This book presents the natural convection heat transfer from a horizontal cylinder with annular fins has been studied numerically. The present numerical investigation is able to capture a complete picture of natural convection over an annular finned horizontal cylinder from where easy visualization of the plume structure and flow field over the tube-fin surface can be obtained pictorially. In the present study, numerical simulations of full Navier-Stokes equation along with the energy equation have been conducted for a horizontal tube with annular fins of constant thickness by varying the Rayleigh number based on fin spacing. Chapter 1 deals with the introduction and literature survey regarding the natural convection heat transfer from horizontal cylinder with annular fins. In Chapter 2, a complete numerical analysis of natural convection from horizontal cylinder with annular fins by varying fin diameter, fin spacing and Rayliegh number. A similar analysis is carried out in chapter 3, taking eccentric fins on horizontal cylinder and results are compared with the concentric one. In chapter 4, an entropy generation analysis of finned tube configuration has been carried out.