1. First Law for A Open Systems (Control Volume)
P M V Subbarao
Professor
Mechanical Engineering Department
Modeling of True Engineering Systems…..

2. Executes a Thermodynamic Cycle using an assembly of CVs
The Steam Power Plant
Executes a Thermodynamic Cycle using an assembly of CVs
Multiple Inflows & Multiple Outlets !!!

3. Laws of Nature for A Control Mass
Conservation of Mass :
Conservation of Momentum :
First law of thermodynamics :

4. Rate Equations for Laws of Nature for A Control Mass
Conservation of Mass :
Conservation of Momentum :
First law of thermodynamics :

5. The Family of Thermodynamic Systems

6. Engineering Symptoms of Civilization
The Pinnacle of Civilization
The Onset of Civilization

7. CVs for Day to Day Use
Supply & Use of LPG through Cylinders

8. Domestic Using of LPG

9. Control Mass or Control Volume
Closed System or Open system
A Representation for Engineering Convenience

10. CM & CV Representation of a Device
Control Mass representation of Can:
The total Deodorant
Control Volume representation of Can:
Deodorant in side the can
At time t = 0, (before spray).
The total mass of Deodorant =Mass of Deodorant in side the can
Control mass is same as control volume

11. CM & CV Representation of a Device
At t = dt (after spraying)
Control mass = control volume + spray
It is possible to relate CM and CV of a device at any instant!
Principle of Conservation mass says that the rate of change of mass for a control mass is always zero.
What about control volume?

12. The Thermodynamic Control Volume
In real engineering devices, we are usually interested in a region of space, i.e, control volume and not particular control mass.
The laws of nature are connected to Control Mass.
Therefore, we need to transform Laws of Conservation for a control mass to a control volume.
This is accomplished through the use of Reynolds Transport Theorem.
Specially derived in thermodynamics for CV .

13. Reynolds' Transport TheoremII
III
At time t0+dt
III has left CV at time t0+dt I II
At time t0
I is trying to enter CV at time t0
The control volume may move as time passes.

14. Laws of Nature for A Control Volume
Conservation of mass:
Conservation of momentum:
Conservation of energy:

15. First Law for CV: Steady State Steady Flow
Properties of CV are Invariant:
Conservation of mass:
NO accumulation or depletion of mass of a CV.
Conservation of energy:
No addition or removal of energy for a CV.

16. Rate of Work and Heat Transfers : SSSF
Both rate of heat transfer and rate of work transfer are invariant.
The work done per unit mass and heat transfer per unit mass are
invariant.
The specific work transfer at various parts of a CV can be different.
The specific heat transfer at various parts of a CV can be different.
Let :