Effects of surface voids on free convection via concentrated double-pipe

Crucial industrial applications that rely on convection over circular concentric gaps between cylinders include solar collectors, heat exchangers, and electronic cooling. In the proposed work, an in-depth laboratory analysis focuses on the impact of cavities on the inner pipe exterior surface on heat transfer via free convection in an encloser's concentric annulus. Twin sets of aluminum cylinders were analyzed; each set had the same length. Two round cylinders, one inside the other, make up each one. An electrical heater is wired into the inner cylinder of the inner set to keep the heat flowing continuously. Results showed that for surface cavities of 0.005, 0. 10, 0.015, 0.020, 0.03, 0.035, and 0.04 m deep, the Nusselt number increases by approximately 151%, 201%, 236%, 289%, 325%, 365%, 391%, and 420%, respectively. For a moderate Rayleigh number, the Nusselt number increases by roughly 190%, 276%, 312%, 361%, and 420% for different cavity bores (2.0, 3.0, 4.0, 5.0, and 6.0 mm).