Abstract: Diffusions of multiple components have numerous applications such as underground water flow, pollutant movement, stratospheric warming, and food processing. Particularly, liquid hydrogen is used in the cooling process of the aeroplane. Further, liquid nitrogen can find applications in cooling equipment or electronic devices, i.e., high temperature superconducting (HTS) cables. So, herein, we have analysed the entropy generation (EG), nonlinear thermal radiation and unsteady (time-dependent) nature of the flow on quadratic combined convective flow over a permeable slender cylinder with diffusions of liquid hydrogen and nitrogen. The governing equations for flow and heat transfer characteristics are expressed in terms of nonlinear coupled partial differential equations. The solutions of these equations are attempted numerically by employing the quasilinearization technique with the implicit finite difference approximation. It is found that EG is minimum for double diffusion (liquid hydrogen and heat diffusion) than triple diffusion (diffusion of liquid hydrogen, nitrogen and heat). The enhancing values of the radiation parameter R_d and temperature ratio θ_w augment the fluid temperature for steady and unsteady cases as well as the local Nusselt number. Because, the fluid absorbs the heat energy released due to radiation, and in turn releases the heat energy from the cylinder to the surrounding surface.

Key words: Unsteady flow, Entropy, Radiation, Quasilinearization technique, Numerical analysis, Quadratic combined convection

摘要： Diffusions of multiple components have numerous applications such as underground water flow, pollutant movement, stratospheric warming, and food processing. Particularly, liquid hydrogen is used in the cooling process of the aeroplane. Further, liquid nitrogen can find applications in cooling equipment or electronic devices, i.e., high temperature superconducting (HTS) cables. So, herein, we have analysed the entropy generation (EG), nonlinear thermal radiation and unsteady (time-dependent) nature of the flow on quadratic combined convective flow over a permeable slender cylinder with diffusions of liquid hydrogen and nitrogen. The governing equations for flow and heat transfer characteristics are expressed in terms of nonlinear coupled partial differential equations. The solutions of these equations are attempted numerically by employing the quasilinearization technique with the implicit finite difference approximation. It is found that EG is minimum for double diffusion (liquid hydrogen and heat diffusion) than triple diffusion (diffusion of liquid hydrogen, nitrogen and heat). The enhancing values of the radiation parameter R_d and temperature ratio θ_w augment the fluid temperature for steady and unsteady cases as well as the local Nusselt number. Because, the fluid absorbs the heat energy released due to radiation, and in turn releases the heat energy from the cylinder to the surrounding surface.

关键词: Unsteady flow, Entropy, Radiation, Quasilinearization technique, Numerical analysis, Quadratic combined convection