Experimental characterization of heat transfer coefficients in a moving-bed shell-and-plate heat exchanger with non-contact temperature measurements

Abstract

Dense particle flows have important applications in moving-bed heat exchangers. Consequently, there is a need to experimentally quantify heat transfer coefficients in these flows. In this work, non-contact techniques—thermal imaging and pyrometry—were used to measure particle temperatures and evaluate local particle-to-wall heat transfer coefficients in a 20 kW shell-and-plate particle-to-sCO₂ heat exchanger. The particle mass flow rate and particle inlet temperature of the heat exchanger were varied from 50 g/s to 175 g/s and 200 °C to 550 °C, respectively. For sintered bauxite particles (CARBOHSP 40/70) with a median diameter of 350 $\mu$m, the measured particle-to-wall heat transfer coefficients ranged from $\sim$110 to 170 W/m²K. Heat transfer coefficient increased with particle mass flow rate from 50 g/s to 100 g/s, but remained nearly constant when mass flow rate was increased further, up to 175 g/s. No clear trends were observed with particle temperatures up to 550 °C, likely due to heat exchanger plate warpage from thermal expansion. A companion plug flow model of a heat exchanger channel was developed to predict heat flux profiles and translate local particle temperature measurements to local heat transfer coefficients. Experimentally determined Nusselt numbers deviated by an average of 16% from predictions with a semi-empirical correlation, with the largest variations (up to 59%) observed for the highest mass flow rates and temperatures. Overall, this paper presents a novel application of non-contact temperature measurements for measuring particle-to-wall heat transfer coefficients in dense granular flows.