Device and method for measuring thermal characteristics of frozen soil based on thermal pulse method

Abstract

The invention discloses a frozen soil thermal characteristic measuring device and method based on a thermal pulse method, and the method comprises the steps: heating a cylindrical heating probe through a heater at a constant power, detecting the temperature of the cylindrical heating probe through a first temperature probe, and uploading the temperature to a cloud through a transmission unit; meanwhile, the data recorder displays the temperature data of the second temperature probe and the first temperature probe in real time; keeping the temperature of the cylindrical heating probe constant; a frozen soil sample is heated by the cylindrical heating probe, a temperature penetration curve of the frozen soil sample is obtained, and then the volume diffusivity and the volume thermal conductivity of the frozen soil sample are obtained. According to the method, the highest space temperature can be effectively kept below the freezing point, so that the overall thermal performance of the quartz sand and the ice content is estimated, and the accuracy of estimating the overall thermal performance of the frozen soil sample in the cold region is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of frozen soil freeze-thaw, and relates to a device and method for measuring thermal characteristics of frozen soil based on a heat pulse method. Background Art

[0002] Freeze-thaw processes are important for quantifying the soil surface energy balance and its interaction with hydrological processes. Significant progress has been made in the past few decades in developing methods to measure soil ice content and improving the accuracy of measurements. Thermal resistance temperature probes, differential scanning calorimetry, TDR, heat pulse methods, and nuclear magnetic resonance have enabled more accurate measurements of soil ice content in frozen soils. However, there are still some challenges with the above methods, such as the melting and refreezing of ice transfers a large part of the energy to phase changes rather than heat conduction; although some researchers have adopted adjustments to address these issues, such as assuming minimum ice melting, integrating latent heat flux into calculations, or using numerical models. However, these adjustments may lead to biased or inaccurate estimates of thermal properties, especially in partially frozen soils.

[0003] Characterization of soil freezing and thawing processes is still hampered by the lack of methods to measure soil thermal properties under freezing or thawing conditions. When using existing heat pulse-based methods, heat is released in a relatively short time or / and with high heat fluxes in order to ensure the accuracy of the detection signal. The temperature increase on the probe surface may exceed the freezing temperature, thus causing thawing of frozen soil and inaccurately capturing the thermal properties of the soil in the temperature range of -5 degrees Celsius and 0 degrees Celsius. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the temperature rise of the probe surface of the heat pulse method in the prior art may exceed the freezing point, thereby causing the frozen soil to melt, and the soil thermal properties cannot be accurately obtained within the temperature range of -5 degrees Celsius and 0 degrees Celsius, and to provide a frozen soil thermal properties measurement device and method based on the heat pulse method.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A device for measuring thermal characteristics of frozen soil based on a heat pulse method, comprising: a test assembly, a variable voltage control device and a data processing device;

[0007] The test assembly includes a cylindrical heating probe, a first temperature probe and a second temperature probe; the cylindrical heating probe, the first temperature probe and the second temperature probe are all arranged in the frozen soil sample to be measured; the variable voltage control device connects the cylindrical heating probe and the first temperature probe to provide energy for the cylindrical heating probe, and the first temperature probe records the surface temperature of the heating probe; the data processing device is connected to the second temperature probe; the second temperature probe measures the temperature change of the frozen soil.

[0008] A further improvement of the present invention is:

[0009] Furthermore, the first temperature probe, the second temperature probe and the cylindrical heating probe are placed in parallel; the first temperature probe, the second temperature probe and the cylindrical heating probe are arranged horizontally or vertically in the frozen soil sample to be measured.

[0010] Furthermore, the data processing device includes a data recorder, a processing unit, a transmission unit and a cloud; the processing unit is connected to the cloud; the cloud is connected to the transmission unit, and the data recorder and the transmission unit are electrically connected to the first temperature probe and the second temperature probe; the transmission unit sends the collected data of the first temperature probe and the second temperature probe to the cloud for storage; the processing unit calls the stored data for analysis, and then stores the processed data again in the cloud; the data recorder displays the temperature data of the first temperature probe and the second temperature probe in real time.

[0011] Furthermore, the variable voltage control device includes a heater and a temperature controller; the heater is connected to the cylindrical heating probe via the temperature controller.

[0012] A method for measuring thermal characteristics of frozen soil based on a heat pulse method, using a device for measuring thermal characteristics of frozen soil based on a heat pulse method, the measuring method comprising:

[0013] The cylindrical heating probe is heated at a constant temperature by the heater, the first temperature probe detects the temperature of the cylindrical heating probe, the second temperature probe detects the temperature of the frozen soil, and the temperature data are uploaded to the cloud through the transmission unit, and the data logger displays the temperature data of the cylindrical heating probe and the frozen soil in real time;

[0014] When the cylindrical heating probe reaches the target temperature, the temperature of the cylindrical heating probe is kept constant through the temperature controller;

[0015] When the frozen soil sample is heated by the cylindrical heating probe, the temperature penetration curve of the frozen soil sample and the energy received by the frozen soil sample are obtained, and then the thermal diffusion coefficient of the frozen soil sample is obtained;

[0016] Based on the heating time of the cylindrical heating probe and the heat output during the heating time, a total output heat of the cylindrical heating probe is obtained;

[0017] Obtain the volumetric heat capacity based on the energy received by the frozen soil sample, the total energy delivered by the cylindrical heating probe, and the volumetric diffusivity of the frozen soil sample;

[0018] Obtain the thermal conductivity based on the thermal diffusivity and the volumetric heat capacity.

[0019] Further, when the cylindrical heating probe controls the energy output power of the heater through a temperature controller to keep the temperature of the cylindrical heating probe constant, specifically: when the temperature reading of the cylindrical heating probe drops to the preset lower temperature limit, turn on the heater power supply and heat with short pulses of low energy output power. After the heating period ends, turn off the heater power supply to keep the temperature of the cylindrical heating probe between the preset upper and lower temperature limits; continuously repeat this step until the measurement of the frozen soil sample is completed.

[0020] Further, obtain the temperature penetration curve of the frozen soil sample, specifically:

[0021] The one-dimensional transient heat conduction process in the cylindrical coordinate system is:

[0022]

[0023] where T is the temperature measured in the soil of the second temperature probe; r is the radial distance of the second temperature probe from the cylindrical heating probe; t is the time for measuring the temperature penetration curve of the frozen soil; the effective radius r e is the radial distance between the second temperature probe and the first temperature probe; r e The minimum value of is equal to the sum of the radii of the first temperature probe and the second temperature probe; D is the volumetric thermal diffusivity;

[0024] When heating the frozen soil with a constant temperature heat source, the target temperature T1 of the frozen soil is higher than the initial temperature T0 but lower than the freezing point;

[0025] At the same time, satisfying the initial condition (T(r,0) = T0 (T0 < 0)) and the boundary condition (T(r e ,t) = T1 (T0 < T1 < 0)), the solution in the Laplace space is as follows:

[0026]

[0027] where K0 represents the modified Bessel function of the second kind of order zero,

[0028]

[0029] where s is the representation of time t in the Laplace space after T(r,t) undergoes the Laplace transform;

[0030] Through the numerical inverse Laplace transform, obtain the spatial distribution T(r,t) of the temperature in the frozen soil at any time;

[0031] The root mean square error (RMSE) is used to evaluate the temperature penetration curve fitting, specifically:

[0032]

[0033] Where, the subscript i is the number of measured temperature responses; N is the total number of measured temperatures; T and represent the measured temperature and predicted temperature respectively.

[0034] Furthermore, the energy received by the frozen soil samples is:

[0035]

[0036] The subscript i represents the i-th discrete spatial interval after the measurement space is radially discretized into M spatial intervals, and the spatial range is from r = r e The radial distance to T = T0;

[0037] Based on the heating time of the cylindrical heating probe and the heat output during the heating time, the total output heat of the cylindrical heating probe is calculated as follows:

[0038] The total output energy Q2(t) of the cylindrical heating probe is measured by the temperature controller; the heating cycle is a heating cycle with a given power P j and heating cycle tp j The total delivered energy is the sum of the delivered energy in each cycle, as shown below:

[0039]

[0040] Where L is the length of the cylindrical heating probe.

[0041] Furthermore, the energy received by the frozen soil sample, the total delivered energy of the cylindrical heating probe and the volume diffusivity of the frozen soil sample are used to obtain the volume heat capacity, which is specifically:

[0042] By volume heat capacity C b =ρ b c b Available,

[0043]

[0044] Among them, ρ b is the density of the medium; c b is the specific heat capacity of the medium;

[0045] Based on the thermal diffusivity and volumetric heat capacity, the thermal conductivity is obtained as follows:

[0046] The bulk thermal conductivity of soil is:

[0047] λ b =DC b .

[0048] Furthermore, when the frozen soil is mixed with other substances, the total heat capacity of the quartz sand sample is

[0049] C=n i c i +n g c g +n s c s

[0050] Where n represents the volume fraction of frozen soil components, c i represents the specific heat capacity of ice; c g represents the specific heat capacity of air; c s represents the specific heat capacity of a solid;

[0051] In saturated frozen soil, the gaseous term is omitted, and the volume fractions of each are obtained based on the total heat capacity C and the specific heat capacities of solids and ice.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The present invention heats the cylindrical heating probe with a heater at a constant power, the first temperature probe detects the temperature of the cylindrical heating probe, and uploads it to the cloud through a transmission unit, while the data recorder displays the temperature data of the second temperature probe and the first temperature probe in real time; the temperature of the cylindrical heating probe is kept constant; the frozen soil sample is heated by the cylindrical heating probe, the temperature penetration curve of the frozen soil sample is obtained, and then the volume diffusivity and volume thermal conductivity of the frozen soil sample are obtained. The present invention can effectively keep the highest space temperature below the freezing point, thereby estimating the overall thermal performance of quartz sand and ice content, and improving the accuracy of estimating the overall thermal performance of the frozen soil sample in cold areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 It is a schematic diagram of the topological structure of the device for measuring thermal characteristics of frozen soil based on the heat pulse method of the present invention;

[0056] Figure 2 It is a schematic flow chart of the method for measuring thermal characteristics of frozen soil based on the heat pulse method of the present invention;

[0057] Figure 3 Schematic diagram of the constant temperature control process using a multi-pulse heating strategy;

[0058] Figure 4 Example plot of spatial temperature distribution along the radial direction at different times t1, t2, and t3 estimated by the ILS model. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0060] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0062] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0063] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0064] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0065] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0066] See also Figure 1 , the present invention discloses a frozen soil thermal characteristic measuring device based on a heat pulse method, comprising: a test component, a variable voltage control device and a data processing device;

[0067] The test assembly includes a cylindrical heating probe, a first temperature probe and a second temperature probe; the cylindrical heating probe, the first temperature probe and the second temperature probe are all arranged in the frozen soil sample to be measured; the variable voltage control device connects the cylindrical heating probe and the first temperature probe to provide energy for the cylindrical heating probe, and the first temperature probe records the surface temperature of the heating probe; the data processing device is connected to the second temperature probe; and the second temperature probe measures the temperature change of the frozen soil.

[0068] The first temperature probe, the second temperature probe and the cylindrical heating probe are placed in parallel; the first temperature probe, the second temperature probe and the cylindrical heating probe are arranged horizontally or vertically in the frozen soil sample to be measured.

[0069] The data processing device includes a data recorder, a processing unit, a transmission unit and a cloud; the processing unit is connected to the cloud; the cloud is connected to the transmission unit, and the data recorder and the transmission unit are both electrically connected to a first temperature probe and a second temperature probe; the transmission unit sends the collected data of the first temperature probe and the second temperature probe to the cloud for storage; the processing unit calls the stored data for analysis, and then stores the processed data again in the cloud; the data recorder displays the temperature data of the first temperature probe and the second temperature probe in real time.

[0070] The variable voltage control device comprises a heater and a temperature controller; the heater is connected to the cylindrical heating probe through the temperature controller.

[0071] See also Figure 2 The present invention discloses a method for measuring thermal characteristics of frozen soil based on a thermal pulse method, comprising:

[0072] S101. Constantly heat the cylindrical heating probe using a heater. The first temperature probe detects the temperature of the cylindrical heating probe, and the second temperature probe detects the temperature of the frozen soil, which is then uploaded to the cloud via a transmission unit. Meanwhile, the data logger displays the temperature data of the cylindrical heating probe and the frozen soil in real time.

[0073] S102. When the cylindrical heating probe reaches the target temperature, maintain the temperature of the cylindrical heating probe constant through a temperature controller.

[0074] When the temperature reading of the cylindrical heating probe drops to the preset lower temperature limit, turn on the heater power supply and heat it using short pulses with a low energy output power. After the heating period ends, turn off the heater power supply to keep the temperature of the cylindrical heating probe between the preset upper and lower temperature limits. Continuously repeat this step until the measurement of the frozen soil sample is completed.

[0075] S103. Under the heating of the cylindrical heating probe, obtain the temperature penetration curve of the frozen soil sample and the energy received by the frozen soil sample, and then obtain the thermal diffusivity of the frozen soil sample.

[0076] Obtain the temperature penetration curve of the frozen soil sample specifically as follows:

[0077] The one-dimensional transient heat conduction process in the cylindrical coordinate system is:

[0078]

[0079] where T is the temperature measured in the soil by the second temperature probe; r is the radial distance from the second temperature probe to the cylindrical heating probe; t is the time for measuring the temperature penetration curve of the frozen soil; the effective radius r e is the radial distance between the second temperature probe and the first temperature probe; r e The minimum value of is equal to the sum of the radii of the first temperature probe and the second temperature probe; D is the volumetric thermal diffusivity;

[0080] When heating the frozen soil using a constant temperature heat source, the target temperature T1 of the frozen soil is higher than the initial temperature T0 but lower than the freezing point;

[0081] Meanwhile, satisfying the initial condition (T(r, 0) = T0 (T0 < 0)) and the boundary condition (T(r e , t) = T1 (T0 < T1 < 0)), the solution in the Laplace space is as follows:

[0082]

[0083] where K0 represents the modified Bessel function of the second kind of order zero,

[0084]

[0085] Where s is the representation of time t in Laplace space after T(r,t) is Laplace transformed;

[0086] Through the Laplace numerical inverse transformation, the spatial distribution of temperature at any time in frozen soil T(r,t) is obtained;

[0087] The root mean square error (RMSE) is used to evaluate the temperature penetration curve fitting, specifically:

[0088]

[0089] Where, the subscript i is the number of measured temperature responses; N is the total number of measured temperatures; T and represent the measured temperature and predicted temperature respectively.

[0090] The energy received by the frozen soil sample is:

[0091]

[0092] The subscript i represents the i-th discrete spatial interval after the measurement space is radially discretized into M spatial intervals, and the spatial range is from r = r e The radial distance to T = T0;

[0093] S104, obtaining a total output heat of the cylindrical heating probe based on the heating time of the cylindrical heating probe and the heat output during the heating time;

[0094] The total output energy Q2(t) of the cylindrical heating probe is measured by the temperature controller; the heating cycle is a heating cycle with a given power P j and heating cycle tp j The total delivered energy is the sum of the delivered energy in each cycle, as shown below:

[0095]

[0096] Where L is the length of the cylindrical heating probe.

[0097] S105, obtaining volume heat capacity based on the energy received by the frozen soil sample, the total delivered energy of the cylindrical heating probe, and the volume diffusivity of the frozen soil sample;

[0098] By volume heat capacity C b =ρ b c b Available,

[0099]

[0100] Among them, ρ b is the density of the medium; c bis the specific heat capacity of the medium;

[0101] S106, obtaining thermal conductivity based on thermal diffusivity and volumetric heat capacity.

[0102] The bulk thermal conductivity of soil is:

[0103] λ b =DC b .

[0104] When the frozen soil is mixed with other substances, the total heat capacity of the quartz sand sample is

[0105] C=n i c i +n g c g +n s c s

[0106] ρ=n i ρ i +n g ρ g +n s ρ s

[0107] Where n represents the volume fraction of frozen soil components, c i represents the specific heat capacity of ice; c g represents the specific heat capacity of air; c s represents the specific heat capacity of the solid; ρ i represents the volume density of ice; ρ g represents the volume density of air; ρ s It represents the bulk density of a solid;

[0108] In saturated frozen soil, the gaseous term is omitted, and the volume fractions of each are obtained based on the total heat capacity C and the specific heat capacities of solids and ice.

[0109] λ g The thermal conductivity of dry quartz sand is shown below:

[0110] λ b1 =7.5 1-Φ 0.51 Φ [(1-λ g )Sr+λ g ] 0.78Φ

[0111] Where Φ is the porosity, Sr is the residual water saturation, 7.5 is the thermal conductivity of quartz particles, and 0.51 is the thermal conductivity of water; λ g is the volume thermal conductivity of air;

[0112] When the pore space of quartz sand is filled with additional components, its content is estimated by the following formula:

[0113]

[0114] Among them, n qtz +nx=1;λ qtz , n x and n qtz , x represent the thermal conductivity and volume fraction of quartz sand and additional components, respectively.

[0115] Example:

[0116] The present invention uses ice, quartz sand and a mixture as a frozen soil sample; the quartz sand used has a particle size of 50 mesh, is composed of more than 99.8% Sio2, and has a porosity of Φ of 0.37. The experiment was conducted using a consistent setup: (1) a cylindrical sample with a diameter of 21 cm and a height of 14 cm was prepared and stored in a refrigerator throughout the experiment to maintain a stable surface and ambient temperature; (2) before the freezing process, a cylindrical heating probe and a first temperature probe and a second temperature probe were installed in the sample to avoid air entrapment at the probe-sample interface during the drilling process; (3) a heating probe with a diameter of 6 mm, a length of 10 cm, and an output power of 150 W was used; (4) the temperature of the heating source was manually adjusted by a voltage regulator, such as Figure 1 (5) Unless otherwise stated, the study assumes that the physical properties of the sample components remain unchanged regardless of temperature. All samples were pre-treated (frozen / thawed) for more than 24 hours before measurement.

[0117] The cylindrical heating probe and sample temperatures were continuously tracked using the first and second temperature probes. The vertical position of the first temperature probe tip was close to the geometric center of the cylindrical heating probe; the temperature measurements of the first and second temperature probes were recorded and stored using a data logger. The temperature readings were taken at 1 second intervals and used to control the energy delivery of the heater. The temperature time series data collected by the temperature probes were analyzed to estimate the soil thermal properties assuming a constant surface temperature of the heat source. Both the first and second temperature probes were calibrated using ice water and boiling water.

[0118] The voltage regulator is used to adjust the energy delivery intensity to facilitate the temperature control of the heat source. Specifically, the constant temperature of the heat source is achieved through the following steps:

[0119] Based on the heater heating the cylindrical heating probe with constant power, the first temperature probe detects the temperature of the cylindrical heating probe, the second temperature probe detects the temperature of the frozen soil, and uploads them to the cloud through the transmission unit, and the data logger displays the temperature data of the cylindrical heating probe and the frozen soil in real time;

[0120] When the cylindrical heating probe reaches the target temperature, the power supply of the heater is turned off, and the energy delivery rate of the heater is reduced through the voltage regulator to keep the temperature of the cylindrical heating probe constant;

[0121] When the temperature reading of the cylindrical heating probe drops to a pre-defined lower temperature limit, turn on the heater power and use short pulses with a low energy transfer rate for heating. After the heating period, turn off the heater power to maintain the surface temperature of the cylindrical heating probe between the preset upper and lower temperature limits. Repeat this step until the frozen soil sample is completely thawed.

[0122] When the frozen soil sample is heated by the cylindrical heating probe, the temperature penetration curve of the frozen soil sample and the energy received by the frozen soil sample are obtained, and then the thermal diffusion coefficient of the frozen soil sample is obtained;

[0123] Based on the constant temperature time and the power consumed during the heating time of the cylindrical heating probe, the total delivered energy of the cylindrical heating probe is obtained;

[0124] The volume heat capacity is obtained based on the energy received by the frozen soil sample, the total transmitted energy of the cylindrical heating probe and the volume diffusivity of the frozen soil sample; the thermal conductivity is obtained based on the thermal diffusivity and the volume heat capacity.

[0125] In the present invention, estimating the thermal properties of frozen soil depends on the description of heat transfer processes, which are mainly controlled by heat conduction in a static mixture of solid, water and gas phases. The model used to describe conductive heat transfer assumes that: (1) heat conduction is the only mechanism driving heat transfer in frozen soil; and (2) the physical properties of frozen soil are isotropic and uniform, that is, there is no spatial and temporal property variation. Therefore, when the thermal properties of soil change significantly during freezing and thawing, the model cannot estimate transient temperature changes.

[0126] The one-dimensional transient heat conduction process in the cylindrical coordinate system is:

[0127]

[0128] Where T is the temperature measured in the soil by the second temperature probe; r is the radial distance between the second temperature probe and the cylindrical heating probe; t is the time to measure the frozen soil temperature penetration curve; the effective radius r e is the radial distance between the second temperature probe and the first temperature probe; r e The minimum value of is equal to the sum of the radii of the first temperature probe and the second temperature probe; D is the volume thermal diffusivity;

[0129] When thawing frozen soil by a constant heat source, the target temperature T1 of the frozen soil is higher than the initial temperature T0, but lower than the freezing point;

[0130] Satisfying both the initial condition (T(r, 0) = T0 (T0 < 0)) and the boundary condition (T(r e , t) = T1 (T0 < T1 < 0)), the solution in the Laplace space is as follows:

[0131]

[0132] where K0 represents the modified Bessel function of the second kind of order zero,

[0133]

[0134] where s is the representation of time t in the Laplace space after the Laplace transform of T(r, t);

[0135] The root mean square error RMSE is used to evaluate the fitting of the temperature penetration curve, specifically:

[0136]

[0137] where the subscript i is the sequence number of the measured temperature response; N is the total number of measured temperatures; T and represent the measured temperature and the predicted temperature, respectively.

[0138] Given specific r, r e and t, fitting the temperature penetration curve to the field or experimental temperature to obtain the volume diffusivity The spatial temperature range can be easily plotted as a function of the radial distance.

[0139] The energy received by the frozen soil sample, specifically:

[0140]

[0141] where the subscript i represents the i-th discrete spatial interval after the radial discretization of the measurement space into M spatial intervals, and the spatial range is from r = r e to the radial distance at T = T0;

[0142] Based on the power consumed by the constant temperature time and the heating time of the cylindrical heating probe, the total delivered energy of the cylindrical heating probe is obtained, specifically:

[0143] See Figure 3 and Figure 4 ; the heating period consists of multiple pulsed heating intervals with a given power P j and a heating period tp j Therefore, the total delivered energy is the sum of the energy delivered in each period, as follows:

[0144]

[0145] Where L is the length of the cylindrical heating probe.

[0146] The energy received by the frozen soil sample, the total delivered energy of the cylindrical heating probe and the volume diffusivity of the frozen soil sample are used to obtain the volume heat capacity, which is:

[0147] By volume heat capacity C b =ρ b c b Available,

[0148]

[0149] Among them, ρ b is the density of the medium; c b is the specific heat capacity of the medium;

[0150] The bulk thermal conductivity of soil is:

[0151] λ b =DC b (8)

[0152] When frozen soil is mixed with other substances, the thermal properties of the quartz sand sample are

[0153] ρ=n i ρ i +n g ρ g +n s ρ s (9)

[0154] C=n i c i +n g c g +n s c s (10)

[0155] Where n represents the volume fraction of frozen soil components, ρ i represents the volume density of ice; ρ g represents the volume density of air; ρ s Represents the volume density of the solid; c i represents the specific heat capacity of ice; c g represents the specific heat capacity of air; c s represents the specific heat capacity of a solid;

[0156] The thermal conductivity of dry quartz sand is shown below:

[0157] λ b1 =7.5 1-Φ 0.51 Φ [(1-λ g )Sr+λ g ]0.78Φ (11)

[0158] Where Φ is the porosity, Sr is the residual water saturation, 7.5 is the thermal conductivity of quartz particles, and 0.51 is the thermal conductivity of water; λ g is the volume thermal conductivity of air;

[0159] When the pore space of quartz sand is filled with additional components, its content is estimated by the following formula:

[0160]

[0161] Among them, n qtz +nx=1;λ qtz , n x and n qtz , x represent the thermal conductivity and volume fraction of quartz sand and additional components, respectively.

[0162] The present invention can effectively minimize the melting process near the freezing point (-5 to 0 degrees Celsius) by keeping the highest domain temperature, i.e., the temperature of the cylindrical heating probe, below the freezing point. In colder frozen soils (temperatures less than -5 degrees Celsius), the melting process can be avoided by setting the maximum temperature far below the freezing point. Therefore, the sensitivity of the input variables in the proposed model was analyzed using the baseline case parameters, as shown in Table 1.

[0163] Table 1 Base case parameters for sensitivity analysis

[0164]

[0165] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A device for measuring thermal characteristics of frozen soil based on the heat pulse method, characterized in that: It includes: a test assembly, a variable voltage control device and a data processing device; The test assembly includes a cylindrical heating probe, a first temperature probe, and a second temperature probe; The cylindrical heating probe, the first temperature probe and the second temperature probe are all arranged in the frozen soil sample to be measured; the variable voltage control device is connected to the cylindrical heating probe and the first temperature probe to provide energy for the cylindrical heating probe, and the first temperature probe records the surface temperature of the heating probe; the data processing device is connected to the second temperature probe; and the second temperature probe measures the temperature change of the frozen soil.

2. The frozen soil thermal characteristics measuring device based on the heat pulse method according to claim 1 is characterized in that: The first temperature probe, the second temperature probe and the cylindrical heating probe are placed in parallel; the first temperature probe, the second temperature probe and the cylindrical heating probe are arranged horizontally or vertically in the frozen soil sample to be measured.

3. The frozen soil thermal characteristics measuring device based on the heat pulse method according to claim 2 is characterized in that: The data processing device includes a data recorder, a processing unit, a transmission unit and a cloud; the processing unit is connected to the cloud; the cloud is connected to the transmission unit, and the data recorder and the transmission unit are both electrically connected to a first temperature probe and a second temperature probe; the transmission unit sends the collected data of the first temperature probe and the second temperature probe to the cloud for storage; the processing unit calls the stored data for analysis, and then stores the processed data again in the cloud; the data recorder displays the temperature data of the first temperature probe and the second temperature probe in real time.

4. The frozen soil thermal characteristics measuring device based on the heat pulse method according to claim 3 is characterized in that: The variable voltage control device comprises a heater and a temperature controller; the heater is connected to a cylindrical heating probe via the temperature controller.

5. A method for measuring thermal characteristics of frozen soil based on a heat pulse method, characterized in that: Using the frozen soil thermal property measurement device based on the heat pulse method as claimed in claim 4, the measurement method includes: The cylindrical heating probe is heated at a constant temperature by the heater, the first temperature probe detects the temperature of the cylindrical heating probe, the second temperature probe detects the temperature of the frozen soil, and the temperature data are uploaded to the cloud through the transmission unit, and the data logger displays the temperature data of the cylindrical heating probe and the frozen soil in real time; When the cylindrical heating probe reaches the target temperature, the temperature of the cylindrical heating probe is kept constant through the temperature controller; When the frozen soil sample is heated by the cylindrical heating probe, the temperature penetration curve of the frozen soil sample and the energy received by the frozen soil sample are obtained, and then the thermal diffusion coefficient of the frozen soil sample is obtained; Based on the heating time of the cylindrical heating probe and the heat output during the heating time, a total output heat of the cylindrical heating probe is obtained; The volumetric heat capacity is obtained based on the energy received by the frozen soil sample, the total delivered energy of the cylindrical heating probe, and the volume diffusivity of the frozen soil sample; Based on the thermal diffusivity and volumetric heat capacity, the thermal conductivity is obtained.

6. The method for measuring thermal characteristics of frozen soil based on the heat pulse method according to claim 5, characterized in that: The cylindrical heating probe controls the energy output power of the heater through the temperature controller to keep the temperature of the cylindrical heating probe constant. Specifically, when the temperature reading of the cylindrical heating probe drops to a preset lower temperature limit, the heater power is turned on and short pulses of low energy output power are used for heating. After the heating period, the heater power is turned off to maintain the temperature of the cylindrical heating probe between the preset upper and lower temperature limits. This step is repeated until the measurement of the frozen soil sample is completed.

7. The method for measuring thermal characteristics of frozen soil based on the heat pulse method according to claim 6, characterized in that: The temperature penetration curve of the frozen soil sample is obtained as follows: The one-dimensional transient heat conduction process in the cylindrical coordinate system is: Where T is the temperature measured in the soil by the second temperature probe; r is the radial distance between the second temperature probe and the cylindrical heating probe; t is the time to measure the frozen soil temperature penetration curve; the effective radius r e is the radial distance between the second temperature probe and the first temperature probe; r e The minimum value of is equal to the sum of the radii of the first temperature probe and the second temperature probe; D is the volume thermal diffusivity; When the frozen soil is heated by a constant temperature heat source, the target temperature T1 of the frozen soil is higher than the initial temperature T0, but lower than the freezing point; At the same time, the initial condition (T(r, 0) = T0 (T0 < 0)) and the boundary condition (T(r e , t) = T1 (T0 < T1 < 0)), the solution in Laplace space is as follows: Where K0 represents the second-kind zero-order modified Bessel function, Where s is the representation of time t in Laplace space after T(r, t) is Laplace transformed; Through the Laplace numerical inverse transformation, the spatial distribution of temperature at any time in frozen soil is obtained T(r, t); The root mean square error (RMSE) is used to evaluate the temperature penetration curve fitting, specifically: Where, the subscript i is the number of measured temperature responses; N is the total number of measured temperatures; T and represent the measured temperature and predicted temperature respectively.

8. The method for measuring thermal characteristics of frozen soil based on the heat pulse method according to claim 7, characterized in that: The energy received by the frozen soil sample is specifically: The subscript i represents the i-th discrete spatial interval after the measurement space is radially discretized into M spatial intervals, and the spatial range is from r = r e The radial distance to T = T0; Based on the heating time of the cylindrical heating probe and the heat output during the heating time, the total output heat of the cylindrical heating probe is calculated as follows: The total output energy Q2(t) of the cylindrical heating probe is measured by the temperature controller; the heating cycle is a heating cycle with a given power P j and heating cycle tp j The total delivered energy is the sum of the delivered energy in each cycle, as shown below: Where L is the length of the cylindrical heating probe.

9. The method for measuring thermal characteristics of frozen soil based on the heat pulse method according to claim 8, characterized in that: The energy received by the frozen soil sample, the total delivered energy of the cylindrical heating probe and the volume diffusivity of the frozen soil sample are used to obtain the volume heat capacity, specifically: By volume heat capacity C b =ρ b c b Available, Among them, ρ b is the density of the medium; c b is the specific heat capacity of the medium; Based on the thermal diffusivity and volumetric heat capacity, the thermal conductivity is obtained as follows: The bulk thermal conductivity of soil is: λ b =DC b 。 10. The method for measuring thermal characteristics of frozen soil based on the heat pulse method according to claim 9, characterized in that: When the frozen soil is mixed with other substances, the total heat capacity of the quartz sand sample is C=n i c i +n g c g +n s c s Where n represents the volume fraction of frozen soil components, c i represents the specific heat capacity of ice; c g represents the specific heat capacity of air; c s represents the specific heat capacity of a solid; In saturated frozen soil, the gaseous term is omitted, and the volume fractions of each are obtained based on the total heat capacity C and the specific heat capacities of solids and ice.

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