# Development of Stereo DIC Measurement on thermal energy storage tank: Determination of mechanical response

G. Alonso Aruffo, Yasmine Lalau, Luc Penazzi, Rébecca Bonnaire

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G. Alonso Aruffo, Yasmine Lalau, Luc Penazzi, Rébecca Bonnaire. Development of Stereo DIC Measurement on thermal energy storage tank: Determination of mechanical response. International Conference in Experimental Mechanics, University of Bologna, Jul 2025, Bologna (ITA), Italy. hal-05327634

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Submitted on 23 Oct 2025

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# DEVELOPMENT OF STEREO DIC MEASUREMENT ON THERMAL ENERGY STORAGE TANK: DETERMINATION OF MECHANICAL RESPONSE

G. Alonso Aruffo<fnref n="1" />, Y. Lalau<fnref n="2" />, L. Penazzi<fnref n="3" /> and R. Bonnaire<fnref n="3" />

## 1. Introduction

A Thermal Energy Storage (TES) system captures thermal energy by heating or cooling a storage medium for later use in heating applications or power generation. This study focuses on TES storage tanks using the thermocline principle, with a packed bed as heat storage material. Currently, there is little to no experimental data in the literature on the response of heat storage tanks to these loads, due to the difficulty in accessing the tank surface because of thermal insulation. This work presents an experimental setup designed to measure displacement (and resulting strains) of the tanks surface using non-contact optical measurement techniques, specifically 3D stereo correlation. Results obtained by this measurement will be used to validate a digital twin.

## 2. Materials and methods

The TES system on which tests were performed on, is a pilot version of the industrial facility described by [1]. For the 3D stereo correlation tests, a horizontal test bench was used with two cameras (Allied vision, 5 MPX resolution). The optics were of the type Kowa CCTV LENS 1"50mm/F1.4. Images were captured using Vic-Snap (Correlated Solution ©) and post processing using the VIC-3D (Correlated Solution ©) softwares. Lighting was ensured by a MHI-type light source using a Dedolight 400D lamp. The storage system used a propane gas burner and fans to achieve thermal load up to 500°C and cooling during the tests.

<figure><img src="image_3.png" /><figcaption>Fig. 1. (left) Porthole design, (right) experimental set up integrated to the TES</figcaption></figure>

This study faced two main challenges in data acquisition: accessing the external surface of the TES and dealing with environmental conditions during the experiments. Outdoor conditions such as wind, sunlight variations, and humidity could affect the quality of images obtained by 3D DIC [2-3]. These

<footnote n="1">¹ IRCER, Université de Limoges, CNRS 7315, Limoges, France</footnote>

<footnote n="2">² RAPSODEE, Université de Toulouse, IMT Mines Albi, Albi, France</footnote>

<footnote n="3">³ Institut Clément Ader (ICA), Université de Toulouse, CNRS, IMT Mines Albi, INSA, ISAE-SUPAERO, UPS, Campus Jarlard, F-81013 Albi, France</footnote>
factors can be mitigated during post-processing. This work focuses solely on developing the experimental setup to access the tank's surface.

The diameter of the porthole (Fig. 1) was chosen to ensure that the measurement area represents the average size of the heterogeneous storage material. To minimize potential heat dispersion caused by the porthole, quartz glass was mounted using high temperature resistant silicone (SILCOSET 158). It is assumed that the presence of quartz glass between the surface and the cameras can be neglected [4]. The tank surface was prepared by cleaning with acetone and ethanol before applying a speckle pattern using high temperature resistant spray paint (Nespoli).

## 3. Results and conclusions

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 2. Displacements and strain variation with temperature</figcaption></figure>

These results were filtered to remove measurement errors related to the test environment. Details of the filtration procedure and subsequent validation are discussed in previous work [5]. The final displacement evolution fields as a function of temperature are shown in Fig. 2. The calculated strains (also in Fig. 2) indicate material elongation due to thermal expansion.

This study significantly improved our understanding of the mechanical response of thermal storage structures, which remains poorly understood and controlled. In addition to the complex experimental conditions, which added value to this work, the quality of the results obtained in terms of repeatability are a real step forward for the implementation of a numerical model.

## 4. Acknowledgements

The research presented in this paper has received funding from the France Relance program.

## 5. References

[1] Lalau, Y., Al Asmi, I., Olives, R., Dejean, G., Meffre, A., & Py, X. (2022). Energy analysis and life cycle assessment of a thermal energy storage unit involving conventional or recycled storage materials and devoted to industrial waste heat valorisation. Journal of Cleaner Production, 330, 129950.

[2] Badaloni, M., Rossi, M., Chiappini, G., Lava, P., & Debruyne, D. (2015). Impact of experimental uncertainties on the identification of mechanical material properties using DIC. Experimental Mechanics, 55, 1411-1426.

[3] Pan, B., Wu, D., & Yu, L. (2012). Optimization of a three-dimensional digital image correlation system for deformation measurements in extreme environments. Applied optics, 51(19), 4409-4419.

[4] Su, Y., Yao, X., Wang, S., & Ma, Y. (2017). Refraction error correction for deformation measurement by digital image correlation at elevated temperature. Optical Engineering, 56(3), 034106-034106.

[5] Alonso Aruffo, G., Lalau, Y., Penazzi, L., Bonnaire, R. Development of a displacement and strain measurement method using optical non-contact method in complex environments - submitted