Applying Infrared Thermography and Image Analysis to Dilute 2-phase Particulate Systems: Hot Particle Curtains

Particle curtains occur in industrial drying and in solar particle receivers and are defined as a stream of particles falling a fixed distance through a gas or fluid phase. In industrial drying optimising heat and mass transfer between the cascading particles and the drying medium is essential for enhancing energy efficiency and reducing emissions. Modelling these devices via pragmatic process systems models and/or with computational fluid dynamics models can contribute to enhanced design and a better understanding of the fundamental processes that occur. Validation of curtain modelling is critical to building confidence in the resultant predictions, but unfortunately traditional methods such as discrete temperature measurement using probes are time consuming and can disturb the flow field. Infrared thermography is an image-based technique with the potential to alleviate some of these issues and to generate whole of field temperature data, well-suited to model validation. In this paper infrared thermographic images of hot particle curtains falling through still air are presented. Image analysis methods for adjusting and scaling images as well as detecting the curtain edges are also described. Experiments involving hot particle curtains (403k-413K) falling through a narrow slot (150×20-60 mm) in a room filled with still air (295K-300K) are presented. Curtain widths were varied by varying the slot width (20 mm and 60 mm) and a range of mass flow rates (0.04 kg/s-0.155 kg/s) and particle diameters (290 μm and 400 μm) were examined. Curtain shape, as defined by the edges of the curtains, was determined using methods adapted from image analysis. The 2D thermal images showed that the shapes of the curtains are strongly dependent on slot width or initial solids volume fraction, which has implications for maximising heat transfer in particle curtain processes.