NEW NIST PUBLICATION

December 21 , 1 ?88

NISTIR 88-3809

Direct Measurement of

Heat of Gasification for

Polymethylmethacrylate

J. L. Jackson, Research Associate

Armstrong World Industries

Lancaster, PA 17604

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

September 1986

Issued October 1988

National Bureau of Standards became the

National Institute of Standards and Technology

on August 23, 1988, when the Omnibus Trade and

Competitiveness Act was signed. NIST retains

all NBS functions. Its new programs will encourage

improved use of technology by U.S. industry.

U.S. DEPARTMENT OF COMMERCE

C. William Verity, Secretary

NATIONAL INSTITUTE OF STANDARDS

AND TECHNOLOGY

Ernest Ambler, Director

NISTIR 88-3809

Direct Measurement of

Heat of Gasification for

Polymethylmethacrylate

J. L. Jackson, Research Associate

Armstrong World Industries

Lancaster, PA 17604

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

September 1986

Issued October 1988

7S Years Stimulating America a Progress

1913-1999

TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES v

Abstract 1

1. INTRODUCTION 2

2 . Background Theory 3

3. Experimental Technique and Procedures 7

3.1 Sample Description and Preparation 7

3.2 Pre-test Setup 8

3.3 Test Conditions 8

4. Results and Discussion 9

4.1 Apparatus Operation 9

4.2 Test Series Results 11

5. Recommendations 13

6. Conclusions 15

7. Acknowledgements 15

8. References 16

9. NOMENCLATURE 17

APPENDIX A 26

iii
List of Tables

Table 1 Heat Flux Losses at Various Incident Flux

’

.

iv
LIST OF FIGURES

Page

Figure 1. Schematic of heat of gasification apparatus 18

Figure 2. Mass loss rate versus time at various incident

heat fluxes for PMMA 19

Figure 3. Peak rate of weight loss versus incident heat fluxes

for PMMA 20

Figure 4. Top surface temperature versus time at various

incident heat fluxes for PMMA 21

Figure 5. Bottom surface temperature versus time at various

incident heat fluxes for PMMA 22

Figure 6. Absorbed heat versus time at various incident

heat fluxes for PMMA 23

Figure 7. Heat of gasification versus time at various

incident heat fluxes for PMMA 24

Figure 8. Asymptotic heat of gasification versus incident

heat fluxes for PMMA 25

Figure A-l. Top Surface Temperature Versus Time at Various

Incident Heat Flux for Fir 27

Figure A- 2. Top Surface Temperature Versus Time of Various

Incident Heat Fluxes for Oak 28

Figure A- 3. Mass Loss Rate Versus Time at Various Heat Fluxes

for Fir 29

Figure A-4. Mass Loss Rate Versus Time at Various Heat Fluxes

for Oak 30

Figure A- 5. Peak Rate of Weight Loss Versus Incident Heat Flux

for Fir 31

Figure A-6. Peak Rate of Weight Loss Versus Incident Heat Flux

for Oak 32

v

DIRECT MEASUREMENT OF HEAT OF GASIFICATION

FOR POLYMETHYLMETHACRYLATE

J. L. Jackson

Abstract

A laboratory scale apparatus has been developed for the direct

measurement of the heat of gasification for solid fuels. The apparatus has

been designed to simulate radiant energy transfer rates found under actual

fire conditions and designed in such a way that the energy gains and losses

with respect to the sample surfaces are well defined. Calculation of the time

dependent heat of gasification for solid fuels relies on the ability to

measure accurately and continuously the time dependent energy transfer rates

and material responses. Tests have been conducted in which samples of

polymethylmethacrylate were subjected to incident heat fluxes ranging from 1

to 4 W/cm2

. Test results indicate that under these conditions the heat of

gasification is significantly influenced by the time dependent thermal

properties of the material and approaches an asymptotic value that varies with

incident heat flux. The asymptotic values decrease with increasing incident

heat flux and approach a value of 1600 J/g which is consistent with values

published by other investigators. Refinement of the apparatus and the testing

of other materials is continuing. Results for two additional materials, fir

and oak are included as Appendix A.

Key words: burning rate; charring materials; gasification;

us ^.^polymethylmethacrylate;- pyrolysis.; solidrrfuels ; the rmahpropertips.

1
1 . INTRODUCTION

One of the continuing concerns and desires of the fire research

community is the development of the ability to predict accurately the burning

rates of solid fuels. To develop the modeling tools necessary to do this,

much information is needed regarding the fundamental properties of materials

and their relationship to material responses under fire conditions. In some

cases the complexities of modeling such properties can be reduced by studying

and modeling the overall effect of several processes. The study of heat of

gasification is an example of such an approach which involves characterization

of the combined energetic effects of all of the chemical processes that

produce fuel gases from the original solid material. The heat of gasification

is therefore defined for this study as the net amount of absorbed energy

required to gasify a unit mass of given material. [

The measurement of heat of gasification has previously been performed

using various indirect methods. The most recent of these methods was developed by Tewarson[ 1- 3 ] . This method involves continuous measurement of the mass

loss of the test sample for various incident heat fluxes. The peak mass loss

rate is then plotted as a function of incident heat flux. For polymethylmethacrylate (PMMA) and various other materials this plotted data suggests a

linear relationship between the peak mass loss rate and the incident heat

flux. The slope of the linear solution derived from a least squares analysis

of the data is equal to the inverse of the heat of gasification. Values for

heat of gasification determined using this method are consistent with values

determined by thermal gravimetric analysis and other techniques. This

2
analysis method however is limited to the use of data which represents steady

state conditions.

Materials receiving external incident flux from the flames of a developing fire undergo a non- steady state thermal energy transfer. Under these

conditions the instantaneous value of the mass loss rate and the net amount of

heat absorbed by the sample will vary as a function of time. This would then

imply that the instantaneous value of the heat of gasification will also vary

as a function of time. The impetus for the work presented in this paper is to

measure this time dependent behavior. The objective of the work has been the

development and construction of a laboratory scale apparatus for the direct

measurement of quantities used to calculate the heat of gasification. The

apparatus has been designed to simulate thermal energy transfer under fire

conditions and designed in such a way that the energy gains and losses with

respect to the sample surfaces are well defined and continuously measurable.

The net energy absorbed by the test sample is the difference between the

energy gained and lost at any time. The mass loss rate can be determined from

the continuous measurement of the sample mass. The heat of gasification at

any given time is then calculated by dividing the net absorbed heat flux by

the mass loss rate at that time. Descriptions of the apparatus, experimental

procedures, analysis approach and test results are included in this paper.

2 . BACKGROUND THEORY

The definition of heat of gasification for this study is:

3
( 1 )

q"^ net

m"

where Lg is the heat of gasification, q" net represents the net absorbed heat

flux and m

M is the mass loss rate per unit area (Section 9. Nomenclature).

The net energy absorbed by the test sample can be calculated from the

energy balance equation, Eq . (2), which describes the energy transfer into

and out of the sample material.

L =

g

q" f = q" i net ^ l n c ref - q c d (2)

Equation (2) is applicable to a configuration where the top surface of the

sample is exposed to an incident radiant flux while the side and bottom

surfaces are thermally insulated. To be able to directly measure the heat of

gasification as a function of time, the time dependent terms in Eq . (2), as

well as the time dependent mass loss rate must be continuously measured.

Figure 1 schematically shows the apparatus which has been designed to obtain

these measurements.

The incident flux is provided by a conical shaped black body radiant

heater comprised of a 6H turn Incoloy electrical heating element. This heater

provides a uniform heat flux 4 cm below the 16 cm diameter base of the heater

with -at most a 3. 5 ^percent "deviation from the - average

rflux t-5 -The -incident flux

from the heater is adjusted prior to each test based on measurements made with

4
a total heat flux gage placed in the position occupied by the test sample

during actual testing. The top of the heater assembly has an orifice through

which a radiometer positioned above it can measure the combined re-radiated

and reflected heat flux from the top surface of the sample. The heater

assembly is positioned on top of a rectangular shaped conduit which serves as

a pyrolysis chamber. The vertical movement of the pyrolysis chamber is

independent of the sample cup and load cell system. This allows the chamber

to be repositioned during tests to keep the regressing top surface of the

sample in the uniform flux area 4 cm below the heater.

The side and bottom surfaces of the test sample are thermally insulated

using a low density ceramic fiber material. From the thermal conductivity of

the insulation material and the measurement of the differential temperature

across the insulation thickness, the energy being conducted away from the side

and bottom surfaces is calculated assuming steady state conditions from Eq

.

(3). More detailed transient calculations were not used because the conductive heat loss is expected to be small.

k.

l

[T,b

- T

cbJJ k. [T - T ] I S cs

cd hb

(3)

A flow of nitrogen is introduced into one end of the pyrolysis chamber

and passes through a porous metal plate to produce a uniform flow pattern

which passes over the top surface of the test sample. Although the nitrogen

flow produces the convective heat loss, it provides three critical functions.

By exhausting much of the pyrolyzates through the end of the pyrolysis

chamber, the nitrogen flow minimizes the effects * of - the pyrolyzates gases

above the fuel surface from attenuating the incident radiant heat flux from

5
the heater [4] and from attenuating the re -radiated and reflected heat flux

being measured by the radiometer. The nitrogen flow also purges the oxygen

from the pyrolysis chamber and prevents the thermally initiated process from

being influenced by the presence of oxygen [5]. Finally, with reduced oxygen

present in the pyrolysis chamber ignition of the combustible pyrolyzates is

prevented. Measurement of the upstream velocity and temperature of the

nitrogen flow, and the temperature of the top surface of the test sample

permits the convected heat loss (q cv ) to be calculated from Eq . (4) which is

the convective heat transfer coefficient for flat plate boundary layer flow

without surface mass injection [6], the geometry of the sample and pyrolysis

chamber and the sample surface to nitrogen gas flow temperature difference as:

cv

1

[r

2 -((x

1

x x

0

+x

0

)/2-x)

2

j

1//2 (0.332)kPr 1/3

u

oo 1/2

1-

f

'N x

o 3/4"

[vxj L lx J j

-1/3

AT . . dx

(x)

(4)

The mass of the test sample is continuously measured using a load cell

system. During the initial stage of sample testing the mass of the test

sample is constant, the mass loss rate is zero, and therefore, from Eq . (2),

the instantaneous value of the heat of gasification is infinite. The value

then decreases as gasification and weight loss begins. In this study, a

multiple regression analysis is used to produce the coefficients for a third

order polynomial which expresses the sample mass as a function of time for the

time period after gasification and mass loss have been established. The first

derivative with respect to time of the polynomial expression then gives the

mass loss rate of the -sample as a function of time. -- -.-

6
3. EXPERIMENTAL TECHNIQUE AND PROCEDURES

3.1 Sample Description and Preparation

Samples of PMMA (Rohm and Hass Plexiglass Type G) 1 were tested. Test

sample dimensions were 2.5 cm thick and 9.0 cm in diameter. A type K thermocouple (0.00787 cm dia.) is thermally embedded in the top surface of the test

sample. The clip leads used to connect the thermocouple to the data acquisition system are of sufficient weight to maintain the contact between the

thermocouple and the test sample while the sample surface regresses during the

test. The side and bottom surfaces were covered with aluminum foil leaving

the top surface and 1.0 cm of the side surface exposed. Low density ceramic -

fiber insulation (3.5 cm thickness on the bottom, 0.8 thickness cm on the

side) is used in the sample cup to minimize the conductive heat loss from the

side and bottom surfaces. Type K thermocouples are positioned on both sides

of the insulation for measurement of the temperature differential across the

insulation.

Results from supplemental tests 2 on two charring materials, fir and oak,

are included in the Appendix.

1 Product identification has been used here to provide an accurate

description of the material tested. The use of this product name does not

constitute an endorsement by the National Bureau of Standards.

- . „ 2 These .tests_ were .conducted by NBS Guest Worker , Mr..*. J i - Jjen Chiou of the

Chung Shan Institute of Science and Technology, Taiwan.

7
3.2 Pre-test Setup

The Gardon3 type radiometer is positioned 31 cm above the test sample

surface. Using a 7 degree view angle restrictor, approximately 90 percent of

the top surface of the test sample can be viewed. Water, held constant at

room temperature and flowing at a rate of 26 cm3 /s , is used to cool the

radiometer and the view restrictor. The nitrogen flow rate for these test

ranged from 2400 to 3200 cm3 /s through the 4 cm by 20 cm by 35 cm pyrolysis

chamber. The incident heat flux from the radiant heater was measured with a

Gardon type total heat flux gage positioned in the location of the test

sample. After setting the heater for the desired incident heat flux the

system is allowed to come to equilibrium over a period of one hour. A shutter

in the bottom of the pyrolysis chamber prevents the sample from being exposedto the incident heat flux until the test begins. After equilibrium has been

reached, zero settings for the radiometer and load cell are established.

3.3 Test Conditions

The PMMA samples were tested at incident heat fluxes ranging from 1 to

4 W/cmz

, simulating the thermal radiation from the flames of a developing

fire. Data from all transducers was recorded every three seconds and then

analyzed at the end of the test using a computer based data acquisition

system. Tests at incident heat fluxes less than or equal to 2 W/cm2 were

terminated at an elapsed time of 60 minutes. Tests at incident heat fluxes

3 "Gardon type"- refers to transducers which provide._ajx.claatrlcal signal

directly proportional to the thermal energy absorbed by its heat- sensitive

surface

.

8
greater than 2 W/cm2 were terminated when the surface regression could no

longer be followed by manually repositioning the pyrolysis chamber and the

surface regressed below the bottom of the pyrolysis chamber. At this point

approximately 60 percent of the sample has been pyrolized. Generally, two

samples were tested at each incident heat flux.

4. RESULTS AND DISCUSSION

4.1 Apparatus Operation

A total heat flux gage placed in the position of the test sample is used

to measure the incident heat flux from the heater. Once equilibrium has been

established for a specific test, the temperature of the heating element is

noted. To maintain a constant heat flux, the voltage to the heating element

is manually adjusted to keep the heating element at the noted temperature.

With this method of operation the variance in the incident heat flux could be

held to within +/- 0.01 W/cm2 of the initial setting. Tests were conducted to

determine the uniformity of the incident heat flux from the conical shaped

heater. These tests showed that in the sample area 4 cm below the heater the

maximum percent deviation from the average heat flux was 3.5 percent.

To overcome the buoyancy driven flow caused by the incident heat flux,

it was necessary to use flow rates of from 2400 to 3200 cm3 /s for the nitrogen

flow to flush fuel products through the side of the chamber. To maintain

these flow rates for long periods of time for tests at the lower incident heat

flux required the use of a large capacity liquid nitrogen tank as the source.

Tests with an oxygen analyzer revealed that no oxygen was present at the

9
leading edge of the sample; however, oxygen was detected at the trailing edge

in concentrations of 1 to 4 percent.

The pyrolysis chamber and the sample cup/load cell assembly were

designed as separate components. This allows the pyrolysis chamber to be

lowered over the sample and allows the chamber position to be continuously

adjusted to maintain the 4 cm distance between the regressing top surface of

the sample and the bottom of the top surface for a distance of approximately

1.5 cm. Attempts to go further would result in the chamber resting on the

sample cup causing erroneous weight measurements.

Due to the sensitivity of the radiometer, it was necessary to thermally

insulate the radiometer, the view restrictor and the tubing for the cooling ~-

water. This was done to minimize the shift in the zero flux reading caused by

small changes in the temperature of the body of the radiometer. It was then

necessary to establish a zero reading after the system had come to equilibrium, just prior to exposing the sample to the incident flux.

For the two charring materials, it was necessary to modify the apparatus

to ensure that the radiative measurement were only the results from the

specimen degradation, i.e., that oxidation did not produce a secondary heat

source from the burning specimen. These modifications included reducing the

area enclosing the sample cup holder to 0.5 cm2 and restricting the length of

the opening for the pyrolysis products exhaust duct to 6.0 cm.

10
4.2 Test Series Results

The results of the test series in which samples of PMMA were tested at

incident heat flux ranging from 1 to 4 W/cm2 are shown in Figures 2-8. These

results indicate that under these conditions the heat of gasification, as

defined in Eq . (1), is significantly influenced by the time dependent thermal

properties of the material.

The results the test series in which samples of two charring materials,

fir and oak, were tested at incident heat flux ranges from 1 to 4 W/cm2 are

shown in Figures A1-A6.

The physical meaning of the peaks in the mass loss rate versus time

curves in Figure 2 is unclear from this data. There are several parameters

which appear to influence the peak mass loss rate values including the time

dependent size of the pyrolysis zone, the thickness of the material, the

thermal diffusivity of the material, the viscosity of the molten polymer, the

surface regression rate, the particular mechanisms by which the material

depolymerizes and degrades, as well as others. The peak mass loss rate versus

incident heat flux data is shown in Figure 3. From a least squares analysis

of this data, the inverse of the slope of the linear solution, i.e. the heat

of gasification as defined by Tewarson [2], is equal to 1890 J/g.

The top surface temperature versus time data shown in Figure 4 indicates

that the top surface reaches a steady state temperature in a short period of

time, particularly at the higher incident heat flux. However, the bottom

11
temperature versus time data in Figure 5 shows that the enthalpy of the system

does not reach a steady state condition for the range of incident flux tested

in this series.

The net heat flux absorbed by the sample as a function of time is shown in

Figure 6. The data for the heat flux losses, used in equation 2 to calculate

net heat flux absorbed by the sample, indicates that the predominant loss is

due to re-radiation and reflection from the top surface. Data for the heat

flux losses at peak mass loss rate for various incident heat fluxes is shown

in Table 1. :

Table 1

Heat Flux Losses As a Function of Incident Heat

q". q" + q

M

. q" d" nine ^ r r ^ ref ^ c v ^ c d

(W/cm2

) (W/cm2) (W/cm2

) (W/cm2)

1.0 0.538 0.157 0.011

2.0 0.904 0.197 0.014

2.5 0.926 0.231 0.012

3.0 0.940 0.235 0.010

3.5 1.156 0.244 0.007

4.0 1.264 0.284 0.003

Figure 7 shows that the time dependent heat of gasification at each

incident heat flux -approaches an asymptotic value that varies with. incident

heat flux. As shown in Figure 8, these asymptotic values decrease with

12
increasing incident heat flux and approach a value of 1600 J_/g which is

consistent with values published by other investigators including Tewarson

[1,2] and Vovelle et al [3].

5

.

RECOMMENDATIONS

There are several areas in which improvements to the apparatus are

needed. It is important to exhaust the pyrolyzates through the exhaust end of

the chamber and not up through the heater orifice. It is also important that

the oxygen in the chamber be completely purged. To achieve this the velocity

of the nitrogen flow should be increased. It is desirable to increase the

velocity of the nitrogen flowby modifying the size and/or configuration of

the chamber as opposed to merely increasing the flow rate. The flow rates

used in this work are approaching prohibitive levels. The best results would

be achieved if the flow rate could actually be reduced to 1600 cm3 /s while

increasing the velocity by 20 to 30 percent. Another modification which would

aid in properly exhausting the pyrolyzates would require reducing the size of

the orifice in the top of the heater assembly. This may also require adjusting the position of the radiometer.

It was observed that the nitrogen flow had a cooling effect on the

apparatus when using the liquid nitrogen tank as the source. This then

required continuously adjusting the heater control to compensate for the

cooling effect and to maintain the incident heat flux. The recommended

improvement would be to use a water bath to allow the nitrogen to reach room

temperature before entering the pyrolysis chamber.

13
Using a multiple regression analysis to curve fit the sample weight data

to a third order polynomial produced excellent results. However, this then

forces the first derivative, which is used to calculate the weight loss rate,

to be a second order polynomial. Better results could be achieved if a higher

order polynomial is used with the multiple regression analysis.

The equation used to calculate the convective heat loss, Eq . (4), was

based on the theoretical determination of the convective heat transfer

coefficient. The convective heat transfer is very complex for this apparatus.

Better results for determining the convective heat loss would be achieved if

the heat transfer coeff icient - is determined experimentally.

The elapsed time of the test is limited by the ability to follow the

regressing sample surface. The sample cup and the method of insulating the

side and bottom surfaces of the sample require modifications that will allow

the repositioning of the pyrolysis chamber, which maintains the relative

distance between the heater and the regressing sample surface, to continue

over longer surface regression distances. This will be especially desirable

for testing samples of greater thickness.

6. CONCLUSIONS

The direct measurement of the heat of gasification using the apparatus

developed in this work shows that in the range of incident heat flux tested

14
the time dependency of the heat of gasification is significant. This implies

that in this range the use of the constant value of heat of gasification, as

determined by the methods of Tewarson and Vovelle et al , to predict mass loss

rate for a given incident heat flux will result in values significantly

greater than the measured values. Refinement of the apparatus and the testing

of other materials is continuing.

7 . ACKNOWLEDGEMENTS

The work presented in this paper was done in the laboratories of the

Center for Fire Research at the National Bureau of Standards under their

research associate program. The generous support from CFR and its staff was

greatly appreciated. The author would also like to thank Mr. Ji-Jen Chiou of '

the Chung Shan Institute of Science and Technology, Taiwan for his assistance

during the PMMA experimentation phases and for his measurements for Fir and

Oak included in the Appendix.

15
8 . REFERENCES

1. TEWARSON, A., " Experimental Evaluation of the Flammability Parameters of

Polymeric Materials". Factory Mutual Research Corporation, Norwood,

Massachusetts. Technical Report 1A6R1.RC (R79-T-9), February 1979.

2. TEWARSON, A., AND PION, R. , "A Laboratory- Scale Test Method for the

Measurement of Flammability Parameters" , Factory Mutual Research

Corporation, Norwood, Massachusetts, Technical Report 22424, (RC77-T-50),

October 1977.

3. VOVELLE, C., AKRICH, R. , AND DELFAU J., "Mass Loss Rate Measurements on

Solid Materials Under Radiative Heating" , Combustion Science Technology . Vol . 36, 1(1984).

4. KASHIWAGI , T., "Radiative Ignition Mechanism of Solid Fuels", Fire

Safety Journal . 3(1981)185-200.

5. KASHIWAGI, T., AND OHLEMILLER, T., "A Study of Oxygen Effects on

Nonflaming Transient Gasification of PMMA and PE During Thermal

Irradiation" , Nineteenth Symposium on Combustion, The Combustion

Institute, (1982)815-823.

6. HOLMAN, J., Heat Transfer, McGraw-Hill, New York, p. 191, 1981.

16
9 . NOMENCLATURE

hb ceramic fiber insultion bottom thickness, 3.5 cm

hs ceramic fiber insulation side thickness, 0.8 cm

k thermal conductivity of nitrogen as a function of temperature

ki thermal conductivity of ceramic fiber insulation 0.0003605 W-°C/cm

L

g heat of gasification, J/g

m" mass loss rate per unit area

Pr Prandtl number as a function of temperature

q" . net absorbed heat flux

q". external incident heat flux

q" cd conductive heat flux loss

d" „ convective heat flux loss

q"

rr re-radiated heat flux

q" ref reflected heat flux

r sample radius, 4.5 cm

Tcb sample cup bottom temperature

Tc

s

sample cup side temperature

Tb sample bottom surface temperature

Ts sample side surface temperature

uTO upstream nitrogen velocity

v kinematic viscosity of nitrogen as a function of temperature

x 1 distance from porous plate to the sample trailing edge

x0 distance from porous plate to the sample leading edge

17
radiometer

Figure 1. Schematic of heat of gasification apparatus
o

IT

Figure 2. Mass loss rate versus time at various incident heat

fluxes for PMMA.

19
Incident Heat Flux, W/cm**2

Figure 3. Peak rate of weight loss versus incident heat fluxes

for PMMA.

20
Top

Surface

Temperature,

degrees

C

00

100.00

200

00

300.00

400

00

500.00

Time, min.

Figure 4. Top surface temperature versus time at various incident

heat fluxes for PMMA.

21
©

o

o

Figure 5. Bottom surface temperature versus time at various incident

heat fluxes for PMMA.

22
Ab

sorbed

Heat,

W/cm**2

00

?

00

3

00

4.00

5

00

i T.e . min

Figure 6. Absorbed heat versus time at various incident heat fluxes

for PMMA.

23
y>O

T 1 rT~

l n

Figure 7. Heat of gasification versus time at various incident heat

fluxes for PMMA.

24
Incident Heat Flux, W/ c t.* * 2

Figure 8. Asymptotic heat of gasification versus incident heat fluxes

for PMMA.

25
APPENDIX A

Results of Test

for Fir and Oak at Incident Heat Flux Ranges from 1 to 4 W/cm2

26
009

in

cm

o

0

J

in

in

z

—

i

x

LU

X

o o

o o

o

o

o o

o o

in CM

^

0 aejfisp •ajrnauadna} aaajjns

27

A1

•

Surface

Temperature

of

Fir

Specimen.
Figure

A2

.

Surface

Temperature

for

Oak

Specimen.

8Z

O

Surface temperature, degree C

ru U) CJ1 cn 0 0 O O 0

0 O

3:

h-i Z:

l

4

-OAK
(o/Xj 2 **tuo 8/eui sscn seen

29

Figure

A3.

Mass

Loss

Rate

for

Fir

Specimen.
W/CM**2

ID

OJ

O

ru

in

UJ

x.

in

o

o

o

OD

o

ID

O o

ru o

o

o o o o

3**UJ3 8/6ui *9ieB ssoi ssew

30

Figure

A4.

Mass

Loss

Rate

for

Oak

Specimen.
-Fin-

(01*) S**ui3 6/Cui ‘a^eu asm seen • xew

31

Incident

Flux

w/cm*#2
OAK-

!»

i

]

!

t

i

I

1

2#*uj 3 s/6tu 'e^ey ssoi ssew *xew

c

e

•Ha

cuaCO

cd O

u

o

4-1

0)

4-1 td

CO

COo

hJ

CO

CO

cd S

a:

«da)

PL,

lO

<

<uu

3

t>0 •H

pL,

32
FORM NBS-1 14A (REV 11-84)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

N I STIR- 88/ 3 80

9

2. Performing Organ. Report No. 3. Publ i cation D ate October 1938

4. TITLE AND SUBTITLE

Direct Measurement of Heat of Gasification for Polymethylmethacrylate

5. AUTHOR(S)

J.L. Jackson^ Research Associate

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s) National Institute of Standards and

Technology

U.S. Department of Commerce

Gaithersburg, MD 20899

7. Contract/Grant No.

8 . Type of Report & Period Covered

S. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FlPS Software Summary, is attached.

li. ABSTRACT I A 200-word or less factual summary of most significant i n format ion . If document includes a significant

bi bl i o graph y or literature survey, mention it here)

A laboratory scale apparatus has been developed for the direct measurement of the heat

of gasification for solid fuels. The apparatus has been designed to simulate radiant

energy transfer rates found under actual fire conditions and designed in such a way

that the energy gains and losses with respect to the sample surfaces are well defined.

Calculation of the time dependent heat of gasification for solid fuels relies on the

ability to measure accurately and continuously the time dependent energy transfer rates

and material responses. Tests have been conducted in which samples of polymethylmethacrylate were subjected to incident heat fluxes ranging from 1 to 4 W/cnT. Test

results indicate that under these conditions the heat of gasification is significantly

influenced by the time dependent thermal properties of the material and approaches an

asymptotic value that varies with incident heat flux. The asymptotic values decrease

with increasing incident heat flux and approach a value of 1600 J/g which is

consistent with values published by other investigators. Refinement of the apparatus

and the testing of other materials is continuing. Results for two additional materials

fir and oak are included as Appendix A.

12.

KEY WORDS (Six to twelve entries; a Iph a beti cal order; capi ta I i ze only proper names; and separate key words by semicolon sj burning rate; charring materials; gasification; polymethylmethacrylate; pyrolysis;

solid fuels; thermal properties

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