Session: 05-02 Metrology in CSP

Paper Number: 116903

116903 - Temperature Characterization of Flowing Particles With Non-Contact Measurement Techniques 

Heated particle flows are found in various applications pertinent to sustainable energy systems. For example, multiple flow regimes of heated particles are seen in particle-based CSP, including dilute particle curtains heated by concentrated sunlight and dense packed-bed flows found in particle heat exchangers. A key difficulty involved in studying high-temperature particle flows is accurate temperature measurements of the particles as they are moving. Thermocouples cannot provide accurate temperatures of a granular medium because the probe is not in continuous contact with the solid phase. Instead, wall temperatures are often measured for packed-bed flows, and particle temperatures are estimated from these values. However, this approach requires knowledge of typically unknown parameters, such as the near-wall air gap and particle-wall heat transfer coefficient, to calculate particle temperatures from a model of the flow. Thus, direct non-contact temperature measurement techniques such as thermal imaging are preferable to thermocouple measurements. However, non-contact temperature measurements come with their own set of challenges. In particle curtains, the primary challenge is the speed at which the particles move; in packed-bed flows, the lack of optical access limits the ability of sensors to “see” into the flow to extract temperature. This work is a demonstration of two different non-contact temperature measurement techniques for flowing particles—thermal imaging with an IR camera (Onca-MWIR-InSb, Xenics) and pyrometry with a ratio (two-color) pyrometer (CTRM-2HSF50-C3, Micro-Epsilon)—for two different flow regimes, particle curtains and packed-bed flows. Two-color pyrometry is chosen for its insensitivity to a material’s radiative properties, provided they are relatively flat over the short wavelength range of interest. This is in contrast to thermal imaging which not only must account for radiative properties, but also for how those properties change with temperature. The techniques are calibrated and validated with measurements of static particle beds at known temperatures before being applied to flowing particles. The results of each technique and flow regime are compared, and the effects of other relevant variables such as material and particle size are quantified. Additionally, a discussion on the advantages and disadvantages of each technique is included to help inform how non-contact temperature measurements can be applied in systems like a particle heat exchanger to study and potentially optimize heat transfer behavior.

Presenting Author: Mike Mayer University of Michigan

Presenting Author Biography: 4th year PhD student in mechanical engineering at the University of Michigan with a research focus in radiation heat transfer for sustainable energy systems