Session: 06-04: Heat Transfer in CSP Applications 2

Paper Number: 138189

138189 - Multiphase Modeling of Fluidization and Heat Transfer in a Csp Receiver 

Abstract: 

The National Renewable Energy Laboratory is developing a novel high temperature Gen3 solar receiver that uses a light trapping planar cavity mechanism. For the light trapping mechanism, a unique receiver configuration is developed and is in the prototype testing phase at King Saud University. This work aims to evaluate the feasibility and effectiveness of the unique receiver configuration designed by modeling the particle flow and heat transfer in the receiver. The receiver uses thermally inert particles in the receiver cavity to absorb the heat from the concentrated solar radiation incident on the receiver panels. To optimize this heat absorption, as the particles fall through the receiver cavity, they are fluidized within the cavity with air as the fluidizing medium. Bubbling fluidized beds have been shown in the literature to help improve the heat transfer coefficient in heat exchangers.  A single receiver module is modeled using the Eulerian-Eulerian granular flow model in Ansys FLUENT to study the counterflow motion between particles and air and the effect of the receiver configuration on the fluidization of particles.  The model matches the system size and assumes a monodisperse particle size distribution equal to the Sauter mean diameter of the particles to be tested experimentally. The effect of changes in air distribution is studied and it is noted that the shape of the receiver demands a distributor that extends well into the receiver cavity and with uneven distribution of air flow to ensure complete fluidization of the particles within the receiver. Heat transfer to the particles from the receiver wall to the particles is modeled. The heat transfer to the particles is tracked spatially as well as monitored over time. A conduction model (Morris, Pannala, Ma, & Hrenya, 2015) is implemented that depends on the solid concentration to obtain the local effective thermal conductivity. This conduction model is studied extensively using the discrete element method (DEM) and its sensitivity to parameters like the minimum conduction distance as well as the conduction lens radius of the particles is studied. The DEM model is validated against a smaller scale experimental system, hence validating the effective conductivity model. This adds confidence to the results obtained from the full-scale FLUENT model. The full-scale model helps understand the scaling between smaller simplified heat exchangers and the prototype receiver.

 

References

Morris, A., Pannala, S., Ma, Z., & Hrenya, C. (2015). A conductive heat transfer model for particle flows over immersed surface. International Journal of Heat and Mass Transfer.

 

Presenting Author: Krutika Appaswamy Purdue University

Presenting Author Biography: Krutika is a PhD Student at Purdue University, working on heat transfer in particle flows.

Authors:

Krutika Appaswamy Purdue University
Aaron Morris Purdue University
Zhiwen Ma National Renewable Energy Laboratory
Janna Martinek National Renewable Energy Laboratory