engineering electromagnetics 9th edition Chapter 3, Slides of Electrical Engineering

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IDE- 314

Thermodynamics

Lecture 3 Engr. Ebrahem Khalid Electrical Engineering Department

Review

Last Lecture Chapter 2

Today’s Lecture

Chapter 3

• Properties of Pure Substance

Pure Substance Phase Mixture as Pure Substance : A mixture of two or more phases of a pure substance is still a pure substance as long as the chemical composition of all phases is the same.

• A mixture of ice and liquid water, for example, is a pure substance because both phases have the same chemical composition.
• A mixture of liquid air and gaseous air, however, is not a pure substance since the composition of liquid air is different from the composition of gaseous air. 4

Phases of a Pure Substance

Phase of a Pure Substance : A phase is identified as having a distinct molecular arrangement that is homogeneous throughout and separated from the others by easily identifiable boundary surfaces Principal Phases : There are three principal phases ----- Solid, Liquid, and Gas

• Intermolecular forces
• Distances between molecules
• Motion pattern
• However a substance may have several phases within a principal phase, each with a different molecular structure. Carbon, for example, may exist as graphite or diamond in the solid phase.

Phase Change Process

• Let's consider the results of heating liquid water from 20C, 1 atm while keeping the pressure constant. We will follow the constant pressure process

Phase Change Process

Compressed Liquid Under these conditions, water exists in the liquid phase, and it is called a compressed liquid, or a sub cooled liquid. Compressed Liquid

Phase Change Process

• As more heat is added the boiling will start (vaporization)
• The temperature stops rising until the liquid is completely vaporized.
• The only change we will observe is a large increase in the volume.
• And steady decline in the liquid level as a result of more liquid turning to vapor 10 Compressed Liquid Saturated Liquid Liquid-Vapor Mix

Phase Change Process

• As we continue transferring heat, the vaporization process continues until all liquid is vaporized (state 4 ).
• At this point, the entire cylinder is filled with vapor
• Any heat loss from this vapor will cause some of the vapor to condense (phase change from vapor to liquid) 11 Compressed Liquid Saturated Liquid Liquid-Vapor Mix Saturated Vapor

Phase Change Process Saturated liquid – vapor mixture

• A substance at states between 2 and 4 is referred to as a saturated liquid – vapor mixture since the liquid and vapor phases coexist in equilibrium at these states. 13 Compressed Liquid Saturated Liquid Liquid-Vapor Mix

Phase Change Process

• As Water in vapors form at 100 0 C is heated
• The temperature will start increasing
• The water vapors will expands, 14 Compressed Liquid Saturated Liquid Liquid-Vapor Mix Saturated Vapor Superheated Vapor

16 Compressed Liquid Saturated Liquid Liquid-Vapor Mix Saturated Vapor Superheated Vapor

Saturation

Temperature and

Saturation Pressure

The temperature at which water starts boiling

depends on the pressure therefore, if the

pressure is fixed, so is the boiling temperature.

Saturation Temperature

• At a given pressure, the temperature at

which a pure substance changes phase is

called the saturation temperature T sat.

Saturation Pressure

• at a given temperature, the pressure at which

a pure substance changes phase is called the

saturation pressure P sat.

17

Saturation Temperature and

Saturation Pressure

• During a phase-change process, pressure and temperature are obviously dependent properties T sat = f ( P sat). liquid–vapor saturation curve
• A plot of T sat versus P sat, such as the one given for water, is called a liquid–vapor saturation curve.

Latent Heat

• The amount of energy absorbed or released during a phase-change process is called the latent heat. Latent heat of fusion
• The amount of energy absorbed during melting is called the latent heat of fusion and is equivalent to the amount of energy released during freezing. Latent heat of vaporization
• The amount of energy absorbed during vaporization is called the latent heat of vaporization and is equivalent to the energy released during condensation.
• The magnitudes of the latent heats depend on the temperature or pressure at which the phase change occurs. At 1 atm pressure, the latent heat of fusion of water is 333.7 kJ/kg and the latent heat of vaporization is 2256. kJ/kg.