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Energy transfer by heating (Infrared Radiation (EM Electric + magnetic…
Energy transfer
by heating
Conduction
Metals > non-metals
Copper > Steel
Glass > wood
Energy transfer depends
on
thermal conductivity
(through conduction) aka
TC
Greater = faster rate of energy transfer by
conduction
Insulators
Keep warm in winter
Home / Outdoors
Low
thermal conductivity
Reduce energy transfer
:
Lo thermal conductivity
Hi
thickness
of layer
Energy transfer factors:
(through layer of insulate)
Temp
diff across material
Thickness
of material
Thermal conductivity
Infrared Radiation
EM
Electric + magnetic waves
Wavelength increase from
violet - red
IR
:
Type of EM
Wave is longer than light
shorter than microwaves
Part of EM spectrum:
R
adiowaves
M
icrowaves
I
nfrared radiation
V
isible light
U
ltraviolet radiation
X
-ray
G
amma radiation
Sun
emits
all
types,
Earth's atmosphere
blocks
most harmful types of radiation,
Doesn't block infrared, light
Hi temp = Hi IR emit
All bodies(obj) emit, absorb IR
Constant temp
:
Emit IR= Absorb IR
Perfect black body
:
Absorbs
all IR
hit by, no reflect
Good absorb = Good emit
Black body radiation
Radiation
emit
by black body
None do
better
Constant temp = IR emit across
continuous
range
Intensity of radiation highest at certain
wavelength
(depends on
temperature
)
Temp increase =
Intensity
increase
Temp increase =
Shorter wavelength
peak intensity
Shorter wavelength = Greater increase in intensity
Infrared
Radiation (2)
Temperature increase
Absorb IR > Emit IR
Light shiny =
reflect
Dark, matt =
Emit
Light shiny blankets
for warmth (patients)
Warm out = light
Warm body = Dark
Earth temperature factors
Light, IR reflect amount
Light, IR emit amount
Atmosphere
No atmosphere = -180°C night
Water Vapour, Methane, CO2 are greenhouse gases
IR pass atm, warms ground
Ground
re-emits
longer IR
CO2 molecules
re-emit IR back to ground again,
prevent
escape
Specific Heat Capacity
Metal SHC < Concrete SHC
Temp rise Factors:
Amount
Energy
supply
Mass
of substance
What
substance
Water SHC = 4200 J/kg°C
Energy needed to raise temperature of 1 kg of substance by 1°C
:star:
E = mcθ
:star:
Storage heaters
Electricity at night (off-peak)
heat special bricks in heater
Energy transfer from bricks keep room warm (high SHC)
Warm slowly, Cool slowly
Heating & Insulating
Loft insulation
:
E.g. Fibreglass
Reduce thermal conductivity
Many layers = thick insulation
Cavity wall insulation
:
Reduce (RET)
(
Insulation > air
) through walls
Insulation
pumped
into cavity
(Space between 2 layer bricks)
Air trap in
Small pockets
Reduce TC, Convection RET
(No air circulation)
Aluminium foil
Between radiator - wall
Reflects
radiation
Reduce RET by
Radiation
Double-glazed windows
2 glass panes
dry air
between or
vacuum
Thicker glass = lower TC
Dry air, good insulator
Reduce
Conduction
RET
Vacuum reduce
Convect
RET
External walls
Thicker
bricks, lower TC
RET will be lower
to outside
Heating cost, less
Solar Panels
Absorb
Sun IR
generate
Electricity
direct
Heat
water
direct
(Cell panels / Heating panels)
N.hemisphere = face
south
Absorb as much IR possible