# Intro to Entropy Balances on Open Systems

In the previous lesson, we studied

#### entropy balances

on closed systems. That was interesting, but not broadly applicable. In this lesson, we will begin by deriving the#### entropy balance for open systems

. We will then show how it can be simplified for steady-state (SS) and single-inlet, single-outlet (SISO) processes.Next, we will consider the significance of the area under an internally reversible (Int Rev) process path on a TS Diagram for an open system and use the result to help us derive the

#### Mechanical Energy Balance Equation

(MEBE). One special case of the MEBE is the#### Bernoulli Equation

, which applies when Ws = 0.In many processes of interest in this course, changes in Epot and Ekin are negligible. This situation yields another special case of the MEBE that we will apply to all of the polytropic processes that we introduced in Lesson 7E.

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