Phase-change cooling - SpeedyLook encyclopedia

The phase-changes cooling is a system of cooling of Computer material based on the principle of the Heat pump.

Principle of operation

Simple assembly stages

A Fluide Frigorigène circulates in a closed circuit; we will take here the R404a like example, having the following characteristics:

Temperature of boiling to a Pressure of 1 bar: -46 °C
Temperature of Condensation to a Pressure of 12 bars: 23 °C

the Température S and the Pression S given in what follows are orders of magnitude.

The R404a, in its phase Liquid, returns in the evaporator to a Température of -50 °C and a Pression of 1 bar. The bottom of the evaporator, always conceived in a Material having good a thermal Conductivity (like the Copper), will make it possible the R404a to store the Chaleur emitted by the Microprocesseur; this last thus will be cooled, and the R404a, whose Température will increase, will vaporize (its Température will be higher than -46 °C with the Pression of 1 bar). The R404a gas then will be evacuated thanks to the compressing .

Multistage assembly: cascade

To be able to practice very important Overclocking (within the framework of attempts at world records for example) a very low Température is required, within the framework of a Extreme cooling. A means of arriving at Temperature S between -150 °C and -200 °C is to use for example Azote liquidates like Fluide Frigorigène, this one having a Température boiling of -196 °C with a Pression of 1 bar. But the problem of the Azote liquidates is its Température of Condensation: -167 °C with a Pressure of 12 bars, impossible to arrive at its Liquefaction with the air of the part. This is why a second stage is necessary, with a Fluide Frigorigène having a Température boiling near to these -167 °C. This new Fluide will be able to condense with a higher Température, is by a third stage if this one is still too weak, that is to say with Air. Here a possible staging:

The R728 is condensed by the R50, itself condensed by the R1150, condensed by the R404a, condensed by the Ambient air.
One can thus arrive at a Température of about -200 °C in the evaporator.

The Condensation of a Fluide by another Fluide is carried out inside an exchanging (also called HX, for Heat eXchanger). In a cascade on 4 floors there are 3 HX: between each étage.
A HX consists of a large pipe where the cooling Fluide will circulate, inside whose will be a finer pipe where will circulate the Fluide to cool. The fine pipe, bathing in the Fluide lower stage, will cool its contents, which will allow the Fluide upper floor to condense, and with that of the lower stage to vaporize by Heat transfer. A HX thus constitutes the evaporator lower stage and the condenser of the upper floor. The Fluide S generally circulate in opposite directions one of the other.

Simple assembly stages: autocascade

It is also possible to reach temperatures of about -100 °C with -150 °C with a simple assembly stages (thus with only one compressing), by carrying out what is called a autocascade. The Fluid which composes this stage is a mixture of several Fluide S Frigorigène S (generally from 2 to 5), present in proportions very spécifiques.
We will take here the example of a autocascade with 2 Fluide S Frigorigène S (as on the diagram opposite):

the Température S and the Pression S given in what follows are orders of magnitude.

The mixture of R404a and R744 leaves the compressing to a Température of 30 °C and a Pression of 12 bars, to arrive at the condenser, which will cool the mixture thanks to the Ambient air. The R404a thus will liquefy, its Température of Condensation being about that of the Ambient air, but this Température is not cold enough so that the R744 also condenses him, it thus will remain in its gas phase. Thus the mixture consists of R404a liquid and R744 gas. It then will penetrate in a bottle so that both phases are separate grace the Pesanteur. The R404a liquid will pass in a Détendeur to have a Pression of 1 bar and a Température of -50 °C.
Both Fluide S will penetrate in a Heat exchanger: the R404a will make condense the R744 and itself will vaporize. The R744, after having seen its Pressure falling to 1 bar thanks to a Pressure reducer, will return in the evaporator to a Température of -80 °C in its phase liquid, will cool the Microprocesseur, and will arise with a Température of -60 °C in its gas form. The two gases then will meet and turn over to the compressor in order to start again a cycle.

One can thus carry out a Refroidissement containing 5 Fluide S Frigorigène S with only one compressor, but with four Bouteille S to separate the phase S and four Heat exchanger. The fact of using only one compressor is a space saver, but a autocascade is a rather delicate system to set up, where it is necessary to introduce the Fluides S in precise quantities, especially if there is much of it.

Sources

Cooling-Masters.com

See too

External bonds and documents

http://www.cooling-masters.com/articles-4-0.html Article detailing the principle of phase-changes cooling.

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