Multi-point temperature measurements in packed beds using phosphor thermometry and ray tracing simulations (Open Access)--颗粒学报PARTICUOLOGY

Xuan, G., Ebert, M., Rodrigues, S. J., Vorhauer-Huget, N., Lessig, C., & Fond, B. (2024). Multi-point temperature measurements in packed beds using phosphor thermometry and ray tracing simulations. Particuology, 85, 77-88. https://doi.org/10.1016/j.partic.2023.03.015

Multi-point temperature measurements in packed beds using phosphor thermometry and ray tracing simulations (Open Access)

Guangtao Xuan ^a, Mirko Ebert ^b, Simson Julian Rodrigues ^c, Nicole Vorhauer-Huget ^c, Christian Lessig^b, Benoît Fond ^{a d *}

a Institute of Fluid Dynamics and Thermodynamics, OVGU Magdeburg, Universitaetsplatz 2, Magdeburg, 39106, Saxony-Anhalt, Germany
b Institute of Simulations and Graphics, OVGU Magdeburg, Universitaetsplatz 2, Magdeburg, 39106, Saxony-Anhalt, Germany
c Institute of Process Engineering, OVGU Magdeburg, Universitaetsplatz 2, Magdeburg, 39106, Saxony-Anhalt, Germany
d ONERA, The French Aerospace Lab, Department of Aerodynamics, Aeroelasticity and Aeroacoustics (DAAA), Paris-Saclay University, 8, rue des Vertugadins, Meudon, 92190, France

10.1016/j.partic.2023.03.015

Volume 85, February 2024, Pages 77-88

Received 23 December 2022, Revised 6 March 2023, Accepted 16 March 2023, Available online 5 April 2023, Version of Record 21 April 2023.

E-mail: benoit.fond@onera.fr

Highlights

• Concept for non-contact multi point thermometry in non-transparent packed beds.

• Particles coated with thermographic phosphors to measure temperatures inside the bed.

• Separation of signal from multiple spheres using linear regression and ray tracing simulations.

• Validation of 3-point measurements in regular bed against thermocouple readings.

• Multi-point measurements used to refine heat transfer model of the whole bed.

Abstract

Packed bed reactors are commonly found in the process industry, for example in flame-assisted calcination for cement production. Understanding the heat transfer inside the bed is essential for process control, product quality and energy efficiency. Here we propose a technique to determine the internal temperature distribution of packed beds based on a combination of lifetime-based phosphor thermometry, ray tracing simulations, and assimilation of temperature data using finite element heat transfer simulations. To establish and validate the technique, we considered a reproducible regular packing of 6 mm diameter aluminum spheres, with one of the spheres in the top layer being electrically heated. If a sphere inside the packing is coated with thermographic phosphors and excitation light is directed towards the packing, luminescence from the coated sphere exits the packed bed after multiple reflection and the sphere's temperature can be determined. Isothermal measurements showed that the temperature obtained by phosphor thermometry is independent of the luminescent sphere location. When imaging the luminescence on a camera, the luminescence distribution in recorded image depended, however, on the position of the sphere. Therefore, in setups with multiple phosphor-coated spheres, their signals can be separated using a least squares fit. We demonstrate the approach using a setup with three luminescent spheres and validated the temperature readings against thermocouple measurements. To obtain the spatial signatures for individual sphere positions required for the least squares fit, ray tracing simulations were used. These provide an efficient alternative to single sphere measurements that are only practical for regular spherical packed beds. Multi-point measurements were used as input to a finite element heat transfer simulations to determine parameters such as particle-to-particle air gap distance. With these, the full temperature distribution inside the bed could be assimilated from the measured values.

Graphical abstract

Keywords

Packed beds; Phosphor thermometry; Ray tracing; Heat transfer simulation; Data assimilation

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