1. Lecture 2 Heat, Expansion
Basic Thermodynamic
Lecture 2
Heat, Expansion

2. ENERGY HEAT INTRODUCTION
The capacity of a system to do work is the energy of that system. Work can be done on the system or work can be done by the system.
The capacity of a system to do work is the energy of that system. Work can be done on the system or work can be done by the system.
When the energy of a system changes as a result of temperature difference between the system and its surroundings, we refer to that energy transferred as heat (q); that is, energy has been transferred as heat.

3. INTRODUCTION
System q q
(+)
(-)
Surrounding

4. Heat The flow of thermal energy from one object to another.
INTRODUCTION
Heat
The flow of thermal energy from one object to another.
Heat always flows from warmer to cooler objects.

5. INTRODUCTION Cup gets cooler while hand gets warmer
For example,
Cup gets cooler while hand gets warmer
Ice gets warmer while hand gets cooler

6. INTRODUCTION Heat (Q) Units Calories [cal ; kcal]
Is the amount of heat energy required to raise the temperature of 1 gram or 1 kg of water up by 1 C (K)
BTU (British Thermal Unit)
Is the amount of heat energy required to raise the temperature of 1 pound [lb] of water up by 1 F
1 BTU = 778 lb.ft = 1054 Joule
International Standard unit
Q = joule [J] or kilojoule [kJ]

7. HEAT CAPACITY Heat Capacity (C)
Heat Capacity of a system is the amount of heat required to change the temperature of the whole system by one degree. It may be measured in J/K or Btu/ oF
Specific Heat Capacity (c)
Specific heat is the amount of heat required to change temperature of one kilogram of a substance by one degree. Specific heat may be measured in J/kg K or Btu/lb oF
Specific heat has same unit with specific gas constant(Rbar) which is equal to work divided by mass

8. CHANGES IN THERMAL ENERGY
Describes the energy transferred by heat that been released, or been absorbed by certain mass (m) of material having changes in temperature (ΔT).
ΔQ = m x c x ΔT
ΔQ = change in thermal energy [Joule]
m = mass of substance [kg]
ΔT = change in temperature (Tf – Ti) [K]
c = specific heat of a substance [J/kg K]

9. Change of State & Latent Heat
Solid
Crystalizing
Freezing
Sublimation
Melting
Vaporize
Liquid
Vapor/gas
Condensation

10. Change of State & Latent Heat
During a change of state, the heat added is called latent heat because there is no change in temperature.

11. Change of State & Latent Heat
Latent Heat of Fusion (Hf)
Conversion from Solid Liquid
Heat of Fusion  Q = m Hf
Latent Heat of Vaporization (Hv)
Conversion from Liquid Gas
Heat of vaporization  Q = m Hv

12. Change of State & Latent Heat
For 0°C
Hf = 80 cal/g = 334 kJ/g
For 100°C
Hv = 540 cal/g = 2,260 kJ/g
Example:
How much heat is required to melt 5.0 kilograms of water at its melting point?
Q = m Hf
= 5 Kg x 334 kJ/Kg
= MJ

13. Thermal Expansion
Distance between molecules increases as their thermal energy increases.
Thermal expansion provides a method of measuring temperature
Linear expansion
Volume expansion

14. Linear expansion depends on:
Thermal Expansion
Linear expansion
Solids expand in all directions: length, width, or thickness when heated, and similarly contract when cooled.
Linear expansion depends on:
change in temperature
original length &
type of material.

15. L =  Lo T Thermal Expansion L = change in length, [m]
Linear expansion
L =  Lo T
L = change in length, [m]
 = coefficient of linier expansion, [C-1 ]
Lo = original length, [m]
T = temperature change, [C]

16. Thermal Expansion  = coefficient of linier expansion Linear expansion
Material
a   (1/Co)
Aluminum
23 x 10–6
Brass
19 x 10–6
Concrete
12 x 10–6
Glass
8.5 x 10–6
Steel
11 x 10–6
Lead
29 x 10–6

17. V= Vo T Thermal Expansion
Volume expansion
Occurs in liquids and gases. It is depend on the change in temperature, original volume, and the type of substance.
V= Vo T
V = change in volume, [m3]
 = coefficient of volume expansion, [C-1 ]
Vo = original length, [m3]
T = temperature change, [C]
 = 3 . 

18. Thermal Expansion β = coefficient of volume expansion Volume expansion
Liquid
b   (1/Co)
Benzene
1240 x 10–6
Ethyl Alcohol
1120 x 10–6
Gasoline
950 x 10–6
Mercury
182 x 10–6
Water
207 x 10–6

19. Thermal Expansion
Over small temperature ranges, the linear nature of thermal expansion leads to expansion relationships for length, area, and volume in terms of the linear expansion coefficient .