The transient operation of a multipass shell-and-tube heat exchanger with baffles is described by a multicell dynamic model where every cell represents a specific part of the exchanger. The proposed modeling technique can be used in a digital computer for the dynamic simulation of almost any type of shell-and-tube heat exchanger. The model includes time-dependent inlet conditions for both the cold and the hot streams. Hence, a number of start-up cases can be simulated and, once the system reaches a stationary operating point, a disturbance can be introduced in the inlet temperatures or the flow rates. This particular feature makes the model very useful not only for design purposes but also for transient analysis and control system design.