The Science Behind It All!!
Natural Convective Heat Transfer
What Is Natural Convective Heat Transfer?
There are Three kinds of heat transfer:
Conductive: This is where one object transfers heat directly through contact with another object.
Radiation: This is when heat is transferred by radiating off of an object.
Convective: This is where heat is carried from one object by a fluid motion in a gas or liquid.
*Convective heat transfer can be
natural or forced.
Forced convection occurs when a fluid flow is induced by an external force.
Natural convection is caused by buoyancy forces due to density differences caused by temperature variations in the fluid.
Forced convection occurs when a fluid flow is induced by an external force.
Natural convection is caused by buoyancy forces due to density differences caused by temperature variations in the fluid.
Here
is one
example of this. This has some similarities to our study. The pot in
the picture is sitting on a discrete heat source, so we could expect
the current flow to be somewhat like the arrows shown in the heating
water. 
Another example of natural
convective heat transfer. Just as the buoyancy forces caused density
differences in the fluid, it does the same in gas or air. Seems kind of intuitive doesn't it?
So, in our case we can expect the natural convective current to behave similarly to be our main source of cooling to our heat source.
We will have to take into consideration all three of the mechanisms of heat transfer.
We will have Radiative, conductive and convective heat transfers involved in some way.
This brings us to the first law of thermodynamics:
Qtotal = Qconv + Qcond + Qrad
nQCond
: We
can measure this with a heat flux gage, or use an
insulating board
nQRad :
We paint the inside of the cube with a black paint to
promote diffuse gray radiant exchange with a
known surface emmissivity.
nQConv :This
is what we are interested in, so our equation can be solved with
Newton's law of cooling:
