Sebastian Sas Brunser


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Sas Brunser

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Sebastian

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0000-0001-6168-829X

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2019 - 201912020 - 202514
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Publications 1 - 10 of 15
  • Introducing FIVER: An Open-Source Tool to Simulate Heat Transfer in Participating Media and Arbitrary Geometries
    Item type: Other Conference Item
    Wetaski, Charles; Sas Brunser, Sebastian; Casati, Emiliano (2024)
  • Optimized Ceria Structures for Enhanced Efficiency in Solar Thermochemical Fuel Production
    Item type: Doctoral Thesis
    Sas Brunser, Sebastian (2025)
    The world’s dependence on fossil fuels and its consequent release of CO₂ is the primary driver of climate change, with the transportation sector contributing approximately 15% of net global emissions. While achieving net-zero CO₂ emissions in passenger car transport is viable via electric motors powered by renewable electricity, this is not yet possible for large vehicles and long-haul travel, particularly in aviation. To address this challenge, a two-step thermochemical cycle shows the potential to make aviation and other fuel-intensive sectors more sustainable by producing synthetic fuels from CO₂ and H₂O using solar energy. This thermochemical cycle takes place in a solar reactor filled with a porous structure made of ceria. The ceria porous structure is directly exposed to concentrated solar radiation, which is absorbed through the structure’s volume, facilitating the efficient high-temperature heat transfer directly to the reaction site. Tailoring the topology and shape of the ceria porous structure can enhance the penetration of solar radiation deeper into the structure, resulting in uniform heating and lower losses, without compromising the structure’s total active mass. In this work, the topology of the ceria structure is optimized using a novel voxel-based Monte Carlo ray-tracing algorithm that simulates radiative heat transfer in a voxel (three-dimensional pixels) discretized representation of the structures. The algorithm identifies ray-solid intersections by querying the voxels’ value (solid or void) along the ray’s trajectory. This approach eliminates the need to solve the 3×3 system of equations required for each ray - solid’s surface combination in a standard ray tracer, resulting in a significant increase in speed (approximately 90 times faster). The new algorithm is verified by estimating the optical properties of known porous media and by simulating the complete radiation heat exchange within a cavity. The results are compared to those obtained by a standard MC ray tracer and the analytical radiosity method. Optimized ceria structures feature hierarchically ordered channels and circumvent the exponential radiative attenuation characteristic of isotropic topologies. These structures achieve a higher and more uniform temperature profile when exposed to concentrated solar radiation compared to state-of-the-art reticulated structures. The higher overall temperatures achieved by these structures improve their redox performance, doubling the amount of carbon monoxide (the fuel) for the same solar energy input. A complete solar reactor is designed using the optimized ceria structures. The ceria structures form a cavity that maximizes the available volume for ceria loading within the solar reactor while avoiding excessively high radiative flux zones. The modular cavity design allows it to be self-supported, maintaining its integrity and stability without requiring additional materials or bonding. The modular design also isolates propagating cracks within the structures. To fabricate the optimized ceria structures, a novel manufacturing technique is implemented for the direct 3D printing of the ceria structures. The 3D printed ceria structures are subsequently vacuum coated and infiltrated to enhance their mechanical robustness and long-term stability. The assembled solar reactor is tested at ETH’s High-Flux Solar Simulator, where up to 5.13 kW radiative power enters the solar reactor’s aperture. The operational parameters of the two-step thermochemical cycle are adjusted, focusing on the solar-to-fuel energy efficiency as the key performance indicator. Experimental results reveal that the 3D printed solar reactor doubles the fuel yield of the benchmark solar reactor containing a reticulated porous ceramic ceria structure. Furthermore, a record solar-to-fuel energy efficiency of 6.29% is achieved, surpassing the previous record established in a significantly larger 50 kW solar reactor. These findings contribute to the economic viability of solar fuels, bringing sustainable aviation closer to reality. While this thesis focuses on the use of ceria and its two-step thermochemical cycle, the methodologies presented can be applied to optimize other absorber materials utilized in various directly irradiated solar reactors.
  • Enhanced Radiative Heat Transfer of Concentrated Solar Energy in Hierarchically Ordered Porous Structures
    Item type: Other Conference Item
    Sas Brunser, Sebastian; Braun, Hugo; Vandenberghe, Roxanne; et al. (2022)
    2022 AIChE Annual Meeting Proceedings
    We report on the testing of novel porous ceria structures for CO2 splitting via a redox thermochemical cycle driven by concentrated solar energy. These structures were 3D-printed using a Direct Ink Writing (DIW) technique and were designed with hierarchically ordered porosity gradients to circumvent Beer-Lambert’s exponential attenuation law and thus enable longer propagation of the incoming radiation. Experimental testing was performed in a solar-driven thermogravimetric analyzer, in which the ceria samples were directly exposed to high-flux irradiation, mimicking the realistic operation of solar reactors. At the same time, their mass change, temperature, and product gas composition were continuously monitored during the redox reactions. Temperatures and reaction extents were compared with those obtained with a reticulated porous ceramic (RPC) structure with comparable mass per unit volume, serving as the state-of-the-art reference. Remarkably, the 3D-printed structures achieved a higher and more uniform temperature profile than the RPC: for a radiative flux equivalent to 1280 suns, equilibrium temperatures in the range 1320-1480°C were measured for the 3D-printed structures vis-a-vis 870-1340°C for the RPC. This is attributed to enhanced volumetric absorption, attaining the so-called volumetric effect where front temperatures are lower than the inner temperatures, reducing radiative heat losses. The higher and more uniform temperatures led to a higher oxygen exchange during the redox cycle, doubling the CO yield.
  • Topology Optimization of 3D-Printed Hierarchically Ordered Porous Structures to Maximize Solar Fuel Yield
    Item type: Other Conference Item
    Sas Brunser, Sebastian; Steinfeld, Aldo (2024)
    We report on the topology optimization of hierarchically ordered structures for CO2 splitting via a redox thermochemical cycle, driven by concentrated solar energy. These structures, made of the redox material ceria, were 3D-printed using a Direct Ink Writing (DIW) technique and were experimentally proven to outperform the state-of-the-art isotropic reticulated porous ceramic (RPC) structures [1]. To maximize their fuel yield, parametrized designs are optimized. The optimization algorithm starts by generating voxelized designs with random parameters by discretizing each of the domains into a 3D binary digital representation of solid/void voxels for the purpose of significantly reducing the computational cost. The algorithm then applies a voxel-based Monte Carlo (MC) ray tracer for solving the 3D radiative exchange at the pore level within the absorbing-reflecting-emitting domain, to obtain the temperature field under thermal equilibrium and the corresponding oxygen evolution for CO2 reduction under thermodynamic equilibrium [2]. These results are interpolated to construct a surrogate function, which, in turn, is minimized to find new sets of parameters for creating better-performing topologies. The process is iterated such that each improved topology is re evaluated by the MC ray tracer to progressively approach the one delivering maximum fuel yield. In particular, the optimized hierarchically channeled structure achieved a 4-fold increase in the volume-specific fuel yield compared to the value obtained for an RPC under the same boundary condition of 1000 suns flux irradiation.
  • Optimization of Porous Structures for Enhanced Radiation Heat Transfer Using a Voxel-Based Ray-Tracing Algorithm
    Item type: Other Conference Item
    Sas Brunser, Sebastian; Steinfeld, Aldo (2022)
    Book of abstracts
  • High-Temperature Thermochemical Heat Storage via the CuO/Cu2O Redox Cycle: From Material Synthesis to Packed-Bed Reactor Engineering and Cyclic Operation
    Item type: Journal Article
    Gigantino, Marco; Sas Brunser, Sebastian; Steinfeld, Aldo (2020)
    Energy & Fuels
    A thermochemical redox cycle based on the CuO/Cu2O pair is considered for high-temperature heat storage in concentrated solar energy applications. A synthesis method is developed for the manufacturing of porous CuO-based granules with yttria-stabilized zirconia (YSZ) as sintering inhibitor. The synthesized granules exhibit high and reversible redox conversion over 100 consecutive cycles in air between 950 and 1050 °C and yield a gravimetric energy storage density associated to the endothermic/exothermic redox reactions in the range from 470 to 615 kJ/kg for 50 to 65 wt% CuO-YSZ granules. A lab-scale packed-bed reactor is designed for direct heat transfer between the granules and an air/N2 flow serving simultaneously as gaseous reactant and heat transfer fluid. The reactor is applied to perform two sets of 30 consecutive redox cycles subjected to either temperature-swing (isobaric) or pressure-swing (isothermal) operational mode. Stable charging-discharging cycling performances are achieved in both modes, with narrow thermal hysteresis between reduction/oxidation onset temperatures (≤10 °C) and self-stabilization of the discharging temperature in the range 1020-1025 °C when operating under an airflow.
  • Design and Optimization of a Solar Reactor for Thermochemical Fuel Production using 3D Printed Ceramic Structures
    Item type: Other Conference Item
    Sas Brunser, Sebastian; Walde, Dario; Steinfeld, Aldo (2023)
  • Solar-Driven Redox Splitting of CO2 Using 3D-Printed Hierarchically Channeled Ceria Structures
    Item type: Journal Article
    Sas Brunser, Sebastian; Bargardi, Fabio; Libanori, Rafael; et al. (2023)
    Advanced Materials Interfaces
    Fuel produced from CO2 and H2O using solar energy can contribute to making aviation more sustainable. Particularly attractive is the thermochemical production pathway via a ceria-based redox cycle, which uses the entire solar spectrum as the source of high-temperature process heat to directly produce a syngas mixture suitable for synthetizing kerosene. However, its solar-to-fuel energy efficiency is hindered by the inadequate isotropic topology of the ceria porous structure, which fails to absorb the incident concentrated solar radiation within its entire volume. Here we design and 3D-print hierarchically channeled structures of pure ceria by Direct Ink Writing (DIW) to enable volumetric radiative absorption while maintaining high effective densities required for maximizing the fuel yield. The complex interplay between radiative heat transfer and thermochemical reaction was investigated in a solar thermogravimetric analyzer with samples exposed to high-flux irradiation, mimicking realistic operation of solar reactors. Channeled structures with a stepwise optical thickness achieved a higher and more uniform temperature profile compared to that of state-of-art isotropic structures, doubling the volume-specific fuel yield for the same solar flux input. Thermomechanical stability of the ceria graded structures, DIW-printed using a novel ink formulation with optimal rheological behaviour, was validated by performing 100 consecutive redox cycles.
  • Introducing FIVER: An Open-Source Tool to Simulate Heat Transfer in Participating Media and Arbitrary Geometries
    Item type: Conference Paper
    Wetaski, Charles; Sas Brunser, Sebastian; Casati, Emiliano (2025)
    SolarPACES Conference Proceedings
    Decarbonization of industrial processes operating at above 1000 °C is a major challenge. A promising answer lies in concentrating solar thermal technologies, but current receivers operate at about 600 °C only. New concepts are needed to achieve the target temperatures with good efficiencies, thus enabling commercial deployments. Further advances require that researchers have access to simulation tools treating heat transfer problems in radiatively participating media accurately, which is seldom the case today. Here we present a first effort to bridge this gap, introducing FIVER (FInite VolumE Ray tracer), an open-source Matlab tool for solving transient radiative-conductive heat transfer problems in participating media with spectral properties and complex geometries. FIVER tackles the challenging simulations needed to design the solar receivers of the future, and we hope it will become a valuable tool for researchers investigating concentrating solar thermal receivers and other technologies needed to decarbonize high temperature processes.
  • Discrete Ray-Tracing Algorithm to Solve Radiative Heat Transfer in Porous Media
    Item type: Other Conference Item
    Sas Brunser, Sebastian; Steinfeld, Aldo (2021)
    Book of Abstracts
Publications 1 - 10 of 15