PROJECT BODY:

CHAPTER ONE

GENERAL INTRODUCTION 1.1 Background of the Study With advancement in science and technology, fluid dynamics has been of great importance over the decades due to its technological, industrial and engineering applications, which include calculating forces and moment of aircraft, determining the mass flow-rate of petroleum through pipelines, predicting weather pattern, modeling fission weapon detonation, traffic engineering, rocket engines, wind turbines, oil pipelines, air condition, turbine system in power generation and air condition.Ferzigerand Peric (1996), Nishigaki et al. (2013) The investigation of laminar natural convection in vertical tubes or annuli has received a lot of attention because of its importance in many engineering applications. The main technical applications of these researches concern cooling systems for electronic devices, electrochemical processes, nuclear reactors, and in solar energy collectors. This interest is due to the fact that researchers need a better understanding of the phenomena of heat and mass transfer in Engineering, Geophysical and Biological sciences. 1.2 Statement of the Problem Wang (1998) investigated free convection between vertical plates with periodic heat input. In his work, he separated the solutions into steady and unsteady regime and stated the condition on which the periodic heat input is significant. But in real life situations, heat transfer is common through cylinders and annuli. It is therefore significant to study free convection flow in a vertical tube and annulus inspired by periodic heating at the surfaces of the cylinders.Hence, this dissertation endeavors to investigate the impact of periodic