Chapter 1 Flashcards
What is heat transfer?
Thermal Energy transit due to spatial temperature difference
What is Conduction?
Heat transfer were the temperature gradient exists in a stationary medium, solid or liquid, aka conduction oven.
What is Convection?
Heat transfer that occurs between a surface and a moving fluid when they are at different temperatures. Aka convection oven.
What is Temperature Gradient?
A temperature gradient is the physical quantity that describes which direction and at what rate the temperature changes most rapidly around a particular location.
What is Thermal Radiation?
Heat transfer between two surfaces at different temperature.
What is the driving force behind conduction?
The driving force behind conduction is atomic and molecular activity. Conduction is the transfer of energy from more energetic to less energetic particles.
Whats is diffusion?
Spreading of something more widely, going to equilibrium all over.
What is heat flux (conduction) and units and symbol?
Rate of heat transfer per unit area and W/m^2 and qx’’.
What is heat rate by conduction and symbol and units?
Heat rate is the heat flux multiplied by the area and qx and watts.
What are the two mechanisms convection is comprised of.
Diffusion (random molecular motion), or by bulk or macroscopic motion of fluid.
What is Sensible energy?
Sensible energy is energy that can be felt like change in temperature.
What is Latent Energy?
Latent energy is related to phase change.
How is energy of radiation transported?
Electromagnetic Waves.
What is surface emissive power? units symbol
Rate at which bounded energy is released. W/m^2 E
What is emissivity? Symbol?
A measure of how efficiently a surface emits energy relative to a blackbody. Epsilon
What is absorptivity? Symbol?
The rate at which radiant energy is absorbed per unit surface area. α
E or EB
Surface emissive power or Surface emissive power of a black body
q’’
heat flux, rate of heat transfer per unit area
G
irradiation-incoming radiation
sigma
stephan boltzman constant
Rt
Thermal Resistance
1st Law Thermo
The first law of thermodynamics states that energy can neither be created nor destroyed; it can changed only from one form to another
2nd Law Thermo
The second law of thermodynamics means hot things always cool unless you do something to stop them.
Two ways energy can cross system boundry in a closed system.
Heat and Work done to or by the system.
Closed System
System that doesn’t allow for transfer of mass in or out of the system.
Control Volume
an imaginary surface enclosing a volume of interest.
Mechanical Energy
sum of kinetic Energy and potential energy
Kinetic Energy equation
1/2*mV^2
potential energy
mgh
Thermal energy consists of
latent and sensible
Ut
Thermal Energy/ unit mass
row v
flow work
q
heat rate transfer W
Heat Engine
any device that operates continuously or cyclically and converts heat to work.
Carnot Efficeincy
High real possible efficiency of a heat motor
Entropy
the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work.
Enthalpy
l
Q
Energy Transfer
the rate at which heat passes through a specified material, W/m^s
Thermal Conductivity
Thermal Conductivity units and symbol
the rate at which heat passes through a specified material, W/m^s and k
Thermal Energy
Movement of atoms and molecules, linked directly to temperature of matter.
Joule Units
W*s
Watt
Joule/Sec
Work
Force*Distance
Fouriers Law
heat flux qx’’=-k*dT/dX
hr meaning and units
Radiation Heat Transfer Coefficient W/m^2*K
h
convection heat transfer coefficient W/m^2*K
What are the units for energy?
Joules
What is a joule? Units?
Energy and Watts*second
What is a watt and units
Power rate of energy transfer and Joules/Sec
Steady State
No change of parameters with respect to time
Driving Force behind convection and conduction
Temperature Difference
Rate Equation for Convection
h A(T final- T surface)
Newtons Law of Cooling
q’‘=h(T surface-T infinity)
Stefan Boltzmann Law and meaning
Eb=Sigma Tsurface^4 Upper limit of emissive power
Gabs equation
G* alpha
alpha
absorptivity
specific heat
amount of heat required to raise 1 kg of material one degree Kelivn. J/kg*K
Specific volume
1/density
