Time and Space Resolved Measurements from Rocket Engines

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Space and Plasma Physics Department KTH, Kungliga Tekniska H¨ogskolan

SE-100 44 Stockholm Sweden

TIME AND SPACE RESOLVED MEASUREMENTS FROM ROCKET ENGINES

August 31, 2012

Author:

Erik Fors

Supervisors:

Eva Sallander

Nickolay Ivchenko

Examinator:

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Abstract

Equipment planned to be part of space missions is put through a substantial series of tests in order to ensure a very high degree of reliability. This also applies to the HPGP thrusters manufactured by ECAPS AB. While conducting live fire tests the temperature is monitored using two separate systems, one pyrometer and one Infrared camera. The two systems show a difference in temperature for the same spot on the thruster. This is believed to be due to changes in the emissivity.

An experimental setup is designed in order to measure the behavior of the emissivity of this material to decrease measurement errors. The emissivity of the main construction, an aerospace alloy called TZM, is proven to change as function of temperature and surface state, thus giving rise to large inaccuracies in temperature when conducting measurements using an infrared camera. The acquired emissivity data are presented together with a suggested method to implement the results back into the system.

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Acknowledgments

I would like to express my gratitude to ECAPS AB in Solna that gave me the opportunity to conduct this masters thesis. I would also like to thank all employees for their valuable input and continuous help throughout the work. Pierre Consigny for good cooperation throughout the work with this masters thesis.

I would also like to thank Stefan Sj¨okvist at Termisk Systemteknik AB for his valuable input regarding heat transfer, as well as help with equipment. Dr. Nickolay Ivchenko at the Space and Plasma Physics Department at KTH for his valuable input as well substantial help with equipment.

One last thanks goes to my friends and family who has always been supportive during both this work as well as my studies in general, and I would definitely have had a hard time complet- ing my studies without you.

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List of Figures

1.1 Emissivity as function of temperature for some common materials [1] . . . 2

1.2 Emissivity as function of wavelength [1] . . . 3

2.1 Blackbody infrared spectra . . . 7

2.2 The difference in spectral emissivity between a blackbody, graybody and a selective emitter [1] . . . 8

2.3 Raytek Marathon MR-series pyrometer [8] . . . 10

2.4 The total amount of radiation reaching the infrared camera [1] . . . 11

2.5 FLIR P620 infrared camera [Photo: FLIR] . . . 12

2.6 The electrical connections of a thermocouple . . . 14

3.1 Black body cavity radiator . . . 18

3.2 Black body calibration source [Photo: Omega] . . . 18

3.3 Thermocouples attached to thruster for temperature monitoring [Photo: Author] 19 4.1 10×10 cm test piece with heaters and thermocouples [Photo: Author] . . . 25

4.2 The vacuum chamber used throughout the experiments [Photo: KTH] . . . 26

4.3 ZnSe BBAR IR transparent glass [Photo: Author] . . . 26

4.4 Internal view of vacuum chamber with sample and heating system [Photo: Author] 27 4.5 Total hemispherical emissivity of Molybdenum (red) and Niobium (green) as function of temperature . . . 29

4.6 Infra Red picture taken during temperature cycle using TZM [Photo: Author] . . 31

5.1 Emissivity of stainless steel as function of temperature and surface condition. The first measurement depicted as red and the second as black . . . 33

5.2 Emissivity of unoxidized TZM as function of temperature and surface condition. The first measurement done correspond to the blue, the second to the red and the last to the black graph, respectively . . . 35

5.3 Emissivity of slightly oxidized TZM as function of temperature. The structure can be described as: TZM #4 is depicted as blue, TZM #5 as red, TZM #6 as black, TZM #7 as magenta and TZM #8 as cyan . . . 37

5.4 The change in TZM surface state during the experiments [Photo: Author] . . . . 39

5.5 Emissivity of severely oxidized TZM as function of temperature . . . 39 5.6 Average emissivity value for each surface state. The curve depicted as red corre-

sponds to the unoxidized surface, the blue curve is the low temperature oxidized

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List of Figures List of Figures

5.9 Corresponding deviation in temperature for unoxidized and slightly oxidized TZM 43 5.10 Comparison between the experimentally obtained values for TZM in red, and the

total hemispherical emissivity of Molybdenum in black . . . 44 6.1 Live fire test chamber at FOI [Photo: ECAPS AB] . . . 45

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List of Tables

4.1 The TZM measurements carried out . . . 31

4.2 The Stainless steel measurements carried out . . . 31

5.1 The emissivity of Stainless steel presented in tabular form . . . 34

5.2 The emissivity of unoxidized TZM presented in tabular form . . . 36

5.3 The emissivity of slightly oxidized TZM presented in tabular form . . . 38

5.4 The emissivity of severely oxidized TZM presented in tabular form . . . 40

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Nomenclature

∆T Temperature difference

∆T (t) Temperature difference between body and fluid

∆x Distance between points λ Wavelength

Φ Total radiated power in the wavelength spectra of the camera φ Radiation angle

ρ Reflection coefficient ρg Density

σ Stefan-Boltzmann constant τ Transmission coefficient ε Emissivity

A Cross sectional surface area

Aλ Amplification constant at wavelength λ b Wien’s displacement constant

c Speed of light

E Total radiated power integrated over all wavelengths h Planck’s constant

h_T Heat transfer coefficient k_B Boltzmann constant k_T Thermal conductivity

M Total radiated power of an object as function of temperature and wavelength Q Thermal energy

S_λ Detector signal at wavelength λ

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List of Tables List of Tables

Tm Melting temperature

x Distance from camera to the target

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Chapter 1

Introduction

ECAPS AB, a Swedish company based in Stockholm, has over the last years developed a new type of fuel, the HPGP (High Performance Green Propulsion) as well as thrusters in a variety of thrust levels. This fuel is a less toxic alternative to the commonly used Hydrazine aboard satellites in order to carry out orbital maneuvers. The concept of HPGP was proven successful during the PRISMA mission launched in June 2010. During development and manufacturing of flight hardware for satellites, extensive testing is carried out in order to obtain a very high degree of reliability. The thrusters are test fired a number of times during which the use of more conventional contact temperature measurement systems, such as thermocouples, can be difficult and inaccurate.

This thesis is focuses on the investigation and implementation of a non-contact temperature measurement system, consisting of a infrared camera. A series of measurements are carried out to determine the emissivity of the materials used in constructing the thrusters, since knowing this is of utmost value. Doing this for a large number of temperatures and surface conditions will enable the possibility to combine these values with the camera output to obtain correct temperature information during a live firing test.

1.1 Problem description

The current method of measuring the temperature of the HPGP thrusters manufactured by ECAPS AB, is the use of a pyrometer, in this case the Raytek Marathon MR. The use of such a method limit measurements to only one point at a time. This implies that a large number of measurements is to be carried out in order to obtain temperature information for the whole engine. This is not practical and to further complicate matters, the surface of the engine will deteriorate over time.

This can be solved by using an IR-camera (infrared) instead of the pyrometer. Both these systems measure the amount of radiation from an object in the infrared spectra, with wavelengths ranging from 0.74 - 300 µm. This can be compared to the spectrum of visible light, between 390 - 750 nm.

1.1.1 Objective

The objective is to set up a system for time and space resolved thermal measurements of rocket engines using a pyrometer and infrared camera. This includes the evaluation and implementation of robust calibration and analysis methods and their implementation into the existing

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Chapter 1. Introduction 1.1. Problem description

The project is divided into two separate parts. The first part focuses on theoretical issues such as: evaluating the emissivity of rocket engine materials, identifying the ideal test environment as well as analyzing the acquired data, and to determine what trade-offs are necessary.

The second part is more hands-on and involves the design of different test setups to further validate the acquired data and implement them with data obtained from live firing tests at FOI.

1.1.2 Variable dependent emissivity

An infrared camera used for temperature measurements actually measures the radiant energy of the material surface. However, for almost all metals, the radiative properties of the surface will vary depending on the ambient environment and material properties. If these variations are not taken into account it might result in a significant difference between the values from the camera, the ”apparent temperature” and ”true temperature”. The solution is to update the emissivity value when conducting the experiments or by post processing in order to get correct temperature values.

Temperature dependency

The emissivity of most common materials vary with temperature. This is due to changes in surface crystallization during heating/cooling cycles. An other contributing factor is oxidization of the surface that for some materials appear for temperatures slightly above room temperature.

This means that objects of a certain temperature can be both cooler or hotter than they appear.

The behavior of the emissivity as function of temperature is shown in Figure 1.1 for some common materials.

Figure 1.1: Emissivity as function of temperature for some common materials [1]

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Chapter 1. Introduction 1.1. Problem description

Wavelength dependency

The usual behavior of metals with good surface condition is that the emission is high at short wavelengths and decreases with increasing wavelength, a behavior shown in Figure 2.1. If the material surface changes in any way, the behavior of the emissivity is much more random. It is shown in Figure 1.2 that the emissivity of common ”dirty” materials is very wavelength dependent. Such materials are called selective emitters. This varies greatly within the wavelength spectra. If a ”small enough” interval is chosen the emissivity can be assumed constant.

Figure 1.2: Emissivity as function of wavelength [1]

This assumption is not valid in this study since the wavelength spectrum is too wide, which means that the materials tested must be treated as selective emitters. Since the temperature sensing system used is a multi band infrared camera that is able to detect all wavelengths between 7.5 and 13 µm, the priority is to visualize the effects of changing temperature and surface condition.

Surface condition

It is quite obvious that the state of the surface will have a great impact on the emissivity of any material [2]. Altering the surface of the material in any way, degrading it through:

• Oxidation

• Corrosion

• Sandblasting

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Chapter 1. Introduction 1.2. Structure

or by somewhat improving it through:

• Polishing

• Painting

will change the radiative properties of the material, i.e both reflection coefficient and emissivity [2, 3]. This is especially important in this case since the surface finish of the thruster will differ greatly depending on operational life time.

1.1.3 Implementation

Since implementation of the non-constant emissivity into the existing measurement system is highly desirable, it is needed to know at what point in time to correct the emissivity. Since the software accompanying the camera does not allow for individual emissivity setting for each frame, a way to implement the corrected emissivity into the current measurement system is to be suggested.

1.2 Structure

The structure of the report is as follows:

• Chapter one gives a detailed description of the company where the masters thesis is carried out as well as the problem presented.

• The fundamentals of thermal radiation, other modes of heat transfer as well as information about the equipment used and their applications are presented in chapter two.

• Several experimental setups have been constructed in order to measure the emissivity, using both non-contact as well as a contact temperature measurements system. A number of these different solutions are reviewed in chapter three.

• Chapter four presents the suggested solution for the problem, describes the series of experiments carried out as well as each subsystem of the constructed experimental setup.

• Chapter five presents the results obtained from the experiments.

• Chapter six describes the existing test setup for live firing as well as a feasibility study as how to perform implementation into the existing system.

• Chapter seven discusses and concludes the experiments carried out and the results obtained.

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Chapter 2

Background

2.1 Heat transfer

There are three different major modes of heat transfer and each of these are explained briefly.

2.1.1 Conduction

Thermal conduction refer to the transfer of heat occurring due to interaction between particles in an object with areas of different temperatures. If the object is allowed to reach a form of steady state conduction, the temperature at a given point of the object is constant. This means that all derivatives of temperature with respect to time are equal to zero.

If the temperature at any part of the object varies in time, its is called transient conduction.

This typically appears when a perturbation in temperature is introduced and thereby changing the thermal state of equilibrium of the object.

Conduction can be described by Fourier’s law for 1-D heat flow through a homogeneous material [4], between two endpoints at constant temperature, according to

dQ

dt = −kTA∆T

∆x (2.1)

in order to describe the one dimensional heat flow between two points at constant temperature, where kT is the thermal conductivity of the material. A higher thermal conductivity increases the left hand side of equation (2.1), the amount of heat transferred. Materials with good thermal conductivities are a number of metals.

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Chapter 2. Background 2.1. Heat transfer

2.1.2 Convection

When heat is transferred between two places through an intermediary fluid it is called convection. A simple example of convection is the heating of a room using an electric radiator. In this case the air in the room acts as the fluid in which the heat propagates. Unlike thermal radiation, convective heat transfer sets in motion the particles in the fluid. This is achieved either by:

Natural convection: The heat transfer is generated by differences in the medium density.

This density difference is caused by the presence of temperature gradients in order for convection to take place.

Forced convection: The desired fluid movement is created through the use of a fan or pump.

This mode of heat transfer/loss can be drastically reduced by the use of a vacuum chamber, since the number of particles available to interact with is much smaller. Situations involving convection can be described by Newton’s law of cooling

dQ

dt = −hT · A∆T (t) (2.2)

The variable hT is the heat transfer coefficient, a material parameter that greatly impacts the amount of heat transferred.

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Chapter 2. Background 2.2. Thermal radiation

2.2 Thermal radiation

The third main mode of heat transfer is thermal radiation, or heat transfer through electromag- netic radiation, which do not need the presence of a transfer medium to occur. This mode of heat transfer is of particular interest in space applications where convection is negligible due to the very low density of space, and conductive heat transfer only enables heat to be transferred between different parts of the object. The only way to dissipate heat is thus through thermal radiation.

2.2.1 Blackbody

All objects with temperature above the absolute zero, 0K (-273.15 ℃) emit energy through thermal radiation. An ideal emitter is called a blackbody and no object can emit more energy [5]. The total radiant power from such a perfect emitter at temperature T and wavelength λ is described using Planck’s law.

M(λ, T ) = 2πhc² λ⁵

1 e

hc

λkB T −1 (2.3)

The radiance as function of wavelength is shown in Figure 2.1.

Figure 2.1: Blackbody infrared spectra

The obvious peaks in figure 2.1 give the wavelength λmax corresponding to the maximum emis- sion from a blackbody of temperature T . The wavelength can be calculated using Wien’s displacement law

λ_maxT = b (2.4)

where the right hand side is Wien’s displacement constant b = 2897.8 (µm·K).

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Chapter 2. Background 2.2. Thermal radiation

The total emittance of a blackbody is obtained by integrating the spectral emittance over all wavelengths according to

E(T ) =

∞

Z

0

M(λ, T )dλ = σT⁴ (2.5)

which is known as the Stefan-Boltzmann law [6].

2.2.2 Emissivity

A blackbody is regarded as a perfect emitter, and no object can emit more radiation. Unfortu- nately such perfect emitters are idealizations and do not exist. The emission from a real object is obtained by multiplying the emittance of a blackbody by the emissivity, a number that describes the radiative properties of the object at hand according to

Φobject(T ) = ε(T ) · Φblackbody(T ) (2.6)

where Φ is defined as the radiated power in the wavelength spectra of the infra red camera and

ε(T ) =

λ2

Z

λ1

ε(λ, T )dλ (2.7)

where λ1 and λ2 is the wavelength spectrum of the detector used, in this case λ1=7.5 µm and λ₂=13 µm .The emissivity is assumed temperature and wavelength dependent as well as depen- dent of the surface state. However, the emissivity can in some cases be assumed constant over all wavelengths. This is called the graybody approximation. The typical appearance of spectral emissivity for the three different emitters are shown in Figure 2.2.

Figure 2.2: The difference in spectral emissivity between a blackbody, graybody and a selective

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Chapter 2. Background 2.3. Remote temperature sensing

Regardless the assumptions, the conservation of energy states that the measured object reacts with the incoming radiation from its surroundings by absorbing, reflecting and transmitting parts of it, giving the following relation [6, 7]

1 = ε(λ, T ) + ρ(λ, T ) + τ(λ, T ) (2.8)

where ε is the emissivity of the object, ρ is the reflection coefficient and τ is the transmission coefficient. For an opaque body τ = 0, this yields a further simplified expression

1 = ε(λ, T ) + ρ(λ, T ) → ρ(λ, T ) = 1 − ε(λ, T ) (2.9)

The emissivity can also be assumed angular dependent, but this is not tested here since it holds that the emissivity is very close to independent of angles up to ∼ 45°. If taken into account the emissivity can be stated as ε(λ, T, φ) for each surface state.

2.3 Remote temperature sensing

2.3.1 Pyrometer

A pyrometer is a non-contact device that is used to measure the temperature at one single point of an object. The two major parts of the pyrometer are the optics, which focuses the thermal radiation emitted by an object, and the detector, which when hit by thermal radiation creates an output signal. This signal then connects the thermal radiation to object temperature through the Stefan-Boltzmann law, equation (2.5) [8].

The pyrometer available is the Raytek Marathon series MR in Figure 2.3. The temperature measurement range extends from 600℃ to 3000℃, which makes it useless for low temperatures.

1-color mode

The 1-color mode of the pyrometer is used for most standard temperature measurements. It is best used for situations were there are no sighting obstructions, solid or gases. In order to deliver accurate results the 1-color mode requires the target to fill the measurement spot, i.e the pyrometer is to be placed ”close enough” to the object of interest. It is also useful for situations where the background has a higher temperature than the target.

2-color mode

The pyrometer also has a special 2-color mode were the temperature is determined from the ratio of radiated energy from two separate wavelength bands, 0.75 to 1.1 µm and 0.95 to 1.1 µm).

This allows for temperature measurements where the target is partially obscured by for example smoke, or for situations where the target is smaller than the field of view of the pyrometer. This requires that the temperature of the target is higher than the background.

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Figure 2.3: Raytek Marathon MR-series pyrometer [8]

Applications

The pyrometer is most widely used in the production industry where non-contact temperature readings are vital. This includes the metal processing industry where it is used to monitor the temperature of the raw material going in to rolling mills, and asphalt industry where a correct temperature is needed to guarantee high quality of the finished product.

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2.3.2 Thermographic (Infrared) camera

A conventional camera creates a picture by detecting radiation of wavelengths visible to the human eye. The infrared camera works in the same way. The difference is the wavelength of the detected radiation, in the infrared spectra between 0.74 - 300 µm. Customarily a picture taken using this type of camera only contains one color channel. The pictures therefore often have a increasing scale from blue (cool) to white (hot) [9].

The infrared spectra was discovered in 1800 by an astronomer named Sir Frederick William Herschel (1738-1822), while breaking down sunlight into separate colors using a prism. He found that the temperature increased while moving from the violet to the red part of the light spectra. Out of curiosity he then measured the temperature of the area just beyond the red, an area that appeared empty, and found that this area had even higher temperature.

The thermographic camera has many advantages compared to the pyrometer. The main advantage is the possibility to take sequential photos at multiple frames per second. This allows for post processing of the data obtained at any given moment.

The total amount of radiation reaching the camera is shown in Figure 2.4. The sources of radiation included are the object, the ambient (surroundings) as well as the atmosphere.

Figure 2.4: The total amount of radiation reaching the infrared camera [1]

The amount of radiation detected by the camera can be written on the following form

Φcamera= τεΦ^bbobject+ τ(1 − ε)Φambient+ (1 − τ)Φatmosphere (2.10)

which is known as the ”Law of total radiation”. Assuming that the transmission coefficient of the atmosphere is τ = 1, equation (2.10) can be simplified to

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Cooled detectors

For ambient temperatures deviating largely from ”room temperature” it might be necessary to use a camera with a cooled detector. Usually the detector is cooled to cryogenic temperatures using an integrated cryocooler. However, there are a number of drawbacks with using a cooled detector. The gear needed to cool the camera is expensive and requires maintenance. Also, a cooling system implies that the detector needs to cool down for several minutes before reaching operational status.

The biggest advantage with using a cooled infrared detector is the superior image quality compared to uncooled detectors.

Uncooled detectors

The uncooled detector is mostly used for applications where it will operate in ambient temperatures close the atmospheric one. Also, the uncooled detector is commonly used in applications were the possibility to move the camera around rapidly is desired. The uncooled detector also has a longer service life than the cooled one, assuming the same operating conditions.

An example of an infrared camera using an uncooled detector, called a microbolometer with 640 × 480 pixels resolution, is the FLIR P620 shown in Figure 2.5. This is also the camera used in this study.

Figure 2.5: FLIR P620 infrared camera [Photo: FLIR]

Applications

Currently, the most common application for thermographic cameras is monitoring electrical and mechanical components. The camera is also used to detect mold in built structures, such as houses. It can also be used for determining ”leakage”, which is areas in houses where the energy

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Chapter 2. Background 2.4. Input variables

2.4 Input variables

There are a number of different variables needed to take into account in order to obtain correct results, which involve material properties, equipment properties, as well as information about the surrounding environment:

• Emissivity, ε

• Distance, x [m]

• Reflected temperature, Tref l [℃]

• Atmospheric temperature, Tatm [℃]

• Relative humidity [%]

• Temperature of external optics, Topt [℃]. (If external optics are not used the temperature is set to ambient)

• Transmission coefficient of external optics. (If external optics are not used the transmission coefficient is set τ = 1)

These variables can be manipulated on the camera itself or in the associated software, Ther- maCAM Researcher Professional. The pyrometer however is only in need of the emissivity, ε as input. In the two-color mode the input is the slope, which is calculated as the ratio of the emissivities of the first and second wavelength. The slope will vary somewhat depending on the surface state of the sample. For Stainless Steel, Cobalt, Steel, Iron and Nickel with oxidized surface the slope is ∼ 1, but ∼ 1.06 for the same materials with polished surface. The slope can be determined by using a thermocouple to measure the temperature of the object, and then adjust the setting of the slope until the pyrometer displays the same temperature.

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Chapter 2. Background 2.5. Thermocouples

2.4.1 Reflected Temperature

The reflected temperature, Tref l, has an impact on the accuracy of the results. It is described as the radiation detected by the thermographic camera from heat being reflected by the sample.

It is therefore crucial to reduce reflections from surrounding walls and materials. This means that the use of external lighting sources emitting radiation in the infrared spectra is not recom- mended. The camera itself is also reflected in the sample, which is clearly visible if the viewing angle is 90° to the sample.

The temperature of the camera reflection can be measured by the use of aluminum foil, attached to a piece of for example cardboard of the same size. This is then placed in front of the camera, with the foil facing the lens, the emissivity set to one and the temperature noted. The effect of the reflected temperature will decrease the higher the temperature of the sample. This is true for other reflections as well.

2.5 Thermocouples

Throughout the attempts to determine the emissivity, the temperature of the object is monitored using a thermocouple. This device consists of two different conductors, usually metal alloys, joined at one end. When the measuring point (hot junction) is exposed to hot or cold material, the temperature difference compared to the cold junction (reference temperature) gives rise to a voltage between the two metal tubes. This can easily be correlated to the temperature of the object. The electrical connections for the thermocouple is presented in Figure 2.6.

Figure 2.6: The electrical connections of a thermocouple

The thermocouple is the attached to the object by spot welding, soldering or Omega high temperature cement. This is a highly conductive filler, which withstands temperatures from -200 ℃ up to 843 ℃. For temperatures above the thermal limit of the cement, the thermocouples are welded to the material.

Assuming the temperature to be uniform throughout the sample, a single thermocouple is used.

It is to be placed in such a way that it will not endanger the validity of the measurements done using the thermographic camera.

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Chapter 2. Background 2.5. Thermocouples

The thermocouples used are manufactured by a company named Omega, and two types are available;

• K-type: made from Ni-Cr (+ Lead) and Ni-Al (- Lead) is usable for temperatures between -200 ℃ - 1250 ℃

• R-type: made from Pt-13% Rh (+ Lead) and Platinum (- Lead) is usable for temperatures between -200 ℃ - 1450 ℃

It must be noted that the R-type thermocouple is not suitable for use in atmospheric conditions due to oxidation. It is also highly sensitive to contamination.

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Chapter 3

Emissivity measurement

The emissivity of a material is an important variable when conducting thermal measurements whether a pyrometer or IR-camera is used since the emissivity is used as input for both devices.

It is therefore crucial to know the emissivity of the material on which measurements are being conducted. The most common application for IR-cameras today is for monitoring industrial processes, i.e. the target is at a steady state temperature.

For such applications the emissivity values for the most common materials are often given in tabular form. For dynamic systems, where temperature will decrease and increase at seemingly random times, tabular values can not be trusted, since little is known about the conditions during which it was determined (wavelength etc.). Another problem is that these values are often given at normal conditions, or at a temperature of particular interest for the material in question.

It has been decided that the simplest way to obtain the emissivity as function of temperature and surface state is therefore to find some means to measure it.

3.1 Measurement techniques

There are a number of different ways to measure the emissivity of materials. These are described and their positive and negative aspects are discussed.

3.1.1 Spectral emissivity measurement

The spectral emissivity measurement is carried out by placing a small sample of the material, typically a 3×3 or 5×5 cm plate a chamber, and the surrounding pressure is lowered to a vacuum-like state. The sample is heated to high temperatures and the radiant energy of the sample is measured using a spectrometer.

The radiant energy of the sample with unknown emissivity is then compared to that of a cavity radiator, an almost perfect black body (ε ∼ 1) at the same temperature.

By doing this the spectral emissivity of the sample can be determined, which is the emissivity as function of wavelength for a certain temperature. In order to obtain the total emissivity, integration over all wavelengths is carried out according to equation (2.6). Using this technique it is possible to obtain emissivity values for temperatures up to ∼ 400 ℃. This measurement system is available at FOI in Link¨oping. The main downside of this measurement technique is

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Chapter 3. Emissivity measurement 3.1. Measurement techniques

Black body cavity radiator

A black body cavity radiator is a device that is used to create a nearly perfect black body, with emissivity close to unity. A simple way of creating a near perfect black body is by using the cavity effect. This is done by creating a tiny hole in an insulated enclosure, as shown in Figure 3.1.

Figure 3.1: Black body cavity radiator

Using this type of black body simulator radiation will enter the cavity and is unlikely to be re-emitted if the cavity is large enough, which is highly desirable since a black body is referred to as a perfect absorber [3]. The inside of such a cavity is preferably covered black if possible to further increase the emissivity. A very similar effect is achieved by drilling a hole in the sample with a depth at least five times greater than the diameter. This is nevertheless a destructive method and therefore not preferred if the test sample is supposed to be used.

Black body calibrator

There are however better sources for black bodies, known as black body calibrators. This is a device that creates a black body cavity at desired temperatures. They are used to calibrate non contact thermal measuring devices such as pyrometers. Using this device complicates matters since there is no way of guaranteeing that the temperature is equal to that of the sample. This type of device is shown in Figure 3.2.

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3.1.2 Temperature monitoring

Another technique often used to determine the emissivity, is to use two types of temperature measurement systems. Normally the temperature is measured using one non-contact system, such as a radiometer, pyrometer or infrared camera. The other system normally consists of a spot welded thermocouple [12].

The thermocouple is placed on the sample in a strategic position, preferably out of view of the camera or pyrometer if these devices are used. This is done in order not to block the field of view, and to reduce the possibility of large errors.

The placement of several thermocouples on a ECAPS thruster is shown in Figure 3.3. These thermocouples are however attached using high temperature cement since the temperature does not exceed 300 ℃.

Figure 3.3: Thermocouples attached to thruster for temperature monitoring [Photo: Author]

The sample is placed in a chamber and the pressure is lowered to near vacuum in order to avoid convection to the surroundings. A certain amount of heat is applied. In this particular case the integrated heating system of the thruster is used. Assuming that the temperature given by the camera is inaccurate, and that the temperature given by the thermocouple is the correct one, the emissivity of the material is calculated by matching the temperatures.

3.1.3 Two-color pyrometer

Another method of measuring the temperature of an object with unknown and varying emissivity is to use a two-color pyrometer. This method differs from the ones described earlier in the way that no information about the emissivity is needed to obtain accurate temperature information. This is the method used in the two-color mode on the Raytek Marathon pyrometer [13, 14]. It uses Planck’s law to calculate the radiative power of the object according to equation (2.3), which is directly proportional to the measured output voltage signal according to

S_λ = Aλε(λ, T )Mλ(λ, T ) = Aλε(λ, T )2πhc² λ⁵

1 e

hc

λkB T −1 (3.1)

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This can be somewhat simplified by setting

C1 = 2πhc²= 3.74 · 10⁻¹⁶W m⁻² (3.2)

C2 = hc

k_B = 1.44 · 10⁻²mK (3.3)

and if temperatures are low enough the following approximation can be made e

hc

λkB T −1 = e^{λkB T}^hc (3.4)

By doing this for two different wavelengths λ1 and λ2, two output signals, S1 and S2, are ob- tained. The emissivity ε in equation (3.1) is unknown but assumed equal for the two wavelengths given that these are close enough to each other. Therefore it can be eliminated if the ratio be- tween S1 and S2 is calculated. The temperature of the object is then obtained according to

T = C2

₁

λ2 −_λ¹

1

ln^S_S¹

2

A2

A1(^λ_λ¹₂)⁵ (3.5)

The result of this method is highly dependent on the chosen wavelengths. If the wavelengths are close to each other, i.e ∆λ is small, the risk of large measurement errors increase. Contrariwise if the gap is wide, i.e ∆λ is large, the validity of the graybody assumption is questionable. Using more than two wavelengths have been adapted in some cases [15, 16].

3.1.4 Active pyrometer

The difference between the passive and active pyrometer lies in that the active system consists of a passive system that works as a receiver. This is then combined with a source of infrared thermal radiation. The active system basically works in two steps when calculating the temperature of an object.

First, the emissivity of the object is determined. This is done by measuring the amount of thermal radiation from the emitter reflected by the object and using the relation in equation (2.9). Second, the temperature of the object is determined by measuring the thermal radiation of the object and combining it with the previously calculated value of object emissivity [17].

Both techniques, described in the two previous sections, have one major disadvantage. A pyrometer is a one-spot thermal measurement system and can therefore only supply accurate information regarding temperature of one point at a time or if the sample is uniform in temperature.

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3.1.5 Surface coatings Electrical tape

The easiest way to determine the emissivity of a material is by using electrical vinyl tape with known emissivity, usually ε = 0.95. This technique is very similar to temperature monitoring described in the previous section.

A piece of the electrical tape is attached to the sample and the emissivity setting on the camera is set to that of the tape, i.e 0.95. The temperature of the tape is measured and assumed to be correct.

The camera is then focused at the sample itself, with unknown emissivity. The emissivity setting on the camera is adjusted so that the temperature of the sample matches that of the tape. This is the emissivity of the material.

Needless to say, this method is only useful for relatively low temperatures, ≤ 100 ℃.

High emissivity flat black paint

The method described in the previous section can be carried out at higher temperatures as well. This is done by replacing the electrical tape, with a coating of known emissivity. Usually, a high emissivity flat black paint is used (ε = 0.90), for example Aeroglaze [18]. This is the same type of paint used to coat the inside of telescopes and measurement systems were reflections must be avoided. This technique can be used for any surface coating with known emissivity.

Using typical high emissivity coatings such as Aeroglaze might be possible but no information is found regarding the change in emissivity of the coating itself. The interesting temperature range is well beyond what these coatings are able to survive.

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Chapter 4

Analysis Method

This chapter describes the methods used to determine the emissivity of the materials the thruster consists of, as well as other materials of interest.

4.1 Suggested solution

For the thruster, the emissivity is far from constant, and must be studied as a function of temperature and surface condition. It has therefore been decided that the best way is to use the temperature monitoring measurement technique.

4.1.1 Emissivity determination

Temperature dependence

By setting up the Law of total radiation, equation (2.10), and using the relation in equation (2.9), it must hold that

εcamΦ(Tcam) + (1 − εcam)Φ(Tref l) = εtrueΦ(Ttrue) + (1 − εtrue)Φ(Tref l) (4.1) where

Φ(T ) =

13µm

Z

7.5µm

M(λ, T )dλ (4.2)

Using equation (4.1) and (4.2), it can be shown that the true emissivity of the object is given according to

εtrue= Φ(Tcam) − Φ(Tref l)

Φ(Ttrue) − Φ(Tref l) · ε_cam (4.3)

which means that it is possible to state the emissivity of the material for a large number of temperatures. It also means that it is critical to measure the reflected temperature.

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Chapter 4. Analysis Method 4.1. Suggested solution

Surface condition

The measurements are carried out on materials with differing surface conditions. This is done in order to visualize the radiative properties of surfaces with degraded finish. The surfaces tested will vary according to the variations they might experience in space. This means that BOL (Beginning of life) condition is tested, a completely new surface. What is considered EOL (End of life) is also to be tested, as well as conditions beyond due to frequently occurring extended missions.

4.1.2 Computations

The data from the thermographic camera is post processed and each frame is exported from the accompanied software ThermaCAM Researcher Professional to Matlab as a 640 × 480 matrix.

This matrix contains temperature information for each single pixel in the thermal image. This also enables the possibility to export and alter system parameters such as the emissivity setting of the camera. This is usually set = 1 in order to simplify equation (4.3) further. Additional outputs available from the camera software are:

• Date and time: Containing the year, month, day and hour the recording was done.

• Scaling: Containing the camera scaling parameters from measurements as well as specifies the type of output (temperature, difference temperature, etc.).

• Object parameters: Containing the parameters set for the object such as emissivity ε, object distance x, reflected temperature Tref l, etc.

the last one being of particular interest, if for some reason the emissivity deviates from one.

A program is written in Matlab that detects the circular sample. It extracts the temperature from the center, where the tip of the thermocouple is located, and computes the radiated power using Planck’s law, equation (2.3). It also extracts the necessary information from the vector containing object parameters. The emissivity setting on the camera as well as the reflected temperature is of interest. The latter is also inserted into Planck’s law in order to calculate the radiated power from surroundings reflected by the sample. The true radiated power is calculated using the temperature from the thermocouple. Lastly, equation (4.3) is used to calculate the true emissivity of the object. All computations are done using Matlab.

Since the power is set to a predetermined setting and the sample allowed to reach equilibrium, the temperatures inserted into Planck’s law from camera and thermocouple are the mean values from each recording. The output is two separate vectors, one containing the emissivity and the other containing the temperature from the thermocouple.

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Chapter 4. Analysis Method 4.2. Laboratory set-up

4.1.3 Ideal test environment

When performing temperature measurements using a thermographic camera, there are a few environmental factors needed to be taken into account in order to obtain accurate temperature values. Equation (2.9) states that the sum of the emissivity and the reflection coefficient equals unity. Given that most metals have a low emissivity it is highly desirable to reduce the reflectivity for all surrounding materials to as close to zero as possible. Doing this will drastically reduce errors in temperature occurring due to radiation of the measured object being reflected by the surrounding walls. Also other sources that emit radiation that can be detected by the camera is to be removed.

This can be achieved by coating the inside of the test chamber with high emissivity paint, or by draping it with black MLI (Multi-layered insulator). Equipment placed near, or on the sample itself, will endanger the accuracy of the results due to reflections. It can also be favorable to reduce the ambient pressure to a minimum in order to reduce the convection, making it easier to heat the sample uniformly if desired.

4.2 Laboratory set-up

4.2.1 Initial set-up

The initial testing made consists of heating plates of stainless steel seen in Figure 4.1, to temperatures ∼ 350 ℃ in atmospheric conditions and ambient temperature of 19 ℃. The samples are placed inside a big box-like structure. The inside is covered flat black in order to reduce reflections. These tests are carried out in order to prove the possibility of measuring the emissivity using two separate temperature measurement systems.

Figure 4.1: 10×10 cm test piece with heaters and thermocouples [Photo: Author]

The temperature is measured by three thermocouples cemented in place. The temperature in the sample varies largely due to large scale convection and can not be assumed uniform throughout the sample. This implies that the emissivity is not equal if choosing two different points on the plate. It is therefore decided that the best idea is to decrease the size of the sample from the original 10×10 cm, as well as making use of a vacuum chamber, which enables the possibility to reach higher temperatures.

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4.2.2 Vacuum chamber

In order to achieve a vacuum-like surrounding, and decrease the convection when conducting measurements, a vacuum chamber is used. The chamber is shown in Figure 4.2 and is borrowed from the Department of Space and Plasma Physics at KTH.

Figure 4.2: The vacuum chamber used throughout the experiments [Photo: KTH]

The camera is positioned at the near end of the chamber focused through a special type of zink-selenide (ZnSe) glass with Broad Band Anti Reflection (BBAR) coating shown in Figure 4.3, that does not block or reflect infrared radiation, like ordinary quartz.

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The vacuum chamber is fitted with a TRIVAC prevacuum pump and a Alcatel CFV100 turbo pump which allows for the pressure to be lowered to less than 4 · 10⁻⁵ Torr (0.005 Pascals).

The test samples are placed, one at a time in a special sample holder in the center of the chamber. The pressure is reduced to the smallest possible before heat is applied. This is done in order to try to eliminate other effects on changes in emissivity than temperature. The complete setup including heating system and sample is shown in Figure 4.4.

Figure 4.4: Internal view of vacuum chamber with sample and heating system [Photo: Author]

4.2.3 Heating system

The heating system is shown in Figure 4.4. It consists of tungsten filaments inserted into a pellet of boron nitride, a ceramic with excellent thermal conductivity [19] and poor electrical properties.

The tungsten filaments are the same as used in a halogen light, which when in use reach temperatures of several thousands of Kelvin. Given a good enough thermal connection with the boron nitride a substantial amount of that heat is transferred conductively to the boron nitride and the sample. The sample is placed in a small cavity of the ceramic, both in order to reduce movement and to ensure good thermal contact.

An advantage gained by using tungsten filaments and boron nitride, is that the melting point is at ∼ 3400 ℃ for tungsten and at ∼ 2900 ℃ for boron nitride which is well above the maximum target temperature of ∼ 1000 ℃. This also holds for the melting point of any sample. Therefore a substantial margin of safety is created.

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This setup allows the sample to reach temperatures close to 1000 ℃ for both the steel and TZM, in vacuum surrounding only since a tungsten filament disintegrates in a matter of seconds if used in atmospheric conditions. The difference in maximum temperature reached is assumed to be due to the substantial difference in thermal conductivity of the tested materials.

The maximum power input needed for the heating system is ∼ 100 W in order to reach maximum temperature.

4.2.4 Samples

The materials of interest is the one currently used in the construction of the thruster as well as another other commonly used material. The temperature is monitored, throughout the test, using a thermocouple which is positioned in a small drilled hole in the side of the sample and soldered in place in order to allow proper thermal contact. The samples are small circular disks with a diameter of 10 millimeters and thickness of 2 mm.

The small size of the samples is motivated by the fact that a smaller sample achieves higher temperature for a given input power than a larger one. It is also prone to reach thermal equilibrium quicker, since the losses through radiation and convection are quickly balanced by the input power.

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TZM (Titanium-Zirconium-Molybdenum)

The TZM alloy is the main material used when constructing the ECAPS thruster. It mainly consists of Molybdenum (Mo), but with small quantities of Titanium (Ti) as well as Zirconium (Zr). The typical composition is Mo-99.4%, Ti-.5% and Zr-.08%.

The basic physical properties of TZM are:

• Melting point, Tm: 2623 ℃

• Density, ρg: 10.22 g/cm³

• Thermal conductivity, kT: 118 W/(m·K)

The TZM alloy is widely used throughout the aerospace industry due to the possibility of very high operating temperatures, low thermal expansion, corrosion resistance and relatively low cost compared to other high temperature alloys, for example Niobium. The total hemispherical emissivity of Niobium and pure Molybdenum, which TZM to 99.4% consists of, are shown as a function of temperature in Figure 4.5, depicted as red, and Niobium as green [20, 21].

Since the total hemispherical emissivity is calculated according to ”in all directions and over all wavelengths”, the experimentally obtained values are not to be directly compared to the ones presented below without caution. The TZM alloy is commonly described as having emissivity

”around 0.2”, or regarded as a ”low emissivity” alloy [22].

0 500 1000 1500 2000 2500

0.05 0.1 0.15 0.2 0.25 0.3

Emissivity of Aerospace alloys

T [^oC]

ε [−]

Figure 4.5: Total hemispherical emissivity of Molybdenum (red) and Niobium (green) as function of temperature

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Stainless steel

A steel alloy with a minimum quantity of 11% Chromium (by mass) is the definition of Stainless Steel. The addition of chromium forms a thin layer on the steel surface. This layer is too thin to see with the naked eye and it is impenetrable by air and water, thus preventing corrosion to reach and weaken the internal structure of the steel.

Basic physical properties:

• Melting point, Tm: 1500 ℃

• Density, ρg: ∼ 8 g/cm³

• Thermal conductivity, kT: 10-50 W/(m·K) (very dependent on alloy)

There are an enormous number of different grades of stainless steel. The resistance to corrosion makes stainless steel relatively low maintenance and therefore very popular in various applications such as: a building material, gun construction, and watches.

The use of stainless steel in this experiment is motivated both by the large number of ap- plications in which it used but it is also used as ”trial”, which means it is used in order to prove the functionality of the measurement system before using TZM.

4.2.5 Test plan

It is critical to have repeatability in the experiments in order to obtain accurate results for the emissivity. In order to visualize the effects of changes in surface condition the same sample is subjected to the same heating treatment multiple times after being exposed to oxidation and other surface altering environments. The first test is to be done using a new surface, for example polished. The condition is to deteriorate throughout the experiments obtaining a severely oxidized surface for the last measurements. The surface state is changed by heating the sample and allowing it to cool in atmospheric conditions between temperature cycles.

The power input of the heating system is increased stepwise and the temperature is allowed to stabilize at each level in order to avoid measurement errors. The input power is increased until a sufficiently high temperature is reached, or the maximum temperature possible for the heater configuration.

The measurement parameters are defined as:

• Temperature span - Defined as the lowest and highest temperatures at which measure- ments are made.

• Final pressure - The pressure reached before heat is applied.

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The TZM parameters are presented in Table 4.1

Sample Name Temperature span [℃] Final pressure [Torr]

TZM #1 351-955 4 · 10⁻⁵

TZM #2 351-894 4 · 10⁻⁵

TZM #3 281-772 4 · 10⁻⁵

TZM #4 294-923 4 · 10⁻⁵

TZM #5 297-806 4 · 10⁻⁵

TZM #6 271-836 4 · 10⁻⁵

TZM #7 369-637 4 · 10⁻⁵

TZM #8 344-874 4 · 10⁻⁵

TZM #9 331-763 4 · 10⁻⁵

Table 4.1: The TZM measurements carried out

The same parameters for the measurements done using stainless steel are presented in Table 4.2.

Sample Name Temperature span [℃] Final pressure [Torr]

Stainless #1 330-763 4 · 10⁻⁵ Stainless #2 520-796 4 · 10⁻⁵ Table 4.2: The Stainless steel measurements carried out

A picture taken during one of the temperature cycles is presented in Figure 4.6. The sample is seen as the small circular, glowing portion in the center of the figure. The contact heater made from boron nitride is the circular area around the sample. The external metallic structures are the connections for the tungsten filaments, they are quite hard to see in this picture. In this picture the heating system is turned off, and yet the sample appears to have a somewhat elevated temperature compared to the surroundings. This is actually the reflections of the camera in the sample giving a 5.5 ℃ difference in temperature between sample surface and background.

Figure 4.6: Infra Red picture taken during temperature cycle using TZM [Photo: Author]

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Chapter 5

Results

The results obtained from the emissivity measurements carried out according to table 4.1 and table 4.2, with both Stainless steel as well as TZM are presented in the following chapter.

5.1 Stainless Steel

The results when measuring the emissivity as function of temperature and surface condition of stainless steel are presented in Figure 5.1. It should be noted that since this sample is solely used as a trial piece, no extra attention is given to the surface state of the test sample before each test. This implies that the results presented are not to be compared to tabular values of the emissivity without extra caution.

300 400 500 600 700 800

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Emissivity of Stainless steel

T [^oC]

ε [−]

Figure 5.1: Emissivity of stainless steel as function of temperature and surface condition. The

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Chapter 5. Results 5.1. Stainless Steel

There is a small decrease present in emissivity for the last data point in one of the measurements, depicted as red in Figure 5.1. This is due to heater failure. This implies that the temperature started to decrease during the measurement causing the temperature to be too low. Also, the

”bump” around 600 ℃ is most likely due to a change in calibration range of the IR camera, from 0-500 ℃ to 300-1500 ℃.

The values obtained from the measurements are also presented in tabular form in Table 5.1.

The first two columns to the left correspond to temperature cycle one depicted as red in Figure 5.1 and the ones to the right to number two respectively (depicted as black).

Stainless #1 Stainless #2 T₁ [℃] ε₁ T₂ [℃] ε₂

330.9 0.150 519.7 0.147 442.2 0.156 591.9 0.154 521.4 0.156 634.4 0.158 586.7 0.163 690.0 0.163 641.3 0.189 730.1 0.163 690.6 0.191 772.2 0.167 737.3 0.191 796.0 0.168

763.1 0.189 - -

Table 5.1: The emissivity of Stainless steel presented in tabular form

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Chapter 5. Results 5.2. TZM

5.2 TZM

The results of the measurements carried out are presented in the figures 5.2, 5.3 and 5.5 for TZM with different surface states. Due to various problems encountered while using an unsheathed R-type thermocouple together with TZM a more conventional K-type probe is used. TZM is not tested in atmospheric conditions due to the alloy being prone to heavily oxidize if subjected to high temperatures.

5.2.1 Unoxidized

In Figure 5.2 the temperature dependent emissivity for unoxidized TZM is shown. The objective is to keep the surface as equal as possible for all three measurement series. Therefore the sample is allowed to cool until it reaches room temperature before any changes or repairs are made to the setup. Theoretically, the graphs should coincide.

200 300 400 500 600 700 800 900 1000

0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095

Emissivity of unoxidized TZM

ε[−]

T[^oC]

Figure 5.2: Emissivity of unoxidized TZM as function of temperature and surface condition.

The first measurement done correspond to the blue, the second to the red and the last to the black graph, respectively

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The TZM measurements are presented in tabular form in Table 5.2.

TZM #1 TZM #2 TZM #3

T1 [℃] ε1 T2 [℃] ε2 T3 [℃] ε3

351.6 0.075 351.7 0.068 281.1 0.064 486.6 0.078 569.1 0.073 330.0 0.066 582.9 0.080 716.9 0.079 401.2 0.068 657.3 0.082 836.7 0.086 488.0 0.073 734.0 0.084 894.3 0.090 586.9 0.077

788.9 0.086 - - 667.5 0.080

842.7 0.089 - - 709.7 0.082

879.4 0.091 - - 740.0 0.084

915.1 0.092 - - 772.0 0.086

954.7 0.094 - - - -

Table 5.2: The emissivity of unoxidized TZM presented in tabular form

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5.2.2 Slightly Oxidized

In order to alter the radiative properties of the surface of the sample, it is oxidized. Since the heater setup used does not allow for heating in atmospheric conditions, the sample is heated to a predetermined temperature and allowed to cool until room temperature. During the cooling, air is let back in to the chamber, i.e. the heating system is turned off and the chamber is opened at the desired temperature. The oxidation of the sample is done according to:

• TZM #4: allowed to cool from 300 ℃

• TZM #5: one additional cooling from 300 ℃ (in addition to TZM #4)

• TZM #6: one additional cooling from 400 ℃ (in addition to TZM #5)

• TZM #7: no further oxidation

• TZM #8: no further oxidation

and the results are graphically presented in Figure 5.3.

200 300 400 500 600 700 800 900 1000

0.075 0.08 0.085 0.09 0.095 0.1

Emissivity of slightly oxidized TZM

T[^oC]

ε[−]

Figure 5.3: Emissivity of slightly oxidized TZM as function of temperature. The structure can be described as: TZM #4 is depicted as blue, TZM #5 as red, TZM #6 as black, TZM #7 as magenta and TZM #8 as cyan

Even though the sample is subjected to oxidative environments multiple times, no clear tendency can be seen regarding the change in emissivity. It is therefor concluded that the additional coolings, before measurement #5 and #6, are not changing the surface enough for a clear change to be visible in figure 5.3. The different surface states presented are therefor treated as equal. In order to visualize a significant increase in emissivity due to oxidation the sample is

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The results from measurements done using slightly oxidized TZM are presented in tabular form in Table 5.3.

TZM #4 TZM #5 TZM #6 TZM #7 TZM #8

T₄ [℃] ε₄ T₅ [℃] ε₅ T₆ [℃] ε₆ T₇ [℃] ε₇ T₈ [℃] ε₈ 385.7 0.081 297.5 0.079 271.1 0.071 368.7 0.075 344.4 0.071 519.7 0.082 370.4 0.080 358.2 0.072 478.8 0.079 480.5 0.075 598.5 0.084 499.3 0.084 500.4 0.074 548.9 0.083 559.6 0.077 671.8 0.087 577.6 0.087 572.6 0.078 637.1 0.086 648.9 0.081

739.4 0.088 662.7 0.090 639.3 0.082 - - 717.5 0.084

826.3 0.094 718.1 0.094 708.8 0.085 - - 779.6 0.087

882.3 0.097 806.1 0.098 780.6 0.089 - - 833.5 0.091

922.8 0.099 - - 821.7 0.094 - - 873.7 0.093

- - - - 836.4 0.095 - - - -

Table 5.3: The emissivity of slightly oxidized TZM presented in tabular form

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5.2.3 Heavily Oxidized

A single measurement is carried out after the sample is allowed to cool until reaching room temperature from ∼ 800 ℃ in order to ensure a severely oxidized surface. The results from this measurement are shown in Figure 5.5. The difference in surface state between this test and the unoxidized surface is shown in Figure 5.4a and 5.4b.

(a) Unoxidized TZM sample with thermo-

couple (b) Heavily oxidized TZM sample with

thermocouple

Figure 5.4: The change in TZM surface state during the experiments [Photo: Author]

The results from this measurement are presented in Figure 5.5.

200 300 400 500 600 700 800 900 1000

0.15 0.155 0.16 0.165 0.17 0.175 0.18

Emissivity of severely oxidized TZM

T[^oC]

ε[−]

Figure 5.5: Emissivity of severely oxidized TZM as function of temperature

Time and Space Resolved Measurements from Rocket Engines

TIME AND SPACE RESOLVED MEASUREMENTS FROM ROCKET ENGINES

August 31, 2012

Author:

Erik Fors

Supervisors:

Eva Sallander

Nickolay Ivchenko

Examinator:

Acknowledgments

Contents

List of Figures

List of Tables

Nomenclature

Chapter 1

Introduction

1.1 Problem description

1.2 Structure

Chapter 2

Background

2.1 Heat transfer

2.2 Thermal radiation

2.3 Remote temperature sensing

2.4 Input variables

2.5 Thermocouples

Chapter 3

Emissivity measurement

3.1 Measurement techniques

Chapter 4

Analysis Method

4.1 Suggested solution

4.2 Laboratory set-up

Chapter 5

Results

5.1 Stainless Steel

5.2 TZM