NL9300834A - Cooling device. - Google Patents

Description

Title: Cooling device.

Description

The invention relates to a cooling device provided with a system, comprising a compressor, an evaporator and connecting pipes and filled with a cooling medium.

Cooling devices of the type described above are known in many embodiments and for many applications. These applications concern partly commercial and partly domestic use.

The system which, as indicated above, contains a compressor, an evaporator and connecting pipes, as is known, is filled with a cooling medium for which the most diverse substances are used. In principle, many of these media are harmful to the environment, especially when they contain chlorine-containing compounds. In many cases CFC-12 or HCFC-22, also referred to as R-12 and R-22, is used as the chlorine-containing medium. R-12 has the chemical composition dichloro-difluoromethane; R-22 has the chemical composition mono-chloro-difluoromethane. As can be seen from the chemical formulas, both substances contain a considerable amount of chlorine which can be released into the environment, for example in the event of leakage or demolition of the relevant cooling device. In particular, due to the release of this chlorine, the ozone layer is apparently affected, which leads to serious environmental consequences. It is therefore desirable not to use these coolants; they are therefore or will be banned in various countries in the short term. Therefore, proposals have already been made to replace these detrimental coolants with others, especially those containing non-chlorine. One of the promising substances is 1,1,1, tetrafluoroethane which is also referred to as HFC-134a or R-134a. This coolant has properties comparable to those of the commonly used R-12 and is therefore very useful as a replacement for the environmentally unfriendly R-12.

In a cooling device provided with a system containing a compressor, an evaporator and connecting pipes, it is necessary that in addition to the actual cooling medium, e.g. of the types indicated above, a lubricant is present. This lubricant must of course be compatible with the cooling medium used, i.e. not interfere with its proper functioning. The known refrigerants R-12 and R-22 generally use a mineral lubricating oil. When using a chlorine-free coolant, such as R-134a, for example, the use of a mineral lubricating oil is not suitable, because it is not miscible with the coolant itself. Mixing with the refrigerant is, however, necessary in order to realize a mixture with a sufficiently low viscosity in the cold part of the circuit, namely the evaporator, which remains well liquid, does not remain in the evaporator and does not lead to blockages. The correct viscosity is also desired at the start-up of the compressor, in order to achieve a favorable start-up characteristic.

When using a chlorine-free coolant, for example R-134a, which is already being marketed by the chemical industry for this purpose, the use of a mineral oil, as hitherto used, is not possible due to the polar molecular character of R- 134a in contrast to R-12. Therefore, when using R-134a, an ester, in particular a polyol ester, is always used as a lubricant. However, compared to mineral oil, these lubricants are much more sensitive and much more hygroscopic and can lead to chemical reactions in the refrigeration circuit, impeding the proper functioning of this circuit, usually through clogging. This makes fabrication of equipment for use with R-134a more difficult, as much more stringent requirements are required regarding moisture, process, component specifications, etc., compared to equipment using R-12. This naturally leads to an increase in costs, although the desired objective, namely environmental friendliness, is achieved. It would therefore be desirable to be able to use a mineral oil also for chlorine-free coolants, for example R-134a. However, given the above fact that a mineral oil is immiscible with these chlorine-free refrigerants, this is impossible.

A particular difficulty still arises when one wishes to convert an already existing cooling device, in which R-12 is used together with a mineral oil, into a device with a chlorine-free coolant, for example R-134a.

However, it has been found to be very difficult and practically impossible to rid the entire refrigerant circuit of the mineral lubricant in such a way that the above-identified problems of replacement with a chlorine-free refrigerant do not arise. Obviously, this problem does not occur with completely new installations.

The object of the invention is therefore to avoid the problems of using a chlorine-free coolant, for example R-134a, in new equipment and in the conversion of existing equipment that works with a chlorine-containing coolant and a mineral oil, without having to resort take to rigorous cleaning measures or a less desirable ester e.g. a polyol ester.

A cooling device according to the invention, provided with a system comprising a compressor, an evaporator and connecting pipes and filled with a cooling medium, is characterized in that the cooling medium consists of a mixture of a chlorine-free cooling liquid, a mineral lubricating oil and one or more of the hydrocarbon propane , isobutane, cyclopropane or dimethyl ether.

It has been found that the addition of one or more of the above-mentioned hydrocarbons to the chlorine-free coolant allows the use of mineral lubricating oil without deteriorating the cooling properties and in some cases even better.

In general, it is not necessary and even undesirable, because of poor mixture formation and flammability of the hydrocarbons to make up no more than 20 weight percent of the mixture consisting of the hydrocarbons. A percentage lower than 1% by weight has of course little effect and can therefore only be used exceptionally.

If, for refrigeration reasons, a weight percentage of 5 to 15% of hydrocarbon is to be used and thus the risk of fire increases, the percentage of hydrocarbon can be reduced, so that it will be between 5 and 15% by weight, by adding a second coolant, for which in particular penta-fluoroethane (HFC-125 / R125) is suitable. The cooling liquid then preferably consists of a mixture of 80-90% by weight HFC-134a / R134a and 0.5 / 5% by weight HFC-125 / R-125.

In a method for manufacturing a cooling device according to the invention, starting from an existing cooling device which contains as cooling medium a mixture of a chlorine-containing cooling liquid and a mineral lubricating oil, wherein this mixture is removed and replaced by a mixture of a chlorine-free coolant and one or more of the hydrocarbons propane, isobutane, cyclopropane and dimethyl ether, it may be desirable that the introduced replacement mixture additionally contain an amount of mineral lubricating oil. As a result, the amount of mineral oil that is still present in the system is supplemented to the correct amount for proper operation. In most cases it can be assumed that the chlorine-containing coolant can simply be replaced by a mixture of a chlorine-free coolant and / or more hydrocarbons.

It is noted that it is known per se, see the publication of R. Camporese et al. In Proceedings - Volume 1, July 14-17, 1992 Purdue University, West Lafayette, Indiana, USA, to use a refrigerator in a refrigerator mixture of R-134a and a small amount of propane. If this mixture is used in a so-called "retrofit" of an installation containing R-12 and a lubricating oil, the publication assumes that the lubricant has also been replaced, which is understandable because, as indicated above, when used of R-134a a polyol ester is always used, while on the other hand when using R-12 a mineral oil is always used as a lubricant.

Claims (7)

Cooling device comprising a system comprising a compressor, an evaporator and connecting pipes and filled with a cooling medium, characterized in that the cooling medium consists of a mixture of a cooling liquid, a mineral lubricating oil and one or more of the hydrocarbons propane, isopropane, cyclopropane and dimethyl ether. Cooling device according to claim 1, characterized in that the total percentage of hydrocarbon is 1-20% by weight of the mixture. Cooling device according to claim 1 or 2, characterized in that the cooling liquid is 1,1,1, tetra-fluoroethane (HFC-134a / R-134a). Cooling device according to claim 1 or 2, characterized in that the cooling liquid is a mixture of 1,1,1-tetrafluoroethane. (HFC-134a / R-134a) and penta-fluoroethane / (HFC-125 / R-125) and the weight percentage of hydrocarbon is 5-15. Cooling device according to claim 4, characterized in that the cooling liquid is a mixture of 80-90% by weight HFC-134a / R134a and 0.5-5% by weight HFC-124 / R-125. Method for manufacturing a cooling device according to claim 1, 2, 3, 4 or 5, characterized in that an existing cooling device is used, which contains as cooling medium a mixture of a chlorine-containing cooling liquid and a mineral lubricating oil, this mixture removed and is replaced by a mixture of a chlorine-free coolant and one or more of the hydrocarbons propane, isopropane, cyclopropane and dimethyl ether. A method according to claim 6, characterized in that the introduced replacement mixture also additionally contains a mineral lubricating oil.