Hydrodynamics, transfer coefficients and reactor models for solid–fluid, gas–liquid and three-hase systems were discussed. Design equations for packed reactors, bubbling fluidised beds, bubble columns, slurry bubble columns, three phase fluidised beds and mechanically agitated slurry reactors were presented. Process design were illustrated with examples for a packed bed catalytic reactor, a catalytic fluidised bed reactor, a catalytic slurry bubble column, and a batch mixing tank.