Aeration method and device for a grain pile based on air flow distribution and pressure distribution

Abstract

This application discloses a method and apparatus for grain pile ventilation based on airflow and pressure distribution. Taking into account various grain storage conditions, including grain silo type, grain loading method, and other storage conditions, it creatively defines the airflow in the grain pile as a steady-state pressure and air velocity distribution governed by the Laplace equation. Differential equations are solved using a central difference scheme discretization method and implicit analysis based on the X and Y directions to calculate the pressure and air velocity distribution at various points in the grain pile. Grain pile ventilation is then performed based on these pressure and air velocity distributions. This application achieves the description and prediction of the ventilation process based on airflow and pressure distribution, particularly the porosity distribution of each layer of the grain pile. This enables more effective grain pile ventilation, saving energy, reducing moisture loss, and achieving the goal of high-quality grain storage.

Description

Technical Field

[0001] This application relates to the field of food science and technology. More specifically, it relates to a method and apparatus for grain pile ventilation based on airflow distribution and pressure distribution. Background Art

[0002] my country is a major agricultural country, and the production and storage of grain are of great significance to ensuring the livelihood and production of its people. With the continuous development of agricultural production and changes in the overall international environment, especially in the face of challenges such as the pandemic, the task of grain reserves has become increasingly important.

[0003] Currently, the main type of national grain storage facility in my country is the tall, flat-roofed warehouse, which has the following advantages: 1) large capacity (approximately 5,000 to 30,000 tons); 2) easy for mechanized operation; 3) can fully utilize the natural cold air in autumn and winter for mechanical ventilation to reduce the temperature of the grain pile. Therefore, since 1998, tall, flat-roofed warehouses have accounted for approximately 85% of modern grain storage facilities in my country, vertical silos for approximately 7%, and shallow round silos for approximately 5%. However, tall, flat-roofed warehouses generally suffer from poor insulation. For example, although there are insulation panels inside tall, flat-roofed warehouses, strong sunlight can still cause grain stored on the sunny side and near the walls to heat up, posing a significant safety hazard to grain storage, especially for grains with high moisture content. Furthermore, vertical silos and shallow round silos generally use a center-entry method, where grain enters from the center of the silo and flows out radially outwards. This keeps most dust and impurities in the central core of the grain pile, while the amount of dust and impurities decreases along the diameter of the silo. This center-entry method results in lower porosity at the center of the grain pile, gradually transitioning to higher porosity towards the warehouse walls. Therefore, targeted and effective ventilation of the grain pile within the warehouse is necessary, requiring prediction of pressure drop and airflow distribution during ventilation.

[0004] To effectively ventilate grain piles, the state has increased its investment in applied basic research in the grain storage and transportation sector. For example, the State Grain Administration issued the "Technical Specification for Mechanical Ventilation of Grain Storage" (LS / T 1202-2002) in 2002, which specified the permissible temperature and humidity conditions for cooling ventilation. However, both the aforementioned grain storage technical specification and monographs in my country's grain storage discipline lack descriptions and predictions of the ventilation process, especially the porosity distribution of different layers of the grain pile. In practice, grain depot engineers need to rely on experience to prepare fans of different power (air volume) and use the highest power (air volume) fans possible for thorough ventilation. This leads to significant moisture loss and high energy consumption during the cooling ventilation of the grain pile.

[0005] In addition, the main abiotic factors in grain piles are temperature, moisture, and the composition of intergranular gas. Variations in temperature and moisture in grain piles primarily lead to moisture migration and the formation of hot spots, while the intergranular air acts as a carrier for heat and moisture migration. Studying the airflow and pressure distribution in grain piles is helpful in designing scientific ventilation systems and maintaining grain quality. However, currently available experimental results in China mainly use anemometers and pressure gauges to measure the apparent wind speed and pressure on the grain surface, without simulating the airflow and pressure distribution in different layers of the grain pile.

[0006] Therefore, there is a need to provide a method and apparatus for ventilating grain piles based on airflow distribution and pressure distribution. Summary of the Invention

[0007] The purpose of this application is to provide a grain pile ventilation method and apparatus based on airflow distribution and pressure distribution, in order to solve the technical problems mentioned in the background section above.

[0008] To achieve the above objectives, this application adopts the following technical solution:

[0009] In a first aspect, this application provides a grain pile ventilation method based on airflow distribution and pressure distribution, the method comprising:

[0010] S100. Determine the steady-state pressure and gas velocity distribution in the grain pile, which are governed by the Laplace equation, and establish the Laplace equation in the XY two-dimensional direction of the grain pile during ventilation.

[0011] S200. The first differential equation for determining the two-dimensional airflow velocity and pressure distribution at a single point in the grain pile based on the central difference scheme discretization method;

[0012] S300. Solve the tridiagonal matrix composed of the coefficients of the first differential equation using the implicit analysis method based on the X and Y directions;

[0013] S400, Calculate the pressure and airflow velocity distribution at the location;

[0014] S500, calculate the pressure and airflow velocity distribution at various points on the grain pile; and

[0015] S600. Ventilate the grain pile based on the pressure and airflow velocity distribution at each point in the grain pile.

[0016] In one specific embodiment, the Laplace equation is:

[0017]

[0018] Where p is the air pressure; u is the air velocity in the X-axis direction; v is the air velocity in the Y-axis direction; |V| is the air velocity in the r direction; Rx, Ry, Sx, and Sy are the two-dimensional drag coefficients of the airflow; u, v, and r form a right triangle, and r is the longer side of the right triangle.

[0019] In one specific embodiment, after step S100, the method further includes:

[0020] S102. Determine the boundary conditions of the Laplace equation as follows:

[0021] When x = 0 and x = WX,

[0022] When y = 0,

[0023] Where WX is the width of the grain pile.

[0024] In one specific embodiment, the first differential equation is:

[0025]

[0026]

[0027] Where u is the airflow velocity in the X-axis direction; Δx and Δy are the interval lengths in the X-axis and Y-axis directions, respectively; μ i+1 μ i-1 ρ represents the airflow velocity along the X-axis at positions (i+1,j) and (i-1,j), respectively; i-1 p, p i+1 p represents the partial pressure of the airflow along the X-axis at positions (i-1,j), (i,j), and (i+1,j), respectively. j-1 p, p j+1 Ri represents the partial pressure of airflow along the Y-axis at positions (i,j-1), (i,j), and (i,j+1), respectively; Ry is the two-dimensional drag coefficient.

[0028] In one specific embodiment, the first differential equation further includes the following differential variables:

[0029]

[0030]

[0031]

[0032]

[0033]

[0034] In one specific embodiment, step S300 includes:

[0035] S301. The Laplace equation is expressed using an implicit analysis method based on the X-direction as follows:

[0036]

[0037] Where Δt is the time step; starting from the p-th theoretical time step, at the (i,j)-th node, This represents pressure; after half a time step, the pressure is...

[0038]

[0039]

[0040]

[0041]

[0042] S302. The Laplace equation is expressed using an implicit analysis method based on the Y-direction as follows:

[0043]

[0044] in,

[0045]

[0046]

[0047]

[0048] and

[0049] S303. For a given value j, the above equation can be written in the following matrix form:

[0050]

[0051] In one specific embodiment, step S500 includes:

[0052] S501. Use the Visual Basic environment to run the program to calculate the pressure and airflow velocity distribution at various points in the grain pile.

[0053] Secondly, this application also provides a grain pile ventilation device based on airflow distribution and pressure distribution, the device comprising:

[0054] The modeling module is used to determine the steady-state pressure and gas velocity distribution in the grain pile, which are governed by the Laplace equation, and to establish the Laplace equation in the XY two-dimensional direction of the grain pile during ventilation.

[0055] The calculation module is used to determine the first differential equation for the two-dimensional airflow velocity and pressure distribution at a single point in the grain pile based on the central difference scheme discretization method; solve the tridiagonal matrix composed of the coefficients of the first differential equation based on the implicit analysis method in the X and Y directions; calculate the pressure and airflow velocity distribution at the point; and calculate the pressure and airflow velocity distribution at each point in the grain pile.

[0056] The execution module ventilates the grain pile based on the pressure and airflow velocity distribution at various points in the grain pile.

[0057] Thirdly, this application also provides a computer device, including a processor and a memory storing a program, characterized in that the processor executes the program to implement the method provided in the first aspect of this application.

[0058] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, characterized in that the program, when executed by a processor, implements the method provided in the first aspect of this application.

[0059] The beneficial effects of this application are as follows:

[0060] This application provides a method and apparatus for grain pile ventilation based on airflow and pressure distribution. The grain pile ventilation method of this application comprehensively considers grain silo type, grain loading method, and various grain storage conditions. It creatively defines the airflow in the grain pile as a steady-state pressure and gas velocity distribution governed by the Laplace equation. Differential equations are solved using the central difference scheme discretization method and implicit analysis based on the X and Y directions to calculate the pressure and airflow velocity distribution at various points in the grain pile. Grain pile ventilation is then performed based on these pressure and airflow velocity distributions. This application achieves the description and prediction of the ventilation process based on airflow and pressure distribution, especially the porosity distribution of each layer of the grain pile, enabling more effective grain pile ventilation, saving energy, reducing moisture loss, and achieving the goal of high-quality grain storage. Attached Figure Description

[0061] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0062] Figure 1 The diagram illustrates the steps of a grain pile ventilation method based on airflow distribution and pressure distribution according to an embodiment of this application.

[0063] Figure 2 A schematic diagram showing the air mass flow in the ventilated grain area according to an embodiment of this application is provided.

[0064] Figure 3 A schematic diagram showing the airflow velocity in the r direction according to an embodiment of this application is shown.

[0065] Figure 4 A schematic diagram illustrating the main dimensions of a simulated grain pile according to an embodiment of this application is shown.

[0066] Figure 5 This diagram illustrates the node distribution in a finite difference grid according to an embodiment of this application.

[0067] Figure 6 A screenshot showing the running result of the software written according to an embodiment of this application is displayed.

[0068] Figure 7 This diagram illustrates the relationship between ventilation volume and pressure at different locations in a wheat pile according to an embodiment of this application.

[0069] Figure 8 This diagram illustrates the vertical wind speed at different locations on a wheat pile under a certain ventilation volume, according to an embodiment of this application.

[0070] Figure 9 This diagram illustrates the vertical pressure at different locations on a wheat pile according to an embodiment of this application.

[0071] Figure 10 A schematic diagram of a grain pile ventilation device based on airflow distribution and pressure distribution according to an embodiment of this application is shown. Detailed Implementation

[0072] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Similar components in the drawings are represented by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be used to limit the scope of protection of this application. It should also be noted that, for ease of description, the parts in the drawings related to this application are omitted. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0073] Since 1998, my country's grain storage silos have primarily been tall, flat-roofed structures, accounting for approximately 85% of newly built storage capacity. These tall, flat-roofed silos have large individual capacities, typically ranging from 5,000 to 30,000 tons, facilitating mechanized operations and allowing for efficient use of cool autumn and winter air for mechanical ventilation to lower grain pile temperatures. Simultaneously, the government has increased investment in applied basic research in grain storage and transportation, with some scholars beginning to explore airflow distribution and pressure drop processes within grain piles. In practical applications, the State Grain Administration issued the "Technical Specification for Mechanical Ventilation of Grain Storage" (LS / T 1202-2002) in 2002, outlining the permissible temperature and humidity conditions for cooling ventilation.

[0074] In my country, the principle of economical land use is adhered to in the construction of grain depots. Currently, in my country's modern grain depots, tall, flat-roofed silos account for approximately 85%, vertical silos for approximately 7%, and shallow cylindrical silos for approximately 5%. From a storage and trade perspective, shallow cylindrical silos and vertical silos represent the future direction. The method of center-feeding grain in cylindrical silos involves grain entering from the center and flowing radially outwards, resulting in the vast majority of dust material remaining in the central core of the grain pile. The amount of dust decreases along the diameter of the silo. This center-feeding method leads to lower porosity at the center of the grain pile, gradually transitioning to higher porosity at the silo walls. In tall silos, such as during rapeseed storage, the static pressure exerted by the upper layers of the grain pile on the lower layers can cause deformation and damage to the rapeseed at the bottom. In simulated experiments, pressures of 20–60 kPa caused a decrease in the content of total phytosterols, β-sitosterol, and brassinosteroids in rapeseed with a moisture content of 13%–16% within the temperature range of 25–30℃, with increasing pressure, moisture content, and temperature. However, the phytosterol content in rapeseed with a moisture content of 7%–9% showed little variation with increasing pressure and temperature. Therefore, it is worthwhile to analyze the airflow distribution and quality-influencing factors in grain piles in shallow circular silos and vertical silos, providing technical support and evaluation indicators for high-quality grain storage.

[0075] The main abiotic factors in grain piles are temperature, moisture, and intergranular gas composition. Variations in grain pile temperature and moisture primarily lead to moisture migration and hot spots, while intergranular air acts as a carrier for heat and moisture migration. Studying airflow distribution in grain piles helps in designing scientific ventilation systems and maintaining grain quality. Grain pile airflow distribution is generally considered as fluid flowing through a porous medium, and grain pile airflow models are used to describe the relationship between airflow pressure drop and airflow velocity. Several interrelated physical factors, such as grain pile porosity and tortuosity, grain shape, and pile height, affect the uniformity of airflow in stored grain, potentially leading to poor airflow zones. To reduce storage losses and costs, it is necessary to understand airflow distribution in shallow circular silos and vertical silos to optimize operations during ventilation. Therefore, numerical simulations demonstrating how to optimize grain silo design and minimize operating costs are becoming increasingly important.

[0076] However, this grain storage technical specification and monographs in my country's grain storage science lack descriptions and predictions of the ventilation process, especially the porosity distribution of each layer of the grain pile. Specifically, currently available domestic experimental results mainly use anemometers and pressure gauges to measure the apparent wind speed and pressure on the grain surface, without simulating the airflow and pressure distribution of each layer of the grain pile, thus making accurate predictions impossible. Under these circumstances, to ensure ventilation effectiveness, grain depot engineers need to prepare fans of different power levels, relying on experience to use the highest power fans for thorough ventilation, resulting in significant moisture loss and high energy consumption during cooling and ventilation.

[0077] Therefore, it is essential to explore the airflow distribution and pressure drop distribution of grain piles. Compared with foreign grain storage methods that use a single grain variety and have a short storage time, considering factors such as grain warehouse type, storage area, grain variety, storage time, grain moisture content, and impurity content in my country, and incorporating these factors into the ventilation process simulation, predicting the airflow distribution and pressure drop distribution of ventilated grain piles is beneficial for saving energy, reducing fan noise, minimizing moisture loss from grain piles, and achieving the goal of high-quality grain storage.

[0078] like Figure 1 As shown in the embodiments of this application, a grain pile ventilation method based on airflow distribution and pressure distribution is provided. The method includes:

[0079] S100. Determine the steady-state pressure and gas velocity distribution in the grain pile, which are governed by the Laplace equation, and establish the Laplace equation in the XY two-dimensional direction of the grain pile during ventilation.

[0080] S200. The first differential equation for determining the two-dimensional airflow velocity and pressure distribution at a single point in the grain pile based on the central difference scheme discretization method;

[0081] S300. Solve the tridiagonal matrix composed of the coefficients of the first differential equation using the implicit analysis method based on the X and Y directions;

[0082] S400, Calculate the pressure and airflow velocity distribution at the location;

[0083] S500, calculate the pressure and airflow velocity distribution at various points on the grain pile; and

[0084] S600. Ventilate the grain pile based on the pressure and airflow velocity distribution at each point in the grain pile.

[0085] This application, taking into account various grain storage conditions, including grain silo type, grain loading method, and other storage conditions, creatively defines the airflow in the grain pile as a steady-state pressure and gas velocity distribution governed by the Laplace equation. Differential equations are solved using the central difference scheme discretization method and implicit analysis based on the X and Y directions to calculate the pressure and airflow velocity distribution at various points in the grain pile. Based on these pressure and airflow velocity distributions, grain pile ventilation is then implemented. Therefore, this application describes and predicts the ventilation process based on airflow and pressure distributions, particularly the porosity distribution of each layer of the grain pile. This allows for more effective grain pile ventilation, saving energy, reducing moisture loss, and achieving the goal of high-quality grain storage.

[0086] In one specific embodiment, the Laplace equation is:

[0087]

[0088] Where p is the air pressure; u is the air velocity in the X-axis direction; v is the air velocity in the Y-axis direction; |V| is the air velocity in the r direction; Rx, Ry, Sx, and Sy are the two-dimensional drag coefficients of the airflow; u, v, and r form a right triangle, and r is the longer side of the right triangle.

[0089] In one specific embodiment, after step S100, the method further includes:

[0090] S102. Determine the boundary conditions of the Laplace equation as follows:

[0091] When x = 0 and x = WX,

[0092] When y = 0,

[0093] Where WX is the width of the grain pile.

[0094] In one specific embodiment, the first differential equation is:

[0095]

[0096]

[0097] Where u is the airflow velocity in the X-axis direction; Δx and Δy are the interval lengths in the X-axis and Y-axis directions, respectively; μ i+1 μ i-1 ρ represents the airflow velocity along the X-axis at positions (i+1,j) and (i-1,j), respectively; i-1 p, p i+1p represents the partial pressure of the airflow along the X-axis at positions (i-1,j), (i,j), and (i+1,j), respectively. j-1 p, p j+1 Ri represents the partial pressure of airflow along the Y-axis at positions (i,j-1), (i,j), and (i,j+1), respectively; Ry is the two-dimensional drag coefficient.

[0098] In one specific embodiment, the first differential equation further includes the following differential variables:

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] In one specific embodiment, step S300 includes:

[0105] S301. The Laplace equation is expressed using an implicit analysis method based on the X-direction as follows:

[0106]

[0107] Where Δt is the time step; starting from the p-th theoretical time step, at the (i,j)-th node, This represents pressure; after half a time step, the pressure is...

[0108]

[0109]

[0110]

[0111]

[0112] S302. The Laplace equation is expressed using an implicit analysis method based on the Y-direction as follows:

[0113]

[0114] in,

[0115]

[0116]

[0117]

[0118] and

[0119] S303. For a given value j, the above equation can be written in the following matrix form:

[0120]

[0121] In one specific embodiment, step S500 includes:

[0122] S501. Use the Visual Basic environment to run the program to calculate the pressure and airflow velocity distribution at various points in the grain pile.

[0123] In this embodiment, it is creatively assumed that the airflow in the grain pile is a steady-state pressure and airflow velocity distribution governed by the Laplace equation, and a two-dimensional drag coefficient is introduced to solve the anisotropic airflow in the grain pile. Then, the pressure and airflow velocity distribution at the ventilated grain pile location are obtained by solving the tridiagonal matrix composed of the coefficients of the differential equation using the central difference scheme discretization method and implicit analysis in the X and Y directions. Finally, the pressure and airflow velocity distribution at each point in the grain pile are calculated using a Visual Basic program.

[0124] The above method will be explained in detail below with a specific example.

[0125] 1. Calculate the pressure and airflow velocity distribution in the grain pile.

[0126] like Figure 2 As shown, Figure 2 This is a schematic diagram of air mass flow within the ventilated grain area. Where ρ is the air density; u is the airflow velocity along the X-axis; v is the airflow velocity along the Y-axis; and Δx and Δy are the interval lengths along the X and Y axes, respectively. Figure 2 middle:

[0127]

[0128]

[0129] Considering that air has a constant density and can stably flow into and out of the grain pile elements, the grain pile elements have spacing lengths Δx and Δy in two directions, as follows: Figure 2 As described in.

[0130] According to the law of conservation of mass, the mass flowing into the component equals the mass flowing out of the component, therefore:

[0131]

[0132] Dividing both sides of the above equation (1) by Δx and Δy, we get:

[0133]

[0134] For incompressible air flow, the above equation is the fluid-mass correlation equation, which can serve as a typical example in the case of a ventilated grain pile. Since the pressure drop across the entire grain pile is on the order of 1% of the absolute pressure (100 kPa) (1 kPa), the application of the above equation is limited to two-dimensional grain pile systems, thus reducing the number of algebraic equations.

[0135]

[0136]

[0137] in, It is the pressure gradient in the X direction; is the pressure gradient in the Y direction; K is the permeability of the grain bed, in meters; μ is the dynamic viscosity of the fluid.

[0138] For example, for corn kernels, K = 2 × 10 -8 m. Under ventilated conditions in the grain pile, μ = 17.75 × 10⁻⁶. -6 Pas / m.

[0139] Differentiating equations (3) and (4) above, we get:

[0140]

[0141]

[0142] Adding the left and right sides of equations (5) and (6) respectively, we get:

[0143]

[0144] When relating equations, inserting equation (2) to the right side of equation (7) yields:

[0145]

[0146] It should be understood that the above equation (8) is the Laplace equation. The Laplace equation governs the steady-state temperature distribution involved in heat transfer when considering thermal conductivity, electrostatic field, idealized fluid flow, and air flow through porous media such as grain storage.

[0147] 2. Calculate the numerical solution

[0148] Typically, actual grain pile systems have the following characteristics: 1) The grain pile is three-dimensional; 2) The grain pile is anisotropic; 3) The airflow resistance can be non-uniform; 4) Due to the presence of impurities, the grain pile area can provide high airflow resistance; 5) The geometry of the grain pile, the design of the ventilation ducts, and the surface of the grain pile are usually quite arbitrary.

[0149] like Figure 3 As shown, Figure 3 A schematic diagram of airflow velocity in the r-direction is shown. Here, u is the velocity component in the X-axis direction; v is the velocity component in the Y-axis direction; the absolute value of V is the velocity in the r-direction; P is the pressure component in the X-axis direction; PH is the pressure component in the Y-axis direction; and PN is the pressure in the r-direction. u, v, and r form a right triangle, with r being the longer side of the right triangle.

[0150] A material is said to be anisotropic when the resistance is different in every direction. Taking grain as an example, the horizontal and vertical pressure gradients can be expressed as:

[0151]

[0152]

[0153] In this embodiment of the application, the two-dimensional drag coefficient R x =2000Pas / m 2 S x =10000Pas / m 2 ; R y =2000Pas / m 2 S y =10000Pas / m 2 ratio = R x / R y .

[0154] The above equations control the pressure and velocity distribution of the ventilated grain bed. The pressure distribution of the grain pile is based on the solutions of equations (9) and (10), which also shows that the grain pile is anisotropic.

[0155] Differentiating equation (9) with respect to x, we get:

[0156]

[0157] Differentiating equation (10) with respect to y, we get:

[0158]

[0159] Divide equation (11) by R x Divide equation (12) by R y Then add the above results together and eliminate the participating items. and Combining equation (2), we know that the equations related to pressure and velocity are:

[0160]

[0161] Multiply both sides of equation (13) by R. x ,get:

[0162]

[0163] Equation (14) is the Laplace equation in the XY two-dimensional direction of the grain pile during the ventilation process established in step S100.

[0164] 3. Determine boundary conditions

[0165] In solving the pressure distribution equations (13) and (14), we encounter boundary conditions that define the equations and reflect the geometry of the ventilated grain pile.

[0166] In practice, it can be assumed that the pressure p relative to air in equations (13) and (14) is measured, that is, the pressure p is the measured pressure. The measured pressure is derived from equations (13) and (14) using the absolute pressure P, and is defined as follows:

[0167] P = P atm +p (15)

[0168] Among them, P atm If atmospheric pressure is used, and the measured pressure p can replace the absolute pressure P, then:

[0169]

[0170]

[0171] In addition, if the pressure on the upper surface of the ventilated grain pile is set to zero, then:

[0172] When y = WY, p = 0 (18)

[0173] Where WY represents the height of the grain pile, which has a simple geometric shape as shown below. Figure 4 As shown. Figure 4 The main dimensions of the simulated grain pile are shown.

[0174] Define the duct pressure as p duct ,get:

[0175] p = p duct x l <x<x u (19)

[0176] Considering that the walls of the granary are airtight, the horizontal component of the velocity u perpendicular to the walls is zero. Since no air flows over the walls, then:

[0177]

[0178] In summary, the boundary conditions are as follows:

[0179] When x = 0 and x = WX,

[0180] When y = 0,

[0181] Where WX is the width of the grain pile.

[0182] 4. Specific steps to determine the numerical solution

[0183] By adding temporary terms to equations (13) and (14) The heat and mass of the assembly are transferred to the equations that control the pressure distribution.

[0184] The revised equation (13) is as follows:

[0185]

[0186] (1) Discretization of the equation

[0187] In numerical solution methods, the value of the pressure variable p is calculated only with a finite number of nodes arranged in a lattice structure. This lattice has nodes uniformly distributed in two dimensions, such as... Figure 5 As shown, Figure 5 A schematic diagram of the node distribution in a finite difference grid is shown.

[0188] exist Figure 5 In this example, assume the width WX of the ventilated grain pile area is 3m and the height WY is 3m. The number of segments along the X and Y axes are NXM1 = NX-1, NYM1 = NY-1; NXM2 = NX-2, NYM2 = NY-2, respectively. Then the interval lengths are:

[0189] X-direction spacing length:

[0190]

[0191] Y-direction spacing length:

[0192]

[0193] The estimated time step is:

[0194]

[0195] False transform term Discretize accurately in the same way:

[0196]

[0197] It should be noted that when the equation contains terms involving velocity, the first derivative is discretized using the backward difference approximation method, which ensures that the numerical solution is stable.

[0198] Equation (23) does not contain terms involving velocity; therefore, a more accurate central difference scheme discretization method is used, which takes the form:

[0199]

[0200] The Laplacian-like terms were also discretized using the central difference scheme, resulting in:

[0201]

[0202] In this embodiment, the pressure p in the assumed terms, including its derivative with respect to y, is known, and the estimated theoretical half-time step Δt / 2 is first solved. For the pressure value in the discrete terms, including its derivative with respect to x, it is considered unknown. The equation is implicit in the y-direction; the value of p is calculated after half a time step, and the discrete equation is implicitly solved in both y and x directions.

[0203] Other differential variables include:

[0204]

[0205]

[0206]

[0207]

[0208]

[0209] (2) Calculate the implicit solution in the X direction

[0210] At the beginning of a time step, all pressure values ​​are known; therefore, the initial values ​​for calculation are specific, or calculated algebraically. At the beginning of the p-th theoretical time step, at the (i,j)-th node, if... This represents pressure, and the pressure after half a time step is... Then equation (14) can be expressed as:

[0211]

[0212] in, The term is unknown, and The item can be determined based on the previous time step. Because... and It is unknown. Implicit expression is not allowed.

[0213] Therefore, the unknown variables on the right-hand side of equation (35) must be grouped. Before grouping, simplify the notation by using i and j as default subscripts and p as a default subscript, therefore:

[0214]

[0215] Therefore, equation (35) can be rewritten as:

[0216]

[0217] in,

[0218]

[0219]

[0220]

[0221]

[0222] First, solve equation (37) for i = 2 to NX-1. Then, for j = 2, solve equation (37) for i = 2, NX-1 and j = 3, up to j = NY-1. Thus, for each row of nodes in the x-direction, the linear algebraic equation for NY-2 can be solved simultaneously.

[0223] For a given value j, the equation can be written in the following matrix form:

[0224]

[0225] At this point, it can be seen that the coefficient matrix is ​​a tridiagonal matrix. In this case, for The equations can be solved very efficiently.

[0226] Perform the above operations on each internal node in the silo structural domain. Specifically, The value is known, at the boundary. The value is set to the value at the start of the integration time step.

[0227] (3) Calculate the implicit solution in the Y direction

[0228] By performing an integral calculation over a time step, the pressure value is calculated along a grid of points with a constant i. Using the equation to calculate the value of j from 2 to NY-1, we get:

[0229]

[0230] in,

[0231]

[0232]

[0233]

[0234]

[0235] At this point, it can be seen that the coefficient matrix is ​​a tridiagonal matrix. In this case, for The equations can be solved very efficiently.

[0236] (4) Determine boundary conditions

[0237] In upward ventilation, the pressure on the upper surface of the grain pile is set to zero, which can be expressed algebraically as:

[0238] p(i, NY) = 0; i = 1, NX

[0239] In this embodiment of the application, the ventilation duct is destined to coincide with the bottom plate of the silo, at which point:

[0240] p(i, 1) = p duct ;i = ndl, ndu

[0241] Where ndl is a node, coincidentally corresponding to the number of nodes on the left side of the air duct, and ndu coincidentally corresponding to the number of nodes on the right side of the air duct. The air duct pressure p duct =300Pa.

[0242] Since the base plate and walls are airtight, the horizontal component of the wind speed, *u*, is zero along the walls. The vertical component of the wind speed, *v*, is zero along the base plate except in the ventilation duct area. That is, the pressure gradient perpendicular to the airtight surface is zero. When the vertical component of the velocity is zero, at the boundary, the pressure gradient discretizes as:

[0243]

[0244]

[0245]

[0246] These gradients are zero, and the pressure along the silo floor can be calculated using the following equations:

[0247]

[0248] The pressure along the left-hand wall is:

[0249]

[0250] The pressure along the right-hand wall is:

[0251]

[0252] It should be noted that the updated pressure values ​​have been calculated at the internal nodes, and equations (43) and (45) are used to update the pressure at the boundary.

[0253] In this embodiment, the above process can also be generalized to a three-dimensional system. Since adaptation is not limited to two dimensions, an alternative to the Peaceman-Rachford method is needed. For example, a three-dimensional alternating direction implicit method can be used to calculate the pressure profile. In one example, a single semi-circular ventilation duct is used in a tall, single-story warehouse; this application is not limited to this.

[0254] (5) Calculate the volumetric air velocity (Q) of the grain pile.

[0255] Penetration rate K p Satisfy the following formula:

[0256]

[0257] When Q = 0 and j = NY-1, for i from 1 to NX, we get:

[0258]

[0259]

[0260] If i = 1, then Q = Q + 0.5·Δx·v i，j (48-1)

[0261] If i = NX, then Q = Q + 0.5·Δx·v i，j (48-2)

[0262] If 1 < i < NX, Q = Q + Δx·v i，j (48-3)

[0263] (6) Calculate the boundary airflow velocity

[0264] For i from 1 to NX, we get:

[0265]

[0266]

[0267] v(i, NY) = v(i, NY-1) (51)

[0268] u(i, NX) = 0 (52)

[0269]

[0270]

[0271]

[0272]

[0273] For j ranging from 2 to NY-1, we get:

[0274] u(1,j)=0 (57)

[0275] u(NX,j)=0 (58)

[0276]

[0277]

[0278]

[0279]

[0280] For i from 2 to NX-1 and j from 2 to NY-1, we get:

[0281]

[0282]

[0283]

[0284]

[0285]

[0286] (7) Calculate the boundary airflow pressure

[0287] The above only solves for the pressure of the internal nodes; the pressure at the boundary is used as the boundary condition. At the top of the grain pile, excluding the ventilation duct, the pressure can be set to 20 Pa. The boundary is airtight; the boundary pressure can be extrapolated from the internal pressure field. The pressure of the corner nodes is used as an algebraic method for their neighboring nodes.

[0288] Calculate the airflow pressure at the bottom corner of the silo to obtain:

[0289] p 1，1 =0.5*(p 1，2 +p 2，1 (68)

[0290] pnx，1 =0.5*(p nx，2 +p nx-1，1 (69)

[0291] The pressure on the upper surface of the grain pile is constant. Corresponding to an airtight wall, for j ranging from 2 to NY-1, we obtain:

[0292]

[0293] PH(1,J)=P(1,J) (71)

[0294]

[0295] PH(NX,J)=PH(NX,J) (73)

[0296] For a non-breathable base plate, for i ranging from 2 to NX-1, we get:

[0297]

[0298] PH(I,1)=P(I,1) (75)

[0299] For i = NDL to NDU, we get:

[0300] P(i,1)=P duct (76)

[0301] PH(i,1)=P(i,1) (77)

[0302] In one specific embodiment, a wheat silo with a diameter of 3 meters and a height of 3 meters is simulated. Screenshots of the software's execution results are shown below. Figure 6 As shown.

[0303] The specific data is as follows:

[0304] like Figure 7 As shown, the air pressure near the ventilation duct is 300 Pa. The vertical air pressure decreases as the grain pile height increases. The atmospheric pressure at the grain surface is 0 Pa, and the initial ventilation volume is 0.135 m³. 3 / s, then gradually stabilized at 0.080m 3 / s.

[0305] like Figure 8As shown, the vertical airflow velocity at six points on the X-axis near the ventilation duct decreases from 0.046 m / s to 0.026–0.275 m / s at the six points on the first 10 layers upwards, and then stabilizes at 0.027 m / s. At the 11th layer, the vertical airflow velocity decreases sequentially from 0.023 m / s (point 1) and 0.037 m / s (points 2–6) to 0.0185 m / s (point 1) and 0.0245 m / s (points 2–6), and then stabilizes at 0.0180 m / s (point 1) and 0.0242 m / s (points 2–6).

[0306] like Figure 9 As shown, with a gradient of 0.3m intervals along the horizontal (X) direction and then 0.3m intervals along the vertical (Y) direction near the ventilation duct, the vertical air pressure inside the grain pile gradually decreases from 300Pa to 0Pa.

[0307] Based on the above real simulation data, it can be seen that this application has achieved the description and prediction of the ventilation process based on airflow distribution and pressure distribution. In particular, the porosity distribution of each layer of the grain pile can be used to ventilate the grain pile more effectively, which is conducive to saving energy consumption, reducing moisture loss of the grain pile, and achieving the goal of high-quality grain storage.

[0308] It should be noted that this application uses a wheat silo as an example for simulation, but it is not limited to the type of grain or the type of silo. For example, the grain pile ventilation method in this application can be gradually scaled up to shallow round silos and tall flat silos. In addition, this application can also detect changes in airflow and pressure in the grain pile during the intelligent ventilation process to achieve the goal of high-quality grain storage.

[0309] like Figure 10 As shown in the embodiments of this application, a grain pile ventilation device based on airflow distribution and pressure distribution is also provided. The device includes:

[0310] The modeling module is used to determine the steady-state pressure and gas velocity distribution in the grain pile, which are governed by the Laplace equation, and to establish the Laplace equation in the XY two-dimensional direction of the grain pile during ventilation.

[0311] The calculation module is used to determine the first differential equation for the two-dimensional airflow velocity and pressure distribution at a single point in the grain pile based on the central difference scheme discretization method; solve the tridiagonal matrix composed of the coefficients of the first differential equation based on the implicit analysis method in the X and Y directions; calculate the pressure and airflow velocity distribution at the point; and calculate the pressure and airflow velocity distribution at each point in the grain pile.

[0312] The execution module ventilates the grain pile based on the pressure and airflow velocity distribution at various points in the grain pile.

[0313] This application also provides a computer device, including a processor and a memory storing a program, characterized in that the processor executes the program to implement the grain pile ventilation method in the foregoing embodiments.

[0314] This application also provides a computer-readable storage medium storing a computer program thereon, characterized in that the program, when executed by a processor, implements the grain pile ventilation method in the foregoing embodiments.

[0315] The grain pile ventilation method, apparatus, computer equipment, and computer-readable storage medium provided in this application embodiment, based on airflow and pressure distribution, comprehensively consider grain silo types, grain loading methods, and various grain storage conditions. It creatively defines the airflow in the grain pile as a steady-state pressure and gas velocity distribution governed by the Laplace equation. Differential equations are solved using the central difference scheme discretization method and implicit analysis based on the X and Y directions to calculate the pressure and airflow velocity distribution at various points in the grain pile. Grain pile ventilation is then performed based on these pressure and airflow velocity distributions. Therefore, this application embodiment achieves the description and prediction of the ventilation process based on airflow and pressure distribution, especially the porosity distribution of each layer of the grain pile, enabling more effective grain pile ventilation, saving energy, reducing moisture loss, and achieving the goal of high-quality grain storage.

[0316] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0317] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0318] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

[0319] Obviously, the above embodiments of this application are merely examples for clearly illustrating this application, and are not intended to limit the implementation of this application. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all implementation methods here. Any obvious variations or modifications derived from the technical solutions of this application are still within the protection scope of this application.

Claims

1. A grain pile ventilation method based on airflow distribution and pressure distribution, characterized in that, The ventilation methods for the grain pile include: S100. Determine the steady-state pressure and gas velocity distribution in the grain pile, which are governed by the Laplace equation, and establish the Laplace equation in the XY two-dimensional direction of the grain pile during ventilation. S200. The first differential equation for determining the two-dimensional airflow velocity and pressure distribution at a single point in the grain pile based on the central difference scheme discretization method; S300. Solve the tridiagonal matrix composed of the coefficients of the first differential equation using the implicit analysis method based on the X and Y directions; S400, Calculate the pressure and airflow velocity distribution at the location; S500, calculate the pressure and airflow velocity distribution at various points in the grain pile; S600. Ventilate the grain pile based on the pressure and airflow velocity distribution at each point of the grain pile. The step S300, which involves solving the tridiagonal matrix composed of the coefficients of the first differential equation using implicit analysis based on the X and Y directions, includes: S301. The Laplace equation is expressed using an implicit analysis method based on the X-direction as follows: in, ∆t For time step; from the first p Starting at the theoretical time step, at node (i,j), This represents pressure; after half a time step, the pressure is... ; ； This refers to the pseudo-instantaneous factor; ； ； ； in, This refers to the airflow pressure at point (i, j); , which is also the airflow pressure at point (i, j); It refers to the ratio of the drag coefficients of different grain varieties in two dimensions; S302. The Laplace equation is expressed using an implicit analysis method based on the Y-direction as follows: in, ； ； ； ； S303. For a given value j, the above equation can be written in the following matrix form: 。 2. The grain pile ventilation method according to claim 1, characterized in that, The Laplace equation is: ； in, p Air pressure; u The velocity of the airflow in the X-axis direction; v The velocity of the airflow in the Y-axis direction; |V| Let be the airflow speed in the r direction; Rx, Ry, Sx, Sy It is the two-dimensional drag coefficient of the airflow; u, v, r forms a right triangle, where r is the longer side of the right triangle.

3. The grain pile ventilation method according to claim 2, characterized in that, After step S100, the method further includes: S102. Determine the boundary conditions of the Laplace equation as follows: when and , ; when , ; Where WX is the width of the grain pile.

4. The grain pile ventilation method according to claim 2, characterized in that, The first differential equation is: ； ； in, u The airflow velocity in the X-axis direction; ∆x and ∆y These are the interval lengths in the X-axis and Y-axis directions, respectively; μ i+1 , μ i-1 These are the airflow velocities along the X-axis at positions (i+1,j) and (i-1,j), respectively. p i-1 , p , p i+1 These are the partial pressures of the airflow along the X-axis at positions (i-1,j), (i,j), and (i+1,j), respectively. p j-1 , p , p j+1 These are the partial pressures of the airflow along the Y-axis at positions (i,j-1), (i,j), and (i,j+1), respectively. Ry It is a two-dimensional drag coefficient.

5. The grain pile ventilation method according to claim 4, characterized in that, The first differential equation also includes the following differential variables: ； and These are the airflow velocities at positions (i,j+1) and (i,j-1) respectively, separated by two characteristic lengths Δy under the implicit scheme in the Y-axis direction and at the previous theoretical half-time step; The implicit format in the Y-axis direction is the explicit format in the X-axis direction; ； These are the airflow velocities at positions (i,j+1) and (i,j-1) respectively, separated by two characteristic lengths Δy in the explicit format along the Y-axis direction during the second theoretical half-time step. The explicit format for the Y-axis direction is the implicit format for the X-axis direction; ； and These are the airflow velocities at positions (i+1,j) and (i-1,j) separated by two characteristic lengths Δx, respectively, under the explicit format in the Y-axis direction at the second theoretical half-time step; the explicit format in the Y-axis direction is the implicit format in the X-axis direction. ； 。 6. The grain pile ventilation method according to claim 1, characterized in that, The calculation of the pressure and airflow velocity distribution at various points in the grain pile in step S500 includes: S501. Use the Visual Basic environment to run the program to calculate the pressure and airflow velocity distribution at various points in the grain pile.

7. A grain pile ventilation device based on airflow distribution and pressure distribution for performing the grain pile ventilation method based on airflow distribution and pressure distribution as described in any one of claims 1-6, characterized in that, The grain pile ventilation device includes: The modeling module is used to determine the steady-state pressure and gas velocity distribution in the grain pile, which are governed by the Laplace equation, and to establish the Laplace equation in the XY two-dimensional direction of the grain pile during ventilation. The calculation module is used to determine the first differential equation for the two-dimensional airflow velocity and pressure distribution at a single point in the grain pile based on the central difference scheme discretization method; solve the tridiagonal matrix composed of the coefficients of the first differential equation based on the implicit analysis method in the X and Y directions; calculate the pressure and airflow velocity distribution at the point; and calculate the pressure and airflow velocity distribution at each point in the grain pile. The execution module ventilates the grain pile based on the pressure and airflow velocity distribution at various points in the grain pile.

8. A computer device, comprising a processor and a memory storing a program, characterized in that, When the processor executes the program, it implements the method as described in any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1-6.

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