ABSTRACT
Batch and continuous processes are the most important operation modes used in the food engineering field. A batch system can operate in unsteady state, while the continuous process works in a steady state. The unsteady state has the characteristic that in any point in the system, the variables measured (concentration, flow rate, temperature, pressure) change through the time. While in the steady state, these properties remain constant through the time; this requires a continuous flow of phases into and out of the system. An example of both types of processes could be illustrated as the baking of a pound cake in a wheeled rack oven (batch) or during the heating of a fluid in a double pipe heat exchanger (Figure 4.1). In both cases, two thermocouples are positioned at different distances, and their kinetic temperatures describe different behaviors. In the first case, the change in temperature is a function of the baking time and the position of the thermocouples. In the second case, the temperature solely changes in function of thermocouple position. Therefore, the continuous processes operate in a continuous or a steady state, and the values of variables, such as temperature, pressure, levels, flow rates, do not change through time, except for small fluctuations around the average value (Foust et al. 1979; Himmelblau and Riggs 2003; Treybal 2003).
