Midterm 1 Flashcards
What is Heat Transfer?
Thermal energy in transit(movement) due to spacial temperature difference
What Thermal Energy?
Refers to energy if a system or object due to microscopic dynamics in the system
What is Conduction?
The transfer of heat through a solid medium.
Energy is transferred by diffusion
What is Diffusion?
1-The process by which particle collisions transfer energy from more energetic particles (higher temps) to less energetic particles (lower temps)
2-Random molecular motion
What is Convection?
The heat transfer that occurs between a surface and a moving fluid when they are at different temperatures
What is Bulk (microscopic fluid motion)
Occurs when a large number of particles are moving together in a fluid
What is Radiation?
Is energy emitted by matter that is at a non-zero temperature
It occurs without an intervening medium
What is Emissive power?
The rate in which the energy is released per unit area
What is Irradiation?
Radiation incident on a unit area surface
What is Fouriers Law equation and what does each variable mean
qx”=-k dt/dx
qx”= heat flux
dt/dx= temperature gradient
K= thermal conductivity
Under Conduction how does the temperature gradient expand: dt/dx
T2-T1/L
What is the equation for Newtons law of cooling? And what does each variable stand for.
q”=h(ts-t(infinite))
q”= convective heat flux
Ts= temp of surface
T(infinite)= temp of fluid
h= convective heat transfer coefficient
What is the equation for Energy outflow due to emission? And what do the variables represent?
E=εEb = e σTs^4
E=2.718 Emissive power
ε=2.718 surface emissuity
Eb = emissive power at a black body
σ= Stefan- Boltzmann constant = 5.67x10^-8
Ts = surface temp
What is Irradiation?
Rate at which radiant energy is absorbed;
Gabs=ζG
What is the formula for radiation between a small and a larger surface?
q”rad= ε σ (Ts-Tsur^4)
What is the 1st law of thermodynamics?
Energy is neither created or destroyed it is only transformed
What is a closed system?
A region of fixed mass
What’s an open system or control volume?
A region of spaced bounded by a control surface through which mass can pass.
What’s the 1st law for a control volume?
The increase in the amount of energy stored in a control volume must equal the amount of energy that enters the control volume minus the energy that leaves the control volume.
What is ΔEst^tot ?
Energy stored in system
What is the formula for change in mechanical and thermal energy stored in a system over time?
Δest = Ein-Eout+Eg
ΔEst = change in thermal and mechanical energy
Ein= Energy entering CV
Eout= Energy leaving CV
Eg= thermal energy generation
What is the heat equation?
PCp dT/dt dxdydz
