Eng Storage 1 Flashcards
Merits of Pumped Hydro ES
mature technology, low running cost, reasonable round trip efficiency, good volume and power, can store for long periods, long life
Cons of pumped hydro ES
geographic restriction, large land use is needed, low energy density, high capex, evaporation losses, environmental concerns
3 types of hydro turbine based on flow
Axial, Radial, Mixed
2 types of hydro turbine based on pressure change
Impulse (no change, ex pelton), Reaction (yes change, ex francis and kaplan)
Friction factor is a function of
Reynolds # and pipe roughness/diameter
Gas turbine power plants are cheaper or more expensive than vapor power plants
cheaper
In air-standard analysis, air behaves…
as an ideal gas
In cold air standard analysis, what is assumed constant
cp wrt temperature
Isentropic processes are also…
adiabatic, but not the other way around
In the brayton cycle, the expansion and compression are treated as
adiabatic
In an ideal brayton cycle, the flow through the energy exchangers is _______ and the flow through compressor/turbine is _____
isobaric; isentropic
Brayton Cycle is for ___; Rankine Cycle is for ____
air(+gas) ; steam
The PV diagram shows _____; the T-s diagram shows _____
Work interactions (int:Vdp); Heat interactions (int:Tds)
Increasing the pressure ratio increases the Brayton cycle ____ and ____ and ____
efficiency, back work ratio, turbine inlet temperature
The biggest source of irreversibility (entropy production) in a gas turbine cycle is
combustion
Name 3 ways of modifying gas cycles
regeneration, multi-stage compression, multi-stage expansion
A regenerator increases ____ by preheating ____
thermal efficiency, air entering the combustor (using the exhaust heat from the turbine)
For a regenerator, the temperature entering the cold side must be ____ than the temperature entering the hot side (exhaust)
less than
SSS’s are … (combined cycle)
synchro self shifting (clutch)
Thrust in a jet engine comes from
Increase in nozzle exit velocity relative to diffuser inlet velocity
Pr in A-22 is
relative pressure
Ideal gas model assumes u and h vary solely with
temperature
dh = cp or cv * dT?
cp
h =
u + pv
Cp =
R+Cv
3 main types of compressed air energy storage
Diabatic, advanced adiabatic, isothermal
k for air =
1.4
Isothermal expansion can deliver electrical energy without…
natural gas combustion for preheating
High efficiency of flywheels is restricted by
storage time - only feasible in short periods
Flywheels can be useful for supplying high ____ specialty needs
instantaneous power
For a flywheel, doubling the mass doubles the force, but doubling the speed…
quadruples the force
Depth of Dischage for a FW is
differnce between max KE (operating at highest speed) and minimum KE (operating at lowest speed)
Liquid Air Energy Storage is also sometimes called
Cryogenic energy storage
Nitrogen liquifies at about…
-196C
For liquid air energy storage, the liquid is stored at ___ pressure
low
The Linde-Hampson cycle is used to
liquify air
The gas in a Linde-Hampson cycle is coolest when it leaves…
the expansion valve
LAES generation scheme without _____ is considered too inefficient to be practical
additional energy input (slide 27)
R134a is an example of an
Organic refrigerant
For generation with LAES, __ and ___ cycles are 2 that could be added to boost net work
Cryogenic Organic Rankine and Cold Brayton
The working fluid in an Organic Rankine cycle has a____
low boiling point
Some advantages to LAES
Low upfront and lifetime costs, long lifetime, can be scales up, uses mature technologies, can be integrated with other industrial processes, not geographically restricted
Disadvantages of LAES
Low round trip efficiency, safety risks, needs large scale to be efficient and cost effective
Electricity, energy transfer, gasoline, etc are examples of
Secondary forms of energy
Working Fluid for pumped thermal ES is often
Air or Argon
Desrues and Howe are examples of
Cycles for Pumped Thermal energy storage
A transcritical rankine cycle uses what as the working fluid
CO2
In a transcritical power cycle, the working fluid is kept as a ___ during compression and as a ___ or as supercritical during expansion
liquid; vapor
At the critical point on the phase diagram, the substance..
is indistinguishable from a liquid and a gas
A saturation state is a state where…
a phase change begins or ends
Curves bordering the vapor dome on a pvt chart are called
saturated vapor lines
saturation temperature designates
the temp at which a phase change occurs at a specified pressure
