Chemical engineers require a thorough understanding of how gases and liquids flow. Important fundamentals include, for example, the famous Bernoulli equation - a statement of conservation of energy:

P + 1/2ρV2 + ρgh = constant

which is applied along the direction of fluid flow. P is the pressure, ρ the liquid's density, V the flow velocity, h the height and g the gravitational constant.

Energy dissipation, due to liquid viscosity, is often important and the types and effects of viscosity are studied. For liquid flowing in a pipe at low flow rates the flow is laminar, which means that the liquid is moving smoothly along the pipe with layers sliding over each other. The viscous energy loss can be calculated using simple models. As the flow rate increases, however, the flow becomes turbulent, dominated by chaotic swirling eddies. Although this regime is less well understood, if the pipe is part of a reactor, for example, then a chemical engineer will make use of this turbulence to help mix the reagents thoroughly.