Patent Grant
8074470
The invention concerns a sorption cooling element with a regulator organ and with a gas-tight multi-layer film for cooling wherein by vapourising a working agent and subsequent sorption of the working agent vapour in a sorption agent under vacuum cold is produced. At the same time the evaporator has a flexible construction to enable to adjust it to suit various cooling tasks.
Sorption cooling elements are devices, in which a solid adsorption agent in the form of vapour sorbs a second agent, the working agent, which boils at lower temperatures while releasing heat (sorption phase). In doing so the working agent is evaporated in an evaporator while taking up heat. Once the adsorption agent is saturated, it can be again desorbed at higher temperature by heat input (desorption phase). At the same time working agent evaporates from the adsorption agent. The working agent vapour can be reliquefied and subsequently evaporated again.
Adsorption devices for cooling with solid sorption agents are known from EP 0 368 111 and DE-OS 34 25 419. Sorption agent containers, filled with sorption agents, draw off the working agent vapour emerging in an evaporator and sorb it while releasing heat. At the same time the sorption heat has to be removed from the sorption agent. The cooling devices can be used for cooling food and keeping it hot in thermally insulated boxes.
WO 01/10738 A1 describes a self-cooling beverage can wherein the evaporator is provided within and a sorber outside of the can. The cooling is started by opening a vapour channel between the evaporator and the sorber. The cold, produced in the evaporator, is transferred over its surface to the beverage to be cooled inside the can. The heat emerging in the sorption agent is stored in a heat buffer. The self-cooling beverage can is strongly modified in comparison with a conventional can and is expensive to produce.
Further, more theoretical configurations of self-cooling barrels are compiled in WO 99/37958 A1. None of the devices can be cost-effectively materialized and manufactured.
Finally, U.S. Pat. No. 6,474,100 B1 describes a self-cooling cooling element on the exterior of a bag for liquids or loose goods. On this occasion the sorption agent is enclosed in a flexible, multi-layer film. The contact with the hot sorption fill is reduced to a minimum by insulating and flow materials as well as by heat-storing masses situated between them. The temperature equalization between the hot sorber fill and the cold evaporator, which lie against one another with a large surface, has to be reduced by using an elaborate insulation.
DE 10 2005 034297 A1 describes a sorption cooling element with a gas-tight film wherein a sorption agent is filled in a gas-tight bag for the sorption agent, that for the purpose of starting the cooling function is cut by a cutting tool. A control of the cooling capacity is thus impossible.
The object of the invention is to provide cost-effective sorption cooling elements for single-use, wherein the cooling can be controlled.
According to the invention the individual components of a cooling element are so sealed under vacuum in a gas-tight, flexible multi-layer film that the working agent vapour, flowing from the liquid working agent, can flow to the sorption agent only through the working agent vapour channel and the regulator organ. The deforming forces, produced by the external air pressure, have to suffice to nestle the multi-layer film around the individual components in such a manner that no path will remain open for the working agent vapour to bypass the regulator organ. Thus the individual components do not have to be joined gas-tight with one another. They only need to be placed into a bag, produced from the multi-layer film and fixed until the bag under the affect of the vacuum abuts firmly against the components and only the working agent vapour channel remains open.
According to the invention the regulator organ can be easily opened and closed by deforming the multi-layer film. Elaborate vacuum ductings are therefore not required.
In a particularly advantageous manner the regulator organ can be formed from a valve seat and a sealing plane matching it. The regulator organ can be opened and closed through the multi-layer film via a lever mechanism and, if required, also used to control the performance. There are no further spring elements required to press the sealing plane against the valve seat when the flexible film so abuts against the sealing plane that the external air can suitably effectively act upon the valve.
In an advantageous manner the hoses used for the working agent vapour channels are such, which withstand the external pressure, but not an additional pressure, e.g. one produced by a squashing tool, that acts externally on the multi-layer film and so strongly squashes the hose that the flow path would be blocked.
A further very cost-effective regulator organ is formed when the sorption agent is sealed within a separate bag. If this bag is pierced through by a sharp-edged cutting tool at the point of contact with the working agent vapour channel, the regulator organ will also open. The cutting tool can, of course, be placed also between the multi-layer film and the separate bag. For triggering the external film has to be deformable at the relevant positions without losing its air-tight nature.
The regulator organ can be expanded in addition to the actual closing element also by a thermostat valve. With the aid of the thermostat valve the temperature of the evaporator can be held at a control temperature. At higher temperatures the thermostat valve opens the path of the working agent vapour to the sorption agent, at lower temperatures the thermostat valve closes the path.
All known elements, which are subjected to change their displacement in case of a temperature change, are suitable as a thermostat. The best known ones are expanding bodies and bimetals. Memory alloys can be also advantageously used. In a particularly cost-effective manner bimetallic spirals can be used for the regulator organ. By virtue of this temperature fluctuations of less than 0.1 K can be achieved.
By building in a thermostat valve the cooling elements can be particularly advantageously used for the temperature-managed cooling of transport insulation containers. Insulated transport containers serve, for example, for the transporting of foodstuff or pharmaceutical products between +2° C. and +8° C. Insulated transport containers, fitted with the cooling elements according to the invention, can be stored for any period. To start the cooling function merely the regulator organ has to be opened and the product to be cooled packed in the interior. The thermostat valve controls the interior for several days within a narrow temperature range, independently from the prevailing external temperature. Because the insulation container can be made from an inexpensive material (e.g. polystyrene), a return transport, often expensive, can be dispensed with.
According to the invention all internal walls of an insulating container can be covered with evaporator surfaces. The temperature of the interior is then homogeneous even when the external temperature strongly fluctuates. Since the evaporator according to the invention has a flexible construction, at least one region of the evaporator can be a foldable one. If required, this region can be folded up and allow full access to the interior.
Under vacuum all flow channels to the sorption agent have to be retained. For this purpose spacers are provided, that let the working agent vapour flow unhindered away from the liquid working agent and at the same time let the cold surfaces contact the film with good thermal conductivity.
According to the invention for this purpose flexible plastic spacers are used, that are adapted to suit the respective cooling task. In any case, it is a prerequisite that the plastic spacers during storage would not release gas and would not have a deleterious affect on the vacuum. It is an advantage when as plastic polycarbonate, polyamide or polypropylene are use, as these materials can be heated to higher temperatures and degassed before or during the manufacturing processes.
Plastic spacers can be cost-effectively manufactured according to known manufacturing methods, like deep drawing, extrusion or thermal blow-moulding. In an advantageous manner care is taken during the manufacturing process that no materials, releasing gases afterwards, like plasticizers, are added.
In the thermal transport containers use currently the transported goods are cooled by ice batteries that have to be provided inside the container. As the size of these ice batteries is many times that of an evaporator according to the invention, either the internal volume is considerably reduced or a larger insulating container is required. Larger containers have, in turn, a greater external surface through which more heat flows into the interior that again has to be counteracted by larger ice batteries.
However, the fields of application are not limited to insulated containers. In principle any object can be fitted with cooling elements according to the invention. Advantageous is, for example, the cooling of tents, where complete tent walls can be replaced by the cooling elements according to the invention. The cooling of patients or injured people in a hot environment or the reduction of body temperature is just as possible as the use of cool vests, cool suits are breath coolers.
In principle they can be used anywhere where nowadays cooling batteries or ice batteries are used. When compared with cooling and ice batteries, the cooling elements according to the invention can be stored for any period of time and can be made to suit the cooling task, as the evaporator has a flexible construction.
During the sorption process sorption agents can achieve temperatures above 100° C. The multi-layer films, conventionally used in the packaging industry, are not always suited for such high temperatures. In particular polyethylene layers, used for sealing, become soft already at 80° C. and render the enclosure permeable under vacuum. In contrast to this, a sealing layer from polypropylene can withstand markedly higher temperatures. Their melting point is above 150° C.
In combination with high temperatures sharp edges, corners and tips of the granules of the sorption agent may cause inadmissible leakages in the films. This danger can be encountered by at least one polyester or polyamide layer within the multi-layer film. Polyamide films are especially resistant to tear and puncturing. The actual gas barrier is ensured by a layer of thin metal film or a metallized layer. For this purpose thin aluminum films with a thickness from 8 μm have proved themselves. Metallized plastic films are less dense. Nonetheless, in the case of short storage periods the use of these metallized films is also possible, especially since they can be more cost-effectively produced than metal films.
The individual layers of a multi-layer film are joined with one another using adhesives. Conventional adhesives contain solvents that during bonding are not completely removed from the adhesive coating. Over longer periods these solvents diffuse through the inside layers and compromise the vacuum within the cooling element. At higher temperatures, like those occurring in the sorption and manufacturing process of the cooling element, the diffusion is intensified. Therefore the adhesives used also have to be designed for high temperatures.
Advantageously, multi-layer films with a polyamide layer thickness of 12-50 μm, an aluminum layer thickness of 6-12 μm and a polypropylene layer thickness of 50-100 μm are used. Such films are used, for example, for the packaging of foodstuff, which after packaging are sterilized for preservation at temperatures above 120° C.
Multi-layer films according to the invention can be obtained, for example, from Wipf AG in Volketswil, Switzerland or from PAWAG Verpackungen GmbH, Wolfurt, Austria. When such films are used, cooling elements with a leakage rate below 10−8 mbarL/sec are achievable. Thus the storage life can be several years, without impairing the cooling ability.
The welding (sealing) of multi-layer films to form bags and the filling with loose goods, as well as the subsequent evacuation are state-of-the-art in the food industry. Therein numerous bag sizes and shapes are used. In particular flat bags, bags with pouring openings, bags with cardboard reinforcement, tear-open bags, bags with peel-effect for easy opening and bags with valves are to be mentioned. With their specific properties they all can have advantages for the cooling element according to the invention.
When filling the solid sorption agent into the bags, dust is produced, that settles on the internal surface of the film. Dust on subsequent sealing positions may lead to leakages if the layer of dust is too thick relative to the polypropylene layer. Polypropylene layer thicknesses of 50-100 μm are adequate to melt dust grains securely and vacuum-tight into the polypropylene layer.
When using films according to the invention, it is possible to envelop hot, sharp-edged and dust-releasing sorption agents without further protective intermediate layers directly under vacuum and store them over a period of several years, without external gases from the film material itself or through it reaching the cooling element that would impair the sorption reaction or completely prevent it.
As sorption agent preferably zeolite is used. In its regular crystalline structure it can reversibly sorb water up to 36% by mass. In the case of the application according to the invention the technically realizable water absorption is approx. 20-25%. Even at relatively high temperatures (above 100° C.) zeolites still have a considerable capacity to sorb water vapour and therefore are particularly suitable to be used in accordance with the invention.
Zeolite is a crystalline mineral that contains silicon and aluminum oxides in a framework structure. The very regular framework structure contains hollow spaces, in which water molecules can be sorbed while releasing heat. Within the framework structure the water molecules are subjected to strong field forces, the strength of which depends on the quantity of water already contained in the framework structure and the temperature of the zeolites.
Natural zeolite types, as they occur in nature, absorb considerably less water. Only 7-11 g water is sorbed per 100 g natural zeolite. This reduced water absorbing capacity is due to the specific crystal structure on the one hand and non-active impurities of the natural product on the other. Therefore for cooling elements, that over longer cooling periods can release the sorption heat through the enclosure, synthetic zeolites with their greater sorption capacity are preferred. For cooling elements with high cooling capacity and/or short cooling period, wherein the sorption agent remains relatively hot, according to the invention natural zeolites are also used. At high sorption agent temperatures synthetic zeolites are namely no longer more advantageous than natural ones. Typically, with a restrained release of the sorption heat and associated high sorption agent temperatures above 100° C., merely 4-5 g water vapour per 100 g dry sorption agent is sorbed by both types. From the economical point of view for such application the natural representatives have a marked advantage, since their price is considerably lower.
Natural zeolites have a further advantage. The non-active admixtures are typically between 10 to 30%. Although they are not actively involved in the generation of the cold, they are heated up by the adjacent zeolite crystals. Thus they act as a built-in, cost-effective heat buffer. The result of this is that the zeolite filling will become less hot and consequently can absorb additional water vapours at lower temperatures.
Natural zeolite granules is made up from broken and squashed fragments and consequently has sharp and pointed geometrical shapes, which under vacuum and increased temperatures can pierce or cut through the multi-layer film.
Among the approx. 30 different, natural zeolites the following can be advantageously used as cooling element according to the invention: clinoptilolite, chabzite, mordenite and phillipsite.
Naturally occurring materials can be returned to the nature without burdening the environment. After their use in cooling elements natural zeolites can be used, for example, as soil improver, liquid binder or to improve the water quality in stagnant waters. Of the synthetic zeolite types the types A, X and Y are to be recommended, each in its cost-effective Na form.
In addition to the zeolite/water combination other solid sorption pairs can also be used in the cooling elements according to the invention. Particular reference is made to bentonite and salts that also represent combinations with the working agent, water. Active carbon, in combination with alcohols, can be also an advantageous solution. Since these material pairs also operate in vacuum, they can be welded into the multi-layer film according to the invention.
According to the invention the amount of sorption agent is to be so measured and provided, that the water vapour flowing in has to overcome only a minimal pressure drop within the sorption agent. In this conjunction the pressure drop should be, particularly when water is the working agent, less than 5 mbar. In addition the sorption agent has to be able to offer sufficient surface to the working agent vapour for settling. To ensure an even sorption within the sorption agent and a small pressure drop, sorption agent granules have particularly proved themselves. Granule diameters between 2 and 10 mm provide the best results. These can be packed without any problem and after evacuation form a hard, pressure resistant body and stable in its shape of the sorption agent, that retains the shape imposed by the evacuation. However, to enable to produce variable geometries with the sorption agent bodies with the stable shape according to the invention the sorption agent is filled into several regions connected only via vapour flow channels. In this case, provided the vapour channel has a flexible construction, the individual firm regions can be displaced relative one another, folded and stacked, for example to make use of narrow spaces yet enable a good airflow.
Advantageous are also zeolite blocks, pre-formed from zeolite powder and resistant to deformation, into which the flow channels can be moulded and their shape is made to suit the required cooling element geometry. The stable zeolite blocks can have hollow spaces in the region of the working agent vapour channel so that not to hinder the flow.
During the sorption reaction sorption heat is released that heats the sorption agent. At higher sorption agent temperatures the absorbing capacity for water is strongly reduced. To maintain a high cooling capacity over a longer period, it is sensible to cool the sorption agent.
When the sorption agent is in direct contact with the multi-layer film, the sorption heat occurring can be removed unhindered through the film to the exterior. As a rule, the heat is carried off to the ambient air. It is also very efficient to cool the sorption container with water.
Because the heat transfer to an airflow from the outside of the sorption agent bag is of the same order of magnitude as the heat transfer of the granules of a sorption agent on the inside of the bag, in principle large film surfaces without ribs are recommended, like for example cylindrical, sheet or tubular geometries. Since zeolite granules have a particularly low heat conduction, the sorption containers are to be so designed, that the average heat conduction path within the sorption agent would not exceed 5 cm.
All applications are characterized in that a cooling element is stored over an unspecified period at any ambient temperature. At the time of commencement of the cooling effect the regulator organ is opened. Beginning from this point in time the working agent vapour can flow to the sorption agent and settle on it. The sorption agent becomes hot because it liquefies and adsorbs the vapour inside its crystal structure. The evaporator cools off and can be used as a cold source. In the case of cooling tasks taking place rapidly (e.g. cooling of a liquid), as a rule the period is not sufficient to cool the sorption agent with any consequence. Therefore the absorbing capacity for the working agent vapour is limited due to the hot sorption agent temperatures if additives do not act as heat buffer.
In the case of cooling elements with longer cooling period the sorption agent can release heat through the multi-layer film and depending on the application transfer this heat at higher temperature level to a product that has to be kept warm.
When being used in the deep-freezing range, adequately dimensioned flow channels and possibly additives, lowering the freezing point, are to be considered in the working agent. With these additives evaporation temperatures below 0° C. can be achieved even when the working agent is water, without the water freezing.
Particularly when being used in temperature-managed transport it may happen that the ambient temperatures are below the control temperature of the thermostats. With falling temperatures first the thermostat closes and the active cooling of the cooling element is interrupted. As soon as the temperature in the evaporator falls below 0° C., if pure water is used, it would solidify and release the solidification heat at 0° C. to the interior. Provided the water fill is adequate, the internal temperature will not fall below the freezing point.
For transport tasks, where 0° C. is too low, instead of pure water an aqueous, eutectic mixture may be used, the transformation point of which is set slightly below the control temperature of the thermostats (e.g. transformation point 3-4° C. and a thermostat control temperature of 5° C.). Thus, provided the temperature of the interior is above the control temperature of the thermostats, in the case of this configuration working agent will evaporate from the aqueous mixture and cool the interior. At temperatures below the control point the thermostat closes the vapour channel. When now the external temperature falls below the transformation point and heat keeps flowing from the mixture into the environment, the temperature falls in the evaporator until the mixture falls below the transformation point. The mixture is now converted and releases heat to the interior. Consequently, in the case of appropriate dimensioning a cooling element according to the invention can cool not only at a constant temperature, but provide transformation heat when it falls short of this temperature and keep the transported goods at least at the transformation temperature.
For applications, wherein no enlargement of the evaporator volume by additional eutectic mixtures is desired, according to the invention a separate heat source may also be provided between the evaporator and the insulation of the container. In the simplest case this heat source itself does not need its own control, as its excess heat will be carried away by its thermostatic control before the higher temperatures would reach the transported goods. The capacity of this heat source should be so calculated, that its heat emission should be sufficient to keep the insulated container at the expected lowest ambient temperatures at least at the required temperature of the internal space. According to the invention the heat source does not have to be homogeneously arranged either within the insulated container. It is rather sufficient to have a point-by-point heat release, since the evaporator acts as a steam heating that distributes and controls the amount of heat absorbed by the heat source over the surface of the evaporator. Water, evaporating in thermal contact with the heat source, condenses within the evaporator structure on the cooler surfaces and heats them to the level of the site to be evaporated. Thus the temperature of the entire evaporator remains homogeneous. As soon as the temperature on the thermostat exceeds its control temperature, the regulator organ opens and lets the working agent vapour flow into the sorption agent until the control temperature is reached again.
For this purpose heating elements, charged by batteries transported with them, are, of course, extremely well suited. In the case of this type of heat source the heating element can be controlled also by an additional, electric thermostat.
In principle all known exothermally operating chemical reactions, which are used to keep bodies warm (e.g. open flame, catalytic combustion, etc.) are suitable as separate heat sources. Particularly advantageous is the oxidation of iron powder with the oxygen of the air in the presence of water, salts and active carbon. The slowly progressing oxidation requires only little oxygen that either diffuses into the interior through the usually porous insulation walls or is directed from the outside onto the heat source via suitably dimensioned openings.
According to the invention the output of these heat sources can be controlled by means of the air supply (oxygen supply). When no heat is required, the air supply can be completely stopped, but further increased when falling below a limit temperature. By controlling the air supply both the cooling capacity of the cooling element and the heating capacity of the heat source can be reduced.
Without control a once activated heat source would heat even when the ambient temperature is again well above the desired temperature of the internal space. In these cases the cooling element would have to carry away the heat coming from the outside as well as the reaction heat released by the heat source. Because during a transport lasting several days the ambient temperatures can fall and rise several times above and below the required temperature of the internal space, a control of the heat source is a sensible one.
According to the invention the air supply for the oxidation process of the heat source can be regulated via its own air thermostat that, depending on the ambient temperature, enables a greater or lesser air supply to the heat source. Advantageously the heat source is inside the insulated container, distributed on one or several surfaces between the inside wall of the insulating box and the evaporator. The air thermostat can comprise a bimetallic element that above a limit temperature closes the external end of an air channel. To enable the flow of oxygen-deficient air from the interior, the airtight bag can be provided with an opening, through which used air can escape into the interior of the insulating container. From there the air can reach the outside through the natural pores of the insulating material, or appropriate outlet openings are made to allow the exchange of air and are deliberately opened when starting the heat element. The deliberate opening of the openings could also prevent during storage the unintentional automatic activation of the heat source at low storage temperatures.
Ideally the inlet opening and the outlet opening are at different height levels. In this case a natural air movement will take place and when the air thermostats are open, supported by the thermal lift of the air heated on the heat source, new oxygen always is transported to the embedded iron powder.
Ideally the supply of fresh air through the air thermostats will commence when the ambient temperature falls below the average value of the control temperature set. The lower the external temperature falls, the wider the air thermostat should open so that to increase the output of the heat source. At the same time a precise control of the output is not necessary, as the precise temperature control is assumed by the thermostat valve in the cooling element. A too high an output of the heat source is carried away by the cooling element before the useful volume would be affected by it. Therefore the heat source is preferably provided between the wall of the insulating container and the evaporator surface.
Only in rare cases is the working agent present in the evaporator in a free form. In most cases it is distributed in an absorbent non-woven fabric and fixed by hygroscopic forces. Particularly cost-effective materials are absorbent papers, like they are used in many cases in households and industry to absorb liquids. The water-storing non-woven fabrics, just like the plastic spacer or natural zeolite, must not release gases under vacuum and higher temperatures. For this purpose particularly suitable are commercially available polypropylene micro-fibres. These fibres are prepared to absorb water and do not release gases that would interfere with the vacuum.
In an advantageous manner in the region of the heat source a somewhat greater amount of non-woven fabric is allocated to the evaporator because more liquid working agent is available there for the vapour heating. In addition, the geometry of the non-woven fabric can be so designed, that a decreasing amount of working agent will be continued to be supplied by virtue of the suction effect of the non-woven fabric.
A further solution is the fixing of the working agent in organic bonding agents, like “Water Lock” of the company Grain Processing Corp, USA. In an advantageous manner several of the above mentioned steps can be combined.
To maintain the required cross-section of the vapour channel between the evaporator and the sorption agent fill despite the external air pressure, according to the invention the vapour channel can be formed and stabilized by several layers of a plastic net. By doing so, adequate cross-section remains for the flow between the net structure. When using polypropylene nets higher temperatures can be permitted without releasing gases. By virtue of the flexible structure of the nets they optimally fit to suit the relevant geometry.
According to the invention the evaporator can be of any shape and made from various materials. Technically it is necessary that during the cooling process a sufficiently large opening remains in the working agent vapour channel for the escape of the water vapour, the working agent in the liquid state remains at the position to be cooled, a carrying away of liquid components is prevented and a good thermal bonding to the object to be cooled is possible.
As a rule the sealing of the multi-layer film is carried out thermally by pressing hot sealing beams on the external film surfaces until the superposed sealing layers become fluid and melt with one another.
The welding process can be carried out inside a vacuum chamber under vacuum. At the same time in this case all gases, which would prevent the subsequent adsorption process, are evacuated in the vacuum chamber from the water and all other further components.
It is also advantageous to evacuate the bag without a vacuum chamber by means of a suction device at a position of the sealing seam that is still open. To keep the suction channel open, a polypropylene spacer, advantageously similar to the material of the structure is placed between the surfaces of the film, said spacer expanding the flow channel inside the cooling element. As soon as the evacuation is completed, the surfaces of the film, including the spacer, are heated by the sealing beams, until the sealing layer and the identical material of the spacer melt with one another and after cooling off produce a gas-tight joint.
FIG. 1—a cooling element according to the invention, still in the flat state, for the cooling of an insulated transport box,
a—a cooling element with almost identical construction, with a separate zeolite bag,
FIG. 2—the flexible evaporator of
FIG. 3—the cooling element according to
a—a heat source,
b—a heat source inside an insulated box,
FIG. 4—a thermostat valve,
FIG. 5—a regulator organ for a single-use cooler,
FIG. 6—a further configuration of an evaporator, illustrated sectioned, and
FIG. 7—a region of the sorption agent with three sorption agent bags.
The cooling element, illustrated in
For the production of the cooling element according to the invention the multi-layer films 7, cut to size, are pre-sealed segment by segment, fitted with the individual components and then welded in the region of the sealing seam 23 up to a small suction opening 40. To the suction opening 40 a vacuum pump is connected, that evacuates from the cooling element the air and gases that may be released. Following this the suction opening 40, through which a portion of a spacer 11 protrudes so that to keep the suction channel open, is heated by suitable welding beams to that extent, that the material of the spacer 11 melts with the sealing layer. Under certain geometric conditions it may be advantageous to evacuate the evaporator 2 and the sorption agent 1 at separate positions.
a shows variations, differing from the single-use cooler of
The manufacture of the single-use cooler according to
a shows an alternative embodiment of a heat source 48 in a gas-tight film enclosure 49 sealed on the edges, that has an entry opening 50 and outlet opening 51. The heat source 48 contains two paper bags filled with reactive iron powder mixtures 58, which upon entry of oxygen experience an exothermic reaction. To ensure air access, further flow paths are kept open inside the film enclosure 49. In the embodiment the flow paths are expanded by a flexible lattice 52. The entry opening 50 is joined in a gas-tight manner with a hose line 53, that at its external end can be closed off by an air thermostat 54. The outlet opening 51 is closed off by an adhesive tape. It is pulled off only to start the heat source 48. The air thermostat 54 can be also closed off by an additional enclosure (not illustrated) until it is used. The heat source is so dimensioned, that it can be folded in the centre and thus can cover two internal surfaces of an insulated box.
b shows the heat source 48 of
In the configuration shown the working agent vapour channel is formed by two layers of a net-shaped spacer 11. The woven fabrics 10 are in thermal contact with the flow channel 37.
Finally,
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 010 981 | Mar 2007 | DE | national |
| 10 2007 057 748 | Nov 2007 | DE | national |
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