Energy Storage 2 Flashcards
In a liquid piston ES system, ____ is used for “head difference”
Pressurized air
Liquid Piston ES is a type of CAES that is…
adiabatic
In a liquid piston ES design, the pressure ratio between charged and discharged states is ____, so the temperature change state to state is ___
Low, low
Pump/turbines for liquids are ____ efficient than compressor/turbines for air
more
What are the 3 main types of thermal energy storage systems?
sensible, latent, thermochemical
In a latent heat ESS, the heat is generated during
phase change
In a sensible heat ESS, the energy storage is base on the change of
temperature
In thermochemical ES, the energy used is the energy released/absorbed when
there is a chemical reaction (energy stored in the bonds of molecules)
What are some common materials for sensible energy thermal storage
water, rock, brick
A solar hot water heater with a tank is an example of a
sensible heat ESS
The thermocline layer is the
mixing layer of different temperature liquids in a storage tank
The heat capacity of a solid is due to
lattice vibrations
For a thermal energy storage system, you may need to consider change in _________ as well as energ
sublimation is the phase change of
solid to vapor
deposition is the phase change of
vapor to solid
PCM stands for
phase change material
Phase equilibrium ratio is
the ratio of mole fractions of species in 2 phases at equilibrium
supercooling is…
process of lowering temperature of a gas or liquid below it’s freezing point without it becoming a solid
Paraffins and fatty acids are ____ types of PCM that goes between ___ and ___ states
Organic, solid-liquid
Flash point is…
the lowest temp at which its vapors ignite if given an ignition source
Auto Ignition temp is…
The temperature that can cause spontaneous combustion (w/o an ignition source)
For a PCM, supercooling is a
drawback - should be avoided
Solid-solid PCMs release/absorb energy by changing between…
Crystalline/semi-crystalline and amorphous/semi-crystalline states
Oxidation means a…
loss of electrons from a substance
Reduction means ….
gain of electrons by a substance (reduce the overall charge)
Oxidation cannot occur without
reduction
sorption is
adsorption and absorption happening in the same reaction
adsorption is a ____ reaction
exothermic
What are the 3 primary combustible elements in common fuels
carbon, hydrogen, sulfur
The enthalpy of a chemical reaction =
Enthalpy of products - enthalpy of reactants
an endothermic process has an ____ in enthalpy of the system
increase (deltaH_rxn > 0)
Define complete combustion
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
AMU stands for _______ and is also called the ___
atomic mass unit, Dalton
Avogadro’s # =
1 / (1 amu)
Stoichiometric air is defined as
minimum theoretical air required for complete combustion, no free O2 in the products
For combustion calculations, the ratio of N2/O2 in air is taken as
3.76 (molecular ratio), different for mass
The Air-Fuel ratio
Moles of air / moles of fuel (or could be mass based)
What are some reasons combustion may be incomplete
incomplete mixing, insufficient time, too little air…
In _____ mole fraction analysis of a combustion reaction is given for all products except for water
dry product analysis
Combustion air can be modeled as…
an ideal gas
The standard state for enthalpy of formation is
T= 298.15 = 25C; P = 1 atm
Enthalpy of formation is in table
A-25
If enthalpy of formation is <0 then the formation is
exothermic (heat is generated) - bonds are formed
The heating value of a fuel is…
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
Definition of adiabatic flame temperature
The temperature of the products that would be achieved if no heat is lost to surroundings (adiabatic)
The maximum ________ corresponds to complete combustion with the theoretical amount of air
adiabatic flame temp
specific enthalpy of some gases are found in table
A-23
Gibbs function = g =
h - T*s
When does sum of H_product = sum of H_reactants?
At adiabatic flame temperature,
Entropy is a measure of…
Thermal energy per unit temperature unavailable for useful work
At an equilibrium state, ___ is maximized and ___ is at it’s minimum
Entropy, Gibbs function
H=
U+pV
R =
8.314 kJ/kmol K
At which electrode does the reduction reaction take place?
Cathode
What is Faraday’s 1st law of electrolysis
The # of moles of product formed is proportional to the # of moles of electrons that passed through the solution
Reversible voltage is
minimum applied cell potential to start a water splitting reaction (electrolysis)
Which requires less total energy input, electrolysis of steam or liquid water?
steam
1 amp =
Coulomb/s
What is the water gas shift reaction?
CO + H20 <-> CO2 + H2
Unsaturated hydorcarbons have ____ between carbon atoms
more than one bond (double, triple)
A reaction is spontaneous if the Gibbs free energy is ____
negative (chap 12 pg 27)
What are 3 main souced of concentrated CO2 (to use for syn gas production)
Flue gas, geothermal, biogas
Primary type batteries are
Not rechargeable
What is the oldest type of battery
lead-acid
High Temp batteries use ___ as electrolytes
molten salt and liquid metal
The energy efficiency of a battery is the product of
coloumbic efficiency and voltage efficiency
3 types of solar energy collection
Solar electrochemical; solar photochemical; photothermal
What is the water gas shift reaction?
CO + H20 <-> CO2 + H2
