METHOD FOR MAKING THE HEAT EXCHANGER OF A THERMAL ABSORPTION MACHINE AND THERMAL ABSORPTION MACHINE COMPRISING SUCH HEAT EXCHANGER

Description

[0001] This invention relates to the field of thermal machines for heat exchange. In particular, the invention relates to a method for making the heat exchanger of a thermal absorption machine.

[0002] The needs to reduce electricity consumption and the increasing demand for climate control for living areas over recent years has pushed the international research towards the study of more efficient systems and lower environmental impact.

[0003] The improvement of living conditions and, consequently, the need to guarantee greater comfort of the rooms causes an increase in energy requirements, in particular in the household and tertiary sectors.

[0004] Air conditioning is currently carried out almost exclusively by means of traditional fluid compression systems driven by electric motors which, however, have the drawback of poor environmental compatibility, as well being characterised by a high electricity consumption.

[0005] Another type of the prior art device is represented by the air-air heat exchange systems for the treatment of the air in buildings configured to operate at atmospheric pressure by operating a recovery of the heat and/or a treatment of the air inside the buildings which before being discharged outside the building (especially during winter) encounters the air arriving from the outside in a suitable heat exchanger to transfer a part of the sensitive heat by pre-heating it.

[0006] This second type of device has an open thermodynamic cycle type operation wherein the heat exchanger is more exposed to the impurities and any foreign bodies which are conveyed through the continuous flow of fluid which passes from the outside environment inside the system, with the risk of rapid deterioration which leads to a reduction in the efficiency of the heat exchanger.

[0007] In this context, the water vapour thermal absorption machines represent an important alternative, which is particularly suitable for the climate control of rooms, since they have a substantially different principle and operating mechanism which overcomes some of the above-mentioned drawbacks present in the types of devices described above.

[0008] In effect, the thermal absorption machines can also be activated with a heat source which has a low temperature, up to 50°C, rendering them particularly suitable for use in combination, for example, with a thermal solar system which allows the use of renewable solar energy, thus reducing the environmental impact and the load on the electricity network, especially during periods in which there is greater need for climate control of the rooms.

[0009] In more detail, absorption machines are thermal machine used for generating heat and cold which do not require fossil fuels or electricity for their operation.

[0010] Structurally, thermal absorption machines require for their operation the presence of the following elements: a thermal source, a capacitor, an evaporator, a bed of absorbent material and a heat carrier fluid.

[0011] The elements indicated above contribute towards defining a closed and sealed system, in such a way as to be able to operate with low absolute water vapour pressure (pressure values ranging from 8 mbar to 12 mbar). This type of device can operate both as a heat pump or as the chiller: in the first case the useful effect is represented by the heat introduced into the outside environment after the condensing process and after cooling of the absorbent bed (absorption heat); in the second case, the useful effect is represented by the evaporation heat of the fluid.

[0012] Despite the positive aspects, the still reduced diffusion of thermal absorption machines is linked to the limited efficiency levels of this type of device, which are less than those of the traditional compression heat pumps. The heat exchanger, that is to say, the component which replaces the traditional electrical compressor and where the absorption or desorption of the water vapour occurs on the porous material with the relative heat exchanges which allow the thermodynamic cycle, still currently has high resistances to heat exchange and mass.

[0013] Three different possible options are known for making the heat exchanger:

• heat exchanger immersed in a bed of granules of absorbent material;
• heat exchanger coated with a layer of absorbent material mixed with a polymeric binder;
• heat exchanger wherein the absorbent is synthesised directly on the surface.

[0014] However, each of these possible technical embodiments has negative aspects which considerably reduce the efficiency.

[0015] With regard to the first type, even though more simple in terms of construction, it is also characterised by the lowest efficiency due to the poor contact between the surface of the heat exchanger and the absorbent material.

[0016] The second type has a greater efficiency, however it has significant mechanical stability problems due to the rigidity of the coating obtained on the surface of the heat exchanger.

[0017] The third type guarantees the best results, however it has considerable construction difficulties relating to the costs, the instrumentation necessary to perform a chemical reaction directly on the surface of the heat exchanger and the limited thicknesses of absorbent material which can be obtained.

[0018] Consequently the result is that the thermal machines currently available are still cumbersome, heavy and with relatively low performance. Example of method in this field can be found in documents KR2010/0000093 and US2015/059578.

[0019] In this context, the technical purpose which forms the basis of this invention is to provide a method for making the heat exchanger of a thermal absorption machine which overcomes at least some of the above-mentioned drawbacks of the prior art.

[0020] In particular, the aim of this invention is to provide a method for making the heat exchanger of a thermal absorption machine which is able to provide a heat exchanger which improves the efficiency and the output of the current thermal absorption machines.

[0021] The technical purpose indicated and the aims specified are substantially achieved by a method for making the heat exchanger of a thermal absorption machine comprising the technical features described in one or more of the appended claims.

[0022] The invention describes a method for making the heat exchanger of a thermal absorption machine comprising the steps of: preparing an electrospinning system comprising a spinneret and a collector; installing a heat exchanger of a thermal absorption machine, made at least partly of metal material, at the collector of the electrospinning system; initialising at least one parameter of the electrospinning system and, finally, placing a layer of an absorbing material on a heat exchanger by electrospinning. Further features and advantages of the invention are more apparent in the detailed description below, with reference to a preferred, but non-exclusive embodiment of a method for making the heat exchanger of a thermal absorption machine, as illustrated in the accompanying drawings, in which:

• Figure 1 schematically shows a the electrospinning system which can be used for performing the method according to the invention;
• Figure 2 shows a block diagram relative to the method according to the invention.

[0023] In accordance with the method according to the invention, the aim is to make the absorber of a thermal absorption machine by means of an electrospinning process.

[0024] Electrospinning is a production process which allows continuous filaments of synthetic material to be obtained with an extraordinarily small diameter. With conventional spinning methods is possible to produce filaments with minimum diameters of a few microns, and sometimes with difficulty.

[0025] In order to produce continuous filaments with a smaller diameter it is necessary to use different production methods, wherein the filament being formed can be stretched with elongation forces which are as uniform and constant as possible, to prevent breakage.

[0026] The most promising technique in this context is electrospinning, wherein a polymer jet 6 is stretched inside a high electrical field.

[0027] The filaments produced in this way can reach diameters which are much less than those which can be obtained using traditional techniques.

[0028] Figure 1 schematically shows the basic components of an electrospinning system indicated generally with the numeral 1.

[0029] The electrospinning system 1 comprises a spinneret 2 and a collector 3.

[0030] A reserve of precursor material 4, either molten or in solution, is inserted inside the spinneret 2 to which an electric field is applied.

[0031] Raising the electrostatic potential applied increases the surface charge of the precursor material 4, until the moment in which, thanks to the surface charge acquired, the precursor material in the liquid state is able to overcome the surface tension which influences the shape and to adopt the shape known as Taylor cone 5, whose shape depends on the ratio between surface tension and electrostatic repulsion of the molecules present in the precursor material.

[0032] Due to the tip effect, there is a concentration of charges in the tip of the Taylor cone 5 and consequently the precursor material 4 tends to be ejected due to the attraction exerted by the electric field applied which is much stronger on the tip, where there is the greatest concentration of charges, rather than on the body of the Taylor cone 5.

[0033] The jet 6 ejected passes through two steps, a first step I in which, still in the liquid state, it proceeds linearly along the electric field applied in the direction of the collector, and a second step II in which, changing to the solid state, the charges present in the jet 6 migrate towards the surface of the fibre which has formed, causing, under the effect of the electric field applied, the curvature and a further thinning. The second step II continues until the fibre reaches the collector 3 where it is finally collected in the form of 'sheets' of non-woven fibres arranged randomly, thus obtaining a 'non-woven fabric' with good mechanical properties.

[0034] Figure 2 shows a block diagram of the method, indicated generally with the numeral 10, made according to the invention.

[0035] The method comprises a step 11 of preparing an electrospinning system 1 equipped with a spinneret 2 and a collector 3, for example as described above, by use of which an absorbent material is placed on the absorber of a thermal absorption machine.

[0036] The method then comprises a step for installing 12 a heat exchanger of a thermal absorption machine, made at least partly of metal material, at the collector 3 of the electrospinning system 1.

[0037] In this way, it is possible to coat the heat exchanger with an absorbing material directly spun from the electrospinning system on the metal parts of the surface of the heat exchanger.

[0038] According to a further possible embodiment, the electrospinning process can be performed on the collector 3 and the absorber deposited in this way is only subsequently picked up from the collector 3 and assembled on the heat exchanger.

[0039] Subsequently, in a step 13 for initialising at least one parameter of the electrospinning system, the operating parameters necessary to perform the process are set up as a function of the specific technical features of the heat exchanger to be made, the absorber to be used and the electrospinning system which has been set up.

[0040] In this way, it is advantageously possible to apply this method to heat exchangers of thermal machines having different features (such as power, dimensions, shape of heat exchanger, materials used), simply modifying some of the parameters of the process according to the result to be obtained or the type of application for which the finished product must be used.

[0041] For example, some of the parameters which might be set during the initialising step 13 are: the voltage applied between the spinneret and the collector, placing time, flow rate of the precursor material 4, distance between spinneret and collector.

[0042] After correctly setting up the system and setting the operating parameters it is possible to proceed with the step 14 of placing an absorbing layer on the heat exchanger by electrospinning.

[0043] In other words, the invention makes it possible to obtain the coating of the metal surfaces of the heat exchanger with layers of fibres of absorbent material obtained by means of an electrospinning process which is preferably carried out directly on the heat exchanger.

[0044] In order to improve the adhesion of the absorbing material deposited on the heat exchanger, so as to render the device more resistant, it is possible to subject it to a curing process, performed after depositing absorbent material.

[0045] The curing process is preferably performed at a temperature of between 70°C and 90°C for a period of 7-9 hours.

[0046] The absorbing layer may be made by electrospinning a precursor material 4 made by means of a mixture of polymeric materials and nanoporous materials.

[0047] Preferably, this mixture is made of polymeric materials with percentages by weight of between 50% and 10% and nanoporous materials placed in solution with percentages by weight of between 50% and 90%.

[0048] By way of a non-limiting example, the polymeric materials can be selected by selecting at least one between: Polymethyl methacrylate, Polyacrylonitrile (PAN), Polyvinyl alcohol (PVA), Polyvinyl acetate, Polyethylene oxide (PEO), Polystyrene, Polytetrafluoroethylene, Polyethylene terephthalate.

[0049] Again by way of a non-limiting example, said nanoporous materials can be selected by selecting at least one between: Silica gel, zeolite-A (LTA), Faujasite (FAU), zeolites belonging to the ZSM-5 family or to the Silicalite-1 family, zeolites belonging to the ferrierite series (FER), BEA, aluminophosphates (AIPO), silicoaluminophosphates (SAPO).

[0050] in particular, the polymeric and nanoporous materials indicated above are placed in solution using, by way of non-limiting example, a solvent such as water, ethanol, acetone, dimethylamine or N, N dimethylformamide.

[0051] For example, the mixture of polymeric materials and nanoporous materials in solution may be made in accordance with the following compositions, wherein the percentages indicated are referred to percentages by weight:

example 1) 60% nanoporous material (SAPO-34); 4.4% Polymer (PEO); 35.6 solvent (Ethanol).

example 2) 70% nanoporous material (Zeolite X); 3.6% Polymer (PVA); 26.4 solvent (Ethanol).

[0052] example 1) 90% nanoporous material (Zeolite Y); 1.15% Polymer (PAN); 8.85 solvent (Dimethylmethanamide). Advantageously, thanks to the technique and to the precursor material 4 used for making the absorbing material it is possible to obtain a coating with an excellent permeability to gases and vapours, a high surface area and good mechanical properties, rendering also possible the depositing of absorbent layers with a thickness of up to 100 mm, or preferably between 10^-1 and 10⁵ µm.

[0053] This invention also relates to a thermal machine characterised in that it comprises a heat exchanger made using the method described above in detail.

[0054] A thermal absorption machine whose heat exchanger has been made using the method according to the invention has considerable advantages with respect to the prior art devices.

[0055] In particular, the invention relates to a thermal absorption machine which comprises a heat exchanger which in turn comprises a support, preferably at least partly made of metallic material, and a layer of absorbing material placed on the support by means of an electrospinning process.

[0056] The absorbing material is made by electrospinning a mixture of polymeric materials and nanoporous materials in solution.

[0057] Preferably, the mixture comprises polymeric materials for a percentage by weight of between 50% and 10% and nanoporous materials for a percentage by weight of, respectively, between 50% and 90%.

[0058] The depositing of the absorbing material by electrospinning, especially if it is performed directly on the surface of the heat exchanger, makes it possible to obtain an excellent absorbing material-heat exchanger contact, which is significantly greater than that which can be obtained if the absorbing material is made in the form of a bed of granules. Advantageously, it is also possible to obtain an absorbing layer with a high permeability to gases and vapours, which is significantly greater than that which can be obtained in heat exchangers coated with a layer of absorbing material mixed with a polymer binder.

[0059] Moreover, unlike what happens for heat exchangers wherein the absorbent material is synthesised directly on the surface, with the prior art techniques, there are not significant limits to the thickness of the layer of absorbent material which can be obtained.

[0060] Lastly, the particular non-woven fabric characteristic given to the layer of absorbing material and made possible thanks to the electrospinning process guarantees that a heat exchanger is obtained with a high surface area allowing a significant increase in the efficiency of the thermal machine to be obtained.

Claims

1. A method for making the heat exchanger of a thermal absorption machine comprising the steps of:

- preparing an electrospinning system comprising a spinneret and a collector;

- installing at least one component of a heat exchanger of a thermal absorption machine, made at least partly of metal material, at the collector of the electrospinning system;

- initialising at least one parameter of the electrospinning system;

- placing a layer of an absorbing material on said component of the heat exchanger by electrospinning;

- subjecting the component of the heat exchanger to a curing process after the step of placing a layer of absorbing material on the collecting surface; characterized in that said curing process is performed at a temperature of between 70-90°C for 7-9 hours.

2. The method according to claim 1, wherein the layer of absorbing material placed during the step of placing a layer of absorbing material has a thickness of between 10^-1 and 10⁵ µm.

3. The method according to any one of the preceding claims, wherein said layer of absorbing material placed is made by electrospinning a mixture of polymeric materials and nanoporous materials in solution.

4. The method according to claim 3, wherein said mixture comprises polymeric materials for a percentage of between 50% and 10% and nanoporous materials for a percentage respectively of between 50% and 90%.

5. The method according to claim 3, wherein said polymeric materials are at least one between: Polymethyl methacrylate, Polyacrylonitrile (PAN), Polyvinyl alcohol (PVA), Polyvinyl acetate, Polyethylene oxide (PEO), Polystyrene, Polytetrafluoroethylene, Polyethylene terephthalate.

6. The method according to claim 3, wherein said nanoporous materials are at least one between: Silica gel, zeolite-A (LTA), Faujasite (FAU), zeolites belonging to the ZSM-5 family or to the Silicalite-1 family, zeolites belonging to the ferrierite series (FER), BEA, aluminophosphates (AIPO), silicoaluminophosphates (SAPO).

7. The method according to claim 1, wherein during the step for initialising at least one parameter of the electrospinning system the at least one parameter is selected between: applied voltage, placing time, flow rate, distance between spinneret and heat exchanger.

8. A thermal absorption machine characterised in that it comprises a heat exchanger made by means of a method according to any one of claims 1 to 7.

Ansprüche

1. Verfahren zur Herstellung des Wärmetauschers einer Absorptionswärmemaschine, umfassend die Schritte:

- Vorbereiten eines Elektrospinnsystems umfassend eine Spinndüse und einen Sammler;

- Installieren mindestens einer Komponente eines Wärmetauschers einer Absorptionswärmemaschine, die zumindest teilweise aus Metall besteht, am Sammler des Elektrospinnsystems;

- Initialisieren mindestens eines Parameters des Elektrospinnsystems;

- Platzieren einer Schicht eines absorbierenden Materials auf die Komponente des Wärmetauschers durch Elektrospinnen;

- Unterziehen der Komponente des Wärmetauschers nach dem Schritt zum Platzieren einer Schicht aus absorbierendem Material auf die Sammelfläche einem Aushärtungsprozess; dadurch gekennzeichnet, dass der Aushärtungsprozess 7 bis 9 Stunden bei einer Temperatur zwischen 70 und 90 °C durchgeführt wird.

2. Verfahren nach Anspruch 1, wobei die Schicht aus absorbierendem Material, die während des Schritts zum Platzieren einer Schicht aus absorbierendem Material platziert ist, eine Dicke zwischen 10^-1 und 10⁵ µm aufweist.

3. Verfahren nach einem der vorhergehenden Ansprüche, wobei die platzierte Schicht aus absorbierendem Material durch Elektrospinnen einer Mischung aus Polymermaterialien und nanoporösen Materialien in Lösung hergestellt wird.

4. Verfahren nach Anspruch 3, wobei die Mischung Polymermaterialien für einen Prozentsatz zwischen 50% und 10% und nanoporöse Materialien für einen Prozentsatz zwischen 50% und 90% umfasst.

5. Verfahren nach Anspruch 3, wobei die Polymermaterialien mindestens eins sind unter: Polymethylmethacrylat, Polyacrylnitril (PAN), Polyvinylalkohol (PVA), Polyvinylacetat, Polyethylenoxid (PEO), Polystyrol, Polytetrafluorethylen, Polyethylenterephthalat.

6. Verfahren nach Anspruch 3, wobei die nanoporösen Materialien mindestens eins sind unter: Kieselgel, Zeolith-A (LTA), Faujasit (FAU), Zeolithe der ZSM-5-Familie oder der Silicalit-1-Familie gehörend, Zeolithe der Ferrierit-Reihe (FER) gehörend, BEA, Aluminophosphate (AIPO), Silicoaluminophosphate (SAPO).

7. Verfahren nach Anspruch 1, wobei während des Schritts zum Initialisieren mindestens eines Parameters des Elektrospinnsystems der mindestens eine Parameter ausgewählt wird unter: angelegter Spannung, Platzierungszeit, Durchflussrate, Abstand zwischen Spinndüse und Wärmetauscher.

8. Absorptionswärmemaschine, dadurch gekennzeichnet, dass sie einen Wärmetauscher umfasst, der mittels eines Verfahrens nach einem der Ansprüche 1 bis 7 hergestellt ist.

Revendications

1. Procédé de fabrication de l'échangeur de chaleur d'une machine thermique à absorption comprenant les étapes de :

- préparer un système d'électrofilage comprenant une filière et un collecteur ;

- installer au moins un composant d'un échangeur de chaleur d'une machine thermique à absorption, constitué au moins partiellement de matériau métallique, en correspondance du collecteur du système d'électrofilage ;

- initialiser au moins un paramètre du système d'électrofilage ;

- placer une couche d'un matériau absorbant sur ledit composant de l'échangeur de chaleur par électrofilage ;

- soumettre le composant de l'échangeur de chaleur à un processus de durcissement après l'étape consistant à placer une couche de matériau absorbant sur la surface de collecte ; caractérisé en ce que ledit processus de durcissement est effectué à une température comprise entre 70 et 90 °C pendant 7 à 9 heures.

2. Procédé selon la revendication 1, dans lequel la couche de matériau absorbant placée pendant l'étape consistant à placer une couche de matériau absorbant comporte une épaisseur comprise entre 10^-1 et 10⁵ µm.

3. Procédé selon l'une quelconque des revendications précédentes, dans lequel ladite couche de matériau absorbant placée est réalisée par électrofilage d'un mélange de matériaux polymères et de matériaux nanoporeux en solution.

4. Procédé selon la revendication 3, dans lequel ledit mélange comprend des matériaux polymères selon un pourcentage compris entre 50 et 10 % et des matériaux nanoporeux selon un pourcentage respectivement compris entre 50 et 90 %.

5. Procédé selon la revendication 3, dans lequel lesdits matériaux polymères sont au moins l'un entre : le polyméthacrylate de méthyle, le polyacrylonitrile (PAN), l'alcool polyvinylique (PVA), l'acétate de polyvinyle, l'oxyde de polyéthylène (PEO), le polystyrène, le polytétrafluoroéthylène, le polyéthylène téréphtalate.

6. Procédé selon la revendication 3, dans lequel lesdits matériaux nanoporeux sont au moins l'un entre : le gel de silice, la zéolite-A (LTA), la Faujasite (FAU), des zéolites appartenant à la famille ZSM-5 ou à la famille silicalite-1, des zéolites appartenant à la série des ferriérites (FER), le BEA, des aluminophosphates (AIPO), des silicoaluminophosphates (SAPO).

7. Procédé selon la revendication 1, dans lequel, pendant l'étape consistant à initialiser au moins un paramètre du système d'électrofilage, ledit au moins un paramètre est choisi entre : la tension appliquée, le temps de placement, le débit, la distance entre la filière et l'échangeur de chaleur.

8. Machine thermique à absorption, caractérisée en ce qu'elle comprend un échangeur de chaleur réalisé au moyen d'un procédé selon l'une quelconque des revendications 1 à 7.

Drawing