Influence of thermal stratification and porous media on transient mixed convection in coaxial pipe systems

The current investigation is being conducted to analyze the influences of both porous media and thermal stratification on the transient flow of mixed convection between two semi-infinite co-axial horizontal fixed pipes. The insights gained are crucial for advancing heat transfer technologies, optimizing thermal efficiency and improving industrial processes. The exploration of porous media and thermal stratification in transient mixed convection flow finds a wide range of applications in energy systems, industrial processes and chemical reactors for improved heat and flow management. These ideas are also applied in the construction, automotive and aerospace sectors. For this analysis, inner pipe flow is assumed in an axial direction, with a fixed boundary condition at its surface. The time-dependent flow and temperature field between the co-axial pipes are examined using a 2-D mathematical model when the external pipe’s outer wall is positioned infinitely far from the surface of the internal fixed pipe and the inner pipe is heated uniformly. The implicit finite difference technique is utilized to numerically solve the coupled equations of the simulated model. The calculated results are geometrically represented using the technically sophisticated software TECHPLOT-360. For the non-dimensional parameters, a detailed explanation of the obtained results is observed for the time-independent velocity, thermal profile, unsteady heat transmission rate and unsteady surface shear and is presented in the results and discussion part. From the graphical representation, it is examined that the fluid flow and thermal profile both decrease as the values of Darcy number rise. Also, the amplitude of unsteady surface shear reduces, whereas the amplitude of the unsteady heat transmission rate is enhanced. The main novelty of this study is asserted by stating that we first acquire numerical results for the steady part, and then these results are applied in the unsteady part in order to overcome the non-linearity.