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Thermodynamics > Definitions > Flashcards

Definitions Flashcards

(51 cards)

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1
Q

First Law of thermodynamics

A

Conservation of energy
Change in E = (Qin - Qout) - (Wout - Win)

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2
Q

Second Law of thermodynamics

A

quality and quantity of energy
direction of decreasing quality of energy

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3
Q

What is a closed system

A
  • System that always contains the same matter
  • No transfer of mass across boundary
  • Energy can cross the boundary in forms of heat and work
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4
Q

Isolated system

A

A type of closed system
No transfer at all, mass or energy

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5
Q

Control Volume

A

A type of open system
-A given region of space through which mass flows
-Mass and energy can cross boundary

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6
Q

What is an intensive property, list them

A

properties that are independent of size
pressure, temperature, density, specific volume

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7
Q

What is an extensive property, list them

A

Properties that are dependent on the size of the system
mass, volume, energy

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8
Q

What is a state

A

a list of properties

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9
Q

What is a process

A

a transformation from 1 state to another

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10
Q

What is an equilibrium

A
  • isolated system, no interactions
  • state can still change as intensive properties tend toward uniform values
  • when changes cease, it as reached equilibrium state
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11
Q

Density

A

an intensive property
row = mass divide by volume

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12
Q

Specific volume

A

reciprocal of density
intensive property

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13
Q

Pressure

A

force / area

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14
Q

different types of pressure (2 types)

A

absolute pressure
- pressure relative to a vacuum
Gage pressure
- pressure relative to atmosphere

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15
Q

Compare vacuum pressure, atmospheric pressure, absolute pressure, and gage pressure

A

P(vac) = P(atm) - P(abs)
P(gage) = P(abs) - P(atm)

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16
Q

describe pressure

A

also called normal stress
- perpendicular to surface
- P = (sigma)(n) = W/A
- pressure in a fluid only changes in the vertical direction
P(atm)= (row)gh

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17
Q

Buoyant force

A

has magnitude = weight of displaced liquid

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18
Q

Pascal’s law

A

Force applied by a fluid is proportional to the surface area
F1/A1 = F2/A2

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19
Q

What is the sign of work

A

W > 0 if work is done by the system on the surroundings
W < 0 if work is done on the system by the surroundings
Wout - Win

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20
Q

Quasi-equilibrium

A
  • An idealized process
  • close enough to equilibrium
  • only minor changes in P, T
  • ” gives time for the whole system to catch up”
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21
Q

What is a polytropic process

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A

one in which PV^n is constant

22
Q

What is Q, and its sign

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A

amount of heat transfer
- Q > 0, transferred into the system
- Q < 0 transferred out of the system
- Qin - Qout

23
Q

What is an isothermal process

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A

A process in which temperature remains constant, other properties can change
dT = 0

24
Q

What is an Adiabatic Process

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A

A process in which the system does not exchange Q with the surroundings
dQ = 0

25
3 modes of heat transfer
Conduction, Convection, and Radiation
26
What is conduction
heat transfer through direct contact, either two solids or solid and stationary fluid
27
What is convection
Energy transfer between solid surface and gas or liquid rate of convection is governed by newtons law of cooling Qc = hA[Tb - Tf]
28
What is radiation
Heat transfer without medium E & M waves governed by Stefan Boltzman Law
29
Fourier's Law does what
governs conduction Q(dot) = -kA(dT/dx) if temp varies linearly dT/dx = T2-T1/L
30
Power cycle
net energy transferred by work combustion gas
31
Efficiency for power cycles
eta = (Wcyc)/((Qin) in general it is what you want divided by what you put in
32
refrigeration cycle
provides cooling, using energy input by work
33
Coefficient of performance for refrigeration cycle
Q/(Wcyc)
34
Heat Pump Cycle
provides heating using energy input by work
35
Coefficient of performance for heat cycles
(Qout)/(Wcyc)
36
How many independent intensive properties do you need to know about a substance to know everything about it?
2
37
What is latent heat of fusion
Energy absorbed during melting, or energy released during freezing
38
What is latent heat of vaporization
energy absorbed during vaporization, or the energy released during condensation
39
what is the critical point
the point at which saturated liquid and saturated vapor states are identical
40
where can you find the triple point
on the P vs. T graph
41
when are pressure and temperature NOT independent
within two phase regions
42
what is quality
the ratio of mass of vapor present x = (mass of vapor) / (mass of vapor + mass of liquid)
43
what is the subscript for saturated liquid and saturated gas
sat. liquid --> f sat. gas --> g fg --> difference between sat. vapor and sat. liquid
44
how do you fix the state
find out temperature and pressure
45
What is specific heat
the energy required to raise the temperature of unit mass of a substance by 1 degree there are two types specific heat at constant volume Cp specific heat at constant pressure Cv
46
Which one is larger, Cp or Cv
Cp, because Cv has no room to expand and you need more energy to change the volume
47
What happens to Cp and Cv if the substance is incompressible
Cp = Cv = C ONLY FOR SOLIDS AND LIQUIDS
48
List ideal gas equations
Pv=RT P=(ro)RT PV=mRT PV=N(Ru)T
49
ideal gas internal energy can be approximated using what variable
Temperature u(T)
50
Ideal Gas specific enthalpy can be approximated using what variable
Temperature h(T)
51
What is the compressibility factor
the deviation from ideal gas behavior Z = (PV) / (RT)

Thermodynamics (2 decks)

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