This article displays a numerical investigation on natural convection within non‐Darcy porous layer surrounded by two horizontal surfaces having sinusoidal temperature profiles with difference in phase and wave number. The Darcy–Brinkman–Forchheimer model and local thermal nonequilibrium condition have been employed. Simulations have been performed for wide ranges of inertia coefficient (10–4 ≤ Fs/Pr* ≤ 10–2), thermal conductivity ratio (0.1 ≤ K r ≤ 100), phase difference (0 ≤ β ≤ π), modified Rayleigh number (200 ≤ Ra* ≤ 1000), wavelength (3 ≤ k ≤ 12), and nondimensional heat transfer coefficient (0.1 ≤ H ≤ 100). Results demonstrate that Nusselt number highly relies on Fs/Pr*, K r, β, Ra*, and k as compared to H. A considerable enhancement in fluid, solid, and overall Nusselt numbers has been observed with diminishing Fs/Pr* and β and increasing k, K r, and H. The raising in β has a significant impact on Nu for smaller k and this effect is almost ignored when k > 12. The increase in Ra*, K r, β, and H and decrease in Fs/Pr* and k acts to reduce the severity of nonequilibrium zone and increase the size of thermal equilibrium zone. The influence of H on nonequilibrium area is more evident than K r.

A Loop Thermosyphon has been designed, fabricated and tested to investigate the heat transfer characteristics by two-phase natural convection. The rig was made from copper tubes connected with each other in closed loop including four main parts: vertical evaporator located in the bottom of the device and surrounded by an electrical coil heater as a heat source ,a horizontal condenser located in the upper part of the device cooled by water, vapor rising adiabatic tube and condensate return adiabatic tube. In this research the effect of heat input and filling ratio of the evaporator on the heat transfer coefficient and temperature distribution on the loop surface was verified experimentally using distilled water as working fluid at operating pressure near-atmospheric pressure. The maximum heat transport capability for evaporator was found to be equal to (3424 W/m 2 o C). A comparison between the present work results with empirical and theoretical correlations of other researchers showed good agreement.