1. Engineering Fundamentals II
Thermodynamics: Units and Dimensions, Problem Solving, and Systems

2. Units and Dimensions Basic Dimensions Derived Dimensions
Length [L] meter foot
mass [m] kilogram pound-mass
Time [t] second second
Temperature [T] K or °C °R or °F
Derived Dimensions
Force [F] Newton pound-force
Energy [E] joule foot-pound

3. Example: Units and Dimensions
Always include units in calculations
E.g.
Dimensional analysis

4. Problem Solving Known properties Find
Schematic and Data (from tables, etc.)
Assumptions (e.g. ideal gas)
Properties
Analysis
Comments

5. Macroscopic and Microscopic
The everyday experience of smoothness of matter is an illusion.
Microscopic – statistical thermodynamics
Explains mechanics of temperature, pressure and latent heats.
Macroscopic – classical thermodynamics
Based on volumes large enough that statistical deviation is not measurable
A limit of statistical thermodynamics where properties are understood as averages.

6. Systems Closed, Isolated, Open Systems Properties and States
Processes and Cycles
Extensive and Intensive Properties
Equilibrium
Temperature

7. Identify the System

8. Defining the boundary is critical!
ENGM 295
Spring 2008
Defining the boundary is critical!

9. Closed: no mass crosses boundary

10. Isolated:
no mass, energy (via work or heat) or entropy crosses boundary ….

11. Open: mass, energy and entropy cross boundary

12. Properties Intensive – independent of “amount of system”
Density (specific volume)
Temperature
Pressure
Also: velocity, voltage
Extensive – dependent on “amount of system”
Weight and mass
Volume
Energy
Entropy
Also: momentum, charge

13. Extensive and Intensive Properties
The sum of its parts
Can have a density attributed to it
e.g. momentum, mass, charge, entropy
Intensive
Remains the same when body is divided
Can vary within a body
e.g. velocity, pressure, voltage, temperature

14. Example: Properties Weight (W) and mass (m)
Volume (V) and specific volume (v = V/m)
Density (ρ = m/V)
Specific weight (γ = W/V)
Specific gravity (SG = ρ/ρ water)
Pressure (p = Force/Area)
Atmospheric pressure = 101 kPa
Pressure Head
Pascal’s law

15. Measuring Pressure

16. Example 2-4

17. States A collection of properties.
Some properties are “state variables”
You can integrate between two states to determine the property’s value
Steady state –properties constant in time

18. Process: change of state
The change in value of a property that is altered is determined solely by the end states.
If the value of a quantity depends on the process, it is not a property.

19. Cycle:
Series of processes that return to the initial state

20. Zeroth law of Thermodynamics
A is in thermal equilibrium with C, and B is in thermal equilibrium with C, then A is in thermal equilibrium with B.

21. Thermal equilibrium means:
Temperature is equalized.
Energy is not necessarily equalized.

22. Temperature and Thermometers
Thermometer in thermal equilibrium with substance being measured.

23. Temperature Ideal gas temperature:
p(T) = p0(1+βT) → p(T) = p0βTK
i.e. pV = mRT → p = (constant)T
Absolute Zero – 0 K (no degree symbol)

24. Quasi-equilibrium Processes
Systems are not always in thermal equilibrium during a process.
Non-equilibrium states exhibit spatial variations of intensive properties.
Quasi-equilibrium
An idealized process
Departure from equilibrium is infinitesimal