1st Law for Transient Processes

Sign convention arrow.
Sign convention arrow.
Inlet mass flow rate.
Inlet mass flow rate.
This diagram shows a closed system with a system boundary enclosing it and sign convention arrows showing that heat transfer is positive when heat flow into the system and work is positive when it is done by the system.

Transient Process

(or unsteady process) :
A process in which one or more properties or process variables change as a function of time.
Transient processes can be very complex. Therefore, we will only consider processes in which we can assume uniform flow and uniform state.
In the previous lesson, we saw how much the uniform flow assumption simplified the differential mass balance equation. In this lesson, we will see how much the uniform flow and uniform state assumptions simplify the differential form of the 1st Law.
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Ch 5, Lesson E, Page 1 - 1st Law for Transient Processes