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In thermal power and manufacturing processes, solar energy utilization has grown extensively. This work investigates the heat diffusion characteristics of an unsteady Oldroyd-B hybrid nano liquid flow across an expanding cylinder. A constant magnetic field is applied in the radial path in the presence of radiant heating, generation, or sinks, and Cattaneo-Christov (CC) heat flow. Hybrid nano liquid composed of two distinct nanoparticles (CoFe 2 O 4 and Fe 3 O 4) embedded in ethylene glycol as the primary fluid. A mathematical model was established and reconstructed into a nonlinear ordinary differential equations (ODEs) system, utilizing the proper likeness conversion. The Matlab inbuilt bvp5c scheme determines the problem's numerical solution. We observed the instabilities in the flow and thermal area and also the local Nusselt number impacted by the pertinent dimensionless characteristics. The findings are addressed graphically and tabularly for several nanoparticle shapes (spherical, brick, and platelet). It has been discovered that spherical shapes are found to have a faster heat conduction rate than brick and platelet nanoparticle shapes for the considered flow case. While unsteadiness parameters tend to increase the temperature field, the augmentation of the temperature relaxation factor reduces the energy profile. • Effective solar energy usage in Parabolic Trough Solar Collectors (PTSC). • Discrete outcomes for spherical, brick, and platelet-shaped nanoparticles. • Spherical-shaped ferro particles showed better heat transfer rates than platelet and brick-shaped particles. • Thermal radiation improves heat transfer in hybrid nano-liquid with platelet-shaped nanoparticles. • The coaxial cylinders can be employed as a central heat pipe for the PTSC's active thermal transport. [ABSTRACT FROM AUTHOR]

Solar thermal energy is a versatile and sustainable form of energy. It has vast applications and can be used to reduce fossil fuel consumption. The sun's heat harnesses this renewable energy; therefore, the energy transmission rate plays a significant role here. This article gives the idea of a new geometric design of solar thermal collector tubes for multiple uses and materials to be used on the tube's outer layer to maximize heat absorption. For this purpose, we investigated velocity, temperature, and heat transfer rates due to different nanoparticle (Cu/Al 2 O 3 /GO) combinations. We assumed the flow of Newtonian/non-Newtonian nanofluids flowing through the coaxial region of the cylindrical shape solar tubes. Here, water and seawater are considered for the Newtonian case, and sodium alginate is regarded for the non-Newtonian case. The governing equations of the flow are converted into ODEs with the help of similarity variables and solved numerically using the Keller box method. The MATLAB code for the Keller box method has been developed to plot graphical results. The primary outcomes are exhibited through graphs and tables. It is perceived that the temperature and heat transfer rates in Newtonian and non-Newtonian fluids are enhanced due to the trihybrid (Cu + Al 2 O 3 +GO) combination. This work can be utilized in an evacuated solar thermal system and gives the idea to develop a sustainable solar thermal system for multipurpose usage. • A sustainable solar thermal system model for multipurpose usage. • Simultaneous outcomes for Newtonian and non-Newtonian cases. • Al 2 O 3 +GO nanomaterial combination enhances the sun's heat absorption rate. • The heat absorption rate of evacuated solar heater tubes can be improved with a Cu + Al 2 O 3 +GO + sea water combination. [ABSTRACT FROM AUTHOR]