1. Energy Transfer by Heat and Work
Chapter 4
Energy Transfer by Heat and Work

2. Types of Energy:
Heat
Work
Kinetic energy
Potential energy
Internal energy

5. The Three Types of Heat Transfer
Conduction: is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles.
Convection: is the mode of energy transfer between a solid surface (or liquid) and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion.
Radiation: is the energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules.

9. Types of Work:
Electrical Work
Mechanical Work
1. Moving Boundary Work
2. Shaft Work
3. Spring Work

11. Mechanical Work: 1. Moving Boundary Work 2. Shaft Work 3. Spring Work11

15. Example 1

16. Example 2

18. Example 3

23. Example 4

25. Example 5

28. Kinetic Energy
Kinetic energy (KE) is the energy associated with velocity and mass flow of material.
KE=½mv2
KE is a state variable.

29. Example KE

30. Example
Determine the kinetic energy in Btu/h for 100 gallon/min flow of water through a 3-inch schedule 40 pipe (inside diameter equal to in.)

31. Potential Energy
Potential energy is the energy associated with elevation changes of material compared to a reference level.
PE is a state variable.
PE=mgh
m- mass
g- gravitational acceleration
h- elevation change

32. Example for Potential Energype

33. Potential Energy with Slope33

34. Conservation of Mass
“Mass cannot be created or destroyed BUT it can be changed from one form to another”

35. Or: Min-Mout=ΔMsystem

39. Example 6

43. Example 8
R-134a
compressor 2
0.8 MPa
50C 1
0.14 MPa

44. Refrigerant-134a enters a compressor as a saturated vapor at a specified pressure, and leaves as superheated vapor at a specified rate. The rates of energy transfer by mass into and out of the compressor are to be determined.
Assumptions 1 The flow of the refrigerant through the compressor is steady. 2 The kinetic and potential energies are negligible, and thus they are not considered.
Properties The enthalpy of refrigerant-134a at the inlet and the exit are (Tables A-12 and A-13)

45. Analysis Noting that the total energy of a flowing fluid is equal to its enthalpy when the kinetic and potential energies are negligible