Ees 2 Lesson 3
Ees 2 Lesson 3
Ees 2 Lesson 3
Conservation Laws
• Heat / Heat Transfer (𝑸) is energy in transit (on the move) from one
body or system to another solely because of a temperature difference
between the bodies or system.
NOTE: 𝑸 is positive when heat is added to the system.
𝑸 is negative when heat is rejected by the system.
CONSERVATION OF ENERGY
• The Law of Conservation of Energy states that the energy is neither
created nor destroyed.
• The conservation of energy principle can be expressed as follows:
The net change (increase or decrease) in the total energy of the system
during a process is equal to the difference between the total energy
entering and the total energy leaving the system during that process.
𝑬 𝒊𝒏 − 𝑬 𝒐𝒖𝒕 = ∆𝑬
FIRST LAW OF THERMODYNAMICS
The First Law of Thermodynamics states that energy can be neither
created nor destroyed during a process; it can only change forms.
𝐸1 = 𝐸2
𝑃𝐸1 + 𝐾𝐸1 + 𝑈1 +𝑊 𝐹1 + 𝑄 = 𝑃𝐸2 + 𝐾𝐸2 + 𝑈2 +𝑊 𝐹2 +𝑊 𝑆𝐹
𝑄 = ∆𝑃𝐸 + ∆𝐾𝐸 + ∆𝑈 + ∆𝑊𝐹 + 𝑊𝑆𝐹
𝑸 = ∆𝑷𝑬 + ∆𝑲𝑬 + ∆𝑯 + 𝑾𝑺𝑭
FIRST LAW OF THERMODYNAMICS
CONVERSIONS:
1 BTU = 1.055 kJ 1kW-hr = 3600 kJ
= 778 lbf–ft = 3413 BTU
= 252 calories = 860 kcal