Heat storage ball with double-layer structure, packed bed heat storage tank and heat storage device

Abstract

The invention provides a heat storage ball with a double-layer structure, a packed bed heat storage tank and a heat storage device.The heat storage ball comprises a first ball body and a second ball body, the first ball body is arranged in an inner cavity of the second ball body, the inner cavity of the first ball body is filled with a first phase-change material, the inner cavity of the second ball body is filled with a second phase-change material, and the first phase-change material and the second phase-change material are arranged in the first phase-change material. The phase change temperature of the first phase change material is lower than that of the second phase change material; compared with a single-layer same-diameter heat storage ball device, the heat storage ball of the double-layer structure can improve the heat storage rate density of the heat storage device, so that the heat storage performance is optimal.

Description

Technical Field

[0001] The invention belongs to the field of energy storage and relates to a double-layer heat storage ball, a packed bed heat storage tank and a heat storage device. Background Art

[0002] As global fossil energy becomes increasingly scarce, the utilization rate of renewable energy is increasing. The latest BP Energy Report shows that in the past five years, the cost of onshore wind and solar power generation has dropped by about 40% and 55% respectively, so the development of renewable energy is imperative. Among renewable energy sources, the richness of solar energy supply potential is the main consideration for its global energy improvement. According to Hoeven's forecast, by 2050, solar energy will account for 27% of global electricity generation, of which photovoltaic (PV) solar energy and concentrated solar power generation (CSP) systems will account for 60% and 40% respectively. At present, the CSP system has been technically evaluated and discussed, and the system power generation cost is as low as about 0.05 euros / kWh. To be precise, in the face of the intermittent supply of wind energy and solar radiation, energy storage technology is used to deploy sustainable energy plans to meet global energy needs. And because the earth is constantly rotating, the supply of solar radiation energy is intermittent, which makes it impossible to get light at night. Therefore, this issue has triggered research in the field of thermal storage, and optimizing the use of solar energy to achieve energy peak regulation has attracted substantial attention. Thermal storage systems with phase change materials (PCM) as the core can store energy on a daily or seasonal basis. Ice is often used as PCM and hot water as HTF in thermal energy storage, and its essence is energy transfer. When solar energy is limited, seasonal heat storage helps to avoid energy shortages. In fact, thermal energy storage applications span many areas of thermal equipment configuration to achieve waste heat recovery. Waste heat recovery generally includes nuclear waste heat recovery, industrial waste heat recovery, waste heat recovery in the oil and gas field, and waste heat recovery from solar power generation.

[0003] The development of thermal energy storage technology (TES) is an effective means to coordinate the balance of energy supply and demand, so that the mismatch between supply and demand can be effectively alleviated. Therefore, the storage of thermal energy has become an important aspect of engineering applications, especially in building energy conservation. For example, the heat collected when there is sufficient sunlight can be stored and then released at night for use in the heating system. Heat storage can also be used in buildings with huge heating needs and can compete with other forms of heating. Phase change energy storage in energy storage technology has gradually become the mainstream because of its fixed melting and solidification temperatures and high energy density. These materials can release and store heat by solidification and melting.

[0004] The largest application of TES is in district heating and cooling networks, where TES can decouple the demand for district heating and cooling from the available power generation, enabling seasonal storage of variable renewable energy. At the beginning of 2021, Denmark had five large thermal storage tanks in operation and connected to the local district heating network.

[0005] The use of TES in district heating in my country is also increasing. The packed bed TES system has attracted widespread attention due to its simple structure and good heat transfer effect. The current representative PCM packaging method is a spherical capsule with a simple shape, which is also commonly used as a PCM packaging unit in a packed bed TES system. Packed bed thermal energy storage (PBTES) is another more cost-effective arrangement that uses low-cost solid fillers in a single tank. Compared with TES, the estimated capital cost of the PBTES heat storage system may be reduced by 20% - 37%; since the 1980s, people have conducted extensive research on the phase change characteristics within a single spherical capsule, especially convection-dominated melting and the heat transfer associated with it. Studies have found that the thermal conductivity of PCM is relatively low, which in turn limits the widespread application of PBTES heat storage systems. At present, the ways to enhance PCM heat transfer are to increase the heat exchange area and increase the thermal conductivity of PCM. Many researchers have conducted experimental and numerical studies on macroscopically encapsulated PCMs in these two ways to analyze the effects of various conditions and geometric parameters on their thermal properties. The studies have found that the melting of the PCM in the center of the traditional spherical capsule is always relatively delayed, which affects the heat transfer of the PCM and thus the heat storage rate of the heat storage device. Summary of the invention

[0006] The purpose of the present invention is to provide a double-layer heat storage ball, a packed bed heat storage tank and a heat storage device, which solves the problem that the PCM melting in the center of the traditional spherical capsule is always relatively delayed, affecting the heat transfer of the PCM and thus causing the defect of the heat storage rate of the heat storage device.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: The present invention provides a double-layer heat storage ball, comprising a first ball and a second ball, wherein the first ball is placed in the inner cavity of the second ball, wherein: The inner cavity of the first sphere is filled with a first phase change material, and the inner cavity of the second sphere is filled with a second phase change material. The phase change temperature of the first phase change material is lower than the phase change temperature of the second phase change material.

[0008] Preferably, the first sphere and the second sphere are connected via a connecting piece.

[0009] Preferably, the diameters of the first sphere and the second sphere are obtained by a numerical simulation method.

[0010] A packed bed heat storage tank comprises a cylindrical heat storage tank body, a top conical heat storage tank body and a bottom conical heat storage tank body, wherein the top conical heat storage tank body and the bottom conical heat storage tank body are respectively connected to the top and the bottom of the cylindrical heat storage tank body, and the inner cavity of the cylindrical heat storage tank body is filled with the heat storage balls.

[0011] Preferably, the top conical heat storage tank body and the cylindrical heat storage tank body are connected via an upper connecting flange, and a fluid inlet is provided at the top thereof.

[0012] Preferably, the bottom conical heat storage tank body and the cylindrical heat storage tank body are connected via a lower connecting flange, and a fluid outlet is provided at the bottom thereof.

[0013] Preferably, flow equalizers are installed at the top and bottom of the inner cavity of the cylindrical heat storage tank.

[0014] Preferably, a metal bracket for supporting the heat storage ball is installed at the bottom of the inner cavity of the cylindrical heat storage tank.

[0015] A heat storage device, comprising a packed bed heat storage tank, a fluid inlet pipe and a fluid outlet pipe, wherein a fluid inlet opened at the top of the packed bed heat storage tank is connected to the fluid inlet pipe, and a fluid outlet opened at the bottom of the packed bed heat storage tank is connected to the fluid outlet pipe; The packed bed heat storage tank is filled with the heat storage balls.

[0016] Preferably, the packed bed heat storage tank comprises a cylindrical heat storage tank body, a top conical heat storage tank body and a bottom conical heat storage tank body, wherein the top conical heat storage tank body and the bottom conical heat storage tank body are respectively connected to the top and the bottom of the cylindrical heat storage tank body.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a double-layer heat storage ball, which is filled with phase change materials with different phase change temperatures. The heat storage phase change material with a higher phase change temperature is placed on the outside. When the heat transfer fluid passes through, a large amount of heat is transferred to the fluid. The heat decays after passing through the outer sphere. The inner heat storage sphere is filled with phase change heat storage balls with a lower phase change temperature, which can increase the melting rate of the inner heat storage sphere. Compared with a single-layer heat storage ball device with the same diameter, the double-layer ball heat storage device can increase the heat storage rate density of the heat storage device, thereby optimizing the heat storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the double-layer heat storage ball structure; Figure 2 Schematic diagram of the structure of the heat storage device.

[0019] In the figure, 1 is a cylindrical heat storage tank structure; 2 is a top conical heat storage tank; 3 is a bottom conical heat storage tank; 4 is a top fluid inlet channel; 5 is a bottom fluid outlet channel; 6 is a top connecting flange; 7 is a bottom connecting flange; 8 is a top flow equalizer; 9 is a bottom flow equalizer; 10 is a double-layer ball heat storage unit filled inside the packed bed; 11 is a metal support frame; 101 is a first sphere; 102 is a second sphere; 103 is a connector. DETAILED DESCRIPTION

[0020] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0021] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0022] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0023] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0024] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0025] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0026] Example 1 like Figure 1 As shown, a double-layer heat storage ball provided in this embodiment includes a first sphere 101 and a second sphere 102, wherein the first sphere 101 is placed in the inner cavity of the second sphere 102, wherein: The inner cavity of the first sphere 101 is filled with a first phase change material, and the inner cavity of the second sphere 102 is filled with a second phase change material. The phase change temperature of the first phase change material is lower than the phase change temperature of the second phase change material.

[0027] The first sphere 101 and the second sphere 102 are connected via a connecting member 103 .

[0028] At least one connecting member is provided, one end of which is connected to the outer wall of the first sphere, and the other end of which is connected to the inner wall of the second sphere.

[0029] The principle of the double-layer heat storage ball involved in this embodiment is: From the analysis of the heat storage process, it can be concluded that for the packed bed heat storage device, along the flow direction, heat exchange continues to occur between the heat exchange fluid and the phase change material. However, during the heat exchange process, the temperature is affected by the thermal resistance and the heat transfer capacity decreases. For the traditional heat storage sphere, it takes a long time for the internal phase change temperature to reach, which affects the heat storage rate of the heat storage unit. The double-layer heat storage sphere structure proposed in this design has a heat storage phase change material with a higher phase change temperature on the outside. When the heat transfer fluid passes through, a large amount of heat is transferred to the fluid. The heat decays after passing through the outer sphere, and the internal heat storage sphere is placed with a phase change heat storage ball with a lower phase change temperature, which can increase the melting rate of the inner heat storage sphere. Compared with a single-layer heat storage ball device with the same diameter, the double-layer heat storage ball can increase the heat storage rate density of the heat storage device, making the heat storage performance optimal.

[0030] Example 2 A packed bed heat storage tank provided in this embodiment comprises a cylindrical heat storage tank body, a top conical heat storage tank body and a bottom conical heat storage tank body, wherein the top conical heat storage tank body and the bottom conical heat storage tank body are respectively connected to the top and the bottom of the cylindrical heat storage tank body, and the inner cavity of the cylindrical heat storage tank body is filled with heat storage balls with a double-layer structure.

[0031] The heat storage ball comprises a first sphere 101 and a second sphere 102, wherein the first sphere 101 is placed in the inner cavity of the second sphere 102, wherein: The inner cavity of the first sphere 101 is filled with a first phase change material, and the inner cavity of the second sphere 102 is filled with a second phase change material. The phase change temperature of the first phase change material is lower than the phase change temperature of the second phase change material.

[0032] The first sphere 101 and the second sphere 102 are connected via a connecting member 103 .

[0033] At least one connecting member is provided, one end of which is connected to the outer wall of the first sphere, and the other end of which is connected to the inner wall of the second sphere.

[0034] The top conical heat storage tank body and the cylindrical heat storage tank body are connected via an upper connecting flange, and a fluid inlet is opened at the top.

[0035] The bottom conical heat storage tank body and the cylindrical heat storage tank body are connected via a lower connecting flange, and a fluid outlet is provided at the bottom thereof.

[0036] Flow equalizers are installed at the top and bottom of the inner cavity of the cylindrical heat storage tank.

[0037] A metal bracket for supporting the heat storage ball is installed at the bottom of the inner cavity of the cylindrical heat storage tank.

[0038] Example 3 like Figure 2 As shown, a heat storage device provided in this embodiment includes a packed bed heat storage tank, a heat storage ball, a fluid inlet pipe and a fluid outlet pipe, wherein: The packed bed heat storage tank comprises a cylindrical heat storage tank body 1, a conical heat storage tank body 2 at the top and a conical heat storage tank body 3 at the bottom, wherein: An upper connecting flange 6 is installed at the upper part of the cylindrical heat storage tank body 1, and a lower connecting flange 7 is installed at the lower part of the cylindrical heat storage tank body 1. Both conical heat storage tank bodies are connected to the cylindrical heat storage tank body 1 via the connecting flanges.

[0039] The top conical heat storage tank body 1 is connected to the fluid inlet channel 4 , and the bottom heat storage tank body 3 is connected to the fluid outlet channel 5 .

[0040] The fluid inlet channel 4 is an inlet channel for the fluid in the heat storage process; the fluid outlet channel 5 is an outlet channel for the fluid in the heat storage process.

[0041] Flow equalizers (8, 9) are installed at the top and bottom of the inner cavity of the cylindrical heat storage tank body 1.

[0042] A metal bracket 11 for supporting heat storage balls is installed at the bottom of the inner cavity of the cylindrical heat storage tank body 1. The heat storage balls 10 are piled up in the cylindrical heat storage tank body 1 to form a packed bed, and the gaps therein serve as heat transfer channels. The heat storage ball 10 includes a first ball 101 and a second ball 102 , wherein the first ball is placed in the inner cavity of the second ball.

[0043] The first sphere is filled with a first phase change material, and the second sphere is filled with a second phase change material.

[0044] The phase change temperature of the first phase change material is lower than the phase change temperature of the second phase change material.

[0045] The first sphere and the second sphere are connected via a connecting piece 103, which is used to limit and fix the first sphere.

[0046] The working principle of this embodiment: The temperature of the heat transfer fluid in the double-layer ball packed bed heat storage device involved in this embodiment is set to t°C, so that the heat transfer fluid (HTF) enters the packed bed conical heat storage device from the top inlet channel, and enters the heat storage ball position after being diverted by the diverter. The temperature of the heat transfer fluid is stored in the heat storage ball in the heat exchange heat storage ball unit in the form of latent heat and sensible heat. The principle of the two-layer heat storage ball involved in this embodiment is: From the analysis of the heat storage process, it can be concluded that for the packed bed heat storage device, along the flow direction, heat exchange continues to occur between the heat exchange fluid and the phase change material. However, during the heat exchange process, the temperature is affected by the thermal resistance and the heat transfer capacity decreases. For the traditional heat storage sphere, it takes a long time for the internal phase change temperature to reach, which affects the heat storage rate of the heat storage unit. The double-layer heat storage ball structure proposed in this design has a heat storage phase change material with a higher phase change temperature on the outside. When the heat transfer fluid passes through, a large amount of heat is transferred to the fluid. The heat decays after passing through the outer sphere, and the internal heat storage sphere is placed with a phase change heat storage ball with a lower phase change temperature, which can increase the melting rate of the inner heat storage sphere. Compared with a single-layer heat storage ball device with the same diameter, the double-layer ball heat storage device can increase the heat storage rate density of the heat storage device, thereby optimizing the heat storage performance.

[0047] Example 4 This embodiment provides a novel heat storage device for a double-layer ball packed bed heating system, which uses a numerical simulation optimization method to determine the diameters of the first sphere and the second sphere. The specific process is as follows: A numerical calculation model of flow and heat transfer in a two-layer variable spherical diameter packed bed heat storage device was established; Based on the above numerical calculation model, the following designs are made to simplify the calculation: the phase change material in the heat storage unit is isotropic; the fluid after the phase change material is melted is an incompressible Newtonian fluid; the volume change of the material during the phase change process is ignored; the density adopts the Boussinesq assumption to simulate the influence of natural convection; except for density, all physical properties do not change with temperature; the density change in the liquid state that drives natural convection is only considered in the momentum term.

[0048] Phase change materials are the basis of phase change heat storage technology. The priority should be materials with larger latent heat values ​​and better performance, followed by research on enhancing the heat transfer effect of phase change materials. Phase change materials have almost unchanged temperature during the phase change process and have more outstanding heat storage capacity than ordinary sensible heat materials, which is about 5-14 times higher. Phase change materials are mainly evaluated comprehensively based on thermodynamic, kinetic, chemical and economic performance indicators and then compared to select suitable materials. Using the analytic hierarchy process (AHP), the thermophysical properties of phase change materials (temperature, density, thermal conductivity, latent heat of fusion and specific heat capacity) were extensively explored as the main indicators. In the research field, some methods have been used to select appropriate PCMs related to the application. In addition, cost and application-specific requirements also determine which PCM to choose.

[0049] Table 1 Common inorganic phase change materials

[0050] Table 1-2 Common organic phase change materials

[0051] The phase change region inside the PCM is considered as a porous medium

[73] . The porosity of each unit is equal to the liquid fraction of the unit. In the solid region, the porosity is equal to zero, and the fluid velocity is also approximately zero. Finally, based on the above assumptions, the following equation is established: Continuity equation: (1) Momentum equation: (2) Energy equation: (3) In the formula is the Hamiltonian operator: (4) In the equation , ,t, , , , g and Represent velocity vector, density, time, dynamic viscosity, thermal expansion coefficient, reference temperature, gravity coefficient and thermal conductivity respectively; P, H and represent the pressure, total enthalpy and momentum source terms respectively.

[0052] The total enthalpy H consists of sensible enthalpy and latent enthalpy: (5) The sensible enthalpy can be expressed as: (6) The latent enthalpy can be expressed as: (7) in is the latent heat, and the liquid phase rate λ in different stages is expressed as: (8) In the momentum source term It is expressed as: (9) The solid-liquid phase transition interface is usually a mushy region, where is the fuzzy region constant, usually between 105 and 107

[75] . .

[0053] The calculation formula is as follows: (13) in, represents the heat storage capacity of the double-ball system, represents the total mass of PCM, represents the initial temperature, represents the phase transition temperature, represents the latent heat of phase change, represents the solid-to-solid ratio heat capacity of PCM, represents the PCM liquid relative heat capacity, Represents the total mass of the fins and the shell.

[0054] After simulation calculation, when the inner sphere diameter is 30 mm, the outer sphere diameter is 50 mm, the wall thickness is 1 mm, and the filling rate is 100%, the melting time is 2144 s and the entropy production is 1.199777497 kJ / (kg∙K).

[0055] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A double-layer heat storage ball, characterized in that: The invention comprises a first sphere and a second sphere, wherein the first sphere is placed in the inner cavity of the second sphere, wherein: The inner cavity of the first sphere is filled with a first phase change material, and the inner cavity of the second sphere is filled with a second phase change material. The phase change temperature of the first phase change material is lower than the phase change temperature of the second phase change material.

2. The double-layer heat storage ball according to claim 1, characterized in that: The first sphere and the second sphere are connected via a connecting piece.

3. The double-layer heat storage ball according to claim 1, characterized in that: The diameters of the first sphere and the second sphere are obtained by a numerical simulation method.

4. A packed bed heat storage tank, characterized in that: The invention comprises a cylindrical heat storage tank body, a top conical heat storage tank body and a bottom conical heat storage tank body, wherein the top conical heat storage tank body and the bottom conical heat storage tank body are respectively connected to the top and the bottom of the cylindrical heat storage tank body, and the inner cavity of the cylindrical heat storage tank body is filled with the heat storage ball according to any one of claims 1 to 3.

5. A packed bed heat storage tank according to claim 4, characterized in that: The top conical heat storage tank body and the cylindrical heat storage tank body are connected via an upper connecting flange, and a fluid inlet is opened at the top.

6. A packed bed heat storage tank according to claim 4, characterized in that: The bottom conical heat storage tank body and the cylindrical heat storage tank body are connected via a lower connecting flange, and a fluid outlet is provided at the bottom thereof.

7. A packed bed heat storage tank according to any one of claims 4 to 6, characterized in that: Flow equalizers are installed at the top and bottom of the inner cavity of the cylindrical heat storage tank.

8. A packed bed heat storage tank according to claim 7, characterized in that: A metal bracket for supporting the heat storage ball is installed at the bottom of the inner cavity of the cylindrical heat storage tank.

9. A heat storage device, characterized in that: It comprises a packed bed heat storage tank, a fluid inlet pipeline and a fluid outlet pipeline, wherein the fluid inlet opened at the top of the packed bed heat storage tank is connected to the fluid inlet pipeline, and the fluid outlet opened at the bottom of the packed bed heat storage tank is connected to the fluid outlet pipeline; The packed bed heat storage tank is filled with the heat storage balls according to any one of claims 1 to 3.

10. A heat storage device according to claim 9, characterized in that: The packed bed heat storage tank comprises a cylindrical heat storage tank body, a top conical heat storage tank body and a bottom conical heat storage tank body, wherein the top conical heat storage tank body and the bottom conical heat storage tank body are respectively connected to the top and the bottom of the cylindrical heat storage tank body.

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