The objective is to develop an accurate dynamic technique which, in a microgravity environment, would enable performance of thermophysical measurements on high-melting-point electrically conducting substances in their liquid state. In spite of the critical need in high temperature technologies related to spacecraft, nuclear reactors, effects of power laser radiation, and in validating theoretical models in related areas, no accurate data on thermophysical properties exist. This is primarily due to the limitation of the reliable steady-state techniques to temperatures below about 2000 K, and the accurate millisecond-resolution pulse heating techniques to the solid state of the specimen. The limitation of the millisecond-resolution techniques to temperatures below the melting point stems from the fact that the specimen collapses due to the gravitational force once it starts to melt. The rationale for the use of the microgravity is that by performing the dynamic experiments in a microgravity environment the specimen will retain its geometry, and thus it will be possible to extend the accurate thermophysical measurements to temperatures above the melting point of high-melting-point substances

Cezairliyan, Ared

Miller, Archie P.

English

NASA Technical Reports Server

N89 -2031 7' 
DYNAMIC THERMOPHYSICAL MEASUREMENTS IN SPACE 
Ared Cezairliyan and Archie P. Miiller 
Thermophysics Division 
National Bureau of Standards 
Gaithersburg, Maryland 20899 
Text of Presentation at the Microgravity Science Review 
February 10-12, 1987 
Marshall Space Flight Center 
A1 ab ama 
PRECEDING PAGE BiAYK NOT FILMED 
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https://ntrs.nasa.gov/search.jsp?R=19890010946 2020-03-20T03:54:30+00:00Z
ABSTRACT 
The objective of this research is to develop an accurate dynamic 
technique which, in a microgravity environment, would enable performance of 
thermophysical measurements on high-melting-point electrically conducting 
substances in their liquid state. 
temperature technologies related to spacecraft, nuclear reactors, effects of 
powerful laser radiation, etc., and in validating theoretical models in 
related areas, no accurate data on thermophysical properties exist. This is 
primarily due to the limitation of the reliable steady-state techniques to 
temperatures below about 2000 K, and the accurate millisecond-resolution pulse 
heating techniques to the solid state of the specimen. 
millisecond-resolution techniques to temperatures below the melting point 
stems from the fact that the specimen collapses due to the gravitational force 
once it starts to melt. The rationale for the use of the microgravity is that 
by performing the dynamic experiments in a microgravity environment the 
specimen will retain its geometry, and thus it will be possible to extend the 
accurate thermophysical measurements to temperatures above the mel.ting point 
of high-melting-point substances. 
The research includes: (1) establishment of the geometrical. stability 
In spite of the critical need j:n high 
The limitation of the 
criteria for specimens when heated rapidly, in a microgravity environment, to 
temperatures above their melting point, (2) development of techni.ques and 
instruments for the accurate measurement of quantities, such as current, 
voltage, temperature, under conditions required for dynamic experiments in a 
microgravity environment, ( 3 )  demonstration of the applicability of the 
millisecond-resolution pulse heating technique by performing, in a 
microgravity-environment, definitive measurements of the heat of fusion of a 
refractory metal such as niobium and tests for heat capacity and electrical 
resistivity measurements in the liquid phase, ( 4 )  exploratory work on the 
feasibility of measuring thermal conductivity of high temperature conducting 
and semiconducting liquids, and (5) design and construction of a system for 
accurate dynamic measurements of thermophysical properties in the Space 
Shuttle. 
764 
1. INTRODUCTION 
1.1. Obiective 
The objective of the research is to develop an accurate dynamic 
technique which, in microgravity environment, would enable thermophysical 
measurements to be performed on high-melting-point electrically-conducting 
substances in their liquid state at temperatures above 2000 K. 
1.2. Rationale 
Reliable thermophysical properties data on high-melting-point substances 
in their liquid phase are almost nonexistent due to the serious and often 
unsurmountable difficulties involved in performing experiments at very high 
temperatures. 
high-temperature technologies related to spacecraft and rocketry (protective 
heat shield, etc.), understanding the behavior of substances exposed to 
powerful laser radiation, studies related to the operation of nuclear 
reactors, as well as in validating the theoretical models and predictions of 
the behavior of substances under extreme conditions. 
Yet, such data are critically needed in various areas of 
Steady-state techniques for the reliable measurements of properties are 
generally limited to temperatures below about 2000 K. Dynamic techniques 
involving rapid pulse heating of the specimen have the potential of extending 
this limit to higher temperatures. 
been developed which can provide accurate data up to about 4000 K. 
techniques, however, are limited to the solid phase of the specimen, since the 
specimen disintegrates and collapses under the gravitational force once it 
reaches its melting point. It seems logical, therefore, that by performing 
the experiments in a microgravity environment, it will be possible to extend 
the limits of the accurate dynamic techniques to temperatures above the 
melting point of the specimen. 
Millisecond-resolution techniques have 
Such 
1 . 3 .  Summary of Research 
The first phase of the work is to establish the geometrical stability of 
a specimen when heated rapidly to temperatures above its melting point in a 
microgravity environment. A system has been designed and constructed which 
765 
permits rapid heating of the specimen to temperatures above its melting point 
and checking of the geometrical stability of the liquid specimen. This system 
has been flown three times on board of KC-135 aircraft. The results suggested 
several refinements imd modifications in the system, which are presently being 
made. Some additional work is needed in this direction to understand the 
complete behavior (geometrical stability) of the liquid specimen .heated 
rapidly by the passage of a high current pulse through it, and as a result, 
optimize the specimen geometry and the operating conditions of thle overall 
sys tem . 
The second phase of the work is to add new measurement capabilities to 
the system and to demonstrate the applicability of the technique by performing 
definitive measurements of the heat of fusion of a refractory metill, such as 
niobium, in a microgravity environment. In addition, measurements of heat 
capacity and electrical resistivity in the liquid phase will also be 
performed. Exploratory research will be conducted to determine the 
feasibility of measuring another important property, thermal conductivity, of 
high temperature conducting or semiconducting liquids utilizing the dynamic 
heating technique in a microgravity environment. 
As much as possible, some of the initial tests will be conducted on 
board of KC-135 aircraft. However, the ultimate goal is the performance of 
the measurements in the Space Shuttle for reasons that it provides a better, a 
more reliable, and a longer microgravity environment essential for the success 
of all the experiments. For this purpose, a miniaturized and highly automated 
millisecond-resolution system will be designed and constructed. 
2. BACKGROUND 
2.1. Measurements on Solids by a Dynamic Technique 
The increasingly critical need for thermophysical properties data above 
the limit of accurate steady-state experiments has motivated the establishment 
of the Dynamic Measurements Laboratory at the National Bureau of Standards. 
As the result of the pioneering research conducted in this laboratmory, a novel 
dynamic technique has been developed for accurate thermophysical measurements 
at high temperatures. During the past decade or s o ,  this laboratory has 
provided reliable data on selected thermal, electrical, and optical properties 
766 
of a number of electrically-conducting solids at high temperatures 
(1500 - 3700 K), up to their melting points. The measured properties include: 
heat capacity, electrical resistivity, thermal expansion, hemispherical total 
emissivity, normal spectral emissivity, temperature and energy of solid-solid 
phase transformations, and melting temperature. 
The technique involves heating the specimen resistively from room 
temperature to temperatures of interest in short times (typically about 1 s )  
by passing an electrical current pulse through it; and simultaneously 
measuring the pertinent experimental quantities with millisecond resolution. 
Because of the short heating time, this dynamic technique circumvents, to a 
very large extent, tlie problems (such as, chemical reactions, evaporation, 
specimen containment, large heat transfers, etc.) which seriously affect the 
reliable operation of conventional steady-state techniques at temperatures 
above about 2000 K. The dynamic technique is limited, however, to 
measurements on solids up to their melting temperatures, at which point the 
specimens become geometrically unstable and collapse due (In large measure) to 
the influence of gravity. 
2.2. Measurements on Liquids bv Dynamic Techniques 
There are two possible options in extending the measurements to 
temperatures above the melting point of the specimen. These options are: (1) 
submillisecond heating of the specimen and performance of the measurements 
with microsecond resolution, and (2) performance of the experiments in a 
microgravity environment with millisecond resolution. 
In the first case, heating of the specimen is very fast in comparison to 
its movement under the gravitational force; thus, all the pertinent 
measurements may be performed on the liquid specimen before the specimen 
collapses. This technique has been used by a few investigators to obtain data 
on liquid metals. However, there are two major objections to this technique: 
(1) because of the very high speeds (microsecond resolution) measurements of  
the experimental quantities are considerably less accurate than those made at 
slower speeds (millisecond resolution), and (2) because of the very high 
heating rates, the validity of the assumption that the specimen is under 
thermodynamic equilibrium at any given instant becomes doubtful and, as a 
767 
result, the significance of determined properties becomes questionable. 
The second case, namely performing the measurements in a microgravity 
environment, is very attractive because it is a natural extension of the 
highly accurate millisecond-resolution technique. 
3. Measurements in a Microgravitv Environment 
3.1. AccomDlishments and Present State 
A research project, supported in part by NASA, was initiated in our 
laboratory to investigate the feasibility of performing thermophysical 
measurements in a microgravity environment utilizing the 
millisecond-resolution dynamic heating technique. The first step was the 
design, construction and testing of an equipment package, and performance of 
preliminary experiments to determine stability of the liquid specirnens at high 
temperatures. For this initial phase, we selected the KC-135 flight program 
from among several NASA facilities for microgravity research (drop tubes, drop 
towers, other research aircraft, etc.) on the basis of compatibility with our 
measurement system requirements: (1) near-zero gravity time of 2 to 5 s 
duration, (2) short time interval (few minutes) between successive 
experiments, (3) "hands-on" access to the experiment package by test 
personnel, ( 4 )  flexibility of performing experiments in a "free-f:toat" or 
"tied-down" mode, and (5) large experiment package (volume -- 40 ft , weight 3 
= 700 lbs). 
3.1.1. Test EauiDment Rackage 
The test equipment package for experiments on board of KC-135 aircraft 
was constructed as two separate units: (1) the pulse-heating system 
(nominally 2 '  wide x 4.5' long x 3.5' high; weight = 450 lbs) which includes 
the specimen cartridge cell and all measuring and recording instruments; and 
(2) the main battery pack (nominally 2' wide x 4' long x 1' high; weight = 
250 lbs) which supplies the electrical power for pulse heating the specimen. 
The instrumentation in the pulse-heating system includes: a 
single-wavelength pyrometer, a high-speed framing camera, a two-channel 
digital storage oscilloscope for recording the specimen temperature and the 
768 
current through the specimen, and a four-channel time delay generator for 
controlling the timing of various events such as, triggering the recording 
system, turning the framing camera on and off, closing and opening two 
fast-acting relay-driven switches which are connected in series in the 
power-pulsing circuit, etc. The second switch is closed 100 ms before and 
opened 100 ms after the first switch and thus serves as a backup in the 
(unlikely) event the first one fails to open at the end of the heating period. 
An "oscillo-streak" attachment on the framing camera enables a streak-image o f  
an analog oscilloscope display of the pyrometer signal and the image of the 
rapidly heating specimen to be simultaneously recorded on the film; this 
feature greatly simplifies the analysis of the high-speed photographs. The 
framing camera is powered by a separate pack of gel cells in order to minimize 
the need for electrical power from sources external to the test equipment 
package. However, approximately 0.5 kilowatts of 110 V (60 Hz) a.c. power is 
required to operate certain instruments such as oscilloscopes and timers. 
Each specimen is mounted inside its own cartridge cell containing argon 
gas at a pressure of 1 atm (gauge). 
be quickly inserted into and removed from the power-pulsing circuit before and 
after each experiment. 
fabricated thereby permitting up to ten specimens to be studied during a 
single KC-135 flight. 
The cells are designed so that they can 
A total of ten identical cartridge cells were 
3 .1 .2 .  Preliminary Experiments on Board of KC-135 
Three series of dynamic experiments under microgravity conditions were 
performed on board of KC-135 aircraft. The objectives were: (1) to test the 
integrity and operation of the equipment package, and (2 )  to investigate 
the behavior of the specimen during melting and postmelting periods. A s  the 
result of the experiments, after each flight, additions and changes were made 
in the equipment and specimen assembly to improve the operation of the system 
and specimen stability in the liquid phase. 
The specimens (niobium) were fabricated in the form of cylindrical rods, 
3 mm in diameter and 18 mm in length (distance between clamps). 
portion of each rod was reduced in diameter or "necked-down" in order to 
define the length of the zone which undergoes melting. 
The center 
The nominal dimensions 
769 
of the melting zone, that is, the "effective" specimen, were as follows: a 
diameter of about 2.5 mm, and an aspect ratio (1ength:diamter) in the range of 
1:l to 3:l. The portions of the rods near the clamps were tapered. to a 
diameter of 2 mm in order to reduce axial heat conduction from the "effective" 
specimen. 
experiment, between approximately 1.8 and 4.5 s .  The corresponding heating 
The duration of the current pulse varied, depending on the 
-1 rates were in the range 700 to 1700 Kos . During pulse heating, the behavior 
of the specimen was photographed by a high-speed framing camera operating at 
500 fps while other pertinent experimental quantities such as the signals from 
the optical temperature sensor and from the accelerometers were recorded every 
5 ms by digital storage oscilloscopes. Analyses of the (surface) radiance 
temperature-time data revealed that "effective" specimens with aspect ratios 
of 1.5:l or less tended to yield the largest excursions (about 50 K) into the 
liquid phase before becoming unstable. 
3 . 2 .  Planned Work 
Research is in progress to establish optimum configuration of the 
specimen geometry and optimum operational conditions of the measurement system 
in order to maximize the temperature excursion of the specimen in the liquid 
phase. A new design, triaxial configuration for the specimen and current 
return paths, for the experiment chamber is being investigated. With this new 
design, it will be possible to balance electromagnetic forces on the specimen, 
and account for the surface tension of the specimen. 
As a step toward thermophysical measurements, research has been 
initiated to design and construct novel high-speed pyrometers (mul.tiwavelength 
and spatial scanning) for temperature measurements and instrumentation for 
pulse electrical measurements. 
measurement of the heat of fusion of niobium has been performed in our 
laboratory utilizing a recently developed microsecond-resolution t:echnique. 
This result will be compared with the data on heat of fusion that will be 
obtained in the first phase of the thermophysical measurements in the 
microgravity environment. 
and electrical resistivity of liquid niobium. 
As a part of the verification scheme, 
The next step will be measurements of heat capacity 
Exploratory work has begun to 
770 
determine the feasibility of measuring another important property, thermal 
conductivity, of high temperature conducting or semiconducting liquids 
utilizing the dynamic heating technique in a microgravity environment. These 
measurements are likely to require experiment durations greater than 20 s .  
Studies of the requirements for the experiments in the Space Shuttle have 
begun. 
board of KC-135 aircraft, design and construction of a highly-automated 
apparatus for thermophysical measurements in the Space Shuttle will be 
started. 
Upon completion of these studies and the preliminary experiments on 
4 .  PUBLICATIONS 
1. A .  Cezairliyan, Dynamic Technique for Measurements of Thermophysical 
Properties at High Temperatures, International Journal of Thermophysics, 
- 5, 177 (1984). 
(This publication is a summary of research performed in the Dynamic 
Measurements Laboratory at NBS and contains 50 references to 
publications describing the results of various aspects of our work until 
1984). 
2. A. Cezairliyan and A.P. Miiller, Heat Capacity and Electrical 
Resistivity of POCO AXM-541 Graphite in the Range 1500-3000 K by a Pulse 
Heating Technique, International Journal of Thermophysics, 6 ,  285 
(1985). 
3 .  A . P .  Miiller and A .  Cezairliyan, Thermal Expansion of Molybdenum in the 
Range 1300-2800 K by a Transient Interferometric Technique, 
International Journal of Thermophysics, 6 ,  695 (1985). 
4 .  A. Cezairliyan and J.L. McClure, A Microsecond-Resolution Transient 
Technique for Measuring Heat of Fusion of Metals: Niobium, International 
Journal of Thermophysics, in press. 
77 1 


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