Fuel cell system

Abstract

We provide technology for removing air bubbles from heat exchangers. [Solution] The fuel cell system 100 of this disclosure comprises a fuel cell 20, a heat exchanger 30 for dissipating heat from the cooling water of the fuel cell 20, a cooling water tank 40 for storing cooling water, a cooling water pump 50 for circulating cooling water between the fuel cell 20 and the heat exchanger 30 via the cooling water tank 40, and a controller 60 for controlling the cooling water pump 50. When it is determined that air has accumulated inside the heat exchanger 30, the controller 60 stops the cooling water pump 50 for a predetermined time.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system. Background Art

[0002] As described in Patent Document 1, a fuel cell system is known which includes a fuel cell, a cooling water tank storing cooling water for the fuel cell, a cooling water circulation pump, and a cooling water heat exchanger that recovers waste heat of the cooling water. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2015-118730 Summary of the Invention Problem to be Solved by the Invention

[0004] The water level of the cooling water tank drops due to transpiration of the cooling water. Therefore, it is necessary to continuously replenish the cooling water tank with water. As water to be replenished to the cooling water tank, for example, water generated along with power generation, condensed water from anode off-gas, and condensed water from cathode off-gas are used. However, since gases such as air are dissolved in these waters, when cooling water flows into the heat exchanger, the cooling water collides against the inner wall of the heat exchanger, the dissolved gas turns into bubbles, and the bubbles stay inside the heat exchanger. If bubbles stay inside the heat exchanger, the heat transfer area decreases and the heat exchange efficiency lowers, so it is necessary to remove the bubbles. It is conceivable to remove the bubbles by increasing the circulation amount of the cooling water, but if the circulation amount of the cooling water is increased, bubbles will enter the cooling water pump, causing abnormal noise and wear of the cooling water pump.

[0005] The present disclosure provides a technique for removing air bubbles from a heat exchanger. Means for Solving the Problem

[0006] The present disclosure: Fuel cells and A heat exchanger for dissipating heat from the cooling water of the fuel cell, A cooling water tank for storing the aforementioned cooling water, A cooling water pump that circulates the cooling water between the fuel cell and the heat exchanger via the cooling water tank, A controller for controlling the cooling water pump, Equipped with, When it is determined that air has accumulated inside the heat exchanger, the controller stops the cooling water pump for a predetermined time. We provide fuel cell systems. [Effects of the Invention]

[0007] According to this disclosure, bubbles can be removed from the heat exchanger. [Brief explanation of the drawing]

[0008] [Figure 1] Configuration diagram of the fuel cell system of the first embodiment [Figure 2] Perspective view of the heat exchanger and cooling water tank [Figure 3] A diagram showing the balance of forces acting on a water droplet at rest on a plane. [Figure 4] A schematic diagram showing the state of the interface between water and air inside a capillary tube. [Figure 5] Flowchart for bubble removal process [Figure 6] Another flowchart for the bubble removal process [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted.

[0010] The accompanying drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0011] (First Embodiment) Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 6.

[0012] [1-1. Configuration] FIG. 1 is a configuration diagram of the fuel cell system according to the first embodiment.

[0013] The fuel cell system 100 includes a fuel cell 20, a heat exchanger 30, a cooling water tank 40, a cooling water pump 50, and a controller 60. The fuel cell 20, the heat exchanger 30, the cooling water tank 40, and the cooling water pump 50 are annularly connected in this order via cooling water passages 10a to 10d so that the cooling water for the fuel cell 20 circulates.

[0014] The fuel cell 20 generates electric power through a chemical reaction between hydrogen and oxygen. The fuel cell 20 is, for example, a polymer electrolyte fuel cell. The fuel cell 20 is cooled by cooling water. Waste heat from the fuel cell 20 is recovered by the cooling water. Water generated along with power generation, condensed water from anode off-gas, and condensed water from cathode off-gas are supplied to the cooling water tank 40 through the water supply passage 12.

[0015] The heat exchanger 30 has a role of radiating heat from the cooling water by causing heat exchange between the cooling water of the fuel cell 20 and another heat medium. Examples of the other heat medium include city water, air, and the like. In the present embodiment, the cooling water dissipates heat to city water in the heat exchanger 30 to generate warm water. The warm water is stored in a hot water storage tank 70. A cooling tower may be provided instead of the hot water storage tank 70.

[0016] The heat exchanger 30 is a liquid-liquid heat exchanger or a gas-liquid heat exchanger. Examples of the liquid-liquid heat exchanger include double-pipe heat exchangers, plate heat exchangers, and the like. An example of the gas-liquid heat exchanger includes a fin-and-tube heat exchanger. The heat exchanger 30 is typically a plate heat exchanger.

[0017] The cooling water tank 40 serves to store cooling water for the fuel cell 20. A temperature sensor 61 is provided in the cooling water tank 40. The temperature sensor 61 detects the temperature of the cooling water stored in the cooling water tank 40.

[0018] The cooling water pump 50 serves to circulate cooling water between the fuel cell 20 and the heat exchanger 30 via the cooling water tank 40.

[0019] Cooling water passages 10a to 10d mutually connect the fuel cell 20, the heat exchanger 30, the cooling water tank 40, and the cooling water pump 50. Specifically, the cooling water passage 10a connects the cooling water outlet of the cooling water tank 40 and the cooling water inlet of the heat exchanger 30. The cooling water passage 10b connects the cooling water outlet of the heat exchanger 30 and the inlet of the cooling water pump 50. The cooling water passage 10c connects the outlet of the cooling water pump 50 and the cooling water inlet of the fuel cell 20. The cooling water passage 10d connects the cooling water outlet of the fuel cell 20 and the cooling water inlet of the cooling water tank 40.

[0020] When the cooling water tank 40 is regarded as a reference position, the heat exchanger 30 is arranged downstream of the cooling water tank 40. The cooling water pump 50 is arranged downstream of the heat exchanger 30. The fuel cell 20 is arranged downstream of the cooling water pump 50.

[0021] In the present embodiment, each of the cooling water passages 10a to 10d is constituted by at least one pipe. The pipe may be a metal pipe or a resin pipe.

[0022] The controller 60 is responsible for controlling the cooling water pump 50. The controller 60 is a DSP (Digital Signal Processor) that includes, for example, an A / D conversion circuit, input / output circuits, arithmetic circuits, and memory devices. The controller 60 stores a program for properly operating the fuel cell system 100.

[0023] A temperature sensor 62 is provided at the water outlet of the heat exchanger 30. The temperature sensor 62 detects the temperature of the water (hot water) at the water outlet of the heat exchanger 30.

[0024] The detection signals from temperature sensors 61 and 62 are input to the controller 60. The controller 60 controls the cooling water pump 50 based on the detection signals from temperature sensors 61 and 62.

[0025] Figure 2 is a perspective view of the heat exchanger 30 and the cooling water tank 40.

[0026] The heat exchanger 30 includes a cooling water inlet 30a, a cooling water outlet 30b, a city water inlet 30c, and a city water outlet 30d. The cooling water inlet 30a is located above the cooling water outlet 30b in the vertical direction VD. The cooling water flows through the cooling water channel inside the heat exchanger 30 from the upper side to the lower side of the vertical direction VD. The city water inlet 30c is located below the city water outlet 30d in the vertical direction VD. The city water flows through the city water channel inside the heat exchanger 30 from the lower side to the upper side of the vertical direction VD. In other words, the flow of cooling water and the flow of city water are in opposition to each other. This enables efficient heat exchange.

[0027] In the example shown in Figure 2, the heat exchanger 30 is a plate heat exchanger. The orientation of the heat exchanger 30 is determined so that each plate constituting the plate heat exchanger is parallel to the vertical direction VD.

[0028] As explained earlier, since air is dissolved in the cooling water, when the cooling water flows through the heat exchanger 30, the cooling water collides with the inner wall of the heat exchanger 30, causing the air to form bubbles that accumulate inside the heat exchanger 30. In this embodiment, when the cooling water flows from the top to the bottom in the vertical direction VD, air bubbles tend to accumulate in the cooling water flow path. According to the technology of this disclosure described below, air bubbles can be easily removed from the cooling water flow path inside the heat exchanger 30.

[0029] The water level WL in the cooling water tank 40 is located above the water level in the cooling water flow path inside the heat exchanger 30 in the vertical direction VD. The water level in the cooling water flow path inside the heat exchanger 30 coincides, for example, with the upper end of the cooling water inlet 30a of the heat exchanger 30. In other words, the water level WL in the cooling water tank 40 is located above the upper end of the cooling water inlet 30a of the heat exchanger 30 in the vertical direction VD. With this configuration, air bubbles can flow from the cooling water flow path inside the heat exchanger 30 into the cooling water tank 40 due to buoyancy.

[0030] The water level WL in the cooling water tank 40 is located above the upper end of the cooling water outlet 40b in the vertical direction VD. In other words, the amount of water in the cooling water tank 40 is controlled so that the water level WL exceeds the upper end of the cooling water outlet 40b.

[0031] The heat exchanger 30 is connected to the cooling water tank 40 by a cooling water passage 10a. The cooling water outlet 40b, which is the connection point between the cooling water tank 40 and the cooling water passage 10a, is located in the same position as the cooling water inlet 30a, which is the connection point between the heat exchanger 30 and the cooling water passage 10a, in the vertical direction VD. Alternatively, the cooling water outlet 40b, which is the connection point between the cooling water tank 40 and the cooling water passage 10a, is located above the cooling water inlet 30a, which is the connection point between the heat exchanger 30 and the cooling water passage 10a, in the vertical direction VD. With this configuration, air bubbles can flow from the cooling water passage inside the heat exchanger 30 to the cooling water tank 40 due to buoyancy.

[0032] The inner diameter of the piping constituting the cooling water path 10a is such that the cooling water cannot maintain surface tension inside the piping. With this configuration, it is possible to avoid the accumulation of air bubbles in the piping constituting the cooling water path 10a connecting the cooling water tank 40 and the heat exchanger 30. The inner diameter of the piping can be calculated based on the theory described below.

[0033] Figure 3 shows the equilibrium of forces acting on a water droplet at rest on a plane. The hydrostatic pressure P of the water droplet is expressed by equation (1), where e is the height of the droplet, ρ is the density of water, and g is the acceleration due to gravity.

[0034]

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[0035] Based on the balance of forces, hydrostatic pressure P and solid-gas surface tension γ S , liquid-gas surface tension γ L , solid-liquid surface tension γ SL , and the contact angle θ of the water droplet E The expression satisfies equations (2A) and (2B). Equation (2B) is Young's equation.

[0036]

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[0037] Equation (3) can be derived from equations (2A) and (2B).

[0038]

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[0039] Figure 4 schematically shows the state of the water-air interface inside a pipe. The Rayleigh-Taylor instability theory can be applied to the phenomenon when the water-air interface inside a pipe collapses. That is, when surface tension acts on the interface, instability occurs when the wavelength λ of the wave occurring at the interface exceeds a certain critical value. The wavelength λ of the wave occurring at the interface is expressed by equation (4). κ is the capillary length expressed by equation (5).

[0040]

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[0041]

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[0042] If the pipe has a diameter greater than or equal to the unstable mode of λ / 2, the interface between water and air can be broken down, and therefore equation (6) holds true.

[0043]

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[0044] If the inner diameter of the pipe is greater than or equal to the wavelength λ, the cooling water inside the pipe cannot maintain surface tension. In one example, the inner diameter of the pipe determined from equation (6) is 10.5 mm or more. With such a configuration, it is possible to avoid the accumulation of air bubbles in the pipes that constitute the cooling water path 10a connecting the cooling water tank 40 and the heat exchanger 30. There is no particular upper limit to the inner diameter of the pipe, for example, 13 mm.

[0045] [1-2. Operation] Figure 5 is a flowchart of the bubble removal process performed by the controller 60. After the fuel cell system 100 starts operation, the controller 60 periodically performs each of the processes shown in Figure 5.

[0046] In step S1, it is determined whether the temperature difference ΔT exceeds the threshold temperature. The temperature difference ΔT is the difference between the temperature of the cooling water in the cooling water tank 40 and the temperature of the city water heated by heat exchange with the cooling water in the heat exchanger 30. The temperature of the city water is the temperature of the city water at the city water outlet 30d of the heat exchanger 30. In this embodiment, the temperature sensor 62 detects the temperature of the city water at the city water outlet 30d of the heat exchanger 30.

[0047] When the temperature difference ΔT exceeds the threshold temperature, it means that the heat exchange efficiency of the heat exchanger 30 has decreased, making it difficult to sufficiently heat the tap water. This decrease in heat exchange efficiency is caused by the accumulation of air bubbles inside the heat exchanger 30. In other words, as shown in the example in Figure 5, the controller 60 determines that air bubbles have accumulated inside the heat exchanger 30 when the temperature difference ΔT exceeds the threshold temperature. The generation of air bubbles inside the heat exchanger 30 can be detected in real time by the temperature change of the cooling water. In this example, the "threshold temperature" is a temperature of 5°C or higher.

[0048] When the temperature difference ΔT exceeds the threshold temperature, that is, when it is determined that air has accumulated inside the heat exchanger 30, the cooling water pump 50 is stopped for a predetermined time in step S2. When the cooling water pump 50 is stopped, the air bubbles that have accumulated inside the heat exchanger 30 flow into the cooling water tank 40 through the cooling water path 10a due to buoyancy. Since the air bubbles can be removed from inside the heat exchanger 30, the heat exchange efficiency of the heat exchanger 30 can be restored. In addition, it is possible to prevent the air bubbles that have accumulated in the heat exchanger 30 from flowing into the cooling water pump 50. Therefore, it is possible to prevent the generation of abnormal noise and wear of sliding parts caused by air bubbles flowing into the cooling water pump 50. In addition, in order to suppress the temperature rise of the fuel cell 20, the flow rate of the cooling water may be increased before stopping the cooling water pump 50 to lower the temperature of the fuel cell 20.

[0049] In step S3, after a predetermined time has elapsed since the cooling water pump 50 was stopped, the operation of the cooling water pump 50 is restarted. The "predetermined time" is a sufficient time to remove air bubbles from inside the heat exchanger 30 and to avoid a significant rise in the temperature of the fuel cell 20. In one example, the "predetermined time" is in the range of 5 to 10 seconds.

[0050] In this embodiment, the controller 60 stops the cooling water pump 50 for a predetermined time while continuing to operate the fuel cell 20. With this configuration, power continues to be supplied to the outside from the fuel cell system 100, improving the convenience of the fuel cell system 100. After the predetermined time has elapsed, the operation of the cooling water pump 50 is restarted. Even if the cooling water pump 50 is stopped for a short period of time, the temperature of the fuel cell 20 will not rise significantly.

[0051] Figure 6 is another flowchart of the bubble removal process performed by the controller 60. The processes in steps ST2 and ST3 are the same as the processes in steps S2 and S3 shown in Figure 5, respectively.

[0052] In step ST1, it is determined whether the operating time of the cooling water pump 50 is greater than or equal to a threshold time. In other words, the controller 60 determines that air has accumulated inside the heat exchanger 30 when a threshold time has elapsed since the start of operation of the cooling water pump 50. This method allows for the removal of air bubbles inside the heat exchanger 30 with a simple configuration.

[0053] For example, the time from the start of operation of the cooling water pump 50 to the point when a predetermined amount of bubbles accumulate in the heat exchanger 30 can be experimentally investigated. Based on this experiment, the "threshold time" can be determined. In one example, the "threshold time" is in the range of 5 to 30 minutes.

[0054] (Note) Based on the above description of embodiments, the following technologies are disclosed.

[0055] (Technology 1) Fuel cells and A heat exchanger for dissipating heat from the cooling water of the fuel cell, A cooling water tank for storing the aforementioned cooling water, A cooling water pump that circulates the cooling water between the fuel cell and the heat exchanger via the cooling water tank, A controller for controlling the cooling water pump, Equipped with, When it is determined that air has accumulated inside the heat exchanger, the controller stops the cooling water pump for a predetermined time. Fuel cell system.

[0056] According to this disclosure, bubbles can be removed from the heat exchanger.

[0057] (Technology 2) The fuel cell system according to Technology 1, wherein the controller stops the cooling water pump for a predetermined time while continuing to operate the fuel cell, and restarts the operation of the cooling water pump after the predetermined time has elapsed. With this configuration, power is continuously supplied to the outside from the fuel cell system, thus improving the convenience of the fuel cell system.

[0058] (Technology 3) A fuel cell system according to Technology 1 or 2, further comprising a cooling water path connecting the cooling water tank and the heat exchanger, wherein the connection portion between the cooling water tank and the cooling water path is located at the same position in the vertical direction as the connection portion between the heat exchanger and the cooling water path, or is located at a position above the connection portion between the heat exchanger and the cooling water path in the vertical direction. With such a configuration, air bubbles can flow from the cooling water flow path inside the heat exchanger to the cooling water tank by buoyancy.

[0059] (Technology 4) A fuel cell system according to any one of the technologies 1 to 3, further comprising a cooling water path connecting the cooling water tank and the heat exchanger, wherein the inner diameter of the piping constituting the cooling water path is such that the cooling water cannot maintain surface tension inside the piping. With such a configuration, it is possible to avoid the accumulation of air bubbles in the piping constituting the cooling water path connecting the cooling water tank and the heat exchanger.

[0060] (Technology 5) The fuel cell system according to Technology 4, wherein the inner diameter of the aforementioned piping is 10.5 mm or more. With this configuration, it is possible to avoid the accumulation of air bubbles in the piping that constitutes the cooling water path connecting the cooling water tank and the heat exchanger.

[0061] (Technology 6) The fuel cell system according to any one of the technologies 1 to 5, wherein the controller determines that air has accumulated inside the heat exchanger when the difference between the temperature of the cooling water in the cooling water tank and the temperature of the heat transfer medium heated by heat exchange with the cooling water in the heat exchanger exceeds a threshold temperature. With this method, the generation of bubbles inside the heat exchanger can be detected in real time by changes in the temperature of the cooling water.

[0062] (Technology 7) The fuel cell system according to any one of the technologies 1 to 6, wherein the controller determines that air has accumulated inside the heat exchanger when a threshold time has elapsed since the start of operation of the cooling water pump. This method allows for the removal of air bubbles inside the heat exchanger with a simple configuration. [Industrial applicability]

[0063] The technology disclosed herein is useful for fuel cell systems. [Explanation of Symbols]

[0064] 10a, 10b, 10c, 10d Cooling water path 12 Water supply routes 20 Fuel Cell 30 heat exchanger 30a Cooling water inlet 30b Cooling water outlet 30c city water entrance 30d City Water Exit 40 Cooling water tank 40b Cooling water outlet 50 Cooling water pump 60 Controllers 61 Temperature Sensor 62 Temperature Sensor 70 Hot water storage tank 100 Fuel Cell Systems WL water level VD Vertical direction

Claims

1. Fuel cells and A heat exchanger for dissipating heat from the cooling water of the fuel cell, A cooling water tank for storing the aforementioned cooling water, A cooling water pump that circulates the cooling water between the fuel cell and the heat exchanger via the cooling water tank, A controller for controlling the cooling water pump, Equipped with, When it is determined that air has accumulated inside the heat exchanger, the controller stops the cooling water pump for a predetermined time. Fuel cell system.

2. The controller continues to operate the fuel cell while stopping the cooling water pump for a predetermined time, and restarts the operation of the cooling water pump after the predetermined time has elapsed. The fuel cell system according to claim 1.

3. The system further comprises a cooling water path connecting the cooling water tank and the heat exchanger, The connection portion between the cooling water tank and the cooling water path is located in the same position as the connection portion between the heat exchanger and the cooling water path in the vertical direction, or is located above the connection portion between the heat exchanger and the cooling water path in the vertical direction. The fuel cell system according to claim 1.

4. The system further comprises a cooling water path connecting the cooling water tank and the heat exchanger, The inner diameter of the piping constituting the cooling water path is such that the cooling water cannot maintain surface tension inside the piping. The fuel cell system according to claim 1.

5. The inner diameter of the aforementioned pipe is 10.5 mm or more. The fuel cell system according to claim 4.

6. The controller determines that air has accumulated inside the heat exchanger when the difference between the temperature of the cooling water in the cooling water tank and the temperature of the heat transfer medium heated by heat exchange with the cooling water in the heat exchanger exceeds a threshold temperature. The fuel cell system according to claim 1.

7. The controller determines that air has accumulated inside the heat exchanger when a threshold time has elapsed since the start of operation of the cooling water pump. The fuel cell system according to claim 1.

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