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FE EXAM Mechanical Concepts > Fluid Mechanics, Thermodynamics, and Heat Transfer > Flashcards

Fluid Mechanics, Thermodynamics, and Heat Transfer Flashcards

Refresh concepts for the FE Mechanical Exam

1
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Front (Question)

A

Back (Answer)

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2
Q

What is viscosity in fluid mechanics?

A

Viscosity is a measure of a fluid’s resistance to flow and deformation by shear or tensile stresses.

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3
Q

How does density affect fluid statics?

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Density influences the hydrostatic pressure in a fluid, with higher densities resulting in higher pressures at the same depth.

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4
Q

Explain Bernoulli’s equation in fluid dynamics.

A

Bernoulli’s equation relates the pressure, velocity, and elevation of a fluid in steady flow, indicating energy conservation.

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5
Q

What distinguishes laminar flow from turbulent flow in internal flow?

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Laminar flow features smooth and constant fluid motion, while turbulent flow is characterized by chaotic fluid fluctuations.

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6
Q

How do boundary layers affect external flow around objects?

A

Boundary layers influence drag and heat transfer rates; thick layers increase drag and reduce heat transfer efficiency.

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7
Q

Define Mach number in compressible flow.

A

The Mach number is the ratio of the fluid velocity to the speed of sound in that medium, important in aerodynamics.

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8
Q

What is isentropic flow?

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Isentropic flow is a flow process that is both adiabatic and reversible, meaning no heat exchange and no entropy change.

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9
Q

How do performance curves aid in pump and turbine analysis?

A

Performance curves graphically represent how pumps or turbines perform at varying conditions of flow rate and pressure.

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10
Q

What are scaling laws in fluid mechanics?

A

Scaling laws are mathematical relationships used to predict changes in performance of fluid systems like pumps when scaled in size.

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11
Q

Describe the properties of ideal gases in thermodynamics.

A

Ideal gases are described by the equation PV=nRT, assuming no interactions between molecules and that volume occupied by molecules is negligible.

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12
Q

What is the first law of thermodynamics?

A

The first law states that energy cannot be created or destroyed, only transferred or changed in form, as in conservation of energy.

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13
Q

Explain the significance of the Carnot cycle in thermodynamics.

A

The Carnot cycle provides a theoretical maximum efficiency for heat engines, serving as a standard for comparing real engines.

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14
Q

How do vapor compression cycles work in refrigeration?

A

Vapor compression cycles use a refrigerant, compressing and expanding it to absorb and release heat, effectively cooling an area.

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15
Q

What is the coefficient of performance (COP) in heat pumps?

A

COP is a measure of a heat pump’s efficiency, calculated as the heat transfer rate divided by the work input.

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16
Q

What role does psychrometrics play in HVAC systems?

A

Psychrometrics involves the study of moist air properties, crucial for designing and analyzing HVAC systems to control humidity and temperature.

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17
Q

How is thermal radiation calculated in heat transfer?

A

Thermal radiation is calculated using the Stefan-Boltzmann law, relating the power radiated to the fourth power of the temperature.

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18
Q

What is Fourier’s law of conduction?

A

Fourier’s law states that the rate of heat transfer through a material is proportional to the negative gradient in the temperature and the area.

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19
Q

How does convection differ from conduction?

A

Convection involves heat transfer through fluid motion, whereas conduction occurs through direct contact and molecular vibration without bulk movement.

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20
Q

Describe the use of heat exchangers in industry.

A

Heat exchangers are used to transfer heat between two or more fluids, crucial in power plants, chemical processes, and HVAC systems.

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21
Q

What is the significance of thermal resistance in conduction?

A

Thermal resistance measures the ability of a material to resist heat flow, used to evaluate and design thermal insulation.

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22
Q

How do convective heat transfer coefficients impact heat transfer?

A

Higher convective heat transfer coefficients indicate more effective heat transfer from a surface to a fluid or vice versa.

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23
Q

What factors affect the performance of heat exchangers?

A

Factors include the type of heat exchanger, flow arrangement, fluid properties, and temperature differences.

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24
Q

Explain the role of transient processes in heat transfer.

A

Transient processes involve time-dependent changes in temperature, important in understanding how quickly systems respond to thermal changes.

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25
Q

What does the lumped capacitance method simplify in heat transfer?

A

It simplifies the analysis of transient heat transfer by assuming uniform temperature within an object, applicable when heat resistance inside the body is negligible.

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26
Q

How does the Stefan-Boltzmann law relate to radiation?

A

It states that the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.

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27
Q

What are Newton’s law of cooling applications?

A

Newton’s law of cooling is used to model the cooling of objects in an environment, assuming a linear rate of cooling proportional to the temperature difference.

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28
Q

What is surface tension in fluid mechanics?

A

Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible.

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29
Q

Describe the role of hydrostatic pressure in fluid statics.

A

Hydrostatic pressure is the pressure exerted by a fluid at equilibrium due to the force of gravity, increasing with depth.

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30
Q

How does the momentum equation apply in fluid mechanics?

A

The momentum equation relates the sum of external forces to the rate of change of momentum, crucial for analyzing fluid motion.

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31
Q

What distinguishes pipe flow characteristics in internal flow?

A

Pipe flow characteristics include flow velocity, pressure drop, and laminar or turbulent flow regimes, dependent on the pipe’s diameter and roughness.

32
Q

Explain the concept of drag in external flow.

A

Drag is the force exerted by a fluid against the motion of an object through it, affecting the object’s speed and energy consumption.

33
Q

Define isentropic flow relationships in compressible flow.

A

Isentropic flow relationships describe how properties like pressure, temperature, and density change in a fluid flow without heat transfer and with entropy constant.

34
Q

What is the significance of normal shock in compressible flow?

A

A normal shock involves abrupt changes in flow properties such as velocity and pressure, occurring when a supersonic flow slows to subsonic.

35
Q

How is efficiency defined in terms of power in fluid systems?

A

Efficiency in fluid systems measures the ratio of useful power output to total power input, indicating the system’s performance.

36
Q

What is the importance of system matching on performance curves?

A

System matching involves aligning equipment characteristics (like pumps) with system requirements to optimize performance and efficiency.

37
Q

How do similarity laws aid in the scaling of fluid systems?

A

Similarity laws allow engineers to predict the performance of fluid systems under varying scales by maintaining geometric, kinematic, and dynamic similarity.

38
Q

What properties of pure substances are crucial in thermodynamics?

A

Properties such as pressure, temperature, volume, and enthalpy are crucial for analyzing and designing thermodynamic systems.

39
Q

Explain the second law of thermodynamics.

A

The second law states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible.

40
Q

Describe the process involved in adiabatic operations.

A

Adiabatic operations involve processes where no heat is transferred to or from the fluid, often resulting in temperature changes due to work done or expansion.

41
Q

What is the role of compressors in thermodynamic cycles?

A

Compressors increase the pressure of a gas, which is essential for increasing the temperature and energy available for power cycles.

42
Q

How do Rankine cycles operate in power generation?

A

Rankine cycles operate by heating a liquid to a high-pressure vapor in a boiler, then expanding it through a turbine to generate power.

43
Q

What are the primary objectives of refrigeration cycles?

A

The primary objectives are to remove heat from a low temperature reservoir and transfer it to a high temperature reservoir, efficiently and reliably.

44
Q

How are nonreacting mixtures of gases analyzed in thermodynamics?

A

Nonreacting mixtures of gases are analyzed based on the individual properties of the gases, their ratios, and the laws governing ideal gas mixtures.

45
Q

What does a psychrometric chart represent?

A

A psychrometric chart represents the physical and thermal properties of moist air, including temperature, humidity, and enthalpy.

46
Q

Discuss the importance of HVAC processes in building design.

A

HVAC processes are crucial for ensuring indoor environmental comfort, energy efficiency, and air quality in building design.

47
Q

What are the challenges associated with combustion in engines?

A

Challenges include optimizing fuel efficiency, reducing harmful emissions, and managing the heat produced during combustion.

48
Q

How does conduction differ in metals and nonmetals?

A

In metals, conduction is mainly due to free electrons, while in nonmetals, it occurs through lattice vibrations (phonons).

49
Q

Describe the role of heat exchangers in refrigeration systems.

A

Heat exchangers transfer heat between the refrigerant and the air or water in refrigeration systems, crucial for the condensation and evaporation processes.

50
Q

What factors influence convection heat transfer?

A

Factors include the fluid’s velocity, its properties (like viscosity and thermal conductivity), the surface area, and the temperature difference.

51
Q

How is radiation heat transfer different from convection?

A

Radiation heat transfer does not require a medium and involves the transfer of energy by electromagnetic waves, while convection requires a fluid medium.

52
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B. Fluid statics

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53
Q

C. Energy, impulse, and momentum

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54
Q

D. Internal flow

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55
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E. External flow

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56
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F. Compressible flow (e.g., Mach number, isentropic flow relationships, normal shock)

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57
Q

G. Power and efficiency

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58
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H. Performance curves

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59
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I. Scaling laws for fans, pumps, and compressors

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60
Q

A. Properties of ideal gases and pure substances

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61
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B Energy transfers

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62
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C. Laws of thermodynamics

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63
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D. Processes

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64
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E. Performance of components

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65
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F. Power cycles

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66
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G. Refrigeration and heat pump cycles

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67
Q

H. Nonreacting mixtures of gases

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68
Q

I. Psychrometrics

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69
Q

J. Heating, ventilation, and air-conditioning (HVAC) processes

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70
Q

K. Combustion and combustion products

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71
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A. Conduction

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72
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B. Convection

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73
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C. Radiation

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74
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D. Transient processes

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75
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E. Heat exchangers

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FE EXAM Mechanical Concepts (6 decks)

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