Session: 06-02: Heat Transfer in CSP Applications 1

Paper Number: 138526

138526 - Heat Transfer Coefficient Calculations and Experiments on Particle Bed Heat Exchangers Using Modulated Photothermal Radiometry 

Abstract: 

Heat Transfer Coefficient Calculations and Experiments on Particle Bed Heat Exchangers using Modulated Photothermal Radiometry

Sarath R. Adapa¹, Xintong Zhang¹, Tianshi Feng¹, Dimitri A. Madden², Renkun Chen¹

¹Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California 92093, United States

²Concentrating Solar Technologies Department, Sandia National Laboratories, Albuquerque, New Mexico 87123, United States

Abstract

Particle heat exchanger is an integral component of the 3^rd generation concentrating solar power plants and its heat transfer coefficient (HTC) has a direct impact on the levelized cost of electricity. In parallel-plate packed particle bed heat exchangers, the dense granular flow falls into the well-known plug-flow regime, but the discrete nature of granular materials alters thermal transport in both the near-wall and bulk regions of the bed. Heat transfer to these confined flowing beds is described with a near-wall thermal resistance which is in series with convection to a continuum plug-flow. Thus, accurate information about these regions and their properties is essential for heat exchanger design and evaluation.

In this presentation, we introduce the use of modulated photothermal radiometry (MPR), a frequency-domain, non-contact radiometry technique for the characterization of flowing particle beds at high temperatures. This technique combined with a numerical fitting model measures both the effective bulk thermal conductivity of the plug-flow continuum and the near-wall thermal resistance as an equivalent air gap layer. Flowing particle beds of three different ceramic particles - CARBOBEAD CP 40/100, HSP 40/70, and HSP 16/30, were measured in a lab-scale single-channel setup at different velocities and temperatures. The properties of flowing packed particle beds were found to differ from the equivalent stationary beds due to changes in both the near-wall and bulk particle interactions, leading to a larger air gap layer and reduced bulk thermal conductivity on the onset of flow. Thus, the measurement of flowing bed properties is important for accurate heat transfer analyses. The measured results of thermal conductivity and air-gap thickness were used as inputs to an HTC correlation to calculate particle-to-wall HTCs for a range of temperatures, velocities, and channel spacings. These calculated coefficients can be useful for evaluating heat exchanger design specific to particle media.

 The MPR technique was also applied for operando thermal transport measurement on a 20 kW_th stainless steel particle heat exchanger with a 3 mm plate spacing. We report the heat exchanger performance under different operating conditions and compare the overall HTC measurements with the particle-to-wall HTC determined from our MPR experiments. Finally, we also demonstrate the feasibility of using the MPR technique for real-time monitoring and diagnostics of particle bed heat exchangers.

Presenting Author: Sarath Reddy Adapa University of California, San Diego

Presenting Author Biography: Sarath Adapa is a PhD candidate in Dr Renkun Chen's research group at the Department of Mechanical and Aerospace Engineering, University of California, San Diego. He obtained his BTech in Mechanical Engineering from the National Institute of Technology, Tiruchirappalli. His research interests are in clean energy, including granular materials for solar energy, and caloric refrigeration.

Authors:

Sarath Reddy Adapa University of California, San Diego
Xintong Zhang University of California, San Diego
Tianshi Feng University of California, San Diego
Dimitri Alexander Madden Sandia National Laboratories
Renkun Chen University of California, San Diego