compressors in refrigiration cycles

[brum]

hello ...i have a question, (im a bit of a newbie to this theory stuff!)

 

in a basic refrigereation cycle there are 4 basic components: evaporater, compressor, condensor and expander.

and a working fluid (wf) or refrigerant flowing through the whole sytem

 

- so the in the evaporater, the wf absorbs the heat from heat source.

- next the wf goes through compressor which compresses it and raises temp.

- next wf goes through condensor and releases heat to the heat sink, hence ruducing wf temp.

- wf then passes through expander which expands the wf, cooling further the temp.

- cycle repeats.

 

so my question, which is probably a silly one, is why is there a need for a compressor to raise the temp?, why not just directly go to the condensor and release the heat?

 

help in understanding will be appreciated.

[YT2095]

it`s job isn`t to raise the temp, that`s a by-product of compression.

when the heat has been taken out of the food compartment, the wf is alot less dense as the heat that was taken create molecular vibration and expansion of the wf, re-compressing it again, makes it once again usefull and ready to absorb more heat.

 

think of it as a Heat Exchange, in fact sometimes it`s even called that, taking it from one place (where you don`t want it) to another place (where you`re not bothered) all by using the vapor pressure of a liquid/gas.

 

hope that helps a little

[insane_alien]

actually when its compressed and heats up it can dissipate heat energy at a greater rate through radiation and it will set up convection currents in the surrounding air which will further aid cooling.

[brum]

thanks you^^^

[Pleiades]

It’s been a while since I learned all this but let me try and explain. It all has to do with heat flow; heat is always trying to flow from a hot area into a cold one, in order to reverse this flow we need a heat pump, air conditioners and refrigerators are types of heat pumps.

 

Imagine it like water: water wants to flow downhill and as it does this we can extract energy from it (think hydroelectric power plants). If we want to move water uphill, we have to spend energy to pump it back up. (In case you are wondering, it is possible to extract energy from heat as it travels from a hot area to a cold one, using sort of a reverse refrigerator)

 

There are two sides to a phase change cooling system (such as a fridge) a hot, high pressure side, and a cold, low pressure side, the compressor is what produces the pressure difference, the expansion valve keeps the two sides from equalizing.

 

Consider what happens in a refrigeration system. The refrigerant (your working fluid) is forced from the high pressure condenser through a small tube (the expansion valve) as a liquid, when it reaches the condenser; the pressure is much lower (because the compressor is sucking from the evaporator) when the liquid comes out of the tube into the low pressure area it evaporates into a gas becoming cold. You may notice the same thing happens when you let the air out of a tire, or spray a can of air duster upside down. As the cold gas travels though the evaporator it picks up heat from inside the fridge. The compressor then raises the pressure of the gas and pumps it into the high pressure condenser, turning it into a liquid (just like the air duster has a liquid in it). The liquid now holds the heat energy from the inside of the fridge and the heat energy from the compressor. Because it is now hotter the heat wants to flow out of the system into the air near the back of the fridge. Once the liquid has passed though the condenser it is more or less the same temperature as the air behind the fridge. The now cooler liquid then goes back through the expansion valve and the cycle begins again.

 

So, in short, the compressor is necessary because it has to force the refrigerant from one phase (gas/liquid) to another.

 

I hope this helps some; I’m still a little fuzzy on the whole idea myself.

[mrblond5311]

It’s been a while since I learned all this but let me try and explain. It all has to do with heat flow; heat is always trying to flow from a hot area into a cold one' date=' in order to reverse this flow we need a heat pump, air conditioners and refrigerators are types of heat pumps.

 

Imagine it like water: water wants to flow downhill and as it does this we can extract energy from it (think hydroelectric power plants). If we want to move water uphill, we have to spend energy to pump it back up. (In case you are wondering, it is possible to extract energy from heat as it travels from a hot area to a cold one, using sort of a reverse refrigerator)

 

There are two sides to a phase change cooling system (such as a fridge) a hot, high pressure side, and a cold, low pressure side, the compressor is what produces the pressure difference, the expansion valve keeps the two sides from equalizing.

 

Consider what happens in a refrigeration system. The refrigerant (your working fluid) is forced from the high pressure condenser through a small tube (the expansion valve) as a liquid, when it reaches the condenser; the pressure is much lower (because the compressor is sucking from the evaporator) when the liquid comes out of the tube into the low pressure area it evaporates into a gas becoming cold. You may notice the same thing happens when you let the air out of a tire, or spray a can of air duster upside down. As the cold gas travels though the evaporator it picks up heat from inside the fridge. The compressor then raises the pressure of the gas and pumps it into the high pressure condenser, turning it into a liquid (just like the air duster has a liquid in it). The liquid now holds the heat energy from the inside of the fridge and the heat energy from the compressor. Because it is now hotter the heat wants to flow out of the system into the air near the back of the fridge. Once the liquid has passed though the condenser it is more or less the same temperature as the air behind the fridge. The now cooler liquid then goes back through the expansion valve and the cycle begins again.

 

So, in short, the compressor is necessary because it has to force the refrigerant from one phase (gas/liquid) to another.

 

I hope this helps some; I’m still a little fuzzy on the whole idea myself.[/quote']

 

 

I'm assuming an ammonia freezer works the same way? Let me know, Thanks!