What keeps the freezer, frozen?

Question

I just don't understand it.

Answer 1

The ice only melts if it's temperature goes over 0 deg C

The only way the temperature of the ice will rise is if heat is added to it.

Some heat creeps into the freezer every time you open the door, and smaller amounts will enter the freezer through the walls, although insulation keeps this heat flow really small.

Heat will flow from hotter to cooler, but there are a number of ways, of altering the temperatures of the hot (source) and cold (sink)

Heat can be removed from the freezer in a number of ways. On a macroscopic level, the simplest is the electrical heat pump, which usally uses the Peltier effect. What happens with them is when a current flows though the device, heat is pulled from one side of the device(the cold side) and is pushed to the hot side. The hot side is hotter than the atmosphere, so the heat then flows into  the sounding air. (a fan is usually used to stop the hot side getting too hot, and burning out)

Other and more common coolers use a vapour-compression  cycle to move the heat. What they do is take a gas, and compress it so it becomes a liquid. This liquid is then at a higher temperature then the "outside" of the freeze, so much of the heat moves out of it( via cooling pipes, usually at the back of the freezer) This pressured liquid is then fed into a pipe in the freezer compartment. While still in the freezer compartment, it passes through a throttle valve, while drops it's pressure, allowing it to boil. For the liquid to vaporise it has to absorb heat, and so you get a temperature drop. As the gas is cooler then the freezer compartment, heat will flow from the freezer compartment, into the gas

Absorption refrigerators use two fluids, which produce a temperature drop when they mix. If the refigerator runs constantly the fluids are seperated, (by distilation) ready to be mixed again.

There's other types of cooling such as vortex tubes, but they tend not be used at home.

Answer 2

It takes advantage of what is called the 'joules-thomson' effect.

When a liquid is under pressure and is then expanded to a lower pressure (in the expansion valve in the system), it requires energy to evaporate. The energy is in the form of heat from it's surroundings. Simply put, that is the concept. When the liquid is dropped in pressure across the expansion valve, the boiling point of the refrigerant is lowered (lowering pressure lowers boiling point, raising pressure raised boiling point of any liquid). The refrigerant is then immediately exposed to the condition where it's boiling point has dropped but it is at the same temperature, hence it MUST evaporate. You cannot stop this evaporation, it must occur. Then when it evaporates, it causes cooling.

An easy way to demonstrate how liquids need energy to evaporate is when you boil water in a saucepan - the flame is on underneath the saucepan, but while the water is boiling it cannot go above 100 deg C (at atmos pressure), it is impossible. You are inputting energy from the flame, but it is not increasing the temperature of the water......So where has this energy gone? It is used to change state from liquid to gas.(vapour) Same for refrigeration.

The refrigerant liquid used will depend on the temperature (or coldness) you need to achieve. It depends on the boiling point of the refrigerant liquid - there are propane refrigerant systems (to take temperature down to the boiling point of Propane i.e. minus 42 deg C. Liquid Nitrogen refrigeration systems are used to take temperatures far lower (cryogenic refrigeration)

Sorry if it's a bit difficult to read, I'm tired.

Answer 3

A freezer doesn't actually cool things, it removes the heat from them. You probably don't want a physics lesson but may wonder where the cold comes from. So here is a little bit more physics. When a gas goes from a state of high pressure to a state of low pressure, the temperature of the gas drops. Your freezer is circulating a gas from high pressure to low pressure over and over again.

Inside the freezer a fan circulates air over the chilled tubing and the refrigerant absorbs the heat from the freezer's relatively warmer air. If you prefer to just think of the fan blowing cold air into the freezer, that's fine, it all works out to pretty much the same results. But technically, the heat is being pumped out rather than the cold being pumped in.

As the air in the freezer cools, the water in the air (humidity) condenses. Water that condenses in the freezer will freeze into frost

here is an interesting note. If the temperature outside a refrigerator or freezer, is too low, the appliance will not cool efficiently.



  

Answer 4

It's the gas that runs through the pipes. It's designed to freeze

Answer 5

Ill try to be simple with my explanation, though I might have to add a little physics into it.

Inside the freezer - behind the inside plastic - there is a long pipe. This pipe connects to a motor and then to a radiator right at the back of the freezer. The radiator has a thinner pipe than the one inside the actual freezer.

Inside these pipes is the cooling liquid. You can often hear the motor start and stop which pumps the cooling liquid round the pipe system. The cooling liquid is pumped through the pipe inside the freezer where it warms up, when it warms up it takes heat from the freezer compartment and cools it down. After it passes though the freezer bit, the warmed liquid goes out the back and through smaller pipes.

Because these pipes are smaller the liquid is pressurised and that also heats the liquid up (thats where the physics comes in Im afraid, the formula P1/V1 x T1 = P2/V2 x T2, (p = pressuer, V = Volume, T = Temperature) means that if the pressure increases in a closed system then either the volume of liquid increases or its temperature increases, in the case of a freezer, its the temperature that increases). Sorry, physics over.

Anyway the cooling liquid heats up and is now hotter than the outside air - so it looses heat to the air. This cools the cooling liquid to air temperature again and heat has been rmoved from the freezer. Before the cooling liquid goes back into the freezer, the pipes get bigger - the pressure drops and so does its temperature, so now th cooling liquid is coler than the freexer insides and the whole lot starts again.

Hope that was clear?

Answer 6

cold stuff.

i guess you dont really want a full blown explaination of the refridgeration system

Ok, so you do want a description, here goes from memory:-

The "stuff" - (refridgerant chemical) in the pipes insdie fridge/freezer is manipulated in such a way that it turns from a liquid to a gas inside the fridge.

When it is outside the fridge, its turned from a gas back to a liquid.

this is due to changing pressures within the whole of the pipework.

When the stuff goes from a liquid to gas, it uses its own internal energy to do this, as a result, it gets colder ( or to think of it another way, it absorbs the thermal energy from the inside of the fridge and so the temperature drops.

When the stuff is outside of the fridge, it is compressed from a gas back into a liquid and as a result it gets hotter ( try putting your hand round the back of the fridge and feel how warm the radiator is )

clever, eh?

try looking up the words enthlapy and entropy.

Also try the phrase "degrees of superheating"

Answer 7

freezing in the freezer is due to two process that happens inside it (a gas is used in these processes which causes freezing)

1. evaporation:  in this the compressed gas is expanded to normal pressure . for expantion the gas requires heat which is absorbed from the atmosphere (This gives the cooling effect)

2 in the second process ie condensation the gas is again compressed in a compressor where the heat absorbed is rejected by the gas.

*NOTE : behind the freezer you must have noticed a black cylindrical thing (it is always hot and is the compresser , that is the place where all the heat  of the freezer is moved to)  

Answer 8

ICE

Answer 9

the chemicals in the compresser cause a cold reaction, a filament/panel cools and water condenses on it causing ice. the air cools through convection cooling the contents. the chemicals contained in the door and housing are extremly poor conductors of heat. so insulate the outside heat from heating up the cool air insinde.

it is like a air conditioner. google air conditioner or go to www.howstuffworks.com and search for freezer/fridge.

Answer 10

Well without going into great detail, the freezer is a very well insulated "box". The insulation gives the freezer a very low heat transfer coefficient through its walls. In addition, this "box" is attached to an electromechanical system that performs a refrigeration cycle (Thermodynamics). This cycle basically allows the "extraction of  heat" from the insulated box until the temperature is low enough so freeze its contents. There is a feed back system somewhere to allow the system to electrochemically start / stop keeping this way the inside of the "box" frozen. I hope this helps.  

Answer 11

Ice is kept as ice by the use of a 'Refrigeration' process.

This uses the 'Cold' produced by the following Thermo-dynamic sequence:

1...Compression of the Refrigerant gas.

2...Cooling and condensation of the gas in the coils behind the fridge/freezer.

3...Expansion of the high pressure, cool liquid into a Low Pressure system. This causes partial vaporisation of the liquid that produces very low temperatures (around

-40 to -50°C) to occur in the refrigerant vapour and liquid. (The 'Joules-Thompson Effect').

4...This is then passed through the 'Cooling coils' of the 'Cold Box' of the fridge/freezer which absorbs heat from the food and water placed inside until it freezes. This process returns all of the refrigerant back into a vapour (gas) form which then returns to the compressor and the above process repeated maintaining the fridge/freezer at the required temperature.

5...A thermostat in the system controls the stopping and re-starting of the compressor motor as needed to maintain the low temperature.

Also, of course, the freezer insulation must be exceptionally good to prevent the ingress of the ambient temperature.

(I've Worked with refrigeration for many years including 'Cryogenics' down to -165°C).

Answer 12

Evaporation causes rapid cooling, its a basic physics thing.

If you blow on your hand, you can feel a drop in temperature. This is because you cause micro amounts of perspiration to evaporate.

The liquid in the cooling system of a freezer is forced to evaporate. Its the evaporation which causes the freezer to freeze.

If you took a bottle of lighter gas and pressed the nozzle so that a large amount of gas was released, you would notice ice foming around the nozzle.

If you try this, wear gloves and don't smoke.

Answer 13

6 Answers so far and not one credible one. Do this experiment, get a bycicle pump and press your finger over the pump outlet and work the pump. what you will feel as the air tries to force out is a burning sensation on your finger OK. What this is showing you is that if you compress air you will get an increase in temperature,this is what is happening in a fridge except they dont use air they use a gas called freon wich is more efficient than air.This compressed and increased temperature gas is then put in contact with the surounding air via a grid and the temperature normalises to the surounding air. The next stage is to pass this compressed gas through the fridge and then reduce the pressure of the gas which does the oposite of compressing, ie lower the temperature which is now lower than the surounding area hence causing cooling. it is called a heat pump