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Transcript
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 03.04.2017 2 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 03.04.2017 3 THERMOCHEMICAL MATERIALS FOR HEAT STORAGE APPLICATIONS - TCM Solid adsorption Sorption Liquid absorption Hydrates, Hydroxides Hydrides Thermochemical Materials - TCM Chemical reaction Carbonate Redox Ammonia Composites 03.04.2017 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 03.04.2017 5 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 03.04.2017 6 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. 03.04.2017 7 SALT HYDRATE DEHYDRATION STA EXPERIMENT • several dehydration steps • Identification of reaction free temperature intervals • Heating rate dependent conversion: input for kinetic models @ TU Wien 03.04.2017 8 METAL OXIDE REDOX CYCLING IN STA • Changing gas conditions during isotherms Oxidation Reduction • Cycling stability – Comparison Δm and ΔHR 03.04.2017 9 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) 03.04.2017 10 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 03.04.2017 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 11 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 / Jkg 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 03.04.2017 12 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 03.04.2017 Powder measurements THB sensor Lab oven 13 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 03.04.2017 coated sample liquid sample holder powder sample holder 14 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 kgm3 Sample (2), =1512 kgm3 0.6 Sample (3), =1505 kgm3 Mean, =1529 kgm3 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 kgm3 Sample (3), =2158 kgm3 Salt 0.5 Mean, =2186 kgm3 0.4 0.3 0.2 0.1 0 0 03.04.2017 Sample (2), =2206 kgm3 0.6 a10-6 / m 2s-1 a10-6 / m 2s-1 0.5 50 100 150 200 250 300 Temperature / °C 350 400 450 500 15 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 03.04.2017 26.2 26.4 26.6 Temperature /°C 26.8 16 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) 03.04.2017 17 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 03.04.2017 18 EFFECTIVE THERMAL DIFFUSIVITY AND CONDUCTIVITY SALT HYDRATE RESULTS 1.6 0.8 ; salt hydrate; =1529 kgm -3 eff; LFA ; salt hydrate; =1529 kgm -3 eff; LFA 1.4 a eff;LFA -3 eff; THB ; salt hydrate; =864 kgm LFA/DSC salt -1 1 eff; THB ; salt; =1547 kgm-3 0.6 -3 0.5 -1 eff / Wm K ; salt; =2186 kgm-3 eff; LFA ; salt; =2186 kgm 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 03.04.2017 19 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. 03.04.2017 20 THANK YOU! Daniel Lager, 3.4.2017 http://www.ait.ac.at/en/research-fields/thermophysics/