A vane radial spiral flow field for electrochemical energy conversion devices

Abstract

A kind of vane radial spiral flow field for electrochemical energy conversion device, the flow field is central symmetry radial spiral structure, entrance position is located in the center of flow field, shortens the flow path of reactant, ensures the uniformity of its concentration distribution and flow field temperature distribution, effectively reduces the temperature difference between reactant entrance and product outlet, can promote energy conversion efficiency;Along the direction of reactant flow, the distance between flow channels also increases from the entrance to the outlet first and then decreases, which can avoid gas blockage, increase the flow rate at the outlet to promote the rapid discharge of gas, and effectively reduce the pressure drop of inlet and outlet;The flow field adopts leaf-shaped rib, the design of the leaf section can reduce the flow resistance, at the same time, the suction surface is at the back of the leaf, the air pressure along its surface is lower, while the pressure surface is at the basin of the leaf, the fluid pressure on one side of its surface is higher, can form a certain pressure difference between adjacent flow channels to enhance the mass transfer process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemistry, and particularly relates to a vane type radial spiral flow field for electrochemical energy conversion devices such as fuel cells, flow batteries and electrolytic cells. BACKGROUND

[0002] With the rapid development of the global economy, mankind is facing the problems of resource depletion, environmental pollution and climate warming, and each country has proposed a series of measures to address this problem. China first proposed the "3060" plan in September 2020, striving to achieve carbon neutrality and carbon peak as soon as possible, so it is urgent to develop green and efficient new energy technologies while saving energy and reducing emissions. Fuel cells, as a portable device that can directly convert chemical energy into electrical energy, have been widely studied in recent years.

[0003] In addition to hydrogen-oxygen fuel cells, direct liquid fuel cells using sodium borohydride, methanol and ethanol as fuel have also attracted attention due to their high energy density, simple structure design and other advantages. Traditional direct liquid fuel cells usually use oxygen as the cathode oxidant, while hydrogen peroxide has been shown to significantly improve the theoretical voltage of the battery and the performance of the battery. The disadvantage is that hydrogen peroxide is easily decomposed under the action of catalysts and heat to produce a large amount of oxygen, resulting in a serious gas-liquid two-phase flow phenomenon in the cathode flow field, which causes uneven current density and pressure distribution. Similarly, when sodium borohydride is used as fuel at the anode, it will hydrolyze to produce hydrogen, which also produces similar gas-liquid two-phase flow, and the gas covers the active sites, thereby affecting the electrochemical reaction.

[0004] Existing technologies usually improve the battery from two aspects of electrode properties and flow field structure. In terms of flow field design, traditional serpentine flow field, interdigital flow field, parallel flow field and new bionic flow field structure each have advantages and disadvantages. The flow velocity distribution in the parallel flow field is uneven, and the pressure difference is small, which can lead to poor flowability; the serpentine flow field can cause gas-liquid accumulation at the bend during flow and has a high pressure drop. Therefore, the existing flow field structure has certain limitations in reducing the negative effects of gas-liquid two-phase flow and ensuring uniformity of reactant concentration distribution.

[0005] In addition to fuel cells, electrolytic cells also involve the uniformity of gas-liquid two-phase flow, and there is currently no related flow field structure design for such problems. Therefore, it is necessary to develop a new type of flow field structure to solve this problem while enhancing the mass transfer process in the flow field, which is also applicable to the field of flow batteries. SUMMARY

[0006] In view of the problems in the prior art, the present application aims to provide a vane-type radial spiral flow field capable of effectively shortening the flow path, enhancing the flow mass transfer process, improving the uniformity of flow velocity distribution in the flow field, and realizing uniform distribution of reactant concentration and current density.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: a cylindrical shell with an annular channel arranged on the inner wall, a gas product outlet and a liquid product outlet arranged on the upper and lower ends of the cylindrical shell and communicated with the annular channel, a reactant inlet arranged on the top center of the cylindrical shell and communicated with the annular channel, and a plurality of vanes installed around the reactant inlet and forming a reactant channel communicated with the annular channel between adjacent vanes.

[0008] The profile surface of the vane is columnar or free curved surface, and the outer cross section is composed of four curves of a vane leading edge, a vane back, a vane basin and a vane trailing edge, wherein the curves of the vane back and the vane basin are selected from quadratic curves or Bezier curves, and the vane leading edge and the vane trailing edge are convex circular arc structures.

[0009] The vanes are arranged in a spiral flow field structure in a circular flow field around the reactant inlet, and the arrangement mode is clockwise arrangement, counterclockwise arrangement or alternate arrangement, and the product outlet and the reactant channel are arranged in parallel to facilitate the flow of the reaction products and the generated gas along the flow lines.

[0010] The distance between the adjacent two vanes gradually increases and then decreases, the flow velocity gradually decreases when the cross-sectional area of the flow channel gradually increases from A1 to A2 from the inlet, and the flow velocity increases and the products are discharged to the annular channel when the flow cross-sectional area decreases to A3.

[0011] The flow cross-sectional area A (m 2 ), the flow velocity v (m / s) and the flow Q (ml / min) of the fluid between the rib flow channels of the adjacent vanes satisfy the following formula:

[0012] Q = v x A

[0013] The fluid between the adjacent vanes is regarded as incompressible fluid, and the density p is constant, the flow velocity at the cross section A1 is v1 (m·s -1 ), the pressure is p1 (Pa), the height is z1 (m), the gravitational acceleration is g (m·s -2 ), the flow velocity at the cross section A2 is v2 (m·s -1 ), the pressure is p2 (Pa), the height is z2 (m), the pressure difference of the two cross sections is Δp (Pa), and the gradually tapered and gradually expanded flow cross-sectional area satisfies the Bernoulli equation:

[0014]

[0015]

[0016] The ratio of the inlet and outlet pressure difference to the outlet dynamic pressure of the spiral flow field structure is the flow resistance coefficient ξ, p in and V in For inlet pressure and velocity, p out and V out For export pressure and velocity, they satisfy the following relationship:

[0017]

[0018] In this invention, the reactant inlet is located at the center of a circular flow field. After flowing in through the inlet, the reactants spiral out radially, converging in an annular channel. Under the influence of centrifugal force and gravity, the liquid reactants flow out from the lower outlet, while the gaseous products flow out from the upper outlet. The trajectory of the inscribed circle within the cross-section is the blade centerline, with its leading and trailing edges being the leading and trailing edges, respectively. The distance between these two points is the chord length *a*, and the angle between the tangents at the leading and trailing edges is the curvature angle *ω*. The radii of the leading and trailing edges are *r1* and *r2*, respectively. These parameters can be adjusted to determine the required blade cross-sectional area when designing flow fields with different orifice ratios. The angle formed by the tangent on the back of each blade and the center of the flow field can be adjusted to change the curvature of the flow channel.

[0019] Furthermore, the blades can create a certain pressure difference between adjacent flow channels to enhance the mass transfer process. The smooth streamlines of the blade surface help reduce flow resistance. In addition, the protrusions at the leading edge of the blade can disperse the bubbles and allow them to flow into the annular channel. The blade back is the suction surface, and the airflow pressure along its surface is lower, while the blade base is the pressure surface, and the fluid pressure on one side of its surface is higher. This can create a certain pressure difference between adjacent flow channels to enhance the mass transfer process.

[0020] As can be seen from the above technical solutions, the present invention has the following advantages:

[0021] 1. The flow field is a centrally symmetrical radial spiral structure with the inlet located at the center of the flow field, which shortens the flow path of the reactants, ensures the uniformity of reactant concentration and temperature distribution, effectively reduces the temperature difference between the inlet and outlet, and can improve the operating efficiency of the device.

[0022] 2. Along the direction of reactant flow, the channel spacing increases and then decreases from the inlet to the outlet, which can avoid gas blockage, increase the flow velocity at the outlet to promote rapid gas discharge, and effectively reduce the pressure drop at the inlet and outlet.

[0023] 3. The flow field adopts the shape of the blade as the rib. The design of this blade section can reduce the flow resistance. The bulges on the leading and trailing edges of the blade can enhance the turbulence and mass transfer process, and disperse bubbles at the outlet of the flow channel, effectively improving the uniformity of the current density distribution.

[0024] 4. The underside of the blade is the suction surface, where the airflow pressure is lower, while the leaf basin is the pressure surface, where the fluid pressure is higher on one side. This can create a pressure difference between adjacent flow channels, thereby enhancing the mass transfer process. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the flow field structure of the present invention;

[0026] Figure 2 for Figure 1 A sectional view;

[0027] Figure 3 This is a schematic diagram of the flow channel between adjacent blade-shaped ribs of the present invention;

[0028] Figure 4 This is a schematic diagram of the blade cross-section in this invention;

[0029] Figure 5 This is a schematic diagram of the fuel cell structure according to an embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram illustrating the application of the present invention in a flow battery;

[0031] Figure 7 This is a schematic diagram illustrating the application of the present invention in an electrolytic cell.

[0032] In the diagram: 1-Reactant inlet; 2-Gas product outlet; 3-Liquid product outlet; 4-Leaf-shaped rib; 5-Annular channel; 6-Leaf-shaped leading edge; 7-Leaf back; 8-Leaf basin; 9-Leaf-shaped trailing edge; 10-Leaf-shaped centerline; 11-Anode flow field; 12-Anode diffusion layer; 13-Anode microporous layer; 14-Anode catalyst layer; 15-Ion exchange membrane; 16-Cathode catalyst layer; 17-Cathode microporous layer; 18-Cathode diffusion layer; 19-Cathode flow field; 20-Positive electrode flow field; 21-Positive electrode current collector; 22-Positive electrode porous electrode; 23-Negative electrode porous electrode; 24-Negative electrode current collector; 25-Negative electrode flow field; 26-Anode diffusion layer; 27-Anode catalyst layer; 28-Proton exchange membrane; 29-Cathode catalyst layer; 30-Cathode diffusion layer; 31-Shell. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0034] See Figures 1-4The present invention includes a cylindrical shell 31 with an annular channel 5 on its inner wall, and a gas product outlet 2 and a liquid product outlet 3 communicating with the annular channel 5 respectively provided at the upper and lower ends of the cylindrical shell 31. A reactant inlet 1 communicating with the annular channel 5 is provided at the center of the top of the cylindrical shell 31, and a plurality of blades 4 are installed around the reactant inlet 1, forming a reactant channel between adjacent blades 4 that connects the reactant inlet 1 and the annular channel 5; the blades 4 have a blade profile of... The blade is cylindrical or freeform, with its cross-section composed of four curves: the leading edge (6), the back (7), the base (8), and the trailing edge (9). The curves for the back (7) and base (8) are quadratic or Bezier curves. The leading edge (6) and trailing edge (9) are arc-shaped structures, with the leading edge (6) being a convex arc. The trajectory of the inscribed circle within the cross-section is the blade centerline, with its endpoints being the leading and trailing edges, the distance between which is the chord length *a*. The angle between the tangents at the leading and trailing edges is the curvature angle *ω*, and the radii of the leading and trailing edges are *r1* and *r2*, respectively. These parameters can be adjusted to determine the required cross-sectional area of ​​the blade when designing different opening ratios for the flow field. The angle between the tangent on the back of each blade and the center of the flow field can be adjusted to change the curvature of the flow channel. The blade rib shape can create a certain pressure difference between adjacent flow channels to enhance the mass transfer process. Its smooth surface streamlines help reduce flow resistance, and the raised position at the leading edge 6 of the blade enables bubble dispersion, allowing it to flow into the annular channel 5. The blades 4 are arranged in a spiral flow field around the reactant inlet 1, forming a spiral flow field structure. The arrangement can be clockwise, counterclockwise, or alternating. The product outlet and reactant channel are arranged parallel to each other, facilitating the discharge of reaction products and generated gas along the streamlines. The distance between adjacent blades 4 gradually increases and then decreases. As the cross-sectional area from the inlet to the flow channel gradually increases from A1 to A2, the flow velocity gradually decreases. After the flow cross-sectional area decreases to A3, the flow velocity increases and discharges the product into the annular channel 5. The flow cross-sectional area A(m²) between adjacent blade 4 ribs is... 2 The flow velocity v (m / s) and flow rate Q (ml / min) satisfy the following equation:

[0035] Q = v × A

[0036] The fluid between adjacent blades 4 is considered an incompressible fluid with a constant density ρ. When flowing from section A1 to section A2, the flow velocity at section A1 is v1 (m·s). -1 The pressure is p1 (Pa), the height is z1 (m), and the gravitational acceleration is g (m·s). -2 The flow velocity at section A2 is v2 (m·s). -1 Let the pressure be p2 (Pa) and the height be z2 (m). Let the pressure difference between the two sections be denoted as Δp (Pa). The gradually contracting and expanding flow cross-sectional areas satisfy Bernoulli's equation:

[0037]

[0038]

[0039] The ratio of the inlet and outlet pressure difference to the outlet dynamic pressure of the spiral flow field structure is the flow resistance coefficient ξ, p in and V in For inlet pressure and velocity, p out and V out For export pressure and velocity, they satisfy the following relationship:

[0040]

[0041] See Figure 5 A specific embodiment of the fuel cell device of the present invention includes an anode flow field 11, a reactant inlet (anode fuel inlet) 1, a gaseous product outlet (anode product outlet) 2, a liquid product outlet (anode product outlet) 3, an anode diffusion layer 12, an anode microporous layer 13, an anode catalyst layer 14, an ion exchange membrane 15, a cathode catalyst layer 16, a cathode microporous layer 17, a cathode diffusion layer 18, and a cathode flow field 19.

[0042] See Figure 6 A specific embodiment of the flow battery device of the present invention includes a positive electrode flow field 20, a reactant inlet (positive electrode electrolyte inlet) 1, a gas product outlet (positive electrode product outlet) 2, a liquid product outlet (positive electrode product outlet) 3, a positive electrode current collector 21, a positive electrode porous electrode 22, a negative electrode porous electrode 23, a negative electrode current collector 24, and a negative electrode flow field 25.

[0043] See Figure 7 A specific embodiment of the proton exchange membrane water electrolyzer device of the present invention includes an anode flow field 11, a cathode flow field 19, an anode diffusion layer 26, an anode catalyst layer 27, a proton exchange membrane 28, a cathode catalyst layer 29, and a cathode diffusion layer 30.

[0044] The reactant inlet is located at the center of the circular flow field. After the reactants flow in from the inlet, they flow out in a radial spiral shape and converge in the annular channel. Under the action of centrifugal force and gravity, the liquid phase reactants flow out from the lower outlet and the gaseous products flow out from the upper outlet.

[0045] Example 1

[0046] like Figure 5 As shown, the working steps of the novel flow field structure of the present invention in a fuel cell are as follows:

[0047] Step S100: Fuel pumped into the flow channel. Taking a fuel cell with hydrogen peroxide as the cathode oxidant as an example, the anode fuel flows into the flow field from the reactant inlet 1 in an active or passive manner, and the cathode oxidant enters the flow channel from the reactant inlet 1. During the mass transfer to the electrode, a decomposition reaction occurs, producing a large amount of oxygen, which will lead to a gas-liquid two-phase flow and an increase in the volumetric flow rate in the flow channel. Under the action of centrifugal force and gravity, the liquid is mainly discharged from the liquid product outlet 3, and the gas is mainly discharged from the gas product outlet 2.

[0048] Step S200: Electrochemical reaction. The anode fuel diffuses and permeates through the anode diffusion layer 12 and the anode microporous layer 13 to the anode catalyst layer 14, where it undergoes an oxidation reaction and loses electrons. The electrons travel through the external circuit to the cathode side. The cathode oxidant diffuses and permeates through the cathode diffusion layer 18 and the cathode microporous layer 17 to the cathode catalyst layer 16, where it gains electrons and undergoes a reduction reaction. This completes one discharge process.

[0049] Step S300: Product discharge process. As the discharge process proceeds, the anode reaction products are discharged from anode product outlets 2 and 3, and the cathode reaction products and a large amount of gas are discharged from cathode product outlets 2 and 3.

[0050] Example 2

[0051] like Figure 6 As shown, the application steps of the novel flow field structure of the present invention in a flow battery are as follows:

[0052] Step S100: Electrolyte inflow process. Under the action of the pump, the positive electrode electrolyte enters the positive electrode of the flow battery through the reactant (positive electrode electrolyte) inlet 1, and is uniformly distributed to the positive porous electrode 22 through convection and diffusion. Similarly, the negative electrode electrolyte is pumped to the negative electrode 23 through the negative electrode electrolyte inlet. For the flow battery, the mass transfer process in the porous electrode is crucial. In this flow field, the blade back is the suction surface, with lower airflow pressure along its surface, while the blade base is the pressure surface, with higher fluid pressure on one side of its surface. This can create a certain pressure difference between adjacent flow channels, thereby enhancing the mass transfer process.

[0053] Step S200: Battery charging and discharging reaction. During charging, the positive electrolyte on the surface of the positive porous electrode 19 undergoes an oxidation reaction and loses electrons. The electrons from the positive electrode are conducted through the positive current collector 18 and the external circuit to the negative current collector 21 and reach the surface of the negative porous electrode 20. The negative electrolyte on the surface of the negative porous electrode 20 gains electrons and undergoes a reduction reaction. During discharging, the electron gain and loss are in opposite directions. The negative electrolyte loses electrons on the surface of the negative porous electrode 20 and undergoes an oxidation reaction, while the positive electrolyte gains electrons on the surface of the positive porous electrode 19 and undergoes a reduction reaction.

[0054] Step S300: Electrolyte discharge process. After the electrolyte has fully reacted on the electrode surface, its concentration is lower when it flows through the discharge zone near the outlet. The smaller cross-sectional area of ​​the single-channel flow path here is conducive to the rapid discharge of reaction products. At the same time, the shorter flow path from the inlet to the outlet helps to reduce flow resistance and inlet / outlet pressure drop, thereby improving the uniformity of electrolyte flow and battery stability.

[0055] Example 3

[0056] like Figure 7 As shown, the application of the novel flow field structure of the present invention in a proton exchange membrane water electrolyzer is as follows:

[0057] During operation, the electrolyte enters the flow channel through inlet 1. Under the capillary pressure in the porous medium, the electrolyte permeates from the anode diffusion layer 26 to the surface of the anode catalyst layer 27. After power is applied to the electrolyzer, liquid water precipitates oxygen and hydrogen ions on the anode electrode surface and releases electrons. The electrons are transferred to the cathode electrode 30 through the external circuit, while the hydrogen ions diffuse through the proton exchange membrane 28 to the cathode catalyst layer 29 and combine with electrons to generate hydrogen gas. For the electrolyzer, a shorter flow path ensures that the hydrogen and oxygen generated by the electrolyte are discharged from the flow channel at a faster speed, preventing airflow blockage and coverage of active sites. The varying flow cross-sectional area within a single flow channel helps reduce the pressure drop at the inlet and outlet, improves the uniformity of temperature distribution, and the raised portion at the trailing edge of the blade at the outlet helps disperse bubbles and reduce airflow blockage.

[0058] Compared to existing technologies, this invention features a centrally symmetrical radial spiral structure for the flow field, with the inlet located at the center of the flow field. This shortens the reactant flow path, ensuring uniformity in reactant and temperature distribution, effectively reducing the temperature difference between the inlet and outlet of the flow channel, and improving the operating efficiency of the electrolyzer. Along the reactant flow direction, the channel spacing first increases and then decreases from the inlet to the outlet, preventing gas blockage, increasing the flow velocity at the outlet to promote rapid gas discharge, and effectively reducing the pressure drop at the inlet and outlet. The flow field uses a blade shape as ribs, and this blade cross-section design reduces flow resistance. The convex angles of the leading and trailing edges of the blades enhance turbulence and mass transfer processes, and disperse bubbles at the outlet of the flow channel, effectively improving the uniformity of the current density distribution.

Claims

1. A blade-type radial helical flow field for an electrochemical energy conversion device, characterized in that: The cylindrical shell (31) includes an annular channel (5) on its inner wall, and gas product outlet (2) and liquid product outlet (3) connected to the annular channel (5) are respectively provided at the upper and lower ends of the cylindrical shell (31). A reactant inlet (1) connected to the annular channel (5) is provided at the center of the top of the cylindrical shell (31), and several blade-shaped ribs (4) are provided around the reactant inlet (1). A reactant channel is formed between adjacent blade-shaped ribs (4) to connect the reactant inlet (1) and the annular channel (5). The blade-shaped rib (4) has a columnar or free-form surface. The cross-section is composed of four curves: the leading edge (6), the back (7), the base (8), and the trailing edge (9). The curves of the back (7) and the base (8) are quadratic curves or Bezier curves. The leading edge (6) and the trailing edge (9) are arc-shaped structures. The distance between two adjacent leaf-shaped ribs (4) increases and then decreases again. When the cross-sectional area of ​​the reactant channel from reactant inlet (1) to annular channel (5) gradually increases from A1 to A2, the flow rate gradually decreases. As the cross-sectional area decreases to A3, the flow rate increases and the product is discharged into annular channel (5).

2. The blade-type radial helical flow field for an electrochemical energy conversion device according to claim 1, characterized in that: The leading edge (6) of the blade is a raised arc structure.

3. The blade-type radial helical flow field for an electrochemical energy conversion device according to claim 1, characterized in that: The blade-shaped ribs (4) are arranged in a spiral pattern around the reactant inlet (1) to form a spiral flow field structure. The arrangement is either clockwise or counterclockwise. The gas product outlet (2) and liquid product outlet (3) are arranged in parallel with the reactant channel in a way that facilitates the discharge of the reaction products and generated gas along the streamline.

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