Thermal, thermodynamic and exergoeconomic investigation of a parabolic trough collector utilizing nanofluids

The exploitation of solar energy facilitates the renewable energy paradigm. In this regard, parabolic trough collectors (PTC) are considered as a useful set-up to absorb solar energy. Simultaneous study of thermal, thermodynamic, and exergoeconomic performance of PTC systems paves the way for designers and manufacturers to not only have a better insight into understanding the underlying concepts about the operation of PTC systems but also to find the most effective and cost-effective circumstances. This study aims at analyzing a practical PTC system by considering an evacuated absorber tube with glass cover, non-uniform heat flux, and taking into account the convective and radiative heat losses. Obtained results demonstrate that employing the glass cover, especially in the low Reynolds numbers regime could remarkably reduce the heat losses up to 22%. The present analysis indicated that considering oil temperature-dependent properties reduced the friction factor around 94 % in the low Reynolds numbers regime compared to that of the cases based on constant properties. In this work a CFD code in the OpenFOAM software was developed to simulate both laminar and turbulent regimes with Lien cubic k -epsilon model (non-linear eddy viscosity model) by adding three types of nanoparticles (Al2O3, Cu, andSWCNT) individually into the synthetic oil. Moreover, the Buongiorno's model (BGM) which considers Brownian, thermophoresis, and turbulence diffusion phenomena was implemented to model the nanoparticles and base fluid interactions. It was found that adding nanoparticles and increasing the Reynolds number have no substantial impact on thermal efficiency of the system, whereas an optimum Reynolds number was found for exergy efficiency and net profit per unit transferred heat load (eta(p)) of the system. Although injecting SWCNT into pure oil led to augmentation of average convective heat transfer coefficient, PEC, and exergy efficiency, it was found not to be cost-effective. It was established that the obtained results by homogenous model (single-phase model) and BGM were roughly the same, with relative difference of less than 3.1 and 2.4% for the average Nusselt number and friction factor, respectively.

Automated summary

The study analyzed the effectiveness of using a glass cover in a parabolic trough collector system to reduce heat losses at low Reynolds numbers. Considering temperature-dependent properties of the oil can greatly reduce the friction factor in the system.