Principles of Momentum Transfer and Applications

1 A Definition of Drag Coefficient for Flow Past Immersed 

Introduction and types of drag. In Chapter 2 we were concerned primarily with the momentum transfer and the frictional losses for flow of fluids inside conduits or pipes. In this section we consider in some detail the flow of fluids around solid, immersed objects. 

The flow of fluids outside immersed bodies appears in many chemical engineering applications and other processing applications. These occur, for example, in flow past spheres in settling, flow through packed beds in drying and filtration, flow past tubes in heat exchangers, and so on. It is useful to be able to predict the frictional losses and/or the force on the submerged objects in these various applications. 

In Fig. 3.1-la the flow of fluid is parallel to the smooth surface of the flat, solid plate, and the force F in newtons on an element of area dA m of the plate is the wall shear stress T times the area dA or x dA. The total force is the sum of the integrals of these quantities evaluated over the entire area of the plate. Here the transfer of momentum to the surface results in a tangential stress or skin drag on the surface. 

In many cases, however, the immersed body is a blunt-shaped solid which presents various angles to the direction of the fluid flow. As shown in Fig. 3.1-lb, the free-stream velocity is Uo and is uniform on approaching the blunt-shaped body suspended in a very 

---

C. J. Geankoplis. Principles of momentum transfer and applications. In Transport Processes and Unit Operations, 3rd edn. Allyn and Bacon, Boston, MA, 1993, pp. 114-213. 

This part, dealing with fundamental principles, includes the following chapters 1. Int. -oduction to Engineering Principles and Units 2. Principles of Momentum Transfer and Overall Balances 3. Principles of Momentum Transfer and Applications 4. Principles of Steady-State Heat Transfer 5. Principles of Unsteady-State Heat Transfer 6. 

---