JP2011020043A - Aeration method and water drop pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aeration method and a water drop pipe, capable of obtaining a high aeration effect at a low cost. <P>SOLUTION: In the aeration method for accelerating aeration by dropping water, a plurality of air holes 4b are formed at the part projected above a water surface of the water drop pipe 4 inserted in the water for a fixed length, and water is poured in through a gradually widened part 4a installed at the upper part of the water drop pipe 4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an aeration method that promotes aeration by falling water and a falling pipe.

  The problem of hypoxia such as urban rivers, lakes and aquaculture ponds in Southeast Asia into which a large amount of domestic wastewater flows is highlighted. In order to prevent such deterioration of water quality due to poor oxygenation in water areas, various methods have been studied (see Non-Patent Documents 1 to 7 and Patent Documents 1 to 5). Specifically, examination of the effect of re-aeration by the flow over the overflow weir installed in the river channel (see Non-Patent Documents 1 and 2), examination of the aeration effect by microbubbles (see Non-Patent Documents 3 and 4), Study to promote oxygen dissolution by enlarging the liquid interface to the limit (see Non-Patent Documents 6 and 7), trying to promote aeration by injecting the gas-liquid mixture onto the baffle plate to increase the contact area of the gas-liquid And the like (see Patent Document 3). These techniques for preventing hypoxia include (1) a method in which compressed air obtained by a compressor is discharged from an underwater diffuser, and a method in which oxygen is supplied from the atmosphere by stirring the vicinity of the water surface with an underwater propeller, etc. Method), (2) Method of aeration by falling water by installing a paragraph or weir in the waterway (method of using natural head), (3) Discharging microbubbles generated by special equipment into water It can be classified into methods.

JP 2001-70773 A JP 2003-265938 A JP 2004-188263 A JP 2000-61489 A JP 2007-307530 A

Nagakatsu Fumi: Research on re-aeration capability in the fall head construction, Deer University agricultural report, 47, pp.37-41, 1997. Yukio Sumimoto, Ken Mori, Eiji Inoue, Tomokazu Haraguchi: Oxygen re-aeration model with falling water over the weir, Kyushu University Agricultural Journal, 57 (1), pp.59-65, 2002. Koji Oku, Toru Kanda, Hirofumi Taisei, Masahito Moriguchi, Masakazu Matsuo, Shizutoshi Shirasawa, Katsumi Matsuo: Water quality improvement and purification efficiency of eutrophication reservoirs by microbubbles, Journal of Hydraulic Engineering, Vol. 45, pp.1201 -1206, 2001. Ikeda, Yuichi, Sasaki, Toshinori, Suga, Junzo: Fundamental experiment on flow pattern and oxygen supply of aeration circulation flow using microbubble generator in bi-stratified waters, Journal of Hydraulic Engineering, Vol.45, pp.1213-1218 , 2001. Satoshi Toyoshima, Kunihiko Amano, Yasuyasu Tanaka: Field observation and evaluation of stratification failure due to aeration circulation in a dam reservoir, Journal of Hydraulic Engineering, Vol. 47, pp.1243-1248, 2003. Takanori Oku, Masayoshi Haneda, Toshio Harada, Tetsuhiko Fujisato, Mabuchi: Research on hydraulics of water purification technology, 61st Annual Conference of Japan Society of Civil Engineers, pp.395-396, 2006. Hanedano Yasuyoshi, Mabuchi, Imai Tsuyoshi, Fujisato Tetsuhiko, Harada Toshio: Fundamental research on DO improvement technology using liquid film, JSCE G, 63 (1), pp.1-11, 2007.

  However, according to the prior art of (1) above, electrical machine devices with relatively high initial and running costs are required. Further, the conventional technique (2) has a drawback that the aeration effect is weak at a point where a sufficient amount of falling water cannot be obtained. Further, the conventional technology (3) has a special microbubble generator and is expensive.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an aeration method and a water pipe that can provide a high aeration effect at low cost.

  A first feature of the present invention is an aeration method in which aeration is promoted by falling water, wherein a plurality of air holes are provided on a portion of the falling water pipe inserted into the water for a certain length and are provided above the falling water pipe. It is to pour water through the gradually expanded part.

  A second feature of the present invention is that in the aeration method, the height position of the lower end of the waterfall pipe is a height position near the water surface, and the lower end of the waterfall pipe is in the atmosphere due to disturbance of the water surface due to waterfall. The height position is not exposed.

  A third feature of the present invention is that, in the aeration method, a flow rate at which a re-aeration coefficient indicating an aeration effect has a peak value is obtained in advance based on the Froude number, and water is poured into the drain pipe at the obtained flow rate. is there.

  According to a fourth aspect of the present invention, in the aeration method, when water is dropped using a natural head, the air hole is installed within the head range and in the vicinity of the highest position of the water pipe. That is.

  According to a fifth feature of the present invention, in the falling pipe used in the aeration method for promoting aeration by falling water, a plurality of air holes are provided in the middle of the circular pipe, and the pipe diameter gradually increases from one end to the other end of the circular pipe. It is to provide the one end of the said circular pipe with the gradually enlarged part expanded.

  A sixth feature of the present invention is that the waterfall pipe is provided with the plurality of air holes on the downstream side of the gradually expanding portion.

  ADVANTAGE OF THE INVENTION According to this invention, the aeration method and the water pipe which can obtain the high aeration effect at low cost can be provided. Therefore, it is possible to effectively aerate water areas such as aquaculture farms and reservoirs that have become hypoxic due to deterioration of water quality, thereby improving water quality.

It is a figure which shows the structure of the aeration apparatus (experimental apparatus) which concerns on embodiment of this invention. It is a figure which shows the structure of the waterfall pipe which concerns on embodiment of this invention. It is a figure which shows the experimental result which concerns on embodiment of this invention. It is a figure which shows the difference in the aeration effect by the difference in falling water height. It is a figure which shows the experimental result which concerns on embodiment of this invention. It is a figure which shows the experimental result which concerns on embodiment of this invention. It is a figure which shows the experimental result which concerns on embodiment of this invention. It is a figure which shows the experimental result which concerns on embodiment of this invention. It is a figure which shows the experimental result which concerns on embodiment of this invention. It is a schematic diagram of the flow condition in the air hole installation method which concerns on embodiment of this invention. It is a figure which shows an example of the utilization scene of the aeration apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the utilization scene of the aeration apparatus which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The present invention experimentally examines and proposes a method for improving the effect, taking into account the aeration caused by the overflow from the overflow weir and the paragraph in the water channel (hereinafter referred to as the “waterfall method”). However, the present invention is not intended only for a water channel where a head can be obtained, but is aimed at a wide general application such as an aquaculture pond or a natural flow-down resource-saving / energy-saving sewage treatment apparatus. In addition, it should be noted that there is no research on the aeration method using the circular tube handled in the present invention as far as the present inventors know. In this report, only the case where the waterfall pipe is a circular pipe was experimentally verified. However, when the cross section of the waterfall pipe such as a rectangle is different, the effect is considered in terms of mechanism, but a similar aeration improvement effect is considered to occur.

  In the experiment, first, a series of experiments will be conducted to clarify the aeration effect of the falling water method using a circular pipe. Then, we propose an aeration method (hereinafter referred to as air hole installation method) in which air holes are installed in a circular pipe, and clarify the aeration improvement effect and mechanism of the method.

<Outline of experiment>
The size of the circular pipe of the experimental device used in the present invention is kept in mind as a prototype to be used at this size in the field, but it can be applied in the field with a larger water area by examining the similarity law of the flow in the full pipe state Can be increased in size.

(1) Experimental apparatus and method An acrylic water tank 1 having a length of 27 cm, a width of 120 cm and a height of 80 cm as shown in FIG. 1 was used for the experiment. Two submersible pumps installed in the aquarium 1 were used to supply water for dropping into the aquarium 1. The water in the water tank 1 was raised to a certain height through a water supply pipe 2 made of vinyl chloride having a diameter of 25 mm connected to a submersible pump, and then dropped into the water tank 1 through a junction 3 and a waterfall pipe 4 of a vertical circular pipe. In addition, when the falling pipe 4 was smaller than the pipe diameter of the water supply pipe 2, it connected using the gradual contraction pipe, and when larger, the gradual expansion pipe was used. In the experiment, various quantities such as pipe diameter, flow rate, and falling water height (height from the water surface to the lower end of the falling water pipe 4) can be set arbitrarily. The flow rate was measured with a flow meter installed in the water pipe 2.

At the start of the experiment, sodium sulfite was added to the water tank 1 to consume oxygen in the water, and the amount of dissolved oxygen was reduced to near zero. After that, when the falling water is started, aeration of the water in the tank 1 is promoted as the falling time elapses, and the dissolved oxygen concentration C _L increases from C _L = 0, and finally the water in the tank 1 becomes the saturated oxygen concentration C _S. Reach and stabilize. In the experiment, a DO meter and a water temperature meter for measuring the aeration effect were installed at a depth of 25 cm in the tank 1 and 30 cm from the middle to the left (see Fig. 1), and measurements were taken every 30 seconds from the start of the experiment. It was confirmed by visual observation during the experiment that the measurement position was not directly affected by air bubbles formed in the water tank 1 due to falling water. In this experiment, the water dropped from the waterfall pipe 4 locally aerated the water in the water tank 1, and the DO concentration in the water tank 1 including the measurement point is increased by subsequent advection. That is, the DO concentration at the measurement point does not necessarily indicate an average value in the water tank 1. However, if the aeration effect of the proposed method is high, it will be reflected in the DO value at the measurement point, so the aeration effect was simply investigated using the value of the DO meter at a fixed point.

The change over time of dissolved oxygen (DO) concentration in tank 1 due to aeration of falling water is expressed by the following equation.

Here, a C _L dissolved oxygen concentration of water in the water tank 1, C _S is the saturation dissolved oxygen concentration, K ₂ is re-aeration coefficient, t is the elapsed time after the start overboard. [Equation 1] is generally derived on the assumption of aeration from the entire surface of the water, and strictly speaking, it does not reproduce the aeration mechanism of the proposed method. However, it can be used to represent the average aeration effect of this method. In addition, the same method has been adopted in the past for evaluation of aeration due to falling water from the weir (see Non-Patent Documents 1 and 2).

In this experiment, the re-aeration coefficient K ₂ is obtained and compared for evaluation of the aeration effect due to falling water under various conditions. In the calculation of K ₂ , data of a region where C _L is 10 to 80% of C _S , in which C _L is stably increased from the C _L -t curve obtained by experiment, was used. . And substituting these data into the following equation by integrating the equation (1), and the value of K ₂ with the average value is obtained.

Here, A = (C _S −C _L ) / (C _S −C ₀ ), C ₀ is the dissolved oxygen amount at the start of measurement, and generally C ₀ = 0.

(2) Outline of the waterfall pipe 4 and parameters governing the phenomenon FIG. 2 shows the waterfall pipe 4 which is a circular pipe used in this experiment. As shown in the figure, in the present invention, experiments were conducted on two patterns.

  Pattern A is a falling water method, and is a case where the flow rate Q is freely dropped at a falling height H from the tip of the falling pipe 4 having a pipe diameter D, as shown in FIG. The experimental result of this pattern A serves as a reference for examining the effect of pattern B described later. On the other hand, as shown in FIG. 2 (b), the pattern B is the same as the falling water method in that the flow rate Q flows from the tip of the falling pipe 4 with the diameter D, but the falling pipe 4 is inserted into the water for the length of L. In the above, n air holes 4b having a diameter d are provided at the position of the opening height l and air is caused to flow into the pipe to improve the re-aeration effect. However, a gradual expansion portion 4a is provided at the upper part of the waterfall pipe 4 so as to promote the mechanism described later. In this report, this pattern B method is called the air hole installation method.

In the present invention, as a factor governing the aeration phenomenon, the total water energy E defined by the lower end of the waterfall pipe of the following equation is adopted using the flow rate Q, the waterfall height H, the pipe diameter D, and the waterfall cross section A for the pattern A. .

  Here, the first term on the right side is the kinetic energy of falling water, and the second term is the potential energy.

  On the other hand, in the pattern B, since air flows in from the air hole 4b having the opening height l, the pressure inside the pipe can be approximately regarded as atmospheric pressure (p = 0). Therefore, it is assumed that the total falling water energy E can be calculated by replacing H in [Equation 3] with l (H = l).

  In the present invention, E is considered as a parameter governing the phenomenon. Although E is considered to be a main parameter, strictly speaking, it is necessary to consider the influence of other parameters such as the pipe diameter D. However, since the main purpose of this report is to clarify the effect of the proposed air hole installation method, the following discussion will proceed using only E.

《Experimental results and discussion》
The experimental results and discussion on the aeration effect in the experiment of pattern A and pattern B are shown.

(1) Experiment and Consideration of Pattern A (Water Falling Method) Table 1 shows a list of pattern A test conditions. As shown in the table, in the experiment, the pipe diameter D was set to two types of 20 mm and 30 mm, and the flow rate Q and the falling water height H were changed.

FIG. 3 shows the relationship between the total energy E and the re-aeration coefficient K ₂ from the experimental results of case 4 (D = 30 mm, flow rate Q = 90 l / min). From the figure, it can be seen that K ₂ increases as E increases (fall water height H increases). In the figure, when the water pipe 4 is in contact with the water surface (H = 0), it is K _{2 to} 0. This is because the contact area between the water and the atmosphere is almost 0, so the aeration effect is extremely high. It means small (E is small, so water surface disturbance is small). In addition, it can be seen that in the region where the falling water height H is small (H = 0, 1 cm), K ₂ rapidly increases relative to E. This is considered to be because, in the same region, when the falling water height H increases, the contact area between the falling water and the atmosphere increases and the amount of horizontal entrainment of air increases. In addition, as a result of the air mixed in the falling water thus forming air bubbles in the water, aeration in the water occurs. The increase mechanism of the re-aeration coefficient K ₂ at this time is assumed to be mechanism I (see FIG. 4 (a)).

On the other hand, the increase of K ₂ with respect to E in the region where H is large is not only due to the air entrainment of mechanism I, but also air contamination due to turbulence of falling water veins, and air contamination due to disturbance of the water surface due to an increase in water falling velocity due to gravity. , Etc. Such a mechanism of increasing K ₂ is referred to as mechanism II (see FIG. 4 (b)). However, it is recognized that the increase in K ₂ relative to E is small in this region. This is because the aeration effect due to air entrainment decreases as the H increases, the air resistance to falling water increases, the air bubbles in the water mass falling in the tank 1 increase, and the buoyancy effect increases. Possible causes such as an increase.

FIG. 5 is a plot of all data from the experiments in Table 1. Trend of E- K ₂ curves for each experiment case flow Q, is found to be similar to Figure 3 regardless of the pipe diameter D. FIG. 6 shows the result of deleting the region where the aeration phenomenon of mechanism I is considered from the data in FIG. 5, that is, data of H = 0 cm and 1 cm. In the same figure, data of a region where the aeration phenomenon of mechanism II occurs is plotted. As shown in the figure, in the mechanism II region, K ₂ increases with an increase in E, but the equation representing the average relationship of the portion surrounded by the alternate long and short dash line including all data in the region is given by the following equation: It is done.

In addition, although data of H = 0 cm and 1 cm in which K ₂ rapidly increased was handled as the region of mechanism I, it is considered that the region division of mechanism I and mechanism II changes depending on the experimental conditions. However, in order to accurately divide both areas, detailed additional studies on both mechanisms are necessary. Therefore, in the present invention, priority is given to engineering applications, and qualitative but simple region segmentation is performed.

(2) Experiment and Consideration of Pattern B (Air Hole Installation Method) In this section, an experimental example of the aeration effect of Pattern B (air hole installation method) proposed in this report is shown. FIG. 7 shows a comparison between an example of the experimental result regarding pattern B and the experimental result of pattern A (the region surrounded by the one-dot chain line in FIG. 6 is shown as a shaded portion). In the experiment of pattern B shown in the figure, the flow rate is Q = 90 l / min, the pipe diameter is D = 50 mm (the gradual expansion part 4a with a diameter from 25 mm to D = 50 mm is installed on the upper part of the falling pipe), the opening height l = 10 cm, the air hole The diameter d = 11 mm, the number of air holes n = 6, and the penetration depth L of the circular pipe is changed to obtain K ₂ .

From FIG. 7, it can be seen that when L is an appropriate size, the value of K ₂ increases to about 4 to 5 times as compared with the experiment of pattern A, and the aeration effect is remarkably improved. In addition, the experimental data of ● in the shaded part in the figure is the same as the experiment of pattern B adopted as a comparison example, and after adopting the same Q and D, H = l = 10 cm, This is to clarify the difference in aeration effect. On the other hand, when L becomes sufficiently large (here, L = 45 cm), it can be seen that K ₂ = 0. This is because the air that has flowed into the pipe from the air hole 4b enters the water and then re-floats in the pipe, so that the water tank 1 cannot be effectively aerated. As described above, it has been clarified that the air hole installation method is influenced by the penetration depth L, although it significantly improves the aeration effect.

Table 2 shows a list of experimental conditions and results that were carried out by changing the flow rate Q and penetration water depth L with a constant pipe diameter D = 50 mm, opening height l = 10 cm in order to systematically investigate the aeration improvement effect of the air hole installation method. Shown in Also, the experimental results in the same table are shown as a three-dimensional graph in FIG. 8 (a). From the figure, it is understood that the re-aeration coefficient K ₂ has a peak value with respect to the flow rate Q when the penetration water depth L is constant. This is because in a region where Q is large, the air flows in a full tube state (a state in which the inside of the tube is filled with water and flows), and therefore K ₂ is reduced because air cannot flow in from the air holes 4b. . On the other hand, since E is small in the region where Q is small, not only the aeration effect is small in the first place, but also the aeration effect improvement mechanism in the air hole installation method described later does not function, so K ₂ is considered to be small. It can also be seen that K ₂ decreases as L increases. This is due to the re-levitation of air in the tube as described above. Therefore, it is considered that the aeration effect becomes higher as L is smaller in a range where the lower end of the falling water portion is not exposed to the atmosphere due to disturbance of the water surface due to falling water.

FIGS. 8 (b) and (c) show three-dimensional graphs of experimental results for K ₂ when only l is increased to l = 30 cm and l = 50 cm in the experimental conditions of Table 2. . From the figure, the aperture height l is increased, overall K ₂ that is increased, the Q giving the peak value of K ₂ is increased, the area of Q where K ₂ is increased becomes larger, L increases But we can see that the decrease in K ₂ is small. This is because when l increases, the inflow of air from the air hole 4b into the waterfall pipe 4 is promoted (see the mechanism described later), the contact time of air and water in the waterfall pipe 4 increases, and the mixing of both becomes stronger. There seems to be a main reason. It should be noted that one of the causes is that the total energy E of falling water increases as l increases.

《Mechanism for improving aeration effect》
The mechanism that improves the aeration effect of the proposed pattern B is discussed by visualizing the flow.

(1) Observation of flow by visualization Table 3 shows a list of experimental conditions for experiments observed by visualization of flow. As shown in the table, the flow rate Q is 70 l / min and the tube diameter D is 5 cm in all experiments.

  Photo 1 (see Fig. 9 (a)) is a visualization of the flow of CASE I (Pattern A) with a falling water height H = 10 cm. From the photograph, it is recognized that the falling water is mild and the aeration effect is weak. The pipe flow is full.

  Photo-2 (see Fig. 9 (b)) is a visualization photo of CASE II (Pattern B), with an intrusion depth of L = 5cm and an opening height l equal to the falling height H of CASE I (H = l = 10cm). In this case, the aeration effect is greatly improved in spite of the fact that the total amount of falling water E is the same as CASE I, that is, the remarkable aeration improvement effect of the air hole installation method is visualized. In CASE I, it flowed in a full pipe immediately after the start of the experiment, whereas in CASE II, it did not flow in a full pipe during the experiment for about 30 minutes. This means that the mechanism for improving aeration functions in CASE II.

  Photo-3 (see Fig. 9 (c)) is a visualization photo of CASE III (pattern B). The opening height l is set to 1 = 55cm higher than CASE II, and other conditions are the same. Looking at the photo, compared to Photo-2, the air mass has penetrated to a deeper position, and the volume of the water mass containing air bubbles is larger, so a higher aeration effect can be obtained. It is possible to infer that This is thought to be because the aeration improvement mechanism described later works more effectively in addition to the increase in E when l increases.

(2) Consideration of the mechanism for improving the aeration effect The video of the CASE III experiment in which the aeration improvement effect of the air hole installation method shown in Table 3 is strong was video-recorded and replayed to observe the flow state. The flow of the falling water pipe 4 obtained by observation and the mechanism for improving the aeration effect are shown in the following list. Note that the falling water behavior is schematically shown in FIG.

(I) Air enters from the air hole 4b toward the gradually expanding portion 4a (25 mm → 50 mm) of the falling pipe 4. Further, when the water that reaches the gradually expanding portion 4a from the water pipe 2 falls into the water pipe 4 having a large pipe diameter, peeling and reattachment phenomenon from the pipe wall occur due to the Coanda effect (see FIG. 10 (a)). The positions of the separation point and the reattachment point are not stable, and the flow axis becomes unstable.

(II) The flow with the flow axis destabilized falls down the pipe 4 while rotating clockwise or counterclockwise (see Fig. 10 (a)) along the wall of the pipe 4 It shows irregular and intermittent behavior such as falling in the center (see Fig. 10 (b)). As a result, the falling water stream is intertwined.

(III) Falling water that exhibits complex and intermittent behavior causes strong turbulence and sufficiently mixes the air flowing in from the air holes 4b, resulting in white turbidity. On the other hand, the entangled flow is separated into an air mass and a cloudy water mass in the waterfall pipe 4 (see FIG. 10 (c)).

(IV) When the air mass falls into the water, it is pushed into the water tank 1 by the subsequent water mass. That is, the air mass becomes air bullets and intermittently enters the water tank 1. At this time, the water in the aquarium 1 is strongly aerated due to the falling water containing sufficient air and the intrusion of intermittent air bullets into the aquarium 1. Photo-3 visualizes the behavior when air bullets penetrate deeply into the water.

<Summary>
The present invention proposes an air hole installation method using a circular pipe as an aeration method, and experimentally verifies its effect. It has been found that the air hole installation method proposed by the present invention provides an aeration effect that is about 4 to 5 times stronger than the case where the air hole 4b is not installed. This is because the air taken in from the air holes 4b is mixed into falling water that is violently disturbed due to the Coanda effect, and aerial bullets are intermittently formed in the falling water pipe 4 and pushed into the water tank 1. It turns out that the mechanism of improvement works.

  In order for the mechanism of the aeration improvement effect of the proposed method to function, it is clear that the penetration depth L should be shorter although the lower end of the downfall pipe 4 is not exposed from the water surface affected by disturbance. It was. On the other hand, it has been clarified that there is an optimum flow rate range for the flow rate Q. Further, the larger the opening height l, the more advantageous, but it should be noted that a larger amount of falling water energy E is required. Therefore, when a natural head is used in a local area such as an aquaculture pond, it is sufficient to increase l. However, when water is generated using a pump, there is a limitation due to the output of the pump from the viewpoint of economy.

  As described above, in the present invention, a plurality of air holes 4b are provided in the portion of the waterfall pipe 4 inserted into the water for a certain length and are exposed on the water surface, and the water is passed through the gradually expanding portion 4a provided at the top of the waterfall pipe 4. I try to pour in. As a result, a high aeration effect can be obtained at a low cost, and it becomes possible to effectively aerate water areas such as aquaculture farms and reservoirs that have become oxygen-depleted to improve water quality.

  In other words, the feature of this construction method is that a special and expensive mechanical device for performing aeration is unnecessary. In particular, it is possible to enhance the aeration effect by performing a little work on the water supply pipe at a point where natural waterfall height can be obtained by using topography at a farm or the like (see FIG. 11). Moreover, as shown in FIG. 12, a high aeration effect can be expected only by installing the drain pipe 4 in the overflow weir 10 or the like in the water channel. In this case, the number of the water pipes 4 is not particularly limited. In consideration of the width of the overflow weir 10 and the installation cost, an appropriate number of water pipes 4 may be installed. As described above, the present invention is low-cost for problems such as deterioration of water quality caused by hypoxia in water areas, which have been a problem in recent years, such as off-flavors, generation of toxic algae, deterioration of living environment, deterioration of aquatic ecosystems, etc. The invention can be applied to a wide range and has a very high practical value.

Incidentally, in the above, although when the penetration depth L and constant re-aeration coefficient K ₂ has been described as having a peak value relative to the flow rate Q, the peak value can be analyzed using the Froude number F _l. Froude number F _l, the flow rate v of the falling water pipe 4, the gravitational acceleration g, using a pipe diameter D is expressed by the following equation. Furthermore, if the cross-sectional ratio of the falling water pipe 4 is taken into consideration, it becomes possible to analyze with higher accuracy. Previously obtained in advance based on the flow rate re-aeration coefficient K ₂ has a peak value in the Froude number F _l, the may be provided flow regulating mechanism for pouring water into drainage tube 4 at a flow rate determined as a matter of course.

DESCRIPTION OF SYMBOLS 1 Water tank 2 Water supply pipe 3 Merging part 4 Falling pipe 4a Gradual expansion part 4b Air hole H Falling height l Opening height L Penetration depth Q Flow rate

Claims (6)

An aeration method that encourages aeration by falling water,
A method of aeration, characterized in that a plurality of air holes are provided in a portion of a waterfall pipe inserted into the water for a fixed length and that protrudes from the surface of the waterfall, and water is poured through a gradual expansion part installed in the upper part of the waterfall pipe.   The height position of the lower end of the water pipe is a height position in the vicinity of the water surface, and is a height position at which the lower end of the water pipe is not exposed to the atmosphere due to disturbance of the water surface due to water falling. The aeration method according to 1.   The aeration method according to claim 1, wherein a flow rate at which a re-aeration coefficient indicating an aeration effect has a peak value is obtained in advance based on the Froude number, and water is poured into the drain pipe at the obtained flow rate.   2. The aeration method according to claim 1, wherein when water is dropped using a natural head, the air hole is installed within the head range and in the vicinity of the highest position of the water pipe. A drain pipe used in an aeration method for promoting aeration by falling water,
A drainage pipe having a plurality of air holes in the middle of the circular pipe and a gradually expanding portion at one end of the circular pipe having a pipe diameter gradually expanding from one end to the other end of the circular pipe.   The falling pipe according to claim 5, wherein the plurality of air holes are provided on the downstream side of the gradually expanding portion.