The paper presents an experimental study of the heat characteristics of the bulk flow of red sand over diamond-shaped tubes in a particle-to-air heat exchanger (PAHX). The objective of this work is to demonstrate the suitability of solid particles as a working medium in applications such as concentrating solar power (CSP). The tests are conducted at the experimental central receiver facility at King Saud University in Riyadh, Saudi Arabia. The PAHX is a custom-made heat exchanger in which the particle flow rate can be controlled by a slide gate at the bottom. A custom-made (100 kW(e)) microturbine is used to heat the particles inside the PAHX as they are circulated inside a tower by a lifting system. Experiments are conducted to investigate the effect of the particle flow rate (particle velocity) on the heat transfer coefficient on the sand side. The results show that the particle velocity strongly affects h(sand). Increasing the sand velocity by less than 20% can cause an increase of more than 100% in h(sand). The maximum h(sand) value of 84 W/m(2).degrees C is obtained at the maximum particle velocity of 0.71 mm/s. However, this value is expected to increase when slightly smaller particles with more uniform shapes are used.