Fully Developed Laminar Flow

Consider a fluid element of length and radius centered on the axis of a horizontal pipe of diameter in a fully developed laminar flow at time (Fig. 3). After certain time , the fluid element moves to a new location and the flat end of the element becomes distorted. Since the flow is fully developed and steady, so the distortion on each end of the fluid element is the same and the convective as well as local acceleration is zero. Thus, every part of fluid element moves along a path line and the velocity varies from one path line to other. This velocity variation combined with fluid viscosity produces shear stress. In addition to this shear force, the pressure drops along the length of the pipe.