A calculation method for the short-term impact of high thermal conductivity of heat pipes in roadbed filling.

Abstract

This invention relates to the field of data processing technology, specifically to a method for calculating the impact of high thermal conductivity of heat pipes on the temperature field of the underlying frozen soil in the short term after roadbed filling. The method includes: collecting geological data, determining the physical parameters of the foundation soil and roadbed fill material, and fitting temperature changes to a periodic boundary condition formula required for calculation; selecting a heat pipe model and calculating its cooling capacity; establishing a heat pipe roadbed model in a permafrost region and adding relevant parameters and boundary conditions; dividing the natural permafrost foundation into a grid, calculating the hydrothermal stability field of the foundation, and obtaining the initial values ​​of the foundation hydrothermal field for heat pipe roadbed calculation; dividing the heat pipe roadbed model into a grid, calculating the negative impact of high thermal conductivity of the heat pipes on the temperature field of the underlying frozen soil in the short term after roadbed filling; and calculating the impact of high thermal conductivity of the heat pipes on the temperature field of the underlying frozen soil under different working conditions. This invention improves the accuracy of determining the impact of high thermal conductivity of heat pipes on the temperature field of the underlying frozen soil in the short term after roadbed filling.

Description

Technical Field

[0001] This invention relates to the field of data processing technology, and specifically to a calculation method for the impact of high thermal conductivity of heat pipes on roadbed filling in the short term. Background Technology

[0002] Approximately 70% of the Qinghai-Tibet Plateau is covered by permafrost. The Qinghai-Tibet Highway, built on permafrost, is characterized by a common yin-yang slope effect, resulting in significant temperature differences in the permafrost beneath the roadbed. Under the combined influence of engineering construction and global warming, this leads to permafrost degradation, causing a series of thermal thawing disasters such as uneven road surface settlement.

[0003] To reduce the interference of roadbed filling and the effects of symmetrical slopes on the original temperature field of permafrost, scholars both domestically and internationally have conducted extensive research on roadbed filling materials, roadbed dimensions, different initial conditions, and the use of heat pipes for cooling. Among these, heat pipes, with their high thermal conductivity, can effectively cool the underlying permafrost and prevent its degradation, making them widely used. Based on the heat transfer equation of permafrost expressed by the sensible heat capacity method, a three-dimensional finite element model of a heat pipe roadbed was established, and the cooling effect of the heat pipes was analyzed. Considering the influence of moisture in the permafrost, the impact of different heat pipe arrangements on the cooling effect of symmetrical slope roadbeds was analyzed based on a hydrothermal coupling model. The negative impact of the high thermal conductivity of the heat pipes was analyzed, and the results show that, over long-term operation, the high thermal conductivity of the heat pipes will weaken the original cooling effect. However, the above calculations for heat pipe roadbeds are based on long-term cooling effects, making it difficult to determine the short-term impact of the heat pipes on the underlying permafrost after filling. Summary of the Invention

[0004] The summary section of this invention provides a brief overview of the concepts, which will be described in detail in the detailed description section that follows. This summary section is not intended to identify key or essential features of the claimed invention, nor is it intended to limit the scope of the claimed invention.

[0005] To address the technical problem of low accuracy in determining the impact of heat pipes on the frozen soil beneath the roadbed in the short term after filling, this invention proposes a calculation method for the impact of the high thermal conductivity of heat pipes in the short term after roadbed filling.

[0006] This invention provides a method for calculating the impact of high thermal conductivity of heat pipes on roadbed filling in the short term. The method includes:

[0007] Collect soil parameters in the area where the roadbed project is located, determine the thermal conductivity, heat capacity, soil density and latent heat of phase change, and determine the soil-water characteristic curve based on the soil parameters; collect annual temperature variation data in the area where the roadbed project is located and fit it to a sinusoidal periodic function as the temperature fitting function; collect wind speed variation data and calculate its average value as the regional average wind speed.

[0008] Select the type of heat pipe to be calculated, and calculate the cooling capacity of the heat pipe based on the cooling capacity equation and the calculated regional average wind speed.

[0009] Based on the collected roadbed cross-sectional dimensions, thermal conductivity, heat capacity, soil density, latent heat of phase change, soil-water characteristic curves, and temperature fitting functions, a water-thermal coupling model for the heat pipe roadbed is established.

[0010] The model of the foundation is divided into grids, and the hydrothermal stability field of the foundation is calculated. The obtained hydrothermal stability field is used as the initial value for the simulation calculation of the heat pipe subgrade.

[0011] The hydrothermal coupling model of the heat pipe roadbed was meshed. Based on the initial values ​​and cooling capacity of the heat pipe during the simulation calculation of the heat pipe roadbed, the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil was calculated in the short term after the heat pipe roadbed was filled.

[0012] By varying the roadbed filling time, the initial temperature of the roadbed fill material, and the thermal conductivity of the heat pipe, the influence of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil under different working conditions was calculated.

[0013] Furthermore, the determination of thermal conductivity, heat capacity, soil density, and latent heat of phase change, and the determination of soil-water characteristic curves based on soil parameters; and the collection of annual temperature variation data of the area where the roadbed project is located and fitting it to a sinusoidal periodic function as the temperature fitting function, includes:

[0014] The thermal conductivity, heat capacity, soil density, and latent heat of phase change were measured through sampling tests.

[0015] By fitting the van Genuchten model, the soil-water characteristic curves were obtained, where the van Genuchten model equation is expressed as follows:

[0016]

[0017] Where θ is the volumetric water content; α, n and m are all fitting parameters, α is the soil air ingress function; n is the soil outflow rate function, which is related to the soil pore size; h is the pressure head; m is the soil parameter of the residual water content function, which is related to the overall symmetry of the soil-water characteristic curve;

[0018] The temperature fitting function is:

[0019]

[0020] Where T is the calculated temperature in °C; T0 is the annual average temperature in °C; A is the amplitude; and t is the time in hours. This is the initial phase.

[0021] Further, the step of selecting the type of heat pipe to be calculated and calculating the cooling capacity of the heat pipe based on the cooling capacity equation and the calculated regional average wind speed includes:

[0022] The heat transfer equation for the heat pipe is:

[0023]

[0024] Where ρ is the density of the heat pipe material; C is the heat capacity of the heat pipe; λ x λ is the axial thermal conductivity of the heat pipe; y Q is the radial thermal conductivity of the heat pipe; v For cooling capacity;

[0025] The equation for the cooling capacity of the heat pipe is:

[0026]

[0027] Among them, T s T a These are the soil temperature and atmospheric temperature in contact with the evaporation section, respectively; R f R s These are the thermal resistances of the condensation section and the soil in contact with the evaporation section, respectively.

[0028]

[0029] Where r2 is the average influence radius of heat transfer in the evaporation section, r1 is the outer radius of heat transfer in the evaporation section, and λ is the thermal conductivity of the frozen soil in contact with the evaporation section.

[0030]

[0031] Where S is the heat dissipation area of ​​the condensation section; eh is the effective heat transfer coefficient of the condensation section;

[0032] eh = 2.75 + 1.51v 0.2

[0033] Where v is the regional average wind speed.

[0034] Furthermore, the establishment of a heat pipe roadbed hydrothermal coupling model based on the collected roadbed cross-sectional dimensions, thermal conductivity, heat capacity, soil density, latent heat of phase change, soil-water characteristic curves, and temperature fitting function includes:

[0035] The temperature field equation in the hydrothermal coupling equation is:

[0036]

[0037] Where ρ is the soil density; λ is the thermal conductivity; L is the latent heat of phase change; θ I Ice content by volume; C wθ is the volumetric heat capacity of water; D is the water diffusion coefficient; θ u K is the volume content of unfrozen water. u Hydraulic conductivity;

[0038]

[0039]

[0040] Among them, C u The heat capacity of unfrozen soil; C f λ is the heat capacity of frozen soil; u λ is the thermal conductivity of unfrozen soil. f The thermal conductivity of frozen soil;

[0041] The water field equation in the hydrothermal coupling equation is:

[0042]

[0043] Where, ρ I ρ is the density of ice. w The density of water; θ I Ice content by volume; D(θ) u ) represents the water diffusion coefficient; θ u K is the volume content of unfrozen water. u Hydraulic conductivity;

[0044] The solid-liquid ratio equation is:

[0045]

[0046] Among them, B I It is the solid-liquid ratio, and it is θ. I and θ u Relationship between T; f is the soil freezing temperature, in °C; b is an empirical parameter.

[0047] Based on the hydrothermal coupling equation, a heat pipe roadbed model is established according to the roadbed cross-sectional dimensions of the project area.

[0048] Furthermore, the hydrothermal coupling model of the heat pipe roadbed is meshed, and based on the initial values ​​and cooling capacity of the heat pipe during the simulation calculation, the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil in the short term after the heat pipe roadbed is filled is calculated, including:

[0049] The hydrothermal coupling model of the heat pipe roadbed is meshed. Based on the initial values ​​and cooling capacity of the heat pipe during the simulation calculation of the heat pipe roadbed, the influence of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil is calculated in the short term after the roadbed filling is completed.

[0050] The negative impact of the high thermal conductivity of the heat pipe is evaluated by the elevation difference of the freezing front, which is the difference between the elevation of the freezing front at different positions on the left side of the heat pipe and the elevation of the lowest point of the freezing front.

[0051] The present invention has the following beneficial effects:

[0052] This invention, starting from the influence of the high thermal conductivity of heat pipes, proposes a calculation method for assessing the impact of high thermal conductivity heat pipe materials on the temperature field of the underlying frozen soil in the short term after the completion of heat pipe roadbed construction. By considering different roadbed filling times, different roadbed filler temperatures, and different heat pipe materials, the non-uniform hydrothermal transfer process around the evaporation section during ground temperature evolution under the influence of high thermal conductivity heat pipes is calculated. This provides a theoretical basis for the selection of heat pipes in road construction in cold regions and has significant engineering application value. Attached Figure Description

[0053] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 A flowchart illustrating a calculation method for the influence of high thermal conductivity of heat pipes on roadbed filling in the short term, according to the present invention;

[0055] Figure 2 This is a schematic diagram of the temperature fitting curve according to the present invention;

[0056] Figure 3 This is a schematic diagram of the field measurement model for frozen soil heat pipe roadbed according to the present invention;

[0057] Figure 4 This is a schematic diagram of the calculation model for frozen soil heat pipe subgrade according to the present invention;

[0058] Figure 5 This is a schematic diagram of the grid division of the foundation according to the present invention;

[0059] Figure 6 This is a schematic diagram of the grid division of the heat pipe roadbed according to the present invention;

[0060] Figure 7 This is a schematic diagram of the distribution cloud map of the frozen front according to the present invention;

[0061] Figure 8 This is a schematic diagram of the freezing front elevation difference curve during the filling of the hot rod subgrade in July according to the present invention;

[0062] Figure 9This is a schematic diagram of the time history variation curves of the lowest point of the freezing front corresponding to different filling times according to the present invention;

[0063] Figure 10 This is a schematic diagram of the freezing front curves under the influence of different roadbed fill temperatures according to the present invention;

[0064] Figure 11 This is a schematic diagram of the freezing front curves under the influence of different thermal conductivity coefficients of heat pipes according to the present invention. Detailed Implementation

[0065] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the specific implementation methods, structures, features, and effects of the technical solution proposed according to the present invention are described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0067] This invention provides a method for calculating the impact of high thermal conductivity of heat pipes on roadbed filling in the short term. The method includes the following steps:

[0068] Collect soil parameters in the area where the roadbed project is located, determine the thermal conductivity, heat capacity, soil density and latent heat of phase change, and determine the soil-water characteristic curve based on the soil parameters; collect annual temperature variation data in the area where the roadbed project is located and fit it to a sinusoidal periodic function as the temperature fitting function; collect wind speed variation data and calculate its average value as the regional average wind speed.

[0069] Select the type of heat pipe to be calculated, and calculate the cooling capacity of the heat pipe based on the cooling capacity equation and the calculated regional average wind speed.

[0070] Based on the collected roadbed cross-sectional dimensions, thermal conductivity, heat capacity, soil density, latent heat of phase change, soil-water characteristic curves, and temperature fitting functions, a water-thermal coupling model for the heat pipe roadbed is established.

[0071] The model of the foundation is divided into grids, and the hydrothermal stability field of the foundation is calculated. The obtained hydrothermal stability field is used as the initial value for the simulation calculation of the heat pipe subgrade.

[0072] The hydrothermal coupling model of the heat pipe roadbed was meshed. Based on the initial values ​​and cooling capacity of the heat pipe during the simulation calculation of the heat pipe roadbed, the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil was calculated in the short term after the heat pipe roadbed was filled.

[0073] By varying the roadbed filling time, the initial temperature of the roadbed fill material, and the thermal conductivity of the heat pipe, the influence of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil under different working conditions was calculated.

[0074] The following is a detailed explanation of each of the above steps:

[0075] refer to Figure 1 The flowchart illustrates some embodiments of a method for calculating the impact of high thermal conductivity of heat pipes during short-term roadbed filling, according to the present invention. This method for calculating the impact of high thermal conductivity of heat pipes during short-term roadbed filling includes the following steps:

[0076] Step S1: Collect soil parameters in the area where the roadbed project is located, determine the thermal conductivity, heat capacity, soil density and latent heat of phase change, and determine the soil-water characteristic curve based on the soil parameters; collect annual temperature variation data in the area where the roadbed project is located and fit it to a sinusoidal periodic function as the temperature fitting function; collect wind speed variation data and calculate its average value as the regional average wind speed.

[0077] In some embodiments, relevant soil parameters of the area where the roadbed project is located can be collected to determine the thermal conductivity λ, heat capacity C, soil density ρ, and latent heat of phase change L. Based on the soil parameters, the soil-water characteristic curve of the soil can be determined. All these parameters are provided to step S3. Annual temperature variation data of the area where the roadbed project is located are collected and fitted into a sinusoidal periodic function as the temperature fitting function, and provided to step S3. Wind speed variation data are collected, and its average value is calculated as the regional average wind speed, and provided to step S2.

[0078] As an example, the thermal conductivity, heat capacity, soil density, and latent heat of phase change are determined, and based on these soil parameters, the soil-water characteristic curve is determined. Annual temperature variation data for the area where the roadbed project is located are collected and fitted to a sinusoidal periodic function. The temperature fitting function may include the following steps:

[0079] The first step is to measure the thermal conductivity, heat capacity, soil density, and latent heat of phase change through sampling tests.

[0080] For example, the thermal conductivity and heat capacity of the soil can be measured through sampling tests.

[0081] The second step is to obtain the soil-water characteristic curve by fitting the van Genuchten model, where the van Genuchten model equation is expressed as follows:

[0082]

[0083] Where θ is the volumetric water content. α, n, and m are all fitting parameters; α is the soil air ingress function; n is the soil outflow rate function, related to the soil pore size; h is the pressure head; m is a soil parameter representing the residual water content function, related to the overall symmetry of the soil-water characteristic curve; h is the pressure head.

[0084] The temperature fitting function is:

[0085]

[0086] Where T is the calculated temperature in °C, T0 is the annual average temperature in °C, A is the amplitude, and t is the time in hours. This is the initial phase.

[0087] It should be noted that the thermal conductivity λ, heat capacity C, soil density ρ, and latent heat of phase change L of the roadbed fill material and foundation soil in the local area can be determined through indoor geotechnical tests, as shown in Table 1.

[0088] Table 1

[0089]

[0090]

[0091] Soil parameters were obtained from indoor tests, and soil-water characteristic curves were fitted to determine parameters related to water migration, as shown in Table 2.

[0092] Table 2

[0093] name <![CDATA[a0]]> m l <![CDATA[θ r ]]> <![CDATA[θ s ]]> <![CDATA[k s [m / s]]]> Roadbed fill 0.66 0.14 0.5 0.25 0.01 <![CDATA[2×10 -6 ]]> silty soil 0.66 0.14 0.5 0.42 0.05 <![CDATA[1×10 -6 ]]> Weathered mudstone 2.65 0.26 0.5 0.42 0.05 <![CDATA[2×10 -9 ]]>

[0094] The boundary conditions required for the calculation can be determined based on the collected local meteorological data. The collected local temperature variation data can be fitted into a sinusoidal periodic function as the temperature condition for the calculation and provided to step S2. The fitted temperature function is the temperature fitting function mentioned above; the fitted temperature curve can be as follows: Figure 2 As shown in Table 3, the values ​​of each parameter in the temperature fitting function can be obtained from these parameters.

[0095] Table 3

[0096]

[0097] in, It was July.

[0098] The heat flux density at the base of the foundation model was obtained through multi-year geothermal observations and is 0.02 W / m³. 2 .

[0099] The boundary conditions of the constructed model do not consider the replenishment and evaporation of water.

[0100] Based on the collected wind speed change data, the average wind speed at the location was determined to be 4.5 m / s.

[0101] Step S2: Select the type of heat pipe to be calculated, and calculate the cooling capacity of the heat pipe based on the cooling capacity equation and the calculated regional average wind speed.

[0102] In some embodiments, the heat pipe model can be selected according to engineering needs: heat pipe diameter 0.1m, condensation section length 2.5m, insulation section length 3m, and evaporation section length 5m. The physical parameters of the heat pipe are substituted into the heat transfer equation and the cooling capacity equation to calculate the cooling capacity of the heat pipe, and the result is provided to step S5.

[0103] As an example, this step may include the following steps:

[0104] The heat transfer equation for the heat pipe is:

[0105]

[0106] Where ρ is the density of the heat pipe material, and C is the heat capacity of the heat pipe. λ x λ is the axial thermal conductivity of the heat pipe. y Q is the radial thermal conductivity of the heat pipe. v This is for generating cooling capacity.

[0107] The equation for the cooling capacity of the heat pipe is:

[0108]

[0109] Among them, T s T a These represent the soil temperature in contact with the evaporation section and the atmospheric temperature, respectively. R f R s These are the thermal resistances of the condensation section and the soil in contact with the evaporation section, respectively.

[0110]

[0111] Where r2 is the average influence radius of heat transfer in the evaporation section, which is generally 1.5–1.8 m based on actual measurements. In this embodiment, 1.5 m can be used based on the actual engineering conditions at the location. r1 is the outer radius of heat transfer in the evaporation section, for example, r1 is 0.1 m. λ is the thermal conductivity of the frozen soil in contact with the evaporation section. For example, λ is 5 m. R can be calculated. s It is 0.0399℃ / W.

[0112]

[0113] Where S is the heat dissipation area of ​​the condensation section, for example, S is 3.7m². 2 eh is the effective heat transfer coefficient of the condensation section.

[0114] eh = 2.75 + 1.51v 0.2

[0115] Where v is the regional average wind speed. If the regional average wind speed is 4.5 m / s, then eh can be calculated to be 4.79; therefore, R can be calculated. f It is 0.0464℃ / W.

[0116] It should be noted that T s -T a As a criterion for whether the heat pipe has started working (when T...) s -T a The system starts operating when the temperature of the soil in contact with the heat pipe is greater than 0.8℃ (i.e., the temperature of the soil is 0.8℃ higher than the atmospheric temperature). This is achieved by defining an if function in the software, as follows:

[0117] Q0 = if(T) s -T a >0.8℃, Q v ,0)

[0118] Substituting the above equation into the second type of boundary conditions, we get:

[0119] The relevant parameters for heat transfer in the heat pipe are shown in Table 4.

[0120] Table 4

[0121]

[0122]

[0123] Step S3: Based on the collected roadbed cross-sectional dimensions, thermal conductivity, heat capacity, soil density, latent heat of phase change, soil-water characteristic curves, and temperature fitting function, establish a heat pipe roadbed hydrothermal coupling model.

[0124] In some embodiments, a hydrothermal coupling model of the roadbed can be established based on the roadbed cross-sectional dimensions observed on site, combined with boundary conditions and parameter values.

[0125] As an example, based on the hydrothermal coupling equation, a heat pipe subgrade model is established according to the measured dimensions of the subgrade cross-section in the project area. Material parameters and boundary conditions are added, and the process of substituting these parameters and boundary conditions into the temperature field and moisture field equations can include the following steps:

[0126] The temperature field equation in the hydrothermal coupling equation is:

[0127]

[0128] Where ρ is the soil density, λ is the thermal conductivity, and L is the latent heat of phase change. IC represents the volumetric ice content. w Let θ be the volumetric heat capacity of water. Let D be the water diffusion coefficient. u This represents the volumetric content of unfrozen water. K u It represents the water conductivity.

[0129] Considering the changes in soil thermal conductivity and heat capacity under different freeze-thaw conditions, then:

[0130]

[0131]

[0132] Among them, C u C represents the heat capacity of unfrozen soil. f λ represents the heat capacity of frozen soil. u λ is the thermal conductivity of unfrozen soil. f The value represents the thermal conductivity of frozen soil.

[0133] The water field equation in the hydrothermal coupling equation is:

[0134]

[0135] Where, ρ I ρ is the density of ice. w θ is the density of water. I D(θ) represents the volumetric ice content. u θ is the water diffusion coefficient. u This represents the volumetric content of unfrozen water. K u It represents the water conductivity.

[0136] To make the equation have a solution, we establish θ I and θ u The relationship between the solid-liquid ratio B I The solid-liquid ratio equation is:

[0137]

[0138] Among them, B I It is the solid-liquid ratio, and it is θ. I and θ u The relationship between T. f ν is the soil freezing temperature, in °C. b is an empirical parameter.

[0139] Based on the hydrothermal coupling equation, a heat pipe roadbed model is established according to the roadbed cross-sectional dimensions of the project area.

[0140] It should be noted that the collected on-site engineering data may include: a foundation 15m high and 50m wide, comprising a 5m high silty sand layer and a 10m high weathered mudstone layer; a roadbed 19m long and 3m high, with a slope ratio of 1:1.5, for which a numerical calculation model was established. Due to the significant difference between sunny and shady slopes in this section, to reduce the temperature field difference in the lower part of the roadbed, heat pipes were only buried on the sunny slope side (i.e., the left shoulder), such as... Figure 3 As shown. To improve computational efficiency during numerical simulation, only the portion from the roadbed center to the left boundary containing the heat pipe is modeled, as shown. Figure 4 As shown.

[0141] Step S4: Divide the model of the foundation into grids and calculate the hydrothermal stability field of the foundation. Use the obtained hydrothermal stability field as the initial value for the simulation calculation of the heat pipe subgrade.

[0142] In some embodiments, in order to obtain the initial values ​​of the foundation moisture and temperature distribution when calculating the heat pipe roadbed, without considering the construction of the heat pipe roadbed, only the foundation part is divided into grids and calculated, and the obtained hydrothermal stability field is provided as the initial value for the simulation calculation of the heat pipe roadbed to step S5.

[0143] As an example, the model can be meshed only for the foundation portion, the hydrothermal stability field of the foundation can be calculated, the calculation time is 50 years, and the obtained stability field can be provided as the initial value for the calculation of the heat pipe subgrade to step S5.

[0144] For example, the model can be divided into grids only for the foundation part, and the temperature field and moisture field of the foundation in the permafrost region can be calculated to obtain the hydrothermal stability field of the foundation. The calculation results can be provided to step S5 as the initial value of the hydrothermal field of the foundation when calculating the heat pipe subgrade.

[0145] It should be noted that the mesh can be generated and calculated only for the foundation portion, such as... Figure 5 As shown. The calculation period is 50 years, and a stable ground temperature field and moisture field are obtained.

[0146] Step S5: Divide the hydrothermal coupling model of the heat pipe roadbed into grids. Based on the initial values ​​and cooling capacity of the heat pipe during the simulation calculation of the heat pipe roadbed, calculate the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil in the short term after the heat pipe roadbed is filled.

[0147] In some embodiments, the construction of a heat pipe subgrade can be considered. The heat pipe subgrade model is divided into a grid, and the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil in the short term after the heat pipe subgrade is filled is calculated. The freezing front elevation difference is proposed to evaluate the impact of the high thermal conductivity of the heat pipe on the temperature of the underlying frozen soil.

[0148] As an example, this step may include the following steps:

[0149] The first step is to divide the hydrothermal coupling model of the heat pipe roadbed into grids. Based on the initial values ​​and cooling capacity of the heat pipe during the simulation calculation of the heat pipe roadbed, the influence of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil in the short term after the completion of the roadbed filling is calculated.

[0150] The second step is to evaluate the negative impact of the high thermal conductivity of the heat pipe by measuring the elevation difference of the freezing front. The elevation difference of the freezing front is the difference between the elevation of the freezing front at different positions on the left side of the heat pipe and the elevation of the lowest point of the freezing front.

[0151] For example, a grid can be generated for the heat pipe subgrade model to calculate the impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil in the short term after the subgrade is filled. The calculation period is from the completion of the subgrade filling to the start of heat pipe operation. The freezing front elevation difference is obtained from the calculation results and used as a basis for evaluating the impact of the high thermal conductivity of the heat pipe.

[0152] It should be noted that the overall model of the thermal radii roadbed can be meshed as follows: Figure 6 As shown in the figure. The calculated ground hydrothermal stability field was imported into the model as the initial values ​​for the water content and temperature of the foundation portion in the heat pipe subgrade. The initial temperature of the subgrade was calculated to be approximately 7°C higher than the natural surface temperature on the day of filling. The calculation started on July 1st and lasted from the start of subgrade filling until the heat pipe operation began. The freezing front elevation difference was proposed to evaluate the negative impact of the heat pipe's high thermal conductivity. The calculated temperature contour map is shown in the figure. Figure 7 As shown in the figure. The curve showing the change in elevation difference of the freezing front can be represented as follows. Figure 8 As shown.

[0153] Step S6: Change the roadbed filling time, the initial temperature of the roadbed fill material, and the thermal conductivity of the heat pipe, and calculate the influence of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil under different working conditions.

[0154] In some embodiments, the subgrade filling time, the initial temperature of the subgrade fill material, and the thermal conductivity of the heat pipe can be varied to calculate the impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil under different working conditions, and measures to reduce the negative impact of the high thermal conductivity of the heat pipe are proposed. During the calculation, only the values ​​of the calculated parameters are changed, while the values ​​of other parameters remain unchanged.

[0155] As an example, different filling times (June, July, August, and September), different initial filling temperatures (9℃, 12℃, and 15℃), and different thermal conductivity coefficients (30.5 [W / (m·K)], 36.5 [W / (m·K)], and 42.5 [W / (m·K)]) can be used to calculate the degree of influence of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil under the above different working conditions.

[0156] It should be noted that the roadbed filling time can be changed. The initial phase value is determined by the initial phase value, and the initial phase values ​​corresponding to different times can be shown in Table 5.

[0157] Table 5

[0158]

[0159] Figure 9 This is a curve showing the variation of the lowest point of the frozen front in different months. Figure 9 It can be seen that the freezing front dropped most severely when the roadbed filling was carried out in July, and the high thermal conductivity of the heat pipe had the greatest negative impact. Therefore, the subsequent calculations on the impact of different parameters (initial temperature of the roadbed filling material and thermal conductivity of the heat pipe) were all based on the roadbed filling condition in July.

[0160] When calculating the effect of different subgrade fill temperatures, subgrade fill temperatures of 4℃, 7℃, and 10℃ were used for calculations, while other parameters remained constant. The calculation results are as follows. Figure 10 As shown. By Figure 10 It can be seen that the elevation difference of the freezing front increases with the increase of the temperature of the roadbed fill material, that is, the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the lower frozen soil is positively correlated with the temperature of the fill material.

[0161] When calculating the effect of different heat pipe thermal conductivity values, three values ​​of 30.5 [W / (m·K)], 36.5 [W / (m·K)], and 42.5 [W / (m·K)] were used for the calculation, while the values ​​of other parameters remained unchanged. The calculation results are as follows. Figure 11 As shown in the figure, the elevation difference of the freezing front increases with the increase of the thermal conductivity of the heat pipe, that is, the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the lower frozen soil is positively correlated with the thermal conductivity.

[0162] This invention provides a calculation method for the negative impact of high thermal conductivity of heat pipes in the short term after roadbed filling. It proposes to evaluate the negative impact of high thermal conductivity materials in heat pipes by using the freezing front elevation difference. By changing different parameters, the degree of negative impact of high thermal conductivity of heat pipes on the underlying frozen soil is calculated, providing a basis for the construction of heat pipe roadbeds in permafrost areas. Specifically, heat pipe roadbeds in permafrost areas should avoid construction during the high-temperature period of July and August. During construction, the temperature of the roadbed filling material should be reduced as much as possible, and heat pipe materials with lower thermal conductivity should be selected without affecting the cooling effect of the heat pipes.

[0163] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A calculation method for the influence of high thermal conductivity of heat pipes on roadbed filling in the short term, characterized in that, Includes the following steps: Collect soil parameters in the area where the roadbed project is located, determine the thermal conductivity, heat capacity, soil density and latent heat of phase change, and determine the soil-water characteristic curve based on the soil parameters; Collect annual temperature variation data of the area where the roadbed project is located and fit it into a sinusoidal periodic function as the temperature fitting function; Collect wind speed variation data and calculate its average value as the regional average wind speed; Select the type of heat pipe to be calculated, and calculate the cooling capacity of the heat pipe based on the cooling capacity equation and the calculated regional average wind speed. Based on the collected roadbed cross-sectional dimensions, thermal conductivity, heat capacity, soil density, latent heat of phase change, soil-water characteristic curves, and temperature fitting functions, a water-thermal coupling model for the heat pipe roadbed is established. The model of the foundation is divided into grids, and the hydrothermal stability field of the foundation is calculated. The obtained hydrothermal stability field is used as the initial value for the simulation calculation of the heat pipe subgrade. The hydrothermal coupling model of the heat pipe roadbed was meshed. Based on the initial values ​​and cooling capacity of the heat pipe during the simulation calculation of the heat pipe roadbed, the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil was calculated in the short term after the heat pipe roadbed was filled. The negative impact was evaluated by the elevation difference of the freezing front, which is the elevation difference between the freezing front elevation at different positions on the left side of the heat pipe and the elevation of the lowest point of the freezing front. By changing the roadbed filling time, the initial temperature of the roadbed fill material and the thermal conductivity of the heat pipe, the influence of the high thermal conductivity of the heat pipe on the temperature field of the underlying frozen soil under different working conditions was calculated. Among them, the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the lower frozen soil is positively correlated with the temperature of the filler; the negative impact of the high thermal conductivity of the heat pipe on the temperature field of the lower frozen soil is positively correlated with the thermal conductivity coefficient.

2. The calculation method for the influence of high thermal conductivity of heat pipes on roadbed filling in the short term, as described in claim 1, is characterized in that... The process involves determining the thermal conductivity, heat capacity, soil density, and latent heat of phase change, and based on these soil parameters, determining the soil-water characteristic curve of the soil. Annual temperature variation data of the area where the roadbed project is located are collected and fitted to a sinusoidal periodic function as the temperature fitting function, including: The thermal conductivity, heat capacity, soil density, and latent heat of phase change were measured through sampling tests. By fitting the van Genuchten model, the soil-water characteristic curves were obtained, where the van Genuchten model equation is expressed as follows: in, Water content by volume; , and These are all fitted parameters. These are parameters related to the air intake value of the soil; This is a parameter related to the outflow rate in the soil and is related to the soil pore size; For pressure head; Soil parameters that are functions of residual water content are related to the overall symmetry of the soil-water characteristic curve; The temperature fitting function is: in, The temperature is calculated, and the unit is °C. The average annual temperature is expressed in °C. The amplitude; Time, in hours; This is the initial phase.

3. The calculation method for the influence of high thermal conductivity of heat pipes on roadbed filling in the short term, as described in claim 1, is characterized in that... The process of selecting the type of heat pipe to be calculated and calculating the cooling capacity of the heat pipe based on the cooling capacity equation and the calculated regional average wind speed includes: The heat transfer equation for the heat pipe is: in, Density of the heat pipe material; The heat capacity of the heat pipe; The thermal conductivity of the heat pipe axis; The radial thermal conductivity of the heat pipe; For cooling capacity; The equation for the cooling capacity of the heat pipe is: in, , These are the soil temperature in contact with the evaporation section and the atmospheric temperature, respectively. , These are the thermal resistances of the condensation section and the soil in contact with the evaporation section, respectively. in, The average radius of influence for heat transfer in the evaporation section. The outer radius of the heat transfer section in the evaporation section; denoted by , where is the thermal conductivity of the frozen soil in contact with the evaporation section; and z is the length of the evaporation section. in, This represents the heat dissipation area of ​​the condensation section; The effective heat transfer coefficient of the condensation section; in, The average wind speed in the region.

4. The calculation method for the influence of high thermal conductivity of heat pipes on roadbed filling in the short term, as described in claim 3, is characterized in that... The process involves establishing a hydrothermal coupling model for the roadbed based on the collected data on roadbed cross-sectional dimensions, thermal conductivity, heat capacity, soil density, latent heat of phase change, soil-water characteristic curves, and temperature fitting functions. This includes: The temperature field equation in the hydrothermal coupling equation is: in, This refers to the soil density. The thermal conductivity of the soil; Latent heat of phase transition; Ice content by volume; This is the volumetric heat capacity of water; The water diffusion coefficient; This refers to the volumetric content of unfrozen water. Hydraulic conductivity; in, Heat capacity of unfrozen soil; The heat capacity of frozen soil; The thermal conductivity of unfrozen soil; The thermal conductivity of frozen soil; The water field equation in the hydrothermal coupling equation is: in, The density of ice; The density of water; Ice content by volume; The water diffusion coefficient; This refers to the volumetric content of unfrozen water. Hydraulic conductivity; The solid-liquid ratio equation is: in, It is the solid-liquid ratio. and Relationships; This refers to the freezing temperature of the soil, expressed in °C. These are empirical parameters; Based on the hydrothermal coupling equation, a heat pipe roadbed model is established according to the roadbed cross-sectional dimensions of the project area.

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