Physics 14: Heat and Heat Transfer Methods Flashcards
Heat
spontaneous transfer of energy due to a temp difference
Kilocalorie (kcal)
most common unit of heat; energy needed to change the temp of 1.00kg of water by 1.00 degree Celsius
Mechanical Equivalent of Heat
the work needed to produce the same effects as heat transfer; 1.000kcal = 4186 J
Specific heat
c; depends on the material and phase; amount of heat necessary to change the temperature of 1.00kg of mass by 1.00 degree Celsius; unit = J/(kg degrees Celsius)
Latent heat coefficients
Lf & Lv; in phase changes, energy enters or leaves a system without causing a temp change in the system, so in effect, the energy is hidden; a physical constant equal to the amount of heat transferred for every 1 kg of a substance during the change in phase of the substance
Sublimation
transition from solid to vapor phase
Heat of sublimation (Ls)
energy required to change 1.00kg of a substance from the solid phase to the vapor phase
Conduction
heat transfer through stationary matter by physical contact; ex heat transferred between the electric burner of a stove and the bottom of a pan
Convection
heat transfer by the macroscopic movement of a fluid; this type of transfer takes place in a forced-air furnace and in weather systems; driven by a large-scale flow of matter
Radiation
heat transfer that occurs when microwaves, infrared radiation, visible light, or another form of electromagnetic radiation is emitted or absorbed; ex warming of the earth by the sun, thermal radiation from the human body
Rate of Conductive Heat Transfer
Q/t = [kA (T2 - T1)]/d; = rate of heat transfer from 1 material to another
k
thermal conductivity of the material
R factor
the ratio d/k; large for a good insulator; rate of conductive heat transfer is inversely proportional to R; most commonly quoted for household insulation, refrigerators, etc.
Stefan-Boltzmann Law of Radiation
rate of heat transfer by emitted radiation; Q/t = sigma e AT^4
Emissivity (e)
measure of how well an object radiates
