02.09 The Complete Energy Balance


The complete energy balance is convenient in the sense that it provides a comprehensive list of everything you need to check to ensure that you have accounted for all energy flows, but it can appear to be a little overwhelming at first glance. Common energy balances (uakron, 14 min) of the energy balance can be used in many situations, but don't forget that the process of analyzing a system and determining its proper model equations is an important part of thermodynamics, and engineering in general. Focus on learning the process, not memorizing the final equations. Energy balance practice (uakron, 18min) with Chapter 2 systems can help you build confidence and quickly prepare for mastering all the example problems in Chapter 2. Try to push pause after each problem statement and work it out for yourself, then resume to provide a check on your analysis.

Comprehension Questions. Write the simplified energy balance for the following:

1. High pressure steam flows through an adiabatic turbine to steadily produce work. 

2. High pressure steam flows into a piston-cylinder to produce work. 

3. Steam at 200 bars and 600°C flows through a valve and out to the atmosphere. 

4. A gas is filling a rigid tank from a supply line.

5. A gas is leaking from a rigid tank into the air. 

6. A sunbather lays on a blanket. At 11:30 a.m., the sunbather begins to sweat. System: the sunbather at 12 noon.