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Termodynamik BD2 > Kap 2 - Lektion 2 > Flashcards

Kap 2 - Lektion 2 Flashcards

1
Q

Thermal-fluid sciences

A 
The physical sciences
that deal with energy and
the transfer, transport,
and conversion of energy.
• Thermal-fluid sciences
are studied under the
subcategories of
ü thermodynamics
ü heat transfer
ü fluid mechanics
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2
Q

System

A

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

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3
Q

Surroundings

A

The mass or region outside the system

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4
Q

Boundary

A

The real or imaginary surface that separates the system from
its surroundings.
• The boundary of a system can be fixed or movable.
• Systems may be considered to be closed or open.

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5
Q

Closed system (Control mass):

A

A fixed amount of mass, and no mass

can cross its boundary

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6
Q

Open system (control volume):

A

A properly
selected region in space.
• It usually encloses a device that involves mass
flow such as a compressor, turbine, or nozzle.
• Both mass and energy can cross the boundary of
a control volume.

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7
Q

Control surface

A

The boundaries of a control

volume. It can be real or imaginary.

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8
Q

Property

A 
Any characteristic of a
system.
• Some familiar properties are
pressure P, temperature T, volume
V, and mass m.
• Properties are considered to be
either intensive or extensive.
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9
Q

Intensive properties

A

Those that
are independent of the mass of a
system, such as temperature,
pressure, and density.

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10
Q

Extensive properties

A

Those
whose values depend on the size—
or extent—of the system.

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11
Q

Specific properties

A

Extensive

properties per unit mass.

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12
Q

Formler for specific properties

A

V=V/m

e=E/m

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13
Q

Continuum

A

Matter is made up of atoms that are
widely spaced in the gas phase. Yet it is
very convenient to disregard the atomic
nature of a substance and view it as a
continuous, homogeneous matter
- The continuum idealization allows us to
treat properties as point functions and to
assume the properties vary continually
in space with no jump discontinuities.
• This idealization is valid as long as the
size of the system we deal with is large
relative to the space between the
molecules.
• This is the case in practically all
problems.

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14
Q

Formel density

A

p=m/V (kg/m3)

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15
Q

Formel specifik volume

A

v= V/m =1/p

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16
Q

Formel og definition for specific gravity

A 
The ratio
of the density of a
substance to the density of
some standard substance
at a specified temperature
(usually water at 4°C).

SG= p/pH2O

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17
Q

Formel og definition for specific weight

A

The weight of a unit volume
of a substance.

ys= pg (N/m3)

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18
Q

Density og specific volume forklaring

A 
Density is
mass per unit
volume;
specific volume
is volume per
unit mass.
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19
Q

Equilibrium

A

A state of balance.
• In an equilibrium state there are no
unbalanced potentials (or driving forces)
within the system.

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20
Q

Thermal equilibrium:

A

If the temperature

is the same throughout the entire system

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21
Q

Mechanical equilibrium

A

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

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22
Q

Phase equilibrium

A

If a system involves
two phases and when the mass of each
phase reaches an equilibrium level and
stays there.

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23
Q

Chemical equilibrium:

A

If the chemical
composition of a system does not change
with time, that is, no chemical reactions
occur.

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24
Q

The State Postulate

A 
The number of properties
required to fix the state of a
system is given by the state
postulate:
üThe state of a simple
compressible system is
completely specified by
two independent,
intensive properties.
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25
Simple compressible | system:
If a system involves no electrical, magnetic, gravitational, motion, and surface tension effects. The state of nitrogen is fixed by two independent, intensive properties. (T og v)
26
Process
Any change that a system undergoes from one equilibrium state to another.
27
Path:
The series of states through which a system passes during a process. 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.
28
Quasistatic or quasi-equilibrium process
When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times.
29
Process diagrams - common properties that are used | as coordinates
temperature T, pressure P, and volume V (or specific volume v).
30
prefix iso-
is often used to designate a process for which a particular property remains constant.
31
Isothermal process
A process during which the temperature T remains constant
32
Isobaric process
A process during | which the pressure P remains constant
33
Isochoric (or isometric) process
A process during which the specific volume v remains constant.
34
Cycle:
A process during which the initial | and final states are identical.
35
The term steady implies
no | change with time.
36
The | opposite of steady is
unsteady, or transient
37
``` A large number of engineering devices operate for long periods of time under the same conditions, and they are classified as ```
steady-flow | devices.
38
Steady-flow process:
A process during which a fluid flows through a control volume steadily.
39
Steady-flow conditions can be closely approximated by devices that are intended for continuous operation such as
turbines, pumps, boilers, condensers, and heat exchangers or power plants or refrigeration systems.
40
``` During a steadyflow process, fluid properties within the control volume may change with position but not with ```
time.
41
``` During a steadyflow process, fluid properties within the control volume may ```
change with position but not with time
42
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. ```
43
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. ```
44
All temperature scales are based on | some easily reproducible states such as
the freezing and boiling points of water: | the ice point and the steam point.
45
Ice point:
A mixture of ice and water that is in equilibrium with air saturated with vapor at 1 atm pressure (0°C or 32°F).
46
Steam point
A mixture of liquid water and water vapor (with no air) in equilibrium at 1 atm pressure (100°C or 212°F).
47
Celsius scale
in SI unit system
47
Celsius scale
in SI unit system
48
Fahrenheit scale:
in English unit | system
49
Thermodynamic temperature scale
A temperature scale that is independent of the properties of any substance
50
Kelvin scale (SI) Rankine scale (E)
51
A temperature scale nearly identical to | the Kelvin scale is the
ideal-gas | temperature scale.
52
ideal-gas temperature scale. The temperatures on this scale are measured using a
constant-volume gas thermometer.
53
A constant-volume gas thermometer would | read -273.15°C at
absolute zero pressure
54
The reference temperature in the original Kelvin scale was
the ice point, | 273.15 K, which is the temperature at which water freezes (or ice melts).
55
The reference point was changed to a much more precisely reproducible point, the triple point of water - what is it?
the state at which all three phases of water | coexist in equilibrium), which is assigned the value 273.16 K.
56
Pressure:
A normal force exerted by a | fluid per unit area
57
Absolute pressure:
The actual pressure at a given position. It is | measured relative to absolute vacuum (i.e., absolute zero pressure).
58
Gage pressure:
The difference between the absolute pressure and the local atmospheric pressure. Most pressure-measuring devices are calibrated to read zero in the atmosphere, and so they indicate gage pressure.
59
Vacuum pressures
Pressures below atmospheric pressure
60
Pressure in a liquid at | rest increases
rest increases linearly with distance from the free surface.
61
Pascal’s law:
The pressure applied to a confined fluid increases the pressure throughout by the same amount.
62
Formel for pascals law
P1=P2 -> F1/A1 = F2/A2 -> F2/F1=A2/A1
62
Formel for pascals law
P1=P2 -> F1/A1 = F2/A2 -> F2/F1=A2/A1
63
The area ratio A2/A1 is | called the
ideal mechanical advantage of the hydraulic lift.
64
Manometer
It is commonly used to measure small and moderate pressure differences. A manometer contains one or more fluids such as mercury, water, alcohol, or oil.
65
Bourdon tube
Consists of a hollow metal tube bent like a hook whose end is closed and connected to a dial indicator needle
66
Pressure transducers
Use various techniques to convert the pressure effect to an electrical effect such as a change in voltage, resistance, or capacitance. • Pressure transducers are smaller and faster, and they can be more sensitive, reliable, and precise than their mechanical counterparts.
67
Strain-gage pressure transducers
Work by having a diaphragm deflect between two chambers open to the pressure inputs.
68
Piezoelectric transducers
Also called solidstate pressure transducers, work on the principle that an electric potential is generated in a crystalline substance when it is subjected to mechanical pressure.
69
Atmospheric pressure is measured by a device called a barometer; thus, the atmospheric pressure is often referred to as the
barometric pressure.
70
A frequently used pressure unit is the standard atmosphere, which is defined as
the pressure produced by a column of mercury 760 mm in height at 0°C (rHg = 13,595 kg/m3) under standard gravitational acceleration (g = 9.807 m/s2).
71
``` The length or the cross-sectional area of the tube has no effect on the height of the fluid column of a barometer, provided ```
that the tube diameter is large enough to avoid surface tension (capillary) effects

Termodynamik BD2 (2 decks)

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