Chapter 2: Energy & energy transfer Flashcards
what can energy cause?
it can cause change and work
what are macroscopic forms of energy?
those a system possesses as a whole with respect to some outside reference frame, such as kinetic and potential energy
what are microscopic forms of energy?
related to the molecular structure of a system and the degree of the molecular activity
what is kinetic energy?
the energy a system possesses as a result of its motion relative to some reference frame
what is potential energy?
the energy that a system possesses as a result of its elevation in a gravitational field
what is internal energy?
Sum of all microscopic forms of energy, it comes from the total kinetic (changes with temperature) and potential energy (changes with state) of molecules which composes the system
Internal = thermal + chemical + nuclear + electric + magnetic
Internal = sensible + latent + chemical + nuclear
what is sensible energy?
portion of internal energy of a system associated with the kinetic energies of the molecules
what is latent energy?
portion of internal energy associated with the phase of a system
what is chemical energy?
portion of internal energy associated with the atomic bonds in a molecule
what is nuclear energy?
portion of internal energy associated with the strong bonds within the nucleus of the atom itself
what is thermal energy?
thermal = sensible + latent
what is a stationary system?
where total energy = total internal energy
since both kinetic and potential energy are equal to zero
what is mechanical energy?
form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device, such as an ideal turbine
what is the mechanical flow energy of a flowing fluid?
pressure
where does total energy occur when in static form?
contained or stored in a system
where does energy interactions occur when in dynamic forms?
at the system boundary
what kind of systems can heat transfer occur in?
closed and open systems
what kind of systems can work occur in?
closed and open systems
what kind of systems can mass transfers occur in?
open systems only
what is heat and when does heat transfer occur?
heat is a form of energy that is transferred between 2 systems or between a system and its surrounding when there is a difference in temperature between them
no temperature difference = no heat transfer
what is conduction?
heat transfer mechanisms that transfers energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interaction between particles (touching)
what is convection?
heat transfer mechanism that transfers energy between a solid surface and the adjacent fluid that is in motion.
Involves the combined effects of conduction and fluid motion: the faster the fluid motion the greater the heat transfer
what is radiation?
heat transfer mechanism that transfers energy due to the emission of electromagnetic waves (or photons)
when is energy recognized as heat transfer?
only when it crosses the system boundary
what is work?
the energy transfer associated with a force acting through a distance.
the energy transfer is not due to temperature differences
the work done is proportional to the force applied and the distance traveled.
what is mechanical work?
work due to the transfer of mechanical energy
work done to raise and/or accelerate a body = change in potential and/or kinetic energy
what are the conditions for mechanical work to occur?
- A force is acting on the boundary of the system
- The boundary must move
both conditions need to be met for work to be done
what are examples of different forms of mechanical work?
- Shaft work: force acting through a moment arm generates a torque, this forced acts through a distance
- Spring work: length of spring changes under influence of a force
- Elastic solid bars work: without permanent deformation, normal stress
- Stretching of a liquid film work: surface tension
- work done to raise or accelerate body = related to potential and kinetic energy
what is electrical work?
non-mechanical form of work where the generalized force is the volt (electric potential) and the generalized displacement is the electrical charge
what is magnetic work?
non-mechanical form of work where the force is the magnetic field strength and the displacement is the total magnetic dipole moment
what is electrical polarization work?
non-mechanical form of work where the force is the electrical field strength and displacement is the polarization of the medium
What kind of functions are heat and work?
path functions, they both are associated with process and their magnitudes depend on the path followed during a process as well as the end states
- they have inexact differentials
what kind of functions are properties?
point functions, associated with state
- exact differentials
difference between energy transfer in a closed vs open system?
In a closed system, only heat transfer and work are included in energy transfer
In an open system, energy transfer also include the flow energy in addition to work and heat
what is the zeroth law of thermodynamics?
If object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then object C is also in thermal equilibrium with object A
what is the first law of thermodynamics?
energy can be neither created nor destroyed during a process, it can only change forms
- total energy remains constant
what is the sign convention for heat transfer to a system and work done on a system?
positive
what is the sign convention for heat transfer from a system and work done by a system?
negative
what does a closed system cycle involve?
only heat transfer and work
total energy = 0, so Q = W
what is energy efficiency?
performance of energy conversion or transfer process
- losses are due to friction or heat
- increased energy efficiency = reduced energy use
what is energy efficiency?
performance of energy conversion or transfer process
- losses are due to friction or heat
- increased energy efficiency = reduced energy use
what is pump and turbine efficiency?
the effectiveness of the conversion process between the mechanical work supplied or extracted and the mechanical energy of the fluid
what is pump and turbine efficiency?
the effectiveness of the conversion process between the mechanical work supplied or extracted and the mechanical energy of the fluid
