Fluid Mechanics, Thermodynamics, and Heat Transfer Flashcards
Refresh concepts for the FE Mechanical Exam
Front (Question)
Back (Answer)
What is viscosity in fluid mechanics?
Viscosity is a measure of a fluid’s resistance to flow and deformation by shear or tensile stresses.
How does density affect fluid statics?
Density influences the hydrostatic pressure in a fluid, with higher densities resulting in higher pressures at the same depth.
Explain Bernoulli’s equation in fluid dynamics.
Bernoulli’s equation relates the pressure, velocity, and elevation of a fluid in steady flow, indicating energy conservation.
What distinguishes laminar flow from turbulent flow in internal flow?
Laminar flow features smooth and constant fluid motion, while turbulent flow is characterized by chaotic fluid fluctuations.
How do boundary layers affect external flow around objects?
Boundary layers influence drag and heat transfer rates; thick layers increase drag and reduce heat transfer efficiency.
Define Mach number in compressible flow.
The Mach number is the ratio of the fluid velocity to the speed of sound in that medium, important in aerodynamics.
What is isentropic flow?
Isentropic flow is a flow process that is both adiabatic and reversible, meaning no heat exchange and no entropy change.
How do performance curves aid in pump and turbine analysis?
Performance curves graphically represent how pumps or turbines perform at varying conditions of flow rate and pressure.
What are scaling laws in fluid mechanics?
Scaling laws are mathematical relationships used to predict changes in performance of fluid systems like pumps when scaled in size.
Describe the properties of ideal gases in thermodynamics.
Ideal gases are described by the equation PV=nRT, assuming no interactions between molecules and that volume occupied by molecules is negligible.
What is the first law of thermodynamics?
The first law states that energy cannot be created or destroyed, only transferred or changed in form, as in conservation of energy.
Explain the significance of the Carnot cycle in thermodynamics.
The Carnot cycle provides a theoretical maximum efficiency for heat engines, serving as a standard for comparing real engines.
How do vapor compression cycles work in refrigeration?
Vapor compression cycles use a refrigerant, compressing and expanding it to absorb and release heat, effectively cooling an area.
What is the coefficient of performance (COP) in heat pumps?
COP is a measure of a heat pump’s efficiency, calculated as the heat transfer rate divided by the work input.
What role does psychrometrics play in HVAC systems?
Psychrometrics involves the study of moist air properties, crucial for designing and analyzing HVAC systems to control humidity and temperature.
How is thermal radiation calculated in heat transfer?
Thermal radiation is calculated using the Stefan-Boltzmann law, relating the power radiated to the fourth power of the temperature.
What is Fourier’s law of conduction?
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.
How does convection differ from conduction?
Convection involves heat transfer through fluid motion, whereas conduction occurs through direct contact and molecular vibration without bulk movement.
Describe the use of heat exchangers in industry.
Heat exchangers are used to transfer heat between two or more fluids, crucial in power plants, chemical processes, and HVAC systems.
What is the significance of thermal resistance in conduction?
Thermal resistance measures the ability of a material to resist heat flow, used to evaluate and design thermal insulation.
How do convective heat transfer coefficients impact heat transfer?
Higher convective heat transfer coefficients indicate more effective heat transfer from a surface to a fluid or vice versa.
What factors affect the performance of heat exchangers?
Factors include the type of heat exchanger, flow arrangement, fluid properties, and temperature differences.
Explain the role of transient processes in heat transfer.
Transient processes involve time-dependent changes in temperature, important in understanding how quickly systems respond to thermal changes.
What does the lumped capacitance method simplify in heat transfer?
It simplifies the analysis of transient heat transfer by assuming uniform temperature within an object, applicable when heat resistance inside the body is negligible.
How does the Stefan-Boltzmann law relate to radiation?
It states that the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.
What are Newton’s law of cooling applications?
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.
What is surface tension in fluid mechanics?
Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible.
Describe the role of hydrostatic pressure in fluid statics.
Hydrostatic pressure is the pressure exerted by a fluid at equilibrium due to the force of gravity, increasing with depth.
How does the momentum equation apply in fluid mechanics?
The momentum equation relates the sum of external forces to the rate of change of momentum, crucial for analyzing fluid motion.
What distinguishes pipe flow characteristics in internal flow?
Pipe flow characteristics include flow velocity, pressure drop, and laminar or turbulent flow regimes, dependent on the pipe’s diameter and roughness.
Explain the concept of drag in external flow.
Drag is the force exerted by a fluid against the motion of an object through it, affecting the object’s speed and energy consumption.
Define isentropic flow relationships in compressible flow.
Isentropic flow relationships describe how properties like pressure, temperature, and density change in a fluid flow without heat transfer and with entropy constant.
What is the significance of normal shock in compressible flow?
A normal shock involves abrupt changes in flow properties such as velocity and pressure, occurring when a supersonic flow slows to subsonic.
How is efficiency defined in terms of power in fluid systems?
Efficiency in fluid systems measures the ratio of useful power output to total power input, indicating the system’s performance.
What is the importance of system matching on performance curves?
System matching involves aligning equipment characteristics (like pumps) with system requirements to optimize performance and efficiency.
How do similarity laws aid in the scaling of fluid systems?
Similarity laws allow engineers to predict the performance of fluid systems under varying scales by maintaining geometric, kinematic, and dynamic similarity.
What properties of pure substances are crucial in thermodynamics?
Properties such as pressure, temperature, volume, and enthalpy are crucial for analyzing and designing thermodynamic systems.
Explain the second law of thermodynamics.
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.
Describe the process involved in adiabatic operations.
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.
What is the role of compressors in thermodynamic cycles?
Compressors increase the pressure of a gas, which is essential for increasing the temperature and energy available for power cycles.
How do Rankine cycles operate in power generation?
Rankine cycles operate by heating a liquid to a high-pressure vapor in a boiler, then expanding it through a turbine to generate power.
What are the primary objectives of refrigeration cycles?
The primary objectives are to remove heat from a low temperature reservoir and transfer it to a high temperature reservoir, efficiently and reliably.
How are nonreacting mixtures of gases analyzed in thermodynamics?
Nonreacting mixtures of gases are analyzed based on the individual properties of the gases, their ratios, and the laws governing ideal gas mixtures.
What does a psychrometric chart represent?
A psychrometric chart represents the physical and thermal properties of moist air, including temperature, humidity, and enthalpy.
Discuss the importance of HVAC processes in building design.
HVAC processes are crucial for ensuring indoor environmental comfort, energy efficiency, and air quality in building design.
What are the challenges associated with combustion in engines?
Challenges include optimizing fuel efficiency, reducing harmful emissions, and managing the heat produced during combustion.
How does conduction differ in metals and nonmetals?
In metals, conduction is mainly due to free electrons, while in nonmetals, it occurs through lattice vibrations (phonons).
Describe the role of heat exchangers in refrigeration systems.
Heat exchangers transfer heat between the refrigerant and the air or water in refrigeration systems, crucial for the condensation and evaporation processes.
What factors influence convection heat transfer?
Factors include the fluid’s velocity, its properties (like viscosity and thermal conductivity), the surface area, and the temperature difference.
How is radiation heat transfer different from convection?
Radiation heat transfer does not require a medium and involves the transfer of energy by electromagnetic waves, while convection requires a fluid medium.
B. Fluid statics
Category(Do you know it?)
C. Energy, impulse, and momentum
Category(Do you know it?)
D. Internal flow
Category(Do you know it?)
E. External flow
Category(Do you know it?)
F. Compressible flow (e.g., Mach number, isentropic flow relationships, normal shock)
Category(Do you know it?)
G. Power and efficiency
Category(Do you know it?)
H. Performance curves
Category(Do you know it?)
I. Scaling laws for fans, pumps, and compressors
Category(Do you know it?)
A. Properties of ideal gases and pure substances
Category(Do you know it?)
B Energy transfers
Category(Do you know it?)
C. Laws of thermodynamics
Category(Do you know it?)
D. Processes
Category(Do you know it?)
E. Performance of components
Category(Do you know it?)
F. Power cycles
Category(Do you know it?)
G. Refrigeration and heat pump cycles
Category(Do you know it?)
H. Nonreacting mixtures of gases
Category(Do you know it?)
I. Psychrometrics
Category(Do you know it?)
J. Heating, ventilation, and air-conditioning (HVAC) processes
Category(Do you know it?)
K. Combustion and combustion products
Category(Do you know it?)
A. Conduction
Category(Do you know it?)
B. Convection
Category(Do you know it?)
C. Radiation
Category(Do you know it?)
D. Transient processes
Category(Do you know it?)
E. Heat exchangers
Category(Do you know it?)
