Apparatus is described for directly measuring the quantity square root of pck of a test specimen such as a wind tunnel model where p is density, c is the specific heat and k is the thermal conductivity of the specimen. The test specimen and a reference specimen are simultaneously subjected to the heat from a heat source. A thermocouple is attached to the reference specimen for producing a first electrical analog signal proportional to the heat rate Q that the test specimen is subjected to and an infrared radiometer that is aimed at the test specimen produces a second electrical analog signal proportional to the surface temperature T of the test specimen. An analog-to-digital converter converts the first and second electrical analog signals to digital signals. These digital signals are applied to a computer for determining the quantity

Corwin, R. R.

Creel, T. R., Jr.

Jones, R. A.

Kramer, J. S.

English

NASA Technical Reports Server

United States Patent 
Fletcher et al. 
[I11 4,027,524 
[45] June 7, 1977 
[ 541 APPARATUS FOR DETERMINING 
THERMOPHYSICAL PROPERTIES OF TEST 
SPECIMENS 
Inventors: James C. Fletcher, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Theodore R. Creel, Jr., 
Yorktown; Robert A. Jones, 
Newport News, both of Va.; Richard 
R. Convin, Xenia; Joseph S. Kramer, 
Dayton, both of Ohio 
[76] 
[22] Filed: Feb. 27, 1976 
[21] Appl. No.: 662,175 
[52] U.S. Ci. ............................................... 73/15 R 
[51] Int. CL2 ........................................ GOlN 25/18 
[58] Field of Search ................ 73/15 R, 15 A, 15 B 
[561 References Cited 
UNITED STATES PATENTS 
3,672,204 611972 Green .................................... 73/15 
3,789,654 211974 Jones ..................................... 73/15 
OTHER PUBLICATIONS 
Katayama et al., “Transient Comparison Methods of 
Simultaneous Measurement of Thermal Properties” in 
Bull JSME (Japan), vol. 12, No. 54, 1969, pp. 
1439-1447. 
Primary Examiner-Herbert Goldstein 
Attorney, Agent, or Firm-Howard J. Osborn; William 
H. King; John R. Manning 
[571 ABSTRACT 
Apparatus for directly measuring the quantity e 
of a test specimen such as a wind tunnel model where 
p is the density, c is the specific heat and k is the ther- 
mal conductivity of the specimen. The test specimen 
and a reference specimen are simultaneously subjected 
to the heat from a heat source. A thermocouple is 
attached to the reference specimen for producing a 
first $ectrical analog signal proportional to the heat 
rate Q that the test specimen is subjected to and an 
infrared radiometer that is aimed at the test specimen 
produces a second electrical analog signal proportional 
to the surface temperature T of the test specimen. An 
analog-to-digital converter converts the first and sec- 
ond electrical analog signals to digital signals. These 
digital signals are applied to a computer for determin- 
ing the quantity @by computing the quantity 
b 2 \ F ; -  
T - T ,  
where Ti is the initial test specimen temperature and t 
is the elapsed time from the time that the specimens 
were first subjected to the heat source. 
7 Claims, 1 Drawing Figure 
23 
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US. Patent June 7, 1977 4,027,524 
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ORIGIN OF THE INVENTION 
4,027,524 
1 
applied to the specimens. The two analog signals are 
converted to digital signals by means of an analog-to- 
digitzl converter and applied to a computer along with 
a signal from the microswitch. The computer then cal- 
5 culates the quantity in accordance with equa- 
tion (1).  A water filter is located between the heat 
Source and the specimens to absorb all wavelengths 
larger than about 1.8 microns. 
BRIEF DESCRIPTION OF THE DRAWING 
The sole FIGURE in this application is a combination 
schematic block diagram of the embodiment of the 
invention selected for illustration. 
The invention relates to apparatus for directly mea- 
suring the quantity - of a test specimen where p is 15 DETAILED DESCRIPTION OF THE INVENTION 
the density, c is the specific heat and k is the thermal Turning now to the embodiment of the invention 
selected for illustration in the drawing, the numeral 11 conductivity of the specimen. 
~ ~ s v ~ ~ ~ l , ' , e , c , " ~ h ~  ti. ~~~~~nf,,',",e,~~$~ designates a sample holder having sidewalls 12. A test specimen 13 and a reference specimen 14 are located 
2O within the sample holder 11. Reference specimen 14 is previous technique consists of using a model made from a low thermal conductivity material covered with 
a phase-change coating which is an accurate surface made from 'OWer and has a l5 attached 
temperature indicator. This indicator called to it on its lower side for producing an analog signal 
pilaq" consists of wax crystals which melt at a pre- proportional to the change in temperature of the 
scribed melting temperature. If the model is heated, the reference specimen 14. This analog signa1 is to 
coating will melt when the surface reaches a calibrated 25 an anab-to-dkital converter 16. A Plurality of tung- 
phase-change temperature. Knowing this melt temper- Sten filament h'lpS 17 with reflectors 18 are mounted 
ature, the time to reach the melt temperature from the imide the sample holder to Provide a radiant heat 
initial temperature, and the heating rate, the combina- Source having a temperature of 5000" F. A water- 
tion of thermophysical properties - is determined cooled shutter 19 is mounted in sample holder 11 SO 
from the equation: 30 that it can be inserted or removed from between the 
heat source and the specimens. A microswitch 20 is 
located underneath the shutter and is tripped just as the 
shutter passes over the region of specimen 13. 
An infrared radiometer 25 is aimed onto the surface 
35 of the test specimen 13 through an opening 26 in the 
walls of the sample holder for producing an analog 
signal proportional to the surface temperature of test 
specimen 13. Infrared radiometers for providing this 
function are commercially available and can be, for 
APPARATUS FOR DETERMINING 
THERMOPHYSICAL PROPERTIES OF TEST 
SPECIMENS 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 10 
85-568 (72 Stat. 435; rw USC 2457). 
BACKGROUND OF THE INVENTION 
( 1  ) 
where Q is the imposed heating rate, T I  is the initial 
model temperature Prior to heating, T is the melting 
temperature and t is the elapsed time from the onset of 
heating until melting occurs. 
In this prior technique a camera was used to record 
surface temperature as indicated by the 
Some Of the dis- 
example, a model n -7A infrared thermometer, manu- 
factured by Barnes Engineering Company. The output 
voltage swing for this device, from 0 to 5 volts, spans 
the 
melting Of the phase-change 
not photograph the sample at the exact time the phase- 
advantages of this technique are that the camera may the temperature range of to 5000 F. The infrared 
measure the temperature over a 0.4-inch target spot at change coating melts; the exact time of phase transition 45 is often difficult to interpret visually; the sample and a distance of 2o inches. Aiming and focusing of the 
to be coated with the phase-change coating; and the in-line through-the-lens viewing. By focusing the objec- results may not be known for several days because of 
delays in photoprocessing and strip ,-hart reading. 50 tive lens, a reticle in the eyepiece indicates to the ob- 
It is the primary purpose of this invention to provide server the precise region of the specimen where tem- 
apparatus for directly measuring the quantity of perature is to be measured. The output of radiometer 
a test specimen that eliminates disadvantages encoun- 25 is applied to analog-to-digital converter 16. 
tered in the measuring technique disclosed in U.S. pat. Since the radiant heat source will be at a temperature 
No. 2,789,654. 55 of 5000" F., it will emit a considerable amount of radia- 
tion over the passband of the infrared radiometer. The 
SUMMARY OF THE INVENTION envelopes of the heating lamps are made of high tem- 
In the present invention a test specimen such as a perature quartz which consist almost entirely of silica. 
model and a reference specimen are simultaneously These materials absorb much of the radiation at wave- 
subjected to the heat from a heat source. A thermo- 60 lengths larger than 5 microns. 
couple is attached to the reference specimen for pro- The absorbed radiation will raise the quartz envelope 
ducing a first analog signal proportional to heating rate temperature considerably higher than the lowest tem- 
Q. An infrared radiometer aimed at the surface of the perature to be measured by the radiometer. The quartz 
test specimen produces a second analog signal propor- envelopes will then reradiate at relatively long wave- 
tional to surface temperature T. A water-cooled shutter 65 lengths extending over the passband of the radiometer. 
is used to simultaneously subject the specimens to the Although the reflectance of the target specimens are 
heat source. A microswitch on the underneath side of small (less than 5%) at these wavelengths and both the 
the shutter is tripped at the instant the heat source is quartz envelopes and the target specimens are diffuse 
thermometer lens has a field-of-view of 0.7" which will 
calorimeter must be taken Out Of the apparatus in Order radiometer Onto the area of interest is accomp~ished by 
4,027.524 
3 
radiators and reflectors, this reradiated energy never- 
theless can represent a significant noise source to the 
radiometer. 
To eliminate this noise source a water absorption 
filter 21 is mounted just above the shutter 19 between 
the specimens and the heating lamps 17. Water filter 21 
consists of two parallel glass plates with water flowing 
between them. The water will absorb all wavelengths 
larger than about 1.8 microns including radiation 
within the spectral passband of the radiometer. The 
water to filter 21 is supplied by a pump 22 from a water 
supply 23. The water to shutter 19 is supplied by a 
pump 24 from water supply 23. 
The two analog signals applied to analog-to-digital 
converter 16 are converted to digital signals which are 
applied to digital computer 27 that computes the quan- 
tity @ in accordance with equation ( 1 ). After 
computation of the heating rate, sample temperature, 
elapsed time and the quantity are printed by a 
teleprinter 28. 
There are many analog-to-digital converters and 
computers which will perform the function provided 
for by analog-to-digital converter 16 and computer 17. 
One such analog-to-digital converter is the Adacus 11-S 
manufactured by Sun Systems, Inc., and one such com- 
puter is Hewlett Packard Model 2 1 OOA computer, two 
Model 12566A Duplex Registers, and one Model 2752 
Buffered Teleprinter Input-Output with 1253 1 b Inter- 
face Kit. The 2 1 OOA is a general digital computer with 
4096 words of core memory designed for a wide range 
of small computer applications. In this application it 
provides intermediate storage for the digitized temper- 
ature and heating rate data, as well as the correspond- 
ing time word; means for linearizing the inherently 
nonlinear output of the infrared thermometer; scaling 
of both signals in terms of degrees F and Btu/ft2/sec for 
the computation of and the control and format- 
ting so that tem erature versus time, heating rate ver- 
sus time and & versus time can be listed on the 
teletype. 
The 12566A Duplex Registers provide the required 
circuitry for interfacing the Two Channel Data System 
with the computer. 
The 2752 Buffered Teleprinter Input/Output pro- 
vides the means for operator communication with the 
computer. This communication can take the form of 
commands or instructions entered through the key- 
board or paper tape reader by the operator, or printed 
output from the computer to the operator. 
In the operation of this invention with the shutter 19 
closed and water passing through the shutter, the lamps 
17 are turned on and the radiometer 25 is aimed in the 
direction of specimen 13. The shutter is then opened 
which trips microswitch 20 sending a signal to the com- 
puter telling it that the computing time is to start. This 
signal telling the computer that the computing time is 
to start could be supplied by other means such as a 
manually op-erated switch. The thermocouple 15 then 
produces an analog signal proportional to the rate of 
change of the temperature of reference specimen 14. 
Infrared radiometer 26 produces a signal proportional 
to the surface temperature of test specimen 13. These 
two analog signals are converted to digital signals by 
means of analog-to-digital converter 16 and applied to 
computer 27 which computes the quantity in 
accordance with equation ( 1 ). The quantities 
heating rate, sample temperature and elapsed time are 
then printed out by teleprinter 28. 
The advantage of this invention is that the quantity 
is measured directly on the specimen or model 
4 
under transient conditions consistent with those experi- 
enced by the model in a wind tunnel. Just as important 
is the fact that thermophysical property data can be 
determined quickly and easily, expediting the analysis 
5 of wind tunnel results. (Seven minutes from initiation 
of the test, is printed by the teleprinter). Also, 
the sample and calorimeter are not removed from the 
apparatus between tests, thus different heating rate 
tests may be applied with little waiting time between 
data are obtained for a num- 
ber of different surface temperatures from a single test 
whereas with the previous method one test was re- 
quired for each sample surface temperature of interest. 
What is claimed is: 
1. Apparatus for directly measuring the quatity 
-of a test specimen where p is the density, c is the 
specific heat and k is the thermal conductivity of the 
specimen comprising: 
10 tests. In addition, 
15 
a reference specimen; 
means for simultaneously subjecting said test speci- 
men and said reference specimen to said heat 
source; 
means attached to said reference specimen for pro- 
ducing a first electrical analog signal proportional 
to the heating rate Q that said test specimen is 
subjected to; 
infrared radiometer means aimed at said test speci- 
men for producing a second electrical analog signal 
proportional to the surface temperature T of said 
computer means receiving said first and second ana- 
log signals for calculating - in accordance 
with the equation: 
2o a heat source; 
25 
30 specimen; and 
35 
where Ti is the initial test specimen temperature and 
t is the elapsed time from the time that the speci- 
mens are subjected to the heat source. 
2. Apparatus according to the claim 1 wherein said 
means for simultaneously subjecting said test specimen 
and said reference specimen to said heat source in- 
45 cludes a water-cooled shutter that shield the test and 
reference specimens from the heat source until the 
shutter is moved. 
3. Apparatus according to claim 1 including a water- 
absorption filter located between the heat source and 
50 said specimen to filter off radiation with wavelengths of 
about 1.8 microns and above. 
4. Apparatus according to claim 3 wherein said wa- 
ter-absorption filter is two plates of glass with running 
water inbetween. 
5. Apparatus according to claim 1 including a micro- 
switch attached to said shutter for applying a signal to 
said computer the instant the specimens are subjected 
to the heat source. 
6. Apparatus according to claim 1 wherein said com- 
60 puter means includes an analog-to-digital converter for 
converting said first end second analog signals to digital 
signals and a digital computer receiving the digital 
signals. 
7. Apparatus according to claim 1 including a tele- 
65 printer means for printing the results of the tests in 
terms of *time, and Q immediately after comple- 
tion of a test. 
40 
55 
* * * * *  


Apparatus for determining thermophysical properties of test specimens

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