5. The First Law of Thermodynamics for a Control Volume
In this chapter, we have introduced the mass and energy conservation equations for control volumes. The general conservation equations for control volumes are explained in Section 5.2. When applying these conservation principles to a thermal device, it is important to evaluate the operation of the device, set up an appropriate control volume, and make appropriate assumptions. This is an important skill that students need to develop through practice.
Section 5.3 demonstrates how to simplify the conservation equations for common steady-state steady-flow devices such as turbines and compressors, throttling valves, pipes and ducts, nozzles and diffusers, mixing chambers, and heat exchangers. It is important to understand that, the equations in Section 5.3 are derived for these devices with certain assumptions. When applying these derived equations to a specific thermal device, a careful evaluation of the assumptions must be done to ensure the derived equations are appropriate for the given conditions.