1. Principles of Thermodynamics and Thermal Fluids (CHPE 203) Chapter 1 Introduction

2. What is thermal sciences?
Thermal-fluid sciences involve the
Transfer of energy
Transport of energy and
Conversion of energy,
usually studied under the sub-categories of
thermodynamics,
heat transfer, and
fluid mechanics.

3. Example of Thermal Fluids in Human Body
The heart is constantly pumping blood to all parts of the human body,
various energy conversions occur in trillions of
body cells, and
the body heat generated is constantly rejected to the
environment.

4. Example of Thermal Fluid Applications
Designing the radiator of a car involves:
the determination of the amount of energy transfer from a knowledge of the properties of the coolant using thermodynamics,
the determination of the size and shape of the inner tubes and the outer fins using heat transfer, and
the determination of the size and type of the water pump using fluid mechanics.

5. What is Thermodynamics?
Thermodynamics can be defined as the science of energy.
words therme (heat) and dynamis (power), the ability to cause changes.
The change in the energy content of a system is equal to the difference between the energy input and the energy output, and the energy balance is expressed as:
ΔE = Ein - Eout

6. Thermodynamic Laws Zeroth Law of Thermodynamics
First Law of Thermodynamics
Second Law of Thermodynamics
Third Law of Thermodynamics

7. Zeroth law of Thermodynamics:
The Zeroth law states that
“Two objects are in thermal equilibrium if both have the same temperature reading even if they are not in contact”.

8. First law of thermodynamics
First law of thermodynamics is simply an expression of the conservation of energy principle, and it states that
“Energy cannot be created or destroyed BUT it can be changed from one form to another”.

9. Second law of thermodynamics
Second law of thermodynamics states that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy.
For example, a cup of hot coffee
left on a table eventually cools to
room temperature, but a cup of
cool coffee in the same room never
gets hot by itself.

10. Third Law of Thermodynamics
Entropy is the measure of molecular disorder or randomness.
As a system becomes more disordered, the position of the molecules becomes less predictable and the entropy increases.
Entropy is the lowest in a solid because molecules are held in place and simply vibrate and highest in a gas where the molecules are free to move in any direction.
Third Law of Thermodynamics States that:
“Entropy of a pure crystalline substance at absolute zero temperature (zero Kelvin) is zero since the state of each molecule is known”.

11. Heat Transfer
Energy that can be transferred from one system to another as a result of temperature difference, also, deals with the determination of the rates and mechanism of energy being transferred.
Thermodynamics:
deals with equilibrium states and changes from one equilibrium state to another.
Heat transfer:
deals with systems that lack thermal equilibrium(non-equilibrium phenomenon), and tell us the rate and mechanism of heat been transferred.

12. Fluid mechanics
Is defined as the science that deals with the behaviour of fluids at rest (fluid statics) or in motion (fluid dynamics).
fluid refers to a substance in the liquid or gas phase
Hydro-dynamics deals with liquid flows in pipes and open channels.
Gas dynamics deals with flow of fluids that undergo significant density changes, such as the flow of gases through nozzles at high speeds.
Aerodynamics deals with the flow of gases (especially air) over bodies such as aircraft, rockets.

13. Unit Systems Any physical quantity characterized by dimensions
called units:
Primary dimensions: such as mass m, length L, time t, and temperature T
Secondary dimensions: such as velocity u, energy E, and volume V are expressed in terms of the primary
dimensions (derived from primary).

14. Units are still in common use today:
1- English system, which is also known as the United States Customary System (USCS), but this has no apparent systematic numerical base, and various units are related arbitrary to each other (12 in in 1 ft (foot), 16 oz in 1 lb, 4 qt in 1 gal, etc.).
2- Metric SI (which known as the International System). meter (m) for length, kilogram (kg) for mass, second (s) for time, degree Kelvin (°K) for temperature).
1 lbm (pound mass) = kg
ft = m

15. Force:
In SI system, N (Newton) force required to accelerate a mass of 1 kg at a rate of 1 m/s2.
In the English system, the force unit is the pound-force (lbf ) and is defined as the force required to accelerate a mass of lbm at a rate of 1 ft/s2. That is,
1 N = 1 kg · m/s2
1 lbf = lbm · ft/s2
Unlike mass, weight W is a force. It is the gravitational force applied to a body, and its magnitude is determined from Newton’s second law,
W = mg = (N) OR Force=mass x acceleration
where m is the mass of the body, and g is the local gravitational acceleration (g is 9.81 m/s2 or ft/s2 at sea level).
The specific weight γ and is determined from γ =ρg, where ρ is density.

16. Energy
energy unit is the Btu (British thermal unit) = energy required to raise the temperature of 1 lbm of water at 68 F by 1 F.
In the metric system, the amount of energy needed to raise the temperature of 1 g of water at 15 oC by 1 oC is defined as
1 calorie (cal), and 1 cal= J.
The magnitudes of the kilo-joule and Btu are almost identical
(1 Btu=1.055 kJ).
Work : a form of energy, defined as force times distance;
therefore, it has the unit “Newton. meter (N ·m),” called a
Joule (J), 1 J = 1 N · m
and, the kilo-joule (1 kJ=103J).

17. Dimensional Homogeneity
In engineering, all equations must be
dimensionally homogeneous. That is, every term in an equation must have the same unit (apples and oranges do not add).
E= 25 kJ + 7 kJ/kg Invalid
Example:
A tank is filled with oil whose density is ρ= 850 kg/m3. If the volume of the tank is V=2 m3, determine the amount of mass m in the tank.
It is clear: m = ρ . V = (850 kg/m3) (2 m3) =1700 kg

18. Operations with Units
Only add and subtract numbers with the same associated units
2 kg + 3 m Invalid
If the dimensions are the same but the units differ, first convert to a common set of units
1 lb g Invalid
1 lb g lb lb = 1.88 lb Valid
You can multiply and/or divide unlike units, but you cannot cancel units unless they are the same
Valid

19. A Conversion Factor in SI
In SI, the conversion factor C used to transform the units of mass, length, and time, to the derived unit of force is obtained from:
F = (mass) (acceleration)
mass acceleration conversion factor g=9.81

20. 1 in = 2.54 cm, 1ft=12 in

21. 1 in = 2.54 cm, 1ft=12 in