Second law and entropy: a broader

The themiodynamics of flow is based on mass, energy, and entropy balances, which have been developed in Chaps. 2 and 5. The application of tliese balances to specific processes is considered in this chapter. The discipline imderlying tlie study of flow is fluid mechanics, which encompasses not only the balances of thermodynamics but also the linear-momentum principle (Newton s second law). This makes fluid mechanics a broader field of study. The distinction between thermodynamics problems and fluid-mechanics problems depends on whether this principle is required for solution. Those problems whose solutions depend only on mass conservation and on the laws of thermodynamics are commonly set apart from the study of fluid mechanics and are treated in courses on thermodynamics. Fluid mechanics then deals with the broad spectmm of problems which require application of the momentum principle. This division is arbitrary, but it is traditional and convenient. 

---