In contrast to thermal receivers that provide heat for steam cycles, in solar thermochemistry often receiver-reactors are used, where materials undergo a reaction while being irradiated by concentrated sunlight. When applied to two-step redox cycles, multiple processes take place in such receiver-reactors, though on different time scales. This leads to design compromises and to high technical requirements for the implementation. A concept for an indirect particle-based system for thermochemical cycles was therefore proposed in which the heat required for the reduction of redox particles is provided by inert heat transfer particles that absorb concentrated solar radiation in a dedicated particle receiver. The novel and central component in this indirect system is the particle mix reactor. It functions by mixing the two particle types for heat transfer and establishing a controlled atmosphere under decreased oxygen partial pressures in a common reactor chamber.

The design of an experimental setup for demonstration and investigation of the particle mix reactor is presented in this work. Potential operation modes and design options for particle heater, mixing unit and oxygen partial pressure decrease are discussed and illustrated. The selection of a mixer type is based on the homogeneity of the obtained mixture. It is supported by the use of Discrete Element Method (DEM) simulations, which were compared to experimental results from a separate setup. Heat loss estimations for the mixing process in the selected mixer geometry are performed for alumina heat transfer particles and strontium iron oxide redox particles.

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