Ishrat Zahan

This study analyzes critical threats to wildlife species' extinction, focusing on human activities, climatic challenges, and the Allee effect within ecological frameworks. We investigate the dynamics of two interacting reaction–diffusion models, particularly examining the harvesting of prey species proportional to their intrinsic growth rates. Our findings reveal significant depletion of prey populations, especially under intense predation pressure, leading to potential extinction. While coexistence between species is possible in the absence of harvesting, one species may drive the other to extinction under certain conditions. The analytical results are supported by numerical examples, emphasizing the need for sustainable harvesting practices to maintain ecological balance and prevent species endangerment.

The increasing global demand for sustainable energy emphasizes the need for improved solar thermal technologies. Parabolic trough solar collectors (PTSCs) in concentrating solar power systems face limited thermal efficiency due to suboptimal heat transfer fluids (HTFs) and outdated absorber designs. Traditional fluids, such as water or oils, have low thermal conductivity, limiting heat absorption and transfer. Smooth absorber tubes also fail to optimize fluid interaction. This model presents a comprehensive computational fluid dynamics (CFDs) analysis of hybrid ionanofluid flow in a PTSC equipped with an axial helically finned absorber pipe for better thermal conductivity, stability, and to enhance convective heat transfer. The working fluid is composed of boron nitride (BN) and nanodiamond (ND) nanoparticles dispersed in 1,3‐dimethylimidazolium methyl phosphonate ([DIMIM][(MeO)(H)PO ₂ ]). The partial differential mathematical model is solved using the finite element technique. Results show that increasing solar irradiation from 300 to 1100 W/m ² at a constant inlet temperature of 298 K and 1% nanoparticles concentration enhances thermal efficiency by 11.96%. Additionally, increasing the nanoparticles volume fraction from 0% to 2% significantly improves thermal performance. At an inlet velocity of 0.006 m/s ( Re = 9.3), with a fixed solar input of 900 W/m ² and an inlet temperature of 298 K, the system shows a 3.36% improvement in efficiency. Among various BN:ND mixing ratios (0:100, 25:75, 50:50, 75:25, and 100:0) at a total 1% concentration, the 25:75 BN:ND ratio yields the highest thermal efficiency. Including internal helical axial fins in the absorber tube enhances heat transfer by increasing surface area, improving convective heat transfer, and lowering thermal resistance. The synergistic effects of fin‐induced turbulence and the superior thermophysical properties of the hybrid ionanofluid—its high specific heat and thermal conductivity significantly enhance the thermal efficiency of the PTSC, surpassing systems that utilize conventional smooth absorber tubes.

Utilizing ionanofluid is one of the best ways to improve the thermal performance of working fluids for storage, energy conversion, and transportation in contemporary thermal systems. It is a group of nano dispersions where ionic liquids create the continuous phase. This article's goal is to examine how various nanofluids perform when natural convection of long single-walled carbon nanotubes (SWCNTs) nanoparticle occurring in a cavity which is made up of two connected oblique triangles. The cavity has a thin cold wall (Tc) with angular diameter √2m. Both half of the left and bottom walls are heated and kept at constant temperature (Th). The remaining walls are insulated. The Navier-Stokes equations and energy conservation equation with appropriate boundary conditions are applied for modeling the considered physics and FEM is used to solve it. The heat transferring mediums are assumed as the ionanofluid of SWCNT and 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide ([C4mim][NTf2]) ionic liquid (IL), nanofluid of water-SWCNT and pure water. The effective parameters in a range of Rayleigh number (103 ≤ 𝑅𝑎 ≤ 106) and solid concentration (0.1% ≤ 𝜙 ≤ 5%) are considered. The findings show that due to higher thermal conductivity and appealing rheological features of ionanofluid, the heat transfer rate is found significantly higher than nanofluid and pure water. A higher solid concentration of SWCNTs represents greater values of mean Nusselt number. Additionally, fluid velocity and heat transfer rate increase at larger values of Ra.

A numerical analysis has been conducted to show the effects of magnetohydrodynamic (MHD) and Joule heating on heat transfer phenomenon in a lid driven triangular cavity. The heat transfer fluid (HTF) has been considered as water based hybrid nanofluid composed of equal quantities of Cu and TiO2 nanoparticles. The bottom wall of the cavity is undulated in sinusoidal pattern and cooled isothermally. The left vertical wall of the cavity is heated while the inclined side is insulated. The two dimensional governing partial differential equations of heat transfer and fluid flow with appropriate boundary conditions have been solved by using Galerkin's finite element method built in COMSOL Multyphysics. The effects of Hartmann number, Joule heating, number of undulation and Richardson number on the flow structure and heat transfer characteristics have been studied in details. The values of Prandtl number and solid volume fraction of hybrid nanoparticles have been considered as fixed. Also, the code validation has been shown. The numerical results have been presented in terms of streamlines, isotherms and average Nusselt number of the hybrid nanofluid for different values of governing parameters. The comparison of heat transfer rate by using hybrid nanofluid, Cu-water nanofluid, TiO2 -water nanofluid and clear water has been also shown. Increasing wave number from 0 to 3 enhances the heat transfer rate by 16.89%. The enhanced rate of mean Nusselt number for hybrid nanofluid is found as 4.11% compared to base fluid.