Thermo Final Exam True / False

Question 1

Kilogram, second, foot, and newton are all examples of SI units.

Answer 1

False

Question 2

The specific volume is the reciprocal of the density.

Answer 2

True

Question 3

The value of a temperature expressed using the Rankine scale is always higher than its value using the Fahrenheit temperature scale.

Answer 3

True

Question 4

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.

Answer 4

True

Question 5

Volume is an extensive property.

Answer 5

True

Question 6

The pound force, lbf, is equal to the pound mass, lb.

Answer 6

False

Question 7

A control volume is a special type of closed system that does not interact in any way with its surroundings.

Answer 7

False

Question 8

A spring is compressed adiabatically. Its internal energy increases.

Answer 8

True

Question 9

If a system’s temperature increases, it must have experienced heat transfer.

Answer 9

False

Question 10

For a power cycle, efficiency is always lower than 100%.

Answer 10

True

Question 11

For heat pumps, the coefficient of performance y is always greater than or equal to one.

Answer 11

True

Question 12

For any cycle, the net amounts of energy transfer by heat and work are equal.

Answer 12

True

Question 13

If a closed system under goes a thermodynamic cycle, there can be no net work or heat transfer.

Answer 13

False

Question 14

The state principle defines the number of independent properties required to fix the state.

Answer 14

True

Question 15

Three phases can exist in equilibrium along the line labeled triple line.

Answer 15

True

Question 16

The dome shaped region composed of the two-phase liquid-vapor states is called the liquid dome.

Answer 16

False

Question 17

If the p-v-T surface is projected onto the pressure - temperature plane, a property diagram known is known as a phase diagram.

Answer 17

True

Question 18

A subcooled liquid is the same as compressed liquid.

Answer 18

True

Question 19

Triple point has the same meaning as critical point on p-T diagram.

Answer 19

False

Question 20

Quality (x) of vapor can be higher than 1.

Answer 20

False

Question 21

As pressure increases toward the critical pressure, the values of vf and vg approach each other.

Answer 21

True

Question 22

Mass flux is the time rate of mass flow per unit area.

Answer 22

True

Question 23

For steady state operation all properties are unchanging in time.

Answer 23

True

Question 24

Mass flow rate is the product of density, area, and velocity for 1D flow.

Answer 24

True

Question 25

As velocity decreases in a diffuser, pressure decreases.

Answer 25

False

Question 26

Volumetric flow rate is expressed in units of kg/s

Answer 26

False

Question 27

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.

Answer 27

True

Question 28

A mixing chamber is a direct-contact heat exchanger.

Answer 28

True

Question 29

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.

Answer 29

True

Question 30

Mass flow rate is the time rate of change of mass within the control volume.

Answer 30

True

Question 31

The mass rate balance is defined as the sum of all inlet mass flow rates minus the sum of all outlet mass flow rates.

Answer 31

True

Question 32

Flow work is the work done on a flowing stream by a paddle wheel or piston.

Answer 32

False

Question 33

A process of a closed system that violates the second law of thermodynamics necessarily violates the first law of thermodynamics.

Answer 33

False

Question 34

The Clausius and Kelvin-Planck statements of the 2nd law are equivalent.

Answer 34

True

Question 35

A process of a closed system that violates the first law of thermodynamics necessarily violates the second law of thermodynamics.

Answer 35

False

Question 36

The Kelvin-Planck statement (the analytical form) foresees the positive work done by the system.

Answer 36

False

Question 37

The maximum thermal efficiency of any power cycle operating between hot and cold thermal reservoirs at 2000 C and 1000 C respectively is 50%.

Answer 37

False

Question 38

Friction associated with flow of fluids through pipes and around objects is one type of irreversibility.

Answer 38

True

Question 39

Generally speaking, the Clausius inequality applies to any cycle.

Answer 39

True

Question 40

The Kelvin scale is the only absolute temperature scale.

Answer 40

False

Question 41

Every process consistent with the conservation of energy and conservation of mass principles can actually occur in nature.

Answer 41

False

Question 42

Internally reversible processes do not actually occur but serve as hypothetical limiting cases as internal irreversibilities are reduced further and further.

Answer 42

True

Question 43

Following the Clausius inequality for a cycle, where some irreversibilities are present, the strength of the inequality is equal to zero.

Answer 43

False

Question 44

Entropy is an extensive property.

Answer 44

True

Question 45

Specific entropy is an extensive property.

Answer 45

False

Question 46

Heat is an intensive property.

Answer 46

False

Question 47

The change in entropy of a closed system is the same for every process between two specified states.

Answer 47

True

Question 48

For phase change of water from saturated liquid to saturated vapor at constant pressure in a closed system, (hg - hf) = T(sg - sf)

Answer 48

True

Question 49

The entropy of a fixed amount of an incompressible substance increases in every process for which temperature increases.

Answer 49

True

Question 50

A closed system can experience a decrease in entropy only when there is heat transfer from the system to its surroundings during the process.

Answer 50

True

Question 51

In an adiabatic and internally reversible process of a closed system the entropy remains constant.

Answer 51

True

Question 52

The entropy of a fixed amount of an ideal gas increases in every isothermal process.

Answer 52

False

Question 53

The energy of an isolated system must remain constant, but the entropy can only decrease.

Answer 53

False

Question 54

The entropy change of a closed system during a process can be greater than, equal to, or less than zero.

Answer 54

True

Question 55

Lowering condenser pressure lowers the average temperature of heat rejection from the Rankine cycle.

Answer 55

True

Question 56

Renewable sources for power generation include hydropower, biomass, wind, and nuclear.

Answer 56

False

Question 57

Superheat involves adding energy by heat to steam to bring it to a superheated vapor condition at the turbine inlet.

Answer 57

True

Question 58

Power plant types that generate electric power include coal-fueled, nuclear-fueled, solar-concentrating, and wind power plants.

Answer 58

True

Question 59

Electric power generation using biomass requires combustion.

Answer 59

True

Question 60

Extraction for a vapor power cycle with Wcycle = 4 MW and Qin = 10 MW, the thermal efficiency is 40%.

Answer 60

True

Question 61

Raising boiler pressure lowers the average temperature at which energy is added by heat transfer to the Rankine cycle.

Answer 61

False

Question 62

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%).

Answer 62

True

Question 63

For a system at steady state, no property values change with time.

Answer 63

True

Question 64

Thermal radiation can occur in a vacuum.

Answer 64

True

Question 65

The only entropy transfers to or from control volumes are those accompanying heat transfer.

Answer 65

False

Question 66

For closed systems undergoing processes involving internal irreversibilities, both entropy change and entropy production are positive in value.

Answer 66

False

Question 67

At liquid states, the following approximation is reasonable for many engineering applications: s(T , P) ≃ sg(T)

Answer 67

False

Question 68

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.

Answer 68

False

Question 69

Including regeneration in a vapor power cycle tends to increase its thermal efficiency by increasing the average temperature of heat addition.

Answer 69

True

Question 70

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.

Answer 70

True

Question 71

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.

Answer 71

False

Question 72

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.

Answer 72

True

Question 73

In a two-stroke internal combustion engine, the intake, compression, expansion, and exhaust operations are accomplished in two revolutions of crankshaft.

Answer 73

False

Question 74

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.

Answer 74

True

Question 75

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.

Answer 75

True

Question 76

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.

Answer 76

False

Question 77

Depending on the back pressure imposed, an ideal gas flowing isentropically through a converging nozzle can achieve supersonic flow at its exit.

Answer 77

True

Question 78

Mach number describes a relation between velocity and pressure.

Answer 78

False

Question 79

The choice of refrigerant affects the type of compressor used.

Answer 79

True

Question 80

The desuperheating section of the refrigerant condenser generally introduces external irreversibilities for the refrigeration system.

Answer 80

True

Question 81

A throttling process is usually modeled as an isentropic process.

Answer 81

False

Question 82

In a vapor-compression refrigeration system, the net power input is equal to the sum of the compressor power input and turbine power output.

Answer 82

False

Question 83

The refrigerant flowing through the compressor in a vapor-compression refrigeration system is generally in the superheated vapor phase.

Answer 83

True

Question 84

The Carnot vapor refrigeration cycle is represented on a T-s diagram as a rectangle.

Answer 84

True