Particle-to-fluid direct-contact counter-flow heat exchanger: Simple-models validation and integration with a particle-based central tower system

Abstract

This paper presents validation studies of two theoretical models of a direct-contact counter-flow particle-to-air heat exchanger. It also describes the integration of the proposed heat exchanger with a particle-based central tower system. Two basic models are analyzed: (1) the mixing model, which treats falling particles as an isolated particle falling downward in unbounded-atmospheric air, and (2) the simple-equilibrium model (SEM), which assumes that both the media reached thermal equilibrium in every segment along the exchanger. The mixing model predicted the outlet temperature quite accurately for the particles with 0.5 mm diameter. For CARBOEAD particles of 0.5 mm diameter, the predicted heat rate was within ±5% of the experimental results. The SEM overpredicted the outlet temperature regardless of particle size. A simple modification was added to the SEM, which led to improve the model predictions greatly. An integrated conceptual system design is also presented and discussed. The use of a double dump valve introduces many advantages towards a practical integrated system. Finally, employing particle strainers at the exchanger outlet is crucial to reduce/eliminate risks about the swept particles.