1. Energy

2. Design Lots of forms of energy Lots of forms of energy transfer
Understand how works
Understand how to calculate or estimate

3. Types of Energy Three main types Kinetic (1/2 mv2) Potential (gmz)
Internal
Bond vibrations
VDW
Charges

4. Types of Energy TRANSFER
Two main types
Heat
Work
What’s the difference between heat and energy?
State function (temperature, energy)
Path function (heat, work)

5. Heat (Q) It is NOT a property
It is a mechanism to transfer energy (thermal)
Flow is always in one direction.
Adiabatic is a lack of heat flow
Insulation
Sometimes want to prevent heat flow

6. Heat Transfer Conduction Convection Radiation Touch the hot stove
Open oven and feel rush of heat
Radiation
Sun
“red hot”

7. Work (W) Electric/Magnetic work Mechanical work (spring work)
Electric Engineers and Physics 2
Circuit
Mechanical work (spring work)
Apply force over a distance
Spring
Boundary work
Boundary changes size
Piston
Shaft work
Rotating shafts
Motor
Flow Work
Pressure change as fluid flows
PV work

8. Flow Work The work it takes to have substances flow
Internal energy + Flow work = enthalpy
U + PV = H
Convenient to combine them
Use enthalpy instead of internal energy for “flow processes”

9. Boundary Work Isochoric – constant V Isobaric – constant P
Isothermal – constant T
Polytropic – common example
PVk = Constant
Let’s calculate each for an IG
But FIRST, CW questions

10. Enthalpy/Internal Energy
Calculate enthalpy, pressure, volume, and internal energy of saturated steam at 40oC
Does H=U+PV?

11. Work/Heat Changes U/H
Some processes are isenthalpic or constant energy
However, in the presence of work or heat, U/H of a substance WILL change
How do we calculate those changes?

12. Changes in Internal Energy or Enthalpy for water
Look up values at the two conditions, calculate difference

13. Changes in Internal Energy (IG)
Heat capacity (C)
For internal energy – Cv
“constant volume”
How much energy it takes to change temperature
ONLY a function of temperature for IG
Energy and Cv

14. Changes in Enthalpy(IG)
For enthalpy – Cp
“constant pressure”
ONLY a function of temperature for IG
Enthalpy and Cp

15. Changes in Internal Energy (IG)
For a room 5 m X 4 m x 3 m at K and 1.0 bar, how much energy would it take to increase the air to 298 K (room temperature)?
For that same change of energy, how much would the quality of water as a saturated liquid (at K) change?

16. Changes for REAL gases
Something called departure functions or residual properties (chapter 5)

17. Other forms of energy change
“Latent” heat
The energy it takes to change phase
Evaporation
Heat of vaporization
Melting
Freezing
Cooling or heating process (sign of enthalpy change)

18. Concept Warehouse
But first, what do you think is safer, steam at 150 oC or 105 oC
WHY?
Enthalpy v energy CW