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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
Q

Simple compressible

system:

A

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)

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26
Q

Process

A

Any change that a system undergoes from one equilibrium state to
another.

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27
Q

Path:

A

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.

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28
Q

Quasistatic or quasi-equilibrium process

A

When a process proceeds in such a
manner that the system remains infinitesimally close to an equilibrium state at
all times.

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29
Q

Process diagrams - common properties that are used

as coordinates

A

temperature T,
pressure P, and volume V (or specific
volume v).

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30
Q

prefix iso-

A

is often used to designate
a process for which a particular property
remains constant.

31
Q

Isothermal process

A

A process during
which the temperature T remains
constant

32
Q

Isobaric process

A

A process during

which the pressure P remains constant

33
Q

Isochoric (or isometric) process

A

A
process during which the specific
volume v remains constant.

34
Q

Cycle:

A

A process during which the initial

and final states are identical.

35
Q

The term steady implies

A

no

change with time.

36
Q

The

opposite of steady is

A

unsteady, or transient

37
Q 
A large number of
engineering devices operate
for long periods of time under
the same conditions, and they
are classified as
A

steady-flow

devices.

38
Q

Steady-flow process:

A

A
process during which a fluid
flows through a control
volume steadily.

39
Q

Steady-flow conditions can be
closely approximated by
devices that are intended for
continuous operation such as

A

turbines, pumps, boilers,
condensers, and heat
exchangers or power plants
or refrigeration systems.

40
Q 
During a steadyflow
process, fluid
properties within
the control
volume may
change with
position but not
with
A

time.

41
Q 
During a steadyflow
process, fluid
properties within
the control
volume may
A

change with
position but not
with time

42
Q

The zeroth law of

thermodynamics

A 
If two
bodies are in thermal
equilibrium with a third
body, they are also in
thermal equilibrium with
each other.
43
Q

By replacing the third
body with a thermometer,
the zeroth law can be
restated as

A 
two bodies are
in thermal equilibrium if
both have the same
temperature reading even
if they are not in contact.
44
Q

All temperature scales are based on

some easily reproducible states such as

A

the freezing and boiling points of water:

the ice point and the steam point.

45
Q

Ice point:

A

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
Q

Steam point

A

A mixture of liquid water
and water vapor (with no air) in
equilibrium at 1 atm pressure (100°C or
212°F).

47
Q

Celsius scale

A

in SI unit system

47
Q

Celsius scale

A

in SI unit system

48
Q

Fahrenheit scale:

A

in English unit

system

49
Q

Thermodynamic temperature scale

A

A
temperature scale that is independent of
the properties of any substance

50
Q

Kelvin scale (SI) Rankine scale (E)

A
51
Q

A temperature scale nearly identical to

the Kelvin scale is the

A

ideal-gas

temperature scale.

52
Q

ideal-gas
temperature scale. The temperatures
on this scale are measured using a

A

constant-volume gas thermometer.

53
Q

A constant-volume gas thermometer would

read -273.15°C at

A

absolute zero pressure

54
Q

The reference temperature in the original Kelvin scale was

A

the ice point,

273.15 K, which is the temperature at which water freezes (or ice melts).

55
Q

The reference point was changed to a much more precisely reproducible
point, the triple point of water - what is it?

A

the state at which all three phases of water

coexist in equilibrium), which is assigned the value 273.16 K.

56
Q

Pressure:

A

A normal force exerted by a

fluid per unit area

57
Q

Absolute pressure:

A

The actual pressure at a given position. It is

measured relative to absolute vacuum (i.e., absolute zero pressure).

58
Q

Gage pressure:

A

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
Q

Vacuum pressures

A

Pressures below atmospheric pressure

60
Q

Pressure in a liquid at

rest increases

A

rest increases
linearly with distance
from the free surface.

61
Q

Pascal’s law:

A

The pressure applied to a
confined fluid increases the pressure
throughout by the same amount.

62
Q

Formel for pascals law

A

P1=P2 -> F1/A1 = F2/A2 -> F2/F1=A2/A1

62
Q

Formel for pascals law

A

P1=P2 -> F1/A1 = F2/A2 -> F2/F1=A2/A1

63
Q

The area ratio A2/A1 is

called the

A

ideal mechanical
advantage of the hydraulic
lift.

64
Q

Manometer

A

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
Q

Bourdon tube

A

Consists of a hollow metal
tube bent like a hook whose end is closed
and connected to a dial indicator needle

66
Q

Pressure transducers

A

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
Q

Strain-gage pressure transducers

A

Work by
having a diaphragm deflect between two
chambers open to the pressure inputs.

68
Q

Piezoelectric transducers

A

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
Q

Atmospheric pressure is measured by a device called a barometer; thus, the
atmospheric pressure is often referred to as the

A

barometric pressure.

70
Q

A frequently used pressure unit is the standard atmosphere, which is defined as

A

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
Q 
The length or the
cross-sectional area of
the tube has no effect
on the height of the
fluid column of a
barometer, provided
A

that the tube diameter
is large enough to
avoid surface tension
(capillary) effects

Termodynamik BD2 (2 decks)

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