Download Experimental approaches to analyse thermophysical

EXPERIMENTAL APPROACHES TO ANALYSE THERMOPHYSICAL
PROPERTIES OF THERMOCHEMICAL HEAT STORAGE MATERIALS
3. April 2017
Daniel Lager
Research Engineer – Center for Energy
[email protected]
http://www.ait.ac.at/en/research-fields/thermophysics/
OVERVIEW
• Thermochemical Heat Storage – principle, requirements and materials
• SolidHeat Projects – objectives, partners and methods
• Experiments @ AIT
• Preliminary STA experiments for further thermophysical characterisations
• DSC experiments for apparent cp(T) measurements
• THB experiments of powdery and liquid samples
• LFA experiments on compacted, powdery and liquid samples
• Liquid measurements and simulation
• Powdery samples in 3 layer model
• Conclusion and Outlook
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THERMOCHEMICAL ENERGY STORAGE - TCES
Principle
• Utilisation of the enthalpy of reversible chemical reactions or sorption effects
• Heat storage is charged as long as both reaction partners are separated and
discharged when they are brought together
A(s,l) + B(g) ↔ AB(s,l)
• Mainly in powder form but also liquids
• No heat loss to the environment in comparison to
sensible and latent heat storage – no thermal insulation necessary
Requirements
• High energy density, reversible without side reactions, fast reaction rates
(kinetics), easy to handle, economic
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THERMOCHEMICAL MATERIALS FOR
HEAT STORAGE APPLICATIONS - TCM
Solid adsorption
Sorption
Liquid absorption
Hydrates, Hydroxides
Hydrides
Thermochemical
Materials - TCM
Chemical reaction
Carbonate
Redox
Ammonia
Composites
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Sorption and Hydrates
4
SOLIDHEAT PROJECTS
Project objectives
• Identify promising materials and
reactions for TCES
• Characterization of physical and
chemical properties
• http://solidheat.project.tuwien.ac.at/
Methods
• STA (TGA-DSC), DSC, LFA, THB,
XRD, XRF, FTIR, BET
Dissemination:
• Systematic search algorithm for
potential thermochemical energy
storage systems
Project Partners
• TU Wien institutes: Energy systems
• High temperature energy storage:
and thermodynamics, Applied
Kinetic investigations of the
Synthetic Chemistry, Chemical
CuO/Cu2O reaction cycle
Engineering, Chemical
Technologies and Analytics
• Academy of fine arts (XRF)
• Austrian Institute of Technology AIT
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STA result
EXPERIMENTS @ AIT
Measured quantities
Mass change and reaction enthalpies ΔHr
• STA and TGA experiments
• Apparent specific heat capacity app. cp(T)
• hf-DSC experiments
• Effective thermal diffusivity and conductivity aeff(T), λeff(T)
• LFA and THB experiments
THB Sensor in
compacted powder
LFA samples with peeled
of graphite coating
DSC sensor
LFA sample with
sputtered Au coating
LFA liquid
sample holder
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PRELIMINARY STA EXPERIMENTS
Preliminary STA experiments
were conducted to identify:
• Reaction free temperature intervals,
educt or product exists at a certain
temperature range
• Reaction rate of the measured
conversion related to sample mass
and applied heating rate
• Reaction enthalpies
• Cycling experiments for
repeatability tests
• not expected results: degradation,
phase transitions, etc.
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SALT HYDRATE DEHYDRATION STA EXPERIMENT
• several dehydration steps
• Identification of reaction
free temperature
intervals
• Heating rate dependent
conversion: input for kinetic
models @ TU Wien
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METAL OXIDE REDOX CYCLING IN STA
• Changing gas conditions
during isotherms
Oxidation Reduction
• Cycling stability –
Comparison Δm and ΔHR
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DSC EXPERIMENTS
• Pure hf-DSC experiments in the identified
loose powder
reaction free temperature intervals
• Direction: AB(s,l)  A(s,l) + B(g)
• Measurement of educt and product in two
consecutive cycles to avoid reaction with
ambient gas conditions
• Sample form: compacted and loose powder
• Mass correction according preliminary
STA results
• Repeatability tests by measuring at least
3 samples
• Measurement uncertainty evaluation based on GUM [1]
compacted
sample
[1] Guide to the expression of uncertainty in measurement - JCGM 100:2008 (GUM 1995 with
minor corrections - Evaluation of measurement data)
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SALT HYDRATE EXPERIMENT
900
700
U
DSC
6
10 / V
600
500
400
800
700
600
500
400
300
300
200
200
100
100
1st run
• Dehydrating the salt
hydrate in the DSC
(pierced lid Al crucibles)
• Cooling back to Tstart using
dry inert gas conditions
0
0
-100
T / °C
800
900
Baseline (1)
Baseline (2)
Baseline (3)
Reference (1)
Reference (2)
Reference (3)
Sample (1)
Sample (2)
Sample (3)
Temperature
20
30
40
50
60
70
-100
t / min
45
40
35
30
25
6
UDSC  10 / V
run
• Measuring the pure salt
using under the same
experiment conditions
• Mass correction according
the STA results
20
800
700
600
500
400
15
300
10
200
5
100
0
0
-5
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900
Baseline (1)
Baseline (2)
Baseline (3)
Reference (1)
Reference (2)
Reference (3)
Sample (1)
Sample (2)
Sample (3)
Temperature
20
30
40
t / min
50
60
70
T / °C
2nd
-100
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APPARENT SPECIFIC HEAT CAPACITY ANALYSIS
2
900
Baseline (1)
Baseline (2)
Baseline (3)
Reference (1)
Reference (2)
Reference (3)
Sample (1)
Sample (2)
Sample (3)
Temperature
700
DSC
run
U
1st
6
10 / V
600
1.5
500
400
800
700
600
500
400
300
300
200
200
100
100
0
0
-1
-100
20
30
40
50
60
70
-100
t / min
1.25
-1
/ Jkg K
T / °C
800
1.75
Salt Hydrate
Salt
Salt NIST-JANAF tables
900
45
0.75
40
2nd run
35
25
6
UDSC  10 / V
30
0.5
20
900
Baseline (1)
Baseline (2)
Baseline (3)
Reference (1)
Reference (2)
Reference (3)
Sample (1)
Sample (2)
Sample (3)
Temperature
800
700
600
500
400
15
300
10
200
5
100
0
0.25
0
-100
-5
0
100
200
T / °C
app. c  10
p
-3
1
0
20
30
300
40
t / min
400
50
60
70
500
-100
600
T / °C
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THB EXPERIMENTS
•
•
•
•
•
•
Transient Hot Bridge Sensor with metal frame
Sample form: powder & liquid
Quantity: Thermal conductivity
Lab oven with ambient gas conditions
Temperature range 25 – 200°C (sensor limit)
THB experiments direction:
• AB(s,l)  A(s,l) + B(g) or direct A(s,l)
Calibration
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Powder measurements
THB sensor
Lab oven
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LFA EXPERIMENTS
• Light and Laser Flash
• Sample form: compacted solid,
coated solid, liquid and powder
containment powdery
• LFA experiments direction:
• AB(s,l)  A(s,l) + B(g) or direct A(s,l)
• Repeatability tests by measuring at least 3 samples
• Measurement uncertainty evaluation based on GUM [1]
compacted
cylinder
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coated
sample
liquid sample
holder
powder
sample holder
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LFA RESULTS SALT HYDRATE
0.7
Starting from the hydrated salt
• Dehydrating destructs the
compacted sample and the
coating
• Thickness is changing
• Data usable before
dehydrating reaction
Sample (1), =1570 kgm3
Sample (2), =1512 kgm3
0.6
Sample (3), =1505 kgm3
Mean, =1529 kgm3
0.4
Salt hydrate
0.3
0.2
0.1
0
0
50
100
150
200
250
300
Temperature / °C
350
400
450
500
0.7
Starting from the dehydrated
salt
• Higher initial density
• Compact sample survives
the measurement
• Data usable over whole
measurement range
Sample (1), =2194 kgm3
Sample (3), =2158 kgm3
Salt
0.5
Mean, =2186 kgm3
0.4
0.3
0.2
0.1
0
0
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Sample (2), =2206 kgm3
0.6
a10-6 / m 2s-1
a10-6 / m 2s-1
0.5
50
100
150
200
250
300
Temperature / °C
350
400
450
500
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LFA EXPERIMENTS LIQUIDS
closed 3-layer sample
holder
• Reference: H2O a(25°C)=0.146 ∙10-6 m²/s
• 3 Layer setup:
• graphite coated steel cover plates
• steel frame outside and PEEK ring inside
• 3 Layer LFA Model with heat loss
• LFA measurement on several samples with varying pulse energy, focus of
the detector, range of model calculation
• Measured a=0,144 ∙10-6 m²/s, σ=2,373∙10-9 m²/s
Thermal Diffusivity /(mm^2/s)
0.150
0.148
0.146
0.144
0.142
0.140
0.138
0.136
26.0
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26.2
26.4
26.6
Temperature /°C
26.8
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LIQUID SAMPLE HOLDER FE MODELL
• Axially symmetric 2D FE Model
• Simulation with water compared to measurement data
steel cover
plates
steel plate
sample
PEEK ring
steel ring
• different run time between
center and edge
• ratio of λPEEK to λsample
crucial
(λPEEK ~ 0,3 Wm-1K-1)
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LFA EXPERIMENTS POWDER
• Powdery sample in special sample holder system
Sample holder system
• 3 Layer setup:
• graphite coated Al cover plates (d=1 mm)
• steel frame with steel screw
• High pulse energy necessary due to thermal mass
and low λeff off the powdery samples – small
sample volume
• Measured aeff depends on
• Bulk density ρB of the packed bed
• Constant sample thickness (deformation of Al cover plates)
• λ of the used gas (λHe=0.154 W∙m−1∙K−1, λAr=0.018 W∙m−1∙K−1)
• Particle form, contact area size, particle arrangement, imperfections in
the bed…
• Further experiments and models on spherical powder with known
properties and sample holder system
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EFFECTIVE THERMAL DIFFUSIVITY AND
CONDUCTIVITY SALT HYDRATE RESULTS
1.6
0.8
; salt hydrate; =1529 kgm
-3
eff; LFA ; salt hydrate; =1529 kgm
-3
eff; LFA
1.4
a
eff;LFA
-3
eff; THB ; salt hydrate; =864 kgm
LFA/DSC salt

-1
1
eff; THB
; salt; =1547 kgm-3
0.6
-3
0.5
-1
eff / Wm K
; salt; =2186 kgm-3
eff; LFA ; salt; =2186 kgm
1.2
0.7
0.8
0.4
0.6
0.3
LFA/DSC salt hydrate
0.4
0.2
THB salt
0.2
0.1
THB salt hydrate
0
50
100
150
200
250
300
350
400
450
500
550
T / °C
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a 10-6 / m2 s-1
eff
a
CONCLUSION & OUTLOOK
• Preliminary STA tests are useful to identify reaction free temperature
intervals, reaction enthalpies, cycling stability and not expected effects
• Evaluation of the apparent cp(T) of educt and product can be evaluated
in one run using the hf-DSC
• λeff measurements of powders and liquids using THB can be done without
much effort in sample preparation
• aeff and λeff measurements of powders and liquids in the LFA need accurate
sample preparation. Side effects of the used sample holder have to be taken
into account.
• Further experiments on spherical powder with known properties using THB,
LFA and HFM are planned.
• The impact of the LFA powder sample holder will be modeled and calculated.
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THANK YOU!
Daniel Lager, 3.4.2017
http://www.ait.ac.at/en/research-fields/thermophysics/