Thermal pulse probe for accurately measuring evaporation capacity of biological crust soil

Abstract

The utility model discloses a thermal pulse probe for accurately measuring the evaporation capacity of biological crust soil, and belongs to the field of soil measuring equipment. The probe comprises a probe handle, and a plurality of heating needles and temperature sensing needles which are vertically fixed on the probe handle and are distributed in n layers, the first layer comprises three temperature sensing needles which are vertically arranged at equal intervals from top to bottom; the second layer to the nth layer take the heating needle as the center, two temperature sensing needles are arranged on the two horizontal sides respectively, the heating needles of the second layer to the nth layer are vertically arranged on one line, and the vertical distances between the heating needles of all the layers are the same; the distances between the three temperature sensing needles in the first layer and the heating needles in the second layer are the same. According to the utility model, the obvious correlation between the soil thermal capacity and the moisture is utilized, the change of the moisture content is calculated by accurately measuring the soil thermal capacity, and the evaporation capacity of the soil covered by the biological crust is obtained. The device has the advantages of quick response, high sensitivity and small disturbance to soil when being used for measuring the soil moisture change, and is suitable for measuring the evaporation capacity of biological crust.

Description

Technical Field

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

[0002] Biological crusts are complex complexes formed by cryptogamous plants such as lichens and mosses and soil microorganisms that are cemented with soil surface particles through mycelium, rhizomes, and secretions. They are widely distributed in various climatic zones around the world. As the "skin" of the soil, biological crusts profoundly affect the physical, chemical, and biological processes of the soil, and play an important role in improving soil structure, influencing soil moisture distribution, promoting soil nutrient cycling, and maintaining surface ecological balance. Although the thickness of biological crusts is limited, they play an important role in influencing the water and heat transfer and water and heat balance of the surface soil. However, due to the complexity and diversity of biological crusts themselves, as well as their sensitivity to environmental changes in ecologically fragile areas, there are still many difficulties and challenges in studying their impact on surface water balance processes.

[0003] As a crucial component of the desert surface, biological crusts have a complex regulatory effect on evaporation. However, current research results vary widely across different climate zones, with findings suggesting that biological crusts can inhibit or promote evaporation, or that their impact on evaporation is constrained by surface soil moisture. Beyond considering the influence of different types of biological crusts and regional climate variations, a unified method for measuring evaporation from biological crusts is currently lacking, particularly for long-term, in-situ, continuous monitoring of evaporation from biological crusts.

[0004] Currently, the most commonly used methods for measuring evaporation in biocrust soils include gravimetric methods and soil moisture sensors. The gravimetric method involves placing the biocrust and underlying soil in a container and periodically measuring the loss of water in the container to calculate evaporation. This method significantly disturbs the biocrust soil and can only characterize evaporation from the entire biocrust soil sample, making it difficult to clearly define the evaporation characteristics of the biocrust layer (approximately 0 to 2 cm). Although some studies have estimated evaporation from biocrust-covered areas based on gravimetric methods and the Penman equation (which requires accurate meteorological data), these methods are often limited by the biocrust coverage and have significant limitations in describing evaporation characteristics at different depths in biocrust-covered soils. In contrast, soil moisture sensors are a common method for measuring evaporation in biocrust-covered soils, capturing moisture changes at different depths. By embedding moisture probes (such as EC5, 5TE, Teros 11, and TDR) at different depths in the soil, changes in soil moisture content are monitored in real time, and evaporation is calculated based on these changes. Although this method is highly accurate and capable of long-term positioning and monitoring, it is limited by the thin nature of biological crusts (a few millimeters to a few centimeters). Currently, the sensing range of most moisture probes far exceeds the crust layer, making it impossible to accurately measure the moisture change in the biological crust layer, resulting in large deviations in the assessment of the evaporation characteristics of the biological crust. Utility Model Content

[0005] The purpose of this utility model is to address the shortcomings of existing technologies by providing a thermal pulse probe for accurately measuring evaporation from soil covered by biological crusts. This probe utilizes the significant correlation between soil heat capacity and moisture content to accurately measure soil heat capacity and infer changes in moisture content, thereby determining the evaporation rate of soil covered by biological crusts. This probe can accurately and stably measure the evaporation process of soil covered by biological crusts over a long period of time, helping to address the technical challenges associated with studying the moisture effects of biological crusts in desert regions.

[0006] The purpose of this utility model is achieved through the following technical solutions:

[0007] A heat pulse probe for accurately measuring evaporation of biological soil crust soil, comprising: a probe handle, a plurality of heating needles and temperature sensing needles vertically fixed on the probe handle. The heating needles and temperature sensing needles are distributed in n layers from top to bottom, n is a natural number, and the number can be increased or decreased according to the measured soil depth, such as n is 3, 4, 5, 6, 7 or 8. Among them, the first layer contains three temperature sensing needles, which are respectively located in three levels from top to bottom, and the vertical interval of each level is the same, preferably 1.0mm. The second to n layers are centered on the heating needle, and each side has one temperature sensing needle. The heating needles in the second to n layers are vertically arranged in one line, and the distance between the heating needle and the temperature sensing needle on both sides is preferably 5.0mm. The vertical distance between the heating needles of each layer is the same, preferably 10.0mm. The distance between the three temperature sensing needles of the first layer and the heating needle in the second layer is the same and preferably 5.0mm. The arrangement of the heating needles and temperature sensing needles is designed according to the thin biological crust and the large change of the surface soil evaporation rate, which can accurately measure the evaporation characteristics of the biological crust layer and the underlying soil. The heating needle is internally provided with a thermocouple and a heating resistance wire, and the temperature sensing needle is internally provided with a thermocouple. The thermocouple is externally connected with a thermocouple extension line, and the heating resistance wire is externally connected with a lead wire. The heating needle and temperature sensing needle are internally filled with high thermal conductivity material for potting.

[0008] The material of the probe handle is preferably epoxy resin.

[0009] The material of the heating needle and temperature sensing needle is preferably stainless steel pipe, the outer diameter is preferably 1.3mm, and the inner diameter is preferably 1.0mm. The thermocouple and heating resistance wire in the heating needle and temperature sensing needle are protected by the stainless steel pipe, and the steel pipe is internally filled with high thermal conductivity material (OMEGA bond-200).

[0010] The thermocouple is preferably an E-type thermocouple (nickel-chromium-copper-nickel).

[0011] The heating resistance wire preferably uses nickel-chromium enamel wire, and the resistance value is preferably 82Ωm -1 .

[0012] The heating needle preferably has a total length of 55.0 mm, with a length of 15.0 mm inside the probe handle and a length of 40.0 mm outside the probe handle; the temperature sensing needle has a total length of 35.0 mm, with a length of 15.0 mm inside the probe handle and a length of 20.0 mm outside the probe handle. The effective length of the thermocouples in the heating needle and the temperature sensing needle outside the probe handle is 20.0 mm; the total length of the heating resistance wire in the heating needle outside the probe handle is 160.0 mm, and the resistance wire is placed in the heating needle by folding it twice, and its effective heating length outside the probe handle is 40.0 mm. Further preferably, the thermocouple in the heating needle is installed in the middle of the heating needle, with a distance of 20.0 mm between it and the top of the heating needle; the thermocouple in the temperature sensing needle is installed at its top.

[0013] This new device utilizes heat pulse technology, applying a short-duration direct current to heating needles, causing them to generate high heat within a short period of time. Temperature sensors on either side of the needles then measure changes in soil temperature. Given the heating duration, the distance between the temperature sensors and the heating needles, and the temperature change measured by the temperature sensors, the device calculates the soil's heat capacity and, based on a curve linking it to water content, deduces soil water storage, ultimately determining how soil evaporation changes.

[0014] The utility model has the following advantages and beneficial effects:

[0015] The probe arrangement of the utility model can accurately measure the evaporation characteristics of the biological crust layer and the underlying soil.

[0016] The utility model can adjust the number of probes according to needs, realize continuous and accurate positioning monitoring of soil evaporation of different thicknesses, and reduce requirements on manpower and material resources.

[0017] The utility model has a rapid response and high sensitivity in measuring soil moisture changes, causes little disturbance to the soil, is suitable for measuring the evaporation of biological crusts, and can solve the technical difficulties in measuring the evaporation of biological crusts. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a three-dimensional structural diagram of the thermal pulse probe of the present invention. In the figure, 1-5 are heating needles, 6-18 are temperature sensing needles, 19 is a probe handle, 20 and 21 are thermocouples, and 22 is a heating resistance wire.

[0019] Figure 2 This is a top view of the thermal pulse probe of the present invention. The first layer contains three temperature sensing needles, and the second to sixth layers are centered around the heating needle, with one temperature sensing needle installed on each side of the horizontal axis.

[0020] Figure 3The 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.

[0021] Figure 4 It is a relationship diagram between the measured heat capacity and moisture content of each layer of soil. DETAILED DESCRIPTION

[0022] 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.

[0023] Example 1

[0024] A heat pulse probe for accurately measuring evaporation of biocrust soil. Taking an 18-pin heat pulse probe as an example, its structure is as follows: Figure 1 、 2 As shown, it includes: a probe handle 19, five heating needles (1, 2, 3, 4, 5) vertically fixed to the probe handle 19, and 13 temperature sensing needles (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18). The heating needles and temperature sensing needles are arranged in six layers from top to bottom. The first layer contains three temperature sensing needles (6, 7, 8). The second to sixth layers are all centered on the heating needle (1, 2, 3, 4, 5), with one temperature sensing needle (9 and 10, 11 and 12, 13 and 14, 15 and 16, 17 and 18) installed on each side horizontally. Among them, the three temperature sensing needles in the first layer are located in three levels from top to bottom, with a vertical interval of 1.0mm between each level; the heating needles in the second to sixth layers are arranged vertically in a line, with the distance between the temperature sensing needles and the heating needles on both sides being 5.0mm, and the vertical distance between the heating needles in each layer is 10.0mm; the distance between the three temperature sensing needles in the first layer and the heating needles in the second layer is 5.0mm.

[0025] The material of the probe handle 19 is epoxy resin. The material of the heating needle and the temperature sensing needle are both stainless steel tubes with an outer diameter of 1.3mm and an inner diameter of 1.0mm. The total length of the heating needle stainless steel tube is 55.0mm, the length when placed inside the probe handle 19 is 15.0mm, and the length when placed outside the probe handle 19 is 40.0mm. The total length of the temperature sensing needle stainless steel tube is 35.0mm, the length when placed inside the probe handle 19 is 15.0mm, and the length when placed outside the probe handle 19 is 20.0mm. Taking the heating needle 1 and the temperature sensing needle 6 as an example, the heating needle has a built-in thermocouple 21 and a heating resistance wire 22, and the temperature sensing needle has a built-in thermocouple 20. The thermocouple is used for soil temperature changes, and the heating resistance wire is used for electric heating to simulate a linear heat source. The thermocouple is an E-type thermocouple (nickel-chromium-copper-nickel), and the heating resistance wire uses nickel-chromium enameled wire with a resistance of 82Ωm -1. The length of the thermocouples in the heating needle and the temperature sensing needle are both 20.0 mm; for the heating needle, the thermocouple is installed in the middle of the stainless steel tube, leaving a distance of 20.0 mm between it and the top of the steel tube; for the temperature sensing needle, the thermocouple is installed at the top of the stainless 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 19 is 160.0 mm. It is folded twice and placed in the heating needle steel tube, that is, the resistance wire is inserted into the top of the steel tube. The thermocouple is externally connected to a thermocouple extension wire of the same type, and the heating resistance wire is externally connected to a wire. The heating needle and temperature sensing needle are filled with high thermal conductivity glue (OMEGA bond-200) for potting.

[0026] The thermal pulse probe is fabricated as follows: The thermocouple and heating resistor wire are placed separately in a stainless steel tube and filled with OMEGAbond-200 glue. The probes are then positioned using a precision mold (by injecting epoxy resin into the mold). Each thermocouple is connected to an extension wire of the same type, while the heating resistor wire requires an external lead. Finally, all the layers of probes are assembled together using a splicing process to complete the probe.

[0027] Example 2

[0028] 1. Obtaining the relationship between soil thermal characteristics and water content

[0029] Soil samples were collected using an acrylic box (20 cm × 20 cm × 10 cm, with a porous mesh on the bottom layer for free drainage). Each layer of the heat pulse probe of the present invention (the probe in Example 1) was completely inserted into the soil. At the same time, the soil sample was saturated with deionized water and covered with plastic wrap and placed in a cool place for 12 hours to drain excess water. The soil sample was placed on a weighing sensor and weighed according to the pressure. Figure 3 As shown, the various parts are connected and the sample is placed at room temperature of 25°C for natural evaporation until it is air-dried to obtain the relationship between soil moisture content and heat capacity during the process of soil drying from wet to dry.

[0030] During the indoor experiments, a CR3000 data logger (Campbell Scientific, Inc., USA) was used to record temperature changes at all probes and voltage changes at the heating probes. Before each heating cycle, the soil temperature was measured for 6 seconds as a background value, and then the heating probes were powered steadily by a battery for 8 seconds. As the temperature of the heating probes rises rapidly, the temperature is transferred through the soil to the surrounding area and detected by the temperature sensing probes. The temperature changes detected by the temperature sensing probes were subsequently processed to deduce the soil heat capacity. During the indoor experiments, temperature changes were recorded every 1 second, and each measurement lasted 5 minutes, with a measurement interval of 1 hour.

[0031] In addition, the above soil samples were placed on an SM50 (Interface Inc., USA; accuracy of ±0.01 g) automatic weighing sensor, and all samples were weighed at intervals of 1 h to obtain the actual volumetric water content change values ​​of the samples.

[0032] The measurements were terminated after the soil samples had air-dried. Each measurement lasted approximately 10 days. Afterward, the soil was resaturated and the experimental procedure repeated three times. After all measurements were completed, the samples were dried at 105°C for 24 hours to determine the soil volumetric water content.

[0033] 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 change in soil temperature over time at a certain distance is shown in Equation (1):

[0034]

[0035] Where T is the temperature change value, unit is °C; q is the heat released per unit time and unit length, unit is W m -1 ;κ is the soil thermal diffusivity, unit is m 2 s -1 ; C is the volumetric heat capacity, unit is 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.

[0036] 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 κ:

[0037]

[0038] Where κ 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:

[0039]

[0040] 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 4 , and perform a linear regression fitting on the two to obtain the water content conversion equation (4):

[0041] θ=aC+b (4)

[0042] Where a and b are constants; therefore, the water content can be inferred by fitting the equation based on the surface soil heat capacity measured in the field.

[0043]

[0044] Where W is the total soil water storage, in mm; θ is the water content of each layer of soil, in cm 3 cm -3 h is the soil depth in mm; i is the soil depth in mm. If the water content of each layer is known, the water storage at that depth can be calculated based on the depth measured by the probe, ultimately determining the soil evaporation (i.e., the change in soil water storage) within the entire probe monitoring range.

[0045] 2. Working procedures for determination using this utility model

[0046] (1) Installation of the probe of the present invention. Carefully dig a pit approximately 10 cm long, 10 cm wide, and 10 cm deep in the area covered by the biocrust sample. Insert the thermal pulse probe of Example 1 horizontally into the soil along the soil surface, ensuring that the first temperature probe is flush with the surface of the biocrust layer. Carefully backfill the excavated soil and evenly sprinkle water to ensure that the biocrust layer in the disturbed area is in contact with the underlying soil.

[0047] (2) Measurement of soil thermal properties. Figure 3The connections shown here include connecting the heat pulse probes to a CR3000 data logger and an AM25T expansion board (Campbell Scientific, Inc., USA). The data logger provides periodic heating and data acquisition. The five heated probes follow a 15-minute heating cycle: ① During the first cycle (0-15 minutes), probes 1, 6, 7, 8, 9, and 10 measure the soil temperature for 6 seconds as a background value. The data logger then applies a 12V voltage to heat heater pin 1 steadily for 8 seconds, while temperature sensors 6, 7, 8, 9, and 10 continuously measure the temperature change for 5 minutes. Between 6 and 15 minutes, the probes stop measuring. ② After the first cycle is complete, the second cycle (15-30 minutes) begins. Similar to the above process, probes 2, 11, and 12 measure the soil temperature for 6 seconds as a background value. The data logger then applies a 12V voltage to heat heater pin 2 steadily for 8 seconds, while temperature sensors 11 and 12 continuously measure the temperature change for 5 minutes. ③ Following this pattern, the five heating probes heat up sequentially, while the temperature sensing probes measure the temperature change over a five-minute period. For example, using an 18-probe heat pulse probe as an example, a complete cycle would take 75 minutes.

[0048] (3) After the above measurements are completed, the soil moisture content at each depth is deduced by combining the obtained fitting equation of the heat capacity and moisture content of the soil covered by the biocrust (Formula 4); and based on the soil moisture content of each layer module and its corresponding soil depth, the soil water storage capacity at the corresponding depth is calculated, and finally the soil evaporation of the entire profile is obtained.

[0049] 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 evaporation in biocrust soil, comprising a probe handle and a plurality of heating needles and temperature sensing needles vertically fixed to the probe handle, characterized by: The heating needles and temperature sensing needles are distributed in n layers from top to bottom, where n is a natural number; the first layer contains 3 temperature sensing needles, which are located in three layers from top to bottom, with the same vertical spacing in each layer; the 2nd to nth layers are centered on the heating needle, with 1 temperature sensing needle on each horizontal side, and the heating needles in the 2nd to nth layers are vertically arranged in a line, with the vertical distance between the heating needles in each layer being the same; the 3 temperature sensing needles in the first layer are at the same distance from the heating needles in the second layer; the heating needles have built-in thermocouples and heating resistance wires, and the temperature sensing needles have built-in thermocouples; the thermocouples are externally connected to thermocouple extension wires, and the heating resistance wires are externally connected to wires; the heating needles and temperature sensing needles are filled with high thermal conductivity glue material for potting.

2. The thermal pulse probe for accurately measuring evaporation of biological crust soil according to claim 1, characterized in that: The three temperature sensing needles in the first layer are located in three levels from top to bottom, with a vertical interval of 1.0 mm in each level; the distance between the temperature sensing needles and the heating needles in the 2nd to nth layers is 5.0 mm, and the vertical distance between the heating needles in each layer is 10.0 mm; the distance between the three temperature sensing needles in the first layer and the heating needles in the second layer is 5.0 mm.

3. The thermal pulse probe for accurately measuring evaporation of 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 evaporation of 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 evaporation of 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 evaporation of 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 evaporation of 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 evaporation of 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 evaporation of biological crust soil according to any one of claims 1 to 7, characterized in that: The total length of the heating needle is 55.0 mm, the length inside the probe handle is 15.0 mm, and the length outside the probe handle is 40.0 mm; the total length of the temperature sensing needle is 35.0 mm, the length inside the probe handle is 15.0 mm, and the length outside the probe handle is 20.0 mm.

10. The thermal pulse probe for accurately measuring evaporation of biological crust soil according to claim 9, characterized in that: The length of the thermocouples in the heating needle and the temperature sensing needle outside the probe handle is 20.0 mm; the total length of the heating resistance wire in the heating needle outside the probe handle is 160.0 mm. The heating resistance wire is folded twice and placed in the heating needle, and its effective heating length outside the probe handle is 40.0 mm.

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