CN111981231A - Variable arc line and variable diameter tee joint based on dissipation function comparative analysis - Google Patents
Variable arc line and variable diameter tee joint based on dissipation function comparative analysis Download PDFInfo
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- CN111981231A CN111981231A CN202010173210.6A CN202010173210A CN111981231A CN 111981231 A CN111981231 A CN 111981231A CN 202010173210 A CN202010173210 A CN 202010173210A CN 111981231 A CN111981231 A CN 111981231A
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- pipe
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L41/00—Branching pipes; Joining pipes to walls
- F16L41/02—Branch units, e.g. made in one piece, welded, riveted
Abstract
The invention discloses an arc-variable and diameter-variable tee joint based on dissipation function comparative analysis. The method comprises the following steps: the pipe diameter of the straight-through pipe in the same direction as the main pipe is smaller than that of the main pipe, the straight-through pipe and the central pipeline of the main pipe are on the same horizontal line, the extending direction of the three-way branch pipe connected with the main pipe is 90 degrees to that of the main pipe, the pipeline connected with the straight-through pipe protrudes upwards, and the upward protruding direction of the pipeline connected with the main pipe is vertical to the original connecting direction. The invention has the effect of drag reduction under the design condition. And when the flow ratio of the three-way straight-through pipe to the branch pipe is changed, the height of the dimensionless arc line is changed
The optimum value of (b) is fixed within a certain range. The height of the arc line of the three-way connecting section can be reduced to a certain degreeThe resistance of the straight pipe section and the branch pipe section of the low tee joint can reach 38.05 percent at most.
Description
Technical Field
The invention relates to the technical field of pipeline local components, in particular to an arc-variable and diameter-variable tee joint based on dissipation function comparative analysis.
Background
In a ventilation air-conditioning system, the power consumption of the operation of a ventilation fan (a blower, a primary fan, etc.) is an important component of the energy consumption of the ventilation air-conditioning system. In china alone, the power consumed by a fan-powered system accounts for 10.4% of the total national power. Although the total amount of energy used is large, the per-person usage of energy is very low, even far below the average level of the world.
During the middle of the last century, particularly after the development of the science of computational fluid dynamics, a large number of researchers began conducting research into the calculation of the resistance of the local components of the pipe. In general, the predecessors have a certain research foundation for researching media such as air, water, steam and the like, or local component types such as elbows, valves, reducing pipes, tee joints and the like.
The three-way branch pipe is a very small local component of the ventilating and air-conditioning pipeline, but is indispensable in the field of ventilating and air-conditioning, and is an important air distribution and transportation device. Meanwhile, because of the large number of the tee joints in the building, the energy consumption caused by the generated local resistance is also huge, and the attention is worthy of being paid, but in the prior art, such as the tee joint in the Chinese patent CN201720349978.8, the resistance reduction research of the tee joint is not carried out on the tee joint.
Disclosure of Invention
The invention aims to provide an arc-variable and diameter-variable tee joint based on dissipation function comparative analysis, which aims to improve pipeline sections at an upstream connecting section and a downstream connecting section. However, few have studied energy savings from such conventional manufacturing processes for tee components, and no have studied how to improve this portion of the pipe section.
The technical scheme adopted for solving the technical problem is to provide a variable arc line and variable diameter tee joint based on dissipation function comparative analysis, which comprises the following steps: the pipe diameter of the straight-through pipe in the same direction as the main pipe is smaller than that of the main pipe, the straight-through pipe and the central pipeline of the main pipe are on the same horizontal line, the extending direction of the three-way branch pipe connected with the main pipe is 90 degrees to that of the main pipe, the pipeline connected with the straight-through pipe protrudes upwards, and the upward protruding direction of the pipeline connected with the main pipe is vertical to the original connecting direction.
In practical use, h represents the height of the convex (or concave) of the variable arc tee joint to be researched,
represents the length of the long side of the cross section of the downstream pipe of the tee,
the magnitude of (d) represents the degree of convexity or concavity of the section of pipe, positive values representing convexity and negative values representing concavity.
Is positive and is convex.
The three-way component is mainly suitable for the three-way pipe fitting with the flow ratio of (1-5): (1-3).
Due to engineering requirements, different tee joints cannot be used at different flow ratios under the same aspect ratio, and based on the consideration, a compromise method is adopted to put forward the concept of the recommended height of the resistance-reducing arc. Under the condition of different flow ratio (1: 3-5: 1), the height of the bulge is higher
When the molar ratio is not less than 0.1, the aim of reducing drag can be achieved.
The specific influence factors of the local resistance coefficients of the straight pipe section and the branch pipe section of the tee joint are analyzed, and dissipation items are compared
Dissipating work
Turbulent kinetic energy dissipation ratio
Convection term
And the local resistance coefficient of the tee joint, and obtaining: local coefficient of resistance of straight pipe
And rate of kinetic energy dissipation of turbulence
The influence is maximum, and can be controlled
To reduce
The value of (c). When the flow of the straight pipe is greater than that of the branch pipe, the local resistance of the branch pipe is subjected to the kinetic energy dissipation rate of turbulent flow
When the flow of the branch pipe is larger than or equal to that of the straight pipe, the local resistance coefficient of the branch pipe is more influenced by the convection term.
The invention has the beneficial effects that: the invention provides a resistance reducing method of a convex structure by imitating the structure of a Venturi tube, and the resistance reducing method is used in a tee joint to obtain a resistance reducing tee joint pipe fitting with a cambered surface deformation structure. The local resistance coefficients in two directions in the shunt tee are optimized, the resistance reduction effect of the optimized tee under different width-to-height ratios and flow ratios is analyzed, and a dimensionless arc height concept is provided. Compared with the traditional tee joint, the novel dimensionless arc tee joint has the local resistance coefficient of the straight pipe section， 
The highest resistance reduction rate of 38.05 percent and the local resistance of the branch section of the tee jointCoefficient of performance
The drag reduction rate can reach 30.62 percent.
Drawings
FIG. 1 is a schematic view of a typical building corridor plumbing arrangement in accordance with an embodiment of the present invention;
FIG. 2 is a height definition of a variable camber tee in accordance with an embodiment of the present invention;
FIG. 3 shows a tee of an embodiment of the present invention divided into three sections of volumes 1-3;
FIG. 4 is a graph of three straight pipe section drag reduction ratios at different flow ratios and different dimensionless camber line heights for an embodiment of the present invention;
FIG. 5 is a graph of three-way leg segment drag reduction at different flow ratios and different dimensionless arc heights for an embodiment of the present invention;
FIG. 6 is a corresponding relationship between the local resistance of the straight pipe section of the tee and each parameter according to the embodiment of the present invention;
FIG. 7 is a diagram illustrating the correspondence between the local resistance of the tee branch pipe section and various parameters according to an embodiment of the present invention;
FIG. 8 is a graph of the turbulent kinetic energy dissipation ratio of a three-way straight tube section of an embodiment of the present invention
The correspondence with the flow ratio;
FIG. 9 is a graph of the turbulent kinetic energy dissipation ratio of a three-way leg segment of an embodiment of the present invention
And convection terms
According to the flow rate ratio.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention and/or the technical solutions in the prior art, the following description will explain specific embodiments of the present invention with reference to the accompanying drawings. It is obvious that the drawings in the following description are only some examples of the invention, and that for a person skilled in the art, other drawings and embodiments can be derived from them without inventive effort. In addition, the term "orientation" merely indicates a relative positional relationship between the respective members, not an absolute positional relationship.
The first embodiment,
The invention relates to an arc-variable and diameter-variable tee joint based on dissipation function comparative analysis, which comprises: the main pipe, the straight-through pipe diameter that is the same with the direction of being responsible for is less than the pipe diameter of being responsible for, and straight-through pipe is on same water flat line with the central line who is responsible for, and the extending direction of the tee bend lateral flow pipe of being connected with the main pipe is 90 degrees with the extending direction of being responsible for, and the pipeline epirelief that is connected with straight-through pipe of being responsible for and epirelief direction are perpendicular with former direction of connection, and variable pitch arc reducing tee bend downstream department is provided with the downstream pipe that is used for being connected with variable pitch arc reducing tee bend, and the ratio of variable pitch arc reducing tee bend epirelief height. Wherein, the upward convex direction is the radial extending direction of the upward convex peak of the pipeline, and the upward convex height is the difference between the radial distance of the upward convex peak and the pipe diameter.
The research idea of the invention is as follows: based on the principle of analyzing drag reduction under the turbulent energy dissipation rate theory, the optimization of the three-way arc shape and the three-way resistance characteristic under multiple working conditions (different flow ratios and height-to-width ratios) are researched by adopting a CFD (computational fluid dynamics software) numerical simulation method.
One basic assumption underlying this study is that drag reduction is only considered for one leg of the tee, and the drag of the other leg need not be considered. Fig. 1 is an example of air return of an air duct in a household room: it is known that the fan is selected based on the worst-case loop, and it is the only way to reduce fan consumption that is to reduce the drag of the worst-case loop. However, for a tee joint, such as the tee joint abc, it has two local resistance coefficients, one is the local resistance coefficient of the tee joint straight pipe
Secondly, the local resistance coefficient of the three-way branch pipe
If the pipeline 1-2-3-4 belongs to the most unfavorable loop, only the reduction is needed
Can play the role of reducing drag
And the resistance calculation and the fan model selection are not influenced. Likewise, if the lines 5-6-7-8 belong to the most unfavorable loop, only a reduction is required
Need not consider
The size of (2). Namely, the resistance of the branch of the three-way valve belonging to the most unfavorable loop is reduced as far as possible on the premise of ensuring that the branch is smooth. The focus of the study herein is therefore: under the same working condition, only the resistance of one passage of the tee joint is considered to be reduced, and the resistance reduction of two passages is not needed.
Defining the length of the long side of the section of the tee upstream (upstream) as
The length of the long side of the downstream (downstream) section of the tee joint is
The length of the long side of the section of the three-way branch flow (branch) is
The length of the short side of the section is 250 mm. The length values of the upstream and downstream pipelines of the tee joint are not specified in the existing specifications, so that the lengths of the upstream and downstream pipelines of the tee joint are equal to the lengths of the long sides of the corresponding pipelines, namely the lengths are respectively
、
、
. Since the relative height of each tee will vary depending on the size of the arc height, a dimensionless arc height is defined
The value is independent of the size of the tee. As shown in fig. 2, h represents the height of the convex (or concave) of the variable camber tee under study,
represents the length of the long side of the section of the downstream pipe of the tee joint,
the magnitude of (d) represents the degree of convexity or concavity of the section of pipe, positive values representing convexity and negative values representing concavity.
The effect of the tee on the fluid in front of and behind is not limited to the tee itself, but also on the fluid in the pipeline connected with the tee, and if only the tee member itself is considered, the effect is inaccurate. Firstly, analyzing the dissipation work of the straight pipe tee joint (the volume 3 of the branch pipe tee joint is changed into the volume 2), and imitating the calculation method of the front local resistance coefficient, wherein the method comprises the following specific steps: respectively dividing the dissipation work of the volume 1 and the volume 3, then adding the volume and the dissipation work, and recording the volume as the dissipation work of the straight pipe section of the pipeline with the tee joint
. The pipeline size of the part 1 is applied to a linear rectangular pipeline, the length of the pipeline is the sum of the lengths of the upstream pipeline and the downstream pipeline, the speed of the pipeline is defined as the speed of an inlet when a tee joint exists, and the volume of the dissipated work of the whole linear pipeline is divided into
. In the same way, a volume 3 is defined, denoted
。
The physical meaning is that the volume of the dissipated work of the straight pipe with the tee joint is subtracted from the volume of the dissipated work of the rectangular straight pipe, so that the influence of the tee joint on adjacent fluids is eliminated. The calculation method of the branch pipe section tee joint is the same as the above, and the volume 3 is changed into the volume 2, as shown in figure 3.
From the basic governing equation of fluid multi-dimensional flow, there are 4 parameters that may be related to the resistance of local components, which are: dissipation term in the NS equation
Convection term in the NS equation
Dissipation work in energy equations
Turbulent kinetic energy dissipation ratio in turbulent energy dissipation ratio equation
. For convenience of expression, the terms dissipation 1, dissipation 2, dissipation 3, and convection are abbreviated as follows:
the drag reduction ratios of the novel tee under the study of the flow dividing tee are listed under 7 flow ratios of 5: 1-1: 3 and 7 dimensionless arc heights of-0.2-0.5, and the drag reduction ratios of the novel tee are totally 49 combination modes, as shown in fig. 4 and 5. As can be seen from the figure, when the height of the dimensionless arc line is less than zero, no drag reduction effect exists between the straight pipe and the branch pipe no matter how the flow rate changes. As the dimensionless arc height of the tee>At 0, the drag reduction ratio of the straight and branch pipes is positive under some conditions. When in use
And =0 to 0.3. The drag reduction rate of the three-way straight pipe is above the dotted line and is irrelevant to the flow ratio. When in use
>When 0.3, the drag reduction rate of the three-way straight pipe can be reduced to below 0; the conditions for branch pipe drag reduction are more severe when
With =0.3, the legs already have no drag reducing effect at certain flow ratios. In conclusion, the drag reduction rate of the straight pipe is far greater than that of the branch pipe and can reach 40% at most, and the variable tee arc has better drag reduction effect on the straight pipe section relative to the branch pipe section.
The turbulence flow inside the tee joint is complex, and the phenomena of vortex and secondary flow can be generated, so that the dimensionless heights corresponding to the tee joint with the optimal shape are different under different flow ratios, as shown in the following table. Meanwhile, due to engineering requirements, different tee joints cannot be used at different flow ratios under the same aspect ratio, and based on the consideration, a compromise method is adopted to put forward the concept of the recommended height of the resistance-reducing arc. The calculation method is as follows: and calculating the drag reduction rate under the same flow ratio and different dimensionless heights. And when the drag reduction rate is greater than 0, counting the height of the dimensionless arc line to obtain the height of the dimensionless arc line under all flow ratios. Wherein the straight pipe section has a dimensionless arc height of
=0.1, 0.2, 0.3; the height of dimensionless arc line of branch pipe section is divided into
=0.1, 0.2. And averaging the drag reduction rate corresponding to the height of the dimensionless arc meeting the condition to obtain the dimensionless height when the drag reduction rate is maximum, namely the recommended height of the drag reduction arc. The tee-joint drag reduction rate at the recommended height of the drag reduction arc may be lower than that at the optimal dimensionless height, but still has a larger drag reduction advantage at the moment, and is beneficial to the application of actual engineering.
By utilizing the research method introduced in the previous section, the dissipation function and the convection function of the tee joint with different flow ratios under the same arc height can be calculated. Multiplying them by a certain multiple and the local resistance coefficient of straight pipe of tee
By comparison, fig. 6 can be obtained. It can be seen that the dissipation 2 and the dissipation 3 have similar fluctuation laws, and generally, as the flow rate ratio decreases, there is a trend of decreasing and then increasing, which is completely different from the situation that the dissipation 1 is always decreased. From the plot alone, the local drag coefficient and dissipation 3 (turbulent kinetic energy dissipation ratio) of a straight tube
) The correlation is highest and the fluctuation trend is close when
As the flow ratio is increased or decreased,
and also increases or decreases, other dissipative or convective functions do not have such a rule. So that the local resistance coefficient of the straight pipe
And rate of kinetic energy dissipation of turbulence
Highly relevant, in which case the available turbulent kinetic energy dissipation rate
And (6) carrying out analysis. Taking reasonable measures to reduce
The local resistance of the three-way straight pipe can be effectively controlled.
Likewise, local resistance coefficient to branch of tee
The influence factors of (2) are analyzed, and fig. 7 can be obtained. The local resistance coefficient of the branch pipe also has a tendency of increasing after decreasing along with the decrease of the flow ratio, and the convection term is also the same as that of the straight pipe and increases along with the decrease of the flow ratio. But unlike the straight pipe, the dissipation 1, dissipation 2 and dissipation 3 under the branch pipe analysis are almost the same, decreasing with decreasing flow ratio. This allows the local resistance coefficient of the branch pipe
The analysis of the influence factors becomes complicated.
Convection terms in fluids
Is the process of energy conversion caused by the movement of the fluid. During the fluid movement, if a linear movement with equal speed and equal flow is always carried out, the value of the term is necessarily 0, but in a three-way pipe system, the ideal flow cannot be always carried out. The tee joint has the function of shunting, and in the T-shaped tee joint researched by the invention, a part of fluid moves along a straight line at the tee joint all the time, the speed direction is unchanged, and the speed of the part of fluid is changed; the other part of the fluid changes the speed and the direction at the tee joint and flows to the branch pipe along the orthogonal direction. Thus, the convection term of the fluid at the branch is significantly greater than the fluid at the straight, which explains why the convection term has increased as the flow ratio decreases (branch flow increases).
When the flow of the straight pipe is greater than that of the branch pipe, the straight pipe fluid is dominant at the moment, and the dissipation effect caused by viscosity is greater than the convection effect caused by a convection item, so that the influence of the local resistance and the dissipation item of the branch pipe is greater; when the flow of the branch pipe is larger than or equal to that of the straight pipe, the branch pipe fluid is dominant at the moment, and the dissipation effect caused by viscosity is smaller than that of the convection item, so that a line graph is observed, and the relationship between the local resistance coefficient of the branch pipe and the convection item is larger.
Therefore, when the flow rate of the straight pipe is greater than that of the branch pipe (5: 1, 4:1, 3:1 and 2: 1), the local resistance coefficient of the branch pipe is at the moment
The same fluctuation trend as the dissipation 1-3 (for simple analysis, dissipation 3 is still used), and the dissipation rate of the available turbulent kinetic energy
Carrying out analysis; when the branch pipe flow is more than or equal to the straight pipe flow (1: 1, 1:2, 1: 3), the local resistance coefficient of the branch pipe
The same fluctuation trend as that of the convection term, and the convection term is available at the moment
And (6) carrying out analysis.
In order to verify the correctness of the analysis of the above influencing factors, h/D was studied in this subsectionus= 0.2, 0, 0.2 three dimensionless arc heights and
convection terms at three flow ratios of =5:1, 1:1 and 1:3
And turbulent kinetic energy dissipation ratio
And (4) comparing the working conditions, wherein the working conditions are 9. And cutting the cross sections in the x direction, the y direction and the z direction for analysis.
As in the previous paragraph, IIIThe main influencing parameter of the resistance of the straight pipe is the turbulent kinetic energy dissipation rate
. Under these 9 conditions, the cross section of the tee at the downstream end of the tee was analyzed for comparative turbulent kinetic energy dissipation ratio, see fig. 8. As can be seen from the figure, when the tee joint is fixed with a dimensionless arc height, namely the size of the tee joint is not changed, the local resistance coefficient of the straight pipe of the tee joint is reduced firstly and then increased along with the reduction of the flow ratio; on the premise of a constant flow ratio, when the height of a dimensionless arc line of the tee joint is increased from-0.2 to 0.2, the local resistance coefficient of the straight pipe of the tee joint is reduced. This also corresponds exactly to the cloud here. The results of the above line graph analysis are demonstrated to have reliability, i.e., the straight tube local drag coefficient
And rate of kinetic energy dissipation of turbulence
Are highly correlated.
As can be seen from the analysis of FIG. 9, when the straight pipe flow is greater than the branch pipe flow (5: 1, 4:1, 3:1, 2: 1), the available turbulent kinetic energy dissipation rate is determined
Carrying out analysis; when the branch pipe flow is greater than or equal to the straight pipe flow (1: 1, 1:2, 1: 3), the convection term can be used
And (6) carrying out analysis. In the 9 working conditions, the turbulent kinetic energy dissipation rate and the convection term are compared and analyzed on the cross section of the tee at the branch end of the tee. The cloud image analysis result at this time was consistent with the line image analysis.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (5)
1. A variable camber line reducing tee based on dissipation function contrastive analysis is characterized by comprising: the pipe diameter of the straight-through pipe in the same direction as the main pipe is smaller than that of the main pipe, the straight-through pipe and a central pipeline of the main pipe are on the same horizontal line, the extending direction of a three-way branch flow pipe connected with the main pipe is 90 degrees to that of the main pipe, and the pipeline connected with the straight-through pipe protrudes upwards and the protruding direction of the pipeline is perpendicular to the original connecting direction.
2. The variable arc and reducing tee joint based on dissipation function comparative analysis according to claim 1, wherein a downstream pipe connected with the variable arc and reducing tee joint is arranged at the downstream of the variable arc and reducing tee joint, and the ratio of the height of the upper projection of the variable arc and reducing tee joint to the length of the long edge of the section of the downstream pipe is a positive value.
3. The arc-variable diameter-variable tee joint based on the dissipation function comparative analysis of claim 2, wherein the ratio of the height of the convex of the arc-variable diameter-variable tee joint to the length of the long side of the section of the downstream pipe is 0.1.
4. The arc-variable diameter-variable tee joint based on the dissipation function comparative analysis of claim 2, wherein the ratio of the height of the convex of the arc-variable diameter-variable tee joint to the length of the long side of the section of the downstream pipe is 0.2.
5. The arc-variable diameter-variable tee joint based on the dissipation function comparative analysis of claim 2, wherein the ratio of the height of the convex of the arc-variable diameter-variable tee joint to the length of the long side of the section of the downstream pipe is 0.3.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113639276A (en) * | 2021-07-30 | 2021-11-12 | 西安建筑科技大学 | Anti-smoke-channeling three-way flue and control method thereof |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113639276A (en) * | 2021-07-30 | 2021-11-12 | 西安建筑科技大学 | Anti-smoke-channeling three-way flue and control method thereof |
| CN113639276B (en) * | 2021-07-30 | 2022-08-16 | 西安建筑科技大学 | Anti-smoke-channeling three-way flue and control method thereof |
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