Thermodynamics Chapters 1-3

Primary (fundamental) Dimensions

• mass

• length

• time

• temperature

Secondary (derived) Dimensions

• velocity

• energy

• volume

System

a region in space chosen for study or a quantity of matter

Boundary

Real or imaginary surface separating the system from the surrounding

Surrounding

the mass or region outside of the system

Closed System

• Has a fixed amount of mass

• No mass crosses the boundary

  • Energy CAN cross the boundary

Isolated System

• Has a fixed amount of mass AND energy

• No mass crosses the boundary

• No energy crosses the boundary

Open System (control volume)

• Encloses a device that involves mass flow

  • e.g., compressor, turbine, nozzle

• Can include real, imaginary, fixed, or moving boundaries

Control Surface

the boundaries of a control volume

Property

• Any characteristic of a system (e.g., P, T, m)

• Two types

  • Intensive

  • Extensive

    • Specific

Intensive Properties

• properties independent of mass

  • T

  • P

  • ρ

Extensive Properties

• properties dependent on mass or related to system size

  • m

  • V

• specific properties are a subsection of these

Specific Properties

• Extensive properties per unit mass

  • specific volume: v=V/m

  • specific total energy: e=E/m

Thermal Equilibrium

When the temperature is the same throughout the system

Mechanical Equilibrium

When there is no change in pressure at any point of the system with time

Phase Equilibrium

When the system has 2 phases and when the mass of each phase reaches an equilibrium level and stays there

Chemical Equilibrium

When chemical composition does not change with time

State Postulate

The state of a simple, compressible system is specified by two independent, intensive properties

Process

Any change the system goes from one phase to another

Path

A series of states the system passes through during the process

Quasi-Equilibrium (quasi-static) Process

When a process occurs in a way that the system remains infinitesimally close to an equilibrium state at all times

Isothermal Process

A process where temperature remains constant

Isobaric Process

A process where pressure remains constant

Isochoric (isometric) Process

A process where specific volume (v) remains constant

Cycle

A process where the system returns to the initial state it began the process with at the end

Steady

No change in time

Unsteady or Transient

When there is a change in time

Uniform

No change with location over a specific region

Steady-flow Process

A process where a fluid flows through a control volume steadily

• these conditions can be considered for turbines, pumps, and boilers

Zeroth Law of Thermodynamics

If two boundaries are in thermal equilibrium with a third body, they are both in thermal equilibrium as well

• two bodies are in thermal equilibrium if both have the same temperature even if they are not in contact

First Law of Thermodynamics

The conservation of energy principle

• energy is a thermodynamic property

Second Law of Thermodynamics

Energy has quality as well as quantity

Absolute Pressure (P_abs)

The actual pressure at a given position

Gage Pressure (P_gage)

The difference between the absolute pressure and the local atmospheric pressure

• P_{gage =} P_abs - P_atm

Vacuum Pressure (P_vac)

The pressure below atmospheric pressure

• P_{vac =} P_atm - P_abs

Barometer

Device that measures atmospheric pressure

Manometer

Uses a glass/plastic U-tube filled with fluid to measure pressure differences according to fluid column height

Total Energy (E)

The sum of all types of energy (potential, kinetic, and internal)

Total Energy Per Unit Mass (e)

e=E/m

Internal Energy

The sum of all microscopic (related to molecular structure of an atom) forms of energy

Kinetic Energy

Energy related to a system’s motion

Potential Energy

Energy of a system due to the elevation in a gravitational field

Mass Flow Rate

The amount of mass flowing through a cross section per unit time

Internal Energy

There are 3 types:

• Sensible energy

• Latent energy

  • Nuclear energy

Sensible Energy

The internal energy of a system related to a molecule’s kinetic energy

Latent Energy

Internal energy associated with a system’s phase

Nuclear Energy

Internal energy associated with strong bonds within the nucleus of atoms

Mechanical Energy

A form of energy that can be converted to mechanical work completely and ideally with an ideal mechanical device

Heat (Q)

A form of energy that is transferred between two systems because of a temperature difference

Adiabatic Process

A process where NO HEAT TRANSFER occurs

This means

• the system is well insulated

• NO pressure difference between the system & surrounding

Conduction

Energy transfer from more energetic particles of a substance to the adjacent less energetic ones

Convection

Energy transfer between the solid surface & adjacent fluid in motion

Radiation

Energy transfer due to the emission of electromagnetic waves

Work

The energy transfer associated with a force acting through a distance

• if the energy crossing the closed system boundary is not heat, it MUST be work

Power

Work done per unit time (kJ/s or kW)

Energy Transfer by Work

Heat and work are both vectors (have magnitude and direction)

• Positive Sign: Heat transfer TO a system and work done BY a system

• Negative Sign: Heat transfer FROM a system and work done ON a system

Electric Work

Electrons crossing the system boundary to do the electrical work on a system

Mechanical Forms Work

Two Requirements

• There must be a force acting on a boundary

  • the boundary must move

Energy Balance

The net change in the system’s total energy is equal to the difference between total energy entering the system and the total energy leaving the system during the process

Efficiency

Indicates how well the energy conversion/transfer is achieved

• When efficiency < 100%, the conversion is less than perfect/there is some losses that have occurred during the conversion

Pure Substance

A substance with a fixed chemical composition

• includes the mixture of two or more phases of the same substance

• does NOT include the mixture of liquid and gaseous air

Homogenous Substance

A substance with a mixture of various chemical elements

Compressed (subcooled) Liquid

A liquid that is not about to vaporize

Saturated liquid

a liquid that is about to vaporize

Saturated vapor

vapor that is about to condense

Superheated vapor

vapor that is not about to condense

Saturation Temperature (T_sat)

the temperature at which a pure substance changes phases

Saturation Pressure (P_sat)

the pressure at which a pure substance changes phases

Latent Heat

the amount of energy absorbed or released during a phase change

Latent Heat of Fusion

The amount of energy released during freezing

Latent Heat of Vaporization

The amount of energy released during condensation

Critical Point

The point at which saturated liquid and saturated vapor states are identical

Critical Temperature (T_crit)

The temperature at which a substance reaches its critical point

Critical Pressure (P_crit)

The pressure at which a substance reaches its critical point

Critical Specific Volume (v_crit)

The specific volume at which a substance reaches its critical point

Enthalpy

the parameter used in power generation and refrigeration

Enthalpy of Vaporization (latent heat of vaporization)

the amount of energy needed by a unit of saturated liquid at a given P and T

Quality (x)

The ratio of the vapor mass to the total mixture’s mass

Characteristics of a saturated vapor

• higher specific volume (v > v_g at a given P or T)

• higher internal energies (u > u_g at a given P or T)

• higher enthalpies (h > h_g at a given P or T)

• higher temperature (T > T_sat at a given P)

• lower pressures (P < P_sat at a given T)

Characteristics of a compressed liquid

• lower specific volume (v < v_g at a given P or T)

• lower internal energies (u < u_g at a given P or T)

• lower enthalpies (h < h_g at a given P or T)

• lower temperature (T < T_sat at a given P)

• higher pressures (P > P_sat at a given T)

Equation of State

any equation related to the P, T, and v of a substance

Ideal-Gas Relation

The simplest and best-known equation of state

Compressibility Factor (Z)

Used to account for the deviation in ideal gas behavior at a given T and P

Principle of Corresponding States

Z factor for all gasses in approximately the same at the same P_R and T_R