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Fett
25-08-2009, 08:58 AM
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

TRASH101
25-08-2009, 09:39 AM
Absolute zero is the theoretical point at which anything to be defined as being at absolute zero must be absolutely stationary i.e.

entropy=0 pressure=0 temp=0(kelvin)

If the above is true then all forces at subatomic levels must be in stationary equilibrium and has become a new state of matter the einstein bose condensate.

nike123
25-08-2009, 11:05 AM
Hi Fett!

Why you are giving non SI units?
I suppose that all of us should learn SI units to be able to communicate around world without need of unit conversions.
Similar as we all here communicate with English language and that we all benefit from that fact.

TRASH101
25-08-2009, 11:11 AM
hysteresis is a way of looking at an interaction between 2 entities one of which creates a change in the other. For there to be any meaningful hysteresis the interaction should have a start and an end so that a hysteresis loop can be generated.

at least I think thats how it goes:)

TRASH101
25-08-2009, 11:22 AM
Why you are giving non SI units?
I suppose that all of us should learn SI units to be able to communicate around world without need of unit conversions.



These young americans eh..Nike ;)

Got no regard for us old europeans who brought the Metric system to the forefront of the worlds scientific community to enrich the lives of mankind.

Or are you a little grumpy today?:D

nike123
25-08-2009, 12:59 PM
These young americans eh..Nike ;)

Got no regard for us old europeans who brought the Metric system to the forefront of the worlds scientific community to enrich the lives of mankind.

Or are you a little grumpy today?:D

They say I am grumpy all my life!;)

Tesla
25-08-2009, 03:22 PM
Hi Fett
There are Five states of matter that we know of at this time. einstein/bose condensate (absolute zero) confirmed in about 1998, solid, liquid, gas, and plasma. And I'm sure the first law of thermodynamics does not work with some things like nuclear and very very small things. These are the old clasical laws, and we know that most of our fore fathers thought the world was flat only 400 years ago, so we are allowed to make a few mistakes and learn from them. Some interesting reading referance - princilples of refrigeration (roy dossat), the quest for absolute zero (1973 vintage), and something on string theory

Fett
25-08-2009, 09:33 PM
Hi Fett!

Why you are giving non SI units?
I suppose that all of us should learn SI units to be able to communicate around world without need of unit conversions.
Similar as we all here communicate with English language and that we all benefit from that fact.


As Trash101 stated earlier!

I am a young american. There is nothing over here in the HVAC field that uses metric so my bad!

Contactor
25-08-2009, 11:10 PM
Think of heat as a form of energy causing vibrations at a molecular level in any substance. Absolute zero is the temperature
at which all motion stops at a molecular level, however some elements are still in the liquid phase at this temperature........... !

Fett
26-08-2009, 02:10 AM
Think of heat as a form of energy causing vibrations at a molecular level in any substance. Absolute zero is the temperature
at which all motion stops at a molecular level, however some elements are still in the liquid phase at this temperature........... !


What is the actual Fahrenheit temperature for Absolute Zero?

Fett
26-08-2009, 02:10 AM
Hi Fett
There are Five states of matter that we know of at this time. einstein/bose condensate (absolute zero) confirmed in about 1998, solid, liquid, gas, and plasma.


I do not know about plasma, care to indulge?

Tesla
26-08-2009, 05:23 AM
Plasma is highly excited gas found in places like the suns corona, space, lightining, fire and scientific labs. Think about the stuff in a flourescent light bulb, when the gas inside is ionised by current it creates plasma. I think plasma will be the next type/level of refrigeration.
As for sublimation it is pressure dependant I have seen water sublime off the clothes on my washing line. If a substance is below its triple point and the temp increases it will sublime.
If you consider a metal ball with molecules inside it - 1 if we increase the temperature the molecules increase thier speed. 2 If we increase the pressure we increase the amount of molecules inside it. Just a basic anology without getting too technical.
If we evacuated a compressor to about 25" and applied a voltage potential of 250 volts we could draw an arc to a distance of 1' aproximatly.

nike123
26-08-2009, 08:04 AM
what is the actual fahrenheit temperature for absolute zero?
-459.67°f ..............

Peter_1
26-08-2009, 09:59 PM
....
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....
I hope you know what a cal is? ;) Or a J ?

Fett
04-09-2009, 09:23 AM
Here guys check this out, Hope some of you have seen this.

The Quest for Absolute Zero!

http://www.youtube.com/watch?v=y2jSv8PDDwA

Contactor
06-09-2009, 12:11 AM
We don't know anything, there will always be questions, it will be no different in 5000 years. We are amazed by the Egyptians, but they didn't have a freaking clue either...

tbirdtbird
06-09-2009, 12:50 AM
Electrical circuits have resistance to electrical flow and we term that 'resistance'

Magnetic circuits or 'flow' or flux also have resistance and that is termed 'hysteresis'

Fett
10-09-2009, 01:45 AM
Magnetic circuits or 'flow' or flux also have resistance and that is termed 'hysteresis'


ooohhh okay, my brain adjusted