Energy is defined as the capacity for doing work. In order to do work, energy is necessary, and a body possesses energy if it has the capacity to do work. The amount of energy required to do a given amount of work is equal to the amount of work done. Consequently, the quantity of energy that a body can possess is always equal to the quantity of work the body can generate.

1. Image: Fundamentals of Materials Science and Engineering by William Callister, Jr.
CONSERVATION OF ENERGY
ENGR. MARCO A. SOLLANO
Instructor/Professor
Aurora State College of Technology
Engineering Department
Brgy. Zabali, Baler, Aurora
THERMODYNAMICS 1
Course Code: ME 313
Course Units: 3 Units ( Lec.- 3 hours, Lab.- 0 hour)
Prerequisite:

2. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Gravitational Potential Energy
 Gravitational potential energy of a body is its energy due to its
position/elevation.
𝑷 = 𝑭𝒈𝒛 =
𝒎𝒈𝒛
𝒌
Δ𝑷 = 𝑷𝟐 − 𝑷𝟏 =
𝒎𝒈
𝒌
(𝒛𝟐 − 𝒛𝟏)
Δ𝑷 = 𝒄𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒑𝒐𝒕𝒆𝒏𝒕𝒊𝒂𝒍 𝒆𝒏𝒆𝒓𝒈𝒚

3. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Kinetic Energy
 Energy or stored capacity for performing work possessed by a moving
body, by virtue of its momentum.
𝑲 =
𝒎𝒗𝟐
𝟐
Δ𝑲 = 𝑲𝟐 − 𝑲𝟏 =
𝒎
𝟐
𝒗𝟐
𝟐 − (𝒗𝟏
𝟐]

4. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Internal Energy
 Is the energy stored within a body or substance by virtue of the
activity and configuration of its molecules and of the vibration of the
atoms within the molecules.
Δ𝐮 = 𝐮𝟐 − 𝐮𝟏
Δ𝑼 = 𝑼𝟐 − 𝑼𝟏
u = specific internal energy (unit mass)
U = mu = total internal energy (m mass)

5. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Work
 Is the product of displacement of the body and the component of the
force in the direction of the displacement.
 Energy in transition – it exist only when a force is moving through a
distance.

6. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Work of a Non-Flow System
𝑽𝟐
1
Piston rod
2
p
V
m n
p
𝑽𝟏
dW
dV
Final piston rod position
Cylinder
Piston
Area
e
f
Work done as the piston moves from e to f
𝒅𝑾 = 𝑭𝒙𝒅𝒙 = 𝒑𝑨 𝒅𝑳 = 𝒑𝒅𝑽
𝑾 =
𝟏
𝟐
𝒑𝒅𝑽
Total work done (points 1 to 2)

7. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Flow work
System
Boundary
L
A = Area of surface
F V
𝑾𝒇 = 𝑭𝑳 = 𝒑𝑨𝑳
𝑾𝒇 = 𝒑𝑽
Δ𝑾𝒇 = 𝑾𝒇𝟐 − 𝑾𝒇𝟏 = 𝒑𝟐𝑽𝟐 − 𝒑𝟏𝑽𝟏
Δ𝑾𝒇 = 𝒄𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒇𝒍𝒐𝒘 𝒘𝒐𝒓𝒌
 Flow work of energy is done in pushing a fluid across a boundary
usually into or out of a system.

8. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Heat
 Heat is the energy in transit (on the move) from one body or system to
another solely because of a temperature difference between the
bodies or systems.
Q is POSITIVE when heat is added to the body or system.
Q is NEGATIVE when heat is rejected from the body or system.
Classification of System
 A CLOSED SYTEM is one in which mass does not cross its
boundaries.
 An OPEN SYTEM is one in which mass crosses its boundaries.

9. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Conservation of Energy
 The law of conservation of energy states that energy is neither
created nor destroyed.
 The first law Thermodynamics states that one form of energy may be
converted into another.
Characteristics of steady flow system
 There is neither accumulation nor diminution of mass within the
system.
 There is neither accumulation nor diminution of energy within the
system.
 The state of the working substance at any point in the system remains
constant.

10. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Steady Flow Energy Equation
System
𝒛𝟏 𝑸
𝑾
𝑷𝟏
𝑲𝟏
𝒑𝟏𝑽𝟏
𝑼𝟏
1
2
𝑷𝟐
𝑲𝟐
𝒑𝟐𝑽𝟐
𝑼𝟐
𝒛𝟐
Datum Level
𝑷𝟏 + 𝑲𝟏 + 𝑾𝒇𝟏 + 𝑼𝟏 + 𝑸 = 𝑷𝟐 + 𝑲𝟐 + 𝑾𝒇𝟐 + 𝑼𝟐 + 𝑾
𝑸 = Δ𝑷 + Δ𝑲 + Δ𝑾𝒇 + Δ𝑼 + 𝑾
Energy entering system = Energy leaving system

11. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
Enthalpy
𝐡 = 𝐮 + 𝐩𝐯
𝑸 = Δ𝑷 + Δ𝑲 + Δ𝑯 + 𝑾
 Is a composite property applicable to all fluids and is defined by
𝐇 = 𝐦𝐡 = 𝐔 + 𝐩𝐕
𝑷𝟏 + 𝑲𝟏 + 𝑾𝒇𝟏 + 𝑼𝟏 + 𝑸 = 𝑷𝟐 + 𝑲𝟐 + 𝑾𝒇𝟐 + 𝑼𝟐 + 𝑾
𝑷𝟏 + 𝑲𝟏 + 𝑯𝟏 + 𝑸 = 𝑷𝟐 + 𝑲𝟐 + 𝑯𝟐 + 𝑾

12. THERMODYNAMICS
Engineering Department, Aurora State College of Technology
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