DE19735334A1 - Solar-operated refrigeration plant - Google Patents

Abstract

The refrigeration plant has a boiler heated directly or indirectly by solar radiation, a condenser and a mixer for providing a mixture of 2 liquids exhibiting a mixing heat of greater than 500 J/ mol, a difference in their boiling temperatures of at least 20 degrees C and at least one of the components having a boiling temperature above 50 degrees C. ENERGY CONVERSION - The plant provides efficient use of solar energy and can be combined with a solar collector system for water heating. ORGANIC CHEMISTRY - Both liquids which are used may be provided by organic liquids.

Description

Field of the Invention

The invention relates to a solar thermal cooling system and a System for combined heating and cooling with solar energy and a Procedures for operating these plants.

State of the art

The cooling of rooms or substances has been practiced since ancient times Technology. So, in ancient times, liquids were in porous, earthen Vessels cooled by allowing liquid to pass through these pores evaporated.

In most modern cooling systems (see below), the Ver vaporize liquids the essential part of the cooling circuit in progress.

In principle, however, low temperatures can also be achieved through a whole Achieve a number of other operations, e.g. B. by mixing substances, which have a positive enthalpy of mixing, i.e. when mixing cooling down. For example, by mixing ice and table salt a temperature of -22 ° C can be achieved.

A chiller that uses the heat of mixing two liquids Generation of refrigeration was used by V.P. Latyshev, Kholod. Tekh. 1982, 34-8. Also based on liquids with positive Mixing heat was based on that of M.G. Verdiev et al. developed Chiller. Two thermoelectric batteries were used. Methyl bromide / propane was used as the pair of substances. (M.G. Verdiev et al., Izv. Vyssh. Uchebn. Zaved., Energ. 1980, 23 (8), 67-71).

The principle of the compression refrigerator, z. B. in most house holding refrigerators is based on the fact that a gaseous Refrigerant is liquefied under pressure. The heat that occurs is  dissipated. The refrigerant evaporates during the subsequent expansion extracts the heat required for evaporation from the cold room. The absorption chiller works like the compression chiller at 2 pressure levels but at 3 temperature levels. Here is the mechanical compressor replaced by a thermal compressor. Working substance is a two-substance mixture consisting of the working or Refrigerant and the sorbent or solvent. The ability of Sorbent dissolving the refrigerant determines the mode of action this process. The material pair is the main material pair Water / lithium bromide and the pair of ammonia / water are used. Recently, other pairs of substances have also been tested. B. the fabric pair 1,1,1,2-tetrafluoroethane (R 134a) / tetraethylene glycol dimethyl ether (DMETEG) (I. Borde et al., Int. J. Refrig. 1995, 18 (6), 387-94). How a continuously working absorption cooling works machine see e.g. B. F. W. Winter, Technical Heat, Verlag W. Giradet, Essen, 275ff.

Such an absorption refrigerator has at least the following 4 main components:

• - a stove (expeller)
  Here ammonia, e.g. B. evaporated by gas heating.
• - a capacitor
  Here the expelled ammonia is condensed and the heat released is dissipated.
• - an evaporator
  Here the ammonia is evaporated at reduced pressure. The heat required for this is extracted from the cold room.
• - an absorber
  Here the water coming out of the stove absorbs the ammonia vapors coming out of the evaporator. The heat of absorption and condensation released is dissipated.

As the drive energy, the absorption chiller requires next to one small proportion of higher quality (e.g. electrical) energy for the solutions only pump inferior thermal energy.

This is certainly one of the reasons why absorption chillers are used solar cooling have been used.

In general, interest in solar cooling is increasing. H. of use Solar heat for cooling purposes. Thereby the solar energy is both for the operation of refrigerators as well as for cooling (air conditioning) of Rooms. Building air conditioning using solar energy is included Particularly interesting as the solar supply and cooling requirements are optimally combined fall (see also Fraunhofer Gesellschaft, 1995 Annual Report, p. 82).

A whole range of systems for solar cooling is put together in the Solar Energy Technology Handbook, Part B, publisher: William C. Dickinson, Paul N. Cheremisinoff, chapters 30, 103ff.

It describes solar-powered absorption refrigeration systems that use the systems ammonia / water, lithium chloride / water and Lithium bromide / water work. After that, the system in particular Lithium bromide / water a certain spread in solar powered Air conditioners found.

As this study also shows, combined solar heating and Solar cooling is significantly more effective than heating or cooling alone.

The absorption refrigerator according to DE-OS 195 35 840 or in DE-OS 195 35 841 described device for air conditioning work with Lithium bromide / water.

For the purposes of solar cooling, the sorption technology is also used with the Material pair of water / zeolite examined. With this system, the high Zeolite binding tendency used for water. So takes place in evacuated system so violently the absorption of water vapor in the zeolite that the water evaporates with the formation of ice. Regeneration of the zeolite, d. H. the water is expelled from the zeolite using solar energy  at temperatures <200 ° C (see also DE-OS 35 21 448 and S. Müller, S. Zech, solar energy 6/96, 22-24).

A cooling system based on activated carbon / ammonia is described by J. Bougard et al. described, Sci. Tech. Froid 1992 (1, Froid a Sorption solid), 302-7. The system for heating and cooling described in DE-OS 43 40 812 works with zeolite as storage medium and ethane as working medium.

Task

The system is of particular interest in the field of solar cooling Zeolite / water found. It is used to regenerate the zeolite however, temperatures <200 ° C are required to drive off the water difficult to achieve with the flat collectors currently in use are. So for the expulsion of the water z. B. special parabolic collectors used. In addition, the handling of such a periodically operating zeolite / water chiller is quite complex (see Stefan Eichengrün et al., Ki Luft- und Kältetechn. 1994, 30 (3) 112).

On the other hand, the solar-powered absorption chillers that come with the material pair lithium bromide / water work, by the salinity in limited their area of application.

In the ammonia / In contrast, water must have relatively high temperatures and pressures are used so that this system with the usual used solar panels is not easy to use. One Way out offers here u. U. those of D.T. Rose et al. (AES (Am.Soc.Mech. Eng.) 1994, 31 (Absorption Heat Pump Conference, 1994), 109-15) described two-stage ammonia / water absorption refrigeration system, the however shows a rather complex structure.

There is still a lack of a solar thermal cooling system or air conditioning, which is simple and without large working pressures gets along.  

solution

It has now been found that the requirements for a solar-powered cooling system are met in an outstanding manner by the cooling system according to the invention, which contains the following components:

• - a directly or indirectly solar heated expeller (cooker),
• - a condenser,
• - a mixing device and
• - a pair of substances consisting of 2 liquids that
  • a) have a heat of mixing ΔH <500 J / mol of mixture,
  • b) show a difference in boiling points of <20 ° C,
  • c) of which at least 1 component has a boiling point <50 ° C.

The invention also relates to a method for cooling by means of solar energy, which is characterized in that a liquid mixture consisting of at least 2 components which have a heat of mixing .DELTA.H <500 J / mol differ with respect to the boiling point by more than 20 ° C. and from where at least one component has a boiling point <50 ° C, in a system containing a directly or indirectly solar-powered expeller (cooker), a condenser (condenser) and a mixing device is circulated, the mixture being expelled into a gaseous component 1 and a non-evaporating component 2 is separated, component 1 is liquefied in the liquefier, the liquid components 1 and 2 are mixed in the mixing device while absorbing energy, and finally the mixture obtained is fed back to the expeller.

Apart from the heat exchange techniques used here (countercurrent cooling, etc.), energy is absorbed at two points in this process: when mixing the two liquids (actual cooling process) and when evaporating (expelling) component 1 in the expeller using solar energy.

The energy is essentially released in the condenser (heat of condensation of component 1 ).

The solar-powered cooling system according to the invention is therefore a very simple system. This system consists essentially of the illustrated in Fig. 1 and Fig. 2 components, that is, a solar-powered expeller, a condenser and a mixing device. The difference to the solar powered absorption chiller is that the cooling is done by mixing and not by evaporation at reduced pressure. As a result, the system usually works at a single (low) pressure level.

It is also essential that the expulsion of the low-boiling component 1 in a temperature range, for. B. 40-180 ° C, or preferably 50-150 ° C, which is easily achieved with the solar panels according to the prior art.

At first glance, the disadvantage is that the invention according to the solar-powered cooling system of quite high evaporation heat is opposed to a mixture heat, which usually only one Fraction of the heat of vaporization, e.g. B. 20%. Against that stands very simple structure of the system and the wide range of applications. In addition, this cooling system according to the invention with no problems combined a solar collector system for domestic water heating can be, the cooling as an additional benefit z. B. for air conditioning arises.

Detailed description of the invention The components of the mixture

A suitable component of the solar-powered cooling system according to the invention is a suitable mixture, ie a suitable pair of substances, consisting at least of components 1 and 2 . If necessary, the mixture can also contain other constituents, these may be used to influence the separation process (influencing an azeotrope) or the rheology of the mixture. In minor proportions, the mixture can also contain stabilizing additives such as. B. contain anti-aging agents.

A suitable pair of substances, ie a suitable mixture, is characterized at least by the following features:

• - a high heat of mixing,
• good separability by evaporating a component,
• - environmental compatibility,
• - Long-term stability.

The is essential for the functioning of the cooling system according to the invention Use of a pair of substances with the highest possible heat of mixing, d. H. the use of a pair of fabrics that cool significantly when mixed. A suitable pair of substances has a heat of mixing ΔH <500 J / mol Mixture or preferably ΔH <1000 J / mol mixture. Especially if it is material pairs with an average molecular weight <80 g / mol is, however, are heat of mixture ΔH <1500 J / mol mixture prefers.

It is generally cheaper to heat the mixture to one kg of mixture to acquire. So the heat of mixing a suitable pair of substances in the general ΔH <10 kJ / kg mixture. One is preferred Mixing heat ΔH <20 kJ / kg mixture.

On the other hand, you can also directly change the temperature when mixing the substances as a criterion for the selection of a suitable pair of substances draw in. As a guide, it can be said that the cooling when mixing at least 4 ° C, better at least 6 ° C or preferred should be at least 8 ° C. Those are particularly preferred Pairs of substances that change by more than 10 ° C during adiabatic mixing cooling down.

In principle, suitable material pairs can be obtained directly from standard Reference works such as B. James J. Christensen et al., Handbook of  Heats of Mixing, John Wiley & Sons, New York and Christensen et al., Heats of Mixing Data Collection (Chemistry Data Series 3 / 1,2), Frankfurt: DECHEMA 1984. In addition, suitable Mixing partners can also be calculated using incremental methods. B. UNIFAC (see also A. Fredenslund et al., AICHE Journal, 21, 1086 (1975) or J. W. Barlow et al., Macromolecules 1988, 21, 2492-2502 and Macromolecules 1989, 22, 374-80).

In general, inorganic and organic liquids are of interest. Interesting as a mixture component is e.g. B. water. However, preference is given to pairs of substances which contain at least one organic liquid. Mixtures in which both components are organic liquids are of particular interest. At least one of the components has a boiling point <50 ° C, preferably <80 ° C. Particular preference is given to pairs of substances in which the higher-boiling component, referred to below as component 2 , has a boiling point <120 ° C. or even more favorably a boiling point <160 ° C.

In general, such substance pairs are interesting, which are chemically very different, so z. B. differentiate in terms of functional groups. Although you can also find pairs of substances with a positive mixture, if component 1 and component 2 belong to the same substance class, z. B. differ only in terms of geometry such. B. the hydrocarbons cyclohexane / heptane. For this pair of substances there is a heat of mixing ΔH approx. 280 J / mol.

Such a value for the heat of mixture is, however, for use in the solar-powered cooling system according to the invention is too low.

According to the invention - as shown - pairs of substances, one Have heat of mixing ΔH <500 J / mol. Particularly suitable however, are those material pairs that have a significantly higher heat of mixing, e.g. B. Show ΔH <2000 J / mol.

The substance class of is of particular interest as a mixing partner pure hydrocarbons, the alkanes. This shows with a whole series other substance classes high heat of mixing.  

The alkane substance class can be used both as volatile component 1 (e.g. pentane) and the less volatile component 2 (e.g. longer-chain hydrocarbons such as dodecane).

Substance classes are listed below that can be combined with aliphatic hydrocarbons according to the invention:

-Halogenated hydrocarbons, e.g. B. fluoroalkanes, chlorinated hydrocarbons,
-Carbonyl group-containing compounds such as

• - ketones, e.g. B. Acetone / Hexadecane ΔH: 2374 J / mol
• - esters, e.g. B. Methyl acetate / dodecane ΔH: 2141 J / mol
• Amides, especially N, N-dialkylamides,
  e.g. B. N, N-dimethylacetamide / heptane ΔH: 1236 J / mol
• - Carboxylic acids, e.g. B. Acetic acid / cyclohexane ΔH: approx. 1000 J / mol

- Nitro compounds, e.g. B. Nitroethane / 2,2-dimethylbutane ΔH: approx. 1610 J / mol
- Amines, e.g. B. Pyridine / Hexane ΔH: 1590 J / mol
- Ether / ketals, also cyclic, e.g. B. Diethylene glycol dimethyl ether / heptane ΔH: 1650 J / mol.

Alcohols are also of interest as mixing partners for alkanes. It however, certain restrictions must be observed. Show alcohols / alkanes a pronounced dependence of the heat of the mixture on the temperature and tend to mix gaps, especially at low temperatures. The temperature dependence of the system is even more pronounced Acetic anhydride / cyclohexane. This system is only at room temperature a small proportion miscible. At an elevated temperature, e.g. B. 60 ° C however miscible and then shows a mixing temperature of ΔH: approx. 3000 J / mol. Such a system is consequently only in the case of an increased one Temperature can be used.

Of the possible combinations with alkanes mentioned here are especially those containing fluoroalkanes and carbonyl groups Systems such as esters or ketones are preferred.  

Just like the possible combinations with alkanes shown here other substance classes can also be combined (see e.g. Christensen et al., Loc. cit.).

It is interesting e.g. B. the combination of methyl t-butyl ether (MTBE) with very polar mix partners. MTBE is a very stable, low boiling compound that has a low heat of vaporization.

The combinations alcohol / ketone are of particular interest, Alcohol / ester and alcohol / nitrile. So the mixture shows isopropanol / ace ton a mixture heat of ΔH: approx. 1600 J / mol, just as clear the isopropanol / methyl acetate mixture (ΔH: approx. 1600 J / mol) is positive.

In principle, the mixing ratio of components 1 and 2 can range from 1: 9 to 9: 1 (parts by weight). In general, however, the components will be used in a ratio of 3: 7 to 7: 3 (parts by weight). In particular, if the system is used exclusively for cooling purposes, it is advantageous to use component 1 , for which the evaporation energy has to be applied, in a deficit. In this case, a ratio of component 1 to component 2 in the range 2: 8 to 4: 6 (parts by weight) is preferred.

Separability of the material pairs in the expeller

Of the material pairs shown above with a heat of mixing ΔH <500 J / mol, these are of particular interest because they have the greatest possible difference in the boiling point. As a rule, this difference should be more than 20 ° C. or preferably more than 40 ° C. The separability of the substances is facilitated if component 2 has a boiling point that is more than 80 ° C higher than that of component 1 . There are particular advantages if components 1 and 2 differ in their boiling point by more than 120 ° C. and do not form an azeotrope.

With such a difference in the boiling point, the separation of the components in the expeller succeeds even with very different energy input. It can be an advantage that with particularly high energy input (i.e. with particularly high solar radiation) component 1 is almost completely expelled in the expeller, with particularly strong cooling then taking place when the almost pure components are mixed, while with only low solar radiation Component 1 can only be driven out of the mixture incompletely, that is to say component 2 still contains considerable amounts of component 1 (for example 20%). This causes a significantly lower temperature drop (see example 10).

So that z. B. an air conditioning system can be realized without additional elaborate regulation gets along.

With regard to a selection of suitable material pairs, the first option is large number of material pairs known from the literature, which a mixture heat ΔH <500 J / mol show a sufficiently large difference with regard to the boiling point and not disturbing the separation Form azeotropic (see also Azeotropic Data 3 (Adv. Chem. Series 116), Washington: ACS 1973).

For example, if one starts from the ketone / alkane pair and selects the ketone as volatile component 1 , a number of mixtures known from the literature are directly suitable. Here are e.g. B. to name (boiling points of the components in brackets):

Acetone (56 ° C) / decane (174 ° C), ΔH: 1978 J / mol,
Ethyl methyl ketone (79 ° C) / dodecane (216 ° C), ΔH: 1664 J / mol.

For example, if you want to deepen the area of application for these mixtures Increase temperatures, so you will choose branched alkanes that have a significantly lower benchmark.

On the other hand, one can also choose the alkane as volatile component 1 and, accordingly, the ketone as the higher-boiling component. Here come as alkanes z. B. the various butanes, pentanes or hexanes in question, as ketones correspondingly higher boiling compounds, for. B. diethyl ketone or cycloalkanones. Only if the system is to work under increased pressure is acetone as component 2 of interest, for example in combination with butane as component 1 .

The pair of substances ester / alkane is to be seen quite analogously. Here, too, when using the ester as volatile component 1 , the substance pairs described in the literature based on low-boiling formates or acetates can be used directly, for example. B. the mixtures:

Methyl acetate (56 ° C) / dodecane (216 ° C), ΔH: 2140 J / mol or
Ethyl acetate (77 ° C) / dodecane (216 ° C), ΔH: 1768 J / mol.

When choosing the alkane as component 1 , however, one will not refer to the substance pairs known from the literature

Hexane (68 ° C) / methyl benzoate (199 ° C), ΔH: 1372 J / mol,
Hexane (68 ° C) / dimethyl carbonate (90 ° C), ΔH: 1896 J / mol,

limit, but instead of hexane, for example, the lower boiling Pentane (34 ° C) and instead of dimethyl carbonate the higher boiling Select diethyl carbonate (121 ° C), which in the literature for example as Mixing partner for dodecane is described.

In general, the mixture of lower alkane (e.g. the various butanes, pentanes, hexanes) / dimethyl or diethyl carbonate is of interest. In general, the boiling point of a component can be reduced for a given mixture by z. B. selects a lower molecular weight component in a homologous series, e.g. B. the mixture of hexane (68 ° C) / diethyl carbonate (121 ° C) instead of the mixture described in the literature dodecane (216 ° C) / diethyl carbonate (121 ° C). The inverse procedure, ie starting from a known mixture to increase the molecular weight of a component, for example to increase the boiling point, is not always possible. Mixing gaps often occur here. In general, at least component 1 of the mixture should have a molecular weight of <100 g / mol. In general, it is advantageous if the higher-boiling component 2 also has a relatively low molecular weight, e.g. B. <400 g / mol.

The substance pairs alcohol / ketone and alcohol / ester are particularly interesting, as they generally show complete miscibility and quite high heat of mixing even when using relatively high molecular weight components. Here are e.g. B. to name as material pairs:
Acetone and ethyl methyl ketone as component 1 and longer-chain, especially also branched alcohols, e.g. B. C4-C10 alkanols or polyhydric alcohols as component 2 , for example ethyl methyl ketone (79 ° C) / 1,3-butanediol (204 ° C), ΔH: approx. 1600 J / mol or acetone (56 ° C) / 1- Hexanol (157 ° C), ΔH: 1784 J / mol.

The possible variations in the ester / alcohol area are even wider. Here z. B. combine lower esters with higher alcohols, e.g. B. ethyl acetate (77 ° C) / 3-methyl-1-butanol (131 ° C), ΔH: approx. 2700 J / mol or lower esters such as methanol, ethanol, propanol and isopropanol as component 1 and higher esters as component 2 , e.g. B. isopropanol / dialkyl esters of dicarboxylic acids such as dialkyl succinates, dialkyl adipates. Esters of diols and high-boiling cyclic esters such as propylene carbonate are also of interest as an ester component. Component 1 is preferably isopropyl alcohol and a diisopropyl ester of a dicarboxylic acid as component 2 .

Requirements for environmental compatibility / long-term stability

In addition to the requirement for the highest possible heat of mixing and one The material pairs must of course have good separability in the expeller be environmentally friendly and stable.

So are alkane / chlorohydrocarbon combinations, in particular Pairs of chlorofluorocarbons are less preferred. In contrast, fluorocarbon / alkane combinations are particularly suitable. These pairs of fabrics show good stability, moreover stand out Fluorocarbons are characterized by a low heat of vaporization. Alkane / ketone and alkane / ester combinations are also suitable.  

However, especially in terms of long-term stability Alcohol / ester combinations can only be used to a limited extent. On the one hand these pairs of substances require the use of drying agents in order to To prevent hydrolysis of the ester, on the other hand there is a risk of Transesterification. For this reason alcohol / ester combinations are included which are the same as the alcohol residue of the ester and the alcohol, especially interesting, e.g. B. Combinations of the isopropyl alcohol / isopropyl ester type. In this case, a transesterification does not change the Mixing and boiling behavior.

In general, it is advantageous to exclude oxygen work and use antioxidants and desiccants.

Requirements for the mixing device and the cooker (expeller)

In principle, components 1 and 2 can be mixed using an agitator. With a view to making the cooling system as simple as possible, however, a stirrer will generally be dispensed with. A simple merging of the components is often sufficient. Suitable mixing devices are e.g. B. described in Ullmann's Encyclopedia of Industrial Chemistry, Vol. B4, 561ff: "Continuous Mixing of Fluids". Static mixers are particularly suitable for mixing components 1 and 2 (see in particular Manfred H. Pahl and E. Muschelknautz, Chem.-Ing.-Tech., 51 (1979), 347-64 and Chem.-Ing.-Tech ., 1980, 52: 285-91).

In principle, the solar collector can be used directly as an expeller (cooker) be used. On the other hand, it is also possible to use the solar panel to operate with a heat transfer medium and thus the expeller too heat. However, the use of the solar collector is preferred as Expeller. If necessary, the exporter will be given a rectifi connect kator. In general one becomes the rectification Keep equipment (e.g. reflux cooler) as small as possible and instead Material pairs with the greatest possible difference in the boiling points  choose. In general, the absorption chillers use known expulsion and rectification techniques.

Particular embodiments of the invention

The solar-powered cooling system according to the invention shows an exception neatly wide range of uses. One of the reasons for this is that the temperatures for separating the components are ideal with the Working areas of the usual solar panels match. It should also be emphasized that the cooling effect used here by mixing 2 liquids not only at room temperature but also at higher temperatures and at low temperatures is applicable.

In general, a work area of e.g. B. + 70 ° C to -80 ° C with be covered by a single pair of fabrics. If you choose special Low temperature or high temperature mixtures is the work area even larger: + 150 ° C to -110 ° C. It is only important to ensure that the Fixed point of the components is deeper than the area of application.

The cooling system according to the invention can be used to operate a Freezer (temperature -18 ° C) or a refrigerator (Temperature approx. 4 ° C) can be used. But is also particularly suitable the use for dehumidification or air conditioning (cooling) of Clearing.

In principle, it is possible to store components 1 and 2 in separate storage containers to achieve a cooling effect even when there is no sun or at night, but as a rule, especially for small devices such as household refrigerators or freezers, you will find storage containers for components 1 and 2 do without and rather keep the total mixture in the system as low as possible.

For large systems, such as for the air conditioning of entire building complexes, it is quite advantageous to store components 1 and 2 in storage containers and mix them according to the cooling requirements.

It is particularly advantageous that the storage of these components e.g. B. is not limited in time at room temperature and also none Insulation required. Especially in household refrigerators and freezers one becomes Bridging the sunless time or bridging the Night hours however z. B. use ice storage or brine storage. Refrigerators and freezers with suitable latent storage are known from DE-OS 24 33 499, EPA 0098052 or EPA 0651214. Such Refrigerators with storage have been designed especially for photovoltaics powered refrigerators or for refrigerators designed with cheap Work night electricity.

In addition to being used as an air conditioner in the home, above all the air conditioning of mobile homes, camping facilities and Vehicles of interest. The use in the area is particularly interesting of camping fridges.

A particularly preferred embodiment of the solar according to the invention operated cooling system is the combined operation of a solar powered Heating especially a solar powered water heating and a refrigeration system.

This enables a particularly effective use of solar energy. In this combined solar heating / cooling system, the solar energy introduced in the vaporizer component 1 is used in the condenser (heat of condensation) to produce hot water (see Fig. 2).

The hot water tank can preferably be called a so-called Operate stratified storage.

When using this form of solar water heating, the refrigeration according to the invention an additional benefit that without major, additional effort is achieved.

Depending on the design of the system (see Fig. 2) - more emphasis on cooling or hot water preparation - it can be an advantage to use substances with a relatively high heat of vaporization as component 1 .

In this embodiment in particular, water is also of interest as component 1 (heat of vaporization: 2253 kJ / kg). In this heating / cooling combination, methanol, ethanol and isopropanol are also very suitable as component 1 .

When used purely as a refrigeration system or as an air conditioning system, however, components 1 with a significantly lower heat of vaporization will be used. Fluorinated compounds and lower hydrocarbons are of particular interest here. So shows z. B. pentane has a heat of vaporization of 383 kJ / kg. But the lower esters such as methyl acetate (heat of vaporization: 406 kJ / kg) are also suitable.

Especially in the combination of solar water heating / solar cooling is the particular benefit of the cooling system according to the invention. It is to emphasize in particular the very simple structure. So there is the whole System apart from the expeller (solar collector) and condenser (Hot water tank) only from a number of tubes and Heat exchangers. The system has particularly stressed moving parts Not. As a rule, the system is driven by a pump, which, for. B. the mixture pumps into the expeller. This pump works advantageously photovoltaic. It can generally be a complex regulation to be dispensed with.

With skillful selection of components 1 and 2 in terms of density, for. B. Density of component 2 significantly higher than density of component 1 (as is the case with an alkane as component 1 and an ester as component 2 ), a pump can be dispensed with entirely. In this case, a hydrostatic drive is possible.

The elimination of complex, moving parts makes the invention System not susceptible to faults, almost noiseless and easy to manufacture.  

Examples

The following examples serve to illustrate the invention but not a limitation.

Examples 1-7 Orientative preliminary experiments to examine the Mixing behavior of components 1 and 2

For the exact determination of the heat of mixing of liquids see e.g. B. Christensen et al. (loc. cit.). For a quick, orientating examination however, it is completely sufficient to add 20 g of liquid in a glass flask, equipped with magnetic stirrer and thermometer to mix and match Watch temperature change. It is only necessary First bring components to the same starting temperature and one quick to use thermometer or thermocouple. There is no need for expensive insulation because of the temperature change takes place very quickly.

example 1

Isopropanol and acetone are mixed in a ratio of 1: 1 (data as Weight ratios) mixed. A cooling of 9.5 ° C. is observed.

Example 2

Methyl acetate and dodecane are mixed in a 1: 1 ratio. A cooling of 7.8 ° C is observed.

Example 3

2-ethylhexanol and methyl acetate are mixed in a 1: 1 ratio. A cooling of 8.9 ° C. is observed.  

Example 4

An ester mixture consisting of 70 wt .-% ethylene glycol diacetate and 30% by weight of ethyl acetate is mixed with pentane in a ratio of 1: 1. A cooling of 7.3 ° C is observed.

Example 5

Isopropanol and propylene carbonate are mixed in a 1: 1 ratio. A cooling of 10.9 ° C. is observed.

Example 6

Isopropanol and propylene carbonate are mixed in a ratio of 3: 5. A cooling of 10.8 ° C. is observed.

Example 7 (not according to the invention)

Ethylene glycol diacetate and acetone are mixed in a 1: 1 ratio. A slight decrease in temperature of approximately 0.3 ° C. is observed.

Example 8 Cooling test with partial heat exchange

The components according to Example 1 , isopropanol and acetone, are mixed continuously with partial heat exchange. For this purpose, the starting materials are pre-cooled by the mixture over a distance of approx. 10 cm. A temperature of 4.3 ° C is established (temperature of the starting materials: 24.6 ° C. This results in a temperature decrease of 20.3 ° C.

Example 9 Mixing test at reduced temperature

In each case 20 g of the components according to Example 3 are used in a Initial temperature of -26.1 ° C mixed. observed cooling to -33.5 ° C.

Example 10 Separation test without rectification

The components of the mixture according to Example 2 (component 1 : methyl acetate, boiling point 56 ° C., component 2 : dodecane, boiling point 216 ° C.) are separated by expelling the methyl acetate.

• 1. Expeller working temperature: 88 ° C
  The expulsion of the methyl acetate is incomplete, the remaining dodecane still contains approx. 12% methyl acetate. When mixing the remaining component 2 with the expelled component 1 , a cooling of 5.4 ° C. is observed.
• 2. Working temperature of the expeller: 95 ° C
  In this case too, the expulsion of the methyl acetate is not yet complete. The remaining dodecane contains approx. 8% methyl acetate. When mixing the remaining component 2 with the expelled component 1 , a cooling of 6.5 ° C. is observed.

With increasing energy input, the separation becomes better and the Cooling effect bigger. The pair of methyl acetate thus allows the structure a solar-powered cooling system without complex temperature control.

Claims (15)

1. Solar thermal operated cooling system, characterized in that it contains as components:

• - a directly or indirectly solar heated expeller (cooker),
• - a condenser,
• - a mixing device,
• - a pair of substances consisting of 2 liquids, the
  • a) have a heat of mixing ΔH <500 J / mol,
  • b) show a difference in the boiling points <20 ° C,
  • c) of which at least 1 component has a boiling point <50 ° C.

2. Solar thermal cooling system according to claim 1, characterized characterized in that the pair of substances a heat of mixing ΔH <1200 J / mol. 3. Solar thermal operated cooling system according to claim 1 and 2, characterized in that the components of the pair of substances, the low-boiling component 1 and the higher-boiling component 2 differ in boiling points by <80 ° C. 4. Solar thermal cooling system according to claims 1-3, characterized in that component 2 of the pair of substances has a boiling point <120 ° C. 5. Solar thermal operated cooling system according to claims 1-4, characterized in that the one component of the pair of substances Hydrocarbon from the group of alkanes is the other Component a substance from the group of halogenated hydrocarbons substances, carbonyl compounds, nitro compounds, ethers, alcohols and Amines.   6. Solar thermal operated cooling system according to claims 1-4, characterized in that the one component of the pair of substances Alcohol is the other component from the group of ketones, esters, nitriles. 7. Solar thermal cooling system according to claims 1-6, characterized in that the expeller directly as a solar collector is designed. 8. Solar thermal operated cooling system according to claims 1-7, characterized in that the mixing device from static Mixers. 9. Solar thermal cooling system according to claims 1-8, characterized in that the condenser (condenser) part of a Hot water tank is. 10. Solar thermal cooling system according to claims 1-9, characterized in that the mixing device is part of a Refrigerator and / or a freezer. 11. Solar thermal cooling system according to claims 1-9, characterized in that the mixing device is part of a Dehumidifier. 12. Solar thermal cooling system according to claims 1-9, characterized in that the cooling system is part of an air conditioning system. 13. A method of cooling by means of solar energy, characterized in that containing in a plant

• - a directly or indirectly solar heated expeller,
• - a condenser,
• - a mixing device

a liquid mixture (pair of substances) consisting of at least 2 components which have a heat of mixing ΔH <500 J / mol, differ in boiling point by more than 20 ° C, and of which at least one component has a boiling point <50 ° C,
is carried out in a circle, the liquid mixture in the expeller being separated into a gaseous component 1 and a non-evaporating component 2 , the component 1 being liquefied in the liquefier, the liquid components 1 and 2 being mixed in the mixing device with the absorption of energy and then the obtained mixture is fed back to the expeller. 14. A method for cooling using solar energy according to claim 13, characterized in that the expeller is directly heated by solar energy. 15. A method for cooling using solar energy according to the claims 13 and 14, characterized in that the condenser for DHW heating is used.