The iso-thermal flow field within several configurations of a Solar Expanding-Vortex Particle Receiver Reactor (SEVR) was investigated, using a combination of multi-plane particle image velocimetry (PIV) and Reynolds-Averaged Navier-Stokes (RANS) computational modeling, at a constant inlet Reynolds number of 12,300. The experimental and numerical results confirmed that the SEVR generates a well established vortex flow pattern, which approaches a forced vortex near to the injection plane and a combined (free and forced) vortex in the main body of the cavity. The SEVR also features a reversed flow in the vortex core region and a complex precessing vortex core (PVC) structure, which is stronger in both the inlet and outlet regions of the cavity. The primary mechanism for particle depcisition was identified as a primary recirculation zone near to the aperture that transports fluid from the main cavity through the aperture. The presence or absence of this recirculation zone was associated with the relative size of the vortex core dimension at the aperture plane and the aperture size. It was also found that the presence of a PVC at the aperture plane further increases the potential for the particle deposition onto the receiver-reactor window by generating a secondary recirculation zone in the vortex core region that transports fluid through the aperture. The use of a sufficiently long cavity or a sufficiently large cone angle can assist both in stabilising the PVC and increasing the size of the vortex core at the aperture plane. These two effects are postulated to reduce the potential for particle deposition onto the receiver-reactor window. (C) 2016 Elsevier Ltd. All rights reserved.