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Thermo > Energy Storage 2 > Flashcards

Energy Storage 2 Flashcards

1
Q

In a liquid piston ES system, ____ is used for “head difference”

A

Pressurized air

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2
Q

Liquid Piston ES is a type of CAES that is…

A

adiabatic

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3
Q

In a liquid piston ES design, the pressure ratio between charged and discharged states is ____, so the temperature change state to state is ___

A

Low, low

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4
Q

Pump/turbines for liquids are ____ efficient than compressor/turbines for air

A

more

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5
Q

What are the 3 main types of thermal energy storage systems?

A

sensible, latent, thermochemical

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6
Q

In a latent heat ESS, the heat is generated during

A

phase change

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7
Q

In a sensible heat ESS, the energy storage is base on the change of

A

temperature

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8
Q

In thermochemical ES, the energy used is the energy released/absorbed when

A

there is a chemical reaction (energy stored in the bonds of molecules)

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9
Q

What are some common materials for sensible energy thermal storage

A

water, rock, brick

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10
Q

A solar hot water heater with a tank is an example of a

A

sensible heat ESS

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11
Q

The thermocline layer is the

A

mixing layer of different temperature liquids in a storage tank

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12
Q

The heat capacity of a solid is due to

A

lattice vibrations

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13
Q

For a thermal energy storage system, you may need to consider change in _________ as well as energ

A
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14
Q

sublimation is the phase change of

A

solid to vapor

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15
Q

deposition is the phase change of

A

vapor to solid

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16
Q

PCM stands for

A

phase change material

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17
Q

Phase equilibrium ratio is

A

the ratio of mole fractions of species in 2 phases at equilibrium

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18
Q

supercooling is…

A

process of lowering temperature of a gas or liquid below it’s freezing point without it becoming a solid

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19
Q

Paraffins and fatty acids are ____ types of PCM that goes between ___ and ___ states

A

Organic, solid-liquid

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20
Q

Flash point is…

A

the lowest temp at which its vapors ignite if given an ignition source

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21
Q

Auto Ignition temp is…

A

The temperature that can cause spontaneous combustion (w/o an ignition source)

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22
Q

For a PCM, supercooling is a

A

drawback - should be avoided

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23
Q

Solid-solid PCMs release/absorb energy by changing between…

A

Crystalline/semi-crystalline and amorphous/semi-crystalline states

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24
Q

Oxidation means a…

A

loss of electrons from a substance

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25
Q

Reduction means ….

A

gain of electrons by a substance (reduce the overall charge)

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26
Q

Oxidation cannot occur without

A

reduction

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27
Q

sorption is

A

adsorption and absorption happening in the same reaction

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28
Q

adsorption is a ____ reaction

A

exothermic

29
Q

What are the 3 primary combustible elements in common fuels

A

carbon, hydrogen, sulfur

30
Q

The enthalpy of a chemical reaction =

A

Enthalpy of products - enthalpy of reactants

31
Q

an endothermic process has an ____ in enthalpy of the system

A

increase (deltaH_rxn > 0)

32
Q

Define complete combustion

A

All C in fuel is burned to CO2; all H is burned to water; all sulfur is burned to SO2; all other combustible elements are fully oxidized

33
Q

AMU stands for _______ and is also called the ___

A

atomic mass unit, Dalton

34
Q

Avogadro’s # =

A

1 / (1 amu)

35
Q

Stoichiometric air is defined as

A

minimum theoretical air required for complete combustion, no free O2 in the products

36
Q

For combustion calculations, the ratio of N2/O2 in air is taken as

A

3.76 (molecular ratio), different for mass

37
Q

The Air-Fuel ratio

A

Moles of air / moles of fuel (or could be mass based)

38
Q

What are some reasons combustion may be incomplete

A

incomplete mixing, insufficient time, too little air…

39
Q

In _____ mole fraction analysis of a combustion reaction is given for all products except for water

A

dry product analysis

40
Q

Combustion air can be modeled as…

A

an ideal gas

41
Q

The standard state for enthalpy of formation is

A

T= 298.15 = 25C; P = 1 atm

42
Q

Enthalpy of formation is in table

A

A-25

43
Q

If enthalpy of formation is <0 then the formation is

A

exothermic (heat is generated) - bonds are formed

44
Q

The heating value of a fuel is…

A

the difference between H_prod and H_react, when the fuel burns completely with air, and products and reactants are at the same T and P

45
Q

Definition of adiabatic flame temperature

A

The temperature of the products that would be achieved if no heat is lost to surroundings (adiabatic)

46
Q

The maximum ________ corresponds to complete combustion with the theoretical amount of air

A

adiabatic flame temp

47
Q

specific enthalpy of some gases are found in table

A

A-23

48
Q

Gibbs function = g =

A

h - T*s

49
Q

When does sum of H_product = sum of H_reactants?

A

At adiabatic flame temperature,

50
Q

Entropy is a measure of…

A

Thermal energy per unit temperature unavailable for useful work

51
Q

At an equilibrium state, ___ is maximized and ___ is at it’s minimum

A

Entropy, Gibbs function

52
Q

H=

A

U+pV

53
Q

R =

A

8.314 kJ/kmol K

54
Q

At which electrode does the reduction reaction take place?

A

Cathode

55
Q

What is Faraday’s 1st law of electrolysis

A

The # of moles of product formed is proportional to the # of moles of electrons that passed through the solution

56
Q

Reversible voltage is

A

minimum applied cell potential to start a water splitting reaction (electrolysis)

57
Q

Which requires less total energy input, electrolysis of steam or liquid water?

A

steam

58
Q

1 amp =

A

Coulomb/s

59
Q

What is the water gas shift reaction?

A

CO + H20 <-> CO2 + H2

60
Q

Unsaturated hydorcarbons have ____ between carbon atoms

A

more than one bond (double, triple)

61
Q

A reaction is spontaneous if the Gibbs free energy is ____

A

negative (chap 12 pg 27)

62
Q

What are 3 main souced of concentrated CO2 (to use for syn gas production)

A

Flue gas, geothermal, biogas

63
Q

Primary type batteries are

A

Not rechargeable

64
Q

What is the oldest type of battery

A

lead-acid

65
Q

High Temp batteries use ___ as electrolytes

A

molten salt and liquid metal

66
Q

The energy efficiency of a battery is the product of

A

coloumbic efficiency and voltage efficiency

67
Q

3 types of solar energy collection

A

Solar electrochemical; solar photochemical; photothermal

68
Q

What is the water gas shift reaction?

A

CO + H20 <-> CO2 + H2

Thermo (4 decks)

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