A method and device for obtaining a gas mass transfer coefficient at a canal water-gas interface

Abstract

The application discloses a kind of canal water-gas interface gas mass transfer coefficient acquisition method and device, comprising: placing wave height instrument on target canal and its tributary, monitoring river wave shape;According to the wave shape monitored by Fourier transform, the characteristic wave period of target canal and its tributary is obtained;According to the characteristic wave period of target canal and its tributary, the mean square slope dominated by ship wave of target canal is calculated, and the mean square slope dominated by wind wave is calculated;Based on the mean square slope dominated by ship wave and the grade of target canal, the gas mass transfer coefficient branch mediated by ship wave is calculated;According to the mean square slope dominated by wind wave, the gas mass transfer coefficient branch mediated by wind wave is calculated;Ship wave-mediated gas mass transfer coefficient branch and wind wave-mediated gas mass transfer coefficient branch are added, and as the water-gas interface gas mass transfer coefficient of target canal.The application has high accuracy and high reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental science and atmospheric research, and particularly relates to a method and device for obtaining gas mass transfer coefficient of water-air interface of a canal. BACKGROUND

[0002] The exchange flux of greenhouse gases at the water-air interface is widely determined by the thin boundary layer method (TBL). TBL is based on the semi-empirical calculation of the gas concentration gradient between the water-air two phases and the given environmental gas mass transfer coefficient, wherein the gas mass transfer coefficient is a key factor for quantifying the gas exchange flux, and its calculation still has great uncertainty. Therefore, how to accurately quantify the mass transfer coefficient has become the focus and difficulty of calculating the gas exchange flux. Traditionally, the wind speed above the water surface is used to calculate the mass transfer coefficient, but for rivers without wind and complex scenes, the calculation error is large, and it is not universally applicable. CN209069555U develops an experimental device for studying the influence of raindrops on gas mass transfer coefficient. In addition to the influence of wind speed, the impact of raindrops on the water surface in the environment is taken as an influencing factor of the gas mass transfer coefficient to improve the calculation accuracy of the water-air interface mass transfer coefficient. Although this method takes into account the influence of raindrops on the gas mass transfer coefficient, for canals which are greatly affected by human factors, compared with the fluctuation of the water surface caused by the falling of raindrops, the fluctuation of the water surface caused by strong ship activities is larger and more intense, and the water surface is in a state of continuous fluctuation, which has a potential influence on the gas mass transfer coefficient. At present, the influence of shipping disturbance on the gas mass transfer coefficient of the canal is not clear. SUMMARY

[0003] The present application provides a method and device for obtaining gas mass transfer coefficient of water-air interface of a canal, which has the advantages of high accuracy and high reliability.

[0004] Technical scheme: The method for obtaining gas mass transfer coefficient of water-air interface of a canal provided by the present application comprises the following steps:

[0005] Placing a wave height instrument on the target canal and its tributaries, and monitoring the river wave form by using the wave height instrument;

[0006] Obtaining the characteristic wave period of the target canal and its tributaries by Fourier transform according to the monitored wave form of the target canal and its tributaries;

[0007] Calculating the characteristic wave wave number of the target canal and its tributaries according to the characteristic wave period of the target canal and its tributaries, and solving the mean square slope dominated by the ship wave of the target canal according to the wave number of the target canal, and solving the mean square slope dominated by the wind-generated wave of the target canal according to the characteristic wave wave number of the tributaries;

[0008] The ship wave mediated gas mass transfer coefficient branch is calculated based on the mean square slope dominated by the ship wave and the target canal grade;

[0009] The wind wave mediated gas mass transfer coefficient branch is calculated according to the mean square slope dominated by the wind wave;

[0010] The ship wave mediated gas mass transfer coefficient branch and the wind wave mediated gas mass transfer coefficient branch are added, and the water-gas interface gas mass transfer coefficient of the target canal is obtained.

[0011] Further, the calculation method for calculating the characteristic wave wave number of the target canal and its tributaries according to the characteristic wave period of the target canal and its tributaries is:

[0012]

[0013]

[0014] In the formula, The characteristic wave wave number of the target canal and its tributaries is represented by h1 and h2, g is the acceleration of gravity, and T1 and T2 represent the characteristic wave period of the target canal and its tributaries.

[0015] Further, the calculation method for calculating the mean square slope dominated by the ship wave of the target canal according to the wave number of the target canal is:

[0016]

[0017] In the formula, s1 2 The mean square slope dominated by the ship wave of the target canal is represented by h1 and h2, g is the acceleration of gravity, and T1 and T2 represent the characteristic wave period of the target canal and its tributaries. The characteristic wave wave number of the target canal is represented.

[0018] Further, the calculation method for calculating the mean square slope dominated by the wind wave of the target canal according to the wave number of the tributary is:

[0019]

[0020] In the formula, s2 2 The mean square slope dominated by the wind wave of the target canal is represented by h1 and h2, g is the acceleration of gravity, and T1 and T2 represent the characteristic wave period of the target canal and its tributaries. The characteristic wave wave number of the tributary is represented.

[0021] Further, the calculation method for calculating the ship wave mediated gas mass transfer coefficient branch based on the mean square slope dominated by the ship wave and the target canal grade is:

[0022] S_k 600 * = α (0.0014s1 2 + 3.4 × 10 -6 )

[0023] S_k 600 * denotes the branch of gas transfer coefficient mediated by ship-generated wave, denotes the correction coefficient, H max denotes the maximum navigable tonnage of the target canal, H max,D denotes the maximum navigable tonnage of the area where the wave height instrument is located, s1 2 denotes the mean square slope dominated by the ship-generated wave of the target canal.

[0024] Further, the calculation method for calculating the branch of gas transfer coefficient mediated by wind-generated wave according to the mean square slope dominated by wind-generated wave is:

[0025] W_k 600 * = 0.0014s2 2 + 3.4x10 -6

[0026] W_k 600 * denotes the branch of gas transfer coefficient mediated by wind-generated wave, s2 2 denotes the mean square slope dominated by wind-generated wave.

[0027] The device for obtaining the gas transfer coefficient at the water-gas interface of the canal according to the present application comprises:

[0028] a wave height instrument placed on the target canal and its tributaries for monitoring the wave shape of the river;

[0029] a Fourier transform module for obtaining the characteristic wave period of the target canal and its tributaries through Fourier transform based on the monitored wave shape of the target canal and its tributaries;

[0030] a first calculation module for calculating the characteristic wave number of the target canal and its tributaries based on the characteristic wave period of the target canal and its tributaries, and solving the mean square slope dominated by the ship-generated wave of the target canal based on the wave number of the target canal, and solving the mean square slope dominated by the wind-generated wave of the target canal based on the characteristic wave number of the tributaries;

[0031] a second calculation module for calculating the branch of gas transfer coefficient mediated by ship-generated wave based on the mean square slope dominated by ship-generated wave and the grade of the target canal;

[0032] a third calculation module for calculating the branch of gas transfer coefficient mediated by wind-generated wave based on the mean square slope dominated by wind-generated wave;

[0033] a fourth calculation module for adding the branch of gas transfer coefficient mediated by ship-generated wave and the branch of gas transfer coefficient mediated by wind-generated wave, and taking the sum as the gas transfer coefficient at the water-gas interface of the target canal.

[0034] Beneficial effects: compared with the prior art, the present application has the remarkable advantages of high accuracy and high reliability, and can solve the problem of k 600 variation caused by various environmental mechanisms including wind speed and ship wave. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a flowchart of the method for obtaining the gas mass transfer coefficient at the water-gas interface of the canal provided by the present application;

[0036] Figure 2 is the layout of the research area and monitoring site of the canal and natural river;

[0037] Figure 3 is the result of comparative analysis of water surface waves and Fourier transform of the canal and natural river;

[0038] Figure 4 is the comparison of wind-generated wave and wind speed calculated gas mass transfer coefficient;

[0039] Figure 5 is the spatial distribution map of k600 mediated by ship disturbance in the canal in Jiangsu Province of Taihu Basin. DETAILED DESCRIPTION

[0040] The embodiment provides a method for obtaining the gas mass transfer coefficient at the water-gas interface of the canal, which calculates the gas mass transfer coefficient through the change of water surface wave, as shown in Figure 1 , comprising the following steps:

[0041] S1, placing a wave height meter on the target canal and its tributaries, and monitoring the river wave form by using the wave height meter.

[0042] The embodiment of the present application adopts wireless digital wave height meter monitoring, and the wave height meter is arranged according to the principle of "water surface undulating wave height does not submerge the monitoring probe", and uses YH-12 wireless data receiver and SDA100 sensor to receive and process wave signals respectively.

[0043] S2, obtaining the characteristic wave periods T1 and T2 of the target canal and its tributaries through Fourier transform according to the monitored wave form of the target canal and its tributaries.

[0044] S3, calculating the characteristic wave wave number of the target canal and its tributaries according to the characteristic wave periods of the target canal and its tributaries, and solving the mean square slope dominated by the ship wave of the target canal according to the wave number of the target canal, and solving the mean square slope dominated by the wind-generated wave of the target canal according to the characteristic wave wave number of the tributaries.

[0045] The shallow water wave speed v is calculated according to the following formula, and the characteristic wave length λ is obtained, and the calculation formula is:

[0046]

[0047] λ = v * T

[0048] In the formula, v is the shallow water wave speed, m / s; g is the acceleration of gravity 9.8 m / s 2 ; h is the water depth, m; λ is the characteristic wave length, m; T is the characteristic wave period, s; the wave number k is calculated from the shallow water wave length s , and the calculation formula is:

[0049]

[0050] In the formula, k s is the wave number, m- 1 ;

[0051] After rearranging the formula, we get

[0052] Therefore, according to the characteristic wave period of the target canal and its tributaries, the formula for calculating the characteristic wave number of the target canal and its tributaries is as follows:

[0053]

[0054]

[0055] In the formula, the characteristic wave number of the target canal and its tributaries is represented by h1, h2, the water depth of the target canal and its tributaries, g is the acceleration of gravity, and T1, T2 is the characteristic wave period of the target canal and its tributaries.

[0056] The water surface wave is divided into ship wave and wind wave, therefore, the calculation method of the mean square slope s1 2 dominated by the ship wave of the target canal is:

[0057]

[0058] The calculation method of the mean square slope s2 2 dominated by the wind wave of the target canal is:

[0059]

[0060] S4, based on the mean square slope dominated by the ship wave and the grade of the target canal, the gas mass transfer coefficient branch S_k 600 * mediated by the ship wave is calculated, and the calculation formula is as follows:

[0061] S_k 600 * = α (0.0014s1 2 + 3.4 × 10- 6 )

[0062] In the formula, denotes the correction coefficient, H max denotes the maximum navigable tonnage of the target canal, H max,D denotes the maximum navigable tonnage of the target canal, and the specific canal navigable capacity and parameters refer to the Inland Waterway Navigable Standard (GB50139-2014).

[0063] S5, the wind-generated wave-mediated gas mass transfer coefficient branch W_k is calculated according to the mean square slope dominated by the wind-generated wave 600 * , the calculation formula is as follows:

[0064] W_k 600 * = 0.0014s2 2 + 3.4x10 -6

[0065] S6, the water-surface wave-mediated gas mass transfer coefficient branch and the wind speed-mediated gas mass transfer coefficient branch are added, and the water-gas interface gas mass transfer coefficient of the target canal is obtained.

[0066] The water-gas interface gas mass transfer coefficient k 600 * of the target canal is obtained. 600 * = S_k 600 * .

[0067] The embodiment also provides a canal water-gas interface gas mass transfer coefficient acquisition device, comprising:

[0068] a wave height instrument placed on the target canal and its tributaries for monitoring the wave shape of the river;

[0069] a Fourier transform module for obtaining the characteristic wave period of the target canal and its tributaries through Fourier transform according to the monitored wave shape of the target canal and its tributaries;

[0070] a first calculation module for calculating the characteristic wave wave number of the target canal and its tributaries according to the characteristic wave period of the target canal and its tributaries, and solving the mean square slope dominated by the ship wave of the target canal according to the wave number of the target canal, and solving the mean square slope dominated by the wind-generated wave of the target canal according to the characteristic wave wave number of the tributaries;

[0071] a second calculation module for calculating the ship wave-mediated gas mass transfer coefficient branch based on the mean square slope dominated by the ship wave and the grade of the target canal;

[0072] a third calculation module for calculating the wind-generated wave-mediated gas mass transfer coefficient branch according to the mean square slope dominated by the wind-generated wave;

[0073] The fourth calculation module is configured to add the ship wave-mediated gas mass transfer coefficient branch and the wind wave-mediated gas mass transfer coefficient branch, and obtain the water-gas interface gas mass transfer coefficient of the target canal.

[0074] The device corresponds to the above method one by one, and the calculation method and the calculation formula correspond one by one. For details, refer to the description of the above method, and no further description is given.

[0075] The present application is experimentally verified as follows.

[0076] The canals in the Taihu Basin are selected as the objects. The Taihu Basin spans three provinces and one city of Jiangsu, Anhui, Zhejiang and Shanghai, with a basin area of 37,000 km 2 , and a water surface rate of 15% ( Figure 2 a). The Beijing-Hangzhou Grand Canal is taken as an example to carry out in-situ monitoring of ship disturbance, and its adjacent tributaries are taken as controls ( Figure 2 b). The Beijing-Hangzhou Grand Canal starts from Hangzhou in the south and reaches Beijing in the north, with a total length of 1797 km and a river width of 15-30 m. The ship traffic volume is large, and in 2014, the ship traffic volume reached 1.4 million. During the monitoring period, the ship traffic frequency of the Beijing-Hangzhou Grand Canal was about 1.3 min / time, plus the “superposition effect” of ship waves in the relatively narrow river, the water surface of the canal was in a state of continuous disturbance, with obvious amplitude, and the maximum wave difference of water level was as high as 14.6 cm ( Figure 3 a). In comparison, the non-navigable tributaries are only affected by natural wind, and the water surface disturbance is small, and the amplitude of the wind-generated wave formed is small, with an average wave difference of only 3.7 cm. After fast Fourier transform, the vibration periods of the navigation wave and the wind-generated wave are 2.3 and 7.1 s respectively ( Figure 3 c).

[0077] The present application is compared with the conventional wind speed calculation gas mass transfer coefficient, and the formula of the conventional wind speed calculation gas mass transfer coefficient is wherein U z is the wind speed monitored at a height of z meters from the water surface; C d10 is the drag coefficient at a height of 10 m; k is the von Karman constant; and z is the monitoring height of the anemometer.

[0078] The tributaries affected only by wind-generated waves are selected as the objects, and the wind-generated wave calculation gas mass transfer coefficient and the conventional wind speed calculation gas mass transfer coefficient are compared ( Figure 4 ). When the wind speed at a height of 1 m above the water surface is 1, 1.5, 2, 2.5, 3 and 3.5 m / s respectively, the k 600 based on wind-generated wave calculation is 2.03, 2.31, 2.64, 3.00, 3.40 and 3.83 cm / h respectively, and the k based on wind speed calculation is 2.36, 2.65, 3.02, 3.46, 3.97 and 4.54 cm / h respectively, and there is no significant difference between the two (R2 = 0.998, p < 0.01). Therefore, the k 600 value based on water surface wave has higher accuracy.

[0079] For ship wave, the k 600 value based on the navigation level of each canal was corrected by a, which was classified according to the size of the ship. The higher the level of the canal, the stronger the disturbance of the ship wave. According to the ship tonnage and the channel parameters of the inland waterway in the "Inland Navigation Standard" (GB50139-2014), the navigation capacity of the third, fourth, fifth and sixth level canals was 1000 t, 500 t, 300 t and 100 t, respectively. In this study, the third level canal of the Beijing-Hangzhou Canal was set to 1.0, and the fourth, fifth and sixth level canals were taken as 0.5, 0.3 and 0.1, respectively. The S_k 600 corresponding to the ship wave mediated was 3.42, 1.71, 1.06 and 0.34 cm / h, respectively. The spatial distribution of S_k 600 in the Jiangsu section of the Taihu Basin is shown in Figure 5 , indicating that the shipping activities have a wide impact on the Taihu River Network, and there is a significant spatial difference.

[0080] The above only discloses a preferred embodiment of the present application, which cannot limit the scope of the present application. Therefore, any equivalent changes made according to the claims of the present application are still within the scope of the present application.

Claims

1. A method for obtaining the gas mass transfer coefficient at the water-air interface in a canal, characterized in that... The method comprises: placing wave height meters on the target canal and its tributaries, and monitoring the waveforms of the canals by the wave height meters; obtaining the characteristic wave periods of the target canal and its tributaries by Fourier transform according to the monitored waveforms of the target canal and its tributaries; calculating the characteristic wave numbers of the target canal and its tributaries according to the characteristic wave periods of the target canal and its tributaries, and obtaining the mean square slope dominated by the ship wave of the target canal according to the wave number of the target canal, and obtaining the mean square slope dominated by the wind-generated wave of the target canal according to the characteristic wave number of the tributary; calculating the gas mass transfer coefficient branch mediated by the ship wave based on the mean square slope dominated by the ship wave and the grade of the target canal; calculating the gas mass transfer coefficient branch mediated by the wind-generated wave according to the mean square slope dominated by the wind-generated wave; adding the gas mass transfer coefficient branch mediated by the ship wave and the gas mass transfer coefficient branch mediated by the wind-generated wave, and taking the sum as the gas mass transfer coefficient of the water-gas interface of the target canal.

2. The method of claim 1, wherein: The calculation method for calculating the characteristic wave numbers of the target canal and its tributaries according to the characteristic wave periods of the target canal and its tributaries is: In the formula, wherein k represents the characteristic wave number of the target canal or branch, h1 and h2 represent the water depth of the target canal or branch, g represents the acceleration of gravity, and T1 and T2 represent the characteristic wave period of the target canal or branch.

3. The method of claim 1, wherein: The calculation method for obtaining the mean square slope dominated by the ship wave of the target canal according to the wave number of the target canal is: In the formula, s1 2 denotes the mean square slope of the target canal ship's wave dominance, denotes the eigen wave number of the target canal.

4. The method of claim 1, wherein: The calculation method for obtaining the mean square slope dominated by the wind-generated wave of the target canal according to the characteristic wave number of the tributary is: where s2 2 denotes the mean square slope of the target channel, denotes the eigen wave number of the tributary.

5. The method of claim 1, wherein: The calculation method for calculating the gas mass transfer coefficient branch mediated by the ship wave based on the mean square slope dominated by the ship wave and the grade of the target canal is: S_k 600 * = a (0.0014s1 2 + 3.4 x 10 -6 ) where S_k 600 * denotes the ship wave mediated gas mass transfer coefficient branch, denotes a correction factor, H max denotes the target canal maximum navigable tonnage, H max,D denotes the maximum navigable tonnage of the area where the wave height instrument is located, s1 2 denotes the target canal ship wave dominated mean square slope.

6. The method of claim 1, wherein: The calculation method for calculating the gas mass transfer coefficient branch mediated by the wind-generated wave according to the mean square slope dominated by the wind-generated wave is: W_k 600 * = 0.0014 s2 2 + 3.4 x 10 -6 where W_k 600 * represents the wind wave mediated gas mass transfer coefficient branch, s2 2 represents the wind wave dominated mean square slope.

7. A device for obtaining the gas mass transfer coefficient at the water-gas interface in a canal, characterized in that... It comprises: a wave height meter placed on the target canal and its tributaries for monitoring the waveforms of the canals; a Fourier transform module for obtaining the characteristic wave periods of the target canal and its tributaries by Fourier transform according to the monitored waveforms of the target canal and its tributaries; a first calculation module for calculating the characteristic wave numbers of the target canal and its tributaries according to the characteristic wave periods of the target canal and its tributaries, and obtaining the mean square slope dominated by the ship wave of the target canal according to the wave number of the target canal, and obtaining the mean square slope dominated by the wind-generated wave of the target canal according to the characteristic wave number of the tributary; a second calculation module for calculating the gas mass transfer coefficient branch mediated by the ship wave based on the mean square slope dominated by the ship wave and the grade of the target canal; a third calculation module for calculating the gas mass transfer coefficient branch mediated by the wind-generated wave according to the mean square slope dominated by the wind-generated wave; a fourth calculation module for adding the gas mass transfer coefficient branch mediated by the ship wave and the gas mass transfer coefficient branch mediated by the wind-generated wave, and taking the sum as the gas mass transfer coefficient of the water-gas interface of the target canal.

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