ABSTRACT
This chapter presents methods to solve problems with two independent variables involving first-order differential equation and first-kind boundary condition. It aims to determine the velocity profile of the fluid between the vertical drums. The basic equations of momentum transfer are not necessary here because the fluid keeps a constant velocity. As plug-flow regime was assumed, a wave front of hot fluid advances through the tube at a velocity. As a first option, the reference could be the tube diameter or a given arbitrary length of the heating tube. Several heating systems are designed to heat a fluid while passing through a tube. Others use electrical resistances either wrapped around the tube or set in a grid at the tube entrance. Also, terms related to temperature variations in the angular direction are zero due to the imposed uniform heating at the tube cross section.
