# Accumulation of Energy

W
Q
Closed
System
ΔEsys
The diagram below shows a

#### uniform-flow process

in which mass flows into and out of a system.

Heat and work interactions also occur.

Consider the process for an interval of time from t1 to t2, where t2 > t1.

At t1 the energy in the system is: Esys(t1).
At t2 theenergy in the system is: Esys(t2).
What is the change in energy of the system during the process from t1 to t2?

## Enthalpy Form of the 1st Law for Open Systems

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### Ch 5, Lesson E, Page 2 - Accumulation of Energy

• Just as we did in the previous lesson, we will analyze a process that takes place over a time interval from t1 to t2.
• In a transient process, the energy of the system may be different at t1 than it is at t2.
• Our goal is to derive an equation to help us evaluate how much the energy of the system changes during such a process.
• But, keep in mind that at any time, Esys is made up of internal energy, kinetic energy and gravitational potential energy.
• The place to start is the enthalpy form of the 1st Law for open systems.
• What do you think the next step is ?  Integration ?
• Flip the page and see for yourself.