Method for measuring heat storage capacity of soil in sunlight greenhouse

Abstract

The invention discloses a method for measuring the heat storage capacity of soil in a sunlight greenhouse, which avoids the defects of poor sample representativeness and poor universality of a traditional measuring method, and finds a new way, applies the basic knowledge of unstable heat conduction of heat transfer theory, and starts from the relationship between heat release and temperature reduction consistency of the soil in the sunlight greenhouse. And measuring and calculating a soil heat release value (summa (Q)) and a soil temperature reduction value (summa delta T), and then calculating the heat storage capacity of the soil through calculation of (summa (Q)) / (summa delta T). According to the measuring method, the heat release amount and the temperature reduction amount of the soil plough layer and the soil below the soil plough layer are measured, the measured data can cover and contain the physical structure difference of the soil in the vertical direction after being analyzed and calculated, and therefore the real heat storage capacity of the soil can be better represented.

Description

Technical Field

[0001] The invention relates to a method for determining heat storage capacity of soil in a solar greenhouse and belongs to the technical field of agriculture. Background Art

[0002] With its unique heat storage and insulation function, solar greenhouses have achieved winter production of thermophilic fruits and vegetables, playing an important role in solving the winter vegetable supply problem in large areas of northern my country. Due to the lag in theoretical research on heat storage and insulation in solar greenhouses, the night temperature in solar greenhouses is generally low during production, resulting in reduced yield and quality of thermophilic fruits and vegetables; in serious areas, solar greenhouses will be idle and cannot be put into winter production, resulting in serious waste of resources. Both production practice and research have proved that soil heat release plays an important role in the formation of nighttime temperature in solar greenhouses, especially on cloudy nights when there is no daytime heat storage and the heat release capacity of the back wall is seriously reduced. Soil heat release plays a decisive role in the nighttime temperature of solar greenhouses.

[0003] In order to increase the night temperature level in the solar greenhouse, improve the temperature environment during the growth of thermophilic fruits and vegetables, and give full play to the role of soil in the heat storage and insulation process of the solar greenhouse, the heat accumulated in the solar greenhouse through the greenhouse effect during the day is transferred and stored in the soil through active heat storage devices. This is an effective measure to improve the heat storage efficiency of the solar greenhouse, increase the soil heat storage, increase the soil temperature, and thus improve the night temperature level of the greenhouse.

[0004] Soil density (ρ) and specific heat capacity (c) are important thermal engineering indicators of soil. Their product (ρc) is 3 The amount of heat accumulated or released when the soil temperature changes by 1°C also indicates the heat storage capacity of the soil. The design and operation of active heat storage devices in solar greenhouse soils, the calculation of soil thermal conductivity (ρc / λ), etc. all require the calculation of the heat storage capacity (ρc) of the soil. For example, the setting of the buried depth of the heat exchange pipe in the soil, the determination of the pipe diameter, the speed of medium circulation, etc. Therefore, strengthening the research on the determination of soil heat storage capacity is of great significance for increasing the soil heat storage capacity and raising the soil temperature through active heat storage, thereby giving full play to the heat storage and insulation function of the soil.

[0005] Due to the differences in soil texture, soil water content and organic matter content in the vast solar greenhouse vegetable production areas in northern my country, the texture of the soil in the vertical direction also varies, resulting in differences in soil density (ρ) and specific heat capacity (c), and the heat storage capacity of the soil (ρc) is also different. Therefore, a method for measuring the heat storage capacity of the soil is urgently needed in production to provide a calculation basis for the design and operation of soil active heat storage equipment. Summary of the invention

[0006] The present invention overcomes the above-mentioned shortcomings of the prior art and provides a method for measuring the heat storage capacity of greenhouse soil. The method avoids the shortcomings of poor sample representativeness and poor universality of traditional measurement methods, takes a different approach, uses the basic knowledge of non-steady-state heat conduction in heat transfer, and measures and calculates the soil heat release value (∫(Q)) and the soil temperature reduction value (∫ΔT) based on the relationship between the consistency of heat release and temperature reduction in greenhouse soil. Then, the heat storage capacity of the soil is calculated by calculating (∫(Q)) / (∫ΔT).

[0007] The present invention provides a method for measuring the heat storage capacity of soil in a solar greenhouse, comprising the following steps:

[0008] Step 1: Set up a heat flux plate on the floor of the solar greenhouse to measure the heat flux density of the soil at different times at night;

[0009] Step 2: Integrate the heat release of the soil in the time direction to calculate the heat release of the soil at night (∫(Q));

[0010] Step 3: Temperature sensors are set at different depths of the soil on the ground and below the ground to calculate the temperature difference (ΔT) of the soil at different depths at the beginning and end of soil heat release;

[0011] Step 4: Integrate the temperature difference between the beginning and the end of heat release in the vertical direction to calculate the temperature drop of the entire soil layer at night (∫(ΔT));

[0012] Step 5: ∫(Q) / ∫(ΔT) is 1m 3 The heat released when the soil temperature changes by 1°C is the heat storage capacity of the soil.

[0013] The measurements at different times of the night in step 1 refer to measurements taken 10-15 times per hour from 6 pm to 6 am, and the average of the 10-15 measured temperatures represents the temperature of that hour.

[0014] The temperature sensors are arranged in a vertical direction below the ground, and are arranged in sequence every 0.08m-0.12m from the ground downward, and 6-8 measuring points are arranged.

[0015] The heat flux plate is set in the middle of the solar greenhouse. The middle here refers to the area excluding the inner side of the gables on the east and west sides of the solar greenhouse, the south side of the north wall, and the south side of the greenhouse near the soil outside the greenhouse.

[0016] Beneficial Effects

[0017] The heat storage capacity of soil is the product of density (ρ) and specific heat capacity (c). Compared with conventional measurement methods, the measurement method of the present invention has incomparable advantages:

[0018] 1) The measuring method of the present invention measures and calculates the heat release (∫(Q)) and the temperature drop (∫(ΔT)) of the soil, and then directly calculates the heat storage (ρc) of the soil, rather than separately calculating the soil density (ρ) and the soil specific heat capacity (c), and then calculating the soil heat storage (ρc) through the soil density (ρ) and the soil specific heat capacity (c).

[0019] 2) When taking soil samples for measurement, conventional measurement methods will destroy the physical structure of the soil, resulting in the sample being unrepresentative, and further resulting in the density (ρ) and specific heat capacity (c) obtained by the test method being unrepresentative, and there being a large deviation between the measured data and the actual data. The measurement method of the present invention measures and calculates the heat release (∫(Q)) and the temperature drop (∫(ΔT)) of the soil without destroying the physical structure of the soil, so the data obtained can truly reflect the heat storage capacity of the soil.

[0020] 3) For sunlight greenhouse soil, due to long-term cultivation, there is a tillage layer in the soil. The tillage layer and the soil below it are different in physical structure, which increases the difficulty of sample representativeness. The density (ρ) and specific heat capacity (c) obtained by measuring the sample are not representative and have errors. The measurement method of the present invention measures the heat release and temperature reduction of the soil tillage layer and the soil below it. After analysis and calculation, the measured data can cover the physical structure differences of the soil in the vertical direction, and thus can better represent the real heat storage capacity of the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Variation of heat flux with time;

[0022] Figure 2 Temperature differences vary with soil depth. DETAILED DESCRIPTION

[0023] The following will further illustrate the technical solution designed in the present invention in conjunction with specific experimental examples. The present invention relates to the relevant embodiments, and the relevant changes and modifications made by those skilled in the art on this basis, if there is no creative work, will be regarded as the protection scope of the present invention.

[0024] The measuring method of the present invention is designed based on the latest progress in the study of non-steady-state heat conduction in heat transfer and the continuous medium hypothesis of fluid mechanics.

[0025] 1. Non-steady-state thermal conductivity research shows that for the heat storage and release of the back wall and soil of the solar greenhouse, heat release and temperature reduction occur simultaneously and are two aspects of the same problem. Temperature reduction is an external manifestation, and heat release is an internal cause. Based on the above basic knowledge, the measurement method of the present invention starts from the two aspects of the amount of heat released and the amount of temperature change, and calculates the amount of heat released ∫(Q) respectively, and then calculates the amount of temperature reduction ∫(ΔT). Finally, these two aspects are combined into one to calculate the heat storage capacity of the soil.

[0026] 2. The integral calculation of soil heat release in the present invention is based on the fact that the heat release of the ground is continuously distributed in the time direction, and the temperature difference at the beginning and end of the soil heat release is also continuously distributed in the vertical downward direction of the ground. Then, the powerful computing power of Matlab is used to calculate the heat release of the soil and the temperature change, and then the heat storage capacity of the soil is calculated.

[0027] 1. Calculation of soil heat release intensity and heat release

[0028] 1. The measuring method of the present invention selects a measuring point in the middle of the soil in a solar greenhouse, installs a heat flux plate (H) at the measuring point, and measures the heat flux density (H) of the soil at different times at night in the greenhouse.

[0029] 2. The nighttime heat release time in Shandong area is calculated from 18:00 at night to 6:00 the next morning, and the data are recorded every 5 minutes. The average of 12 data measured every hour represents the heat flux density of that hour. The ground heat flux density at night is H 18:00 , H 19:00 , H 20:00 , H 21:00 , H 22:00 , H 23:00 , H 0:00 , H 1:00 , H 2:00 , H 3:00 , H 4:00 , H 5:00 , H 6:00 .

[0030] 3. Integrate the 13 data obtained from the above measurements to obtain the integral value of the nighttime heat release density (∫(H)).

[0031] 4. The integral value (∫(H))×3600(seconds) gives the heat release of the soil at night (∫(Q)).

[0032] 2. Calculation of the reduction in soil temperature difference

[0033] 1. The measuring method of the present invention selects a measuring point in the middle of the soil in a solar greenhouse, and installs temperature sensors T0, T1, T2, T3, T4, T5, and T6 at 0m, 0.1m, 0.2m, 0.3m, 0.4m, 0.5m, and 0.6m below the ground in the vertical direction, respectively, to measure the soil temperature at different soil depths. The data measured by T0, T1, T2, T3, T4, T5, and T6 are represented by T0, T1, T2, T3, T4, T5, and T6.

[0034] 2. The nighttime heat release time in Shandong area is calculated from 18:00 to 6:00 the next morning, and the temperature is recorded every 5 minutes. The average of 12 data measured every hour represents the temperature of that hour. The temperature of each measuring point at night is T 0-18:00 、T 0-19:00 、T 0-20:00 、T 0-21:00 、T 0-22:00 、T 0-23:00 、T 0-0:00 、T 0-1:00 、T 0-2:00 、T 0-3:00 、T 0-4:00 、T 0-5:00 、T 0-6:00 .

[0035] By analogy, the temperatures of the following measuring points are T 1-18:00 、------------T 1-6:00 ; T 2-18:00 、------------T 2-6:00 ; T 3-18:00 、------------T 3-6:00 ; T 4-18:00 ,------------T 4-6:00 ; T 5-18:00 ,------------T 5-6:00 ; T 6-18:00 ,------------T 6-6:00 .

[0036] 3. Calculate the temperature difference (ΔT) at each temperature measuring point from the beginning to the end of heat release:

[0037] ΔT0=T 0-18:00 -T 0-6:00 , ΔT1=T 1-18:00 -T 1-6:00 ,---------and so on ΔT6=T 6-18:00 -T 6-6:00 .

[0038] The temperature differences ΔT0, ΔT1, and --------ΔT6 at the beginning and end of heat release at each measuring point are integrated in the soil depth direction to obtain the fitting function of the temperature difference change.

[0039] 4. Calculate the fitting function of the temperature difference change to obtain the shallowest soil depth when ΔT is 0. This soil depth is the depth at which the soil heat balance is balanced during the day and night, that is, the heat release depth of the soil during the day and night (h).

[0040] 5. Integrate the temperature difference change fitting function in the interval (0, h) to obtain the integral value of the soil temperature difference change (∫(ΔT)).

[0041] 3. Calculation of soil heat storage capacity

[0042] The soil heat storage capacity, that is, the heat storage capacity of the soil, is obtained by using the soil heat release integral value (∫(Q)) / soil temperature difference change integral value (∫(ΔT)) calculated above.

[0043] 4. Calculation Example

[0044] The example point is inside the experimental greenhouse of the experimental base of the Vegetable Research Institute of Shandong Academy of Agricultural Sciences.

[0045] 1. Calculation of soil heat release intensity and heat release

[0046] The variation of heat flux density at different time points at night and its fitting function are shown in Figure 1 .

[0047] Integrate the fitted function in the graph:

[0048]

[0049] Soil heat release (∫(Q)) = ∫(H)*3600 (seconds)

[0050] =173.3759W / m 2 *3600 (seconds)

[0051] =624153.24J / m 2

[0052] 2. Calculation of soil temperature difference reduction

[0053] The temperature difference of each measuring point at the beginning and end of heat release varies with soil depth and its fitting function is shown in Figure 2 .

[0054] Calculate the fitting function in the figure:

[0055] The soil depth when the shallowest function value is 0 is 0.2465m, which is also the heat release depth of the soil during that day and night.

[0056]

[0057] 3. Calculation of soil heat storage capacity

[0058] Soil heat storage capacity = (∫(Q)) / (∫(ΔT))

[0059] =(624153.24J / m 2 ) / (0.3915℃·m)

[0060] =1594261.1494J / ℃·m 3

[0061] 5. Calculation of the range of soil heat storage capacity

[0062] 1. Heat Transfer, edited by Zhang Jingzhou and Chang Haiping and published by Science Press, records on page 61 that the calculation method of soil heat storage capacity (ρc) is the product of soil density (ρ) and specific heat capacity (c).

[0063] 2. Due to the different textures and structures of soils, the influence of the cultivation environment, the depth of the tillage layer, the soil moisture content and the sampling error, it can be seen from the data that the density and specific heat capacity of the soil vary greatly (Table 1). As can be seen from Table 1, the density range of the soil varies greatly, ranging from 900 to 1800 kg / m 3 The specific heat capacity varies greatly, between 1200 and 1800 J / (kg·℃). The soil heat storage capacity varies greatly, between 1080000 and 3240000. This is because there are many factors that affect the soil heat storage capacity.

[0064] Table 1

[0065]

[0066]

[0067] 3. Basic data of thermal engineering

[0068] According to the book "Basics of Thermal Engineering" edited by Liu Chunze and Li Guobin and published by the Machinery Industry Press, the heat storage capacity of loess is 880kg / m 3 ×1170J / (kg·℃)=1029600 joules; Sand heat storage capacity: 1420kg / m 3 ×1510 J / (kg·℃)=2144200 joules;

[0069] The structure of loam (soil that can be cultivated) is between loess and sand. The heat storage capacity of solar greenhouse soil is between 1029600 and 2144200 joules. Considering the large differences between loam, loess and sand, the soil heat storage capacity will be located in the middle of the range.

[0070] The above discussion is based on the fact that there are many factors that affect the density and specific heat capacity of the greenhouse soil, and the accuracy of calculating the soil density and specific heat capacity from the front is low. At present, there are few accurate values ​​of the density and specific heat capacity of the greenhouse soil. By comparing the density and specific heat capacity of the soil from the side, the heat storage capacity of the greenhouse soil will be between 1029600 and 2144200 joules; considering the structural difference between loam and loess, the heat storage capacity of the greenhouse soil will be much greater than 1029600 joules; also considering the structural difference between clay and loam, the heat storage capacity of the greenhouse soil will be much less than 2144200 joules, which is located in the middle of this area. This range is consistent with the value of 1594261.1494 J / ℃·m calculated as an example in the patent application of this invention. 3 It is relatively close, indicating that the test results of this application are reasonable.

Claims

1. A method for determining the heat storage capacity of soil in a solar greenhouse is characterized by: The following steps are involved: Step 1: Set up a heat flux plate on the floor of the solar greenhouse to measure the heat flux density of the soil at different times at night; Step 2: Integrate the heat release of the soil in the time direction to calculate the heat release of the soil at night (∫(Q)); Step 3: Temperature sensors are set at different depths of the soil on the ground and below the ground to calculate the temperature difference (ΔT) of the soil at different depths at the beginning and end of soil heat release; Step 4: Integrate the temperature difference between the beginning and the end of heat release in the vertical direction to calculate the temperature drop of the entire soil layer at night (∫(ΔT)); Step 5: ∫(Q) / ∫(ΔT) is 1m 3 The heat released when the soil temperature changes by 1°C is the heat storage capacity of the soil.

2. The method for determining the heat storage capacity of soil in a solar greenhouse according to claim 1 is characterized in that: The measurements at different times of the night in step 1 refer to measurements taken 10-15 times per hour from 6 pm to 6 am, and the average of the 10-15 measured temperatures represents the temperature of that hour.

3. The method for determining the heat storage capacity of soil in a solar greenhouse according to claim 1 is characterized in that: The temperature sensors are arranged in a vertical direction below the ground, and are arranged in sequence every 0.08m-0.12m from the ground downward, and 6-8 measuring points are set.

4. The method for determining the heat storage capacity of soil in a solar greenhouse according to claim 1 is characterized in that: The heat flux plate is set in the middle of the solar greenhouse, where the middle refers to the area excluding the inner side of the gables on the east and west sides of the solar greenhouse, the south side of the north wall, and the south side of the greenhouse close to the soil outside the greenhouse, which are set as measuring points.

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