MEEN 315 Final Review
Which number perpetual motion machine violates the second law of thermodynamics?
PPM 2
two versions of the IGL
PV=nRuT PV=mRT
Which of the following can be assumed to be reversible? burst membrane combustion a piston compressing a gas resistance heater
a piston compressing a gas
Which of the following are intensive properties? a 10m^3 volume a pressure of 90 kPa a mass of 75 kg
a pressure of 90 kPa
Seen<0 for:
all IMPOSSIBLE processes
Sgen>0 for:
all REAL processes
Irreversibilities present during operation of a forced-air, natural gas-fueled furnace include all of the following
chemical reaction fluid friction heat transfer
mechanisms of heat transfer
conduction radiation convection
convective heat transfer involves
conduction and fluid motion
the point that connects the saturated liquid line to the saturated vapor line is called the
critical point
TF in a closed system, containing a simple, compressible substance, is at equilibrium at some T and P, there can only be one phase present
false triple point = 3 phases Tsat / Psat = 2 phases
TF if a system's temperature has increased, it must have experienced heat transfer
false xfer by work or KE/PE or U
TF work and heat are properties
false xfer mechanisms
which of the following would use a control volume? air in a tire filling gas cylinder with He an office chair
filling a gas cylinder with helium
what is the difference between internal energy and enthalpy?
flow work
a manometer reads what type of pressure?
gage pressure
The coefficient of performance of a reversible refrigeration cycle is always __________ the coefficient of performance of an irreversible refrigeration cycle when each operates between the same two thermal reservoirs.
greater than
a system undergoing an adiabatic process
has no thermal energy interactions with its surroundings
For heating a home, does electrical resistance baseboard heating or a heat pump use less electricity?
heat pump
if one property can be varied while the other is held constant, they are:
independent
intensive property
independent of system size, property doesn't change when system is "cut in half"
what key words tell you a system is adiabatic?
insulated no heat transfer isolated thermal equilibrium
which thermodynamic property is the best measure of a molecular activity of a substance
internal energy
a throttling process is ______________
irreversible
What type of pump that would require the LEAST energy input to move fluid?
irreversible carnot
TF the energy of an isolated system can only increase
it cannot change at all
a carnot cycle is of special interest because
it establishes an upper limit of efficiency
what are absolute T scales?
kelvin rankine
what are the primary dimensions?
kg, m, s NOT: J or lbf
______ energy is the energy associated with phase change
latent energy
energy xfer mechanisms for a steady flow system
mass heat work
on what basis is quality calculated?
mass basis volume is not constant in the quality zone
internal energy is equal to
mass times the specific internal energy
what type of work is related to a force acting through a distance and requires the movement of a boundary?
mechanical work
what type of work is occurring in a Carnot cycle?
moving boundary work (PdV)
Is it possible for a heat engine to operate without rejecting any waste heat to a low temperature reservoir?
no
a carnot cycle is...
only theoretical 4 rev processes 2 isothermal processes 2 adiabatic processes
on a T-V diagram, the line under the curve is a line of constant ____________
pressure
A substance that is uniform and invariable in chemical composition is called a
pure substance
a fluid about to condense is called
saturated vapor
for a sub cooled liquid or a mildl compressed liquid, where do we look to find the properties?
saturation tables a liquid is a liquid is a liquid
a windmill is an example of what kinda work
shaft work
what phase is entropy lowest for?
solid
an equation of state is any equation that relates the following properties of a substance
specific volume pressure temperature
Clothes are hung on a clothesline to dry in Wisconsin on a freezing winter day. The clothes dry due to:
sublimation
Steam at 2 kPa is saturated at 17.5C. In what state will the steam be at 40C if the pressure remains the same?
superheated
If the temperature is greater than the liquid-vapor saturation temperature at a given pressure, the state is in the
superheated vapor region
what is the correct definition of quality?
the mass of vapor/total mass
A heat pump is
the same as a refrigerator with a different objective
what is the state postulate?
the state of a simple, compressible system is completely specified by two independent, intensive properties
our attention is focused on what kind of energy in thermo?
total energy
TF Air can be considered to be a pure substance
true
TF a mixing chamber is a direct contact heat exchanger
true
TF for heats pumps, the COP is always greater than or equal to 1
true
TF if a closed system undergoes a process for which the work is negative and the heat transfer is positive, the change in total energy must be positive
true
TF pressure is intensive
true
TF: A rotating flywheel stores energy in the form of kinetic energy.
true
TF: For compressors and pumps, the power in the energy rate balance is negative in value.
true
TF: If a closed system undergoes a process for which the work is negative and the heat transfer is positive, the total energy of the system must increase.
true
TF: In an adiabatic and internally reversible process of a closed system the entropy remains constant.
true
TF: The Kelvin-Planck and Clausius statements of the second law of thermodynamics are equivalent because a violation of one statement implies the violation of the other.
true
TF: The change in entropy of a closed system is the same for every process between two specified end states.
true
TF: The entropy change of a closed system during a process can be greater than, equal to, or less than zero.
true
TF: The entropy of a fixed amount of an incompressible substance increases in every process for which temperature increases.
true
TF: When a substance undergoes a throttling process through a valve, the specific enthalpies of the substance at the valve inlet and valve exit are equal.
true
TF: When analyzing heat exchangers operating at steady state, heat transfer with the surroundings is often significantly smaller than the heat transfer rates within the heat exchanger from one stream to the other. In many analyses, this stray heat transfer with the surroundings is ignored.
true
Given the temperature and specific volume at a state, if the specific volume is greater than the saturated liquid specific volume and less than the saturated vapor specific volume evaluated at the given temperature, the fluid is in the
two phase liquid vapor region
what are some pure substances?
water CO2 vapor/liquid water mixture AIR IS NOT PURE
when is flow through a control volume steady?
when there is no change with time at any position
boundary work is
-PdV -associated with the moving surface of a control system -due to a volume difference
entropy facts:
-limits the direction a process can occur in -its generation degrades process performance -it is a property and can be found in the property tables
For a closed system, entropy ________
-may be produced within the system -may be transferred across its boundary -may remain constant throughout the system
2nd law
-prediction of the direction of a spontaneous process -definition of the Kelvin T scale -definition of entropy -establishment of the conditions for equilibrium
work facts:
-the differential for work is inexact -work is a path function -work is always zero for constant volume process -NOT the area under a P-T diagram
The thermal efficiency of a power cycle can be evaluated as:
1-Qc/Qh
what are the english units of energy?
BTU
Cp and Cv relation for IG
Cp=Cv+R
is it possible to compress an ideal gas isothermally in an adiabatic piston/cylinder device?
NO
can you use the IGL for water?
NO or for sat mix, steam, anything with quality value
TF for a control volume at SS, mass can accumulate in the control volume
false no change in mass with time
a process that violates the 2nd law violates the 1st law
false to work, both must be met
equation for calculating pressure for a manometer
Pm = Patm + pgh
the cross sectional area of a nozzle
decreases along the direction of flow
in a diffuser, the velocity of the fluid _________ and the pressure ___________
decreases, increases
which SSF devices result in a drop in P? which don't?
do: nozzle throttle turbine dont: pump diffuser
TF- If a closed system consisting of a simple compressible substance is at equilibrium, only one phase can be present.
false
TF- the 2nd law states the conservation of entropy
false
TF: A process of a closed system that violates the second law of thermodynamics necessarily violates the first law of thermodynamics.
false
TF: A two-phase liquid-vapor mixture with equal volumes of saturated liquid and saturated vapor has a quality of 0.5.
false
TF: Flow work is the work done on a flowing stream by a paddle wheel or piston.
false
TF: For a control volume at steady state, mass can accumulate within the control volume.
false
TF: For a gas modeled as an ideal gas, cv = cp + R, where R is the gas constant for the gas.
false
TF: For a one-inlet, one-exit control volume at steady state, the volumetric flow rate at the exit equals the volumetric flow rate at the inlet.
false
TF: For a specified inlet state, exit pressure, and mass flow rate, the power input to a compressor operating adiabatically and at steady state is less than what would be required if the compression occurred isentropically
false
TF: If a system's temperature increases, it must have experienced heat transfer.
false
TF: The energy of an isolated system can only increase.
false
TF: When an isolated system undergoes a process, the values of its energy and entropy can only increase or remain the same.
false
TF the pressures in thermo tables are gage pressures
false absolute
TF the volume of a closed system cannot change
false closed system = no change in mass
TF a significant increase in pressure can be achieved by introducing a restriction into a line through which a gas or liquid flows
false decrease in P
