illustration of an optical heat-flux gauge
according to the present invention applied to a surface.
FIG. 2 is a schematical representation of the
thermographic-phosphor layers applied to a surface according to the
present invention, together with heat flux and interrogating light
incident on the layers.
FIG. 3 is a perspective view of a heat-flux gauge according to the
present invention deposited over a section of a surface for which
spatial heat flux information is desired, with the light source
scanning the surface of the gauge.
DETAILED DESCRIPTION
The present invention provides a heat-flux gauge which can be
deployed in high-temperature environments, and which does not
require any electrical leads. The above referenced patents on which
the applicant is a co-inventor disclose optical heat-flux gauges
employing thermographic phosphors with an insulator between
phosphor layers. However, a problem exists if these gauges are used
in high-temperature environments, in that the insulator can melt at
high temperatures. The present invention improves on these patents
and discloses a gauge which has no insulator.
The new heat-flux gauge can be best understood by referring to FIG.
1, where a schematic illustration of optical heat-flux gauge 10
applied to a surface 11 according to the present invention is
shown. Optical heat-flux gauge 10 comprises thermographic-phosphor
layer 12 and thermographic-phosphor layer 14, without any
intervening insulator.
As shown, heat flux 13 is incident on optical heat-flux gauge 10,
as is light from light source 15 which is focused onto heat-flux
gauge 10 by lens 18. Heat flux 13, in passing through gauge 10 into
surface 11, will create linear temperature gradients across
phosphor layer 12 and phosphor layer 14, as is required for
heat-flux determination. The heat-flux quantity, Q, for a gauge not
having an insulative layer is determined by formulae which will be
derived below.
Attention should now be redirected to FIG. 1. In passing through
phosphor layers 12, 14, the light from light source 15 is absorbed
exponentially throughout each layer, and is proportional to the
optical-absorption coefficient, .alpha.. The intensity of the light
at any depth, x, within each layer 12, 14 can be represented as
where I.sub.o represents the initial intensity of light absorbed
from light source 15, and .alpha. is the optical absorption
coefficient.
For the reason that luminescence is generated at each point within
thermographic layers 12, 14 which is traversed by light from light
source 15, the emitted luminescence 16, 17 from layers 12, 14
respectively is actually emitted from a distribution of points
within layers 12, 14. This results in luminescence 16, 17 appearing
to come, on average, from a point within each of layers 12, 14.
When layer 12 and layer 14 are at different temperatures, as they
are when heat flux 13 is incident on surface 11, there exists a
linear temperature gradient across each layer 12, 14. Thus, with
this knowledge, and the knowledge about luminescence 16, 17
appearing to emanate from a point in each layer 12, 14, one can
determine the temperature at any point within each layer 12, 14.
The two temperature points needed for determining the heat flux are
the temperature at the interface between surface 11 and layer 14
and the temperature at top surface 12a of layer 12. With knowledge
of these two temperatures, and of the thermal conductivities,
optical absorption coefficients, and thicknesses of
thermographic-phosphor layers 12, 14, heat flux 13 can be
calculated by inserting the values into the formulae developed
herein. This allows the present invention to perform as a remote,
insulatorless heat-flux gauge capable of performing in
high-temperature environments.
In developing this derivation, it will be helpful to refer to FIG.
2, wherein a labeled schematical view of phosphor layer 12
overlying phosphor layer 14, which is adjacent to surface 11. For
the purposes of this derivation, phosphor layer 12 is referred to
as Material 1, or M.sub.1, and phosphor layer 14 is referred to as
Material 2, or M.sub.2. Following is a list of terms to be used in
the derivation:
K.sub.1 =thermal conductivity of M.sub.1 ;
K.sub.2 =thermal conductivity of M.sub.2 ;
For each material, M.sub.1, M.sub.2 :
.alpha..sub.tu =total ultraviolet (uv) absorption
coefficient=.alpha..sub.au +.alpha..sub.pu ;
.alpha..sub.au =the contribution to .alpha..sub.tu corresponding to
nonradiative uv absorption;
.alpha..sub.pu =the contribution to .alpha..sub.tu corresponding to
radiative absorption, that is radiation which results in the
emission of an optical photon;
.alpha..sub.to =total optical absorption coefficient;
.alpha..sub.to .apprxeq..alpha..sub.ao, the contribution to
.alpha..sub.to that corresponds to nonradiative optical absorption
(the assumption, which is borne out through experiment, is that
virtually no optical photons result from optical absorption);
G=a largely geometric factor that determines the fraction of
optical radiation created by M.sub.1 and M.sub.2 that arrives at a
detector exterior to M.sub.1 and M.sub.2.
L=the thickness of each material, M.sub.1 and M.sub.2.
I.sub.o =the intensity of the uv light incident on M.sub.1.
As I.sub.o passes through M.sub.1, it is absorbed according to the
classical absorption law, so the intensity of I.sub.o at a point x,
within M.sub.1, is given by
The probability of a photon created at x arriving at an external
detector after being subject to absorption is
Then the differential number of photons emitted from the surface of
M.sub.1 is given by
and the total number of photons emitted from M.sub.1 is ##EQU1##
The intensity of the uv light at the interface, i, between M.sub.1
and M.sub.2 (at x=L.sub.1) is
By arguments similar to those made above, the number of photons
returning to the interface from within M.sub.2 is ##EQU2## and the
number emitted from the surface of M.sub.1 is given by
Substituting the expression of equation 17 for N.sub.2 (L.sub.1)
into equation 18 yields ##EQU3## Evaluating N.sub.01 and N.sub.02,
we have
where
A.sub.1 =.alpha..sub.tu1 +.alpha..sub.au1 and
A.sub.2 =.alpha..sub.tu2 +.alpha..sub.au2.
It is now necessary to determine the depth from which the average
photon originates in M.sub.1 and M.sub.2. Inasmuch as dn may be
thought of as a distribution function, the effective depths X.sub.1
and X.sub.2 are given by the following expressions: ##EQU4##
Evaluation of equations 22 and 23 yields ##EQU5##
Consider a heat flux, Q, per unit area, incident on surface 11.
Assuming one-dimensional heat flow, which is reasonable for long,
thin insulating materials, the heat flux obeys the standard
heat-flux formula (Equation 10) for this case. Since it is
continuous,
where T(X.sub.1) and T(X.sub.2) are the temperatures measured at an
effective distance x into the phosphor materials, by the
fluorescence coming from the phosphor materials. Equations 25 and
26 can be solved for T.sub.i as follows:
It is also to be noted that: ##EQU6## Solving Equation 28 for
T.sub.0, and substituting Equation 27, yields ##EQU7##
It is now necessary to substitute Equation 30 into Equation 26,
which yields ##EQU8##
Now, all expressions for the quantities necessary to calculate heat
flux on surface 11 using thermographic-phosphor layers without an
intervening insulator are at hand. The important expressions are
summarized below: ##EQU9## where Q is the desired measurement of
heat flux; K.sub.1 and K.sub.2 are the measurable thermal
conductivities of the thermographic-phosphor layers; L.sub.1 and
L.sub.2 are the measurable thicknesses of the
thermographic-phosphor layers; .alpha..sub.tu1, .alpha..sub.tu2,
.alpha..sub.au1 and .alpha..sub.au2 are the measurable absorption
coefficients of the thermographic-phosphor layers; and T(X.sub.1)
and T(X.sub.2) are temperatures indicated by the
thermographic-phosphor layers.
It should be noted that, for any insulatorless gauge design, the
quantities for K, L, and .alpha. are fixed quantities, that when
combined, yield a calibration factor such that
Therefore, once the calibration factor is known, a gauge according
to the present invention obeys a formula for heat flux that is
analogous to Equation 10.
Optical heat-flux gauge 10, if an integral unit, can be attached to
surface 10 using a high-thermal-conductivity epoxy if the expected
temperature is not so high as to damage the epoxy. For higher
temperatures, an air brush (not shown) could be used to deposit
thermographic-phosphor layer 14 as a thin layer directly onto
surface 11. Thermographic-phosphor layer 12 would then be deposited
as a thin layer on top of layer 14. With air-brush deposition, the
thermographic phosphors are mixed with a high-temperature
binder.
Other methods of depositing layers 12, 14 include E-beam deposition
and RF sputtering. If desired for protection of optical heat-flux
gauge 10 at low temperatures, a thin layer of a transparent
material having high thermal conductivity could be deposited over
thermographic-phosphor layer 12.
It is important that the phosphor layer 12 be thin enough to permit
a substantial portion of light from lamp 15 to pass through layer
12 and into layer 14. With some thermographic phosphors whose
optical-absorption coefficients do not permit a substantial portion
of light from lamp 15 to pass through thermographic-phosphor layer
12, it will be necessary to embed the thermographic phosphor
material into an insulating transparent matrix which is capable of
not being damaged by the expected temperature ranges. This
insulating transparent matrix could be uv-transparent glass, or a
glass-like matrix.
To insure that incident heat flux 13 can be accurately determined,
it is, of course, necessary that thermographic-phosphor layer 12
comprise a thermographic phosphor different than the thermographic
phosphor which comprises thermographic-phosphor layer 14. This is
so that the different materials will exhibit different spectral
lines for the same or different temperatures of layers 12, 14.
The choice of the materials for thermographic-phosphor layer 12 and
thermographic-phosphor layer 14 initially involves choosing
thermographic phosphors which have high rates of change in emission
spectra over the temperature range of interest for surface 11.
Presently, thermographic phosphors are available over the range of
0K to 2000K. The choices of particular thermographic phosphors for
layers 12, 14 are subject to the criteria for the intended
application. Two thermographic phosphors which could be used are
YVO.sub.4 :EU and YVO.sub.4 :Dy.
Light source 15 can be an ultraviolet lamp or a laser having
efficiency and accuracy. Light source 15 should operate at a
wavelength which will most efficiently excite the desired spectral
lines of the chosen phosphors. A wavelength that is acceptable for
many applications and that is readily available from commercially
available uv lamps or lasers is 254 nm. Of course, any light source
that, such as a mercury lamp can produce a wavelength slightly
shorter than the shortest-wavelength emission line of
thermographic-phosphor layers 12, 14 can be used to produce
luminescences 16, 17.
Luminescences 16, 17 contain sufficient information through
interpretation of their spectral lines to determine the
temperatures of thermographic-phosphor layer 12 and
thermographic-phosphor layer 14. With the temperature information,
the heat flux, Q, can be calculated using the formulae developed
herein.
The embodiment of a means for collecting and interpreting
luminescences 16, 17 is also illustrated in FIG. 1. As illustrated
schematically, light from light source 15 is focused by lens 13
onto the top surface of gauge 10. As a result, luminescences 16,
17, being phosphor luminescences indicative of temperature, are
emitted from gauge 10, and are collected by lens 22 and inserted
into optical fiber 24 for transmission into spectrometer 26 through
a lens coupler (not shown).
Spectrometer 26 receives luminescences 16, 17 through optical fiber
24, and the resulting luminescence signal is dispersed and
collected on diode array 28, which, for example, may be an EG&G
Reticon, diode array. The data from diode array 28 is recorded and
processed by optical multichannel analyzer (OMA) 30, which may be
an EG&G model 1460 optical multichannel analyzer. Optical
multichannel analyzer 30, having internal computer 30a, is a
conventional optical multichannel analyzer, and converts light
incoming on optical fiber 24 into electrical signals. These
electrical signals are then analyzed by computer 30a to determine
heat flux 13, using the temperature differences between
thermographic-phosphor layer 12 and thermographic-phosphor layer
14.
In an embodiment of the invention, spatial distribution of heat
flux across a surface may be accomplished by depositing heat-flux
gauge 10 over the area of surface 11 for which measurements of heat
flux are desired. Such an arrangement is shown in FIG. 3. Here, the
light 15a from light source 15 (FIG. 1) is scanned across gauge 10,
and the luminescences (not shown) from different points on gauge 10
is gathered by lens 22 (FIG. 1). By this method, flux rates for
discrete areas of surface 11 can be monitored. FIG. 3 also
illustrates thermographic layer 14 embedded into transparent matrix
19.
The foregoing description of embodiments of the present invention
has been presented for purposes of illustration and description. It
is not intended to be exhaustive or to limit the invention to the
precise forms disclosed, and obviously many modifications and
variations are possible in light of the above teachings. The
embodiments were chosen and described in order to best explain the
principles of the invention and its practical applications to
thereby enable others skilled in the art to best utilize the
invention in various embodiments and with various modifications as
are suited to the particular use contemplated. It is intended that
the scope of the invention be defined by the claims appended
hereto.
* * * * *