Thermodynamics: Energy Transfer and Analysis

macroscopic forms of energy

those a system processes as a while with respect to some outside reference frame

kinetic and potential

microscopic forms of energy

those related to the molecular structure of a system and the degree of the molecular activity

internal energy (U)

the sum of all the microscopic forms of energy

kinetic energy

the energy a system possesses as a result of its motion relative to some reference frame

potential energy

the energy as system possesses as a result of its elevation in a gravitational field

total energy

sum of all internal, kinetic, and potential energy

mass flow rate of a flowing fluid

what does it mean when a variable has a dot above it

the rate of change of that variable over time (derivative)

ex. w-dot is the work done per unit time

energy flow rate of a fluid

sensible energy

portion of the internal energy of a system associated with the kinetic energies of the molecules

latent energy

the internal energy associated with the phase of a system (solid, liquid, gas)

chemical energy

internal energy associated with chemical bonds

nuclear energy

internal energy associated with the strong bonds within the atom’s nucleus

thermal vs internal energy

static/organized energy

the total energy of a system, can be contained or stored in a system

dynamic/disorganized energy

forms of energy not stored in a system

recognized at the system boundary as they cross it, and they represent the energy gained or lost by a system during a process

energy transfer

energy can cross the boundary of a system in two distinct forms: heat and work

formal sign conventions for energy transfer

positive: heat transfer to a system and work done by a system

negative: heat transfer from a system and work done on a system

energy transfer for an open system

energy can also cross the boundary of a system as it is carried by the flowing mass

organized and disorganized energy conversion

we can completely convert organized energy to disorganized, but cannot completely convert disorganized energy into organized

mechanical energy

the form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device

familiar forms kinetic and potential

the change in rate of mechanical energy of a fluid during incompressible flow (eqn)

mass flow rate * (pressure/density, kinetic energy, potential energy)

the change in mechanical energy for a fluid during incompressible flow per unit mass

pressure/density, kinetic energy, potential energy

rule for pressure

pressure is not a form of energy, but it has the ability to do work

can fluid flow from low to high pressure

yes, as long as the system has a shape and configuration that allows either KE or PE to stay constant and the other to decrease

heat

the form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference

rate of energy transfer depends on the temperature difference

heat transfer per unit mass

q = Q/m (kJ/kg)

amount of heat transfer with constant rate

amount of heat transfer when the rate is changing

adiabatic process

no heat or matter is transferred during a process (Q = 0)

not the same as isothermal, internal temperature can still change

conduction

The transfer of energy from more energetic particles to adjacent less energetic ones due to particle interaction

convection

the transfer of energy between a solid surface and the adjacent moving fluid, involving the combined effects of conduction and fluid motion

radiation

the transfer of energy through electromagnetic waves or photons

work

all energy interaction not caused by a change in temperature

work done per unit mass

w = W/m

heat and work

both are recognized as they cross the boundary of a system (boundary phenomena)

systems process energy, but not heat or work. they are associated with a process not a system

both magnitudes depend on the system’s path, initial, and final point (path functions)