Radiation & Condensation Video Lecture | Heat Transfer - Mechanical Engineering

welcome to electron line and here is an
interesting example related to radiation
and in particular we're going to talk
about condensation now all of us have
experienced when you leave things out at
night that you wake up in the morning
you go to them and they're all wet it'll
be moisture on the top of the car
they'll be moisture on the grass they've
been washed on anything you let you
leave outside and why does that happen
well at night when the Sun Goes Down and
everything is exposed to open space we
get very very little radiation from
space represented by the little black
arrows and a lot of radiation going out
into space as objects cool down and so
what happens is as objects cool down
that means that the ability and of
course not only objects but also the air
so what happens is that we have like air
molecules
they'll be bouncing up against the
surface as the surface cools down
because the radiation causing the heat
escape from the surface the surface
cools down any air molecules hitting
that surface will cool down and as they
cool down as the temperature of the of
the atmosphere cools down above the
surface what happens is that the
relative humidity increases so what that
means is as the temperature is high
let's say at 80 degrees Fahrenheit the
air can hold a fair amount of moisture
but at 40 degrees Fahrenheit let's say
it cools down to 40 degrees Fahrenheit
there can no longer hold that most
moisture and any moisture in the air
that is above what the what the
atmosphere can hold will condense so
whenever we get to what we call the
condensation point of the the atmosphere
water will begin to come out of the
atmosphere and begin to distribute
itself on top of surfaces and so that
has to do with the relative humidity if
it's if it's fairly high and the
temperature the air goes down the
moisture will begin to come out of the
air so how can you prevent that from
happening well in one case let's say and
let me get a different color out let's
say that we had a particularly dry day
and the relative humidity is much lower
so even though the temperature may goes
down to 40 degrees Fahrenheit
condensation will not appear on surfaces
because the temperature is such that the
relative humidity stays below 100% and
we never get to what we call the dew
point so like this is called a
condensation point or the dew point so
we may never reach the dew point another
thing that we can do to prevent
conversations to to occur an object is
to cover them over let's say you put a
shed over the the car in such a way that
then the energy that gets radiated out
into space will hit the shed and then
the shed will begin to radiate energy
back to the car and therefore keeping
the serves the car much warmer well
relatively speaking not as cold I should
say then if it was exposed to open space
and if that happens then the temperature
of the car will not drop down to the dew
point so maybe we can prevent the car
from getting so cold maybe it'll only be
60 degrees Fahrenheit and then we don't
get to the dew point and if you don't
get to dewpoint then no condensation
will collect on top of the surface and
that's how we can relate conversation to
the radiation effect