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Refrigeration Terms - I need help

3K views 16 replies 10 participants last post by  ModelAFan 
#1 · (Edited)
I'd like to learn more about refrigeration, especially the terms. I want to learn what "superheat" and "subcooling" means. I'd also like to learn how technicians figure superheat and subcooling. Please help and any help is appreciated.

(Also, I don't want to work on my own equipment. I'm just interested in learning refrigeration.)
 
#13 ·
ChantryOntario said:
Ok, here's the semi-blind leading the blind.:whistling2:

The way I see it, and I'm sure I'll be corrected if I'm wrong, is.....

Mechanical refrigeration as we know it today is largely possible because of the principle stated in Boyle's law.

As the pressure on a liquid increases, it's boiling point increases.

You can't boil water at 212 degrees if it's under pressure. You can superheat water to 500 degrees if it's under enough pressure in a pipe or containment vessel, and it still won't boil, because there's nowhere for it to expand into gas or vapors. If you did that, the water would technically be superheated 288 degrees, or it's heated 288 degrees past it's normal boiling point. The same applies to r-22 or any refrigerant. Refrigerants have vastly lower boiling points than water, which makes them suitable for absorbing more heat under less pressure, then releasing it in good amounts by simply lowering the pressure outside of the area to be cooled..

If we can get a refrigerant to absorb a lot more heat that it normally would, by keeping it in a pressurized system, then we can transfer that superheated refrigerant to another area, lessen the pressure on it, say by allowing it to expand through a txv, and it will boil into gas, and release it's heat, or a lot of the heat anyway.

Remember that boiling, or turning into vapor and gas, releases heat from whatever's boiling. That allows us to release the heat from your fridge interior into another area, say your kitchen, by compressing the refrigerant enough so that it absorbs heat from the interior of the fridge, putting the refrigerant in a superheated condition,then allowing it to boil and release its heat outside the fridge, like from the coils on the back of your fridge. The txv or whatever valve is used on your fridge is the way to control the boiling/expansion of the superheated refrigerant coming from the inside of your fridge.

Air conditioning uses the same principle, but collects the heat in your room, superheating the refrigerant because its in a pressurized line, then moving the refrigerant outside your room and allowing it to naturally expand and release its heat outside.
Boiling absorbs heat, and superheat applies to gas/vapor.

OP, if you really want to learn, you should look into a basic refrigeration course. Or, if you're interested in mechanical systems altogether, take a first level instrumentation course which will give you a solid foundation of the principles behind mechanical systems.
 
#15 ·
If you really want to learn about refrigeration go to the library and get a book/textbook "Fundamentals of Refrigeration". You also need to understand basic thermodynamics and psychrometric properties of air. Also need to know some of the basic gas laws like Boyles and Charles laws. Put that together and you get an idea what the Pros went thru.
 
#3 · (Edited)
So, here is what basically happens:

At the evaporator coil, the high-pressure liquid (refrigerant) picks up heat then turns into a low-pressure vapor. Then, it is pumped through an accumulator (if the unit has one) and the filter drier by the compressor. Then it is pumped through the condensing coil, where the heat is dispersed, then the vapor turns into a liquid and returns to the evaporator coil via the suction line. The TXV (thermal expansion valve) allows a certain amount of refrigerant into the evaporator coil.

But I always thought that the suction line (the big line) carried the liquid back to the evaporator coil. But then why is the smaller line called the "liquid line?" Also, how does the TXV work? I think that it senses the temperature of the (liquid line?) and when the temperature of the (liquid line?) increases, it increases the flow of refrigerant (allowing more refrigerant into the evaporator coil.)

Sorry, I'm new at this, and I want to learn as much about refrigeration as I can. But, I'm thinking I'm starting to learn something here! :thumbup: But, I still don't understand subcooling.

I think I know what superheat is. It says that it is the amount of heat added to the refrigerant in order to turn it from a liquid to a vapor at the evaporator?
 
#6 ·
Superheat is the increase in temperature of the vapor above the saturation temperature based on its pressure. Subcooling is the decrease in temperature of the liquid below the saturation temperature based on its pressure. Vaopr in the big line, liquid in the small line... makes sense if you think of mass flow rates and density.

You should just google this stuff and spend some time reading up on it... then come back with practical questions.
 
#11 ·
Just one simple principle will explain refrigeration work:

Heat always goes to cold. It is a basic physics law and the basis of the fundamental cooling and heating systems everywhere.

How it happens is for another chapter.

But yes, get some schooling and read a lot if you want to learn the trade.
 
#12 · (Edited)
Ok, here's the semi-blind leading the blind.:whistling2:

The way I see it, and I'm sure I'll be corrected if I'm wrong, is.....

Mechanical refrigeration as we know it today is largely possible because of the principle stated in Boyle's law.

As the pressure on a liquid increases, it's boiling point increases.

You can't boil water at 212 degrees if it's under pressure. You can superheat water to 500 degrees if it's under enough pressure in a pipe or containment vessel, and it still won't boil, because there's nowhere for it to expand into gas or vapors. If you did that, the water would technically be superheated 288 degrees, or it's heated 288 degrees past it's normal boiling point. The same applies to r-22 or any refrigerant. Refrigerants have vastly lower boiling points than water, which makes them suitable for absorbing more heat under less pressure, then releasing it in good amounts by simply lowering the pressure outside of the area to be cooled..

If we can get a refrigerant to absorb a lot more heat that it normally would, by keeping it in a pressurized system, then we can transfer that superheated refrigerant to another area, lessen the pressure on it, say by allowing it to expand through a txv, and it will boil into gas, and release it's heat, or a lot of the heat anyway.

Remember that boiling, or turning into vapor and gas, releases heat from whatever's boiling. That allows us to release the heat from your fridge interior into another area, say your kitchen, by compressing the refrigerant enough so that it absorbs heat from the interior of the fridge, putting the refrigerant in a superheated condition,then allowing it to boil and release its heat outside the fridge, like from the coils on the back of your fridge. The txv or whatever valve is used on your fridge is the way to control the boiling/expansion of the superheated refrigerant coming from the inside of your fridge.

Air conditioning uses the same principle, but collects the heat in your room, superheating the refrigerant because its in a pressurized line, then moving the refrigerant outside your room and allowing it to naturally expand and release its heat outside.
 
#16 ·
Sorry to mislead anyone, I guess I was actually hoping for some clarification just like the op was. So then, superheat is a term only applied to gas and vapor? Thanks for setting me straight on that. I thought it could also be applied to liquids.

I now realize that I had the evaporation and condensation stages totally reversed. Thanks for clearing that part up also. I'll be more careful in future to not lead anyone astray. I guess I jumped the gun trying to pass on incorrect knowledge. Thanks for the help guys. Lesson learned. I'll stay in the background .
 
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