Safe and energy-saving flat heat pipe air-cooled fuel cell stack and heat management method

Abstract

The invention discloses a safe and energy-saving flat heat pipe air-cooled fuel cell stack and a heat management method, and relates to the technical field of hydrogen energy technology fuel cell heat management. The flat heat pipe air-cooled fuel cell stack is formed by combining two end plates, a collector plate, a plurality of membrane electrodes and a plurality of groups of bipolar plates, the plurality of membrane electrodes and the bipolar plates are alternately arranged between the two end plates, part or all of the bipolar plates are attached to a micro heat pipe array, and the micro heat pipe array is attached to the collector plate. The micro heat pipe array can transfer heat generated by contact of hydrogen and air through the proton exchange membrane to a condensation section of the micro heat pipe array, and heat dissipation is achieved through natural convection or forced convection of an external fan. According to the invention, heat dissipation of the fuel cell can be realized, the temperature uniformity in the stack is increased, and the reliability is improved.

Description

[0001] This application is a divisional application. The application number of the original application is 202110916267.5, the application date is August 11, 2021, and the invention title is "A Safe and Energy-saving Flat Heat Pipe Air-cooled Fuel Cell Stack and Thermal Management Method". Technical Field

[0002] The present invention relates to the technical field of fuel cell thermal management in hydrogen energy technology, and particularly relates to a safe and energy-saving flat heat pipe air-cooled fuel cell stack and thermal management method. Background Art

[0003] Hydrogen energy is a clean secondary energy carrier that can be easily converted into electricity and heat with relatively high conversion efficiency and has multiple source channels. As a bridge connecting renewable energy and traditional fossil energy, it is an important part of future energy transformation.

[0004] Hydrogen fuel cells have the advantages of high fuel energy conversion rate, low noise, and zero emissions, and can be widely used in transportation such as automobiles, airplanes, trains, and fixed power stations. As the most promising fuel cell, proton exchange membrane fuel cells (PEMFCs) generate a certain amount of heat and water while generating electricity during operation. The optimal operating temperature of PEMFCs is 60°C to 80°C. When the optimal operating temperature is not reached, the heat generated inside the fuel cell stack is beneficial to improving the activity of the catalyst, accelerating the electrochemical reaction rate, and improving the output performance of the stack. However, when the temperature is too high, it will cause the proton exchange membrane to dehydrate, affect the transmission of protons, increase the internal resistance of the stack, and reduce the stack performance. At the same time, as the temperature rises, the temperature difference at different positions inside the stack will become larger and larger, which is not conducive to the uniformity of the internal temperature distribution of the stack and will also reduce the service life of the stack. Therefore, the thermal management of PEMFC batteries plays a crucial role in their performance, safety, and stability.

[0005] Conventional fuel cell stacks have a dedicated cooling system to cool the stack, and the cooling medium is liquid, such as water, etc., but the system is relatively complex and is generally used for cooling high-power fuel cell stacks. In small fuel cells, air cooling is commonly used to cool the stack. There are two common cooling forms for conventional air-cooled stacks: the first is that the cathode flow channel is both a reaction gas channel and a cooling flow channel, which is called the cathode air cooling method; the second is that the reaction gas flow channel and the cooling gas flow channel are separated, which is called the reaction air and cooling air separation method. The stack structure of the cathode air cooling method is simple, and the main structure is relatively smaller than the second one, but the control strategy of the battery will be very complex. The main body volume of the stack of the reaction air and cooling air separation method is relatively larger than the first one because after the reaction air and cooling air are separated, independent cooling gas flow channels must be opened on the battery plate to cool the stack. Its advantage is that the control of the stack operation is simpler than that of the cathode air cooling method stack.

[0006] In the above two air-cooling methods, since the cross-sectional area of the air flow channels in the bipolar plates is very small, the flow resistance is very large, and the power consumption of the fan is relatively high. In addition, due to the relatively small specific heat of air, the temperature difference between the inlet and outlet is relatively large, that is, the temperature uniformity inside the fuel cell stack is poor. Too much air passing through the reaction channels will also cause dehydration of the proton exchange membrane, seriously affecting the service effect and lifespan of the battery.

[0007] Currently, heat pipes are also used in the PEMFC heat dissipation and cooling system. The evaporation section of the heat pipe absorbs the heat generated during the operation of the PEMFC, transfers the heat to the condensation section through the flow of the working fluid inside the heat pipe, and then transfers the heat to the environment through natural convection and forced convection.

[0008] Chinese Patent Application for Invention CN103715441A discloses a proton exchange membrane fuel cell thermal management method based on phase change heat transfer of an array of heat pipes. However, this technical solution has the following problems:

[0009] First, the circular heat pipes with a diameter of 0.3 cm - 0.5 cm are used in this solution. The existing fuel cell bipolar plates are relatively thin, and the thickness of the circular heat pipes has exceeded the thickness of the bipolar plates, so the size of the fuel cell stack will be increased, and the volume power density will be reduced. Second, in this solution, the circular heat pipes are inserted into the copper panel at equal intervals. The contact area between the heat pipes and the heat generation area of the fuel cell is relatively small, and the area without heat pipes can only conduct heat through the copper panel. When the heat generation is high, it affects heat dissipation and easily causes uneven temperature distribution inside the fuel cell stack. Third, in this solution, the evaporation section and the condensation section of the heat pipe form an angle of 90 - 120 degrees, which will cause too little power for the internal condensed working fluid to flow back, seriously affecting its heat transfer performance. Fourth, the failure of any single heat pipe will cause the loss of heat dissipation capacity in a certain area, resulting in local overheating damage and triggering chain damage.

[0010] Chinese Patent Application for Invention CN109037726A discloses an air-cooled module for heat transfer and temperature uniformity in fuel cells. However, this technical solution has the following problems: First, the heat pipe with vapor chamber is made of copper or copper alloy plates welded around. Each heat pipe with vapor chamber is an integral heat transfer unit with internal communication. Local damage will cause the heat pipe with vapor chamber to fail to work effectively. Therefore, using the vapor chamber for stack heat dissipation not only has high cost but also low reliability and little practicality. Second, there is no conductive medium inside the heat pipe with vapor chamber. Therefore, the current generated by the reaction can only be transferred through the edge of the heat pipe with vapor chamber, resulting in excessive internal resistance of the fuel cell stack and seriously affecting the output power. Third, during the low-temperature cold start process, hot air blown by the fan is used to heat the condensation section of the heat pipe with vapor chamber, and reverse heat transfer is carried out by the capillary force inside the heat pipe with vapor chamber. This method has a worse effect than forward heat transfer. Fourth, the vapor chamber cannot withstand internal pressure. When the temperature of the fuel cell stack exceeds the saturation temperature of the working medium in the vapor chamber under atmospheric pressure, the vapor chamber will bulge, causing system damage. Therefore, it is difficult to be actually used.

[0011] US Patent for Invention US20050026015A1 discloses "Micro Heat Pipe embedded bipolar plate for fuel cell stacks" in which micro heat pipes are embedded in the bipolar plates of fuel cells, and it also has the first two disadvantages in Chinese Patent Application for Invention CN103715441A. Summary of the Invention

[0012] In view of the problems of uneven internal temperature and large parasitic power in the existing small-power air-cooled fuel cell technology, the present invention provides a safe and energy-saving air-cooled thermal management system and method for fuel cell stacks using flat heat pipes.

[0013] To achieve the above object, the present invention adopts the following technical solutions:

[0014] A safe and energy-saving flat heat pipe air-cooled fuel cell stack, comprising a fuel cell stack, a micro heat pipe array, and an external fan;

[0015] The fuel cell stack is composed of two end plates, current collectors, a plurality of membrane electrodes, and multiple groups of bipolar plates. Between the two end plates, the plurality of membrane electrodes and bipolar plates are arranged alternately. Part or all of the bipolar plates are attached to the micro heat pipe array. The micro heat pipe array is attached between the anode plate and the cathode plate to form a bipolar plate with a micro heat pipe array. The part of the micro heat pipe array attached to the anode plate and the cathode plate is the evaporation section of the micro heat pipe array, and the part of the micro heat pipe array extending out of the fuel cell stack is the condensation section of the micro heat pipe array; the external fan is fixed on the side of the fuel cell stack, facing the condensation section of the micro heat pipe array, and can send air to the condensation section of the micro heat pipe array to form forced convection;

[0016] The micro heat pipe array is a flat heat conductor with a porous structure formed by extruding a metal material. It has multiple micro heat pipes arranged side by side, which are not connected to each other and operate independently. The hydraulic diameter of each micro heat pipe is 0.2 - 3.0 mm, and the internal phase change working fluid is a non-conductive medium. The conductivity of a single micro heat pipe is adjusted by adjusting the width of the partition wall between the micro heat pipes;

[0017] It further includes heat dissipation fins, and the heat dissipation fins are attached to the condensation section of the micro heat pipe array;

[0018] The micro heat pipe array includes a linear micro heat pipe array and an L-shaped micro heat pipe array, and an electric heating sheet is attached to the bent part at the lower part of the L-shaped micro heat pipe array.

[0019] A thermal management method for a safe and energy-saving flat heat pipe air-cooled fuel cell stack uses a safe and energy-saving flat heat pipe air-cooled fuel cell stack. The heat generated by the contact of hydrogen and air through a proton exchange membrane is transferred to the condensation section of the micro heat pipe array through the evaporation section of the micro heat pipe array attached between the anode plate and the cathode plate, and is dissipated by natural convection or forced air cooling by the external fan;

[0020] Heat dissipation fins are attached to the condensation section of the micro heat pipe array. After the fan is turned on, air enters the flow channel between the fins from the side, cools the fins, and then discharges upward from the condensation section of the micro heat pipe array;

[0021] The L-shaped micro heat pipe array is attached to several groups of bipolar plates at intervals, and an electric heating sheet is attached to the bent part at the end of the L-shaped micro heat pipe array. When starting in a low-temperature environment, the electric heating sheet is first turned on to heat the L-shaped micro heat pipe array, thereby heating the fuel cell stack. When the internal temperature of the fuel cell stack reaches the starting temperature, the battery is started.

[0022] Furthermore, when using the external fan for heat dissipation, when it is detected that the internal temperature of the fuel cell stack reaches the set value, the control system turns on the external fan to perform forced convection heat dissipation on the condensation section of the micro heat pipe array.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] A safe and energy-saving flat heat pipe air-cooled fuel cell stack and a thermal management method thereof. A flat micro heat pipe array is attached between the anode plate and the cathode plate inside the fuel cell stack to transfer the heat generated by the internal reaction of the fuel cell to the external air-cooled fins, and forced convection is carried out under the action of a fan to dissipate the heat into the air, so as to realize the heat dissipation of the fuel cell. On the one hand, the flat micro heat pipe array can be closely attached to each anode plate and cathode plate. Even the heat generated by the plates in the middle can be exported from the inside of the fuel cell stack by using the micro heat pipe array, and the temperature uniformity performance of the micro heat pipe array can ensure the temperature uniformity inside the fuel cell stack and avoid the generation of "hot spots". On the other hand, since the micro heat pipe array is a flat heat conductor with a porous structure formed by extruding a metal material, and there are multiple non-connected micro heat pipes arranged side by side inside, and the hydraulic diameter of each micro heat pipe is only 1.0 mm or even smaller, and the pressure-bearing capacity of the pipe wall is extremely high, so the leakage problem can be almost ignored, and the phase change working medium is a trace amount of non-conductive medium. Even if it is damaged and leaked in extreme cases, it will not cause damage to the fuel cell; moreover, the thin micro heat pipe array saves the size of the fuel cell stack, thereby reducing the volume power density. In addition, the flat micro heat pipe array is made of aluminum material and has good electrical conductivity, and the electrical conductivity of a single heat pipe can be adjusted by adjusting the width of the partition wall between the micro heat pipes, which plays an electrical conductivity function inside the fuel cell, does not increase the internal resistance of the fuel cell, and can also reduce the internal resistance to a certain extent and improve the power generation performance of the fuel cell.

[0025] At the same time, when the fuel cell needs to be "cold started" in a low-temperature environment for a long time, the fuel cell must be preheated. Otherwise, the water generated by the reaction will freeze and block the cathode channel, hindering the progress of the reaction. "L"-shaped heat pipes are attached between several anode plates and cathode plates, and an electric heating film is attached to the bottom of the lower bend. Before starting in a low-temperature environment, the bottom of the heat pipe is heated by direct current. After the heat pipe responds quickly, the fuel cell is heated. When the temperature reaches above zero (or 20 °C), the heating is stopped to realize the cold start function.

[0026] The condensation section of each micro heat pipe array is attached to the air-cooled fin with thermal conductive silicone to increase the heat exchange area with the cooling air side.

[0027] A safe and energy-saving flat heat pipe air-cooled fuel cell stack of the present invention and a fuel cell stack air-cooled heat management method using flat heat pipes utilize the advantages of good heat transfer performance of the micro heat pipe array and easy combination with the flat bipolar plate for heat dissipation of the air-cooled fuel cell stack, realizing the separation of reaction air and cooling air, avoiding excessive reaction air from reducing the humidity of the proton exchange membrane and affecting the conductivity. At the same time, the micro heat pipe array realizes uniform temperature inside the stack, avoiding large differences between individual single cells, thereby ensuring efficient power generation of the stack. At the same time, the micro heat pipe array combined with the electric heating film / electric heating sheet can realize the rapid cold start of the stack in a low-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FIG. is an assembly schematic diagram of an embodiment of an air-cooled fuel cell stack based on flat heat pipes;

[0029] Figure 2 FIG. is a schematic diagram of the composition of the anode plate, cathode plate and membrane electrode fitted with the micro heat pipe array;

[0030] Figure 3 FIG. is a schematic diagram of a single anode plate and cathode plate fitted with the micro heat pipe array;

[0031] Figure 4 FIG. is a schematic diagram of the combination of the micro heat pipe array for single heat dissipation and the fins;

[0032] Figure 5 FIG. is a schematic diagram of the combination of the micro heat pipe array with heat dissipation and heating functions, the fins and the electric heating film.

[0033] In the figure: 1 - fuel cell stack, 1-1 - end plate, 1-2 - anode plate, 1-3 - cathode plate, 1-4 - membrane electrode, 2 - micro heat pipe array, 2-1 - evaporation section of the micro heat pipe array, 2-2 - condensation section of the micro heat pipe array, 3 - fins, 4 - fan, 4-1 - cooling fan, 4-2 - fan for providing reaction air, 5 - electric heating sheet. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To understand the content of the present invention more clearly, it will be described in detail through the attached Figures 1-5 drawings and specific embodiments, but the embodiments of the present invention are not limited thereto.

[0035] Embodiment 1

[0036] As Figures 1-3As shown in the figure, this embodiment is a fuel cell stack with a safe and energy-saving flat micro heat pipe air-cooling method, which consists of a fuel cell stack 1, a micro heat pipe array 2, and a fan 4. The fuel cell stack 1 includes two end plates 1-1, a current collector, multiple membrane electrodes 1-4, and multiple groups of bipolar plates. The multiple membrane electrodes 1-4 and bipolar plates are arranged alternately. Some bipolar plates are attached to the micro heat pipe array 2 to form bipolar plates with a micro heat pipe array, and some bipolar plates are not attached to the heat pipes and are formed into a single plate by one-time processing. The bipolar plate with the micro heat pipe array 2 consists of multiple anode plates 1-2 and cathode plates 1-3 with the micro heat pipe array 2 attached in the middle. The micro heat pipe array 2 is attached between the anode plate 1-2 and the cathode plate 1-3 and is closely arranged within the activation area. The part of the micro heat pipe array 2 attached to the bipolar plate is the evaporation section 2-1 of the micro heat pipe array. The length of the micro heat pipe array 2 is greater than that of each group of bipolar plates to form an extended part, and the extended part serves as the condensation section 2-2 of the micro heat pipe array. The heat generated by the contact of hydrogen and air through the proton exchange membrane is transferred to the condensation section 2-2 of the micro heat pipe array through the evaporation section 2-1 of the micro heat pipe array attached between the anode plate 1-2 and the cathode plate 1-3. The micro heat pipe array 2 is a flat heat conductor and electrical conductor with a porous structure formed by extruding a metal material. It has multiple micro heat pipes arranged side by side that do not communicate with each other and operate independently. The hydraulic diameter of each micro heat pipe is 1 mm, and the internal phase change working medium is a non-conductive medium, making the micro heat pipe array 2 a heat conduction element and electrical conduction element with enhanced heat transfer effect. The fan 4 includes a cooling fan 4-1 and a fan 4-2 that provides reaction air, both of which are axial fans 4. The fan 4-2 that provides reaction air is attached to the outer surface of the fuel cell stack 1 to provide the air required for the electrochemical reaction; the cooling fan 4-1 is fixed on the fan 4-2 that provides reaction air and is arranged facing the condensation section 2-2 of the micro heat pipe array to send air to the condensation section 2-2 of the micro heat pipe array, forming forced convection and quickly dissipating heat.

[0037] A thermal management method for a fuel cell stack using a safe and energy-saving flat heat pipe air-cooling type, adopting the above fuel cell stack 1. The heat generated by the contact of hydrogen and air through the proton exchange membrane is transferred to the condensation section 2-2 of the micro heat pipe array through the evaporation section 2-1 of the micro heat pipe array attached between the anode plate 1-2 and the cathode plate 1-3. When it is detected that the internal temperature of the fuel cell stack 1 reaches the set value, the control system turns on the external cooling fan 4-1 to perform forced convection heat dissipation on the condensation section 2-2 of the micro heat pipe array, achieving the effect of dissipating heat from the fuel cell stack 1.

[0038] Embodiment 2

[0039] The fuel cell stack of this embodiment using a micro heat pipe array air-cooling method for thermal management adds fins 3 on the basis of Embodiment 1.

[0040] As Figure 4As shown, in order to increase the heat exchange area, the protruding parts of each of the micro heat pipe arrays 2 are attached to the upper fins 3 using thermally conductive silicone. Through the operation of the cooling fan 4-1 installed above the fins 3, heat is taken away from inside the battery, achieving the effect of dissipating heat from the fuel cell.

[0041] Embodiment 3

[0042] For a fuel cell stack using the air cooling method of the micro heat pipe array for thermal management in this embodiment, based on the structure of Embodiment 1 or Embodiment 2, the micro heat pipe array 2 not only includes the linear micro heat pipe array 2, but also includes the L-shaped micro heat pipe array 2, and an electric heating sheet 5 is provided on the L-shaped micro heat pipe array 2.

[0043] As Figure 5 shown, several groups of bipolar plates are spaced apart, and the L-shaped micro heat pipe array 2 is attached between the anode plate 1-2 and the cathode plate 1-3, or in other words, part of the linear micro heat pipe array 2 is replaced with the L-shaped micro heat pipe array 2. The electric heating sheet 5 is attached to the bent part at the end of the L-shaped micro heat pipe array 2.

[0044] For a fuel cell stack using the air cooling method of the micro heat pipe array for thermal management, adopting the above thermal management system, the micro heat pipe array 2 is attached between the anode plate 1-2 and the cathode plate 1-3, and the heat generated by the contact of hydrogen and air through the proton exchange membrane is transferred to the condensation section 2-2 of the protruding part of the micro heat pipe array. When it is detected that the internal temperature of the battery stack reaches the set value, the control system turns on the cooling fan 4-1, and uses the external air-cooled fins 3 for forced convection heat dissipation. When starting is required when the battery temperature is lower than the second set value, first turn on the electric heating sheet 5 to heat, and heat the battery through the micro heat pipe array 2. When the internal temperature of the battery stack is higher than 0°C (or 20°C), then start, realizing the cold start function.

[0045] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any form of change that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A safe and energy-saving flat heat pipe air-cooled fuel cell stack, characterized in that, it includes a fuel cell stack, a micro heat pipe array and an external fan; The fuel cell stack is composed of two end plates, current collectors, multiple membrane electrodes and multiple groups of bipolar plates. Between the two end plates, multiple membrane electrodes and bipolar plates are arranged alternately. Some or all of the bipolar plates are attached to the micro heat pipe array. The micro heat pipe array is attached between the anode plate and the cathode plate to form a bipolar plate with a micro heat pipe array. The part of the micro heat pipe array attached to the anode plate and the cathode plate is the evaporation section of the micro heat pipe array, and the part of the micro heat pipe array extending out of the fuel cell stack is the condensation section of the micro heat pipe array; The external fan is fixed on the side of the fuel cell stack and is arranged facing the condensation section of the micro heat pipe array, and can send air to the condensation section of the micro heat pipe array to form forced convection; The micro heat pipe array is a flat heat conductor with a porous structure formed by extruding a metal material. It has multiple micro heat pipes arranged side by side and operating independently without communication. The hydraulic diameter of each micro heat pipe is 0.2 - 3.0 mm, and the internal phase change working medium is a non-conductive medium. The conductivity of a single micro heat pipe is adjusted by adjusting the width of the partition wall between the micro heat pipes; It also includes heat dissipation fins, and the heat dissipation fins are attached to the condensation section of the micro heat pipe array; The micro heat pipe array includes a straight micro heat pipe array and an L-shaped micro heat pipe array, and an electric heating sheet is attached to the bent part of the lower part of the L-shaped micro heat pipe array.

2. A thermal management method for a safe and energy-saving flat heat pipe air-cooled fuel cell stack, characterized in that, using the safe and energy-saving flat heat pipe air-cooled fuel cell stack described in claim 1, the heat generated by the contact of hydrogen and air through the proton exchange membrane is transferred to the condensation section of the micro heat pipe array through the evaporation section of the micro heat pipe array attached between the anode plate and the cathode plate, and natural convection heat dissipation or forced heat dissipation by the external fan is carried out; A heat dissipation fin is attached to the condensation section of the micro heat pipe array. After the fan is turned on, air enters the fin inter-channel from the side, cools the fins and then discharges upward from the condensation section of the micro heat pipe array; Several groups of the bipolar plates are spaced apart and attached to the L-shaped micro heat pipe array, and an electric heating sheet is attached to the bent part of the end of the L-shaped micro heat pipe array. When starting in a low-temperature environment, first turn on the electric heating sheet to heat the L-shaped micro heat pipe array, thereby heating the fuel cell stack. When the internal temperature of the fuel cell stack reaches the starting temperature, then start the battery.

3. According to the thermal management method of the safe and energy-saving flat heat pipe air-cooled fuel cell stack described in claim 2, characterized in that, when using the external fan for heat dissipation, when it is detected that the internal temperature of the fuel cell stack reaches the set value, the control system turns on the external fan to perform forced convection heat dissipation on the condensation section of the micro heat pipe array.

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