Cooling system with an air-liquid heat exchanger for a fuel cell system, fuel cell system

Abstract

The invention relates to a cooling system (1) for a fuel cell system, in particular for a mobile fuel cell system, comprising: - an air-liquid heat exchanger (2) with a cooling element (3) which encloses a cavity (5) that can be supplied with a liquid coolant (4) and has an outer surface (6) exposed to airflow, and - a humidification device (7) for humidifying at least part of the outer surface (6) of the cooling element (3). The invention further relates to a fuel cell system, in particular a mobile fuel cell system, with a cooling system (1) according to the invention.

Description

The invention relates to a cooling system with an air-liquid heat exchanger. Preferred areas of application of the invention are fuel cell systems, in particular mobile fuel cell systems. The invention therefore also relates to a fuel cell system, in particular a mobile fuel cell system, having a cooling system according to the invention.Prior ArtThe cooling capacity of an air-liquid heat exchanger depends in particular on its dimensions and on the temperature difference between the temperature of the coolant and the ambient temperature. An increase in the cooling capacity can accordingly be achieved by increasing the dimensions and / or by increasing the temperature difference. However, both are possible only to a limited extent. In mobile applications, in particular, the small installation space available sets limits.The invention is concerned with the object of achieving an increase in the cooling capacity of an air-liquid heat exchanger for mobile applications, which can be implemented as far as possible in a neutral and simple manner of installation space.To achieve the object, the cooling system having the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the dependent claims. Furthermore, a fuel cell system, in particular a mobile fuel cell, having a cooling system according to the invention is specified.Disclosure of the InventionThe cooling system proposed for a fuel cell system, in particular for a mobile fuel cell system, comprises:an air-liquid heat exchanger having a cooling body which encloses a cavity to which a liquid coolant can be applied and has an outer surface around which air flows, anda moistening device for moistening the outer surface of the cooling body at least in regions.During operation of the cooling system, the outer surface of the cooling body can be moistened, in particular moistened with water, with the aid of the moistening device. The moisture or the water evaporates and reduces the surface temperature of the cooling body by evaporation cooling. In this way, the cooling capacity of the air-liquid heat exchanger is increased, namely without changing its dimensions, so that the increase is essentially neutral in terms of installation space. Only the humidifying device requires additional space.If the cooling system is used in a fuel cell system, a further advantage can be achieved. This is because water which is produced as a reaction product during operation of the fuel cell system, so-called product water, can be used for moistening. The use of product water reduces the amount of liquid water that is usually discharged to the environment during operation of the fuel cell system. Since in mobile fuel cell systems the water discharged to the environment reaches the road, there is the risk that a slippery water film will form on the road or, at low external temperatures, a slippery ice layer will form. Both represent a safety risk which is reduced by means of the proposed invention. It is noteworthy in this context that during operation of a fuel cell vehicle, significantly more water, in particular liquid water, is produced in comparison with a vehicle with an internal combustion engine, which water is usually discharged to the environment. Reducing the amount of product water during operation of a fuel cell vehicle is therefore desirable. The present invention contributes to this.In a development of the invention, it is proposed that the outer surface of the cooling body has, at least in regions, a characterization and / or coating which increases the water retention capacity and / or the wetting capacity. This measure has the effect that the outer surface of the cooling body can be moistened better, since more water can be absorbed by the outer surface or more water can be retained. Accordingly, more water can evaporate and the surface temperature can be further cooled down by evaporation cooling.The characterization can form, for example, capillaries, pores, channels and / or pockets, in which water is retained and is successively discharged by evaporation.According to a preferred embodiment of the invention, the moistening device comprises at least one spraying or spraying device, for example in the form of a nozzle. The water can be atomized by means of the spraying or spraying device, so that a fine mist of water is produced, which is deposited on the outer surface of the cooling body. Since, during operation, the outer surface of the cooling body is surrounded by air, the spraying or spraying device is preferably arranged in front of the cooling body in the direction of flow of the air, so that the air transports the water droplets in the direction of the cooling body.Alternatively, it is proposed that the moistening device comprises means for forming a water mist. The means can be, for example, a pipe system which-analogously to an irrigation hose-has perforations via which water can be discharged in the form of a water mist. Depending on the arrangement of the means, these can be driven by gravity alone or can be actuated by means of pressurization. Furthermore, the air flow around the cooling body can be used-at least supporting-as a transport means. For this purpose, the means are arranged in front of the cooling body in the direction of flow of the air.Furthermore, the moistening device preferably comprises a water reservoir. Water can be stored in the water reservoir so that sufficient water is always available. This is advantageous in particular if product water which is produced during operation of the fuel cell system is used, since the amounts of product water are not always of the same magnitude. Furthermore, the water reservoir is preferably coupled to a water separator, with the aid of which product water can be separated from a gas stream.Furthermore, a fuel cell system, in particular a mobile fuel cell system, having a cooling system according to the invention is proposed. The cooling system according to the invention not only has an increased cooling capacity, but also helps to reduce the amount of product water produced during operation of the fuel cell system, since the product water is supplied to a utilization in the cooling system. This is advantageous in particular in mobile fuel cell systems, since less product water then has to be discharged to the environment, in particular to the road. This reduces the risk of forming a slippery water film or layer of ice on the road.The cooling system is preferably used to cool the fuel cell system, in particular a fuel cell stack of the fuel cell system. For this purpose, the cooling system preferably has a cooling circuit, in which the air-liquid heat exchanger is integrated, so that the cavity enclosed by the cooling body can be charged with the coolant of the cooling circuit. The heat absorbed by the coolant is then dissipated to the environment via the cooling body. For this purpose, ambient air flows around the heat sink. The circulating coolant can be, in particular, water or glycol.The humidifying device of the cooling system according to the invention may be activated as needed, for example, when the fuel cell system requires stronger cooling. By activating the humidifying device, the cooling capacity of the cooling system can then be increased.Preferred embodiments of the invention are explained in more detail below with reference to the attached drawings. These show: FIG. 1 shows a schematic longitudinal section through a first cooling system according to the invention, FIG. 2 shows an enlarged detail of FIG. 1 in the region of a microstructured outer surface of the heat sink, and FIG. 3 shows a schematic longitudinal section through a second cooling system according to the invention.DETAILED DESCRIPTION OF THE DRAWINGSFIG. 1 shows a first preferred embodiment of a cooling system 1 according to the invention, which comprises an air-liquid heat exchanger 2 and a humidifying device 7. The cavity 5 is charged with a liquid coolant 4 which is circulated via a cooling circuit (not shown). The coolant 4 can be, for example, water or glycol.The cooling body 3 has an outer surface 6 around which air flows. The direction of flow of the air is indicated by an arrow and the reference sign 15. The outer surface 6 of the cooling body 3 is provided at least in regions with a structurization 8 which forms pockets 10 to improve the water retention capacity. The pockets 10 are open counter to the flow direction 15 of the air (see FIG. 2 ). If the cooling capacity is to be increased, the outer surface 6 of the cooling body 3 can be moistened with the aid of the moistening device 7, wherein water collects in the pockets 10 of the structurization 8 (see FIG. 2 ). This water gradually evaporates, whereby an increase in cooling capacity is achieved by evaporation cooling.The moistening device 7 shown in FIG. 1 has a spraying or spraying device 11 in the form of a nozzle which, when activated, generates a fine spray mist, so that the outer surface 6 of the cooling body 3 is evenly wetted with water and the pockets 10 are filled with water. The spraying or spraying device 11 is arranged in front of the cooling body 3 in the direction of flow 15 of the air, so that the air transports the water droplets in the direction of the cooling body 3.FIG. 2 shows a second preferred embodiment of a cooling system 1 according to the invention. this likewise comprises an air-liquid heat exchanger 2 and a humidifying device 7. Furthermore, the heat sink has an outer surface 6 around which air flows. The flow direction 15 is indicated by an arrow.The outer surface 6 of the cooling body 3 is provided with a coating 9 in the present case for improving the wetting ability. The moistening device 7 also does not have a spraying or spraying device 11, but rather has means 12 for forming a water curtain 13. The means 12 comprise in the present case a tube which is arranged above the cooling body 3 and can be supplied with water from a water reservoir 14 (see reference numerals in brackets). Water can be discharged via closely adjacent outlets (not shown) of the pipe, so that a water mist 13 is formed. Assisted by the air flow, the water mist 13 is placed on the outer surface 6 of the cooling body 3, so that a water film is formed thereon. The coating 9 helps the outer surface 6 to be wetted uniformly with water.The different embodiments of the cooling bodies 3 and of the moistening devices 7 illustrated in FIGS. 1 and 3 can be interchanged. This means that the humidifying device 7 of FIG. 1 can be used in combination with the heat sink 3 of FIG. 2 and / or the humidifying device 7 of FIG. 2 can be used in combination with the heat sink 3 of FIG. 1.

Claims

Cooling system (1) for a fuel cell system, in particular for a mobile fuel cell system, comprising - an air-liquid heat exchanger (2) having a cooling body (3) which encloses a cavity (5) to which a liquid coolant (4) can be applied and has an outer surface (6) around which air flows, and - a moistening device (7) for moistening the outer surface (6) of the cooling body (3) at least in regions.Cooling system (1) according to Claim 1, characterized in that the outer surface (6) of the cooling body (3) has, at least in regions, a copolymerization (8) and / or coating (9) which increases the water retention capacity and / or the wetting capacity.Cooling system (1) according to claim 2, characterised in that the structurisation (8) forms capillaries, pores, channels and / or pockets (10).Cooling system (1) according to one of the preceding claims, characterized in that the moistening device (7) comprises at least one spraying or spraying device (11), for example in the form of a nozzle.Cooling system (1) according to one of the preceding claims, characterized in that the moistening device (7) comprises means (12) for forming a water mist (13).Cooling system (1) according to one of the preceding claims, characterized in that the moistening device (7) comprises a water reservoir (14).Fuel cell system, in particular mobile fuel cell system, having a cooling system (1) according to one of Claims 1 to 6.

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