NASA Technical Memorandum 102322

Total Hemispherical Emittance Measuredat High Temperatures by theCalorimetric Method

Frank DiFilippo

Case Western Reserve University

Cleveland, Ohio

Michael J. Mirtich and Bruce A. Banks

Lewis Research Center

Cleveland, Ohio

Curtis Stidham and Michael Kussmaul

Cleveland State University

Cleveland, Ohio

Prepared for the

16th International Conference on Metallurgical Coatings

sponsored by the American Vacuum Society

San Diego, California, April 17-21, 1989

TOTAL HEMISPHERICAL EMITTANCE MEASURED AT HIGH TEMPERATURES

BY THE CALORIMETRIC METHOD

Frank DiFilippo*Case Nestern Reserve University

Cleveland, Ohio 44106

Michael J. Mirtich and Bruce A. BanksNational Aeronautics and Space Adminlstration

Lewis Research CenterCleveland, Ohio 44135

Curtis Stidham and Michael Kussmau!

Cleveland State UniversityCleveland, Ohio 44115

C_t_

!L_

ABSTRACT

A calorimetric vacuum emissometer (CVE) capable of measuring total hemi-spherical emittance of surfaces at elevated temperatures was designed, built,and tested. Several materials with a wide range of emittances were measuredin the CVE between 773 to 923 K. These results were compared to values calcu-lated from spectral emittance curves measured In a room temperature Hohlraumreflectometer and in an open-air elevated temperature emissometer. Theresults differed by as much as 0.2 for some materials but were in closer agree-ment for the more highly-emitting, diffuse-reflecting samples. The differ-ences were attributed to temperature, atmospheric, and directlonal effects,and errors in the Hohlraum and emissometer measurements (±5 percent). Theprobable error of the CVE measurements was typlcally less than 1 percent.

INTRODUCTION

Some proposed space power systems (solar dynamic and nuclear, forexample) will require large radiators for waste heat rejection. The mass andsize of the radiators will be minimized by using a material with a high ther-mal emittance. The goal for the SP-IO0 system radiators (fig. I) is a totalemittance of 0.85 or better at an operating temperature of 700 to 900 K.

Many methods, such as sandblasting (ref. l), ion-beam discharge chamber

texturing (ref. 2), and carbon arc electrical discharge texturing (ref. 3),have been used at NASA Lewis Research Center to achieve high emittance. Spec-

tral emittance measurements between 1.7 and 14.7 _m have been made at room tem-perature using the Hohlraum reflectivity attachment of a Perkin-Elmer Model 13

spectrophotometer and at elevated temperature (900 K) using the emissivity

attachment (ref. 4). The total emittance was then calculated by normalizing

the spectral emittance to the blackbody radiation distribution function at the

desired temperature.

*Summer Intern at NASA Lewis Research Center.

Although these methods have been used by many experimenters to calculate

total emittance (ref. 5), the values obtained may not be equal to the total

hemispherical emittance at elevated temperature. The spectral emittance of

materials can be temperature dependent. For example, the Hagen-Rubens rela-

tion states that the spectral emissivity of metals is proportional to the

resistivity to the one-half power for wavelengths longer than about 5 um

(ref. 6). Hence, the spectral emittance of pure metals can be expected to

increase with temperature, along with the resistivity. Other factors which

affect the spectral emlttance are surface chemistry and morphology, which often

change as a result of heating to 900 K in a reactive atmosphere such as air

(ref. 4). Additionally, there may be problems with directional effects. The

Hohlraum attachment measures hemispheric-angular spectral reflectance, and the

emissivity attachment measures normal spectral emittance, neither of whichmeasures total hemispherical emittance.

An instrument which actually measured total hemispherical emittance with-

out being subject to the above complications was the calorimetric vacuum emis-

someter (CVE). By conducting high temperature measurements under vacuum with

the sample surface radiating hemispherically, the effects of temperature, sur-

face chemistry, and directionality were minimized, yielding results more compa-

rable to those expected in space. Total emittance measurements for materialswith a wide range of emittances were measured using the CVE, the Hohlraumreflectometer, and the emissometer. The measured total emittance values are

presented and compared along with an evaluation of the relative uncertainties.

APPARATUS AND PROCEDURE

The CVE used in this experiment originally had been designed to measure

total emittance of 5.1 by 5.1 cm (2 in. by 2 in.) samples at 323 to 423 K by

means of a heat flux transducer (ref. 7). The sample holder and heater needed

to be redesigned in order to make measurements at temperatures between 700 to

900 K, but the remaining components of the instrument were unchanged. The

vacuum chamber and pump system for the CVE are shown in figure 2. The systemconsisted of a mechanical pump and diffusion pump which enabled pressures of

about 5xlO-5 tort to be reached in about 2 hr. A cylindrical blackbody cavity

cooled with liquid nitrogen was supported inside the vacuum chamber. Two type

T thermocouples were used to monitor the temperature of cavity and the liquidnitrogen exit port. The base pressure was typically 5xlO -7 torr when the cavity

was cooled with liquid nitrogen. The interior of the cavity was coated with

3M Nextel Black Velvet paint, which has an emissivity of about 0.95. The emis-

sivity of the cavity (40 cm long, 15 cm diameter) was calculated to be about

0.998 by the method of Gouff_ (ref. 8).

A photograph of the redesigned sample holder for the CVE is shown in fig-

ure 3. A cutaway drawing of the sample heater/holder is shown in figure 4.

There were two main components of the sample heater/holder: the heat shield

and the sample mount plate. The heat shield was a 8.26 cm (3.25 in.) long,

4.45 cm (1.75 in.) diameter copper cylinder with swaged nichrome heater wire

(l.O mm (0.040 in.) diameter) coiled around and brazed to the cylinder. Cop-per wire leads connected the heater Wife to a Kepco 36 V, 8 Adc power supply.

Two l.O mm (0.040 in.) diameter swaged type K thermocouples were peened into

the heat shield to measure the temperature at both the front and back. The

sample mount plate (fig. 5) was a hollowed copper disk, 22.2 mm (0.875 in.) indiameter and 6.4 mm (0.250 in.) thick. A 1.0 mm (0.040 in.) diameter swagedtype K thermocouple was peened in the center of the sample mount plate, and a1.0 mm (0.040 in.) diameter swaged nichrome heater wire was brazed to theinside of the plate. The nichrome wire was terminated inside the sample mountplate, and 0.5 mm (0.020 in.) diameter copper wire leads were attached to thenichrome wire with 0.5 mm (0.020 in.) diameter copper connectors. The copperleads were insulated with ceramic beads and were coiled inside the heat shieldto improve thermal contact. A Kepco 25 V, 20 A dc power supply was used forheating the sample mount plate. The back side of the sample mount plate wascovered with three 0.25 mm (0.010 in.) thick tantalum disks, which served asradiation shielding. The entire sample holder assembly was mounted to the

flange of the vacuum chamber by means of two 6.4 mm (0.25 in.) diameter stain-

less steel rods. The flange also contained several feedthroughs to which the

heater leads and thermocouple leads were connected.

The sample holder was designed for samples which could also be used inthe Hoh]raum reflectivity attachment and the emissivity attachment of a Perkin-Elmer Model 13 spectrophotometer. The samples were 2.38 (15/16 in.) to 2.54 cm(1 in.) diameter disks with thicknesses ranging from 0.4 mm (0.015 in.) to1.9 mm (0.075 in.). The sample temperature was measured with a 0.25 mm(0.010 in.) dlameter swaged type K thermocouple which was peened to the backside of the sample through a milled groove (fig. 6). Carbon paint was used tobind the sample to the sample mount plate to Improve therma] contact. Beforemounting, the back side of the sample and the front side of the sample mountplate were coated lightly with GC Electronics Television Tube Koat carbonpaint and allowed to dry. Afterwards, more carbon paint was applled to thesample mount plate, and the sample was placed on top of the plate and held inplace for about 1 min unt11 the paint was dry enough to hold the sample. Thethermocouple lead was wrapped around the heat shield twice before it was con-nected to the flange. The sides and front of the heat shield were coveredwith two sheets of tantalum foll radiation shielding to reduce the power neededfor heating. A tantalum foil ring was placed around the sample and samplemount plate; the ring was made wide enough so that the sides of the samplecould not be seen, preventing radiation from the sample edge. The sample andsample mount plate were held lightly in place with four 0.5 mm (0.020 in.)diameter stainless steel prongs. Figure 7 shows a photograph of a properlymounted sample.

After high vacuum (

THEORY

A schematic of the experiment is shown in figure 8. The heated samplewas allowed to radiate hemispherically to the cavity so that an equilibriumtemperature was established. The current and resistance for the sample mountplate heater were measured, and the total power input to the sample could thenbe calculated. The experiment was designed to virtually eliminate all otherforms of power dissipation besides radiation to the cavity. Much of this goalwas accomplished by using the heat shield, which was maintained at the sametemperature as the sample mount plate. Afterwards, the total hemisphericalemittance could be calculated from the Stefan-Boltzmann radiation law.

Figure 9 illustrates the possible sources of heat generation and dissipa-tion from the sample and sample mount plate. Mathematically, the heat flowscan be expressed by the following heat balance equation"

where

Oel

+ mC ('dT]Oel + Qabs = Qrad + Qcond p\d'_/

power introduced by the sample mount plate heater

(1)

Qabs power gained by the absorption of radiation

Qrad power lost by radiation

Qcond power lost through thermal conductlon

mCp(dTldt) power causing a temperature change in the sample and sample mount

plate (m = mass, Cp = heat capacity, T = temperature, t = time)

The Qrad and Qcond terms on the right side of the equation (I) each

consist of several individual terms. Power could be radiated by the front

surface of the sample to the cavity (Qrad,f), by the sides of the sample and

the sample mount plate (Qrad,s), and by the back side of the sample mount

plate (Qrad,b)"

Qrad = Qrad,f + Qrad,s + Qrad,b (2)

During the experiment, the sample mount plate and the heat shield were kept atthe same temperature to prevent heat transfer between them, but the sample wasI0 to 40 K cooler than the heat shield. The tantalum foil ring around the sam-ple served as radiation shielding, minimizing radiation heat transfer throughthe sides of the sample. The tantalum disks behind the sample were needed tocover the hole in the back of the heat shield in order to minimize radiationheat transfer through the back of the sample mount plate. Hence, equation (2)reduces to:

Qrad = Qrad,f (3)

Thermal conduction losses could occur through the heater leads (Qc,h),through the sample thermocouple (Qc st), through the sample mount plate thermo-

couple (Qc pt), through the prongs used to mount the sample (Qc,p), andthrough air-conduction (Qc,a):

Qcond : Qc,h + Qc,st + Qc,pt + Qc,p + Qc,a(4)

All of these conduction losses were madenegligible by the experimental design.The heat shield was used as a heat barrier for the sample mount plate so thatthermal conduction losses would originate from the heat shield instead of thesample mount plate. The copper heater leads were coiled inside the heatshield to improve thermal contact, therefore minimizing Qc h. Qc st wasmadenegligible by using a small diameter thermocouple and _y wrapping thelead around the heat shield. Qc,pt was minimized by passing the thermocouplelead through the center of the heal shield. _ was negligible because theprongs were in good thermal contact with the ._ shield (clamped down withset screws) and were in poor thermal contact with the sample (just resting onthe surface). The last term, Qc a, was negligible because experiments wereperformed at 10-6 torr. In short, equation (3) was reduced to:

Qcond = 0 (5)

simply by the experimental design.

Combining equations (I), (3), and (5) yields"

- + mC #dT_Qel = Qrad,f Qabs p\d-tY (6)

Since measurements were made at equilibrium, dT/dt = O, and"

Qel = Qrad,f - Qabs (7)

The power dissipated by the sample mount plate heater, Qel, could be easilycalculated from the equilibrium current (I) and the measured electricalresistance (R)"

Qel = 12R (8)

The radiative power emitted (Qrad,f) and absorbed (Qabs) by the sample areexpressed by the Stefan-Boltzmann radiation law:

Qrad,f = Cs_coATs4 (9)

Qabs = _scc°ATc 4 (I0)

where

CS

mS

CC

_C

A

total emittance of the sample

total absorptance of the sample

total emittance of the cavity

total absorptance of the cavity

Stefan-Boltzmann constant = 5.6703xi0 -12 W-cm-2-K -4

sample area (cm 2)

Ts sample temperature (K)

Tc cavity temperature (K)

By using the above relationships and Kirchoff's law (spectral emittance :spectral absorptance), equation (7) becomes"

12R : CsccoA(T_ -T_) (II)

The cavity was cooled with liquid nitrogen, and the sample temperature was

high enough so that T_ >> T_. Also, it was shown previously that the cavity

was nearly a perfect blackbody, with a total emittance _c very close to uni-

ty. Using these facts, the total hemispherical emittance could be calculated

directly from:

12Rc s - (12)

aAT 4S

UNCERTAINTIES

The total fractional random uncertainty was calculated was from:

(13)

The current was measured across a shunt by a millivoIt meter and had a proba-ble error of 0.2 percent. Resistance was measured as R = V/I; hence, &R/R =

[(aV/V) 2 + (AI/I)2] ]/2, with a probable error in the voltage measurement of

0.06 percent. The sample area was calculated as"

_d 2A - 4(0.01) (14)4

where d was the sample diameter in centimeters. The second term (0.04 cm2)was the total area covered by the four wire prongs, with each prong covering 1mm2; the estimated uncertainty in this term was ±O.Ol cm2. The diameter was

measured with digita] calipers, having an uncertainty of =0.005 cm The I_ta]uncertainty in the area was therefore: &A/A = [2(0.005/d) L + (O.Oi/A)2] I

The temperature was measured with a Doric Trendicator 400 A digital meter withan accuracy of ±] K. In order to evaluate the last term of equation (13), theheat capacity of the sample and sample mount plate were needed. The product

mCp was estimated at room temperature by measuring the power input and timefor a 20 K increase in the sample mount plate temperature and was found to be4.8 J-K -I. From this result, it was found that the time required for a 1 Ktemperature increase with an excess power of 0.01W was 8 min. Hence, 8 minwas taken to be a sufflcient equilibrium time for the experiment. The finalexpression for the total random uncertainty was thus:

:_3(0.002) 2 + (0.0006)

There were many terms in equations (2) and (3) which were neglected.Most of the conductlon terms (Qc h, Qc,st, and Qc p) were negligible to firstorder because the objects involved were in good thermal contact with the heatshield, which was at the same temperature as the sample mount plate. The ther-mocouple lead for the sample mount plate was not in good thermal contact withthe heat shield, and Qc nt was a possible source of systematic error. Thepower conducted by the t_rmocouple lead was estimated to be 0.02 W under theassumption that there was no heat exchanged with the heat shield; thus, thefractional error resulting from the conduction losses was no more than

(0.02/12R). The air conduction term, Qc,a, was completely negligible underhigh vacuum. For a pressure of 5xlO-6 torr, the power lost by air conductionwas on the order of lO-4 W (ref. 7). Among the radiation terms of equation

(2), Qrad_b_ was completely negligible to first order because the heat shieldwas at same temperature as the sample mount plate and because the opening

for the thermocouple and heater leads was very small. There was a significant

systematic error from Qrad,s, however. The sample temperature was often con-siderably lower than the sample mount plate temperature (up to 40 K). Assum-

ing the foil shielding was at the same temperature was the heat shield, the

power absorbed by the sides of the sample was CecfoAs(T_s - T_), where c e

and cf were the emittances of the edge and the foil (estimated to be 0.3 and0.I, respectively) and As was the area of the sample edge. The total frac-tional systematlc error was therefore:

__ Qc,st + Qrad,sI2R

• + . )oA s Th_0 02 (0 3)(0.1 I -T4s)

12R

(16)

Combining the results from equations (15) and (16) yielded the total frac-

tional probable error for the experiment'

(17)

Figure I0 illustrates the dependence of the error on the emittance and tempera-ture of the sample. For high-emitting samples, the fractional error 16c/el

was smallest (0.6 percent) but the absolute error 6c was largest (0.007).

On the other hand, the low-emitting samples had the largest fractional errors

(3 percent) and the smallest absolute errors (O.OOl). The errors were also

smaller at higher temperatures. Since the candidate radiator materials to be

tested will have high emittances, the CVE measurements will be fairly accurate

(< l percent) in comparlson to Hohlraum and open-air emlssometer measurements.

RESULTS AND DISCUSSION

Total emittance measurements were made for eight different samples havinga wide range of emittances. For each measurement, there was a differencebetween the sample temperature and the sample mount plate temperature. Fig-ure 11 shows a plot of the sample temperature versus the sample mount platetemperature for each sample. The high-emitting samples tended to have largertemperature differences than the low-emitting samples because more power hadto be conducted through the carbon paint barrier. However, there was no con-slstent relationship between the emittance and the temperature difference. Inorder to accurately determine the sample temperature, a thermocouple wasdirectly attached to the back of the sample. Attaching the thermocoupleinvolved considerable time and effort and also involved the possibility of dam-aging the sample surface. The experiment could be done more quickly but lessaccurately if a thermocouple was not attached to the sample. The sample tem-perature would instead be estimated from figure II and from the emittance,which could be calculated by Iteration. This method would work best for Iow-emitting materials because the temperature difference would be small.

The total hemispheric emittance results from the CVE and the derivedhemispheric-angular Hohlraum reflectometer measurements are plotted in fig-ure 12. For plasma-sprayed alumina (fig. 12(a)), the CVE and Hohlraum resultsagreed to within O.Ol. However, the results from the two instruments did notagree as well for the other materials. The total emittance measured by theCVE was consistently higher than that measured by the Hohlraum reflectometerfor the remaining seven samples (figs. 12(b) to (h)). This was to be expec-ted, since the CVE measured total hemispherical emittance, and the Hohlraummeasured hemispheric angular emittance. With the exception of the black paintsample (fig. 12(e)), the difference between the results was smaller for thehigh-emitting samples (figs. 12(b) to (d)) than for the low-emitting samples(figs. 12(f) to (g)). This result is not surprising since the high emittancesamples had more diffuse reflectances, therefore their emittance values meas-ured in the Hohlraum reflectometer would be closer to a total hemisphericalmeasurement (ref. 6).

The differences between the results can be attributed in part to errorsin the spectral reflectance measurements made by the Hohlraum reflectometer.The uncertainties in the CVE measurements were small (typically less thanI percent); on the other hand, the uncertalnty for the Holraum reflectometerwas much larger (5 percent) (ref. 9). The Hohlraum reflectometer was espe-cially inaccurate for measuring emittances of polished metals. Emittance val-ues of -0.02 for polished stainless steel (fig. 12(h)) and -0.08 for polishedcopper (fig. 12(g)) were obtained. These results indicated that the Hohlraumwas measuring reflectances greater than unity, which would result from nonuni-form temperatures in the Hohlraum's heated cavity. The samples were held in awater-cooled sample holder and were positioned at the top of the cavity, andit was likely that the top of the cavity was cooler than the bottom. If thiswere the case, the reference beam originating from the top of the cavity wouldbe less intense than the reflected radiation originating mainly from the bottomof the cavity, resulting in a higher measured reflectance and a lower calcula-ted emittance. This would explain the fact that the total emittance measuredby the Hohlraum was lower than that measured by the CVE, especially for thesamples with low emittance. The only exception was the plasma-sprayed aluminasample (fig. 12(a)), but the spectral emittance of this material is known todecrease significantly at higher temperatures (ref. I0).

Onearea of agreement for the CVEand Hohlraum total emittance measure-ments was the temperature dependenceof the results. The slopes of the totalemittance versus temperature data from the CVEand the Hohlraum agreed for allmaterials tested, except for a slight difference for sandblasted Nb (I percentZr) (fig. 12 (d)). All materials tested except for plasma-sprayed alumina(fig. 12(a)) showedan increase in total emittance with temperature.

Total emittance as a function of temperature was also obtained for plasma-sprayed alumina and high temperature black paint by normalizing the spectralemittance measuredat elevated temperature (873 K) in air using the emissome-ter attachment. These data are shown in figure 13, along with emittance meas-urements from the CVEand the Hohlraum. For the plasma-sprayed alumina, therewas close agreementbetween the CVEand emissometer. The emittance valuesdiffered by no more than 0.02. Oxidation was a problem whenever elevated tem-perature measurementswere madein air (ref. 4). Onewould not expect thisproblem for the plasma-sprayed alumina, which was already oxidized. To elimi-nate the oxidation effect for the black paint sample, the emissometer measure-ments were done before the CVEmeasurementsin order to insure that the samplewas fully oxidized in both cases. The surface texture for the plasmasprayedalumina wasvery rough in comparison to the black paint, and the alumina wasmore likely a dlffuse reflector than the black paint. The black paint samplewould therefore exhibit directional effects to a greater extent, and thiscould explain the differences between the CVEand emissometer measurements.Also, temperature effects were confirmed to be significant. Figures 13(a) and(b) comparetotal emittance versus temperature measuredby the room tempera-ture Hohlraumreflectometer to the other elevated temperature techniques.There were large differences in the Hohlraum and emissometer results foralumina below 700 K and for the alack paint at all temperatures.

CONCLUDINGREMARKS

The CVEwas successful in measuring the total hemispherical emittance ofcandidate space radiator materials at elevated temperatures. The CVEhas sev-eral advantages over the Hohlraum reflectometer and emissometer attachments.The probable error of the CVE(typically less than I percent) is smaller thanthat of the Hohlraumor the emissometer (±5 percent). Since measurementsareperformed under vacuum, samples measured in the CVEdo not have problems withoxidation or other chemical processes which might occur in the open-air emis-someter. CVEmeasurementsare madeat elevated temperature, while Hohlraummeasurementsare calculated from room temperature data. Directional effectsalso play a significant part in the Hohlraum and emissometer measurements,which measurehemispheric-angular and normal spectral emittance, respectively.In short, the CVEaccurately measurestotal hemispherical emittance in vacuumat elevated temperatures, which is the desired engineering value for spaceradiator design; the Hohlraum and the emissometer do not.

Nonetheless, there is an important advantage for the Hohlraum reflectome-ter. A Hohlraummeasurementrequires less than an hour, while a CVEmeasure-ment takes muchlonger becauseof the time required to attach the thermocoupleto the sample, pumpdownthe system, and bring the sample temperature to equi-librium. Hohlraummeasurementsare also fairly accurate for diffusely reflect-Ing samples. Hence, the Hohlraum reflectometer is ideal for screeningcandidate radiator materials. The materials with high emittances measured in

the Hohlraum could then be measured in the CVE to obtain more reliablemeasurements.

REFERENCES

]. S.K. Rut]edge, B.A. Banks, M.J. Mirtich, R. Lebed, J. Brady, D. Hotes, and

M. Kussmaul, "High Temperature Radiator Materlals for Applications In theLow Earth Orbital Environment," NASA TM-IOOlgO, 1987.

2. M.J. MIrtich and M.T. Kussmau], "Enhanced Thermal Emittance of Space Radia-tors by Ion-Discharge Chamber Texturing," NASA TM-lOO137, 1987.

3. B.A. Banks, S.K. Rut]edge, M.J. Mirtich, T. Behrend, D. Hotes,

M. Kussmaul, J. Barry, C. Stidham, T. Stueber, and F. DiF1]ippo, "Arc-Tex-tured Metal Surfaces for High Thermal Emlttance Space Radiators," NASA

TM-I00894, 1988.

4. M. Mlrtlch, F. DiF]llppo, J. Barry, and M. Kussmau], "The Emittance of

Space Radiator Materials Measured at Elevated Temperatures," NASATM-I01948, 1988.

5. J.C. Richmond, ed., Measurement of Thermal Radiation Properties of Solids,

NASA SP-31, (Natlonal Aeronautics and Space Admlnistration,

Washington, D.C., 1963).

6. R. Siegel and J.R. Howe11, in Thermal Radiation Heat Transfer, Second Ed]-

tlon, (Hemisphere Publishing Corp., Washington, D.C., 1981) Chapter 5.

7. G.T. O'Connor, "Thermal Radiation from Hot Surfaces Measured by Optical

and Calorimetric Methods," M.S. Thesis, University of Arizona, 1982.

8. W.L. Wolfe and G.J. Zissis, eds., The Infrared Handbook, (Office of Naval

Research, Dept. of the Navy, Washington, D.C., 1978) pp. 2-2 to 2-4.

9. "Infrared Reflectivity Attachments," Manual from the Perkin-Elmer Corp.,Norwalk, CT, p. 3.

10. C.H. Liebert, "Spectral Emittance of Aluminum Oxide and Zinc Oxide on theOpaque Susbstrates," NASA TN D-3115, 1965.

lO

C-85-5481

FIGURE I, - SPIO0 SPACF NUCI[AR POWER SYSHM (RAUIAIOI_ PANIIS COMPRISE 111[ FXTERIOR OF _HE

SYSIFM).

I I('_UR[: 2, CV[ VACUUM CHAMBER ANI) PUI_P SYSIEM.

11 OP_GINAL PAGE

BLACK AND WH1TE PHOrOGRAPH

I IGURE 5, CVI SAMPLE HOi DER.

3.250 IN. - ...... f

[[ " ,-#G-32 SETSCREW /-I/4 IN.

TYP W D )I ,,---_rBACK MOUNTING ,) DIAMEIER'E K S AGE T.C, 7 t{ _ PLAIE _ TUBE

#4-40 SETSCREW'7 , ____,c__Z_',DlI_ _:_.i_,, .............. C_.__l_. ......... II' " - _ i- HEAl -t ...............................

TANTALUM (_ --' ' -"' \'' '"'""'\ ''\''''" ''_' ' _F{ONNsDu_CATT_RD]. WIIRTEH

SAMPLE-- _:y-I ."TANTALUM\ f>::-_,-C'"-:_:\ ":,: :'t . ? '_'"_ jJ I FLANGE

COIL AND SAMPLE 74,v/ _/ I -_.--: --: -_ .... l :_ :7 ' ,_' -v • • ' " % ,, TYPE K SWAGED T CMOUNT PLATE _" ',_i!| - /_ I,", \ ,_:,_ -':'q L i'" _I---"""N_'_,, T " '

STAINLESS 'I q' I' ; r _ IF'

STEEL WIRE J" _\i_\\'• ....'\,_' _ "&'"RC' \_: , ......... 2_ _:'\_N _ \',C{g,,,_ ,_,,,,,_,_,_=:..... _ ' '_\'X_",',_." "--#10--32--- SOCKET HEAD

OUTSIDE ' I_ SWAGED HEATER COIL,l! __;- "_- -'_----;-- - _-_LOf, IG__; ...... 7J__ l

DIAMETER J LL_. WRAPPED ON 1/2 IN. If I_ ................................ , 7J'(-,-........... JJ

FIGURE q. - CUTAWAY DRAWING OF IHE CVE HEATER/HOLDER.

12OIIellNAD P,_V3_

_ . NICHROME WIRE

l_il TERMINAIED HERE

CONNECTORS __ _ IANIALUM DISKS

" ""._J['-JL-JL-"-,,covLRBOIIOM_-_'__ SUR[ ACE

_AI)_ I) COPP_ R LtADS

SWAGED

THERMOCOUPE[ :

FIGURE 5, - SAMPLE MOUN[ PLAIE.

FIGURE 6. - PHOTO Of THERMOCOUPLE SAMPLE (BACK SURFACE).

13 07_._iNA: PAGE

BLAOK A_,'D VVHITE r',_OTOGRApFI

PIbUId 1, MOUNIF[) SAMPI

HIAI ,'q#]IrP II_AIlI(

eiIDheollela .-

SAMPLE MOUN IPLATE POWER

INPUT - " . _--_

____J_ " _ SAMPI ESAMPLE MOUNT

THERMOCOUPI [ J/ II[i I

I 1 ....THERMOLOI/PI [ \DIG11AI \,,_ LN2_COOLEDTHERMON[ II R BLACKBODYCAVITY

I IUURI _S. SCiIINATIC Ol Ifll IXPIRIMINI.

14

BLAOK ANO ',NI-I_TEP_RAPH

SAMPLE

MOUNT

PLATE//

THERMOCOUPLE J

FIGURE 9. - HEAT ERANSFER SCHEMATIC.

.008 --

.006 --

.004 --

.002 --

0

2

0

t I I I I(a) ABSOLUI[ ERROR VERSUS [:MIIIANCE.

T " 92S K

1 I I I I.2 ,q .6 .8 1.0

EMITIANC[

(b) ERACTIONAL ERROR VERSUS EMIITANCE.

FIGURE 10. - PROBABtE ERROR AS A FUNCTION OF EMIITANCI

AND TEMPERATURE.

15

923 -- SAMPLE

EMITTANCE ,_

.72.97

873 -- O .&5

D .950

_ 823

i 775

723

I I I I I723 773 825 873 925

SAMPLE PLATE TEMPERAFURE, K

FIGURE 11.- SAMPEE TEMPERATURE AS A FUNCTION OF SAMPLE

PLATE TEMPERATURE FOR SAMPLES OF VARIOUS EMITTANCES.

16

J, o p 0 CvE _--| -- HOHLRAUM 0000

r.6.4 I ] 1 I I I I I I I I i I t I I

(a) PLASMA-SPRAYED A12%, (b) CARBON PAINT ON STAINLESS ST[El.

.6

,4

.21 I I I I I I I I(c) ARC-TEXTURED IITAN]UM.

E

1.0--

.8--

o00O

.6

• 4

.2

0tlLlllll

(e) HIGtI-IEMPERATURE BLACK PAINT.

I 0000

I t I r 1 [(d) SANDBLASTED Nb (1% Zr).

---T-'T-I

I I

0000

I i L i i(f) SANDED STAINLESS STEEl•

_2V t I I I I I I '1 I I I I I I I I300 400 500 600 700 800 900 1000 1100 300 400 500 GO0 700 800 900 lO00 1100

TEMPERA]URE, K

(g) POt ISHED COPPER. (h) POLISHED STAINLESS STEEL.

FIGURE 12. - EVE TOTAL HEMISPHERIC EMITTANCE AND HOHLRAUM HEMISPHERIC ANGULAR

EMITTANCE MEASUREMENIS.

1.0

.8

.6

.4

,2

-- -- O000

-- 0 CVE

EMISSOMETER

HOHLRAUM

o i I t I I I ] I I i i I I I i i300 400 500 GO0 700 800 900 1000 ]100 300 400 500 GO0 700 800 900 1000 ]100

IEMPERAIURE, K

(a) PLASMA-SPRAYED AI203. (b) HIGH TEMPERATURE BLACK PAINT.

FIGURE 13. - TOTAL EMITTANCE MEASURED WITH THE EMISSOMETER AND THE CVE.

17

Report Documentation PageNabol_ai Ae_orhaLdlc>, ,_ll_.J

Space Admdnrslrati_ln

1. Report No, 2. Government Accession No. 3. Recipient's Catalog No.

NASA TM- 102322

5. Report Date4. Title and Subtitle

Total Hemispherical Emittance Measured at High Temperatures

by the Calorimetric Method

7. Author(s)

Frank DiFilippo, Michael J. Mirtich, Bruce A. Banks.Curtis Stidham, and Michael Kussmaul

9, Performing Organization Name and Address

National Aeronautics and Space AdministrationLewis Research Center

Cleveland, Ohio 44135-3191

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

Washington, D.C. 20546-0001

6. Performing Organization Code

8. Performing Organization Report No.

E-4704

10. Work Unit No.

586-01-11

11. Contract or Grant No.

13, Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared for the 16th International Conference on Metallurgical Coatings sponsored by the American Vacuum

Society, San Diego, Calilbrnia, April 17-21, 1989.

16. Abstract

A calorimetric vacuum emissometer (CVE) capable of measuring total hemispherical emittance of surfaces at

elevated temperatures was designed, built, and tested. Several materials with a wide range of emittances were

measured in the CVE between 773-923 K. These results were compared to values calculated from spectral

emittance curves measured in a room temperature Hohlraum reflectometer and in an open-air elevated temperature

emissometer. The results differed by as much as 0.2 for some materials but were in closer agreement for the

more highly-emitting, diffuse-reflecting samples. The differences were attributed to temperature, atmospheric, and

directional effects, and errors in the Hohlraum and emissometer measurements (+ 5%). The probable error of the

CVE measurements was typically less than 1%.

17. Key Words (Suggested by Author(s))

Emittance

Calorimetry

Emissivity

18. Distribution Statement

Unclassified- Unlimited

Subject Category 31

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No of pages

Unclassified Unclassified 18

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