Thermal pulse probe for accurately measuring condensed water amount of biological crust soil

Abstract

The utility model discloses a thermal pulse probe for accurately measuring the condensed water amount of biological crust soil, and belongs to the field of soil measuring equipment. The thermal pulse probe comprises a probe handle, a heating needle and a temperature sensing needle, wherein the heating needle and the temperature sensing needle are vertically fixed on the probe handle; the number of the heating needles is one, the number of the temperature sensing needles is four, the four temperature sensing needles are arranged in a rectangle shape, and the heating needles are located in the center of the rectangle. A thermocouple and a heating resistance wire are arranged in the heating needle, and the heating resistance wire is externally connected with a wire; a thermocouple is arranged in the temperature sensing needle and is externally connected with a thermocouple extension wire; and the heating needle and the temperature sensing needle are filled with a high-thermal-conductivity material for potting. After the heating needle is heated, the temperature sensing needle measures the heat capacity of the soil by sensing heat pulses, and the change of the biological crust condensed water is obtained according to the relationship between the heat capacity and the water content. The device is high in sensitivity, small in soil disturbance and capable of accurately positioning and monitoring the biological crust soil condensation water amount for a long time.

Description

Technical Field

[0001] The utility model belongs to the field of soil measuring equipment, and in particular relates to a thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil. Background Art

[0002] Land degradation in arid and semi-arid regions is a major issue affecting regional development. However, in degraded, exposed surfaces in desert regions, biocrusts, formed by the interaction of microorganisms such as mosses, lichens, algae, bacteria, and fungi with surface soil particles, develop extensively. These biocrusts rapidly fill degraded patches and profoundly impact the physical, chemical, and biological processes of the soil. Condensation, the basis for biocrusts to maintain their functional activity during droughts, can alleviate drought stress on plants to a certain extent. Measuring the amount of condensation in biocrusts can further study soil water cycling and reveal water balance in desert regions.

[0003] Common methods for measuring condensation in biocrust soil include the gravimetric method and the flannel method. The gravimetric method measures the difference in mass change between a soil sample in the evening and the next morning to determine the daily condensation level. The flannel method, on the other hand, involves placing a dry flannel cloth over a defined area tightly against the biocrust surface, creating a condensation surface. The condensation level is then estimated based on the mass or volume of the condensation collected. While these methods can measure condensation in biocrusts to a certain extent, they are time-consuming and labor-intensive, and cannot achieve continuous monitoring over an extended period of time. Utility Model Content

[0004] The purpose of this utility model is to address the shortcomings of existing technologies by providing a thermal pulse probe for accurately measuring the amount of condensed water in biocrust soil. This probe utilizes the relationship between soil heat capacity and water content to accurately detect subtle changes in soil water content and measure the amount of condensed water in biocrust soil. This probe can stably and accurately measure the amount of condensed water in biocrust soil, making it particularly useful for research related to water balance in biocrusts in desert regions.

[0005] The purpose of this utility model is achieved through the following technical solutions:

[0006] A thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil comprises: a probe handle, a heating needle vertically fixed to the probe handle, and four temperature sensing needles. The four temperature sensing needles are arranged in a rectangular shape, with the heating needle located in the center of the rectangle. The length and width of the rectangle are preferably 12 mm and 5 mm, respectively, that is, the distance between the heating needle and the four temperature sensing needles is 6.5 mm, the distance between the temperature sensing needles that are farther apart is 12 mm, and the distance between the temperature sensing needles that are closer is 5 mm. The arrangement order of the heating needles and the temperature sensing needles is designed based on the fact that the biological crust is thin and the daily change of soil condensed water is small. This arrangement can improve the accuracy of measuring the condensed water in biological crust. The heating needle has a built-in thermocouple and a heating resistance wire, and the temperature sensing needle has a built-in thermocouple. The thermocouple is externally connected to a thermocouple extension wire, and the heating resistance wire is externally connected to a wire. The heating needle and the temperature sensing needle are filled with high thermal conductivity material for potting.

[0007] The material of the probe handle is preferably epoxy resin.

[0008] The heating needle and temperature sensing needle are preferably made of stainless steel tubes with an outer diameter of 1.3 mm and an inner diameter of 1.0 mm. The thermocouple and heating resistor wire in the heating needle and temperature sensing needle are protected by the stainless steel tubes, and the interior of the steel tubes is filled with a high thermal conductivity material (OMEGA bond-200).

[0009] The thermocouple is preferably an E-type thermocouple (nickel-chromium-copper-nickel).

[0010] The heating resistance wire is preferably nickel-chromium enameled wire, and the resistance is preferably 82Ωm -1 .

[0011] Preferably, the total length of the heating needle and temperature sensing needle is 55 mm. The length of the two when placed inside the probe handle is 15.0 mm, and the length when placed outside the probe handle is 40.0 mm. The effective length of the thermocouples in the heating needle and the temperature sensing needle is 20.0 mm. The thermocouples are respectively installed in the middle part of the stainless steel tube, leaving a 20 mm space between the top of the steel tube. The total length of the heating resistance wire in the heating needle is 200.0 mm, and the expanded length outside the probe handle is 160.0 mm. It is placed in the heating needle steel tube by folding it twice, that is, the heating resistance wire is inserted into the top of the steel tube, and its effective heating length outside the probe handle is 40.0 mm.

[0012] This new system utilizes heat pulse technology, applying a short-duration direct current to the heating needles, causing them to generate a high level of heat energy in a short period of time. The surrounding temperature probes sense changes in soil temperature. Knowing the heating duration, the distance between the temperature sensing needles and the heating needles, and the temperature variation over time, the isotropic heat conduction equation is solved to determine the soil's thermal characteristic parameters (heat capacity). Using the relationship curve between heat capacity and moisture content, the soil moisture content is ultimately estimated, and thus the changes in condensation water in the biocrust are deduced.

[0013] The utility model has the following advantages and beneficial effects:

[0014] The probe arrangement of the utility model can improve the accuracy of measuring biological crust condensation water.

[0015] The utility model has a small volume and causes little disturbance to the soil during burial and measurement.

[0016] The utility model has good performance in measuring soil thermal characteristics and water content, with high accuracy and stability, and is suitable for accurate and long-term positioning monitoring of condensation water in biological crust soil, thereby reducing the requirements for manpower, material resources and time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a three-dimensional structural diagram (A) and a top view (B) of the thermal pulse probe of the present invention. In the figure, 1 is a heating needle, 2-5 are temperature sensing needles, 6 is a probe handle, 7 and 9 are thermocouples, 10 is a heating resistance wire, and 8 and 11 are stainless steel tubes.

[0018] Figure 2 The utility model is a schematic diagram of a device for measuring the relationship between soil heat capacity and water content using the thermal pulse probe of the utility model.

[0019] Figure 3 This is a graph showing the relationship between heat capacity and water content of soils with biological crusts and soils without crusts.

[0020] Figure 4 This is a graph showing the results of measuring condensation water in biological crust and non-crust soil using the thermal pulse probe of the utility model. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0022] Example 1

[0023] A heat pulse probe for accurately measuring the amount of condensed water in biological crust soil, the structure of which is as follows Figure 1The probe handle 6, a heating needle 1 fixed vertically on the probe handle 6, and four temperature sensing needles (2, 3, 4, 5). The four temperature sensing needles are arranged in a rectangle, and the heating needle is located in the center of the rectangle. The length and width of the rectangle are 12 mm and 5 mm, respectively, that is, the distance between the heating needle and the four temperature sensing needles is 6.5 mm, the distance between the temperature sensing needles far apart (for example, 2 and 4, 3 and 5) is 12 mm, and the distance between the temperature sensing needles close to each other (for example, 2 and 3, 4 and 5) is 5 mm.

[0024] The material of the probe handle 6 is epoxy resin. The materials of the heating needle and the temperature sensing needle are both stainless steel pipes, with an outer diameter of 1.3 mm and an inner diameter of 1.0 mm. Taking the heating needle 1 and the temperature sensing needle 2 as an example, the total length of the heating needle stainless steel pipe 11 and the temperature sensing needle stainless steel pipe 8 is 55 mm, with 15 mm inside the probe handle 6 and 40 mm outside the probe handle 6. The heating needle has two elements, a thermocouple 9 and a heating resistance wire 10, and the temperature sensing needle has a thermocouple 7. The thermocouple is used to measure the temperature change of each layer of soil, and the heating resistance wire is used to simulate a linear heat source. The thermocouple is an E-type thermocouple (nickel-chromium-copper-nickel), and the heating resistance wire is a nickel-chromium enamel wire with a resistance of 82Ωm -1 . The effective length of the thermocouple in the heating needle and the temperature sensing needle is 20.0 mm, and the thermocouple is arranged in the middle part of the stainless steel pipe, with a space of 20 mm between the top end of the steel pipe. The total length of the heating resistance wire in the heating needle is 200.0 mm, and the unfolded length outside the probe handle 6 is 160.0 mm. The resistance wire is inserted into the top end of the steel pipe by folding it twice. The thermocouple is connected with the same type of thermocouple extension wire, and the heating resistance wire is connected with a lead wire. The heating needle and the temperature sensing needle are filled with high thermal conductivity glue (OMEGA bond-200) for sealing.

[0025] The thermal pulse probe is manufactured as follows: The total length of the temperature sensing needle and heating needle steel tubes is 55 mm. Thermocouples are placed in each of the five probe steel tubes, and a heating resistor wire is placed in the middle heating needle steel tube. For the thermocouples, the effective length of the middle thermocouple in each temperature sensing needle and heating needle is 20 mm, that is, there is a 20 mm space between the thermocouple and the bottom of the steel tube. For the heating resistor wire, the total length of the heating needle resistor wire is 200 mm, and the extended length outside the probe handle is 160 mm. It is folded in half twice and placed into the heating needle steel tube with an effective length of 40 mm outside the probe handle, that is, the resistor wire is inserted all the way to the top of the steel tube. After the thermocouples and / or resistor wires are inserted, the thermocouples are connected to the same type of thermocouple extension wires, the heating resistor wires are connected to the wires, and the heating needles and temperature sensing needles are filled with high thermal conductivity glue (OMEGAbond-200) for potting. After the temperature sensing needle and heating needle are made, the probe handle mold is filled with high polymer epoxy resin to make the probe handle. The probe handle is used to fix the probes so that they are placed side by side. The arrangement rules of each probe are as follows:

[0026] 1) The length of all temperature sensing needles and heating needles exposed to the handle is 40mm, that is, the effective length of the stainless steel tube outside the epoxy resin is 40mm.

[0027] 2) The five probes are arranged with the heating needle at the center, and the four temperature sensing needles are located around the heating needle, and the distance between the heating needle and the temperature sensing needle is 6.5 mm.

[0028] 3) The distance between the temperature sensing needles that are farther apart is 12 mm, and the distance between the temperature sensing needles that are closer is 5 mm.

[0029] Example 2

[0030] 1. Determination of soil thermal properties

[0031] A 10 cm high, 10 cm long petri dish was used to collect soil samples. The soil samples were saturated with deionized water in a room for 24 hours. Five small holes were then made 5 cm from the middle of the side of the petri dish so that the heat pulse probe of Example 1 could be fully inserted into the soil sample. The surface of the sample was covered with plastic wrap and placed in a cool place for 12 hours to drain excess water. The heat pulse probe was carefully inserted into the soil sample and placed on the weighing sensor. Figure 2 The parts were connected as shown, and the samples were placed at room temperature of 25°C for natural evaporation until air-dried.

[0032] During the experiment, a CR3000 data logger (Campbell Scientific, Inc., USA) was used to record temperature and voltage changes at all probes. During the experiment, five probes measured soil temperature for 6 seconds as a background value. The data logger then controlled a battery to apply a steady 12V voltage to the heating probes for 8 seconds, generating a heat pulse. At this point, the heating probes' temperatures rose rapidly, and this temperature was then transferred through the soil and detected by the surrounding sensing probes. The temperature changes at the sensing probes were then processed to derive soil thermal parameters. In this experiment, temperature changes were recorded every 1 second, with each measurement lasting 5 minutes and a 1-hour interval between measurements.

[0033] To measure soil thermal properties, samples were placed on an SM50 (Interface Inc., USA; accuracy: ±0.01 g) automatic weighing cell, and all samples were weighed at 1-hour intervals. As the soil saturated and air-dried, the thermal properties at low water contents were measured more frequently, with samples weighed at 30-minute intervals. This ensured the accuracy of the fitted line at low water contents and enabled better determination of condensation water in the biocrust.

[0034] The measurements were terminated after the soil samples air-dried, with each measurement period lasting approximately 10 days. Afterward, the thermal properties and mass change measurements were repeated on saturated soils, with each sample subjected to three replicates. After all measurements were completed, the samples were oven-dried at 105°C for 24 hours to determine the soil's mass water content. Finally, the volumetric water content was calculated based on the soil's bulk density.

[0035] Soil thermal characteristics to estimate water content: Based on the significant linear relationship between soil heat capacity and corresponding water content, a calibration equation for heat capacity and water content was obtained through linear regression. This experiment calculated soil heat capacity based on the heat conduction equation of infinitely long short-term heat pulse theory. The core of this equation is that the determination of soil thermal characteristics is based on the temperature change of a linear pulse heat source within a certain distance range. Heat is conducted radially away from the heater, and the temperature change at that distance with time is shown in Equation (1):

[0036]

[0037] Where T is the temperature change (K), unit is ℃; q is the heat released per unit time and unit length, unit is Wm -1 ; k is the soil thermal diffusivity, unit is m 2 s -1 ; C is the volumetric heat capacity, in MJ m -1 K -1 ; Ei is the exponential integral; r is the radius, in m; t0 is the time to start measurement, in s.

[0038] Taking the partial differential of t for formula (1) and making the result equal to 0, we can get the t corresponding to the maximum temperature rise. m , we can get the expression (2) about k:

[0039]

[0040] Where k is a function of r, t, and t0. Substituting formula (2) into formula (1) yields the expression for the volumetric heat capacity C of the soil:

[0041]

[0042] Where t m is the time when the maximum soil temperature occurs, in seconds; ΔT m is the maximum temperature rise at a distance r from the heat source corresponding to t, in °C; λ is the thermal conductivity of the soil, in W m -1 K -1 ; The relationship between the heat pulse probe and water content measured indoors is as follows Figure 3 , and perform a linear regression fitting on the two to obtain the water content conversion equation (4):

[0043] θ=aC+b (4)

[0044] Where a and b are constants; therefore, the condensation water content θ of the biological crust soil can be calculated by combining the surface soil heat capacity measured in the field and fitting the equation to inversely infer the water content.

[0045] 2. Working procedures for measuring biological crust condensation water using this utility model

[0046] The first step is to install the thermal pulse probe described in Example 1 in the field. Carefully dig a pit approximately 10 cm long, 10 cm wide, and 5 cm deep in the biocrust-covered area. Insert the thermal pulse probe horizontally along the soil surface into the biocrust layer. Carefully backfill the excavated soil and evenly water it to ensure the biocrust layer adheres to the underlying soil.

[0047] The second step is to measure the condensation water 15 days after the probe is buried. Figure 2 As shown, the various parts are connected, including connecting the heat pulse probe to the CR3000 data collector (Campbell Scientific, Inc., USA), and heating and data collection are completed through the data collector to obtain the soil thermal properties (heat capacity).

[0048] The third step is to transfer the data in the data collector to the computer, and combine it with the fitting equation of the heat capacity and moisture content of the biocrust soil measured indoors to reversely calculate the condensation water content of the biocrust soil.

[0049] Example 3

[0050] Application of the utility model to measure the condensation water content of biological crust soil

[0051] In August 2022, typical aeolian soil with moss crust and non-crust soil were selected in the northern part of the Loess Plateau in China, and the soil condensation water content was measured using the utility model.

[0052] Field deployment: Dig a small pit (10 cm long, 10 cm wide, 5 cm deep) in a typical biocrust-covered area. Insert the heat pulse probe from Example 1 horizontally into the biocrust layer and the non-crust soil, ensuring the central heating needle is buried at a depth of 1 cm. Place the accompanying data logger, battery, and other equipment in a rainproof box, powered by solar panels.

[0053] Measurement process: The five needles first measure the soil temperature for 6 seconds as the background value, and then the data logger controls the heating needles to steadily apply a 12V voltage for 8 seconds. At this time, the temperature of the heating needles rises rapidly, and its temperature is transferred to the surrounding area through the soil. The temperature sensing needles located in the surrounding area can monitor the heat pulses of the heating needles. The temperature changes of the sensing needles are then processed separately to deduce the soil thermal characteristic parameters. In this experiment, soil temperature measurements all start at the top of the hour, and all temperature acquisitions are controlled by the data logger program. Temperature changes are recorded once every 1 second, each measurement lasts for 5 minutes, and the measurement interval is set to 30 minutes. A CR3000 data logger is used to record the temperature changes and power input of all needles every 1 second.

[0054] The results of the condensation water content determination of biological crust and non-crust soil are as follows Figure 4 The amount of condensed water shows a clear daily variation pattern: during the day, due to the influence of light and temperature, water evaporates quickly, and the soil moisture content continues to decrease, reaching a minimum around 18:00 in the afternoon, with the biocrust being approximately 0.11 cm 3 cm -3 , no crust is about 0.025cm 3 cm -3 However, at night, as the temperature decreases and the humidity increases, the amount of soil condensation water gradually increases, reaching a maximum around 6:00 in the morning, with a crust of approximately 0.18 cm 3 cm -3 , no crust is about 0.09cm 3 cm -3 During the experiment, there was no rainfall, so the change in soil moisture in this area is the change in condensation water. Therefore, the sensor of this utility model can better measure the amount of condensation water in soil with and without biological crust.

[0055] The above results show that in arid and semi-arid areas, although the surface soil moisture content is low, the difference in the change of condensation water at night can still be measured by the sensor of the utility model.

[0056] The above embodiments illustrate the basic principles, main features, and advantages of the present invention. However, the present invention is not limited to the above embodiments. Various changes and improvements are possible without departing from the spirit and scope of the present invention, and all such changes and improvements fall within the scope of protection claimed by the present invention.

Claims

1. A thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil, comprising a probe handle, a heating needle and a temperature sensing needle vertically fixed to the probe handle, characterized by: The number of the heating needles and temperature sensing needles is one and four respectively. The four temperature sensing needles are arranged in a rectangle, with the heating needle located in the center of the rectangle; the heating needle has a built-in thermocouple and a heating resistance wire, and the temperature sensing needle has a built-in thermocouple; the thermocouple is externally connected to a thermocouple extension wire, and the heating resistance wire is externally connected to a wire; the heating needles and temperature sensing needles are filled with high thermal conductivity materials for potting.

2. The thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil according to claim 1, characterized in that: The length and width of the rectangle are 12 mm and 5 mm respectively.

3. The thermal pulse probe for accurately measuring condensation water in biological crust soil according to claim 1, characterized in that: The material of the probe handle is epoxy resin.

4. The thermal pulse probe for accurately measuring condensation water in biological crust soil according to claim 1, characterized in that: The heating needle and the temperature sensing needle are both made of stainless steel tubes.

5. The thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil according to claim 4, characterized in that: The outer diameter of the stainless steel tube is 1.3 mm and the inner diameter is 1.0 mm.

6. The thermal pulse probe for accurately measuring condensation water in biological crust soil according to claim 1, characterized in that: The thermocouple is an E-type thermocouple.

7. The thermal pulse probe for accurately measuring condensation water in biological crust soil according to claim 1, characterized in that: The heating resistance wire is nickel-chromium enameled wire.

8. The thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil according to claim 7, characterized in that: The resistance of the nickel-chromium enameled wire is 82Ωm -1 .

9. The thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil according to any one of claims 1 to 7, characterized in that: The total length of the heating needle and the temperature sensing needle is 55 mm. The length of the heating needle and the temperature sensing needle placed inside the probe handle is 15.0 mm, and the length of the heating needle and the temperature sensing needle placed outside the probe handle is 40.0 mm.

10. The thermal pulse probe for accurately measuring the amount of condensed water in biological crust soil according to claim 9, characterized in that: The effective length of the thermocouples in the heating needle and the temperature sensing needle is 20.0 mm. The thermocouples are respectively installed in the middle part of the stainless steel tube, leaving a 20 mm space between the top of the steel tube; the total length of the heating resistance wire in the heating needle is 200.0 mm, and the unfolded length outside the probe handle is 160.0 mm. The heating resistance wire is folded twice and placed in the heating needle steel tube, and its effective heating length outside the probe handle is 40.0 mm.

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