First-Law Analysis for a Control Volume

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1 First-Law Analysis for a Control Volume
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2 6.1 CONSERVATION OF MASS AND THE CONTROL VOLUME

3 Let us consider the conservation of mass law as it relates to the control volume.
Rate of change = + in – out Continuity equation:

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6 6.2 THE FIRST LAW OF THERMODYNAMICS FOR A CONTROL VOLUME
1st law for a control mass, ( rate equation for a process) (energy per unit mass at a state )

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8 Rate of Flow Work 1 2

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10 3 Delta=In-Out

11 6.3 THE STEADY-STATE PROCESS
V

12 IN OUT

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14 Application of Steady State

15 6.4 EXAMPLES OF STEADY-STATE PROCESSES
superheated It is thought as a constant pressure process, even only a small pressure drop. No work is done by the control volume, i.e. Wcv is 0. Both kinetic and potential energy changes of the control volume are negligible

16 ( No heat transfer across the control surface, but heat exchange happened insides. )

17 Solution 2

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21 1 2 3 1 2 3

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24 1 2

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34 6.5 THE TRANSIENT PROCESS For example, filling closed tanks with a gas or liquid, or discharge from closed vessels is called transient process.

35 （1）

36 （2）

37 Example6.10

38 u2 P2

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40 Example 6.12