Thermo Final Exam True / False Flashcards
Kilogram, second, foot, and newton are all examples of SI units.
False
The specific volume is the reciprocal of the density.
True
The value of a temperature expressed using the Rankine scale is always higher than its value using the Fahrenheit temperature scale.
True
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
Volume is an extensive property.
True
The pound force, lbf, is equal to the pound mass, lb.
False
A control volume is a special type of closed system that does not interact in any way with its surroundings.
False
A spring is compressed adiabatically. Its internal energy increases.
True
If a system’s temperature increases, it must have experienced heat transfer.
False
For a power cycle, efficiency is always lower than 100%.
True
For heat pumps, the coefficient of performance y is always greater than or equal to one.
True
For any cycle, the net amounts of energy transfer by heat and work are equal.
True
If a closed system under goes a thermodynamic cycle, there can be no net work or heat transfer.
False
The state principle defines the number of independent properties required to fix the state.
True
Three phases can exist in equilibrium along the line labeled triple line.
True
The dome shaped region composed of the two-phase liquid-vapor states is called the liquid dome.
False
If the p-v-T surface is projected onto the pressure - temperature plane, a property diagram known is known as a phase diagram.
True
A subcooled liquid is the same as compressed liquid.
True
Triple point has the same meaning as critical point on p-T diagram.
False
Quality (x) of vapor can be higher than 1.
False
As pressure increases toward the critical pressure, the values of vf and vg approach each other.
True
Mass flux is the time rate of mass flow per unit area.
True
For steady state operation all properties are unchanging in time.
True
Mass flow rate is the product of density, area, and velocity for 1D flow.
True
As velocity decreases in a diffuser, pressure decreases.
False
Volumetric flow rate is expressed in units of kg/s
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
A mixing chamber is a direct-contact heat exchanger.
True
For a one inlet, one exit control volume at steady state, the mass flow rates at the inlet and exit are equal but the inlet and exit volumetric flow rats may not be equal.
True
Mass flow rate is the time rate of change of mass within the control volume.
True
The mass rate balance is defined as the sum of all inlet mass flow rates minus the sum of all outlet mass flow rates.
True
Flow work is the work done on a flowing stream by a paddle wheel or piston.
False
A process of a closed system that violates the second law of thermodynamics necessarily violates the first law of thermodynamics.
False
The Clausius and Kelvin-Planck statements of the 2nd law are equivalent.
True
A process of a closed system that violates the first law of thermodynamics necessarily violates the second law of thermodynamics.
False
The Kelvin-Planck statement (the analytical form) foresees the positive work done by the system.
False
The maximum thermal efficiency of any power cycle operating between hot and cold thermal reservoirs at 2000 C and 1000 C respectively is 50%.
False
Friction associated with flow of fluids through pipes and around objects is one type of irreversibility.
True
Generally speaking, the Clausius inequality applies to any cycle.
True
The Kelvin scale is the only absolute temperature scale.
False
Every process consistent with the conservation of energy and conservation of mass principles can actually occur in nature.
False
Internally reversible processes do not actually occur but serve as hypothetical limiting cases as internal irreversibilities are reduced further and further.
True
Following the Clausius inequality for a cycle, where some irreversibilities are present, the strength of the inequality is equal to zero.
False
Entropy is an extensive property.
True
Specific entropy is an extensive property.
False
Heat is an intensive property.
False
The change in entropy of a closed system is the same for every process between two specified states.
True
For phase change of water from saturated liquid to saturated vapor at constant pressure in a closed system, (hg - hf) = T(sg - sf)
True
The entropy of a fixed amount of an incompressible substance increases in every process for which temperature increases.
True
A closed system can experience a decrease in entropy only when there is heat transfer from the system to its surroundings during the process.
True
In an adiabatic and internally reversible process of a closed system the entropy remains constant.
True
The entropy of a fixed amount of an ideal gas increases in every isothermal process.
False
The energy of an isolated system must remain constant, but the entropy can only decrease.
False
The entropy change of a closed system during a process can be greater than, equal to, or less than zero.
True
Lowering condenser pressure lowers the average temperature of heat rejection from the Rankine cycle.
True
Renewable sources for power generation include hydropower, biomass, wind, and nuclear.
False
Superheat involves adding energy by heat to steam to bring it to a superheated vapor condition at the turbine inlet.
True
Power plant types that generate electric power include coal-fueled, nuclear-fueled, solar-concentrating, and wind power plants.
True
Electric power generation using biomass requires combustion.
True
Extraction for a vapor power cycle with Wcycle = 4 MW and Qin = 10 MW, the thermal efficiency is 40%.
True
Raising boiler pressure lowers the average temperature at which energy is added by heat transfer to the Rankine cycle.
False
A two-phase liquid-vapor mixture has 0.2kg of saturated water vapor and 0.6 kg of saturated liquid. The quality is 0.25 (25%).
True
For a system at steady state, no property values change with time.
True
Thermal radiation can occur in a vacuum.
True
The only entropy transfers to or from control volumes are those accompanying heat transfer.
False
For closed systems undergoing processes involving internal irreversibilities, both entropy change and entropy production are positive in value.
False
At liquid states, the following approximation is reasonable for many engineering applications: s(T , P) ≃ sg(T)
False
For a vapor power cycle with a turbine that produces 5 MW and a pump that requires 100 kW, the net power produced by the cycle is 5100 kW.
False
Including regeneration in a vapor power cycle tends to increase its thermal efficiency by increasing the average temperature of heat addition.
True
The maximum coefficient of performance of any heat pump cycle operating between cold and hot reservoirs at 40 F and 80 F, respectively is 13.5.
True
Although the exhaust gas temperature of a simple gas turbine is typically well above the ambient temperature, the exhaust gas is normally discarded to the surroundings for operational simplicity.
False
If two reciprocating piston-cylinder engines have the same displacement volume, the one with the lower mean effective pressure will produce the lesser net work and, if the engines run at the same speed, lesser power.
True
In a two-stroke internal combustion engine, the intake, compression, expansion, and exhaust operations are accomplished in two revolutions of crankshaft.
False
The Otto, Diesel, and Dual cycles differ from each other only in the way the heat addition process that replaces combustion in the actual cycle is modeled.
True
For the same pressure rise, a gas turbine compressor requires a much greater work input per unit of mass flow than the pump of a vapor power plant.
True
The thermal efficiency of a power cycle formed by combining a gas turbine power cycle and a vapor power cycle is the sum of the individual thermal efficiencies.
False
Depending on the back pressure imposed, an ideal gas flowing isentropically through a converging nozzle can achieve supersonic flow at its exit.
True
Mach number describes a relation between velocity and pressure.
False
The choice of refrigerant affects the type of compressor used.
True
The desuperheating section of the refrigerant condenser generally introduces external irreversibilities for the refrigeration system.
True
A throttling process is usually modeled as an isentropic process.
False
In a vapor-compression refrigeration system, the net power input is equal to the sum of the compressor power input and turbine power output.
False
The refrigerant flowing through the compressor in a vapor-compression refrigeration system is generally in the superheated vapor phase.
True
The Carnot vapor refrigeration cycle is represented on a T-s diagram as a rectangle.
True
