CN107201705B - Method for improving ventilation efficiency of ventilation pipe roadbed - Google Patents
Method for improving ventilation efficiency of ventilation pipe roadbed Download PDFInfo
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- CN107201705B CN107201705B CN201610152051.5A CN201610152051A CN107201705B CN 107201705 B CN107201705 B CN 107201705B CN 201610152051 A CN201610152051 A CN 201610152051A CN 107201705 B CN107201705 B CN 107201705B
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
- E01C3/00—Foundations for pavings
- E01C3/04—Foundations produced by soil stabilisation
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D27/00—Foundations as substructures
- E02D27/32—Foundations for special purposes
- E02D27/35—Foundations formed in frozen ground, e.g. in permafrost soil
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Abstract
The invention relates to a method for improving ventilation efficiency of a ventilation pipe subgrade, which is characterized in that duckbilled pipe orifices are buried at one side or two sides of a side slope of a embankment. The duckbill-shaped pipe orifice comprises a closed top surface, an open outer section and a bottom section, and is connected with the ventilation straight pipe, and the horizontal width of the maximum section of the whole appearance is 1 to 3 times of that of the ventilation straight pipe; the outer cross section is perpendicular to the axis of the straight ventilation pipe. The invention can effectively improve the flow field condition of air at the inlet section of the ventilation pipe, obviously increase the flow velocity of the air in the ventilation pipe and the convective heat transfer intensity of the ventilation pipe roadbed, and lay an important foundation for effectively playing the role of ventilation roadbed engineering measures to protect the frozen soil roadbed.
Description
Technical Field
The invention relates to the technical field of frozen soil engineering, in particular to a method for improving ventilation efficiency of a ventilation pipe roadbed.
Background
In permafrost regions such as Qinghai-Tibet plateau and northeast China, through long-term evolution, development and change, thick-layer underground ice with the thickness of several meters, even more than ten meters and various forms is formed. With the change of climate environment and the influence of human engineering activities, the degradation and melting of frozen soil and underground ice are caused, thereby causing various engineering disasters and having important influence on the stability of various major engineering buildings.
In the face of the departure of the national strategy planning of thirteen five, the Qinghai-Tibet expressway is about to be constructed, but compared with the ordinary expressway, the ordinary expressway has more prominent frozen soil problem compared with the railway. The existing research shows that (Shuqihao, etc., key problem research on the construction of freeways in permafrost regions in China. China science (technical science), 2014, 44 (4): 425-432), because of the strong heat absorption of black pavements, water isolation of asphalt pavements and the influence of preventing water from evaporating and radiating, the heat absorption strength of highway subgrades under the same conditions is more than 3 times of that of railways, and the main way of heat absorption of the subgrades is mainly concentrated at the central part of the embankments and is difficult to radiate heat to surrounding frozen soil. And the appearance of the phenomenon is more dramatic on the expressway than on the ordinary highway. When the width of the roadbed of the highway is increased by about 1 time, the heat absorption intensity of the bottom surface of the embankment is increased by about 0.6 time, and the heat absorption of the roadbed is further gathered at the central part of the roadbed, thereby generating more obvious heat accumulation effect and causing more rapid degradation of frozen soil.
In the face of higher technical standard and wider highway pavement, the thermal action between the highway and the frozen soil is more obvious, and the highway constructed in the permafrost region can face more prominent frozen soil problems and technical building problems. Due to the fundamental changes in heat transfer path, strength, etc., the successful experience and advanced technology obtained through Qinghai-Tibet railway, etc. are difficult to be directly applied in the construction of Qinghai-Tibet freeways.
By adopting the measure of protecting the frozen soil engineering, the frozen soil foundation is actively cooled, and the method is a key way for ensuring the long-term safe operation and stability of the frozen soil engineering. Among these measures, the effective regulation and control of the convective heat transfer process of frozen soil engineering is an important method for protecting frozen soil foundation. In this field, the innovation of the prior art mainly lies in the aspects of ventilation and heat exchange modes of a ventilation roadbed or a composite structure of a ventilation pipe and other measures, such as: the composite temperature control ventilated roadbed (patent number: ZL 200410002135.8) mainly aims at innovation of heat exchange modes of the roadbed in different seasons, and achieves the purpose of enhancing the cooling efficiency by inhibiting the influence of heat in warm seasons; the composite ventilating and cold accumulating roadbed (patent number: 200510043153.5) achieves the aim of integrally and actively cooling the roadbed by combining the ventilating pipes and the layer of the block stone and improving the working conditions of convective heat exchange and heat conduction of the block stone layer. However, innovative technologies related to ventilation and heat exchange efficiency of the ventilation pipe are not yet lacked.
The formula of Deutsche Bell of the heat exchange efficiency of the convection heat exchange surface is as follows:
wherein: h is the convective heat transfer coefficient, lambda is the thermal conductivity of static air, re is the Reynolds number, pr is the Plantt number, L is the characteristic length, mu is the dynamic viscosity, cp is the specific heat capacity at constant pressure, rho air density, v is the motion speed, and L is the characteristic length.
According to the formula, the roughness of the pipe wall of the precast concrete ventilation pipe is relatively stable, and the heat exchange coefficient mainly depends on the air flow rate in the ventilation pipe under the condition that the air physical property and the pipe diameter of the pipe are not changed. And the heat exchange coefficient is in direct proportion to the air flow speed, namely, the increase of the flow speed in the pipe is the improvement of the heat exchange coefficient, and is the most effective method for increasing the heat exchange strength. Therefore, the present invention is made mainly for the problem of improving the air flow process inside the ventilation duct and enhancing the air flow rate.
Disclosure of Invention
The invention aims to provide a method for improving the ventilation efficiency of a ventilation pipe subgrade, which has low cost and good stability.
In order to solve the above problems, the method for improving ventilation efficiency of the ventilation pipe subgrade of the invention is characterized in that: the method is characterized in that duckbill-shaped pipe orifices are buried in one side or two sides of a side slope of the embankment; the duckbill-shaped pipe orifice comprises a closed top surface, an open outer section and a bottom section, and is connected with the straight ventilation pipe, and the horizontal width of the largest cross section of the integral appearance of the duckbill-shaped pipe orifice is 1-3 times that of the straight ventilation pipe; the outer cross section is perpendicular to the axis of the straight ventilation pipe.
The top surface is one or the combination of two or more of a curved surface, a semicircular surface and a plane.
The outer section is in any one shape of a parabola, a semicircle and a rectangle, and the inclination angle of the section is 10-90 degrees.
The distance between the bottom section and the bottom surface of the straight ventilation pipe is 0-1.5 times of the diameter of the straight ventilation pipe.
The length of the bottom section along the axis of the ventilation straight pipe is 0-2 times of the diameter of the ventilation straight pipe.
Compared with the prior art, the invention has the following advantages:
1. a significant increase in the air flow rate within the ventilation duct.
The invention effectively eliminates the problems of air turbulence, vibration energy consumption, flow speed reduction and the like caused by the shape of the original straight pipe inlet, effectively reduces the fluctuation and energy loss of air by changing the shape of the inlet ventilation pipe, increasing the air pressure of the inlet part and improving the inflow conditions, and simultaneously increases the power and flow of the air entering the ventilation pipe, thereby obviously increasing the flow speed of the air in the pipe. Compared with the common ventilating pipe roadbed, the flow in the pipe is increased by 20-40%, and the convective heat exchange efficiency of the ventilating pipe is obviously improved.
2. And the convection heat exchange efficiency of the ventilation pipe is enhanced.
Firstly, due to the increase of the air flow rate in the ventilation pipe, the heat exchange strength of the air in the ventilation pipe and the pipe wall of the ventilation pipe is effectively increased; secondly, the overall heat exchange strength of the embankment increases due to the increase of the air flow.
3. The engineering effect is obviously improved.
As the straight pipe inlet mode is adopted in the prior art, the fluctuation and the heat exchange performance of air at the inlet section of the ventilation pipe are strongest and are weakened along with the increase of the depth from the pipe opening. Meanwhile, the air has the lowest temperature at the inlet section of the ventilation pipe, so that the phenomenon that the heat exchange process of the air in the ventilation pipe is strongest at the inlet section is caused, and the overall earth temperature field of the ventilation embankment is asymmetric. The invention improves the air flow guiding efficiency of the inlet of the ventilation pipe, reduces the air fluctuation of the inlet section, balances the whole heat exchange process of the ventilation pipe, relieves the asymmetry of a ground temperature field, and reduces the generation of the negative and positive slope effect of the embankment.
4. The stability of the frozen soil engineering is effectively increased.
Firstly, due to the enhancement of the heat convection efficiency, the cooling efficiency of the measure on the frozen soil roadbed is greatly increased, and the strength of the frozen soil foundation is enhanced due to the reduction of the ground temperature of the frozen soil roadbed. Secondly, due to the enhancement of the symmetry of the ground temperature field, the technical requirements of integral and uniform cooling required by high-grade highways are further enhanced, thereby further increasing the stability of the frozen soil roadbed.
5. And the construction cost is reduced.
Due to the fact that the efficiency is increased to a large degree, the larger distance between the ventilation pipes can achieve the cooling effect of the original smaller distance. Therefore, in actual engineering, if the ventilation structure mode is adopted, the using number of ventilation pipes and air pipes can be reduced under the same cooling effect, so that the construction cost is reduced, and the engineering construction speed is increased.
6. Wide application range.
The invention only invents the technology for the ventilating pipe orifice, not only can be used for ventilating pipe roadbed engineering under construction, but also can be used for ventilating pipe roadbed engineering under construction, thereby having wider application range.
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
FIG. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a schematic view of the overall structure of the present invention.
FIG. 3 is a schematic view of the combination of the semicircular opening and the straight tube according to the present invention.
FIG. 4 is a schematic view of the combination of a rectangular opening and a straight tube according to the present invention.
Fig. 5 is a flow chart of the vicinity of a nozzle of a general air pipe roadbed.
Fig. 6 is a flow chart of the vicinity of the nozzle of the ventilated roadbed according to the invention.
FIG. 7 is a graph showing the air flow rate in a ventilation pipe of the present invention compared with a conventional ventilation pipe under different external wind speed conditions.
In the figure: 1-duckbill type mouth of pipe 2-top surface 3-outer cross section 4-end cross section 5-ventilation straight tube 6-integral structure 7-semicircle 8-rectangle.
Detailed Description
As shown in fig. 1, a method for improving ventilation efficiency of an air duct roadbed is that duckbilled pipe orifices 1 are buried at one side or two sides of a side slope of a embankment.
The duckbill-shaped pipe orifice 1 comprises a closed top surface 2, an open outer section 3 and a bottom section 4, and is connected with a ventilation straight pipe 5, and the maximum horizontal width of the section of the integral appearance is 1-3 times of that of the ventilation straight pipe 5; the outer section 3 is perpendicular to the axis of the straight ventilation pipe 5.
Wherein:
the top surface 2 is one or the combination of two or more of a curved surface, a semi-circular surface and a plane.
The outer section 3 is in any one shape of a parabola, a semicircle and a rectangle, and the inclination angle of the section is 10-90 degrees.
The height of the bottom section 4 from the bottom surface of the ventilation straight pipe 5 is 0-1.5 times of the diameter of the ventilation straight pipe 5.
The length of the bottom section 4 along the axis of the straight ventilation pipe 5 is 0-2 times of the diameter of the straight ventilation pipe 5.
When the duckbill spout 1 is in the integral structure 6, it is shown in fig. 2.
When the top surface is a semicircle 7, the combination with the straight ventilation pipe 5 is shown in fig. 3.
The combination when the top surface is planar and the outer cross-section 3 is rectangular 8 is shown in figure 4.
When in use, the invention is buried at one side or two sides of the side slope of the embankment.
The working principle of the invention is as follows:
firstly, the shape of the mouth of the ventilating pipe is changed, and under the condition of the same external wind speed and wind direction, the flow speed and the flow of the air in the pipe are increased by increasing the inlet air pressure, improving the air flow path and reducing the local energy loss of the air at the mouth of the pipe. Therefore, the convective heat transfer strength of the inner pipe wall of the ventilation pipe is improved, and the heat transfer and cooling of the whole roadbed are increased; secondly, the shape of the pipe orifice and the air flowing process are changed, the turbulence intensity of air at an inlet is reduced, the air heat exchange intensity at the inlet is reduced, and the loss of air cold energy is effectively avoided, so that the convective heat exchange intensity of the middle section and the outlet section of the ventilation pipe is enhanced, the asymmetry of heat exchange along the wind speed direction is reduced, and the stability of the roadbed is improved.
Example 1 of specific application of the present invention:
referring to the attached figure 1, a method for improving the ventilation efficiency of a ventilation roadbed adopts an integral duckbill ventilation pipe orifice structure, and the top surface of the integral duckbill ventilation pipe orifice structure is a closed curved surface with streamline characteristics. The diameter of the straight pipe 5 part of the vent pipe is 0.4m, and the maximum diameter of the duckbill-shaped pipe orifice is 0.8m.
The outline of the outer section 3 is parabolic and the section inclination is 21.8 deg..
The height of the duckbill orifice bottom section 4 is 1 time of the diameter of the straight pipe 5. The length along the axis of the ventilation tube is 1 times the diameter of the straight tube 5.
In order to verify the effectiveness of the invention, numerical simulation calculation is performed. The size that the model embankment got is road surface width 13.0m, and fill height 3.0m, the bank protection slope is 1:1.5, the axial height of the ventilation pipe is 1m. The parameters were selected according to the actual measurement data of the meteorological station at the north foot of the Tibet plateau and the experimental section of the high-grade highway in Tibet, and the average atmospheric pressure was 57.7kPa, the density was 0.737kg/m3, the air viscosity was 1.75X 10-5Pa ≤, and the ambient temperature was 273K.
Comparison of results of numerical simulation calculations performed under the same boundary conditions: one group is duckbilled ventilation pipe roadbed, and the other group is common straight pipe ventilation pipe orifice roadbed. The numerical simulation calculation results are shown in fig. 5 to 7.
Fig. 5 and 6 are flow charts of the vicinity of the nozzle of the ventilation pipe roadbed and the ventilation pipe roadbed in the normal ventilation pipe roadbed under the condition that the external natural wind speed is 5 m/s. As can be seen from the comparison between FIG. 5 and FIG. 6, the ventilating nozzle of the present invention effectively improves the flow process of the air at the inlet section, reduces the degree of separation of the boundary layer, and has more smooth flow lines and larger curvature. Figure 6 shows that the local losses caused by the fluid entering the pipe by the bypass flow are reduced and the flow into the pipe is greater at the same ambient natural wind speed.
Fig. 7 is a comparison of wind speeds in the ventilation pipe roadbed and the common ventilation pipe roadbed under the conditions of different external wind speeds. As can be seen in the figure, under the same external conditions, the flow velocity of the ventilation pipe is about 20-40% greater than that of the ventilation pipe in the common ventilation pipe roadbed pipe.
Therefore, by applying the invention, the air flow field condition of the inlet section of the ventilating pipe can be effectively improved, the flow velocity of air in the ventilating pipe and the convective heat transfer strength of the ventilating pipe roadbed are obviously increased, and an important foundation is laid for effectively playing the role of protecting the frozen soil roadbed by ventilating roadbed engineering measures.
Claims (1)
1. A method for improving ventilation efficiency of a ventilation pipe roadbed is characterized by comprising the following steps: the method is characterized in that a duckbill-shaped pipe orifice (1) is embedded in one side or two sides of a side slope of the embankment; the duckbill-shaped pipe orifice (1) comprises a closed top surface (2), an open outer section (3) and a bottom section (4), and is connected with the ventilation straight pipe (5), and the top surface (2) is a closed curved surface with streamline characteristics; the diameter of the straight pipe (5) of the vent pipe is 0.4m, and the maximum diameter of the duckbill pipe orifice (1) is 0.8m; the contour line of the outer section (3) is a parabola, and the inclination angle of the section is 21.8 degrees; the height of the bottom section (4) is 1 time of the diameter of the ventilation straight pipe (5); the length along the axial line of the ventilation pipe is 1 time of the diameter of the ventilation straight pipe (5).
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| Application Number | Priority Date | Filing Date | Title |
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| CN201610152051.5A CN107201705B (en) | 2016-03-17 | 2016-03-17 | Method for improving ventilation efficiency of ventilation pipe roadbed |
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| CN201610152051.5A CN107201705B (en) | 2016-03-17 | 2016-03-17 | Method for improving ventilation efficiency of ventilation pipe roadbed |
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| CN107201705B true CN107201705B (en) | 2023-03-21 |
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| CN110878501A (en) * | 2019-12-12 | 2020-03-13 | 四川浩克山青水绿科技有限责任公司 | Novel ventilation pipe for treating frozen expansion and thawing settlement diseases of existing line roadbed |
| CN116145486B (en) | 2023-01-17 | 2023-07-14 | 中国科学院西北生态环境资源研究院 | Airflow enhanced roadbed ventilation structure, composite roadbed structure and construction method thereof |
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| DE102008026117A1 (en) * | 2008-05-30 | 2009-12-10 | Airbus Deutschland Gmbh | Fresh air intake for an aircraft |
| DE102008030399B4 (en) * | 2008-06-26 | 2019-03-21 | Airbus Operations Gmbh | Air duct for ambient air supply in an aircraft |
| CN101392685B (en) * | 2008-10-29 | 2010-06-09 | 南京航空航天大学 | Internal waverider hypersonic inlet and design method based on random shock form |
| CN202450406U (en) * | 2011-12-29 | 2012-09-26 | 中交第一公路勘察设计研究院有限公司 | Permeable-wall ventilating duct and fragment stone composite road bed |
| CN203505390U (en) * | 2013-10-17 | 2014-04-02 | 山东农业大学 | Orientation atomizing device for cotton operation |
| CN203878178U (en) * | 2014-01-26 | 2014-10-15 | 包头北方铁路产品有限责任公司 | Flexible duckbilled induced draft cylinder for axle heat treatment cooling |
| CN104895676A (en) * | 2015-04-14 | 2015-09-09 | 中国科学院力学研究所 | High supersonic speed variable cross section air intake duct and design method thereof |
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Effective date of registration: 20220728 Address after: 730000 No.318 Donggang West Road, Chengguan District, Lanzhou City, Gansu Province Applicant after: NORTHWEST INSTITUTE OF ECO-ENVIRONMENT AND RESOURCES, CHINESE ACADEMY OF SCIENCES Address before: Chengguan District of Gansu city of Lanzhou province Donggang West Road 730000 No. 320 Applicant before: COLD AND ARID REGIONS ENVIRONMENTAL AND ENGINEERING Research Institute,CHINESE ACADEMY OF SCIENCES |
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