Many key ＇＇issues＇＇ in design for the process industries are related to the behaviour of fluids in turbulent f low, often involving more than one phase, chemical reaction or heat transfer. Computational-Fluid-Dynamics (CFD) techniques have great potential for analysing these processes and can be of great help to the designer, by reducing the need to resort to ＇＇cut and try＇＇: approaches to the design of complex equipment. The paper presents the fundamental principles of CFD within the context of the so-called finite-domain technique. The procedure can handle one-, two-, and three-dimensional distributions of the variables in space, steady or transient processes, multi-phase processes, and effects such as turbulence, compressibility of phases, buoyancy, phase-change, chemical reactions, gravity stratification, etc. Demonstrations are made of the application of the procedure to the numerical computation of some process industry situations, such as those occurring in adsorbers/regenerators, combustors, cement kilns, and heat - exchangers. It is concluded that: The finite -domain versions of the differential equations are soluble, with modest computer costs; The solutions are always physically plausible; and, There is a need for extensive evaluation and validation of CFD physical and chemical sub-models, particularly those concerning turbulence, chemical kinetics and interphase-transport processes.