NASA/TM--1998-208809

Remote Heat Flux Using a Self Calibration

Multiwavelength Pyrometer and a

Transparent Material

Daniel Ng

Lewis Research Center, Cleveland, Ohio

November 1998

https://ntrs.nasa.gov/search.jsp?R=19990008950 2018-05-11T16:57:15+00:00Z
The NASA STI Program Office... in Profile

Since its founding, NASA has been dedicated to

the advancement of aeronautics and space

science. The NASA Scientific and Technical

Information (STI) Program Office plays a key part

in helping NASA maintain this important role.

The NASA STI Program Office is operated by

Langley Research Center, the Lead Center for

NASA's scientific and technical information. The

NASA STI Program Office provides access to the

NASA STI Database, the largest collection of

aeronautical and space science STI in the world.

The Program Office is also NASA's institutional

mechanism for disseminating the results of its

research and development activities. These results

are published by NASA in the NASA STI Report

Series, which includes the following report types:

TECHNICAL PUBLICATION. Reports of

completed research or a major significant

phase of research that present the results of

NASA programs and include extensive data

or theoretical analysis. Includes compilations

of significant scientific and technical data and

information deemed to be of continuing

reference value. NASA's counterpart of peerreviewed formal professional papers but

has less stringent limitations on manuscript

length and extent of graphic presentations.

TECHNICAL MEMORANDUM. Scientific

and technical findings that are preliminary or

of specialized interest, e.g., quick release

reports, working papers, and bibliographies

that contain minimal annotation. Does not

contain extensive analysis.

CONTRACTOR REPORT. Scientific and

technical findings by NASA-sponsored

contractors and grantees.

CONFERENCE PUBLICATION. Collected

papers from scientific and technical

conferences, symposia, seminars, or other

meetings sponsored or cosponsored by

NASA.

SPECIAL PUBLICATION. Scientific,

technical, or historical information from

NASA programs, projects, and missions,

often concerned with subjects having

substantial public interest.

TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific

and technical material pertinent to NASA's

mission.

Specialized services that complement the STI

Program Office's diverse offerings include

creating custom thesauri, building customized

data bases, organizing and publishing research

results.., even providing videos.

For more information about the NASA STI

Program Office, see the following:

• Access the NASA STI Program Home Page

at http:/lwww.sti.nasa.gov

• E-mail your question via the Internet to

help@sti.nasa.gov

• Fax your question to the NASA Access

Help Desk at (301) 621-0134

• Telephone the NASA Access Help Desk at

(301) 621-0390

Write to:

NASA Access Help Desk

NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076

i

_! J ii
NASA/TM--1998-208809

Remote Heat Flux Using a Self Calibration

Multiwavelength Pyrometer and a

Transparent Material

Daniel Ng

Lewis Research Center, Cleveland, Ohio

National Aeronautics and

Space Administration

Lewis Research Center

November 1998
NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Price Code: A03

Available from

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Price Code: A03

i:| | i i
RemoteHeatFluxMeasurement usingaSelfCalibrationMultiwavelengthPyrometer

andaTransparent Material

Introduction

Daniel Ng

NASA Lewis Research Center

A self calibrating multiwavelength pyrometer (Ref. I) was used to conduct remote heat flux measurements using a

transparent sapphire disk by determining the sapphire disk's front and back surface temperatures. Front surface

temperature (Tfs) was obtained from detection of surface emitted radiation at long wavelengths (_ > 6 ,am). Back surface

temperature (Tbs) was obtained from short wavelength (1 to 5 ,am) radiation transmitted through the sapphire disk. The

thermal conductivity _¢of the sapphire disk and the heat transfer coefficients h_ and h2 of its surfaces are determined

experimentally. An analysis of the heat flux measurement is presented.

Method and Experiment

Heat flux sensing is achieved using a sapphire disk and a thin layer of graphite paint deposited on one of the disk's

surfaces. The sensor is positioned at the opening of a black body furnace maintained at temperature Tb with the graphite

coated surface oriented to receive the radiative and convective heat fluxes from the furnace. The furnace temperature Tb

is measured separately by a thermocouple. During the experiment, the multiwavelength pyrometer spectrometer recorded

the spectra (Figure I) of radiation coming through the sapphire sensor in response to the temperature changes of the

black body furnace.

Because of the small thickness (two coatings using the application brush) of the graphite paint layer, its temperature is

assumed to be the same as that of the sapphire disk surface (Tbs) on which the graphite paint is deposited. The thermal

conductivity of the sapphire disk is 1¢.The heat transfer coefficients of the sapphire sensor surfaces are ht at the (hotter)

surface inside the black body furnace and h= at its other (colder) surface. The temperature at distances far away from the

front surface is T=.

Short and long wavelength radiation are detected by the heat flux sensor and recorded by the multiwavelength

pyrometer. The self calibrating pyrometer described in Ref. I is applied to determine the sapphire's back (Tbs) and front

(Tf_) surface temperatures. The availability of several radiation spectra at several different temperatures is crucial to a

successful determination of the sapphire surface temperatures without knowing the emissivity and transmissivity of the

elements in the optical path of the system.

The following heat flux equations are applicable during heat transfer taking place at the graphite paint interface:

K"

From Eqns. (1) and (2) we obtain by addition and elimination

e/,o(TJ 4 - T,4)+ h,(Tt,- Tb.,)= S S(Z,Th.,)d_" + h2(Tf., - T_ ) (3)

In these equations, 0 is the Stefan-Bo]tzman radiation constant, E:bis the graphite paint spectral emissivity, and t = 6

mm, is the thickness of the sapphire disk. S(_.,Tbs) is the radiation spectrum coming from the graphite paint and z_ is the

sapphire transmissivity in Eqn (5). The integral .[S(_.,ThDd_. in the equations contains the radiative heat flux transmitted

through the sapphire disk from the graphite paint surface, and is evaluated from the experimental spectrum numerically.

To a very good approximation, the black body furnace emissivity and graphite emissivity are very close to unity,

although in the pyrometric determination of temperature from the radiation spectra transmitted through the sapphire

disk, the exact values of graphite paint emissivity and the sapphire transmissivity are not necessary.

A commercial spectrometer/radiometer equipped with an indium antimonide/mercury cadmium telluride detector and

filter wheel monochromator for radiation from 1.3 to 14.5 .am was used to acquire the spectra in Fig. (1). The self

NASAFFM--1998-208809 I
calibratingfeatureof themultiwavelength pyrometerliminatedtheneedtoknowthegraphitemissivityandsapphire

transmissivityfortemperaturedetermination. ForallthespectrainFig.1,twowavelengths, _.t= 3.878pmand_,2= 5

gmwereselectedandthedataanalyzedaccordingto

A'(22)_-_ x(22,0)+ 1]_-I

z,

cl z_

Z'(_)_qf x(,,_, ,) + 1 -1

F c, -1

Y(t)-s(_'t)-E A'(_) c, ]_' ÷1 1

(4)

This equation is obtained from Eqn (12) of Re(. I, after replacing the quantities V(_,t) and A(X) by S(X,t) and A'(X) in

that equation according to

g,_

A'(Z)- A(Z) _ £.,tr_ (6)

ga

(7)

where S(K,t) is the spectrum intensity at wavelength _. at time t when the temperature is T(t), gz is the spectrometer

calibration constant. L(X,T(t)) is Planck's equation defined by:

cl 1

L(_t,T(t)) (8)

X _ (exp(c 2 //%T(,))-1)

c_ and Cz are the usual radiation constants, y(t) and x(t) are now the experimentally measured quantities. The quantity

A'(K2) = cx'cx is determined from these measured data at wavelengths L_ and K2 using statistical least square methods.

The resulting curve fitting is shown in Fig. 2.

After A'(X2) is determined, it is used to determine the back surface temperatures T(t) of all the spectra according to

c2 / _ (9)

r(t)= (A'(Z,) c, +,)

Because sapphire is not transmitting to radiation at wavelength longer than about 6 jam, the sapphire front surface

temperature is determined by fitting a Planck curve of temperature Tf_ to the radiation spectrum in this region. A

constant sapphire emissivity is used in the curve fitting. The result is shown in Fig. (3).

Heat Flux Results

The temperatures of the black body furnace and the sapphire disk front and back temperatures at which the experiments

were conducted are:

Table I. Measured Temperatures (K)

Blackbody 1329. I 1200,8 1079.1 961.9 85 ! ,9 746.9

Front Surface 730 645 570 505 455 410

Back Surface 904 776 673 587 516 459

¢

NASA/TM--1998-208809

i1 li
Eqn (1) is transformed into

T'4 t¢

- -h 1 (10)

,

To a good approximation, the emissivity inside the black body furnace and the emissivity of the graphite paint are safely

taken to be unity. The quantity on the left hand side is easily calculated because the integral can be evaluated

numerically from the measured spectrum. Some error may be introduced in the numerical integration because a

triangular approximation estimated the integral from zero wavelength to the shortest wavelength measured (an over

estimate), and a truncation occurred after the longest wavelength measurement (an under estimate). The left hand side

quantity is plotted against the quantity (Tt,s-Tfs)/(Tb-Tbs). The result is shown in Fig. (4), fitted by a straight line of slope

vdt = 0. ]05 and intercept -hi = -0.012.

Eqn (2) is equivalent to

-_,rlt) _ (ti)

Shown in Fig. (5) is a plot of Tbsagainst Tr, giving a straight line, whose slope is (l+h2/(ledt)) = 1.38 , the intercept is

-(hJ(r,./t))T. = -I 14. From the intercept and slope, we obtain T. = 300 K, which is room temperature. Because _l has

been determined from Eqn (10), we obtain h2 = 0.0399.

Eqn. (3) is rewritten to provide another estimate of hi and h2

ea(T;-Tb:)+ IearaL()_'Tb')d_" h (T,,-T.) (12)

(r0- "

The quantity on the right is plotted against (Tfs- T.)/(Tb-Tb0 to produce a straight line (Fig. (6)) of slope h2 = 0.038 and

intercept -h, = -0.01. The heat transfer coefficients h, and ha are in good agreement with the results determined from Eqn

(10) and Eqn (1 I). From the results of Eqn (10) and Eqn (11), 1¢= 6 Wm-IK -1, this is lower than the reported value of 15

to 30 Wm-lK -I. However the sapphire disk used is slightly yellowish in color.

The measured heat flux (el sensed by the sapphire/graphite paint is the sum of conductive and radiative contributions

given by

q=.( r - r,:,)+ I S(3. )d,_ (13)

The incident heat flux from the black body furnace: c(Tba-Tbs4)+ht(Tt,-Tb0, the quantity of Eq (13) and radiative heat

flux in the experiment are summarized in Table II. The columns represent values at different temperatures. The

maximum radiative heat flux contribution is less than 7.5 %.

Table II. Input, Measured and Radiative Heat Flux, (W/cm 2)

Input Heat Flux 18.1 14.0 10.6 7.9 5.9 4.4

Measured Flux 18.8 14.0 10.8 8.5 6.3 5.1

Radiative Flux 1.34 0.78 0.46 0.27 0.17 0.10

Radiative Flux (%) 7.4 5.5 4.3 3.4 2.8 2.3

Conclusion

A remote heat flux sensing is achieved using a transparent sapphire disk coated with a thin graphite layer. The total

conductive and radiative heat fluxes were measured. Under the measurement conditions, the dominant component is

conductive, with radiation comprising about 7 % of the total heat flux. The ambient temperature, the thermal

conductivity of the sapphire disk and the convective heat transfer coefficients of it surfaces were determined.

References

(1) Ng, Daniel, Self Calibration of a 2-wavelength Pyrometer, NASA/TM---1998-208808, 1998.

NASA/TM--1998-208809 3
RADIATION SPECTRUM

0.25 -

0.2o

j X

Z i _ .......

w ? ' .....

I-- 0.10 , ....-v . "_. z /

0.05 _ / .. ...- ..................... ".............. ..'--,

0.00: _ /," "........'"i .......... .... , .................. >_"::_':_-_ .... U0 2 4 6 8 10 12 14

WAVELENGTH, pm

16

Figure l

90 7

80 "

]

70

60-

I

507

>' 404

30

20 -,

10-

0 -;-- x-X

0

PLOT OF y(t) vs x(t)

X1 = 3.878 _m

X2= 5_m

=

!

_ X

I

20 40 60 80

x(t)

Figure 2

i

J

l

100

NASA/'_I--1998-208809

q I
0.01

_ _ t ...............

0.00 =............... 8 9

6 7

WAVELENGTH, _m

10 11

Figure 3

0.04 -

$ 0.03-

b

"2" 0.02-

"o

.O

t-- 0.01

if)

A.

h, & _/t DETERMINATION

0.00 -

-0.01 4/

-0.02 _ ............ 0.3 0.4

0 0.1 0.2

(Tb,-T_)/(Tb'Tb_)

Figure 4

NASArFM_I998-208809
1000

h2, r.jt & T=

DETERMINATION _.._

800 6OO _-_-

,_ 400

!-

200

0

-200 - , , , , , , , '

0 100 200 300 400 500 600 700 800

Tf,, (K)

Figure 5

h 1 & 5 2 DETERMINATION

0.03 - +

%-

0.02

,_ 0.01

t_

-0.01

0 0.2 0.4 0.6 0.8 1

(Tfs-To.)/(Tb-Tbs)

Figure 6

1.2

NASA/TM-- 1998-208809

':1 !_
Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188

Publicreportingburdenfor this collectionof informationis estimatedto average1 hour perresponse,includingthe timefor reviewinginstructions,searchingexistingdatasources,

gatheringandmaintainingthedataneeded,andcompletingand reviewingthecollectionof information.Sendcommentsregardingthis burdenestimateor anyotheraspectof this

collectionof information,includingsuggestionsfor reducingthisburden,to WashingtonHeadquartersServices,Directoratefor InformationOperationsand Repods,1215Jefferson

DavisHighway,Suite1204,Arlington,VA 22202-4302,andto the Officeof Managementand Budget,PaperworkReductionProject(0704-0188),Washington,DC 20503

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

November 1998 Technical Memorandum

4. TITLE AND SUBTITLE S. FUNDING NUMBERS

Remote Heat Flux Measurement Using a Self Calibration Multiwavelength

Pyrometer and a Transparent Material

;6. AUTHOR(S)

Daniel Ng

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

WU- 523-21 - i 3-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-11399

10. SPONSORING/MONITORING

AGENCY REPORTNUMBER

NASA TM-- 1998-208809

11. SUPPLEMENTARY NOTES

Responsible person, Daniel Ng, organization code 5510, (216) 433-3638.

12a. DISTRIBU_FION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category: 35 Distribution: Nonstandard

This publication is available from the NASA Center for AeroSpace Information, (301) 621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximurn 2OOwords)

A self calibrating multiwavelength pyrometer was used to conduct remote heat flux measurements using a transparent

sapphire disk by determining the sapphire disk's front and back surface temperatures. Front surface temperature (Tfs) was

obtained from detection of surface emitted radiation at long wavelengths (_, = 6 lam). Back surface temperature (Tbs) was

obtained from short wavelength (1 to 5 wn) radiation transmitted through the sapphire disk. The thermal conductivity t¢ of

the sapphire disk and the heat transfer coefficients h I and h 2 of its surfaces are determined experimentally. An analysis of

the heat flux measurement is presented.

14. SUBJECT TERMS

Heat flux; Pyrometer; Heat flux sensor

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

NSN 7540-01-280-5500

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

15. NUMBER OF PAGES

12

16. PRICE CODE

A03

20. LIMITATION OF ABSTRACT

Standard Form 298 tRey. 2-89)

Prescribed by ANSI Std Z39-1B

298-102
!t I Y-