Dynamics of Biological Systems, Chapter 2: Development of a General Environmental Control Model

First paragraph. Conservation of mass and conservation of energy are the two key issues in the solution of an environmental control problem. To develop these key issues, it is expedient to use the concept of a control volume developed in Chapter 1. The boundary of the control volume can be the entire exterior surface of a building or an arbitrary part of the total volume of product. For example, in the modeling of grain drying, the bulk is divided into thin layers and an individual layer is treated as a control volume.