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Thermodynamics and propulsion > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

What is a thermodynamic system?

A

a region of space denoted by boundires containing a quantity of matter

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2
Q

Definition of a closed system

A

contains a fixed amount of mass
work and heat can cross boundaries
boundaries are impermeable but may be movable

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3
Q

Definition of an open system

A

mass can flow in and out - boundaries are permeable
work and heat can cross boundaries

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4
Q

Thermodynamics Properties - convenient

A

temperature
pressure
volume
mass

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5
Q

Thermodynamic Properties - Less convenient

A

Specific Volume
Density
Internal Energy
Enthalpy
Entropy

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6
Q

Thermodynamic Properties - Less convenient

A

Specific Volume
Density
Internal Energy
Enthalpy
Entropy

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7
Q

Types of Properties

A

Intensive
Extensive
Specific Properties

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8
Q

Intensive definition

A

does not depend on the mass of the substance in a system

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9
Q

Extensive properties definition

A

depends of the mass of the substance in a system

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10
Q

Specific Properties definition

A

are reduced to the unit mass of a substance to acquire the meaning of intensive properties

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11
Q

Process vs Cycle

A

a process is when it changes from one state to another and a cycle is where the start and end states are identical

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12
Q

Isothermal process

A

constant temperature

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12
Q

Isothermal process

A

constant temperature

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13
Q

Isobaric Process

A

constant pressure

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14
Q

isochoric process

A

constant volume

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15
Q

adiabatic process

A

no heat crosses system boundries

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16
Q

reversible process

A

the ideal case moves between continuous succession of equilibrium states, with no degradation of quality energy

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17
Q

Irreversible process

A

all real processes, heat transfer occurring and cannot be returned, energy quality is degraded

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18
Q

Process diagrams allow us to…

A

summerise whats happening in a process

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19
Q

PV = constant process diagram shape

A

Concave shape

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20
Q

1st law of thermodynamics

A

energy can be transferred, this can primarily accomplished by work and heat transfer

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21
Q

Work

A

is done by a force when the point of force application undergoes a displacement

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22
Q

Conservation of energy

A

when the total energy of an isolated system remains constant

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23
Q

conservation of energy in a closed system

A

Wnet + Qnet = 0

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24
Q

what does positive Wnet mean

A

means that work is done on a system by the surroundings

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25
Q

Power input

A

W = W per cycle x cycle/sec

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26
Q

Internal energy

A

the energy associated with the motion of molecules

27
Q

when there is no work done but heat transfer to surroundings the change of energy is…

A

the change in internal energy

28
Q

thermally insulated system

A

cannot have heat transfer across the boundary but work can take place
adiabatic
changes in thermal energy balance the work

29
Q

thermally isolated system

A

where to heat of work transfer can take place

30
Q

Enthalpy

A

H=U+pv

31
Q

Specific enthalpy

A

h=u+pv

32
Q

Specific Heat capacity

A

the quantity of heat required to raise the temperature of a system by 1 degree

33
Q

Heat Capacity (J/K)

A

C=dQ/dT

34
Q

Specific heat capacity equation (J/KgK)

A

C= dq/dT

35
Q

Specific heat capacity with constant volume

A

cv = dq/dT=dU/dT
dq = du as there is not change in work
cv= (U1-U2) / (T1-T2)

36
Q

Specific Heat Capacity with constant pressure

A

cp = dq/dt = dh/dT
cp = qp/T1-T2

37
Q

heat engine works by

A

receiving heat from a hot reservoir and converts some of the heat into work it also rejects heat to the cold reservoir and work in a cycle

38
Q

what must a heat engine have ( define each )

A

heat source - supplies heat
heat sink - absorbs rejected heat
work output - the use of heat engines
prime mover - the moving parts that deliver work

39
Q

thermal energy reservoirs

A

large bodies of heat that do not change in temperature

40
Q

thermal efficiency

A

n = W/Q

41
Q

thermal efficeincy ( 1- equation )

A

n = 1- Qout/Qin

42
Q

thermal efficeincy ( temperature equation )

A

n = 1-T1/T2

43
Q

Carnot efficiency

A

the max efficiency for a heat engine that operates reversibly between the heat source and heat sink.

44
Q

Carnot for an irreversible heat engine

A

n < ncarnot

45
Q

Carnot for reversible heat engines

A

n = ncarnot

46
Q

Carnot for impossible engines

A

n > ncarnot

47
Q

thermal resistance in heat engines

A

engine hot is a lower temperature than the heat source and engine cold is a higher temperature than the heat sink

48
Q

why is work output sometimes reduced

A

some of the work can be dissipated by heat

49
Q

LOOK AT PV DIAGRAM FOR THE HEAT SINK

A

squashed parallelogram

50
Q

Ordered energy

A

when all atoms have the same energy, they all have the same kinetic energy so move at the same speed and have the same potential energy

51
Q

Disordered energy

A

atoms move randomly and have different amounts of energy

52
Q

High Temperature vs Low temperature how disordered

A

low temp is more disordered

53
Q

Work vs Heat

A

work is ordered and heat is disordered

54
Q

Energy interactions

A

when a hot objects interacts with a cold energy moves randomly between atoms and disperses from the hot to cold

55
Q

Heat sinks output … energy

A

ordered

56
Q

Entropy

A

S=k loge W
k=1,38054x10^-23

57
Q

most disordered = … entropy

A

highest

58
Q

work has … entropy

A

0

59
Q

as heat disperses from hot to cold

A

the entropy increases

60
Q

entropy equation

A

change in S = Q/T

61
Q

entropy in a real process

A

Change in S system + Change in S surroundings > 0

62
Q

entropy in an ideal process

A

Change in S system + Change in S surroundings = 0

63
Q

entropy for any process

A

Change in S system + Change in S surroundings >= 0

64
Q

entropy in hot and cold sources

A

dSh = dQ/Th
dSc = dQ/Tc
dSh<dSc

Thermodynamics and propulsion (1 decks)

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