Comparative analysis on single- and multi-walled carbon nanotubes suspended for enhanced thermal energy transfer past stretching surfaces

Flat and parabolic trough solar collectors concentrate sunlight onto a receiver tube containing the heat transfer liquid. Particularly, CNT nanofluids enhance the efficacy of energy harvesting in these systems. Flat plate collectors are simple in design and cheaper than parabolic shape collectors. Based on this idea, the present investigation focuses on how energy transmission helps harvest solar energy. Thus, three-dimensional, electrically conducting carbon nanotubes suspended in engine oil formed nanofluid flowing past a stretching porous surface with thermal slip are investigated numerically. Through the utilization of similarity transformations, the governing nonlinear partial differential equations are converted into a set of coupled ordinary differential equations. After that, the shooting approach is applied to these equations together with the fourth-order Runge–Kutta method to solve them. The study investigates the influence of various flow parameters on the velocity, temperature, skin friction coefficients, and Nusselt number near the wall. A comparative study of single- and multi-walled carbon nanotubes is made. From the theoretical calculations, the momentum of flow is higher, and temperature is lower for multi-walled carbon nanotubes than single-walled ones. The heat transfer rate enhances with an increase in Pr and S, and it is opposite when R, St, and δ increases. This study shows that the energy transmission rate is better in multi-walled carbon nanotubes, which act as better cooling liquid.