FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention
AIR-CONDITIONING MACHINE
2. Applicant(s)
Name Nationality Address
FRAUNHOFER-GESELLSCHAFT
ZUR FÖRDERUNG DER
ANGEWANDTEN FORSCHUNG E.V. GERMAN Hansastraße 27c 80686 München, Germany
Name Nationality Address
FRAUNHOFER-GESELLSCHAFT
Hansastraße
ZUR FÖRDERUNG DER GERMAN
27c 80686 München, Germany ANGEWANDTEN FORSCHUNG E.V.
3. Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be
performed

The invention relates to an air-conditioning machine having an evaporator structure forming a heat transfer surface and a working medium reservoir containing a working fluid, the evaporator structure having a cooling medium flow, and to a method for operating such an air-conditioning machine. The working fluid is also referred to as a working medium or refrigerant.
Such air-conditioning machines are designed as either refrigerating machines or heat pumps. The evaporator structure is cooled by working fluid evaporating at the evaporator structure. The evaporated working fluid is first adsorbed on an adsorber. The loaded adsorber is raised to a higher temperature level, whereupon the working fluid is desorbed again and condensed on a condenser as a condensate. A refrigerating machine uses the cooling of the evaporator structure for a technical application, whereas a heat pump uses the heating of the condenser and/or the adsorber for a technical application. The evaporator structure is therefore also referred to as a heat exchanger or heat exchanger structure. The useful heat flow can be removed from the air-conditioning machine by a refrigerant flow through the evaporator structure. In this way, a closed circuit of the refrigerant is realized.
In such air-conditioning machines, which can be designed as adsorption refrigerating machines or adsorption heat pumps, for example, the working medium is cyclically evaporated and adsorbed or desorbed and condensed. Refrigerating machines of this type can have a sorber and a component which combines condenser and evaporator structure, as disclosed in EP 1 278 028 B1, for example. The evaporator structure is then operated in an alternating mode as an evaporator and condenser. This means that the working fluid is evaporated alternately in time sequence at the evaporator and

condensed again at the evaporator at condensation temperature after adsorption and desorption at the sorber.
Heat exchangers have so far been used in adsorption heat pumps and refrigerating machines for evaporation/condensation and operate according to the principle of partially flooded pool evaporation, partly also in connection with capillary structures, on the surface of which the working fluid evaporates out of thin films. In air-conditioning machines designed as absorption refrigerating machines, sprinkled pipe bundles are usually used as evaporator or heat exchanger structures. The heat exchanger structure is sprinkled or sprayed with refrigerant from above. The refrigerant forms a thin film (trickle film) on the heat exchanger structure and evaporates on the surface of this film. When an air-conditioning machine is operated in this mode, very high heat transfer coefficients from the heat exchanger structure to the working fluid are achieved with good refrigerant distribution on the surface due to the thin films and due to convection in the trickle film. However, a circulating pump is required for the working fluid, since refrigerant that has not evaporated collects in the sump, i.e. in the working fluid accumulated in the working medium reservoir, and has to be applied to the heat exchanger structure again.
A widespread approach in adsorption refrigerating machines and adsorption heat pumps is a partially flooded operating mode, as disclosed in DE 1 00 33 972 B4, for example. In this operating mode, the evaporator structure is partially flooded by the working fluid, i.e. partially immersed in the sump (structural flooding). Thin films of the working fluid can here be produced on the heat transfer surface and have a low heat-conducting resistance. In DE 10 2008 028 854 A1, for example, the heat transfer surface is wetted with working fluid by taking advantage

of the capillary effect. The heat transfer surface is here formed by a low finned pipe and thus forms a capillary structure. The capillary structure has a dual function during the evaporation of the working fluid: on the one hand, it increases the heat-transfer surface; on the other hand, the capillary effect draws the refrigerant against the gravitational force onto the capillary structure where it is distributed evenly. The working fluid evaporates from the resulting films which are very thin in some areas along the so-called 3-phase boundary between vapor, liquid and metal.
DE 10 2011 015 153 A1 discloses an in situ storage of working medium during the condensation/desorption phase on horizontal heat transfer surfaces, as they exist e.g. in finned heat exchangers. During the evaporation/adsorption phase, the working fluid present on the structure is evaporated again. The problem with this approach is that working fluid condenses even at places where it does not form a thin film but completely fills the structure areas, partially drips off and thus cannot be activated thermally or only with a very high thermal resistance.
The working fluid is evaporated in the air-conditioning machines described by silent boiling or convective boiling, which means boiling without the formation of bubbles. The heat transfer during the evaporation is essentially limited by the transport of heat through the refrigerant film during silent (convective) boiling with refrigerant films larger than 1 mm. The greater the film thickness, the greater the heat transfer resistances to be overcome. In the case of a flooded heat exchanger, such as the one used for boiling water in containers, the thermal resistances are very high because only the water surface contributes to the evaporation. In order to achieve the best possible

heat transfer, the aim is therefore to achieve very low film thicknesses of the working fluid on the heat transfer surface of the evaporator structure.
In some embodiments of the invention, water as a pure substance is evaporated in a temperature range from 0°C to 30°C. Accordingly, the pressures are low in the range from 0.006 bar (0°C) to 0.042 bar at 30°C. In other embodiments of the invention, water as a pure substance is cyclically transferred from the solid to the gaseous phase in a temperature range from -10°C to 0°C. The density difference between the liquid phase and the vapor phase is very large. At 10°C, the density of the liquid phase is 999.7 kg/m3 and that of the gaseous phase is 0.0094 kg/m3. This results in a density quotient of approximately 100000. In the implementation of evaporators in apparatus according to the prior art, the large density quotient must be taken into account in particular by design forms in which evaporation takes place into a free volume instead of boiling in a flow in order to keep pressure losses low and to avoid blocking of the heat exchanger with vapor cushions that do not escape due to the high pressure loss. In addition to the design requirements for the installation space, wall overheating of more than 20 K is required for water as a working fluid in the described pressure and temperature range on smooth surfaces and wall overheating of at least 7 K on structured surfaces in order to achieve continuous bulk boiling with high heat transfer coefficients. Wall overheating of the above magnitude is not feasible in heat pump or refrigeration applications, as high wall overheating is synonymous with increased cold water temperatures or with reduced boiling pressures, which have an unfavorable effect on the required compression ratio or sorption pressure and thus on the efficiency of the cycle. Furthermore, for water in particular, the freezing point is another limiting operating parameter.

The object of the present invention is to provide an air-conditioning machine and a method for using it, which reduces the disadvantages of the prior art and in particular shall allow an improvement regarding the performance at driving temperature differences comparable to the prior art and the use of water as working fluid.
According to the invention, this object is achieved by a device according to claim 1 and a method according to claim 11. Advantageous developments of the invention can be found in the subclaims.
An air-conditioning machine according to the invention has an evaporator structure forming a heat transmission surface and a working medium reservoir containing a working fluid, i.e. a working medium sump. The evaporator structure has a coolant duct. According to the invention, a bubble generation structure is provided, wherein the bubble generation structure is arranged in the region of the working medium reservoir in such a way that it is at least partially flooded by the working fluid and/or can be wetted with working fluid. The evaporator structure is arranged in a spraying region of the working fluid, e.g. above the working medium reservoir, in such a way that the heat transfer surface is wetted with a working fluid film by working fluid that is carried along by gas bubbles which can be generated and/or introduced in the working fluid by the bubble generation structure and which are rising in the working fluid. The spraying region is here referred to as a volume area that is reached by the working fluid entrained and ejected from the working medium reservoir by the gas bubbles, i.e. into which the working fluid is sprayed (spraying of the working fluid) and/or deflected via components. For the purposes of the present description,

the term "gas bubble" refers to a vapor bubble generated by the bubble generation structure in the reservoir of the working fluid and rising in the working fluid.
In this way, a hybrid evaporator is provided, particularly for low pressure applications. The heat exchanger concept realized according to the invention serves as an evaporator especially in refrigerating machines and heat pumps. It can therefore be used e.g. in sorption systems in low-pressure applications but also for the distribution of trickle films e.g. in absorption processes. It is thus possible to form, on the heat transfer surface of the evaporator structure, a thin liquid film of the working fluid which has to be evaporated almost completely and offers a low thermal resistance between the heat transfer surface and the adjacent surface of the working fluid. During the operation of the air-conditioning machine, heat can be introduced into the working fluid sump, which leads to the local formation of gas bubbles. The refrigerant, i.e. the working fluid, thus sprayed hits the evaporator structure where it forms the desired thin liquid film. By regulating a heating capacity, the formation of bubbles in the working fluid sump and thus the evaporation capacity can be adjusted. At low pressure, the working fluid may be sprayed strongly. The heating power can here be introduced e.g. by constant basic heating and control by a second, additional heat source and/or by spot-like heating, e.g. by an electrical resistor.
In some embodiments of the invention, the evaporator structure can thus be separated by design from the bubble generation structure such that the energy introduced into the working medium reservoir for the generation of the gas bubbles by the bubble generation structure is at least essentially independent of the temperature of the cooling liquid in the coolant duct of the evaporator structure and/or can be controlled.

In some embodiments of the invention, the evaporator structure of the air-conditioning machine according to the invention thus contains at least two structural areas, wherein one structural area which is the bubble generation structure is arranged in the working medium reservoir in a flooded or at least partially flooded fashion and is designed in such a way that bubble or bulk boiling can be initiated on its structure outside. As a result of the large density quotient between liquid and vapor, gas bubbles produced as vapor bubbles reach a large volume which, when the gas bubbles are detached and rise, leads to a strong entrainment of the working fluid. Due to bulk boiling, the working fluid is ejected out of the working medium reservoir and, in the second structural region which is designed as an evaporator structure, hits its heat transfer surface, which is designed as the outside of a heat exchanger which, by virtue of its geometric nature, is designed in such a way that the working fluid is distributed over a large area and can evaporate out of thin films thus formed.
The evaporator structure to be wetted in this way can be arranged above or to the side of the bubble generation structure. It can be completely or partially immersed in the working fluid sump. In the case of partial immersion, additional absorption of the working fluid from the working fluid sump can be effected at least if capillarily active distribution structures are provided on the surface of the evaporator structure. No pump is required within the vacuum system, i.e. the system in which the working fluid is evaporated. As a result, no mechanically moving parts have to be present, which can lead to a long service life. Furthermore, a simple control of the air-conditioning machine is possible via the energy supply of the bubble generation structure. Controllable wetting of the heat transfer surface with thin working fluid films is made

possible so that high heat transfer coefficients can be achieved. This does not require a pump or a structure that distributes refrigerant in a capillary way. This provides an evaporator with high power density at small driving temperature differences, especially for water as working fluid and other low-pressure working fluids, such as methanol. The results, which can be achieved with the air-conditioning machine according to the invention with the evaporation from thin water films that are sprayed, i.e. generated from the sprayed working fluid, achieve at least 15 % higher performances with comparable driving temperature differences compared to water films generated in a capillary way. At the same time, moving parts are undesirable, especially in adsorption devices, as this has a negative effect on vacuum stability and energy consumption, causes additional maintenance and downtimes due to wear and tear and should not be abandoned as a technical
advantage over absorption. During the operation of an air-conditioning machine according to the invention, gas bubbles are generated with a small proportion of the energy required for the operation and/or extracted from a coolant, the task of which is to distribute refrigerant, i.e. working fluid, over the evaporator structure or structures. The targeted generation of gas bubbles in the working fluid can be achieved by designing structures or also by supplying energy only in phases.
The bubble generation structure is advantageously equipped with a fluid-guiding pipe for the generation of gas bubbles by bulk boiling. A coolant can be guided through the fluid-guiding pipe, from which heat is extracted to generate the gas bubbles. It may be the same coolant that is passed through the coolant duct of the evaporator structure. In this way, heat is extracted from the coolant during both the generation of bubbles and the evaporation of the working fluid.

The hydraulic interconnection of the two fluid-carrying structures, i.e. the coolant duct of the evaporator structure and the fluid-guiding pipe of the bubble generation structure, can be either serial or parallel. It is advantageous that the fluid-guiding pipe and the coolant duct are arranged in series one behind the other in a coolant circuit. The coolant first flows through the fluid-guiding pipe, as a result of which there is a higher coolant temperature than in the coolant duct. The energy for the generation of gas bubbles, i.e. the formation of bubbles, is fed thermally to the working medium reservoir through the preflow of the coolant circuit, e.g. a cold water circuit, formed by the coolant. The thermal energy for generating the gas bubbles is thus introduced directly via the coolant circuit by passing through it serially, i.e. the largest temperature difference between the coolant and the working fluid lies in the bubble generation structure. In this embodiment, a heat exchanger can be used as a bubble-forming structure and is designed in such a way that its cold water inlet area allows bubble-forming overheating.
The bubble generation structure can have electrical heating means and/or a heat pipe and/or mechanical means for generating the gas bubbles. The energy for the bubble formation can then be fed additionally or alternatively for the thermal supply by the preflow of the e.g. cold water circuit or other heat transporting fluid circuits, by electrical heating elements, such as electrical resistors, or the introduction of microwaves and/or heat pipes and/or by mechanical methods, such as vibration and/or the introduction of ultrasound. If it has to be assumed when energy is supplied by other fluid circuits or the latter options that the wall overheating, i.e. the temperature of the outer wall of the bubble generation structure which is in contact with the working fluid, substantially exceeds that of the heat transfer surface of

the evaporator structure through which the coolant circuit, e.g. a cold water circuit, is guided, the bubble generation structure must be thermally well insulated from the evaporator structure.
The bubble generation structure can advantageously have a pipe deflection and/or surface structures to increase a heat transfer to the working fluid and/or to improve a bubble separation of the gas bubbles. Surface structures that serve to support the gas bubble formation and to support the gas bubble separation can form gaps and/or cavities. In addition, the fluid-guiding pipe can have an inhomogeneous surface condition, in particular partial surface insulation and/or alternating hydrophilic and hydrophobic regions. The gas bubbles forming on the bubble generation structure can grow to a considerable size, e.g. several centimeters. Depending on the installation space, this can cause strong spraying and pronounced convection during bubble tearing. The formation of bubbles can often be locally assigned to gaps at the structural edge of the bubble generation structure with a gap width of less than 1 mm or to heat-conducting microstructures, e.g. fibers and/or grooves. Such surface structures serve to improve the bubble detachment and/or bubble formation.
The spraying of the working fluid can, for example, be intensified by a specific geometric arrangement of fluid-guiding pipes or channels of the bubble generation structure and/or by structures applied to or incorporated into the heat-transferring surface of the bubble generation structure, such as pins, pivots, grooves, fabric, perforated foils, fibers, sponges, etc. At certain distances, e.g. gaps of less than 3 mm, between the fluid-guiding pipes/channels, the working medium is locally overheated at points, such as pipe deflections, so that vapor bubbles are formed more quickly there and working medium is sprayed

out of the working medium reservoir. A further possibility for improving the generation of steam bubbles is the introduction of materials with poor heat conductivity at the interface between the working fluid and the outer surface of the bubble generation structure, e.g. a structure through which fluid flows. Such an arrangement creates large temperature differences on the surface of the bubble generation structure, which supports bubble formation and detachment.
In a further embodiment, the bubble generation structure has means for introducing a two-phase flow of the working fluid containing the gas bubbles into the working medium reservoir. The gas bubbles required for spraying the working fluid can also be generated by introducing a two-phase flow, which, for example, is produced from the pressure difference in the working fluid between a condenser and the evaporator structure by means of a throttling element. The two-phase mixture forming the two-phase flow is fed into the refrigerant pool, i.e. the working medium reservoir, from below. The gas bubbles then rising in the working fluid generate the entrainment of the liquid refrigerant, i.e. the working fluid.
An advantage is that the evaporator structure has fins (cooling fins or cooling ribs) arranged on the coolant duct for increasing the heat transfer surfaces and/or the coolant duct is at least partially plate-shaped for this purpose and/or the coolant duct is at least partially designed as pipes running parallel to one another for this purpose. The heat exchanger structure, i.e. the evaporator structure, onto which refrigerant, i.e. working fluid, is sprayed by the resulting gas bubbles, is arranged in such a way that it is easily accessible for the sprayed refrigerant. This can be achieved, for example, in the form of vertically or laterally aligned fins above the working medium reservoir, plates

through which the refrigerant flows or pipes arranged one above the other in alignment. In order to avoid splashing working fluid outside the space of the evaporator structure, which could, for example, lead to a transfer of working fluid into other components that is unfavorable for the method, an offset arrangement of the structure can be formed in the uppermost structure row in the case of an evaporator structure formed in several rows of structures arranged one above the other. A terraced arrangement of the structure rows can also be provided, so that outflowing refrigerant is collected and evenly distributed.
If a surface structuring and/or a hydrophilic coating and/or a porous layer is applied to the heat transfer surface of the evaporator structure, an improvement in the distribution of the working fluid can be achieved. The heat transfer surface to be wetted is thus characterized by very good wetting behavior. This can be achieved either by surface structuring formed by mechanical structuring in the form of e.g. grooves, pins, etc., specifically generated roughnesses, porous layers with a structure height of less than 1 mm and/or by a hydrophilic or contact angle-reducing surface coating and/or chemical pretreatment of the heat transfer surface. The heat transfer surface, on which the thin film of the working fluid, e.g. a water film, evaporates, can also have properties that contribute to an even distribution of the working fluid, on the one hand, and also to an increase in the residence time and mixing of the working fluid, on the other hand. These can be e.g. fishbone-like wave structures and/or also structural specifications, which can be determined by the design of embossed grooves or applied porous structures, e.g. fibers, fabrics, sponges.
In some embodiments of the invention, the working fluid can have a density quotient between about 4000 and about 60000. In other

embodiments of the invention, the working fluid can have a density quotient between about 15000 and about 60000 or between about 7000 and about 25000 or between about 4000 and about 14000. In some embodiments of the invention, the working fluid can have a density quotient of more than about 4000 or more than about 7000 or more than about 12000. In some embodiments of the invention, the working fluid can have a density quotient of less than about 55000 or less than about 25000 or less than about 14000. In some embodiments of the invention, the working fluid can contain or consist of water and/or methanol and/or ethanol. Optionally, e.g. an additive can be added to reduce the surface tension. In particular water as working fluid is very environmentally friendly and therefore harmful substances such as CFCs or ammonia can be avoided. A good power density can be achieved with the air-conditioning machine according to the invention, which shows a wall overheating of only 3 to 5 Kelvin at the heat transfer surface of the evaporator structure.
Porous particles can be introduced into the working fluid. Such particles embedded in the liquid refrigerant are especially inert, highly porous and good heat conductors. By means of convection in the working medium reservoir, these particles are repeatedly thrown to the surface of the working fluid where they can quickly evaporate refrigerant due to their very large contact surface to the vapor space above the working medium reservoir. The heat required for this is first extracted from the particle which, after entering the liquid of the working fluid, withdraws it from the working fluid and thus e.g. from a cold water circuit. The particles mixed into the refrigerant are strongly moved due to the formation of bubbles. If these particles are inert, highly porous and good heat conductors, they can quickly release the refrigerant stored in them in the vapor space. The heat extracted from the particle

is fed back to it as soon as the particle immerses into the working fluid sump again and can thus be extracted from the coolant circuit, e.g. a cold water circuit, via the working fluid sump. In this embodiment, the evaporator structure can also be integrated into the bottom or the sides of the working medium reservoir. A partially introduced bubble generation structure must be thermally well insulated.
Fabric structures and/or wire structures can be arranged in the working medium reservoir. If the evaporator structure is partially immersed in the working medium reservoir, an additional suction of the working fluid from the working fluid sump can be effected at least if capillarily active distribution structures are present on the surface of the evaporator structure. With this approach, open-pore fabric or wire structures can be used to distribute the working fluid. The structure that guides coolant, e.g. cold water, can also be incorporated directly into the fabric structure.
It is advantageous to provide, in the spraying region, means for expanding and/or deflecting the spraying region, in particular a distributor structure for collecting working fluid entrained by the gas bubbles and for distributing the working fluid on and/or over the evaporator structure, i.e. the heat transfer surface thereof, and/or a working medium conveying tube which is immersed with an open end in the working medium reservoir. The distributor structure forms part of the evaporator structure.
If an e.g. funnel-shaped working fluid conveying tube is provided, the working fluid conveying tube being immersed in the working medium reservoir with an open end, in the case of the funnel shape the wide funnel filling end, rising gas bubbles can pump working fluid, i.e.

refrigerant, upwards against gravity through the working medium conveying tube, so that the spraying region can be enlarged upwards e.g. beyond the evaporator structure. In this way, for example, liquid refrigerant can be distributed from above on the heat transfer surface. By narrowing the cross-section of the working medium conveying tube or other fluid guiding structures, the liquid refrigerant can be conveyed to a level above the heat exchanger from where it is distributed to the evaporator structure by gravity. In this way, a pump is realized which transports the liquid refrigerant specifically into the higher evaporator structure. The mechanical energy required for this purpose is drawn from the thermally driven bubble formation and the resulting increase in the volume of the refrigerant. This virtually does not reduce the efficiency of the evaporation process since the mechanical energy required to pump a quantity of refrigerant to be evaporated is only a negligible fraction of the amount of heat converted. For example, for 1 gram of water raised by 0.1 meter, 0.001 joules of mechanical energy is required compared to 2400 joules/gram of evaporation enthalpy. It is also possible to combine a wetting of the evaporator structure from below and above. When wetting from above, the driving force of the rising gas bubbles is used to sprinkle the evaporator structure with working fluid from above. This can be done, for example, by means of a distribution network as a distributor structure, which ends specifically above the evaporator structure or its parts which form the heat transfer surface and is acted upon from above. For this purpose, the distributor structure should be sufficiently porous to allow the vapor of the working fluid present in the gas bubbles to flow to the adsorber without entraining the liquid. The buoyancy force of the gas bubbles can also be used to move elements such as valves, flaps and flow carriers.

The method according to the invention for operating an air-conditioning machine according to the invention comprises the following method steps:
- generating and/or introducing gas bubbles into the working fluid by means of the bubble generation structure in the working medium reservoir,
- wetting the heat transfer surface of the evaporator structure with working fluid entrained by gas bubbles rising in the working fluid and spraying in the spraying region, and
- cooling a coolant flowing through the coolant duct by evaporation of the working fluid wetting the heat transfer surface.
It is thus possible to realize an efficient cycle process of a refrigerating machine or a heat pump.
If in a subsequent method step the desorbed working fluid is condensed on the evaporator structure, an additional module forming a condenser can be dispensed with. The operation of the evaporator structure of an air-conditioning machine according to the invention is possible as both a pure evaporator and a combined evaporator/condenser in one component. In the latter mode of operation, the working fluid condenses on the structures through which the fluid flows actively, i.e. the coolant duct, of the evaporator structure, wherein excess condensate can drip off from the unflooded evaporator structure and collect in the working medium reservoir in which the second structure, i.e. the bubble generation structure, is located. An advantage of this

design is that even with increasing refrigerant liquefaction, a constant condensation surface is available and all working fluid, even if it condenses at undesirable points, can be reactivated or vaporized, since the working medium reservoir is preferably located at the bottom of a component which spatially encloses the working fluid and its vapor.
Less than 5 percent of the heat energy amount extracted from the coolant when cooling the coolant flowing through the coolant duct, i.e. a coolant circuit, e.g. a cold water circuit, can be advantageously used to generate the gas bubbles. The bubble generation structure, by means of which bulk boiling is generated is characterized by the fact that high heat flux density in the form of wall overheating of more than 10 Kelvin can be applied locally to a very limited extent. The heat and/or energy flow generated in this way from the bubble generation structure into the working fluid can be generated by thermal or electrical energy or by measures such as vibration, ultrasound or microwaves. The energy supply is designed in such a way that the heat input into the liquid refrigerant remains low and is limited to the generation of bubbles. Significantly less than 5 %, rather less than 1 %, of the thermal energy extracted from the cold water circuit, for example, should be used as energy for the bubble generation.
In addition to supplying energy to the bubble formation structure via the coolant circuit, available heat for gas bubble formation can be supplied alternatively or additionally at other temperature levels, i.e. at different temperature levels to the temperature level of the coolant circuit. When using an electrically supplied heat source or also the other mentioned options of the embodiments of the bubble formation structure, a significantly higher temperature level and thus a higher wall overheating can also be generated than the wall overheating on the

heat transfer surface of the evaporator structure, which is intended for refrigerant evaporation and wetted with a thin film of the working fluid. This heat supply at a higher temperature level causes only a very low heat input. A good thermal separation of the areas of high wall overheating from the other evaporation areas, in particular the evaporator structure, is here provided.
The energy used to generate the gas bubbles is advantageously supplied discontinuously to the bubble generation structure by means of a power control module. With discontinuous supply, the energy required to generate the bubbles is supplied in phases, in pulsating fashion and/or according to process requirements with controlled power.
Special embodiments of the present invention are explained in more detail below with reference to the enclosed drawings, wherein:
Figure 1 shows an embodiment of an air-conditioning machine
according to the invention, the bubble generation structure of which has a fluid-guiding pipe.
Figures 2a and 2b show an embodiment of an air-conditioning machine according to the invention, the bubble generation structure of which has electrical heating means.
Figure 3 shows an embodiment of an air-conditioning machine
according to the invention, the bubble generation structure of which comprises means for introducing a two-phase flow of the working fluid into the working medium reservoir.

Figure 4 shows an embodiment of an air-conditioning machine
according to the invention, which provided in the spraying region a distributor structure for collecting working fluid entrained by the gas bubbles and for distributing the working fluid on the evaporator structure and provides a working medium conveying tube.
Figure 1 shows an embodiment of an air-conditioning machine 1 according to the invention, the bubble generation structure 2 of which has a fluid-guiding pipe 3. For this purpose, the bubble generation structure 2 arranged in the area of the working medium reservoir 5 is partially flooded by working fluid 7 collected in the working medium reservoir 5. In the structure area formed by the bubble generation structure 2, strongly spraying gas bubbles 8 are specifically generated in the working fluid 7. Working fluid 7 carried along by gas bubbles 8 rising in the working fluid 7 is sprayed beyond the surface 9 of the working fluid 7 in the working medium reservoir 5 and into a spraying region of the working fluid 7. A refrigerant flows through the fluid-guiding pipe 3, the temperature of which is sufficient to introduce sufficient heat energy into the working fluid 7 to produce the gas bubbles 8 by bulk boiling.
An evaporator structure 10 is arranged in the spraying region above the working medium reservoir 5 and the bubble generation structure 2 arranged therein in partially flooded fashion. The evaporator structure 10 is formed by a pipe forming a coolant duct 11. The evaporator structure 10 has a heat transfer surface 13 which is formed by a porous material (porous layer) and which is wetted with a working fluid film by the entrained working fluid 7. The latter is symbolically represented by the gas bubbles 8 impinging on the evaporator structure 10. The evaporator structure 10 is a heat exchanger which allows a flat wetting

with thin working fluid films. The working fluid 7 of the working fluid film evaporates, thus cooling the coolant duct 11 and the coolant flowing through the duct. In the illustrated design variant intended for adsorption refrigerating machines and adsorption heat pumps, the two structures through which the fluid flows, namely the evaporator structure 10 and the bubble generation structure 2, are arranged spatially one above the other and can act as evaporator and condenser in cyclic alternation.
The partially flooded bubble generation structure 2, which is based in this embodiment on pipe geometries, transfers heat from the coolant flowing through it to the working fluid 7 and can therefore also be described as a lower heat exchanger. The two heat exchangers can be connected hydraulically in series or in parallel. The drawings only outline the connections of the coolant duct 10 and of the fluid-guiding pipe 3, which also conducts coolant.
In some embodiments of the invention, the bubble generation structure 10 can be designed with different gap distances of the grooves 15. A larger overheating can occur between narrower gap distances, as a result of which the generation of the gas bubbles 8 can be localized to certain parts of the longitudinal extension of the fluid-guiding pipe 3. The gap distances of the grooves 15 are here advantageously in a range of less than 1 mm. The grooves 15 thus form surface structures to increase the heat transfer to the working fluid. In other embodiments of the invention, the increase in the heat transfer to the working fluid can also be achieved by round or flat pipes arranged close to one another as well as by deflections, so that a larger local heat input occurs. Furthermore, a change in the surface condition, e.g. hydrophilic/hydrophobic, can support the gas bubble separation. The

partial flooding of the bubble generation structure 2 ensures that a sufficiently large working fluid reservoir 5 is available, from which the working fluid 7 is ejected and can thus wet the evaporator structure 10, which is arranged higher up.
As an alternative to the illustrated embodiment of the evaporator structure 10 formed as an upper heat exchanger with a pipe/channel through which coolant flows and on the outer surface of which a porous structure is applied, good wetting behavior can also be achieved by a surface treatment of the heat transfer surface of the evaporator structure. Porous structures have the advantage that they prolong the residence time of the working fluid, but must be thermally well connected to the heat emitting pipe, i.e. the coolant duct, and should only have a small thickness of less than 5 mm. Examples of porous structures are metallic fibers, sponges and/or foams. The advantages of these porous structures are the high specific surface areas, which allow good absorption of the spraying working fluid, the good working fluid distribution due to capillary action and the increased thermal conductivity due to the metallic porous structure compared to the thermal conductivity of pure water.
In the illustrated embodiment, the bubble generation structure 2 is incorporated into the working fluid sump, i.e. the working medium reservoir 5, but can also be supplied with working fluid 7 from a working fluid pool by means of capillary structures, for example. If the evaporator structure 10 is used alternately as evaporator and condenser, the working fluid sump can serve as condensate collection area. When used in parallel, the condensate is supplied from the condenser via a throttling element. The pressure difference present here, which is about 10 to 50 mbar, can also be used to generate

spraying gas bubbles 8 by selectively introducing the two-phase flow. The working medium reservoir 5 and the bubble generation structure 2 of the heat exchanger concept according to the invention are preferably arranged at the bottom of a sorption module 17, i.e. below an evaporator structure. This has the advantage that all working fluid 7 dripping off during condensation collects at the bottom of the working fluid sump where it can be evaporated again. Consequently, working fluid 7 cannot be lost, i.e. can get to places where it is difficult to activate/evaporate.
Figures 2a and 2b show an embodiment of an air-conditioning machine 1 according to the invention, the bubble generation structure 2 of which has, for example, electrical heating means (pins) for supplying heat to the working fluid 7. These heating means, e.g. formed by electrical resistors, represent boiling structures 20 and are arranged at the bottom of the working medium reservoir 5 so that boiling areas are formed there. The figures show two different arrangements of boiling areas and evaporator structures 10. In Figure 2a, the evaporator structure 10 is arranged flat above the working medium reservoir 5. The heating means are distributed over the entire surface of the bottom of the working medium reservoir 5. The evaporator structure 10 has cooling fins 22 distributed evenly along its coolant duct 11. In figure 2b, the heating means of the bubble generation structure 2 are only arranged in the areas with free channel cross-sections of the evaporator structure 10 at the bottom of the working medium reservoir 5. They thus form locally arranged boiling structures. The evaporator structure 10 has several partial evaporators, each with a coolant duct 11 comprising cooling fins 22. The areas between the partial evaporators are referred to as free channel cross-sections. The heating means can also be distributed in the working medium reservoir or introduced in the form of

a heat exchanger. Heating takes place from the underside or the bottom of the working medium reservoir 5. In addition to the two-dimensional thermal heat supply, e.g. small electrical heating elements and/or heat pipes could be integrated in the individual pins. If the required energy for the as bubble formation is not supplied by a cold water circuit, the bubble generation structures 2 should be thermally insulated.
In this embodiment, too, the heat exchanger to be wetted, i.e. the evaporator structure 10, is easily accessible above or to the side of the bubble generation structure 2. The evaporator structure 10 is
characterized by very good wetting behavior. This can be achieved, for example, by mechanical processing in the form of grooves, pins, specifically generated roughness and/or by a hydrophilic or contact angle-reducing surface coating and/or chemical pretreatment.
Figure 3 shows an embodiment of an air-conditioning machine 1 according to the invention, the bubble generation structure 2 of which has means for introducing a two-phase flow 30 of the working fluid 7 into the working medium reservoir 5. In this embodiment, bulk boiling and the associated spraying of the working fluid 7 are not initiated by a completely or partially flooded structure 35 for heating the working fluid 7, but e.g. by feeding the condensate backflow from a condenser. The rising vapor or gas bubbles 8 cause the working fluid 7 to be sprayed and the evaporator structure 10, which is not flooded and carries the cooling liquid, or its heat transfer surface to be wetted with a film 31 of working fluid. The means for introducing a two-phase flow 30 of the working fluid are designed as a pipe provided with perforations. The structure 35, e.g. a pipe carrying a coolant, is arranged in the illustrated embodiment in flooded fashion in the working medium reservoir 5. This

pipe can be used to preheat the working medium 7 in the working medium reservoir 5.
Figure 4 shows an embodiment of an air-conditioning machine 1 according to the invention, which provides a distributor structure 40 in the spraying region to collect working fluid 7 entrained by the gas bubbles 8 and to distribute the working fluid over the heat transfer surface of the evaporator structure 10, and to provide a working medium conveying tube 42. The working fluid 7 carried along by the gas bubbles 8 does not wet the heat transfer surface of the evaporator structure 10 directly, as is the case with the embodiments of figures 1 to 3, or only partially wets it directly, but the wetting is generated in channeled fashion by a distribution system 44 of the distributor structure 40. The evaporator structure 10 has two partial evaporators, each of which is formed by a coolant duct 11 with fins 22 extending parallel and forming heat transfer surfaces. The heat transfer surface of the evaporator structure 10 can also be formed, for example, only by the surface of the coolant duct 11. The distributor structure 40 has a distributor cap designed as a splash guard 45 for the working fluid and the distribution system 44 designed e.g. as a fabric and/or a wire structure for the distribution of the working fluid.
The funnel-shaped working medium delivery tube 42 (funnel shape) serves to exploit the buoyancy force of the gas bubbles 8 in order to spray or sprinkle the evaporator structure 10 with working fluid 7 from above. For this purpose, the wide, open filling end 47 of the funnel shape is immersed in the working fluid 7 in the working medium reservoir above a heating means forming the bubble generation structure 2. The heating means transfers the heat into the working fluid 7 for gas bubble generation. The gas bubbles 8 rising above the heating means in the

working fluid 7 are trapped by the funnel shape and lead to the working fluid 7 being sprayed out of the narrow open end 48 of the funnel shape. The working fluid thus sprayed into the spraying region is deflected downwards by the distributor cap. This leads to a corresponding extension of the spraying region to the area of the distribution system 44 and the evaporator structure 10.
The invention relates to an air-conditioning machine 1 with an evaporator structure 10 forming a heat transfer surface 13 and a working medium reservoir 5 containing a working fluid 7, wherein the evaporator structure 10 has a coolant duct 11 and to a method for operating it.
A bubble generation structure 2 is here provided, wherein the bubble generation structure 2 is arranged in the region of the working medium reservoir 5 in such a way that is at least partially flooded by the working fluid 7 and/or can be wetted with working fluid 7, and wherein the evaporator structure 10 is arranged in a spraying region of the working fluid 7 in such a way that the heat transfer surface 13 is wetted with a working fluid film 31 by working fluid 7 that is carried along by gas bubbles 8 which can be generated and/or introduced in the working fluid 7 by the bubble generation structure 2 and are rising in the working fluid 7.
It goes without saying that the invention is not limited to the illustrated embodiments. Therefore, the above description should not be considered limiting but explanatory. The following claims should be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the claims and the above description define “first”

and “second” embodiments, this designation serves to distinguish between two similar embodiments without determining a ranking order.

WE CLAIM:
1. Air-conditioning machine (1) comprising an evaporator structure
(10) forming a heat transfer surface (13) and a working medium
reservoir (5) containing a working fluid (7), the evaporator
structure (10) having a coolant duct (11), characterized in that
a bubble generation structure (2) is provided, wherein the bubble generation structure (2) is arranged in the region of the working medium reservoir (5) in such a way that it can be at least partially flooded by working fluid (7) and/or wetted with working fluid (7) and wherein the evaporator structure (10) is arranged in a spraying region of the working fluid (7) in such a way that the heat transfer surface (13) can be wetted with a working fluid film (31) by working fluid (7) that is carried along by gas bubbles (8) which can be generated and/or introduced in the working fluid (7) by the bubble generation structure (2) and which are rising in the working fluid (7), wherein the bubble generation structure (2) has a fluid-guiding pipe (3) for generating the gas bubbles (8) by means of bulk boiling, and the fluid-guiding pipe (3) and the coolant duct (11) are arranged in series one behind the other in a coolant circuit.
2. Air-conditioning machine (1) according to claim 1, characterized in that the bubble generation structure (2) further has at least one electrical heating means and/or one heat pipe and/or means for mechanically generating the gas bubbles (8).
3. Air-conditioning machine (1) according to any of claims 1 to 2, characterized in that the bubble generation structure (2) has a pipe deflection and/or surface structures (15) for increasing a

heat transfer to the working fluid (7) and/or for improving a bubble detachment of the gas bubbles (8) and/or in that the fluid-guiding pipe (3) has an inhomogeneous surface condition, in particular partial surface insulations and/or alternately hydrophilic and hydrophobic regions.
4. Air-conditioning machine according to any of claims 1 to 3, characterized in that the bubble generation structure (2) has means for introducing a two-phase flow (30) of the working fluid (7) that contains the gas bubbles (8) into the working medium reservoir (5).
5. Air-conditioning machine (1) according to any of claims 1 to 4, characterized in that the evaporator structure (10) has fins (22) and/or ribs arranged on the coolant duct (11) and/or in that the coolant duct (11) is at least partially plate-shaped and/or in that the coolant duct (11) is at least partially designed in the form of pipes running parallel to one another.
6. Air-conditioning machine (1) according to any of claims 1 to 5, characterized in that a surface structuring and/or a hydrophilic coating and/or a porous layer is applied to the heat transfer surface (13) of the evaporator structure (10).
7. Air-conditioning machine (1) according to any of the claims 1 to 6, characterized in that the working fluid has a density quotient between about 4000 and about 60000 or
in that the working fluid has a density quotient of more than about 4000 or more than about 7000 or more than about 12000, or

in that the working fluid has a density quotient of less than about 55000 or less than about 25000 or less than about 14000.
8. Air-conditioning machine (1) according to any of claims 1 to 7, characterized in that the working fluid (7) contains or consists of water and/or ethanol and/or methanol.
9. Air-conditioning machine (1) according to any of claims 1 to 7, characterized in that porous particles are introduced into the working fluid (7) and/or in that fabric structures and/or wire structures are arranged in the working medium reservoir (5).
10. Air-conditioning machine (1) according to any of claims 1 to 9, characterized in that means are provided in the spraying region for expanding and/or deflecting the spraying region, in particular a distributor structure (40) for collecting working fluid (7) entrained by the gas bubbles (8) and for distributing the working fluid (7) on and/or over the evaporator structure (10) and/or a working medium conveying tube (42) which dips with an open end into the working medium reservoir (5).
11. Method for operating an air-conditioning machine (1) according to any of claims 1 to 10, comprising the method steps of
- generating and/or introducing gas bubbles (8) in the working fluid (7) by means of the bubble generation structure (2) in the working medium reservoir (5), which has a fluid-guiding pipe (3) for generating the gas bubbles (8) by bulk boiling, the fluid-guiding pipe (3) and the coolant duct (11) being arranged in series one behind the other in a coolant circuit,

- wetting the heat transfer surface (13) of the evaporator structure (10) with working fluid (7) that is carried along by gas bubbles (8) rising in the working fluid (7) and spraying into the spraying region, and
- cooling a coolant flowing through the coolant duct (11) by evaporating the working fluid (7) wetting the heat transfer surface (13).

12. Method according to claim 11, characterized in that, in a subsequent method step, the desorbed working fluid is condensed on the evaporator structure (10).
13. Method according to any of claims 11 or 12, characterized in that less than 5 per cent of the amount of thermal energy which is extracted from the cooling fluid when cooling the cooling fluid flowing through the coolant duct (11) is used to generate the gas bubbles (8).
14. Method according to any of claims 11 to 13, characterized in that the energy used for generating the gas bubbles (8) is supplied discontinuously to the bubble generation structure (2) by means of a power control module and/or is controlled and/or feedback-controlled on the basis of the power requirement of the adsorber.
15. Method according to any of claims 11 to 14, characterized in that the wetting of the heat transfer surface (13) of the evaporator structure (10) is additionally effected by absorbing the working

fluid from the working fluid sump by means of capillarily active distribution structures.