3. Introduction

Three factors play major roles in convection heat transfer: (i) fluid motion, (ii) fluid nature, and (iii) surface geometry.

Using experimental observations by Isaac Newton, it is postulated that surface flux in convection is directly proportional to the difference in temperature between the surface and the streaming fluid. That is, \[q \propto (T_s-T_\infty)\] \(T_s\) is surface temperature and \(T_\infty\) is the fluid temperature far away from the surface. Introducing a proportionality constant to express this relationship as equality, we obtain \[\boxed{q = h(T_s-T_\infty)}\] This result is known as Newton’s law of cooling. The constant of proportionality \(h\) is called the heat transfer coefficient.