A plug-type heat flux gauge formed in a material specimen and having a thermoplug integrally formed in the material specimen, and a method for making the same are disclosed. The thermoplug is surrounded by a concentric annulus, through which thermocouple wires are routed. The end of each thermocouple wire is welded to the thermoplug, with each thermocouple wire welded at a different location along the length of the thermoplug. The thermoplug and concentric annulus may be formed in the material specimen by electrical discharge machining and trepanning procedures

Koch, John, Jr.

Liebert, Curt H.

English

NASA Technical Reports Server

United States Patent 1193 
Liebert et al. 
[ i  11 Patent Number: 5,048,973 
[45] Date of Patent: Sep. 17, 1991 
[54] PLUG-TYPE HEAT FLUX GAUGE 
[75] Inventors: Curt H. Liebert, Middleburg Hts.; 
[73] Assignee: United States of America, as 
John Koch, Jr., Medina, both of Ohio 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[2l] Appl. No.: 531,433 
[22] Filed: May 31, 1990 
[51] Int. Cl.5 ...................... GOlK 17/16; GOlK 17/06 
374/208; 250/356.1; 136/200 
Field of Search ....................... 374/29, 30, 31, 32, 
374/180, 134; 136/216, 223, 213; 250/356.1 
[52] U S .  Cl. ......................... 374/29; 374/180; 
[58] 
[561 References Cited 
US. PATENT DOCUMENTS 
2,818,490 12/1957 Dixon et al. . 
3.232.113 2/1966 Malone . 
3,372,588 3/1968 Ziernke et al. . 
3,382,714 5/1968 Miller et al. . 
3.531.989 10/1968 Nasa ................ 377/29 
3,724.267 4/1973 Zoschak ................................ 374/30 
3,757,206 9/1973 Dorst .............................. 374/180 X 
4.245.500 1/1981. Malang .............. 374/30 
4,5 10,799 4/1985 Overmier ................. 73/151 
4,527,908 7/1985 Arisi .................................. 374/29 X 
4,571,094 211986 Wynnyckyj et al. ....... 374/29 
FOREIGN PATENT DOCUMENTS 
1171674 8/1985 U.S.S.R. ................................ 374/29 
1312409 5/1987 U.S.S.R. ................................ 374/29 
OTHER PUBLICATIONS 
High Temp (USA) vol. 10, No. 2 (3/72). 
Product Engineering, vol. 35 #26, 12/21/64. 
Liebert, “Heat Flux Measurements”, NASA Technical 
Memorandum 101428, Jun. 4, 1989. 
Primary Examiner-Stuart S. Levy 
.4ssistant Examiner-Joseph A. Rhoa 
Attorney, Agent, or Firm-Kent N. Stone; Harold W. 
Adams; Gene E. Shook 
[571 ABSTRACT 
A plug-type heat flux gauge formed in a material speci- 
men and having a thermoplug integrally formed in the 
material specimen, and a method for making the same. 
The thermoplug is surrounded by a concentric annulus, 
through which thermocouple wires are routed. The end 
of each thermocouple wire is welded to the thermo- 
plug, with each thermocouple wire welded at a differ- 
ent location along the length of the thermoplug. The 
thermoplug and concentric annulus may be formed in 
the material specimen by electrical discharge machining 
and trepanning procedures. 
8 Claims, 2 Drawing Sheets 
https://ntrs.nasa.gov/search.jsp?R=19910022294 2020-03-24T07:01:46+00:00Z
U.S. Patent Sep. 17, 1991 Sheet 1 of 2 5,048,973 
US. Patent Sep. 17, 1991 Sheet 2 of 2 5,048,973 
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In order to achieve the foregoing and other objects, 
in accordance with the purposes of the present inven- 
tion as described herein, a thermoplug is formed in a 
specimen material using, for example, electrical dis- 
5 charge machining and trepanning procedures. The ma- 
chining produces an annulus that surrounds an integral 
thermoplug. Because the thermoplug is an integral part 
of the specimen material, there is no seam between the 
thermal plug and the active surface of the specimen 
10 material. Therefore, the very large errors in heat flux 
measurement due to  the seam present in prior art plug- 
type heat flux gauges do not occur in the present inven- 
tion. Also, there is no need to  determine the uncertainty 
PLUG-TYPE HEAT FLUX GAUGE 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the U S .  Government and may be manufactured 
and used by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or  therefore. 
BACKGROUND OF T H E  INVENTION 
1. Field of the Invention 
The present invention generally to heat flux of heat flux measurement caused by the presence of gauges and methods of producing heat flux gauges, and 15 such a seam. 
more particularly to plug-type heat flux gauges having 
thermoplugs that are formed into a 'pecimen 
The ends of thermocouple wires are welded along the 
length of the  thermoplug in order to form hot junctions. 
The thermocouple wires are routed through the annulus 
to the rear of the specimen material, where they may be 
20 connected to larger diameter leadwire assemblies. A 
reliable. accurate and easily built heat flux gauges. For back may be welded to the back wall of the speci- 
and steady-state surface heat flux data for verification of annulus and trapping a thermal insulator, e,g,, air, 
models relating to heat transfer, durability and aerody- within the annulus and behind the thermoplug, 
namics. In many applications, heat flux gauges are re- 25 In a preferred method of making the invention, elec- 
quired to be accurate Over wide ranges Of heat flux trical discharge machining is used to intermittently 
that vary Over wide temperature ranges. For discharge an electric spark through a gap between the 
example, in order to  obtain rapid transient surface heat specimen material and an electrode, which includes a 
flux measurements on turbine blades utilized in space- hole along its length. The specimen material and the 
craft, a heat flux gauge may be required to provide 30 electrode are immersed in a dielectric fluid, and as cur- 
accurate rent is applied, sparks are emitted from the end of the 
electrode tube, detaching portions of the specimen ma- 
range of 100 to 1200K. terial. The thermoplug is formed within the hole of the 
for mea- electrode, as the electrode descends into the specimen 
S ~ e m e n t  o about 10 MW/m2, but Only at surface 35 material, thereby forming the thermoplug as an integral 
peratures that are maintained between 280 to 360K. and unitary part of the specimen material. 
Also, water-cooled heat flux gauges tend to be relative These and other features and advantages of the pres- 
large, e.g., often greater than 2.0 cm in diameter and ent invention will become more apparent with refer- 
length. Thus, because of their relatively large Size and ence to  the following detailed description and draw- 
narrow temperature range, water-cooled heat flux 40 ings. However, the drawings and description are merely 
gauges often cannot be used. illustrative in nature and not restrictive. 
Another type of heat flux gauge is the plug-type heat 
flux gauge. Typically, plug-type heat flux gauges in- BRIEF D ~ S C R I P T I O N  OF T H E  DRAWINGS 
clude a thermoplug that is screwed or  welded into a The accompanying drawings illustrate several as- 
specimen material having an active surface, creating a 45 pects of the present invention, and together with the 
seam between the active surface and the thermoplug. descriptions serve to explain the principles of the inven- 
This seam can introduce large discontinuities in surface tions. In the drawings: 
temperature, resulting in very large errors in heat flux FIG.  1 is an overall view of the plug-type heat flux 
measurement. It is extremely difficult to determine the gauge according to the present invention; and 
uncertainty in the resulting heat flux measurements due 50 FIG. 2 is a graph that shows relative agreement be- 
to the seam. Thus, the lack of accuracy and precision of tween the heat flux values obtained from the plug type 
conventional plug-type heat flux gauges may prohibit heat flux gauge of the present invention and conven- 
their use. tional heat flux gauges. 
D E T A I L E D  DESCRIPTION OF THE 
PREFERRED EMBODIMENTS 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an im- 
proved plug-type heat flux gauge that is accurate over FIG.  1 shows an overall view of a plug-type,heat flux 
wide ranges of heat flux values that vary over wide gauge 1 according to  the present invention. A thermo- 
temperature ranges. plug 2 is integral with material specimen 3. Material 
Another object of the invention is to provide an im- 60 specimen 3 includes front surface 4 (lower surface in 
proved plug-type heat flux gauge that is accurate, reli- FIG. 1) and back surface 5 (upper surface in FIG.  1). 
able and u,hich may be small in size. Front surface 4 of material specimen 3 is exposed to an 
Still another object of the invention is to provide an energy source, e.g., an arc-lamp for radiating incident 
improved plug-type heat flux gauge .that accurately thermal radiation 6.  Thermoplug 2 is insulated on all 
measures transient and steady-state surface heat flux. 65 surfaces except front surface 4, and therefore heat trans- 
Yet another object of the invention is to provide a fer within thermoplug 2 may be assumed 1-dimensional. 
method for easily producing an improved plug-type Concentric annulus 7 surrounds the sides of thermoplug 
heat flux gauge that achieves the foregoing objects. 2. Because concentric annulus 7 is formed only partially 
material and methods for producing same. 
2. Description of the Related Art 
Recently, there has been increasing need for 
example, heat flux gauges are needed to obtain transient men materia], thereby enclosing the thermoplug and 
for surface heat flux 
from about 0.3 to 6 MWIm2 Over a 
Water-cooled heat flux gauges are 
5 5  
5,048,97 3 
3 
through material specimen 3, a floor 8 of concentric 
annulus 7 is formed a finite distance from front surface 
4 of material specimen 3. Concentric annulus 7 is 
formed into material specimen 3 using any appropriate 
method, e.g., trepanning, electrical discharge machin- 5 
ing or the like. Trepanning consists of machining a 
circular groove into a material. For  example, a hole saw 
may be applied to back surface 5 of material specimen 3 
in order to form concentric annulus 7 and to form ther- 
moplug 2 integral with material specimen 3. The length 10 
of thermoplug 2 is taken as the distance from front 
surface 4 of material specimen 3 to a back surface 9 of 
thermoplug 2. 
Since thermoplug 2 is an integral part of material 
specimen 3, there is no seam connecting thermoplug 2 
to material specimen 3. As discussed above, conven- 
tional plug-type heat flux gauges include such seams, 
which can cause large errors in heat flux measurement. 
Further, determination of the uncertainty in heat flux 
measurement caused by such seams is very difficult. 
Therefore. a plug-type heat flux gauge according to the 
present invention is advantageous in that there is no 
such seam. In a preferred method of forming concentric 
annulus 7 into material specimen 3, a process known as 
electrical discharge machining is used. Electrical dis- 
charge machining is well known in the machining art. 
One example of an electric discharge machining appara- 
tus is described in U S .  Pat. No. 2,818,490, issued to 
Dixon et al. Thermoplug 2 and concentric annulus 7 are 
formed by intermittently discharging an electric spark 
through a gap between material specimen 3 and an 
electrode. Material specimen 3 and the electrode are 
immersed in a dielectric fluid, e.g., refined kerosene. 
The electrode, which is made from a conductor, e.g., 
copper-tungsten, includes a hole along its length. 
Sparks are emitted from the electrode and strike mate- 
rial specimen 3, thereby detaching material. The elec- 
trode forms thermoplug 2 and concentric annulus 7 as 
the electrode descends into material specimen 3, Le., 
thermoplug 2 is formed within the hole of the electrode. 
Concentric annulus 7 is machined only part way 
through material specimen 3, thereby forming thermo- 
plug 2 as an integral part of material specimen 3. Ther- 
moplugs of all sizes and shapes may be formed using this 
process. For  example, thermoplug diameters of 0.1 to 
0.2 cm, thermoplug lengths of 0.1 to 0.3 cm and concen- 
tric annulus widths of 0.03 to 0.08 cm have been formed 
using electric discharge machining. Thus, plug-type 
heat flux gauge 1 according to the present invention 
may be made relatively small compared with the size of 
conventional water-cooled heat flux gauges. Conse- 
quently, plug-type heat flux gauge 1 according to the 
present invention may be utilized in measuring heat flux 
in extremely small material specimens. 
As shown in FIG.  1, a back cover 10 encloses ther- 
moplug 2 and concentric annulus 7. Back cover 10 is 
secured, e.g., welded, to back surface 5 of material 
specimen 3, thereby trapping a thermal insulator, e.g., 
air, within concentric annulus 7 and behind thermoplug 
2. This thermal insulator minimizes heat transfer be- 
tween thermoplug 2, the surrounding wall of material 
specimen 3, and back cover 10. The thermal insulator 
also forces heat absorbed from front surface 4 of mate- 
rial specimen 3 to be transferred nearly one-dimension- 
ally along thermoplug 2. 
The ends of thermocouple wires 11, e.g., Chromel- 
Alumel, are spot-welded along thermoplug 2, at various 
distances from front surface 4 of material specimen 3. 
15 
20 
25 
30 
35 
40 
45 
50 
55  
60 
65 
4 
Thermocouple wires 11 are routed through concentric 
annulus 7 to back surface 5 of the specimen material 3. 
Ceramic material may be placed between thermocouple 
wires 11 and the walls of material specimen 3 and ther- 
moplug 2, thereby preventing the bare thermocoupled 
wires 11 from touching metallic parts. Thermocoupled 
wires 11 may be connected, e.g., spliced, to larger diam- 
eter lead wire assemblies 12 fastened to back surface 5 
of material specimen 3. 
Heat flux may be calculated from measured thermo- 
plug temperatures using a temperature variant thermal 
property inverse heat conductive problem method, e.g., 
heat storage equation: 
SYMBOLS 
C,, 
L length of thermoplug. crn 
qS surface heat flux. X1W/rn2 
T temperature. K. 
I time. sec 
Z 
p density. kg/m3 
specific heat at constant pressure, J/kg K 
thermocouple location along axis of thermoplug. rn 
In this equation, ST/& is evaluated by differentiating 
least-squares curve fit equations expressing measured 
thermoplug temperatures as a function of time at each 
temperature measurement location. Thermal properties 
are evaluated at local temperatures measured on the 
thermoplug. 
EXAMPLE 
A plug-type heat flux gauge 1 according to the pres- 
ent invention was formed in back surface 5 of a flat plate 
material specimen having a thickness of 0.350 cm. Ther- 
moplugs 2 were formed by electrical discharge machin- 
ing to have a diameter of 0.188 cm and a length of 0.330 
cm. Chromel-Alumel thermocouple wires 11 were spot- 
welded at distances of 0.00508, 0.0279, 0.175 and 0.330 
cm measured from front surface 4 of material specimen 
3. Lead wire assemblies 12 included Choromel-Alumel 
wires having a diameter of 0.015 cm encased in ceramic 
tubing. The ceramic tubing, in turn, was encased in 
Inconel @ sheath material to form an assembly which 
was then swaged to size. The diameter of each thermo- 
couple wire 11 was 0.00762 cm. Each thermocouple 
wire 11 was spot-welded to thermoplug 2, forming a 
cylindrical hot junction having a diameter of 0.0152 cm 
and a thickness of 0.00508 cm. The hot junction closest 
to the front surface 4 of material specimen 3 was welded 
to the bottom of a hole drilled through floor 8 of con- 
centric annulus 7 along a line parallel to and 0.100 cm 
from the centerline of thermoplug 2. The width of con- 
centric annulus 7 was 0.080 cm. This hole was drilled at 
a depth of 0.00508 cm from front surface-4 of material 
specimen 3. The other three hot junctions were \velded 
to thermoplug 2 and were circumferentially located 
120" from each other. The thermocouple waires 11 \ v u e  
extended from the hot junction in a direction perpendic- 
ular to the surface on which they were \velded, and 
then routed to lead wire assemblies 12. 
As shown in FIG.  2. satisfactory agreement in both 
transient and steady-state surface heat flux measure- 
ments between conventional \vater-cooled gauges and 
5,048,973 
5 6 
plug-type heat flux gauge 1 was obtained. An arc lamp said thermocouple wires being in heat conducting 
was used as the energy source. The arc lamp start-up contact with said thermoplug at a predetermined 
time period between about 0.3 and 0.7 seconds is de- point, the spacing between each predetermined 
fined in FIG. 2 as the region of transient heat flux, while point and said first surface being different for each 
time after about 0.7 seconds is defined as the region of 5 thermocouple wire, and 
steady-state heat flux. The timing of these regions was means for covering said annular chamber at said see- 
confirmed with a photodetector that simultaneously ond surface whereby said wires and contact points 
measured an increase in millivolt output of the arc lamp are insulated. 
of about 3 to 54 M V  at 0.3 to 0.7 sec (128 MV/sec) after 2. A plug-type heat flux gauge as recited in claim 1 
which the photodetector output remained constant. 10 wherein said thermoplug is cylindrical and said annulus 
The round and 'quare represent the mean Of 
three repeated measurements taken with three separate 3. A plug-type heat flux gauge as recited in claim 2, 
gauge 1. The solid single line in the transient region 
represents the cubic least-squares curve-fit relative to 15 
100 transient heat flux data points taken with the con- 
ventional water-cooled heat flux gauges. The mean of 
the steady-state heat flux data is also shown in FIG. 2. 
Numerous modifications and adaptations of the pres- 
ent invention will be apparent to those so skilled in the 20 
art and thus, it is intended by the following claims to 
all modifications and adaptations which fall 
within the true spirit and scope of the invention. 
surrounding said thermoplug is concentric thereto. 
thermocouple On each plug-type heat flux wherein said thermocouple wires are routed through 
said concentric annulus. 
wherein: 
4, A plug-type heat flux gauge as recited in claim 1, 
each of said thermocouple wires forms a hot junction 
5. A plug-type flux gauge as recited in claim 1 further 
a plurality of lead wires, each of said lead wires hav- 
ing a diameter greater than that of a corresponding 
one of said thermocouple wires and electrically What is claimed is: 
1. A plug-type heat flux gauge, including an integral 25 connected to a second end Of said 
thermoplug, comprising: one of said thermocouple wires. said second end of 
a member having a first surface exposed to an energy said thermocouple wires being opposite said first 
source which heats said member and a second sur- end. 
face oppositely disposed from said first surface 6. A Plug-tYPe heat flux gauge as recited in claim 1 
away from said energy source with an annulus 30 further 
extending from said second surface toward said a thermal insulator within said concentric annulus 
first surface, and adjacent a first end of said thermoplug; and 
a thermoplug extending from said first surface to said a back cover secured to said material specimen and 
second surface through said annulus with the sur- enclosing said thermoplug and said annulus and 
face of said thermoplug being spaced from the 35 adjacent said first end of said thermoplug. 
surface of said annulus thereby forming a annular 7. A plug-type heat flux gauge as recited in claim 6, 
chamber, said thermoplug being integrally formed 
from a portion of said member in said annulus so said thermal insulator is a gaseous medium. 
that said thermocouple is of the same material as 8. A plug-type heat flux gauge as recited in claim 1 
said member whereby no seam connects the same, x) wherein the means for covering the annular chamber 
at least three thermocouple wires extending into said comprises a back cover secured to the second surface. 
annular chamber from said second surface. each of 
at each of said predetermined points. 
comprising: 
wherein: 
* * * * *  
45 
50 
55 
60 
65 


Plug-type heat flux gauge

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