5. Fluid Mechanics: Basic Concepts

The various unit operations used in the processing and manufacturing of materials have been grouped, based on the commonality of some underlying principles, together into three fundamental, molecular-level transfer (or transport) processes: mass transport, heat transport, and momentum transport. As we will see later, there exists mathematical analogy among these three processes, and although their physical mechanisms are totally different, in the elementary sense they can be described by the same general equation. Fluid mechanics addresses the study of momentum transport in a fluid and much of food engineering is concerned with the handling of fluids. Many food products are fluids or are in a fluid stage at some point in their processing. In addition, fluids such as water, steam, refrigerants, and air are used to heat, cool, and otherwise process foods. This chapter will introduce the engineering principles of fluid mechanics that underlie the study of the forces on fluids and their utility in the use and handling of fluids. Fluid mechanics includes both fluid statics and fluid dynamics (Fig. 5.1). It is based on the principle of conservation of mass, energy, and momentum (following Newton’s second and third laws). Additionally, fluids are assumed to represent a continuum rather than discrete parts, and the fact that a fluid is composed of discrete molecules is ignored.