Chapter 1 Flashcards
The science of energy
Thermodynamics
The ability to cause changes
Energy
The name thermodynamics stems from the Greek words…
Therme(heat) and dynamis(power)
Conservation of energy principle
During an interaction, energy can change from one form to another but the total amount of energy remains constant
First law of thermodynamics
Energy cannot be created or destroyed; it can only change forms
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
A macroscopic approach to the study of thermodynamics that does not require a knowledge of the behavior of individual particles
Classical thermodynamics
A microscopic approach, based on the average behavior of large groups of individual particles
Statistical thermodynamics
Any physical quantity can be characterized by ______
Dimensions
The magnitudes assigned to the dimensions are called _____
Units
Primary or fundamental dimensions
Mass (m)
Length (L)
Time (t)
Temperature (T)
Second dimensions or derived dimensions
Expressed in terms of the primary dimensions
Velocity (V)
Energy (E)
Volume (V)
A simple and logical system based on a decimal relationship between the various units
Metric SI system
It has no apparent systematic numerical base, and various units in this system are related to each other rather arbitrarily
English system
Length
Meter (m)
Mass
Kilogram (kg)
Time
Second (s)
Temperature
Kelvin (K)
Electric current
Ampere (A)
Amount of light
Candela (cd)
Amount of matter
Mole (mol)
Specific weight
The weight of a unit volume of a substance
A typical match yields about ____ of energy if completely burned
One Btu or one kJ
Dimensional homogeneity
All equations must be dimensionally homogenous
Unity conversion ratios
Identically equal to 1, unitless
A quantity of matter or a region in space chosen for study
System
The mass or region outside the system
Surroundings
The real or imaginary surface that separates the system from its surroundings
Boundary
The boundary of a system can be
Fixed or movable
Systems may be considered to be
Closed or open
Closed system (control mass)
A fixed amount of mass
No mass can cross its boundary (but energy can)
Open system (control volume)
A properly selected region in space
Usually encloses a device that involves mass flow - compressor, turbine, nozzle
Mass and energy can cross the boundary of a control volume
The boundaries of a control volume. It can involve fixed, moving, real or imaginary boundaries.
Control surface
Any characteristic of a system
Property - intensive or extensive
Intensive properties
Those that are independent of the mass of a system
Temperature, pressure, density
Extensive properties
Those whose values depend on the size - or extent - of the system
Mass, volume
Extensive properties per unit mass
Specific properties
Made up of atoms that are widely spaced in the gas phase
Matter
Viewing substances as a continuous, homogenous matter with no holes
Continuum
The ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4 degrees C)
Specific gravity
The weight of a unit volume of a substance
Specific weight
Mass per unit volume
Density
Volume per unit mass
Specific volume
Thermodynamics deals with _____ states
Equilibrium
A state of balance
Equlibrium
In an equilibrium state…
There are no unbalanced potentials (or driving forces) within the system
If the temperature is the same throughout the entire system
Thermal equilibrium
If there is no change in pressure at any point of the system with time
Mechanical equilibrium
If a system involves two phases and when the mass of each phase reaches an equilibrium level and stays there
Phase equilibrium
If the chemical composition of a system does not change with time, that is, no chemical reactions occur
Chemical equilibrium
The number of properties required to fix the state of a system is given by the ____
State postulate
State postulate
The state of a simple compressible system is completely specified by two independent, intensive properties
If a system involves no electrical, magnetic, gravitational, motion, and surface tension effects
Simple compressible system
Any change that a system undergoes from one equilibrium state to another
Process
The series of states through which a system passes during a process
Path
To describe a process completely
One should specify the initial and final states, as well as the path it follows, and the interactions with the surroundings
When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium states at all times
Quasistatic or quasi-equilibrium process
Often used to designate a process for which a particular property remains constant
Iso-
A process during which the temperature T remains constant
Isothermal process
A process during which the pressure P remains constant
Isobaric process
A process during which the specific volume V remains constant
Isochoric (or isometric) process
A process during which the initial and final states are identical
Cycle
No change with time
Steady
Opposite of steady
Unsteady, transient
A large number of engineering devices operate for long periods of time under the same conditions, and they are classified as
Steady-flow devices
A process during which a fluid flows through a control volume steadily
Steady-flow process
Can be closely approximated by devices that are intended for continuous operation
Steady-flow conditions
Devices that are intended for continuous operation
Turbines, pumps, boilers, condensers, heat exchangers, power plants, refrigeration system
During a steady-flow process, fluid properties within the control volume…
May change with position but not with time
Under steady-flow conditions, the mass and energy contents of a control volume…
Remain constant
The zeroth law of thermodynamics
If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other
By replacing the third body with a thermometer, the zeroth law can be restated as…
Two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact
A mixture of ice and water that is in equilibrium with air saturated with vapor at 1 atm pressure
Ice point
Ice point value
0 degrees C
32 degrees F
A mixture of liquid water and water vapor (with no air) in equilibrium at 1 atm pressure
Steam point
Steam point value
100 degrees C
212 degrees F
Celsius scale
in SI unit system
Fahrenheit scale
In English unit system
A temperature scale that is independent of the properties of any substance
Thermodynamic temperature scale
Kelvin scale
SI
Rankine scale
E
A temperature scale nearly identical to the Kelvin scale is the
Ideal-gas temperature scale
The temperatures on the ideal-gas temperature scale are measured using a
Constant-volume gas thermometer
The reference temperature in the original Kelvin scale was the _____
Ice point, 273.15K
The state at which all three phases of water coexist in equilibrium
Triple point of water, 273.16K
Steam point in ITS-90
99.975 degrees C
Steam point in IPTS-68
100 degrees C
A normal force exerted by a fluid per unit area
Pressure
The actual pressure at a given position. It is measured relative to abosolute vacuum
Absolute pressure
The difference between the absolute pressure and the local atmospheric pressure
Gage pressure
Pressures below atmospheric pressure
Vacuum pressures
The pressure of a fluid at rest
Increases with depth (as a result of added weight)
In a room filled with gas, the variation of pressure with height is
Negligible
Pressure in a liquid at rest ____ with distance from the free surface
Increases linearly
The pressure applied to a confined fluid increases the pressure throughout by the same amount
Pascal’s law
Ideal mechanical advantage of the hydraulic lift
The area ratio A2/A1
Atmospheric pressure is measured by a device called a
Barometer
Atmospheric pressure is often referred to as the
Barometric pressure
Pressure produces by a column of mercury 760mm in height at 0 degrees C under standard gravitational acceleration
Standard atmosphere
Used to measure small and moderate pressure differences
Manometer
Consists of a hollow metal tube bent like a hook whose end is closed and connected to a dial indicator needle
Bourdon tube
Use various techniques to convert the pressure effect to an electrical effects such as a change in voltage, resistance, or capacitance
Pressure transducers - smaller and faster, more sensitive and reliable and precise
Work by having a diaphragm deflect between two chambers open to the pressure inputs
Strain-gage pressure transducers
Also called solid-state pressure transducers, work on the principle that an electric potential is generated in a crystalline substance when it is subjected to mechanical pressure
Piezoelectric transducers
