CN106770439A - Rock-soil layer is layered Determination of conductive coefficients method - Google Patents

Abstract

The invention provides a rock-soil layer layered thermal conductivity test method for accurately obtaining the thermal physical property parameters of the rock-soil body and measuring the layered soil thermal conductivity without disturbing the formation. Drilling holes with a drilling rig, installing temperature measuring cables in the water inlet and outlet pipes of U-shaped buried pipes; laying a number of temperature measuring probes on the temperature measuring cables as measuring points; measuring the temperature of the water inlet and outlet of each measuring point through the temperature measuring probes and according to Based on the linear heat source theory, the average thermal conductivity of the strata below each measuring point is calculated by the slope method; and the thermal conductivity of each stratum is calculated accordingly. Accurately obtain the thermophysical parameters of the rock and soil without disturbing the strata, measure the thermal conductivity of each layer of the soil, understand the underground soil structure and groundwater flow, and understand the heat transfer capacity of the buried pipe heat exchanger. The design of the source heat pump system provides basic parameters to ensure long-term efficient operation of the system.

Description

Test method for layered thermal conductivity of rock and soil layers

technical field

The invention relates to a method for testing the layered thermal conductivity of rock and soil layers.

Background technique

The thermal physical parameters of rock and soil can be measured in the laboratory by drilling samples, but the collected samples have changed greatly from the actual conditions in the ground, including considerable differences in structure and moisture content, and the samples It also cannot reflect the overall condition of underground rocks and soils at a considerable depth, and the measured results are difficult to use in engineering practice.

The traditional thermal response testing technology can only monitor the temperature of the water inlet and outlet, and roughly estimate the heat transfer capacity of the entire formation. The actual geological situation of the stratum is relatively complex. There are as many as 10 rock and soil layers with different properties within 100m. How to know the heat transfer capacity of strata at different depths and find out the superior heat transfer layer plays an important role in the design of ground source heat pumps. .

At present, the existing domestic experimental testing equipment and testing methods mainly obtain the comprehensive and average thermal conductivity of underground soil through thermal response experiments. This method of testing and data analysis is affected by objective factors such as the environment to a certain extent, and cannot truly reflect the heat transfer conditions of different formations. There are few researches on layered temperature measurement technology at home and abroad. If the thermophysical parameters of rock and soil can be accurately obtained without disturbing the stratum, and the heat transfer capacity of the underground heat exchanger can be understood, it will provide a basis for the design of the ground source heat pump system. Basic parameters to ensure long-term efficient operation of the system.

Apply the system test idea to the actual engineering test to measure the thermal conductivity of stratified soil. Understand the underground soil structure and groundwater flow, so as to provide a scientific basis for the site selection of buried tube heat exchangers and the maximum utilization of shallow geothermal energy, and contribute to the promotion of ground source heat pump technology.

Soil thermophysical parameters include: soil thermal conductivity, volume specific heat capacity, and soil thermal resistance. Thermal conductivity plays a key role in the design of ground source heat pumps. When the thermal conductivity of the underground rock and soil deviates by 10%, the designed underground pipe length deviation is 4.5% to 5.8%. Deviations in borehole length will result in variations in the overall length of the borehole.

The design calculation of the buried tube heat exchanger is mainly that the heat or cold extracted by the circulating fluid in the tube from the underground soil must be within the range of the design requirements during the entire service life cycle of the buried tube heat exchanger. One requires the calculation of the total length of the borehole heat exchanger.

The pipe material of the buried pipe heat exchanger is made of PE pipe, and the temperature measuring cable is made of distributed temperature measuring cable. Compared with the traditional temperature measuring cable, it has the advantages of convenient wiring, high precision, not affected by the environment, and high cost performance.

Contents of the invention

Aiming at the above technical problems, the present invention provides a layered thermal conductivity test method for accurately obtaining the thermal physical parameters of rock and soil mass and measuring the thermal conductivity of layered soil without disturbing the formation.

The present invention adopts following technical scheme to realize:

The method for testing the layered thermal conductivity of rock and soil layers comprises the steps of:

(1) Drilling holes with a drilling rig, respectively installing temperature measuring cables in the water inlet and outlet pipelines of the U-shaped underground pipe; laying a number of temperature measuring probes on the temperature measuring cables as measuring points; The temperature measuring probes correspond to each other, and the formation is divided into different formations;

(2) The medium continues to flow in the buried pipe, and the temperature of the water inlet and outlet of each measuring point is measured by a temperature measuring probe; Measured by temperature probe;

(3) According to the linear heat source theory, the average thermal conductivity of the stratum below each measuring point is calculated by the slope method; and the thermal conductivity of each stratum is calculated accordingly.

The process of calculating the comprehensive thermal conductivity of rock and soil by the slope method in step 3 is as follows:

The borehole wall temperature of the linear heat source model is:

In the formula, Q is the constant heating power; T ₀ is the average original temperature of the rock and soil; ρ _s is the soil density; C _s is the specific heat of the soil; τ is the time; H is the depth of the borehole pipe; d _b is the borehole diameter; λ _s is the comprehensive thermal conductivity of rock and soil; is an exponential integral function;

Thermal resistance of rock and soil outside the borehole but

Among them, T _f is the average temperature of the circulating fluid, T _in is the water inlet temperature of the buried pipe, T _out is the water outlet temperature of the buried pipe; R _b is the heat transfer resistance in the borehole;

According to (1)(2), the average temperature of the circulating medium at time τ is derived:

Under the condition of constant heating power, formula (3) can be expressed as a linear equation of time logarithm:

T _f ＝K·ln(t)+b (4)

Among them, the slope of the linear fitting line of the average temperature of the water in and out of the buried pipe and the logarithm of time The intercept of the vertical axis of the fitted line In the formula, a is the thermal diffusivity,

From the slope of the linear fitting line, the comprehensive thermal conductivity of rock and soil can be obtained as:

The distance between the temperature measuring probes on the temperature measuring cable is 8-10 meters.

The number of temperature measuring probes on the temperature measuring cable is 11, and the formation is divided into 10 formations.

The present invention has the following advantages:

The present invention accurately obtains the thermophysical parameters of the rock and soil without disturbing the formation, measures the thermal conductivity of each layer of the soil, understands the underground soil structure and the flow of underground water, and understands the heat exchange capacity of the underground pipe heat exchanger. Provide basic parameters for the design of the ground source heat pump system to ensure long-term efficient operation of the system.

Description of drawings:

Fig. 1 is a schematic diagram of the method of the present invention.

Fig. 2 is the change curve of the average temperature T _f of the fluid in the tube and the test time τ obtained under the heating power state of the thermal response test of the present invention.

Fig. 3 is the logarithmic change curve of the average temperature time logarithm of the inlet and outlet water in the thermal response test of the present invention.

detailed description:

As shown in Figure 1, the drilling rig is used to drill holes, and temperature measuring cables are installed in the inlet and outlet pipes of the U-shaped buried pipes. The U-shaped buried pipes and temperature measuring cables are lowered into the boreholes and then backfilled.

The length of the temperature measurement cable is 100m, and a total of 11 temperature sensors are arranged at the 2m, 10m, 20m, 30m, 40m, 50m, 60m, 70m, 80m, 90m, and 100m. The corresponding temperature measurement cables 1 are A, B, C, There are 11 probes in D, E, F, G, H, I, J, and k, and the same temperature measurement cable 2 is A1, B1, C1, D1, E1, F1, G1, H1, I1, J1, and k1. The probe divides the formation into 10 formations of 2-10m, 10-20m, 20-30m, 30-40m, 40-50m, 50-60m, 60-70m, 70-80m, 80-90m, and 90-100m.

The buried pipe enters the water from the right side and flows out from the left side after exchanging heat with the soil, and then flows to the water inlet on the right side. This repeated cycle of heat exchange with the soil finally achieves the stability of the water temperature at the inlet and outlet of the heat exchanger.

The medium in the buried pipe heat exchanger flows continuously, and the temperature sensor can continuously monitor the medium temperature. For formation 1 on the right, the temperature monitored by A1 can be regarded as the water inlet temperature, and the temperature obtained by monitoring B1 can be regarded as Water outlet temperature, and so on. For stratum 2 on the right, the temperature monitored by B1 can be regarded as the water inlet temperature, and the temperature obtained by C1 monitoring can be regarded as the outlet temperature.... For the stratum on the right 10, the temperature monitored by J1 can be regarded as the water inlet temperature, and the temperature obtained by k1 monitoring can be regarded as the outlet temperature. For stratum 10 on the left, the temperature obtained by monitoring k can be regarded as the water inlet temperature, and the temperature obtained by monitoring J can be regarded as the outlet temperature. For stratum 9 on the left, the temperature obtained by monitoring J can be regarded as the water inlet temperature Temperature, the temperature obtained by monitoring I can be regarded as the temperature of the water inlet... For formation 1 on the left, the temperature obtained by monitoring B can be regarded as the temperature of the water inlet, and the temperature obtained by monitoring A can be regarded as the temperature of the water outlet temperature.

According to the linear heat source theory, the slope method is commonly used to calculate the comprehensive thermal conductivity of rock and soil:

The borehole wall temperature of the linear heat source model is:

In the formula, Q is the constant heating power (W); T ₀ is the average original temperature of rock and soil (°C); ρ _s is the soil density (kg/m ³ ); C _s is the specific heat of soil [J/(kg K) ]; τ is the time (s); H is the depth of the borehole buried pipe (m); d _b is the diameter of the borehole (m); λ _s is the comprehensive thermal conductivity of rock and soil [W/(m k)]; is an exponential integral function, when the time is long enough, that is hour, γ is Euler's constant, γ≈0.577216;

Thermal resistance of rock and soil outside the borehole but

Among them, T _f is the average temperature of the circulating fluid (°C), T _in is the water inlet temperature of the buried pipe (°C), T _out is the water outlet temperature of the buried pipe (°C); R _b is the heat transfer resistance in the borehole (m·k/W);

According to (1)(2), the average temperature of the circulating medium at time τ can be derived:

Under the condition of constant heating power, formula (3) can be expressed as a linear equation of time logarithm:

T _f ＝K·ln(t)+b (4)

Among them, t is time, the slope of the linear fitting line between the average temperature of the water entering and leaving the buried pipe and the logarithm of time The intercept of the vertical axis of the fitted line In the formula, a is the thermal diffusivity (m ² /s),

From the slope of the linear fitting line, the comprehensive thermal conductivity of rock and soil can be obtained as:

Calculation example of thermal conductivity coefficient by line heat source slope method: the change curve of the average temperature T _f of the fluid in the tube and the test time τ obtained under the heating power state of the 100m deep single U tube test hole is shown in Figure 2, and T _f ~ The relationship curve of ln(τ) is shown in Fig. 3, K=2.235 is obtained by straight line fitting, the average heating power Q=5.183kW, and the comprehensive thermal conductivity λ _s of the hole is finally calculated to be 1.85W/(m·K).

For the stratum on the right, the average thermal conductivity below the A1 measuring point is λ1, the average thermal conductivity below the B1 measuring point is λ2, the average thermal conductivity below the C1 measuring point is λ3..., the average thermal conductivity below the J1 measuring point The coefficient is λ10

The method of finding λ1: the temperature of the water inlet of A1 and the temperature of the water outlet of A are obtained according to the calculation method of thermal conductivity.

The method of finding λ2: the temperature of the water inlet of B1 and the temperature of the water outlet of B are obtained according to the calculation method of thermal conductivity.

The method of finding λ3: the temperature of the water inlet of C1 and the temperature of the water outlet of C are obtained according to the calculation method of thermal conductivity.

 …

The method of finding λ10: the temperature of the water inlet of J1 and the temperature of the water outlet of J are obtained according to the calculation method of thermal conductivity.

So the thermal conductivity of layer 1 on the right is:

Thermal conductivity of formation 2 on the right:

 …

Thermal conductivity of the formation 10 on the right: λ ₁₀ .

Among them, L _AB , L _BC , ......, L _JK are the pipe lengths of this section of buried pipe.

For the formation on the left, the average thermal conductivity below the J measuring point is λ10, the average thermal conductivity below the I measuring point is λ9, the average thermal conductivity below the H measuring point is λ8......, the average thermal conductivity below the A measuring point The coefficient is λ1

The method of finding λ10: the temperature of the water inlet of J1 and the temperature of the water outlet of J are obtained according to the calculation method of thermal conductivity.

The method of finding λ9: I1 water inlet temperature, I water outlet temperature, obtained according to the calculation method of thermal conductivity.

The method of finding λ8: the water inlet temperature of H1 and the water outlet temperature of H are obtained according to the calculation method of thermal conductivity.

 …

The method of finding λ1: the temperature of the water inlet of A1 and the temperature of the water outlet of A are obtained according to the calculation method of thermal conductivity.

So the thermal conductivity of layer 1 on the left is:

Thermal conductivity of formation 2 on the left:

 …

Thermal conductivity of formation 10 on the left: λ ₁₀ .

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also possible. It should be regarded as the protection scope of the present invention.

Claims (4)

1. The layered thermal conductivity test method of rock and soil layer is characterized in that: comprising steps: (1) Drilling holes with a drilling rig, respectively installing temperature measuring cables in the water inlet and outlet pipelines of the U-shaped underground pipe; laying a number of temperature measuring probes on the temperature measuring cables as measuring points; The temperature measuring probes correspond to each other, and the formation is divided into different formations; (2) The medium continues to flow in the buried pipe, and the temperature of the water inlet and outlet of each measuring point is measured by a temperature measuring probe; Measured by temperature probe; (3) According to the linear heat source theory, the average thermal conductivity of the stratum below each measuring point is calculated by the slope method; and the thermal conductivity of each stratum is calculated accordingly. 2. the rock-soil layer layered thermal conductivity testing method according to claim 1, is characterized in that: described step 3 slope method calculates rock-soil comprehensive thermal conductivity process as follows: The borehole wall temperature of the linear heat source model is: ${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&pi;\&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; 16</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; \&tau;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ In the formula, Q is the constant heating power; T ₀ is the average original temperature of the rock and soil; ρ _s is the soil density; C _s is the specific heat of the soil; τ is the time; H is the depth of the borehole pipe; d _b is the borehole diameter; λ _s is the comprehensive thermal conductivity of rock and soil; is an exponential integral function; Thermal resistance of rock and soil outside the borehole but ${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ Among them, T _f is the average temperature of the circulating fluid, T _in is the water inlet temperature of the buried pipe, T _out is the water outlet temperature of the buried pipe; R _b is the heat transfer resistance in the borehole; According to (1)(2), the average temperature of the circulating medium at time τ is derived: ${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&pi;\&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; 16</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; \&tau;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ Under the condition of constant heating power, formula (3) can be expressed as a linear equation of time logarithm: T _f ＝K·ln(t)+b (4) Among them, the slope of the linear fitting line of the average temperature of the water in and out of the buried pipe and the logarithm of time The intercept of the vertical axis of the fitted line In the formula, a is the thermal diffusivity, From the slope of the linear fitting line, the comprehensive thermal conductivity of rock and soil can be obtained as: 3. The method for testing thermal conductivity of rock and soil layer layers according to claim 1, characterized in that: the distance between the temperature measuring probes on the temperature measuring cable is 8-10 meters. 4. The method for testing the layered thermal conductivity of rock and soil layers according to claim 1, characterized in that: the number of temperature-measuring probes on the temperature-measuring cable is 11, and the strata are divided into 10 strata.