Quality of a substance at saturated conditions

When a substance exists as part liquid and part vapor at saturation conditions, its quality (x) is defined as the ratio of the mass of the vapor to the total mass of both vapor and liquid.

Subcooled Liquid or Compressed Liquid

If the temperature of the liquid is lower than the saturation temperature for the existing pressure,it is called either a subcooled liquid (implying that the temperature is lower than the saturation temperature for the given pressure) or a compressed liquid (implying that the pressure is greater than the saturation pressure for the given temperature).

Moisture

The moisture content of a substance is the opposite of its quality. Moisture (M) is defined as the ratio of the mass of the liquid to the total mass of both liquid and vapor.

Saturated Vapor and Superheated Vapor

If a substance exists entirely as vapor at saturation temperature, it is called saturated vapor.

When the vapor is at a temperature greater than the saturation temperature, it is said to exist as superheated vapor.

Property Diagrams

Property Diagrams: The phases of a substance and the relationships between its properties are most commonly shown on property diagrams. There are six different types of commonly encountered property diagrams. These are: Pressure- Temperature (P-T) diagrams, Pressure-Specific Volume (P-ν) diagrams, Pressure-Enthalpy (P-h) diagrams, Enthalpy-Temperature (h-T) diagrams, Temperature-entropy (T-s) diagrams, and Enthalpy-Entropy (h-s) or Mollier diagrams.

Mollier diagram

The Mollier diagram can be used to determine various properties of a fluid.

Mollier diagram is an h versus s plot. 

Can only be used when quality is greater than 50% and for superheated steam.

Contains a series of constant temperature, constant pressure, constant moisture content, and constant superheat lines.

Triple Point & Critical Point

The point where the three lines(sublimation, fusion and vaporization line) meet is called the triple point. The triple point is the only point at which all three phases can exist in equilibrium. 

The point where the vaporization line ends is called the critical point.

Sublimation Line, Fusion Line & Vaporization Line

The line that separates the solid and vapor phases is called the sublimation line. 

The line that separates the solid and liquid phases is called the fusion line. 

The line that separates the liquid and vapor phases is called the vaporization line.

Saturation Temperature, Saturation Pressure and Vapor Pressure Curve

The term saturation defines a condition in which a mixture of vapor and liquid can exist together at a given temperature and pressure.

The temperature at which vaporization (boiling) starts to occur for a given pressure is called the saturation temperature or boiling point. 

 

The pressure at which vaporization (boiling) starts to occur for a given temperature is called the saturation pressure.

The graphical representation of this relationship between temperature and pressure at saturated conditions is called the vapor pressure curve.

Sublimation, Vaporization, Condensation and Fusion or Melting

Sublimation - change of phase from solid to vapor

Vaporization - change of phase from liquid to vapor

Condensation - change of phase from vapor to liquid

Fusion or melting - change of phase from solid to liquid

Triple point

Triple point - the temperature and pressure at which all three phases can exist in equilibrium .

Critical Point

Critical Point:- The temperature and pressure above which there is no distinction between the liquid and vapor phases.

Second Law of Thermodynamics

It is impossible to construct a device that operates in a cycle and produces no effect other than the removal of heat from a body at one temperature and the absorption of an equal quantity of heat by a body at a higher temperature.

First Law of Thermodynamics

Energy can neither be created nor destroyed, only altered in form.

Throttling Process

A throttling process is defined as a process in which there is no change in enthalpy from state one to state two, h1 =h2 ; no work is done, W = 0; and the process is adiabatic, Q = 0

Polytropic Process

When a gas undergoes a reversible process in which there is heat transfer, the process frequently takes place in such a manner that a plot of the Log P (pressure) vs. Log V (volume) is a straight line. Or stated in equation form PVn

= a constant. This type of process is called a polytropic process.

Isentropic Process

An isentropic process is one in which the entropy of the fluid remains constant. This will be true if the process the system goes through is reversible and adiabatic. An isentropic process can also be called a constant entropy process.

Adiabatic Process

An adiabatic process is one in which there is no heat transfer into or out of the system. The system can be considered to be perfectly insulated.

Irreversible Process

An irreversible process is a process that cannot return both the system and the surroundings to their original conditions.

Reversible Process

A reversible process for a system is defined as a process that, once having taken place, can be reversed, and in so doing leaves no change in either the system or surroundings.