A method of making a plug-type heat flux gauge in a material specimen in which a thermoplug is integrally formed in the specimen is disclosed. The thermoplug and concentric annulus are formed in the material specimen by electrical discharge machining and trepanning procedures. 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

Koch, John, Jr.

Liebert, Curt H.

English

NASA Technical Reports Server

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US005086204A 
United States Patent [191 [ i l l  Patent Number: 5,086,204 
Liebert et al. [45] Date of Patent: Feb. 4, 1992 
METHOD OF PRODUCING A PLUG-TYPE 
HEAT FXUX GAUGE 
Inventors: Curt H. Liebert, Middleburg Hts.; 
John Koch, Jr., Medina, both of Ohio 
Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. No.: 685,062 
Filed: Apr. 8, 1991 
Related U.S. Application Data 
Division of Ser. No. 531,433, May 31, 1990, Pat. No. 
5,048,973. 
Int. C l . 5  ............................................... B23H 9/00 
U.S. C1. ................................... 219/69.17; 374/29; 
40/703 
Field of Search ................. 219/69.15, 69.17, 69.2; 
408/1 R, 703; 374/29, 30; 29/592.1, 854, 868 
References Cited 
U.S. PATENT DOCUMENTS 
3,382,714 5/1968 Miller et al. .......................... 374/29 
4,386,248 5/1983 Inoue ................................ 219/69.17 
4,450,315 5/1984 Waterman .......................... 29/592.1 
4,477,687 10/1984 Finney ............................... 29/592.1 
4,500,234 2/1985 Orth et al. ........................... 408/703 
4,510,799 4/1985 Overmier .............................. 73/15] 
4,693,644 9/1987 Takahashi et al. .................. 408/703 
OTHER PUBLICATIONS 
Liebert et al., “Heat Flux Measurements”, NASA 
Technical Memorandum 101428, Jun. 4, 1989. 
Primary Examiner-Geoffrey S .  Evans 
Attorney, Agent, or Firm-Gene E. Shook; Harold W. 
Adam; James A. Mackin 
[571 ABSTRArn 
A method of making a plug-type heat flux gauge in a 
material specimen in which a thermoplug is integrally 
formed. The thermoplug and concentric annulus are 
formed in the material specimen by electrical discharge 
machining and trepanning procedures. The thermoplug 
is surrounded by a concentric annulus through which 
thermocouple wires are routed. The end of each ther- 
mocouple wire is welded to the thermoplug, with each 
thermocouple wire welded at a different location along 
2,818,490 12/1957 Dixon et al. ..................... 219/69.15 
3,232,113 2/1966 Malone .................................. 374/30 
the length Of the themoplug. 
3,372,588 3/1968 Ziemke et al. ........................ 374/29 5 Claims, 2 Drawing Sheets 
https://ntrs.nasa.gov/search.jsp?R=19920012795 2020-03-24T07:09:00+00:00Z
U.S. Patent Feb. 4, 1992 Sheet 1 of 2 5,086,204 
L L  
US, Patent Feb. 4, 1992 Sheet 2 of 2 5,086,204 
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5,086,204 
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Still another object of the invention is to provide an 
improved plug-type heat flux gauge that accurately 
measures transient and steady-state surface heat flux. 
Yet another object of the invention is to provide a 
5 method for easily producing an improved plug-type 
heat flux gauge that achieves the foregoing objects. 
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 
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 material, there is no seam between the 
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 to determine the uncertainty 
such a seam. 
length of the thermoplug in order to form hot junctions. 
The thermocouple wires are routed through the annulus 
25 to the rear of the specimen material, where they may be 
back may be welded to the back wall ofthe speci- 
men material, thereby enclosing the thermoplug and 
and trapping a thermal insulator, e.g., air 
METHOD OF PRODUCING A PLUGTYPE HEAT 
FLUX GAUGE 
ORIGIN O F  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 
or therefor. 
p ' ~ s e s  without the p a p e n t  Of any royalties thereon 10 specimen material using, for example, electrical dis- 
STATE O F  COPENDENCY 
This application is a division of application Ser. No. 
531,433 which Was fied May 31, 1990, now U.S. pat. 15 thermal plug and the active surface of the specimen 
No. 5,048,973. 
FIELD O F  T H E  INVENTION 
m e  present invention relates generally to methods of 
the production of plug-type heat flux gauges having 
material. 
producing heat flux gauges? and more particularly to 20 of heat flux measurement caused by the presence of 
themoplugs that are integrally formed into a The ends ofthermocouple wires are welded along the 
DESCRIPTION O F  T H E  RELATED ART 
reliable, accurate and easily built heat flux gauges. For 
example, heat flux gauges are needed to obtain transient 
and steady-state surface heat flux data for verification of 
models relating to heat transfer, durability and aerody- 3o the annulus and behind the thermoplug. 
quired to be accurate over wide ranges of heat flux is used to intermittently 
values 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 material and an electrode which includes a 
flux measurements on turbine blades utilized in space- 35 hole along its length. The specimen and the 
accurate measurements for surface heat flux values rent is applied, are emitted from the end of the 
varying from about 0.13 to 20 MW/m2 Over a tempera- electrode tube, detaching portions of the specimen ma- 
ture range of 100 to 1400 K. terial. The thermoplug is formed within the hole of the 
Water-cooled heat flux gauges are available for mea- 40 electrode, as the electrode descends into the specimen 
surement to about 10 MW/m2, but only at surface tern- material, thereby forming the thermoplug as an integral 
peratures that are maintained between 280 to 360 K. and unitary part of the specimen material. 
Also, water-cooled heat flux gauges tend to be rela- These and other features and advantages of the pres- 
tively 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 45 ence to the following detailed description and draw- 
narrow temperature range, water-cooled heat flux 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 DESCRIPTION OF THE 
dude  a thermoplug that is screwed or welded h t o  a 50 The accompanying drawings illustrate several as- 
specimen material having an active surface, creating a 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 in- 
This seam can introduce large discontinuities in surface ventions. 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 55 gauge according to the present invention; and 
uncertainty in the resulting heat flux measurements due 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. 
DETAILED DESCRIPTION O F  THE SUMMARY O F  T H E  INVENTION 
PREFERRED EMBODIMENTS 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. 65 plug 2 is integral with material specimen 3. Material 
Another object of the invention is to provide an im- 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 which may be small in size. Front surface 4 of material specimen 3 is exposed to an 
Recently, there has been increasing need for small, connected to larger diameter lead-wire assemblies. A 
namics. In many applications heat flux gauges are re- In a preferred method of making the invention elec- 
discharge 
craft, a heat flux gauge may be required to provide electrode are immersed in a dielectric fluid and, as cur- 
60 
5,086,204 
energy source, e.g., an arc-lamp for radiating incident 
thermal radiation 6. Thermoplug 2 is insulated on all 
surfaces except front surface 4 and, therefore, heat 
transfer within thermoplug 2 may be assumed one- 
dimensional. Concentric annulus 7 surrounds the sides 
of thermoplug 2. Because concentric annulus 7 is 
formed only partially through material specimen 3, a 
floor 8 of concentric annulus 7 is formed a finite dis- 
tance from front surface 4 of material specimen 3. Con- 
centric annulus 7 is formed into material specimen 3 
using any appropriate method, e.g., trepanning, electri- 
cal discharge machining 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 thermoplug 2 integral with material speci- 
men 3. The length of thermoplug 2 is taken as the dis- 
tance 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 electrical discharge machining appa- 
ratus 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, i.e., 
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 having been 
formed using electric discharge machining. Thus, plug- 
type heat flux gauge 1 according to the present inven- 
tion may be made relatively small compared with the 
size of conventional water-cooled heat flux gauges. 
Consequently, 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 heat ab- 
sorbed from front surface 4 of material specimen 3 to be 
4 
transferred nearly one-dimensionally along thermoplug 
2. 
The ends of thermocouple wires 11, e.g. Chromel- 
Alumel, are spot-welded along thermoplug 2 at various 
5 distances from front surface 4 of material specimen 3. 
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- 
10 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: 
15 
20 
SYMBOLS 25 
C,: specific heat at constant pressure, J /kg K 
L: length of thermoplug, cm 
q2: surface heat flux, MW/m2 
T temperature, K 
Z: thermocouple location along axis of axis of thermo- 
P:pdensity, kg/m3 
In this equation, 6T/6t is evaluated by differentiating 
35 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- 
45 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 
50 3. Lead wire assemblies 12 included Choromel-Alumel 
wires having a diameter of 0.01 5 cm encased in ceramic 
tubing. The ceramic tubing, in turn, was encased in 
Inconel sheath material to form an assembly. The diam- 
eter of each thermocouple wire 11 was 0.00762 cm. 
55 Each thermocouple wire 11 was spot-welded to ther- 
moplug 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 mate- 
rial specimen 3 was welded to the bottom of a hole 
60 drilled through floor 8 of concentric annulus 7 along a 
line parallel to and 0.100 cm from the centerline of 
thermoplug 2. The width of concentric 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 
65 three hot junctions were welded to thermoplug 2 and 
were circumferentially located 120" from each other. 
The thermocouple wires 11 were extended from the hot 
junction in a direction perpendicular to the surface on 
30 t: time, sec 
plug, m 
40 
5 
which they were welded, and then routed to lead 
assemblies 12. 
As shown in FIG. 2 satisfactory agreement in 
5,086,204 
6 
wire 
both 
disposed from said first surface away from said energy 
source, said method comprising the steps of 
removing material from said second surface of said 
transient and steady-state surface heat flux measure- 
ments between conventional water-cooled gauges and 5 
plug-type heat flux gauge 1 was obtained. An arc lamp 
was used as the energy source. The arc lamp start-up 
time period between about 0.3 and 0.7 seconds is de- 
fined in FIG. 2 as the region of transient heat flux, while 
the after about o.7 seconds is defined as the region of 10 
steady-state heat flux. The timing of these regions was 
confirmed with a photodetector that simultaneously 
measured an increase in millivolt output of the arc lamp 
which the photodetector output remained constant. 
The round and square symbols represent the mean of 
member in a circular groove thereby forming an 
annulus, 
forming a floor in said annulus at a Predetermined 
finite distance from said first surface thereby form- 
ing said thermoplug from the material of said mem- 
ber which extends from said first surface to said 
second surface with no seam between said thermo- 
plug and said member and said annulus encircling 
said thermoplug from said floor to said second 
surface, 
securing a plurality of thermocouple wires to said Of about to 54 MW at 0.3 to Oa7 (128 MV/sec) after 15 themoplug at predetermined distances 
from said frs t  surface, and 
covering said annulus and thermocouple wires. three repted m asurements taken with three =parate 
themocouple On each plug-typ heat flux 2. A method of producing a plug-type heat flux gauge as claimed in claim 1 wherein air is trapped in the annu- 
gauge l. The solid single line in the transient region 2o lus by a cover. 
represents the cubic least-squares curve-fit relative to a plug-type heat flux gauge 
1 0  transient heat flux data points taken with the con- as claimed claim wherein a groove is ma- 
the steady-state heat flux data is also shown in FIG. 2. 
ent invention will be apparent to those so skilled in the 
art and thus it is intended by the following claims to 
cover all modifications and adaptations which fall 
within the true spirit and scope of the invention. 
3. A method of 
ventiond water-cooled heat flux gauges. The mean Of chined in the second surface of the member by trepan- 
ning. 
4. A method of producing a plug-type heat flux gauge 
as claimed in claim 1 wherein the material is removed 
from the member by electrical discharge machining. 
5. A method of producing a plug-type heat flux gauge 
as claimed in claim 4 wherein a thermoplug having a 
30 diameter between about 0.1 cm and about 0.2 cm with a 
length between about 0.1 cm and 0.3 cm and an annulus 
with a width between about 0.03 cm and about 0.08 cm 
is formed in said member. 
Numerous modifications and adaptations Of the pres- 25 
What is claimed is: 
1. A method of producing a plug-type heat flux gauge 
with a thennoplug integrally formed in a member hav- 
ing a first surface exposed to an energy source which 
heats said member and a second surface oppositely * * * * *  
35 
40 
45 
50 
55  
65 


Method of producing a plug-type heat flux gauge

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