Background of the Invention It is well known that the transmission of the static pressure of the downward flowing liquid in a riser pipe can be stopped based on the theory of annular flow, and many solutions have been used in engineering practice. However, since many factors affect the flow state of the fluid in the riser pipe and the actual situation is changeful, it is usually difficult to stabilize the state of annular flow in a riser pipe, causing pressure fluctuation at the lower end of the riser pipe. On the other hand, under the condition of large pressure difference, the connection way of the system would usually affects the overall arrangement, or the investment of equipment, or the operation reliability and efficiency of the system, making it one of the central issues concerning the determination of the overall arrangement of the system.

Summary of the Invention The object of the invention is to provide a device for eliminating the static pressure of downward flowing liquid, which has a low cost, is simple in structure and can operate reliably. The device of the invention can be applied to heating or air conditioning system to eliminate the static pressure of downward flowing liquid.

To achieve the object of the invention, according to the first aspect of the invention, there is provided a device for eliminating the static pressure of downward flowing liquid, comprising: a riser pipe, the upper end of the riser pipe being connected with a first pipe for transporting fluid with a high static pressure, and the lower end of the riser pipe being connected with a second pipe for transporting fluid with a low static pressure; and flow guiding means provided in the upstream section of the riser pipe and extending in the axial direction of the riser pipe; wherein a fluid passage being formed between the flow guiding means and the inner wall of the riser pipe, said fluid passage comprising a spiral passageway to guide the high-static-pressure fluid coming from the first pipe and make it take the form of quasi-annular flow or annular flow; the static pressure eliminating device further comprising air compensating means, the air compensating means being communicated with the section of the riser pipe where annular flow is formed to maintain stable annular flow.

According to the invention, the liquid passage formed in the riser pipe comprises a spiral or helical passageway, the spiral passageway turns the downward flowing liquid into a rotating liquid flow, strengthening the flow guiding function and making the downward flowing liquid take the form of water film. In addition, it should be pointed out that the air compensating means referred to herein should be interpreted in a broad sense,"compensation"means that when the pressure of the air core in the section of the riser pipe where a annular flow is formed decreases due to the decrease of the air, outside air will enter the air core from outside; it can also means that when the pressure of the air core increases due to the increase of air, part of the air will be discharged into the atmosphere.

Preferably, the lower end of the riser pipe is connected with an air collecting means, said air collecting means has a remarkably larger flow area than the riser pipe, and the top of the air collecting means is formed with a controllable outlet for releasing collected air. The outlet is used to release the air carried by the downward flowing water.

Preferably, the outlet of the air collecting means is connected with an air-water separator via a pipe, the air-water separator is located above the air collecting means; the cylindrical guiding member is a tube, the lower orifice of the tube opens to the part of the riser pipe where the annular flow is formed; the air outlet of the air-water separator is connected with the upper orifice of the tube via an air circulating pipe, and the water outlet of the air-water separator is connected with the air collecting means via a pipe at the bottom of the air collecting means.

Thus, the flow guiding member can communicate with the air core in the center of the annular flow in the riser pipe, whereby a small amount of air carried by the downward flowing water can return to the riser pipe via the air-water separator. As a result, outside air is prevented from mingling with the working water flow, realizing the dynamic enclose of the air in the riser pipe and facilitating the prevention of the harmful effects of the air.

Preferably, the device further comprises a pressure limiting means which is attached to the riser pipe, said pressure limiting means is located under the flow guiding means and is communicated with the section of the riser pipe where the annular flow is formed to ensure the operation safety of the system.

Preferably, the pressure limiting device is a U water-seal tube.

According to the second aspect of the invention, there is provided a device for eliminating the static pressure of downward flowing liquid, comprising : a riser pipe, the upper end of the riser pipe being connected with a first pipe for transporting fluid with a high static pressure, and the lower end of the riser pipe being connected with a second pipe for transporting fluid with a low static pressure; flow guiding means provided in the upstream section of the riser pipe and extending in the axial direction of the riser pipe, an axial fluid passage formed between the flow guiding means and the inner wall of the riser pipe, said axial fluid passage being used for guiding the high-static-pressure fluid coming from the first pipe and making it take the form of quasi-annular flow or annular flow; the static pressure eliminating device further comprising air compensating means, said air compensating means being communicated with the section of the riser pipe where annular flow is formed to maintain stable annular flow; the lower end of the riser pipe being connected with an air collecting means, the air collecting means having a remarkably larger flow area than the riser pipe, and the top of the air collecting means being formed with a controllable outlet for releasing collected air.

According to yet another aspect of the invention, there is provided a heating system, the heating system comprising a high-pressure zone and a low-pressure zone, the heating system being provided with a device for eliminating the static pressure of downward flowing liquid according to the first and second aspects.

With the flow guiding member provided in the inlet section of the riser pipe, the air collecting means and the air-water separator means of the invention, the dynamic enclose of the air core in the riser pipe is formed while the annular flow is formed in the riser pipe. With a closed system which isolates the water flow from the atmosphere by a water seal, it is possible to eliminate the oxygen corrosion problem and the air lock problem of the system. This device of the invention is simple in structure and has no moving components, thus having the same operation life as the system itself.

Brief Description of the Accompanying Drawings The embodiments of the invention will be described in detail in connection with the accompanying drawings, in which Fig. 1 is a schematic view showing the structure of the device for eliminating the static pressure of downward flowing liquid in accordance with the first embodiment of the invention, the device is installed between the high-pressure zone and the low-pressure zone in a heating system; Fig. 2 is a plan view of the device for eliminating the static pressure of downward flowing liquid shown in fig. 1 ; Fig. 3 is a sectional view taken along line A-A in fig. 1; Fig. 4 is a sectional view taken along line B-B in fig. 1; Fig. 5 is a schematic view showing the structure of the device for eliminating the static pressure of downward flowing liquid in accordance with the second embodiment of the invention; Fig. 6 is a schematic view showing the structure of the device for eliminating the static pressure of downward flowing liquid in accordance with the third embodiment of the invention, Fig. 7 is a schematic view showing a left handed spiral flow- guiding plate used in the static pressure eliminating device of the invention; Fig. 8 s a schematic view showing the structure of a horizontal air- collecting bucket used in the static pressure eliminating device of the invention; Fig. 9 is a view showing the installation of the static pressure eliminating device of the first embodiment shown in fig. 1 in a heating system; Fig. 10 is a view showing the installation of the static pressure eliminating device of the third embodiment shown in fig. 6 in a heating system, in which a horizontal air-collecting bucket is used; Fig. 11 is a view showing the installation of the static pressure eliminating device of the second embodiment shown in fig. 5 in a heating system.

Detailed Description of the Preferred Embodiments Figs. 1-4 shows the first embodiment of the device for eliminating the static pressure of downward flowing liquid in accordance with the invention, which is used for connecting the high-pressure zone and the low-pressure zone in a heating system. Fig. 9 shows the installation of the static pressure eliminating device in accordance with the first embodiment of the invention in a heating system.

As shown in figs 1-4, the device for eliminating the static pressure of downward flowing liquid in accordance with the first embodiment of the invention comprises a riser pipe 3, the internal diameter of the riser pipe is determined in accordance with the circulating water amount in a heating system. An elbow is provided on the top of the riser pipe, an air- circulating pipe 10 is inserted into the riser pipe 3 through the wall of the elbow. Between the air circulating pipe 10 and the riser pipe 3 there is provided a sealing means. The part of the air circulating pipe 10 which is inserted into the riser pipe is coaxial with the riser pipe 3, and is connected coaxially with a flow guiding tube 1 at a proper location via a reducing pipe 11 of truncated cone type. As a result, the upper end of the flow-guiding tube is communicated with the air-circulating pipe, and the lower end of the flow guiding tube is communicated with the riser pipe 3.

The flow guiding tube 1 is located at the inlet section of the riser pipe, namely at the upstream of the riser pipe, and can be fixed to the inner wall of the riser pipe by means of connection members 25, as shown in Fig. 3.

On the upper portion of the outer wall of the flow guiding tube, there is provided a spiral flow guiding plate 2, the flow guiding tube and the spiral flow guiding plate 2 forms a flow guiding means of the static pressure eliminating device. The outer diameter and the axial length of the flow guiding tube, the pitch, the outer diameter and the overall axial height of the flow guiding plate can be determined according to the practical needs. A left handed or right handed spiral flow guiding plate is selected according to the geographic location where the static pressure eliminating device is used, i. e. a left handed spiral flow guiding plate is for the Northern Hemisphere while a right handed spiral flow guiding plate is for the Southern Hemisphere. Fig. 7 shows a left handed spiral flow guiding plate.

The riser pipe 3 is provided with a U-shaped water seal tube 4, the effective water sealing length of the U water seal tube can be determined according to the actual situation. The inlet end of the U-tube 4 is communicated with the riser pipe 3, and its outlet end is communicated with the atmosphere. The inlet end of the U-tube is connected to the riser pipe at the downstream of the flow guiding tube 1, and is axially spaced apart from the lower end of the flow guiding tube by a predetermined distance. In practical use, the inlet end of the U-tube should be located above the hydrodynamic pressure line of the low-pressure zone.

An air-collecting bucket 6 is provided at the lower end of the riser pipe 3. The air collecting bucket 1 is a cask provided coaxially with the riser pipe. The lower end 5 of the riser pipe 3 extends downwards into the air collecting bucket by a proper distance, so that a circular air collecting space is defined between the outer wall of the riser pipe and the internal cylindrical wall of the bucket. The bottom of the air-collecting bucket is communicated with the return pipe of the heating system via a pipe coupling 7. The mounting position of the pipe coupling 7 on the bucket could be selectively determined, it can be mounted at the bottom as shown in full line in fig. 1 ; it can also be mounted at the lower side portion as shown in dotted line in Figs. 1 and 4.

The device for eliminating the static pressure of downward flowing liquid of the invention further comprises an air-water separator 9, which is located under the hydrodynamic pressure line of the low-pressure zone when the static pressure eliminating device of the invention operates. The distance between the air-water separator 9 and the hydrodynamic pressure line of the low-pressure zone can be determined according to actual situation, and preferably not less Im. The top of the air-water separator 9 is communicated with the flow guiding tube 1 via the air-circulating pipe 10 so as to guide the air into the flow guiding tube. Furthermore, the air- water separator 9 is connected with air collecting bucket at the top and the lower portion of the air collecting bucket respectively via an air collecting pipe 8 and a water circulating pipe 12. One end of the air collecting pipe 8 is connected to the air-water separator 9 at its upper portion, while the other end is connected with the air collecting bucket 6 at its top.

Preferably, the mouth of the air-collecting pipe 8 is adjacent to the top of the air-collecting bucket so as to facilitate the collection of the air. One end of the water circulating pipe 12 is connected with the air-water separator at its bottom, while the other end is connected with the air collecting bucket 6 at its lower portion, as shown in Fig. 1.

When installing the device for eliminating the static pressure of downward flowing liquid of the invention, the elbow on top of the return riser 3 is connected in a sealed manner with the return pipe 16 of the high pressure zone of the heating system, the lower end of the return riser is connected with the pipe coupling 7 via the air collecting bucket 6. In addition to meeting the general requirements when installing the device, it should be ensured that the hydrodynamic pressure line of the lower pressure zone of the heating system is above the air-water separator 9 and under the inlet end of the U water seal 4 as shown in Figs. 9-11, in which line I-I designates the hydrodynamic pressure line of the lower pressure zone.

During the operation of the static pressure eliminating device of the invention, when the return water of the high-pressure zone of a heating system flows into the riser pipe, the return water is subjected to the guidance of the passageway formed between the flow guiding tube 1, the spiral flow guiding plate 2 and the internal wall of the riser pipe. And under the action of the gravity and the centrifugal force caused by the spiral flow guiding plate, the downward flowing water turns into left handed or right handed rotating water film after passing through the flow guiding means of the static pressure elimination device; i. e. after passing through the flow guiding means, the downward flowing water becomes rotating annular flow with an air column in the center. During the course of downward flowing, the rotation of the water flow decreases gradually until reaching the hydrodynamic pressure line of the low pressure zone where the riser pipe is full of water. Accordingly, in the section of-the riser pipe where annular flow is formed, an air core with the axis of the riser pipe as a axis is formed, and the interface between the air and the water forms an isostatic pressure surface, thus eliminating the static pressure of the return water of the high-pressure zone.

The flowing speed of the water flowing into the air collecting bucket 6 decreases suddenly due to the sudden increase of the cross section of the air collecting bucket 6, causing the air carried by the water flow to rise up to the circular space in the upper portion of the air collecting bucket 6. Since the riser pipe 3 is inserted into the air collecting bucket by a proper distance with its mouth being positioned under the water level, and the water in the riser pipe continuously flows downward, almost all the air carried by the water flow is substantially accumulated in the circular space. Under the action of the pressure of water in the section of the riser pipe which is full of water or in the air collecting bucket, the air in the circular space enters the air collecting pipe 8 via the pipe mouth, passing through the water in the air collecting pipe and entering the air- water separator 9 to be separated. The water separated returns to the lower portion of the air-collecting bucket via the water-circulating pipe 12, forming the circulation loop for the water. The water circulation loop creates a pressure difference due to the air-collecting pipe 8 containing air and the water circulating pipe 12 not containing air, speeding up the rising of the air bubble. The air separated in the air-water separator goes into the air core in the center of the riser pipe via the air circulating pipe 10 and the flow guiding tube 1, forming an air circulation loop for the air contained in the water flow. The above explains the normal operation of the heating system provided with the device foe eliminating the static pressure of downward flowing water of the invention.

If the pressure in the system occasionally exceeds the working pressure of the U-water seal 4, the water will be discharged from the outlet of the U-tube to release pressure; while the water seal will remain closed under normal system pressure. Thus, the U-water seal 4 can functions as a safety valve. Furthermore, the U-water seal 4 also has a "breathing function", i. e. when the pressure of the air core in the section of the riser pipe where a annular flow is formed decreases due to the decrease of the air, outside air will enter the air core via the water seal; on the contrary, when the pressure of the air core increases due to the increase of air, part of the air can be discharged into the atmosphere via the water seal. As a result, the U water seal 4 can function as an air compensating means. With the device for eliminating the static pressure of downward flowing liquid of the invention, since both ends of the riser pipe are connected with the heating system, the air in the riser pipe is kept sealed when the U-water seal remains closed. Only part of the air, which is carried by the water flow, participates the circulation from the air- collecting bucket, the air-water separator to the riser pipe. During this circulation, the air dissolved in and carried by the water flow will be collected in the air core of the riser pipe, becoming dynamic part of the air core in the riser pipe. If only the heating system keeps in operation, the closed state of the air core in the riser pipe will be maintained. Obviously, the air lock phenomenon, which affects the normal heating and results form the air carried by the water flow, will be eliminated. At the same time, since the air is kept in a closed state over a long period of time, oxygen in the air will be exhausted firstly. As a result, the air core in the riser pipe comprises only inert gases, thus creating an oxide-etch-free working condition for the heating system equipped with the static pressure eliminating device of the invention.

Fig. 9 shows a heating system equipped with the static pressure eliminating device in accordance with the first embodiment of the invention. In fig. 9, reference numeral 16 designates the return pipe of the high-pressure zone of a heating system; 26 the supply pipe of the high- pressure zone; 17 the automatic exhaust valve; 18 the heating riser pipe; 19 the drain valve of the high-pressure zone; 20 valves; 21 the pressure water pump for the high-pressure zone; 22 the thermometer; 23 pressure gauge; 24 the check valve; 27 the radiator; 28 the return pipe of the low- pressure zone; 29 the supply pipe of the low-pressure zone; 30 the outdoor return pipe; 31 the outdoor supply pipe; 32 the flow control valve.

As shown in Fig. 9, part of the water from the outdoor supply pipe is supplied to the low-pressure zone of the heating system via the supply pipe 29 of the low pressure zone; and the water returns to the outdoor return pipe 30 via the return pipe 28 of the lower pressure zone after flowing through the radiators. The remaining water is supplied to the high-pressure zone of the heating system via the high pressure zone supply pipe 26 by means of the pressure water pump 21; after flowing through the radiators, the water first flows through the static pressure eliminating device of the invention via the return pipe of the high pressure zone, whereby the static pressure of the high pressure zone return water is eliminated. Thereafter, the return water of the high-pressure zone returns to the outdoor return pipe 30 via a pipe.

An example of the device for eliminating the static pressure of downward flowing water in accordance with the first embodiment of the invention will be described below.

In this example, the overall flow rate of the high pressure zone is 20m3/h ; the highest point of the system is 65m; the full pipe specific friction resistance (at given flow rate and given internal diameter, the pressure loss per meter) of the return pipe of the high pressure zone is about 47pa/m; the full pipe flow velocity is 0.65m/s. The riser pipe 3 is a welded steel pipe with an internal diameter of 106mm (nominal diameter is DN100). The nominal diameter of the air circulating pipe 10 is DN20, the air circulating pipe is inserted into the riser pipe by 300mm and is connected coaxially with the flow guiding tube 1 via the reducing pipe 3, the reducing pipe has a length of 1500mm and an outer diameter of 57mm.

The spiral flow guiding plate 2 has a pitch of 300mm, an outer diameter of 102mm and a length of 450mm. The effective water sealing height of the U water seal tube 4 is lm, the U water seal tube is installed on the riser pipe at the elevation of 38m. The air collecting bucket 6 is located at the elevation of 17m, the air-water separator 9 is located at a position which is one meter lower than the minimum height of the hydrodynamic pressure line of the low pressure zone. The height of the hydrodynamic pressure line of low pressure zone of the heating system is between 22- 37m.

Fig. 5 illustrates the second embodiment of the device for eliminating the static pressure of downward flowing liquid in accordance with the invention. As shown in Fig. 5, in the static pressure eliminating device in accordance with the second embodiment of the invention, the air-circulating pipe 10 is connected with the flow guiding tube 1 via a reducing pipe 11 and a bend pipe 13. The reducing pipe 11 is located outside the riser pipe 3, its small-diameter end is connected to the top end of the air circulating pipe 10 and its large-diameter end is connected to the bend pipe 13. The bend pipe 13 extends through the wall of the riser pipe and is communicated with the flow guiding tube at the tube wall.

The top of the flow guiding tube 1 is closed with a plate member 14, and the bottom of the flow guiding tube is communicated with the riser pipe.

The bend pipe is connected in a sealing manner with the riser pipe 3. The spiral flow guiding plate 2 is provided at the lower portion of the flow guiding tube 1, being located under the connection point of the bend pipe 13 and the flow guiding tube 1. The air collecting pipe 8, which connects the air-water separator 9 and the air collecting bucket 6, inserts into the air-water separator from its bottom, with its mouth at a certain height from the bottom of the air-water separator. The other components of the static pressure eliminating device of the second embodiment are the same as those in the first embodiment.

Fig. 11 illustrates the arrangement of the device for eliminating the static pressure of downward flowing liquid in accordance with the second embodiment of the invention in a heating system.

Fig. 6 illustrates the third embodiment of the device for eliminating the static pressure of downward flowing liquid in accordance with the invention. As shown in fig. 6, the static pressure eliminating device of the third embodiment is substantially the same as that shown Fig 5. The difference lies in that the bend pipe 15 is semicircular in shape and is connected with the top of the flow guiding tube. The other components are the same as those described in connection with the second embodiment, their description is thus omitted. Fig. 10 shows the arrangement of the device for eliminating the static pressure of downward flowing liquid in accordance with the third embodiment of the invention in a heating system.

Fig. 8 shows an alternative of the air-collecting bucket used in the device for eliminating the static pressure of downward flowing liquid in accordance with the invention. As shown in fig. 8, the air-collecting bucket is a horizontal cask which is connected in a sealing manner with the lower end 5 of the riser pipe 3 at its top, the end 5 of the riser pipe is inserted into the cask. The lower end of the air collecting tube 8, which is connected with the air-water collector 9, is connected with the cask at its apex. The water circulation pipe 12 of the air-water separator and the pipe coupling 7 are connected to the cask at its lower portion. The connection position of the riser pipe 3 with the air collecting bucket and the mounting position of the pipe coupling 7 on the air collecting bucket are not limited to those shown in the figures but can be changed according to actual situation. The dotted line in Fig 8 shows another possible connection.

With the horizontal air-collecting bucket, the vertical height of the air- collecting bucket is small, thus facilitating the arrangement of the static pressure eliminating device.

In the embodiments described above, the device for eliminating the static pressure of downward flowing liquid comprises: a flow guiding means which is composed of a flow guiding tube 1 and a spiral flow guiding plate 2 mounted on the flow guiding tube; a U water-seal tube 4; an air collecting bucket 6; and an air circulation means which is composed of the air collecting bucket 6, an air collecting pipe 8, a water circulation pipe 12, an air-water separator 9 and an air circulating pipe 10.

However, it should be pointed out that although a static pressure eliminating device comprising the components described above is a preferred solution, some of the components are not indispensable for achieving the object of the invention. Moreover, various embodiments can be obtained by combining some of the components. The following are only some examples of the possible combinations.

Example 1 The device for eliminating the static pressure of downward flowing liquid comprises: a flow guiding means composed of a flow guiding tube 1; a U water-seal tube 4; an air collecting bucket 6; and an air circulation means which is composed of the air collecting bucket 6, an air collecting pipe 8, a water circulation pipe 12, an air-water separator 9 and an air circulation pipe 10.

Example 2 The device for eliminating the static pressure of downward flowing liquid comprises: a flow guiding means composed of a flow guiding tube 1 and a spiral flow guiding plate 2 mounted on the flow guiding tube; an air collecting bucket 6; and an air circulation means which is composed of the air collecting bucket 6, an air collecting pipe 8, a water circulation pipe 12, an air-water separator 9 and an air circulation pipe 10. The air circulation means forms an air compensating means.

Example 3 The device for eliminating the static pressure of downward flowing liquid comprises: a flow guiding means composed of a flow guiding tube land a spiral flow guiding plate 2 mounted on the flow guiding tube; and a U water-seal tube 4. The U water-seal tube is used as an air compensating means.

Example 4 The device for eliminating the static pressure of downward flowing liquid comprises: a flow guiding means composed of a flow guiding tube 1 and a spiral flow guiding plate 2 mounted on the flow guiding tube; and a U water-seal tube 4; and an air collecting bucket 6 with a controllable outlet on its top for releasing the collected air.

Furthermore, as an example of the alternative embodiments, the device for eliminating the static pressure of downward flowing liquid can only comprises: a flow guiding means composed of a flow guiding tube 1 and a spiral flow guiding plate 2 mounted on the flow guiding tube; and an air circulation pipe 10. The air circulation pipe is communicated with the atmosphere and is used as an air compensating means.

In the embodiments described above, the device for eliminating the static pressure of downward flowing liquid is described in connection with a heatng system. However, the application of the static pressure eliminating device of the invention is not limited to a heating system, it can also be used with other liquid transportation systems such as petroleum transportation system.

Persons skilled in the art will appreciate that various modifications can be made to the embodiments without departing from the spirit and scope of the invention.