Introduction to Heat Transfer Video Lecture | Heat Transfer - Mechanical Engineering

welcome to a lecture online and our next
topic in thermodynamics is heat transfer
now that's a big topic and what we're
going to do here is talk about some
basic definition basic terminology and
hopefully gain some basic understanding
of what heat transfer is now in nature
there are three main ways in which heat
can be transferred one is called
conduction the other one is called
convection and the third one is called
radiation and all three occur in nature
at all times
now conduction is a method by which the
heat travels along a medium everything
stays in place let's say we have some
hot object and some cold object and some
paths in between a physical path that
doesn't move doesn't change and so what
we expect is that heat would be
traveling from the hot object to the
cold object through that medium so it's
actually taking a road or path on that
medium convection is a means by which
heat is transferred through the movement
of a medium for example we have a hot
object in a room it heats the air up
around it the air will then move expand
and tends to move and the he will then
travel along with the hot air typically
hit the seal and come around and come
down and heat a person on the other side
of the room by having warm air move
towards that person so here the heat
takes a ride on the medium it's the
medium that moves and the heat just
comes along for the ride the third
method doesn't need a medium at all it
doesn't need a path it doesn't need
something that it can go piggyback along
it just radiation is just a means by
which heat moves so one point in space
to another point in space and it doesn't
have to be anything in between now there
is space in between and space is
something but again we think of space as
a vacuum that doesn't have any atoms
within it and so when heat radiates out
from a hot object it goes in all
directions tends to go out at the speed
of light its electromagnetic radiation
and essence that moves out and if you
place two objects together a hot object
and a cold object we will learn later
that the hot object radiates way more
heat and therefore cools down a cold
object will
also radiates out heat and also cooldown
however if it's placed in the presence
of hot objects it will receive the
radiation from the hot object which
tends to increase its temperature and
likewise the hot object will receive
radiation from the cold object which
would tend to increase the temperature
however since the hot object is rating
it out more heat and it's receiving the
net result is that the temperature will
go down for a hot object since the cold
object is receiving more heat and it's
radiating out it will tend to rise in
temperature and again as you will see in
all three methods conduction convection
or radiation heat will be transferred in
such a way that hot objects will tend to
cool down and cold objects tend to heat
up until everything tends to be in
thermal equilibrium so that's usually
the end result or at least the end goal
in nature of heat transfer so we'll talk
about the specifics a little bit more
but for conduction the way he travels
across a conductor or a heat conductor
is the physical motion of the atoms the
vibration will be transmitted molecules
next to it they will begin to vibrate
more and it will be transferred so if
the vibrational mode of the hot object
can be transferred through a path we
then say that that pad is a heat
conductor in convection it's simply that
the air molecules are moving it could
also be water molecules or any kind of
fluid and so as the molecules are being
heated by some hot object they then move
and the heat and transfers along with it
in the case of radiation it comes from
the atom spinning the object vibrating
back and forth since their Associated
electric fields with the vibrating atoms
and molecules those electric fields then
will all slide back and forth which
causes electromagnetic radiation to
expand and and not expand but to radiate
away and so the amount of radiation does
depend upon the temperature and the
hotter it is the more they radiate the
colder is the less they radiate and so
there tends to be a nickel even that's
eventually reached so that's the basics
of heat transfer and in the next several
videos we'll talk a little bit more
about the details of each and how to
calculate the actual amount of heat
being transferred via those three
methods