A transient heat transfer model for high temperature solar thermochemical reactors

Like Li*, Chen Chen, Abhishek Singh, Nima Rahmatian, Nick AuYeung, Kelvin Randhir, Renwei Mei, James F. Klausner, David W. Hahn, Jörg Petrasch

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

19 Citations (Scopus)

Abstract

We present a heat transfer model for energy transport in a solar thermochemical reactor for CO 2 and/or H 2 O splitting to produce chemical fuels CO and/or H 2 . The reactor is comprised of a horizontal cavity-receiver packed with several insulation layers, an array of tubular absorbers in which the reactive metal oxide is loaded, and a windowless aperture that allows the incident concentrated solar energy to enter the receiver. A framework for modeling the complex multimode thermal transport within the reactor system is developed. The concentrated solar radiation from a high flux solar simulator to the cavity-receiver is simulated using a Monte-Carlo ray tracing model. Heat transfer within the tubular absorbers, including conduction, convection, radiation, and chemical reactions, is simulated using a lattice Boltzmann (LB) model. These two models are coupled by taking into account the temperature-dependent radiative emission from the absorber surfaces. Two particular techniques are employed to improve the numerical accuracy and stability: appropriate rescaling of the relaxation coefficients in the LB method and implicit treatment of the heat source/sink terms due to chemical reactions. The numerical method is validated with two test cases for which analytical solutions are available. Simulation results for the heating process and one thermal reduction step under near-vacuum pressures are presented. The predicted solar-to-fuel energy conversion efficiency varies from 5% to 10% and is determined based on the simulated O 2 release during the reduction step. The model is able to provide insight into the optimum operating conditions, the reactor design and the scale-up. The results suggest that high temperatures for both reduction and oxidation steps and near-vacuum pressure (∼10 -4 atm) for thermal reduction are critical for improved solar-to-fuel conversion efficiency with the ceria-based reactive material.

Original languageEnglish
Pages (from-to)2307-2325
Number of pages19
JournalInternational journal of hydrogen energy
Volume41
Issue number4
DOIs
Publication statusPublished - 30 Jan 2016
Externally publishedYes

Keywords

  • Heat transfer
  • Lattice Boltzmann
  • Monte-Carlo ray tracing
  • Solar reactor
  • Thermochemical fuel production

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