A method for predicting freezing time of road salt solution for anti-icing

Abstract

The present invention discloses a method for predicting the freezing time of a road salt solution for anti-icing, comprising: setting a target concentration of the salt solution and determining the initial amount of salt; establishing a road-salt solution-ice layered system and defining material properties; analyzing the heat exchange information between the system and the external environment and within the system, setting boundary conditions and establishing control equations; discretizing the system and solving the control equations of discrete nodes; establishing a salt solution freezing algorithm; calculating the temperature field of the system, outputting the relationship between the temperature, concentration and freezing point value of the salt solution and time; based on the change in the latent heat of the salt solution, outputting the relationship between the thickness of ice and time, and obtaining the freezing time of the salt solution on the road surface. The present invention considers anti-icing by spreading salt when there is water on the road surface, predicts the effect of anti-icing, characterizes the ice formation process by the ice thickness-time relationship, and obtains the time when ice begins to appear, which is of great significance for the application in the field of road anti-icing.

Description

Technical Field

[0001] The invention relates to the technical field of anti-icing application of road salt solution, and in particular to a freezing time prediction method of road salt solution used for anti-icing. Background Art

[0002] Under certain low temperature conditions, water on the road surface is easy to freeze into ice. Road icing reduces the road surface's anti-skid ability and threatens traffic safety. In order to prevent the threat of road icing, spreading salt on the road surface to lower the freezing point of road surface water before the arrival of cold weather is an effective way to prevent icing.

[0003] Considering that the use of salt may cause environmental pollution and other problems, an efficient and convenient method is used to predict the freezing time of road surface water under the influence of salt, which has certain guiding significance for the application of salt and the evaluation of anti-icing effect. At present, most of the research on anti-icing of road surface salt solution is focused on the research and development of new materials and new structures. The anti-icing effect of salt solution is mostly based on indoor and outdoor tests. There are few numerical simulation studies on anti-icing of salt solution, especially the lack of prediction methods for freezing time based on the freezing mechanism of salt solution. The invention patent with authorization announcement number CN109146208 discloses a method for predicting the amount of road deicing salt, including: step A, predicting the temperature change trend of road salt solution during the deicing process according to the data of external temperature and external wind speed; step B, obtaining the salt solution temperature at the end of the deicing salt deicing reaction; step C, obtaining the freezing point temperature of the salt solution at the end of the deicing salt deicing reaction; step D, knowing the concentration of the salt solution at the end of the deicing reaction; step E, calculating the predicted amount of deicing salt according to the thickness of the ice layer and the upper surface area of ​​the ice layer to be melted and the concentration of the salt solution in step D. Although the method for predicting the amount of road deicing salt proposed in this method can determine the use of road deicing salt as much as possible under different external temperatures, different wind speeds, different ice thicknesses, etc., while taking into account the ice melting effect; however, in low temperature weather, when there is water on the road surface, it is impossible to judge the freezing time based on the amount of salt used, and it is impossible to predict the freezing time of water on the road surface under the influence of salt.

[0004] Therefore, there is an urgent need for a method to predict the freezing time of road salt solution for anti-icing to guide the application of salt in road anti-icing. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting the freezing time of road salt solution for anti-icing, so as to solve the problem mentioned in the background technology that there are currently few numerical simulation studies on salt solution anti-icing, especially the lack of a method for predicting the freezing time based on the freezing mechanism of salt solution, which makes it impossible to judge the freezing time according to the amount of salt used and impossible to predict the freezing time of water on the road surface under the influence of salt.

[0006] To achieve the above object, the present invention provides a method for predicting the freezing time of a road salt solution for anti-icing, comprising the following steps:

[0007] Step 1: Set the target concentration of the salt solution and determine the initial amount of salt based on the rainfall and the size of the salt spreading area;

[0008] Step 2: Establish a road-salt solution-ice layer system and define the material properties of each layer, salt solution and ice in the road structure layer in the system;

[0009] Step 3: Based on the heat transfer theory, analyze the heat exchange information between the road-salt solution-ice layer system and the external environment and the internal system, set boundary conditions for each layer in the road structure layer and the salt solution-ice layer in the system, and establish control equations;

[0010] Step 4, using Matlab software to discretize the road-salt solution-ice layer system, and using the finite difference method to solve the control equations of the discrete nodes;

[0011] Step 5: Based on the freezing mechanism and phase change theory of the salt solution, and according to the freezing point and latent heat value of the salt solution, a salt solution freezing algorithm is established;

[0012] Step 6, solving the temperature field of the road-salt solution-ice layer system, and outputting the relationship between the temperature, concentration and freezing point of the salt solution and time;

[0013] Step 7: Based on the change of latent heat of the salt solution, output the relationship between the thickness of ice and time, and combine the initial amount of salt to obtain the freezing time of the salt solution on the road surface.

[0014] Furthermore, in step 1, the target concentration of the salt solution is set to c The area of ​​the salt spreading area is S , the density of water is ρ w , assuming that the thickness of the water on the road surface remains unchanged after adding salt, the total thickness of the salt solution-ice layer formed is d , then the initial amount of salt is .

[0015] Furthermore, in step 2, the road structure layer includes an asphalt concrete surface layer, a base layer and a soil base arranged in sequence from top to bottom; the salt solution-ice layer is arranged on the top surface of the road structure layer; and the material properties include density, thermal conductivity and specific heat capacity.

[0016] Furthermore, in step 3, the heat exchange information between the road-salt solution-ice layer system and the external environment includes the amount of solar radiation reaching the surface of the system. q s , the amount of solar radiation absorbed by the road surfaceq in , the amount of heat radiation emitted from the road surface q out , convective heat flux caused by airflow over the salt solution-ice surface q conv , heat flow generated when the salt solution freezes q ss and the evaporation heat flow on the salt solution surface q eva The heat exchange information inside the system includes the heat conduction along the vertical direction of the system q cond .

[0017] Furthermore, the governing equations for each layer in the road-salt solution-ice layer system are established as follows:

[0018] (1);

[0019] In formula (1), T m ( x , t) is the first m Temperature of the layer; x It is m The distance from the layer to the surface of the salt solution; t For time; ρ m , c m , k m Respectively m The density, specific heat capacity and thermal conductivity of the layer; when m =1, indicating salt solution-ice layer. q p is the heat source term generated during the freezing process of the salt solution; m ≥2, it means each layer in the road structure layer. q p is 0.

[0020] Furthermore, the boundary conditions include the upper boundary conditions of the system, the boundary conditions inside the road structure layer, the lower boundary conditions of the system and the initial conditions of the system; wherein the upper boundary conditions of the system are:

[0021] (2);

[0022] In formula (2), k si is the thermal conductivity of the salt solution-ice layer; T si is the temperature of the salt solution-ice layer;

[0023] The boundary conditions inside the road structure layer are:

[0024] (3);

[0025] (4);

[0026] In formula (3) and formula (4), k m and k m+1 Respectively m Layer and m +1 layer material thermal conductivity; T m and T m+1 Respectively m Layer and m +1 layer temperature;

[0027] The lower boundary condition of the system is:

[0028] (5);

[0029] In formula (5), k bot is the thermal conductivity of the bottom layer of the system; T bot is the temperature of the bottom layer of the system;

[0030] The initial conditions of the system are:

[0031] (6);

[0032] In formula (6), T initial represents the initial temperature of the system.

[0033] Furthermore, the step 4 specifically includes:

[0034] Step 4.1: Use Matlab software to discretize the road-salt solution-ice layer system into multiple subunits, each of which is controlled by a discrete node; the time step of the discrete node is Δ t The discrete nodes from the salt solution-ice layer to the bottom of the road structure layer are nodes 1, 2, ... m-1, m, m+1, ... n, and the total thickness of the salt solution-ice layer is d , controlled by node 1; the spatial step length of the road structure layer is Δ x， Controlled by nodes 2-n;

[0035] Step 4.2: Use the finite difference method to discretize the control equation, and for the salt solution-ice layer, the finite difference equation is:

[0036] (7);

[0037] In formula (7), ρ si represents the density of the salt solution-ice layer, c si represents the specific heat capacity of the salt solution-ice layer; represents the temperature of the salt solution-ice layer at the pth time step, represents the temperature of the salt solution-ice layer at the p+1 time step; It represents the temperature of the surface layer of the road structure at the pth time step;

[0038] For the surface layer of the road structure in the road-salt solution-ice layer system, the finite difference equation is:

[0039] (8);

[0040] In formula (8), ρ sur , k sur , c sur Respectively represent the density, thermal conductivity and specific heat capacity of the surface layer of the road structure; Δ x / 2 is the control unit thickness of the surface layer of the road structure; It represents the temperature of the surface layer of the road structure layer at the p+1 time step; It represents the temperature of the layer below the surface of the road structure layer at the pth time step;

[0041] For the interior of the road structure, the finite difference equation is:

[0042] (9);

[0043] In formula (9), , Respectively represent the temperature of the mth layer at the pth time step and the p+1th time step; , Respectively represent the temperature of the m-1th layer and the m+1th layer at the pth time step;

[0044] For the interface of different material layers in the road structure, the finite difference equation is:

[0045] (10);

[0046] In formula (10), ρm+1 , k m+1 and c m+1 Respectively represent m +1 layer’s density, thermal conductivity and specific heat capacity; ρ m-1 , k m-1 and c m-1 Respectively m -1 Density, thermal conductivity and specific heat capacity of the layer.

[0047] Furthermore, the step 5 is specifically as follows: a salt solution freezing algorithm is established according to the relationship between the freezing point, latent heat value and concentration of the salt solution; wherein, after the salt solution freezing algorithm is completed at each time step, a temperature field entering the road structure is calculated once.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) A method for predicting the freezing time of a road salt solution for anti-icing of the present invention is programmed by Matlab software according to the freezing mechanism of the salt solution, and the temperature field of the road-salt solution-ice layer system is solved, and the freezing process in which the salt solution temperature reaches the freezing point and pure ice is precipitated, while the concentration of the salt solution continues to increase during the cooling process is considered. The present invention can better consider that when there is water on the road surface, a salt solution of a certain concentration is obtained by spreading salt to anti-ice, and the effect of anti-icing is predicted, that is, the freezing process of the salt solution is characterized by the temperature-time relationship, concentration-time relationship and freezing point-time relationship of the salt solution, and the ice formation process is characterized by the ice thickness-time relationship, so as to obtain the time when ice begins to appear.

[0050] (2) The freezing time prediction method of the road salt solution for anti-icing of the present invention determines the freezing point and latent heat of the salt solution according to the concentration of salt in the salt solution. It is also applicable to other types of low-freezing-point deicing salts when the relationship between their freezing point and concentration, and between their latent heat and concentration is known. The predicted temperature-time relationship curve, concentration-time relationship curve, freezing point-time relationship curve and ice thickness-time relationship curve provide an important reference for predicting the anti-icing effect of the salt solution, help to adjust the initial salt dosage according to the weather forecast, and select the salt solution concentration with better anti-icing effect according to the traffic conditions, which is of great significance for optimizing the application of salt in the field of road anti-icing.

[0051] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0053] Figure 1 Schematic diagram of the process of the method in the embodiment of the present invention;

[0054] Figure 2 A schematic diagram of a preferred structure of a road-salt solution-ice multilayer system structure in an embodiment of the present invention;

[0055] Figure 3 is the 24h ambient temperature in the embodiment of the present invention;

[0056] Figure 4 This is a flow chart of a salt solution freezing algorithm in an embodiment of the present invention;

[0057] Figure 5 The temperature-time curve of the salt solution in the embodiment of the present invention;

[0058] Figure 6 is the concentration-time curve of the salt solution in the embodiment of the present invention;

[0059] Figure 7 is the freezing point-time curve of the salt solution in the embodiment of the present invention;

[0060] Figure 8 : This is an ice layer thickness-time curve in an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The present invention will be described in detail below in conjunction with the various embodiments shown in the accompanying drawings, but it should be noted that these embodiments are not limitations of the present invention, and equivalent changes or substitutions in functions, methods, or structures made by ordinary technicians in the field based on these embodiments are all within the scope of protection of the present invention.

[0062] See also Figure 1 This embodiment provides a method for predicting the freezing time of a road salt solution for anti-icing, which includes the following steps:

[0063] Step 1: Set the target concentration of the salt solution and determine the initial amount of salt based on the rainfall and the size of the salt spreading area. Specifically, set the target concentration of the salt solution to c = 3%, the area of ​​the salt spreading area is S =1m 2 , the total thickness of the salt solution-ice layer is d =0.003m, the density of water is ρ w=1000kg∙m -3 , then the initial amount of salt is .

[0064] Step 2: Establish a road-salt solution-ice layer system, and define the material properties of each layer, salt solution, and ice in the road structure layer in the system; for ease of explanation, the embodiment of the present invention numbers the materials of each layer in the road-salt solution-ice layer system in order from top to bottom, and the numbers of the materials of each layer in the road-salt solution-ice layer system are 1, 2, ..., m-1, m, m+1, ..., n. Specifically, the following steps are included:

[0065] Step 2.1 Establish a one-dimensional road-salt solution-ice layer system, which includes a road structure layer and a salt solution-ice layer. The road structure layer includes an asphalt concrete surface layer, a base layer, and a soil base arranged in sequence from top to bottom. The salt solution-ice layer is formed on the surface (top surface) of the road structure layer by freezing the salt solution. The material properties include density, thermal conductivity, and specific heat capacity. The schematic diagram of the road-salt solution-ice layer system and the thickness of each layer are shown in Figure 2. Figure 2 , the material properties of each layer are shown in Table 1.

[0066] Table 1 Material properties of each layer

[0067]

[0068] Step 3: Based on the heat transfer theory, analyze the heat exchange information between the road-salt solution-ice layer system and the external environment, as well as the heat exchange information within the system, set boundary conditions and establish control equations for each layer in the system. Specifically: The heat exchange information between the road-salt solution-ice layer system and the external environment includes the amount of solar radiation reaching the surface of the system. q s , the amount of solar radiation absorbed by the road surface q in , the amount of heat radiation emitted from the road surface q out , convective heat flux caused by airflow over the salt solution-ice surface q conv , heat flow generated when the salt solution freezes q ss and the evaporation heat flow on the salt solution surface q eva ; The heat exchange information inside the system includes the heat conduction along the vertical direction of the system q cond .

[0069] The governing equations for each layer in the road-salt solution-ice layer system are:

[0070] (1);

[0071] in, T m (x, t) is the first m Layer material at a time t is the temperature (K); t is the time (s); x It is m Distance from layer material to the surface of salt solution (m); ρ m , c m , k m Respectively m Density of layer material (kg·m -3 ), specific heat capacity (J·kg -1 ·K -1 ) and thermal conductivity (W·m -1 ·K -1 ).when m =1, m Indicates salt solution-ice layer, at this time q p is the heat source term generated during the freezing process of the salt solution; m ≥2, m Indicates each layer in the road structure layer. q p is 0.

[0072] The boundary conditions of the road-salt solution-ice layer system are set, including the upper boundary conditions of the system, the boundary conditions inside the road structure layer, the lower boundary conditions of the system, and the initial conditions of the system; among which, the upper boundary conditions of the system are:

[0073] (2);

[0074] In the formula, k si is the thermal conductivity of salt solution-ice (kg·m -3 ); T si is the temperature of the salt solution-ice (W·m -1 ·K -1 ).

[0075] The boundary conditions inside the road structure layer are:

[0076] (3);

[0077] (4);

[0078] In formula (3) and formula (4), km and k m+1 Respectively m Layer and m +1 layer material thermal conductivity (W·m -1 ·K -1 ); T m , T m+1 Respectively m Layer and m +1 layer material temperature (K); where m Layer and m +1 layer is the layer in the road structure layer, that is m ≥2.

[0079] The lower boundary condition of the system is:

[0080] (5);

[0081] In formula (5), k bot is the thermal conductivity of the underlying material of the system (W·m -1 ·K -1 ); T bot is the temperature of the bottom material of the system (K).

[0082] The initial conditions of the system are:

[0083] (6);

[0084] In formula (6), T initial Indicates the initial temperature of the system. In this embodiment, the temperature of the system is uniformly distributed at the beginning. T initial is 5℃.

[0085] Step 4: Discretize the road-salt solution-ice layer system using Matlab software, and use the finite difference method to solve the control equations of the discretized nodes; specifically,

[0086] Step 4.1: Use Matlab software to discretize the road-salt solution-ice layer system into multiple subunits, each of which is controlled by a discrete node. The time step of the discrete node in the system is Δ t= 3.6s, the total thickness of the salt solution-ice layer is d =0.003m, the total thickness of the road structure is 3m, and the spatial step length of the road structure is Δ x = 0.01m, total time 24h, total thickness of the system 3.003m. 24h ambient temperature Figure 3 shown.

[0087] Step 4.2: Use the finite difference method to express the control equation of the node: The finite difference equation of the salt solution-ice layer is:

[0088] (7);

[0089] In formula (7), ρ si represents the density of the salt solution-ice layer (kg·m -3 ), c si represents the specific heat capacity of the salt solution-ice layer (J·kg -1 ·K -1 ); represents the temperature of the salt solution-ice layer at the pth time step (K), represents the temperature of the salt solution-ice layer at the p+1th time step (K); Represents the temperature (K) of the surface layer of the road structure at the pth time step.

[0090] For the surface layer (surface) of the road structure in the road-salt solution-ice layer system, the finite difference equation is:

[0091] (8);

[0092] In formula (8) ρ sur , k sur and c sur Respectively represent the density of the surface layer of the road structure (kg·m -3 ), thermal conductivity (W·m -1 ·K -1 ) and specific heat capacity (J·kg -1 ·K -1 );Δ x / 2 is the control unit thickness of the surface layer of the road structure (m); represents the temperature of the surface layer of the road structure layer at the p+1th time step (K); It represents the temperature (K) of the layer below the surface of the road structure layer at the pth time step.

[0093] For the interior of the road structure, the finite difference equation is:

[0094] (9);

[0095] In formula (9), ρ m , km and c m Respectively represent the inner part of the road structure layer m Layer density (kg·m -3 ), thermal conductivity (W·m -1 ·K -1 ) and specific heat capacity (J·kg -1 ·K -1 ); , Respectively represent the temperature (K) of the mth layer at the pth time step and the p+1th time step; , Represent the temperature (K) of the m-1th layer and the m+1th layer at the pth time step respectively.

[0096] For the interface of different material layers in the road structure layer, the finite difference equation is:

[0097] (10);

[0098] In formula (10), ρ m+1 , k m+1 , c m+1 represent the density of the m+1th layer (kg·m -3 ), thermal conductivity (W·m -1 ·K -1 ) and specific heat capacity (J·kg -1 ·K -1 ); ρ m-1 , k m-1 , c m-1 represent the density of the m-1th layer (kg·m -3 ), thermal conductivity (W·m -1 ·K -1 ), specific heat capacity (J·kg -1 ·K -1 ).

[0099] Step 5: Based on the freezing mechanism and phase change theory of the salt solution, and according to the freezing point and latent heat of the salt solution, a salt solution freezing algorithm is established; specifically, the following steps are included:

[0100] Step 5.1 Based on the freezing mechanism and phase change theory of the salt solution, determine the relationship between the accumulated latent heat and the freezing latent heat during the cooling process of the salt solution, calculate the temperature of the salt solution-ice layer, and consider the relationship between the freezing point, latent heat and concentration of the salt solution, and then establish a salt solution freezing algorithm.

[0101] Freezing point of salt solution The relationship between the concentration can be calculated according to the following formula:

[0102]

[0103] parameter

[0104] c is the target concentration of the saline solution.

[0105] Latent heat of freezing of salt solution Q ss Calculate according to the following formula:

[0106]

[0107] The initial concentration of the salt solution is According to the above formula, the salt solution can be obtained t = 0. When cooling, the temperature of road-salt solution-ice gradually decreases from above 0℃. The concentration, freezing point, temperature, accumulated latent heat, freezing latent heat, and ice thickness of the salt solution in step p are The concentration, freezing point, temperature, accumulated latent heat, freezing latent heat, and ice thickness of the salt solution in step p+1 are The salt solution freezing algorithm is as follows, and the algorithm flow chart is as follows: Figure 4 :

[0108] Among them, during the salt solution-ice cooling process:

[0109] when hour, ;

[0110] if ,but ;

[0111] if ,but , ice begins to form, and the thickness of the ice is:

[0112] ;

[0113] The concentration of salt solution is ;

[0114] and With the updated concentration In other cases, The value of is the same as in the previous step.

[0115] Among them, during the salt solution-ice heating process:

[0116] when hour, ;

[0117] if ,but , the ice begins to melt, the thickness of the ice and salt solution concentration Calculate using the same formula as above; in other cases, The value of is the same as in the previous step.

[0118] Step 5.2 After the freezing algorithm of the salt solution is completed at each time step, the temperature field calculation in the road structure layer is performed.

[0119] Step 6: Solve the temperature field of the road-salt solution-ice layer system, and output the changes in the temperature, concentration and freezing point of the salt solution over time. Specifically, based on the road-salt solution-ice layer system established in step 2, the external climate conditions and internal material parameters are used as the input values ​​of the model, and the finite difference equation and salt solution freezing algorithm are used to solve it, and the temperature value of each time step in 24 hours is output. T , concentration value c and freezing point ,like Figure 5 , 6 , as shown in Figure 7.

[0120] Step 7: Based on the change of latent heat, output the change of ice thickness over time, and combine the initial amount of salt to obtain the freezing time of the salt solution on the road surface. Specifically, based on the change of latent heat, output the change of ice thickness over time, and the time when ice appears and disappears can be obtained from the relationship between ice thickness and time. Combined with the initial amount of salt, the freezing time of the salt solution on the road surface is obtained. In this embodiment, the ice thickness at each time step in 24 hours is output. H like Figure 8 The following code is set in Matlab software to output the time ice_start starts to freeze. In this embodiment, the freezing time is 3.8h.

[0121]

[0122]

[0123] The code for outputting the time ice_end when the ice layer is completely melted is as follows, which is 8.6h in this embodiment:

[0124]

[0125]

[0126] The present invention provides a method for predicting the freezing time of a road salt solution for anti-icing, which can use software to perform numerical simulation on the process of road salt solution anti-icing based on the freezing mechanism of the salt solution. The present invention uses the target concentration of the salt solution as the input value, establishes the control equations of each layer based on the heat transfer and phase change theory for the road-salt solution-ice layer system, and solves them using the finite difference method. Finally, the relationship between the temperature, concentration, freezing point and thickness of the ice layer of the salt solution and time is output, so as to predict the freezing time of the road salt solution.

[0127] The present invention fully considers the environmental conditions under natural conditions, reflects the temperature drop process of the salt solution from the temperature, concentration and freezing point of the salt solution, reflects the ice formation process through the thickness of the ice layer, and obtains the predicted freezing time to reflect the anti-icing effect of the salt solution. This helps the relevant departments to adjust the salt spreading measures according to the traffic conditions, optimize the application of salt and maintain traffic safety, and promote the application of salt solution anti-icing in the field of numerical simulation.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting freezing time of road salt solution for anti-icing, characterized in that: The steps include: Step 1: Set the target concentration of the salt solution and determine the initial amount of salt based on the rainfall and the size of the salt spreading area; Step 2: Establish a road-salt solution-ice layer system and define the material properties of each layer, salt solution and ice in the road structure layer in the system; Step 3: Based on the heat transfer theory, the heat exchange information between the road-salt solution-ice layer system and the external environment and the system is analyzed, and the boundary conditions and control equations are set for each layer of the road structure layer and the salt solution-ice layer in the system; wherein the heat exchange information between the road-salt solution-ice layer system and the external environment includes the solar radiation reaching the surface of the system q s , the amount of solar radiation absorbed by the road surface q in , the amount of heat radiation emitted from the road surface q out , the convective heat flux q caused by the airflow over the salt solution-ice surface conv , the heat flow q generated when the salt solution freezes ss and the evaporation heat flux q on the salt solution surface eva The heat exchange information inside the system includes the heat conduction quantity q along the vertical direction of the system cond ; The governing equations for each layer in the road-salt solution-ice layer system are: In formula (1), T m (x, t) is the temperature of the mth layer in the road-salt solution-ice layer system; x is the distance from the mth layer to the salt solution surface; t is the time; ρ m 、c m , k m are the density, specific heat capacity and thermal conductivity of the mth layer respectively; when m = 1, it represents a salt solution-ice layer, at this time q p is the heat source term generated during the freezing process of the salt solution; when m≥2, it represents each layer in the road structure layer, at this time q p is 0; The boundary conditions include the upper boundary conditions of the system, the boundary conditions inside the road structure layer, the lower boundary conditions of the system and the initial conditions of the system; wherein the upper boundary conditions of the system are: In formula (2), k si is the thermal conductivity of the salt solution-ice layer; T si is the temperature of the salt solution-ice layer; The boundary conditions inside the road structure layer are: T m (x,t)| x＝m =T m+1 (x,t)| x＝m (3); In formula (3) and formula (4), k m+1 are the thermal conductivity of the m+1th layer of material; T m and T m+1 are the temperatures of the mth layer and the m+1th layer respectively; The lower boundary condition of the system is: In formula (5), k bot is the thermal conductivity of the bottom layer of the system; T bot is the temperature of the bottom layer of the system; The initial conditions of the system are: T m (x,t)| t＝0 =T initial (6); In formula (6), T initial represents the initial temperature of the system; Step 4: discretize the road-salt solution-ice layer system using Matlab software, and solve the control equations of the discrete nodes using the finite difference method; Step 5: Based on the freezing mechanism and phase change theory of the salt solution, and according to the freezing point and latent heat value of the salt solution, a salt solution freezing algorithm is established; Step 6, solving the temperature field of the road-salt solution-ice layer system, and outputting the relationship between the temperature, concentration and freezing point of the salt solution and time; Step 7: Based on the change in latent heat of the salt solution, output the relationship between the thickness of ice and time, and combine the initial amount of salt to obtain the freezing time of the salt solution on the road surface.

2. The method according to claim 1, characterized in that In step 1, the target concentration of the salt solution is set to c, the area of ​​the salt spreading area is S, and the density of water is ρ w , assuming that the thickness of the water on the road surface remains unchanged after adding salt, and the total thickness of the salt solution-ice layer formed is d, then the initial amount of salt used is M = c·ρ w ·S·d.

3. The method according to claim 1, characterized in that In step 2, the road structure layer includes an asphalt concrete surface layer, a base layer and a soil base arranged in sequence from top to bottom; the salt solution-ice layer is arranged on the top surface of the road structure layer; and the material properties include density, thermal conductivity and specific heat capacity.

4. The method according to claim 1, characterized in that: The step 4 specifically includes: Step 4.1, using Matlab software to discretize the road-salt solution-ice layer system into multiple subunits, each subunit is controlled by a discrete node; the time step of the discrete node is Δt, and the discrete nodes from the salt solution-ice layer to the bottom of the road structure layer are nodes 1, 2, ... m-1, m, m+1, ... n, respectively, and the total thickness of the salt solution-ice layer is d, which is controlled by node 1; the spatial step of the road structure layer is Δx, which is controlled by nodes 2-n; Step 4.2: Use the finite difference method to discretize the control equation, and for the salt solution-ice layer, the finite difference equation is: In formula (7), ρ si represents the density of the salt solution-ice layer, c si represents the specific heat capacity of the salt solution-ice layer; represents the temperature of the salt solution-ice layer at the pth time step, represents the temperature of the salt solution-ice layer at the p+1 time step; It represents the temperature of the surface layer of the road structure at the pth time step; For the surface layer of the road structure in the road-salt solution-ice layer system, the finite difference equation is: In formula (8), ρ sur , k sur 、c sur They represent the density, thermal conductivity and specific heat capacity of the surface layer of the road structure respectively; Δx / 2 is the control unit thickness of the surface layer of the road structure; It represents the temperature of the surface layer of the road structure layer at the p+1 time step; It represents the temperature of the layer below the surface of the road structure layer at the pth time step; For the interior of the road structure, the finite difference equation is: In formula (9), Respectively represent the temperature of the mth layer at the pth time step and the p+1th time step; Respectively represent the temperature of the m-1th layer and the m+1th layer at the pth time step; For the interface of different material layers in the road structure, the finite difference equation is: In formula (10), ρ m+1 , k m+1 and c m+1 Respectively represent the density, thermal conductivity and specific heat capacity of the m+1th layer; ρ m-1 , k m-1 and c m-1 represent the density, thermal conductivity and specific heat capacity of the m-1 layer respectively.

5. The method according to claim 1, characterized in that The step 5 specifically includes: establishing a salt solution freezing algorithm according to the relationship between the freezing point, latent heat value and concentration of the salt solution; wherein, after the salt solution freezing algorithm is completed at each time step, a temperature field in the road structure is calculated once.

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