CHAPTER 3 PROPERTIES OF PURE SUBSTANCES

OBJECTIVE

1. Introduce the concept of a pure substance.
2. Discuss the physics of phase-change processes.
3. Illustrate the P-v, T-v, and P-T property diagrams and P-v-T surfaces of pure substances.
4. Demonstrate the procedures for determining thermodynamic properties of pure substances from tables of property data.
5. Describe the hypothetical substance “ideal gas” and the ideal-gas equation of state.
6. Apply the ideal-gas equation of state in the solution of typical problems.
7. Introduce the compressibility factor, which accounts for the deviation of real gases from ideal-gas behavior.
8. Present some of the best-known equations of state.

3.1 PURE SUBSTANCE

• A substance that has a fixed chemical composition.
• A mixture of various chemical elements or compounds as long as the mixture is homogeneous, which is in the same phase either is in solid, liquid or gas.

3.2 PHASES OF A PURE SUBSTANCE
Solid

• Molecules are arranged in 3D pattern that is repeated throughout.
• Attractive forces of molecules on each other are large and keep the molecules at fixed positions.
• Molecules cannot move relative to each other but oscillate about their equilibrium positions.
• At high temperature, the velocity reach the point where the intermolecular forces are overcome.
• Molecules break away and melting process is began. 

Liquid

• Molecules no longer at fixed positions as they can rotate and translate freely.
• Intermolecular forces are weaker than solids and stronger than gas.
• Distance between molecules generally slight increase as solid turn liquid.

Gas

• Molecules are far apart from each other and order is nonexistent.
• Molecules move randomly and colliding with each other and the wall of container.
• Low density and very small intermolecular forces.
• The energy level of molecules are higher than solid and liquid.
• They are needed to release a large amount of energy before they can condense or sublime.

3.3 PHASE CHANGE PROCESSES OF PURE SUBSTANCES

  

   

- Compressed liquid/ subcooled liquid - when water exists in liquid phase and it is not about to vaporizes

- As more heat is transferred, heat addition will cause some of the liquid to vaporize, that is a phase-change process from liquid to vapor is about to take place. A liquid that is about to vaporize is called saturated liquid.

- During a boiling process, the only change is a large increase in the volume and a steady decline in the liquid level as a result of more liquid turning to vapor.

- The vaporization process is continued until the last drop of liquid is vaporized, any heat loss from this vapor will cause some of the vapor to condense

- A vapor that is about to condense is called saturated vapor. 

- Saturated liquid- vapor mixture is occurred since the liquid and vapor phases coexist in equilibrium.

- " The temperature at which water starts boiling depend on the pressure, therefore if the pressure is fixed, so is the boiling temperature."

- Saturation temperature is the temperature at which a pure substance changes phase at a given pressure

- Saturated pressure is the pressure at which a pure substance changes phase at a given temperature

3.4 PROPERTY DIAGRAMS FOR PHASE-CHANGE PROCESSES
  T-V Diagram
  P-V Diagram

  P-T Diagram


3.5 PROPERTY TABLES
Formula that involve:

CHAPTER 2 : ENERGY,ENERGY TRANSFER , AND GENERAL ENERGY ANALYSIS

Objectives 

• Introduce the concept of energy forms.
 • Discuss the nature of internal energy. 
• Define the concept of heat and three mechanisms of heat transfer: conduction, convection, and radiation.
 • Define the concept of work, including electrical work and several forms of mechanical work. 
• Introduce the first law of thermodynamics, energy balances, and mechanisms of energy transfer to or from a system. 
 • Define energy conversion efficiencies. 
 • Implications of energy conversion on the environment

Introduction

The first law of thermodynamics: 
energy can be neither created nor destroyed during a process; it can only change forms.
Energy can transfer between a system and surroundings

*the total energy (E) of a system constitutes all the forms of energy inside a system (Internal energy + mechanical energy)

*Thermodynamics deals only with the change of the total energy. 

Forms Of Energy

• Energy can exist in numerous forms:

Internal energy, U, (thermal energy, chemical and nuclear energy),

i. Kinetic energy, KE: The energy that a system possesses as a result of its motion relative to some reference frame

ii. Potential energy, PE: The energy that a system possesses as a result of its elevation in a gravitational

iii. Flow energy, Ė: The energy that a system possesses as a result of its
motion due to pressure difference

Physical Insight to Internal Energy

Sensible energy: The portion of the internal energy

of a system associated with the kinetic energies of

the molecules.

Latent energy: The internal energy associated with

the phase of a system.

The various forms of microscopic energies that make up sensible energy

*sensible and latent energy*

https://www.youtube.com/watch?v=b76-iRvSDGE

Energy Transfer By Work

The energy transfer associated with a force acting through a distance.

A rising piston, a rotating shaft, and an electric wire crossing the system boundaries are all associated with work interactions

Formal sign convention: Heat transfer to a system and work done by a system are positive; heat transfer from a system and work done on a system are negative.

Alternative to sign convention is to use the subscripts in and out to indicate direction.

*energy transfer by work*

https://www.youtube.com/watch?v=sZG-zHkGR4U

Sign convention and units

THE FIRST LAW OF THERMODYNAMICS

- Known as the conservation of energy principle
- States that energy can be neither created nor destroyed during a process, it can only change forms.

ENERGY CHANGE OF A SYSTEM

 The net change 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.

KE & PE : macroscopic form of energy ( those a system possesses as a whole with respect to some outside reference frame)

U : sum of all the microscopic form of energy ( those related to a molecular structure of a system and the degree of the molecular activity)

*energy changes*

https://www.youtube.com/watch?v=W0zUnmr9r4U

Energy Conversion Efficiency
- It indicates how well an energy conversion or transfer process is accomplished. 

CHAPTER 1 INTRODUCTION AND BASIC CONCEPTS

OBJECTIVE

• Identify the unique vocabulary associated with thermodynamics through the precise definition of basic concepts to form a sound foundation for the development of the principles of thermodynamics.
• Review the metric SI and the English unit systems.
• Explain the basic concepts of thermodynamics such as system, state, state postulate, equilibrium, process, and cycle.
• Review concepts of temperature, temperature scales, pressure, and absolute and gage pressure.
• Introduce an intuitive systematic problem-solving technique.

  

1.1 THERMODYNAMICS AND ENERGY

1. Thermodynamics can be defined as the science of energy.

2. Energy can be viewed as ability to cause changes.

3. The most fundamental laws of nature is the conservation of energy principle which states that during an interaction, energy can change from one to another but the total amount of energy remains constant.

4. The change in energy content of a body or system is equal to the different between energy input and output, and can be expressed as Ein - Eout = Ediff 

*introduction to thermodynamic*

https://www.youtube.com/watch?v=jR8vZHtOLdA

First law of thermodynamics is simply an expression of the conservation of energy principle , and it asserts that energy is a thermodynamic property.

Second law of thermodynamics asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy.

*zero and first law of thermdynamic*

https://www.youtube.com/watch?v=T0hOWt5AAPE

*laws of thermodynamics*

https://www.youtube.com/watch?v=KTHiIwxcexI

1.2 IMPORTANT OF DIMENSIONS AND UNITS

Some unit conversion ratios that involve in thermodynamics are:
1 atm = 101.325 kPa
1 bar = 100 kPa
1 J = 1 N.m

1.3 SYSTEMS AND CONTROL VOLUMES

There are 2 types of system -  closed system and open system.

Closed system, also known as control mass because it consists of a fixed amount of mass, and no mass can cross its boundary. However, the energy in the form of work or heat can cross the boundary.

Open system, also known as control volume encloses the device that involves mass flow such as compressor nozzle and turbine.Flow through these devices is best studied by selecting the region within the device as the control volume. Both mass and energy can cross the boundary of the control volume.

                  * closed and open system*

https://www.youtube.com/watch?v=H7M6xGvsaY0


1.4 PROPERTIES OF A SYSTEM

There are 2 types of properties - intensive properties and extensive properties.

Intensive properties are those that are independent of the mass of the system, such as temperature, pressure and density.

Extensive properties are those whose values depend on the size or extent of the system. For example mass, volume and momentum.

An easy way to determine whether a property is intensive or extensive is to divide the system into 2 equal parts with an imaginary partition, and the result is each part will have the same value of intensive properties as the original system, but half the value of the extensive properties.

1.6 STATE AND EQUILIBRIUM

The word equilibrium implies a state of balance which is a system experience no changes in thermal, mechanical, phase and chemical when it is isolated from its surroundings.

- Thermal equilibrium : temperature is same
- Mechanical equilibrium : no change in pressure
- Phase equilibrium : involving 2 phases where each phase reaches                                     an equilibrium level
- Chemical equilibrium : chemical reaction occurs

*state of equilibrium*

https://www.youtube.com/watch?v=mAg7RUftc_8

The state postulate requires two intensive properties (e.g. temperature, pressure) to fix the state


1.7 PROCESS AND CYCLE

Process: a system undergo changes from one equilibrium state to another

  >>>>>>>>>>>>>>                >>>>>>>>>>>>>>>>
                             process                                                                        




- The series of states through which a system passes during a process is called process path.
- When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, it is called quasi-static/ quasi-equilibrium process.
- Quasi-equilibrium process : a sufficiently slow process that allows the system to adjust itself internally.

Cycle - a system is said to be undergo cycle when it returns to its initial state at the end of the process.

The Steady -Flow Process
- A process during which a fluid flows through a control volume steadily.
- The fluid properties can change from one point to point within the control volume, but at any fix point they remain the same during the entire process.
- Steady-flow devices such as turbine, pump, boiler, refrigeration system

1.8 TEMPERATURE AND THE ZEROTH LAW OF THERMODYNAMICS

The zeroth law of thermodynamics states that if 2 bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.

1.9 PRESSURE

Defined as a normal force exerted by a fluid per unit area. It has a unit of newton per square meter, which is called pascal. The actual pressure at a given position is called absolute pressure and it is measured relative to absolute vacuum. Besides, the difference between the absolute pressure and the atmospheric pressure is called gage pressure and pressure below atmospheric pressure is called vacuum pressure.

1.10 MANOMETER

- A device that contains one or more fluids and commonly used to measure small and moderate pressure differences.

- A manometer is used to measure the pressure in a tank. 

What Is a Barometer?

A barometer is a widely used weather instrument that measures atmospheric pressure (also known as air pressure or barometric pressure) - the weight of the air in the atmosphere.

There are two main types of barometers – the most widely available and reliable

Mercury Barometers, or the newer digital friendly Aneroid Barometer.

How does a Barometer Work?

The classic mercury barometer is typically a glass tube about 3 feet high with one end open and the other end sealed. The tube is filled with mercury. This glass tube sits upside down in a container, called the reservoir, which also contains mercury. The mercury level in the glass tube falls, creating a vacuum at the top. The first barometer of this type was devised

by Evangelista Torricelli in 1643.

The barometer works by balancing the weight of mercury in the glass tube against the atmospheric pressure just like a set of scales. If the weight of mercury is less than the atmospheric pressure, the mercury level in the glass tube rises. If the weight of mercury is more than the atmospheric pressure, the mercury level falls.

Atmospheric pressure is basically the weight of air in the atmosphere above the reservoir, so the level of mercury continues to change until the weight of mercury in the glass tube is exactly equal to the weight of air above the reservoir.

In areas of low pressure, air is rising away from the surface of the earth more quickly than it can be replaced by air flowing in from surrounding areas. This reduces the weight of air above the reservoir so the mercury level drops to a lower level.