Local thermal nonequilibrium effects in unsteady squeezing flow through a porous circular tube

Abstract Accurate prediction of coupled fluid flow and heat transfer in deformable porous tubes is important for physiological transport, filtration devices, porous heat exchangers, and thermal management systems, in which the fluid and solid phases may maintain different local temperatures. However, the combined effects of unsteady tube squeezing, porous-medium resistance, and local thermal nonequilibrium (LTNE) have received limited attention. This study investigates unsteady incompressible Newtonian fluid flow in a squeezing circular tube embedded in a homogeneous porous medium under LTNE conditions. A Darcy-type resistance model with a modified effective viscosity is adopted, and separate energy equations are formulated for the fluid and solid phases, including interfacial heat exchange. The governing nonlinear partial differential equations are transformed into ordinary differential equations using similarity variables and solved numerically through the implicit Keller-box method. The numerical results show good agreement with classical benchmark solutions. Increasing the squeeze number reduces the momentum boundary-layer thickness. It enhances convective cooling, whereas increasing the inverse Darcy number suppresses the core velocity and raises fluid- and solid-phase temperatures because of reduced convection. Higher Prandtl and effective heat capacity ratios decrease both phase temperatures. Increasing the Biot number strengthens inter-phase heat transfer. It accelerates the transition from local thermal nonequilibrium to equilibrium, while greater porosity-scaled conductivity sustains the temperature difference and delays thermal equilibrium. These findings provide useful insight into controlling flow resistance, heat retention, and fluid–solid thermal equilibration in deformable porous tubular systems.