Parabolic trough solar collectors (PTSCs) are generally utilized to reach high temperatures in solar-thermal applications. The current work investigates entropy production analysis and the influence of nano solid particles on a parabolic trough surface collector (PTSC) installed within a solar powered ship (SPS). For the current investigation, the non-Newtonian Maxwell type, as well as a porous medium and Darcy–Forchheimer effects, were used. The flow in PTSC was produced by a nonlinear stretching surface, and the Cattaneo–Christov approach was used to assess the thermal boundary layer’s heat flux. Similarity transformation approach has been employed to convert partial differential equations into solvable ordinary differential equations allied to boundary conditions. Partial differential and the boundary conditions have been reduced into a group of non-linear ordinary differential equations. A Keller-box scheme applied to solve approximate solutions of the ordinary differential equations. Single-walled carbon nanotubes -engine oil (SWCNT-EO) and Multiwalled carbon nanotubes/engine oil (MWCNT-EO) nanofluids have been utilized as working fluid. According to the findings, the magnetic parameter led to a reduction in the Nusselt number, as well as an increment in skin friction coefficient. Moreover, total entropy variance over the domain enhanced for flow rates through Reynolds number and viscosity fluctuations were monitored by using Brinkman number. Utilizing SWCNT-EO nanofluid increased the thermal efficiency between 1.6–14.9% in comparison to MWCNT-EO.

In this study, the structural and magnetic properties of a series of functionalized Co_100−xNi_x (x = 20, 30, 40, 50, 60, 80, 85) nanoparticles (NPs) were analyzed with the objective of attaining a high specific absorption rate (SAR). The magnetic nanoparticles (MNPs) obtained by ball milling at 1425 rpm lie in the range of 03–29 nm and are studied as potential candidates for magnetic fluid hyperthermia. Magnetic measurements show that all samples possess soft ferromagnetic properties with the reduction in the Curie temperature (T_C) by Ni substitution in Co_100−xNi_x alloys and by ball milling. The specific absorption rate (SAR) and specific loss power (SLP) obtained from magnetothermal measurements for powder and fluid samples lie in the range 4.4–83 W/g and 19–382 W/g, respectively, showing strong dependence on structural and magnetic properties. The SAR/SLP values as a function of the applied field at 425 kHz display a square dependence on the applied magnetic field below 165 Oe, which is expected for single domain ferromagnetic nanoparticles, but deviate from this at higher values of the applied field. We also obtained the effective anisotropy constant $K_{eff}$ for ball-milled nanoparticles at 1425 rpm for 200, 300, and 500 min. within the framework of linear response theory, showing strong dependence on average crystallite size. Additionally, the toxicity of the prepared nanoparticles in the form of percentage hemolysis was controlled with oleic acid.

Cobalt-doped potassium hexa-titanate (Co_x:K₂Ti₆O₁₃ (x = 0.05, 0.10, 0.15 mole%)) ceramics were synthesized by the solid-state reaction method. The XRD patterns confirmed single-phase development in a monoclinic symmetry of various samples, and they were used for different structural calculations of Co_x:K₂Ti₆O₁₃ ceramics. The dielectric constant, tanδ, electrical modulus, and ac conductivity of Co-doped K₂Ti₆O₁₃ were studied in the temperature range of 100–500 °C. Anomalies were observed in graphs of the dielectric constant versus temperature, showing the transition phase in the studied samples. Dielectric peaks at transition temperature decreased with an increasing frequency, and the peaks shifted toward higher temperatures, illustrating the relaxation of the dielectric materials. The composition with x = 0.10 showed low dielectric loss and a higher dielectric constant and can be utilized for high-temperature dielectric material. Small doping of cobalt improved the ac conductivity of K₂Ti₆O₁₃ ceramics due to the increase in the spin–phonon interaction and dominant electron hopping conduction; however, the conductivity diminished with substantial doping because of the contraction of the tunnel space and ambushing of conduction electrons. The uniqueness of this study is in the high dielectric optimization of lead-free ceramic Co_x:K₂Ti₆O₁₃ and the discovery of positive temperature coefficients of the resistivity of these ceramic samples.