Basics or is it?

[Fett]

Here are some basics which may or may not be important, feel free to chime in!


Refrigeration/AC - This is the transfer of HEAT from a place where it is not needed/wanted to a place where it is unobjectionable(not wanted/needed).

The first Law of Thermodynamics is that HEAT is energy and cannot be destroyed(only moved).

The second Law of Thermodynamics is that HEAT flows from a warmer object or area to a cooler object or area. The greater the temperature difference between that object and or area the greater the transfer of heat.

There are five sources of heat that I am aware of.

Light from a light bulb or the sun etc...

Electricity(the flow of electrons) such as the filament in a light bulb heating up when electrons pass through it(due to resistance).

Magnetism which is the Hysteresis of Iron? I am do not completely understand Hysteresis yet.

Chemical such as the combustion in a vehicles engine.

And Mechanical such as Friction, Compression and Percussion.

There are three ways to move heat that I am aware of.

Conduction is the transfer of heat from a one molecule to another molecule without any movement of those molecules. This is heat transfer through solids such as sticking a cold spoon in a pot of boiling water and you feel the other end of the spoon getting hotter.

Convection is the transfer of heat by a flowing medium which can be air, water, refrigerant etc... Uhhh... I'm sure everyone have a convection oven laying around!

Last but not least is Radiation which is the transfer of HEAT by a "wave-form" energy(a prime example is light from the sun). It can pass through a vacuum, and the density of the object it strikes determines the amount of heat transfer.

I hope everyone knows what a British-Thermal Unit is!
A BTU is the amount of heat that is REQUIRED for raising or lowering one pound of water one degree Fahrenheit.

Example: X Pound of Water times the desired temperature change equals total BTUs.

50 degrees to 150 degrees = 100 degree change.

2 pounds of water times 100 degree change equals 200 BTUs.
2Lbs x 100 = 200btu
A BTU is also known as quantity of heat.

Now this may be confusing...

Specific Heat... this is the amount of heat required to raise or lower the temperature of one pound of a SUBSTANCE(not necessarily water) one degree Fahrenheit and thus specific heat is expressed in BTUs per pound(BTU/Lb).

Here is a prime example:

The specific heat value of ice is .5

0 degree's F to 32 degree's F is a 32 degree change.

1 pound of ice times .5 specific heat value times 32 degree's F equals 16 BTUs.
1Lb x .5 x 32 = 16

So basically if you had one pound of ice it would take 16 BTUs of HEAT to bring that ice from zero degree's F up to 32 degree's F without melting the ice.

Which brings us to the two basic forms of heat...

Sensible heat is the heat measured by a thermometer.

Latent heat which is the heat a substance has to absorb to change the state of that substance without a sensible change. A change of state is a vapor to liquid/liquid to solid and vise versa.

There are a few types of latent heat and they are:

Latent heat of Fusion which is the amount of heat required to change one pound of a solid substance to one pound of a liquid substance and vise versa without a change in sensible temperature.
Latent heat of Fusion is also known as Latent heat of melting and freezing.

Latent heat of Vaporization(also known as Latent heat of Evaporization) is the heat required to change one pound of liquid completely to a vapor(gas) and back again without a sensible change in temperature.

Latent heat of Confusion err I mean Condensation... this is the heat REMOVED from one pound of a vapor substance to change its state to a liquid without a sensible change in temperature.

There is one more and that is called Latend heat of Sublimation and this is the change of state directly from a SOLID to a VAPOR without changing to a liquid first... such as Dry Ice.

It takes 970 BTUs of LATENT heat to change one pound of Liquid Water to Vapor Water or at 212 degree's F. It will take 144 BTUs of Latent Heat to change one pound of ICE to a Liquid at 32 degree's F.

If you take a cup of ice and ofcourse the ice is at 32degrees F. You let this ice melt into a liquid. The liquid will remain at 32 degrees F until all of the ice is melted.

Example: Ice Machine... The Ice Machine has to bring the temperature of all the water circulating before it can make ice. Once the water reaches 32 degrees F then the only thing left is that small amount of latent heat which is 144 BTUs to form ice.

If anyone wants to chime in to add to this, feel free.
Does anyone know about Hysteresis?
Does anyone know what Absolute Zero is?

Cheers!
-Fett