Session: 07-01: Experimental Characterization of Particle Flows

Paper Number: 170013

170013 - Experimental Characterization of Local and Average Heat Transfer Coefficients Up to 700 °C in Gravity-Driven Dense Granular Flow 

Abstract: 

Dense granular flows of ceramic particles are attracting growing interest for their use in moving-bed heat exchangers. These heat exchangers can operate at high temperatures (600–800 °C), which enables higher efficiency power cycles in technologies like particle-based concentrated solar power (CSP) plants. There has been a heightened focus on modeling and measuring the heat transfer behavior of these dense particle flows. However, most prior experiments have obtained heat transfer coefficients at moderate temperatures up to 500 °C and/or only quantify an overall or a channel-averaged heat transfer coefficient based on the inlet and outlet particle temperatures, which does not provide spatial information about the heat transfer over the length of the channel. Even when local heat transfer coefficients are measured, these are deduced values based on integrating measurements with existing correlations for continuum fluid flow. Recent experimental efforts in our group have emphasized the value of direct particle temperature measurements using non-contact techniques such as thermal imaging and pyrometry in obtaining local particle-to-wall heat transfer coefficients. In this study, we extend this work and apply operando particle temperature measurements to characterize both local and average particle-to-wall heat transfer coefficients in a 1-meter-long vertical flow channel for temperatures ranging from 200-700 °C with particle flow rates ranging from 10-30 g/s. Even though this is a single channel, it has been designed to represent design/flow conditions relevant to moving-bed heat exchangers in particle-based CSP plants.

Particles are heated using cartridge heaters in a hopper situated at the top of the channel and flow through the channel driven by gravity. At the bottom of the channel, controlling the opening size of a slide gate regulates the mass flow rate of the particles. We utilized porcelain (Raytech) particles with a mean diameter of 2 mm. Using a combination of instrumentation techniques, including infrared thermal imaging, pyrometry, wall thermocouples and a heat-flux gauge, we measure the local heat transfer coefficients at 20 cm from the channel inlet, in addition to an overall channel-averaged heat transfer coefficient. The average particle-to-wall heat transfer coefficients ranged from 50 W/m²K to 100 W/m²K for inlet temperatures of 200-700 °C and mass flow rate from 10-30g/s, respectively, while the local heat transfer coefficients are at higher values. This study found that the heat transfer coefficients were more strongly affected by the mass flow rate than the inlet temperature while demonstrating a positive correlation with both parameters. Future work for this study will be discussed, including the effects of varying particle size, shape, and composition. Furthermore, these results will be used to validate discrete element method (DEM) models, which will provide further insights into the heat transfer behavior of dense granular flows.

Presenting Author: Xinsheng Wei University of Michigan

Presenting Author Biography: Xinsheng Wei is a first-year Master of Engineering student at the University of Michigan. He joined the Transportation and Reaction Engineering for Sustainable Energy (TREE) Laboratory in the fall of 2024. He is involved in the instrumentation and post-processing of data for the experimental characterization of heat transfer coefficients at high temperatures. Xinsheng has a strong interest in heat transfer and energy systems and aims to earn his master’s degree by 2026.