Liquefied natural gas research at the National Bureau of Standards: Progress report for the period 1 July- 31 December 1978

NBSIR 79-1603

LIQUEFIED NATURAL GAS RESEARCH

at the

NATIONAL BUREAU OF STANDARDS

PROGRESS REPORT FOR THE PERIOD
1 July - 31 December 1978

MEASUREMENT

SCIENCE

REFERENCE

DATA

LNG

TECHNOLOGY

TECHNOLOGY

TRANSFER

THERMOPHYSICAL PROPERTIES DIVISION. NATIONAL ENGINEERING LABORATORY.
NATIONAL BUREAU OF STANDARDS. BOULDER. COLORADO

NBSIR 79-1603

LIQUEFIED NATURAL GAS RESEARCH

at the

NATIONAL BUREAU OF STANDARDS

Thermophysical Properties Division
National Engineering Laboratory
National Bureau of Standards
Boulder, Colorado 80303

Progress Report for the Period

1 July - 31 December 1978

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Prepared for:

American Gas Association, Inc.

1515 Wilson Boulevard
Arlington, Virginia 22209

LNG Density Project Steering Committee

(in cooperation with the American Gas Association, Inc.)

Pipeline Research Committee
(American Gas Association, Inc.)

Gas Research Institute
10 West 35th Street
Chicago, Illinois 60616

U. S. Department of Commerce
Maritime Administration
Washington, DC 20235

U. S. Department of Commerce
National Bureau of Standards
National Engineering Laboratory
Boulder, Colorado 80303

U. S. Department of Commerce
National Bureau of Standards
Office of Standard Reference Data
Washington, DC 20234

U. S. Department of Commerce
National Bureau of Standards
Office of International Standards
Washington, DC 20234

LNG Custody Transfer Measurements Supervisory Committee

National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135

ABSTRACT

The objective of this report is to:

1. provide all sponsoring agencies with a semiannual report on the
activities of their individual programs;

2. inform all sponsoring agencies on related research being conducted
at the Themophys ica 1 Properties Division;

3. provide a uniform reporting procedure which should maintain and
improve communication while minimizing the time, effort and
paperwork at the cost center level.

The work is supported by NBS and seven other agencies and represents the
collective expenditure of $400,000 during the 6-month reporting period. The
contents of this report augment quarterly progress meetings for certain of
our sponsors and provide a perspective which is missing when the parts are
viewed individually. Distribution of this document is limited and intended
.primarily for the supporting agencies. Data or other information must be
considered preliminary, subject to change and unpublished, and therefore not
for citation in the open literature .

During this reporting period we have issued the first supplement to the
" LNG Material and Fluids" Users Manual.

Key words: Cryogenics; liquefied natural gas; measurement; methane;

properties; research.

CONTENTS

Cost Center

Page

I .

REFERENCE DATA

a)

THERMOPHYSICAL PROPERTIES DATA FOR PURE

COMPONENTS AND MIXTURES OF LNG COMPONENTS
(Gas Research Institute; American Gas
Association, Inc.; NASA Lewis Research
Center)

7360574,

7360548

1

b)

FLUID TRANSPORT PROPERTIES

(NBS-Of f ice of Standard Reference Data)

7362290

5

c )

PROPERTIES OF CRYOGENIC FLUIDS ( NBS )

7360122

7360124

7360125

7

d)

PROPERTIES OF CRYOGENIC FLUID MIXTURES
(NBS; NBS-Office of Standard Reference
Data; GRI)

7360123,

7362289,

7368574

11

e)

DENSITIES OF LIQUEFIED NATURAL GAS MIXTURES
(LNG Density Project Steering Committee -
AGA)

7361574

13

f )

PROGRAM FOR REDUCING THE COST OF LNG SHIP
HULL CONSTRUCTION — PHASE II SHIP STEEL
IMPROVEMENT PROGRAM (Maritime
Administration)

7363430 ,
7361430,
7362430

15

II .

MEASUREMENT SCIENCE

a )

CUSTODY TRANSFER - LNG SHIPS (Maritime
Administration; LNG Custody Transfer
Measurements Supervisory committee

7360460,

7361575,

7362575,

7363575,

7311573,

7311577

17

b)

HEATING VALUE OF FLOWING LNG (Pipeline
Research Committee - AGA)

7362570

19

c )

LNG DENSITY REFERENCE SYSTEM (American Gas
Association, Inc.; Gas Research Institute

7367574

20

d )

LNG SAMPLING MEASUREMENT STUDY (Pipeline
Research Committee - AGA)

7363570

22

Ill .

TECHNOLOGY TRANSFER

a)

SURVEY OF CURRENT LITERATURE ON LNG AND
METHANE (American Gas Association, Inc.;
Gas Research Literature)

7369574

24

IV

CONTENTS (continued)

b) LIQUEFIED NATURAL GAS TECHNOLOGY TRANSFER
(Maritime Administration; American Gas
Association, Inc.; Gas Research Institute;
NBS-Office of Standard Reference Data)

c) OIML JOINT SECRETARIAT ON LNG MEASUREMENTS
(American Gas Association, Inc.; NBS-
Office of International Standards;
NBS-Thermophys ical Properties Division)

Page

7360403,

27

7361403,

7364574 ,

7368574,

7362287,

7360461,

7360594

7360290

29

v

1 .

Title .

THERMOPHYSICAL PROPERTIES DATA FOR PURE COMPONENTS AND MIXTURES
OF LNG COMPONENTS

Principal Investigators . R. D. Goodwin, H. M. Roder, G. C. Straty,

W. M. Haynes, R. D. McCarty, D. E. Oilier, and B. A. Younglove

2 . Cost Center Numbers . 7360574, 7360548

3. Sponsor Project Identification . Gas Research Institute Grant No.
5010-362-0019 and American Gas Association, Inc., Project BR-50-10.
National Aeronautics and Space Administration, Lewis Research Center,
Purchase Order C-78014-C.

4. Introduction . Accurate phase equilibrium, equation of state (PVT), and
thermodynamic properties data are needed to design and optimize gas
separation and liquefaction processes and equipment, and for mass and
heat transfer calculations. Accurate data for the pure components and
selected mixtures of hydrocarbon systems will permit developing
comprehensive accurate predictive calculation methods which take into
account the dependence of the thermophysical properties of mixtures on
the composition, temperature, and density.

This project will provide comprehensive accurate thermophysical
properties data and predictive calculation methods for compressed and
liquefied hydrocarbon gases and their mixtures to support the
development of LNG technology at NBS and throughout the fuel gas
industry. It will also serve as the base for a comprehensive mixtures
prediction methodology.

5. Objectives or Goals . The objectives of our work are the determination
of comprehensive accurate thermophysical properties data and predictive
calculation methods for the major pure components (methane, ethane,
propane, butanes, and nitrogen) and selected mixtures of liquefied
natural gas and hydrocarbon mixtures at temperatures between 80 K and
320 K and at pressures up to 35 MPa (5000 psi). Our goal is to provide
a range and quality of data that will be recognized as definitive or
standard for all foreseeable low temperature engineering calculations.

6. Background . Liquefied natural gas is expected to supply an increasing
percentage of the United States' future energy requirements. It is
likely that massive quantities of liquefied natural gas will be imported
during the years 1978 - 1990. Ships and importation terminals are being
built for transporting, storing, and vaporizing liquefied natural gas
for distribution. Accurate physical and thermodynamic properties data
for compressed and liquefied natural gas and hydrocarbon mixtures are
needed to support these projects. For example, accurate compressibility
and thermodynamic properties data are needed to design and optimize
liquefaction and transport processes; accurate data for the heating
value, which for liquefied natural gas mixtures depends on the total
volume, the density, and the composition, are needed to provide a basis
for equitable custody transfer. Accurate mixture data prediction
methods are needed for use in automated heat transfer calculations.

Accurate thermodynamic properties data for liquefied gas mixtures must
be based on precise compressibility and calorimetric measurements;
compressibility data give the dependence of thermodynamic properties on
pressure and density (at fixed temperatures); calorimetric data give the
dependence of thermodynamic properties on temperature (at fixed
pressures and densities). It is impossible, however, to perform enough
compressibility and calorimetric measurements directly on multicomponent
mixtures to permit accurate interpolation of the data to arbitrary
compositions, temperatures and pressures. Instead, thermodynamic
properties data for multicomponent mixtures must usually be predicted

1

(extrapolated) from a limited number of measurements on the pure
components and their binary mixtures. This project was initiated to
provide the natural gas and aerospace industries with comprehensive
accurate data for pure compressed and liquefied methane, the most
abundant component in LNG mixtures. We have published National Bureau
of Standards Technical Note 653, "Thermophysical Properties of Methane,
From 90 to 500 K at Pressures to 700 Bar," by Robert D. Goodwin (April
1974), and National Bureau of Standards Technical Note 684, "Thermophys- I
ical Properties of Ethane, From 90 to 600 K at Pressures to 700 Bar," by
Robert D. Goodwin, H. M. Roder, and G. C. Straty (August 1976). These
reports contain the most comprehensive and accurate tables available for
the thermophysical properties of pure gaseous and liquid methane and
ethane, and provide an accurate basis for calculating thermophysical
properties data for LNG and other hydrocarbon mixtures.

7 . Program and Results .

7.1 Propane, PVTx and Dielectric Constant Measurements -- W. M. Haynes j

The experimental measurements of the densities of liquid mixtures of LNG
components have been completed. The LNG density project used the same
apparatus that is now being employed for PVT and dielectric constant
measurements on propane. A summary of the LNG density project is given
in the report for cost center 7361574.

After testing the dead weight gauge measurement system, PVT measurements
have been carried out for liquid propane at pressures to 360 bars along
three isotherms at 146, 160, and 178 K (approximately 14 data points per .
isotherm) . These data have been compared with the calculated values
from the equation of state for propane developed by R. D. Goodwin. The 1
maximum difference between the calculated and experimental densities was |
0.07% while the average deviation was 0.02%. No problems were
encountered in using the apparatus at high pressures.

This apparatus utilizes a magnetic suspension densimeter, which is based
on an application of Archimedes' principle. The uncertainty in the
measured density depends directly upon the uncertainty in the
determination of the volume of the magnetic float. The volume of the
float changes with pressure. Thus measurements have been carried out by
H. M. Ledbetter of our division to determine the bulk modulus of the
float material (barium ferrite) as a function of temperature between 76
and 300 K. These measurements demonstrated that the change in the
volume of the float is less than 0.03% for a pressure change of
360 bars. (The bulk modulus (or compressibility coefficient) of barium
ferrite changes approximately 2% from 76 to 300 K. This corresponds to
a volume change of less than 0.001% for a pressure of 500 bars. For all
practical purposes it can be assumed that the bulk modulus of barium
ferrite is independent of temperature over the temperature range of the
propane measurements.)

One of the coaxial leads to the capacitor used in the dielectric
constant measurements broke when an effort was being made to remove a
short to ground from the capacitor cylinder to which this coaxial cable
was connected. The apparatus must be disassembled and the coaxial cable
replaced .

7.2 Calculational Methods — R. D. McCarty

Work is continuing, at a partial staff-year level, on the extension and
optimization of the corresponding states method to mixtures of methane
with nitrogen and other fluids. The transformation of the methane
surface to N 2 , C>2' Ar > H 2 anc ^ C 2 H 4 ^ as been accomplished and
the development work on the transformation function itself has begun. |

2

We have determined that the transformation function previously used for
liquid density near saturation is inadequate for a broader range of
pressure and temperature. Initial efforts in finding a new function are
encouraging.

7.3 Propane, Specific Heat Data -- R. D. Goodwin

This project is complete and the results published in "Specific Heats of
Saturated and Compressed Liquid Propane," by R. D. Goodwin, J. Res. Nat.
Bur. Stand. (U.S.) 83, 449-58 (Sep-Oct 1978).

7.4 Butane, Preliminary Thermophysical Properties Data -- R. D. Goodwin

The objective is to prepare provisional tables of thermodynamic
properties of normal and isobutane, using available physical properties
data. In this work we expect to discover those areas of properties data
most in need of further experimental measurements.

In general, there is an abundance of quite inconsistent data from
different laboratories, requiring tedious weightings, selections, and
eliminations. There are few data for liquid butanes at LNG
temperatures .

Satisfactory formulations have been developed for the virial equation,
the saturated liquid densities, specific heats for the saturated liquid
below the boiling point, and for the ideal gas thermodynamic functions
for both fluids.

By thermal loops, in a procedure first developed by W. T. Ziegler, we
have derived new "data" (where none existed) from the triple- to the
boiling-point for vapor pressures, densities of the saturated vapor, and
for heats of vaporization. The vapor-pressure equation has been
adjusted to include these new data, and a provisional description has
been developed for the heats of vaporization up to the critical point.

Manuscripts for reports on the equation of state and provisional tables
of thermodynamic properties for both n-butane and i-butane are complete
and in the final stages of the NBS review process. They will be
published as NBS Interagency reports.

The work on isobutane was done sooner than planned because of a
Department of Energy funded experimental project on that fluid which
will be used as a geothermal working fluid. The latter work is being
done at NBS-Gaithersburg and the two projects will be done on a
collaborative basis so that the resulting 'final' tables will serve both
projects. The need for measurements to be made on i-butane at Boulder
will be, consequently, reduced greatly.

7.5 Pure Nitrogen and Nitrogen-Methane PVTx Property Measurements —

G. C. Straty and D. E. Diller

Gas expansion PVT measurements on pure compressed and liquefied nitrogen
have been completed. About 300 measurements were made at 21 densities
in the range 11.2 - 28.4 mol/L, 80 - 270 K, 1 - 350 bars. These
measurements were made to provide more accurate pure component data for
an accurate mathematical model of the PVT properties of nitrogen-methane
mixtures .

Twelve isochoric gas-expansion PVT runs have been made on a gravimetri-
cally prepared 50.115 mole % nitrogen-49.885 mole % methane mixture in
the T, P, p range 82 - 320 K, 2 - 350 bar, 11 - 28.6 mol/L. The
measurements are being compared with the extended corresponding states
model (R. D. McCarty, NBSIR 77-867 (Oct 1977), which was previously

3

optimized to saturated liquid density measurements on this mixture at
temperatures below 140 K. Differences between calculated and measured
densities range from several tenths percent at low temperatures and high
densities to several percent near the critical temperature (~ 161 K) and
critical density (~ 10.5 mol/L) . About eight more measurement runs are
planned.

7.6 Sound Velocity of Propane — B. A. Younglove

New measurements of the sound velocity of propane have been initiated.

We will evaluate the performance of the sound velocity approach in
liquid propane at 100 K to see if the previous geometry is satisfactory.
Drawings were made for a new configuration of spacer length twice the
old length in case the former arrangement does not work. Calculations
for dispersion from correlations available in the literature indicate
that this should not be a problem. This and other features of the
proposed measurements were recently discussed during a visit by Bruce
Gammon of DoE , Bartlesville, Oklahoma, an expert in the field of sound
velocity measurements. We have installed and tested a new vacuum jacket
for the sound velocity cryostat which allows much more convenient
dismantling of the system. The computer programming necessary for
experimental sound velocity measurement has commenced. We have a
computer file for computation of propane density from measured values of
temperature and pressure, and a file for computation of sound velocity
from a measurement of frequency using the information obtained from the
previously mentioned calculation. The latter file is not in complete
form. We will next work on checking the system as mentioned above for
general behavior in liquid propane. Also we will check the sample
holder system for temperature gradients, temperature measurement
accuracy and other features required for proper measurement of sound
velocity .

8. Problem Areas . None.

9. Level of Effort . July 1 - December 31, 1978.

Staff-years expended

Equipment and/or Services Purchased

Approximate expenditures, total

10. Future Plans.

1.1

11 . 2K$
9 6 . 4K$

Objectives and Schedule: Quarter 1 2

Evaluate and optimize promising

calculation methods for the

thermodynamic properties of
methane-nitrogen mixtures.

Measure, analyze and report PVT and
dielectric constant data for propane.

Publish provisional tables of thermo-
dynamic properties for the butanes
and develop an accurate equation of
state .

Measure, analyze and report sound
velocity data for propane.

4

Title . FLUID transport properties

Principal Investigator . Howard J. M . Hanley-
Cost Center Number. 7362290

Sponsor Project Identification . NBS-Office of Standard Reference Data

Introduction . Methods for predicting the transport properties of fluid
mixtures are unreliable and data are scarce. Prediction methods are
needed, however, to supply the necessary design data needed to increase
efficiency and reduce costs.

Objectives or Goals . The long range or continuing goal of the program
is to perform a systematic study of the theories and experimental
measurements relating to transport properties, specifically the
viscosity and thermal conductivity coefficients, of simple mixtures over
a wide range of experimental conditions. The specific objectives of the
program include: 1) the systematic correlation of the transport

properties of simple binary mixtures and the development of prediction
techniques, 2) development of a mixture theory for the dilute gas region
and the dense gas and liquid regions, 3) extension of the theory and
prediction techniques to multicomponent systems, and 4) suggested
guidelines for future areas of experimental work.

Background . A continuing program has successfully expanded the state-
of-the-art of transport phenomena for pure fluids. Information for pure
fluids is required as a prerequisite for mixture studies. The theory of
transport phenomena has been developed and applied to produce practical
numerical tables of the viscosity, thermal conductivity and diffusion

( 3 )

coefficients of simple fluids: Ar, Kr, Xe , N^, 0 F 2 , He, H^, CH^,

r h {4) c h (5)
C 2b ' C 3 H 8 *

It has been shown that a successful mixture program can emerge from
combining the results for pure fluids with mixture equation of state
studies. The equation of state work is being carried out by other
investigators in this laboratory.

Program and Results . We continue to develop the prediction procedure
for the transport properties of mixtures reported previously. '

We have recently studied the fundamentals via computer simulation^ ' to
assess the scientific justification of the corresponding states
approach .

The critical point behavior remains of interest^) and preliminary
results are in process of publication.

The transport properties of pure ethylene are being correlated.

Problem Areas . The lack of suitable experimental mixture transport
properties data for comparison purposes is the main problem. Also
equation of state (PVT) data for mixtures are needed.

Level of Effort . July 1 - December 31, 1978.

Staff-years expended

Equipment and/or Services Purchased

Approximate expenditures, total

0.4
2. 5K$
3 6 . 7K$

10 .

Future Plans .

The corresponding states predictive procedure for

mixtures will be more fully developed and expanded in line with the
concurrent equation of state studies. We intend to investigate, in
particular, the behavior of the transport properties at gas/liquid and
liquid/liquid equilibria. Computer simulation studies will be expanded
Mixtures in which the components are very different (shape, size, mass,
etc.) will be emphasized.

References

1. H. J. M. Hanley, Prediction of the Viscosity and Thermal Conductivity
Coefficients of Mixtures, Cryogenics, Vol 16, No. 11, 643-51 (Nov 1976)
H. J. M. Hanley, Prediction of the Thermal Conductivity of Fluid
Mixtures, Proceedings 7th ASME Conf . on Thermophysical Properties;

H. J. M. Hanley in "Phase Equilibria and Fluid Properties in the
Chemical Industry," ACS Symp. Series No. 60 (1977).

2. H. J. M. Hanley, Transport Coefficients in the One-Fluid Approximation:
Behavior in the Critical Region, J. Res. Nat. But. Stand. (U.S.) 8_2 , 18
( 1977) .

3. H. J. M. Hanley, W. M. Haynes and R. D. McCarty, The Viscosity and

Thermal Conductivity Coefficients for Dense Gaseous and Liquid Methane,
J. Phys. Chem. Ref. Data, Vol 6, No. 2, 597-609 (1977).

4. H. J. M. Hanley, K. E. Gubbins and S. Murad, A Correlation of the

Existing Viscosity and Thermal Conductivity Coefficients of Gaseous and
Liquid Ethane, J. Phys. Chem. Ref. Data, Vol 6, No. 4, 1167 (1977).

5. H. J. M. Hanley, P. M. Holland, K. E. Gubbins and J. M. Haile, J. Phys.

6 .

Chem. Ref. Data (in press 1978).

D. J. Evans and H. J. M. Hanley, Phys. Rev. (submitted).

6

Title - PROPERTIES OF CRYOGENIC FLUIDS

Principal Investigators . G. C. Straty, N. A. Olien, B. A. Younglove,

H. M. Roder, L. A. Weber, B. J. Ackerson, and D. E. Diller

Cost Center Numbers . 7360122, 7360124, 7360125

Sponsor Project Identification . NBS

Introduct ion . Accurate thermophysical properties data and predictive
calculation methods for cryogenic fluids are needed to support advanced
cryogenic technology projects. For example, liquefied natural gas is
expected to supply an increasing percentage of the United States' energy
requirements through 1990. Liquefaction plants, ships and receiving
terminals are being constructed to transport and store natural gas in
the liquid state (LNG). Accurate thermophysical properties data for LNG
are needed to design low temperature processes and equipment. Accurate
data will benefit the energy industries and the consumer by providing
for safe and efficient operations and reduced costs. We are now
examining the data needs of a number of higher temperature industries
such as the synthetic natural gas (SNG) industry. This area of
technology as well as the liquefied petroleum gas (LPG) industry are
logical extensions of the current LNG work. SNG mixtures can be
characterized as much more complex than natural gas, containing unlike
(including highly polar) molecules. Interactions between unlike
molecules are not well understood and the accurate data necessary to
quantitatively understand the interactions are lacking. The needs for
accurate predictive methods for SNG are essentially the same as LNG,
i.e., to reduce capital and operating costs and improve energy
ef f iciency .

Objectives or Goals . The objectives of this project are to provide
comprehensive accurate thermodynamic, electromagnetic and transport
properties data and calculation methods for technically important
compressed and liquefied gases (helium, hydrogen, oxygen, nitrogen,
methane, ethane, etc.) at low temperatures. In addition we intend to
develop the capability to perform accurate PVT measurements on gaseous
mixtures and pure components at high pressures and above room
temperature. Precise compressibility, calorimetric and other physical
property measurements will be performed to fill gaps and reconcile
inconsistencies. Definitive interpolation functions, computer programs
and tables will be prepared for engineering calculations. The immediate
goals of this work are to obtain accurate sound velocity and thermal
diffusivity data for compressed and liquefied gases by using laser light
scattering spectroscopy techniques; design, construct and performance
test a precision PVT apparatus for the region 250 - 900 K with pressures
to 35 MPa; and design, construct and performance test a transient
hot-wire thermal conductivity apparatus for the region 70 - 350 K with
pressures to 80 MPa.

Background . The application of laser light scattering techniques to
obtaining thermophysical properties data was initiated to complement and
check other measurement methods and to solve measurement problems
inherent in more conventional methods. For example, laser light
scattering techniques permit measurements of sound velocities for fluids
under conditions for which sound absorption is too large to perform
ultrasonic measurements; laser light scattering techniques permit
measurements of thermal dif fusivities under conditions for which
convection interferes with measurements of thermal conduction. The
feasibility of light scattering experiments to obtain data on binary
diffusion coefficients has also been demonstrated.

7

Light scattering allows thermal diffusivity measurements in the region
where density fluctuations are relatively large, but accuracy drops
significantly as you pass outside the extended critical region. To
complement the scattering method, thermal conductivity measurements can
be made with more conventional techniques such as a hot-wire technique.
In the latter method a very small platinum wire is surrounded by the
fluid and a voltage pulse is applied to the wire. The temperature of
the wire is momentarily raised and the resistance increases. A series
of very closely spaced resistance measurements would describe the return
of the wire to equilibrium. These resistance vs. time measurements can
be related to the rate of heat dissipation in the surrounding fluid and
thus the thermal conductivity (provided convection heat transfer is
prevented ) .

The development of accurate mathematical models (equation of state) for
fluid mixtures requires accurate PVT data for the pure constituents and
binary mixtures of key molecular pairs. Experience with LNG has
identified the type and accuracy of the data required. In addition to
that, work on SNG at high temperatures is a logical follow-on to the low
temperature work on LNG. Typical constituents of raw SNG from coal via
the Lurgi process are: water - 50.2%; hydrogen - 20.1%; carbon

dioxide - 14.7%; carbon monoxide - 9.2%; methane - 4.7%; ethane - 0.5%;
hydrogen sulfide and others - 0.6%.

An apparatus has been assembled for laser light scattering spectroscopy
measurements on compressed and liquefied gases (76 - 300 K, 35 MPa).

The apparatus consists of a high pressure optical cell, a cryostat
refrigerated by means of liquid nitrogen, an argon ion laser and
low-level light detection equipment.

The light scattered from fluctuations in the fluid can be analyzed with
either digital autocorrelation techniques for the examination of the
very narrow lines associated with scattering from temperature
fluctuations (Rayleigh scattering) or with a scanned Fabry Perot
interferometer for the measurement of the Doppler frequency shifts
associated with the scattering from propagating density (pressure)
fluctuations (Brillouin scattering).

Apparatus for photon-counting and digital autocorrelation has been
assembled, interfaced with computer facilities and programmed to enable
on-line data accumulation and analysis. Initial problems associated
with signal modulations from excessive building vibrations have been
solved by levitating the apparatus on an air suspension system. A
small, highly stable capacitor has also been designed, constructed and
installed inside the scattering cell to permit the dielectric constant
of the scattering fluid to be determined, which should allow more
accurate fluid densities to be obtained for use in the data analysis.
Apparatus tests on well characterized, strongly scattering, test fluids
have been made to verify data analysis programs.

Extensive thermal diffusivity data have been obtained for methane.
Measurements have been made along the coexistence curve, the critical
isochore, and critical isotherm. The measurements extend outside the
critical region as well as deep into the critical region. In the deep
critical region the effect of temperature gradients and impurities have
been investigated. Outside the critical region, these effects do not
affect measurements beyond experimental accuracy. The range of the
measurements extends from 150 K to 230 K and 3 mol/L to 22 mol/L. The
inaccuracy of the measurements is about 5% in the critical region,

nalysis of the
reporting

the results has been submitted to the Journal of Chemical Physics.

increasing to 10% or greater further away. A detailed
data and experimental error has been made and a paper

fit

8

Some preliminary results on a mixture of 70% methane and 30% ethane were
obtained very near the vapor-liquid critical point (plait point). The
results are interesting in that the thermal conductivity of the mixture
does not exhibit a critical anomaly whereas pure methane does exhibit an
anomaly in the thermal conductivity as the critical point is approached.
The anomalous behavior of pure fluids and nonanomalous behavior of
mixtures is qualitatively and quantitatively in agreement with theoreti-
cal predictions (see preceding title 'Fluid Transport Properties'). We
hope to be able to perform more definitive measurements on hydrocarbon
mixtures in the near future.

7 . Program and Results .

7.1 Transient Hot-Wire Apparatus . The assembly of the apparatus is
complete and some preliminary measurements on air at low pressure and
near room temperature have been made. Some difficulties have arisen due
to the limited precision of the Nova minicomputer. The machine carries
only 16 binary digits precision and must be run in double precision.
Operation in this mode, however, increases execution time by a factor of
three. The data acquisition on this type of apparatus dictates that a
number of measurements be acquired in a little over two seconds. The
number of data points read in double precision is only marginally
adequate. Software means of circumventing this problem are now being
explored .

7.2 Laser Light Scattering Measurements . During the past reporting
period some additional measurements were made on a 70% methane-30%
ethane binary mixture near the mixture critical point (plait point).
These results are not definitive enough to establish for certain the
existence or non-existence of an anomaly in the thermal conductivity.
What is needed is a systematic study of the behavior of a series of
well-characterized mixtures, especially as the concentration of one
component goes to zero.

7.3 High Temperature PVT Apparatus . Adequate funding for this program
was obtained in December 1978; as a result design, procurement and
construction will proceed at a level of effort of approximately 1.5
staff-years/year. An automatic self-balancing thermometry bridge has
been obtained and checked out. Two precision quartz pressure
transducers (to 35 MPa) have been received and are installed in the NBS
Pressure Calibration System for calibration and long term stability
testing. Preliminary design of the experimental method and cell are in
progress as well as an examination of available high temperature baths.

A desktop calculator for data acquisition and experimental control is on
order .

8. Problem Areas . Light scattering has proven to be a valuable tool for

obtaining thermal diffusivity data on fluids. This is particularly true
in a broad temperature and density range around the critical point,
where more conventional experimental methods fail or are severely
limited. The intensity of the scattered light however decreases
drastically as one moves away from the critical region. Data accuracy
in this region becomes limited by the statistical nature of the
scattering process and the ability to maintain stability and precise
experimental parameters over the extended periods of time necessary for
data accumulation.

The difficulties outlined in 7.1 regarding the processing capabilities
of the present minicomputer persist in delaying the start of
experimental measurements at low temperature and high pressure.

9

9. Level of Effort . July 1 - December 31, 1978.

Staff-years expended

Equipment and/or Services Purchased
Approximate expenditures, total

0.8
6. 3K$
61 .0K$

10. Future Plans.

Objectives and Schedule: Quarter

1

2

Complete performance test transient
hot-wire thermal conductivity

apparatus. ^

Design, construct and performance

test high temperature-high

pressure PVT apparatus.

Laser light scattering measurements

on well-characterized binary

systems .

References

1. B. J. Ackerson and G. C. Straty, Rayleigh Scattering from Methane, J.
Chem. Phys . 6_9, 1207-12 (Aug 1978 ).

2. B. J. Ackerson and H. J. M. Hanley, The Thermal Diffusivity of Methane
in the Critical Region, Chem. Phys. Lett. 5_3 , 596-8 (Feb 1978 ).

10

Title. PROPERTIES OF CRYOGENIC FLUID MIXTURES

Principal Investigators . M. J. Hiza, A. J. Kidnay (part-time), and
R. C. Miller (part-time)

Cost Center Numbers . 7360123, 7362289, 7368574

Sponsor Project Identification . NBS , NBS (OSRD) , GRI

Introduction . Accurate thermodynamic properties data and prediction
methods for mixtures of cryogenic fluids are needed to design and
optimize low temperature processes and equipment. This project provides
new experimental measurements on equilibrium properties and compilations
of evaluated equilibrium properties data which are suitable for direct
technological use or for the evaluation of prediction methods.

Objectives or Goals . The overall objectives of this project are to
provide critically evaluated data on the phase equilibria and thermo-
dynamic properties of cryogenic fluid mixtures. The program has been
divided into the following elements:

a) Preparation of a comprehensive bibliography on experimental
measurements of equilibrium properties for mixtures of selected
molecular species of principal interest in cryogenic technology.

b) Selection and/or development of methods for correlation, evaluation
and prediction of equilibrium properties data.

c) Retrieval and evaluation of experimental data for specific mixture
systems selected on the basis of theoretical and/or technological
importance .

d) Preparation of guidelines for future research based on the
deficiencies noted in (a), (b), and (c).

e) Performing experimental research to alleviate deficiencies and
provide a basis for improvement of prediction methods.

Background . A physical equilibria of mixtures research project was
established in the Thermophysical Properties Division in 1959. The
initial effort, based on a bibliographic search and other considera-
tions, was directed toward the acquisition of new experimental data on
the solid-vapor and liquid-vapor equilibria and physical adsorption
properties for a limited number of binary and ternary mixtures of
components with widely separated critical temperatures. Most of the
systems studied included one of the light hydrocarbon species —
methane, ethane, or ethylene (ethene) — with one of the quantum
gases -- helium, hydrogen, or neon. The data for these systems led to
significant improvements in the predictions of physical adsorption
equilibrium and a correlation for the prediction of deviations from the
geometric mean rule for combining characteristic energy parameters. In
addition, significant new information was obtained for interaction third
virial coefficients which was used in a correlation by one of our
consultants, J. M. Prausnitz. The approach taken in this work has been
as fundamental as possible with the intention of having an impact on a
broad range of mixture problems.

Recent efforts have been directed toward problems associated with
systems containing components with overlapping liquid temperature
ranges, such as nitrogen + methane, methane + ethane, etc.

11