Direct absorption solar collector (DASC) modeling and simulation using a novel Eulerian-Lagrangian hybrid approach: Optical, thermal, and hydrodynamic interactions

• Published in: Applied energy 2018-12, Vol.231, p.1132-1145
• Main Authors: Sharaf, Omar Z., Al-Khateeb, Ashraf N., Kyritsis, Dimitrios C., Abu-Nada, Eiyad
• Format: Article
• Language: English
• Subjects: Direct absorption solar collector; Discrete particle modeling; Eulerian-Lagrangian; Nanofluid; Particulate flow; Volumetric absorption
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2018.09.191

•A novel continuous-discrete two-way coupled approach for modeling DASCs.•Fully-resolved local NP concentration coupled with NF optical and thermal properties.•After a critical Re, assumption of homogenous NPs distribution becomes inacceptable.•Spatial variations in NF optical properties due to non-uniform distribution of NPs.•Transverse particle migration affects radiation attenuation in upper surface vicinity. A novel two-way coupled Eulerian-Lagrangian hybrid approach was used to model nanofluid-based direct absorption solar collectors via a transient in-house code. By capturing the discrete nature of nanoparticles as well as motion and temperature slips between the carrier and dispersed phases, the proposed approach overcomes limitations of fully-continuous models by coupling the fully-resolved local nanoparticle concentration with the nanofluid optical and thermal properties. In particular, it was established that the non-uniform distribution of nanoparticles results in the spatially non-uniform attenuation of solar radiation due to spatial variations in the nanofluid optical properties. Moreover, the volumetric absorption and temperature fields were computed and compared to the conventional fully-continuous fields generated based on a homogeneous nanoparticle distribution assumption. The Reynolds number was found to have a strong effect on the local nanoparticle distribution in the flow of a nanofluid in a direct absorption solar collector, which greatly affects optical and thermal properties and performance of the nanofluid and collector. A critical flow Reynolds number was identified, after which the assumption of a homogenous particle distribution becomes inacceptable, and the homogeneous, fully-continuous modeling approach yields inaccurate results. In particular, the fully-continuous Eulerian modeling approach increasingly overestimates solar radiation extinction in vicinity of the channel top surface with an increase in Reynolds number, especially for Reynolds numbers ≥1. Effects on the coupled optical, thermal, and hydrodynamic interactions within the direct absorption solar collector due to the deviation of local nanoparticle distribution from the commonly-used homogeneous-nanoparticle-distribution assumption were investigated. Namely, new insights have been gained with regards to the impact of transverse nanoparticle migration, flow Reynolds number, mean nanoparticle concentration, and nanoparticle material type on the nanofluid temperature