ME 305 Test 1
When a system undergoes a process, the terms work and heat do not refer to what is being transferred. ____________ is transferred when work and/or heat occurs.
Energy
True or False? A vessel holding 0.5 kg of oxygen (O2) contains 16 lb of O2.
False
True or false? an open feedwater heater is a special type of a counterflow heat exchanger.
False- An open feedwater heater is type of direct contact heat exchanger.
Energy transfers by heat
Induced only as a result of a temperature difference between the system and its surroundings and occur only in the direction of decreasing temperature
The change in total energy of a closed system other than changes in kinetic and potential energies are accounted for by the change in ______________ energy.
Internal Energy
Is heat a property?
NO!
When a system is isolated
its mass remains constant, its temperature may change and its pressure may change
The time rate of mass flow per unit area is called:
mass flux
What are some factors that make heat transfer (Qcv) =0?
-The outer surface of the control volume is well insulated -the outer surface area is too small for there to be effective heat transfer -The temperature difference between the control volume and its surroundings is so small that the heat transfer can be ignored. -The gas or liquid passes through the control volume so quickly that there is not enough time for significant heat transfer to occur.
What is a compressor?
A device in which work is done on a gas to increase the pressure and/or elevation.
What is a nozzle?
A flow passage of varying cross-sectional area in which the velocity of a gas or liquid increases in the direction of flow.
A subcooled liquid is alternatively referred to as a __________ liquid.
Compressed
When work is done, ______________ is transferred or stored.
Energy
Are the kinetic and gravitational potential energies of a closed system intensive or extensive properties?
Extensive
True or False? Cooling of computer components achieved by a fan-induced air flow falls within the realm of radiation heat transfer.
False
True or False? If a closed system undergoes a thermodynamic cycle, there can be no net work or heat transfer.
False
True or False? Systems can be studied only from a macroscopic point of view.
False
True or False? The value of the temperature expressed using the Celsius temperature scale is always higher than its value expressed using the Kelvin scale.
False
True or False? For an electric motor as a closed system, the rate of energy transfer in by electric current must equal the rate of power out through the rotating shaft plus the rate of energy transfer by heat from the motor to its surroundings.
False-
True or False? A control volume is a special type of closed system that does not interact in any way with its surroundings.
False- A control volume is given region of space through which mass flows. The description given is for an isolated system, which is a special case of the closed system.
True or False? If a system's temperature increases, it must have experienced heat transfer.
False- Energy transfer by work can also cause a temperature rise.
True or False? The composition of a closed system cannot change.
False- For a closed system there can be no transfer of mass across its boundary.
True or False? The total energy of a closed system can change as a result of energy transfer across the system boundary by heat and work and energy transfer accompanying mass flow across the boundary.
False- For a closed system, no mass crosses the boundary so there can be no energy transfer associated with mass flow.
True or False? For gases modeled as ideal gases, the ratio (Cp/Cv) must be greater than one.
False- K is >1 and Cp>Cv
True or false? A significant increase in pressure can be achieved by introducing a restriction into a line through which a gas or liquid flows.
False- a significant decrease in pressure can be achieved by introducing such a restriction
True or False? In thermodynamics, a system can gain or lose "heat."
False- a system can only gain or lose "energy"
True or False? For a control volume at steady state, mass can accumulate within the control volume.
False- all properties are unchanging in time therefore the total amount present at any instant remains constant
True or False? As velocity decreases in a diffuser, pressure decreases.
False- as velocity decreases in a diffuser, pressure increases
True or False- A two-phase liquid-vapor mixture with equal volumes of saturated liquid and saturated vapor has a quality of 0.5.
False- at saturated liquid states, x=0 and saturated vapor states, x=1.0
True or False? The rate of heat transfer at steady state by conduction through a plane wall is greater if the wall is fabricated from plywood than from concrete, assuming the same wall area and temperature gradient.
False- if they are the same thickness and temperature, then there is the same rate of heat transfer
True or False? Where mass crosses the boundary of a control volume, the accompanying energy transfer is accounted for by the internal energy of the mass only.
False- it is also necessary to account for kinetic and gravitational potential energies and flow work
True or False? One nanosecond equals 10^9 seconds.
False- it is equal to 10^-9
True or False? Mass is an intensive property.
False- mass is an extensive property
True or False? Air can always be regarded as a pure substance.
False- pure substances depend on the composition
True or False? 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- specific volumes and volumetric flow rates are different
True or false? Steam diverted from a supply line through a throttling calorimeter operating at steady state and then exhausted to the atmosphere is modeled as undergoing a throttling process. Consequently, there is no change in specific internal energy of the steam passing through the calorimeter.
False- the specific enthalpy does not change, but the specific internal energy does
True or False? Kilogram, second, foot, and newton are all examples of SI units.
False- they are English base unit
For gases modeled as ideal gases, the ratio K must be _________.
Greater than 1
Is work a property?
No!
What direction is the net energy transfer by work for a power cycle: in or out?
Out
A process during which the departure from thermodynamic equilibrium is at most infinitesimal is called ________________ process.
Quasiequilibrium (or quasistatic) process
True or False? A mixing chamber is a direct-contact heat exchanger.
True
True or False? A rotating flywheel stores energy in the form of kinetic energy.
True
True or False? A two-phase liquid-vapor mixture has 0.2 kg of saturated water vapor and 0.6 kg of saturated liquid. The quality is 0.25 (25%).
True
True or False? As pressure approaches zero (or specific volume approaches infinity) in a gas at fixed temperature, molecular interactions become less frequent and intermolecular forces are minimal.
True
True or False? As pressure increases toward the critical pressure, the values of and approach each other.
True
True or False? At steady state, conservation of mass asserts the total rate at which mass enters the control volume equals the total rate at which mass exits.
True
True or False? For any cycle, the net amounts of energy transfer by heat and work are equal.
True
True or False? For every control volume at steady state, the total of the entering rates of mass flow equals the total of the exiting rates of mass flow.
True
True or False? For pure, simple, compressible systems, temperature and specific volume can be regarded as independent intensive properties.
True
True or False? Gage pressure indicates the difference between the absolute pressure of a system and the absolute pressure of the atmosphere existing outside the measuring device.
True
True or False? If a closed system consisting of water vapor undergoes a process at constant specific volume from a specified initial state to a specified final pressure, the final state is fixed.
True
True or False? If a closed system operates at steady state, the net rate of energy transfer in by heat equals the net rate of energy transfer out by work.
True
True or False? 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
True or False? If a system is isolated from its surroundings and no changes occur in its observable properties, the system was in equilibrium at the moment it was isolated.
True
True or False? If the only force acting on a body is the force of gravity, the sum of the kinetic and gravitational potential energies remains constant, but energy can be converted from one form to another.
True
True or False? In an axial flow turbine such as those in vapor power or gas turbine power plants, superheated steam or gas enters the turbine and expands to a lower pressure as power is generated.
True
True or False? In local surroundings at standard atmospheric pressure, a gage will indicate a pressure of 0.2 atm for a refrigerant whose absolute pressure is 1.2 atm.
True
True or False? In principle, expansion or compression work can be evaluated using (integral pdV) for both actual and quasiequilibrium expansion processes.
True
True or False? Power is related mathematically to the amount of energy transfer by work by integrating over time.
True
True or False? Pressure is an intensive property.
True
True or False? Specific volume, the volume per unit of mass, is an intensive property whereas volume and mass are extensive properties.
True
True or False? Temperature is the property that is the same for each of two systems when they are in thermal equilibrium.
True
True or False? The choice of system, boundary, and surroundings is arbitrary ans depends on the convenience it allows in the subsequent analysis.
True
True or False? The first steps in a thermodynamic analysis are defining the system and identifying relevant interactions with the surroundings.
True
True or False? The following assumptions apply for a substance modeled as an incompressible substance: The specific volume (and density) is constant and the specific internal energy is a function of temperature only.
True
True or False? The pressure unit psia indicates an absolute pressure expressed in pounds force per square inch.
True
True or False? The pressures listed in thermodynamic tables are absolute pressures, NOT gage pressures.
True
True or False? The properties of velocity and elevation are not included in the specification of an intensive thermodynamic state.
True
True or False? The unit of 1 watt for electric power is equal to 1 volt times 1 ampere.
True
True or False? The value of a temperature expressed using the Rankine scale is always higher than its value expressed using the Fahrenheit temperature scale.
True
True or False? The value of compressibility factor (Z) varies with pressure and temperature.
True
True or False? Thermal radiation can occur in vacuum.
True
True or False? Using the ideal gas for air (Tables A-22 and A-22E) to determine changes in internal energy or enthalpy allows for variation of specific heat and is equivalent to integration of the respective specific heat functions.
True
True or False? When an ideal gas undergoes a polytropic process with n= 1, the gas temperature remains constant.
True
True or False? 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
True or false? For one-dimensional flow, mass flow rate is the product of density, area, and velocity.
True
How many phases does a system of liquid water and water vapor contain? What about a system of liquid water and ice (or slush)?
Two phases
Yes or no? Can the specific heat (Cp) be evaluated for substances that do not follow the ideal gas model?
Yes
Yes or no? Does p and u fix the state of a superheated vapor?
Yes
The control volume is a system that
allows a transfer of matter across its boundary
For a refrigeration cycle operating between two thermal reservoirs, the coefficient of performance is defined as the ratio of the energy input to the cycle be heat transfer from the ____________ body divided by the net work into the system to accomplish this effect.
cold
The mode of energy transfer that can take place within solids, liquids, or gases as a result of the transfer of energy from more energetic particles to adjacent particles that are less energetic is commonly referred to as ___________ heat transfer.
conduction
What is the difference between heat transfer and work transfer?
difference in temperature (heat transfer needs a temperature change)
The specific enthalpy of the mass entering or exiting a control volume accounts for the internal energy transfer accompanying the mass crossing the boundary and the _____________.
flow work
Energy Transfer (W) into a system is
negative
heat transfer (Q) from a system is
negative
In general, the component of the velocity _____________ to dA in the direction of flow is used to calculate the mass flow rate.
normal
Steady flow devices that result in a drop in working fluid pressure from inlet to exit are-
nozzle, turbine, throttling device
Energy transfer (W) from a system is
positive
Heat transfer (Q) into a system is
positive
What are some examples of compressor types?
reciprocating, axial flow, centrifugal, and Roots type
A system is said to be at ______________________ if none of its properties changes with time
steady state
The ideal gas model includes the ideal gas equation of state to relate pressure specific volume and temperature, and the fact that the specific internal energy and specific enthalpy each depend only on ___________.
temperature
What are some examples of intensive properties?
temperature, pressure, specific volume, specific internal energy, and specific enthalpy
When a gas in a rigid container interacts with a hot plate, what happens to the energy?
the Energy of the gas is increases even though no work is done
What are some examples of phase change?
vaporization, melting, and sublimation
The mass flow rate of a flow modeled as one-dimensional flow depends upon which of the following quantities at a particular flow boundary? Select all that apply
velocity of working fluid, density of working fluid, and cross-sectional area through which flow passes
A generalized form of the equation of state for gases that can be derived from the methods of statistical mechanics is called the ________ equation of state.
virial
The energy of simple compressible systems can be changed by heat transfer and by work associated with __________.
volume change
