CN107542674A - Centrifugal compressor - Google Patents

Abstract

The present invention provides a centrifugal compressor, comprising at least two stages of impellers, a diffuser, a reflux flow plate and a reflux device, the diffuser, the reflux flow plate and the reflux form a communication The stage flow path between the two-stage impellers, the centrifugal compressor also includes an air supply channel, the air supply channel includes an air supply port, an air outlet, and a cooling channel, and the cooling channel is arranged on the diffuser, the Inside at least one of the flow plate of the reflux device and the reflux device, the gas outlet is connected to the stage channel, the supplementary medium enters from the gas supply port, flows through the cooling channel, and passes through the gas outlet The outflow enters the stage channel and mixes with the gas in the stage channel.

Description

centrifugal compressor

technical field

The invention relates to the technical field of compression equipment, in particular to a centrifugal compressor.

Background technique

Since the specific volume ν of the gas at high temperature is very large, and the temperature of the refrigerant gas in the compressor will rise sharply after being compressed, the energy consumption of the compressor will increase sharply under the condition that the unit has the same cooling capacity. In order to reduce the power consumption of the compressor and improve the refrigeration efficiency, a multi-stage compression refrigeration cycle system is often used. The most widely used at present is the "two-stage compression intermediate incomplete cooling refrigeration cycle system" with flash vapor separator (commonly known as economizer or flasher).

In the traditional two-stage compression refrigeration cycle system, the flash steam separated from the flasher is directly mixed with the exhaust gas from the low-stage compression, which reduces the pressure of the next stage of compression to a certain extent. The intake air temperature is lower, so that the specific volume of the refrigerant gas is reduced, and the energy consumption of the compressor is reduced. However, the range of cooling through this air supply method is limited. At this time, the mixed refrigerant still has a high degree of superheat, which has not reached or approached the ideal dry saturation state, and the superheat loss is still relatively serious; and it is separated from the flasher. The flash steam that comes out is often a refrigerant in a mixed state of vapor and liquid. When the heat exchange is insufficient, it is easy to cause part of the refrigerant entering the next stage of compression to still be in the state of liquid droplets, and the phenomenon of "air supplementation with liquid" occurs. Convection channel And the impeller of the next stage forms a liquid impact, which affects the reliability of the compressor operation.

Contents of the invention

Based on this, it is necessary to provide a centrifugal compressor capable of sufficient heat exchange.

A centrifugal compressor comprising at least two stages of impellers, a diffuser, a reflux flow plate, and a reflux device, wherein the diffuser, the reflux flow plate, and the reflux form a two-stage impeller connected to each other. The centrifugal compressor also includes an air supply channel, the air supply channel includes an air supply port, an air outlet, and a cooling channel, and the cooling channel is arranged on the diffuser, the reflux device Inside at least one of the flow plate and the reflux device, the air outlet is connected to the stage flow channel, the supplementary medium enters from the air supply port, flows through the cooling channel, and flows out through the air outlet into the The stage channel and mixes with the gas in the stage channel.

In one of the embodiments, the cooling channels include a first cooling channel located in the reflux, a second cooling channel located in the flow plate of the reflux, and a third cooling channel located in the diffuser. aisle;

The air outlet includes a first air outlet, a second air outlet and a third air outlet;

The first air outlet communicates with the first cooling channel, the second air outlet communicates with the second cooling channel, and the third air outlet communicates with the third cooling channel.

In one of the embodiments, the air supply port includes a main branch and a plurality of auxiliary branches communicating with each other, and the first cooling channel, the second cooling channel and the third cooling channel are respectively connected with at least one of the The auxiliary branch is connected.

In one of the embodiments, flow vanes are arranged between the flow plate of the reflux device, the diffuser and the reflux device, flow holes are arranged in the flow flow blades, and the flow holes Used to connect the air supply port with the second cooling channel and the third cooling channel.

In one of the embodiments, the auxiliary branch includes a first auxiliary branch, a second auxiliary branch and a third auxiliary branch, the first cooling channel has a first air inlet, and the second cooling channel having a second air inlet, the third cooling passage having a third air inlet;

The first sub-branch communicates with the main branch and the second sub-branch sequentially through the flow-through plate of the recirculator and the flow hole on the flow vane between the recirculator and the diffuser. Three air inlets;

The second sub-branch is located in the flow plate of the reflux device, and is used to communicate with the first sub-branch and the second air inlet;

The third auxiliary branch directly communicates with the main branch and the first air inlet.

In one of the embodiments, the first air inlet and the first air outlet are arranged along two radial ends of the reflux device;

The second air inlet and the second air outlet are arranged at both radial ends of the flow plate of the reflux device;

The third air inlet and the third air outlet are arranged along two radial ends of the diffuser.

In one embodiment, the auxiliary branches connected to the same cooling channel can be opened or closed independently.

In one of the embodiments, there is an included angle between the gas outlet and the stage channel, and the included angle is less than 60°.

In one of the embodiments, the first gas outlet, the second gas outlet and the third gas outlet are arranged at intervals along the gas flow direction of the stage channel.

In one embodiment, the cross-sectional diameter of the second cooling passage is 0.3-0.6 times the thickness of the flow plate of the reflux device.

By opening the air supply channel, the refrigerant supplemented from the air supply port circulates in the air supply channel for a long time before it is mixed with the refrigerant compressed in the previous stage in the stage flow channel, which prolongs the relationship between the subsequent supplementary refrigerant and the compressed refrigerant in the previous stage. The heat exchange time of the refrigerant compressed by the previous stage. The design of the supplementary air channel increases the heat exchange process and heat exchange area, so that the heat exchange between the subsequent supplementary refrigerant and the refrigerant compressed by the previous stage in the stage flow channel is more sufficient, and the impact on the previous stage compression is greatly reduced. The cooling rate of the refrigerant. The temperature of the mixed gas entering the subsequent compression is lower, reducing the energy consumption of the compressor and improving the efficiency of the refrigerant. At the same time, sufficient heat exchange can fully absorb heat and vaporize the liquid components in the refrigerant entering from the air supply port, avoiding the existence of liquid droplets in the refrigerant entering the subsequent compression process, and the phenomenon of "air supply with liquid" occurs, while A liquid impact is formed on the flow channel of the first stage and the impeller of the next stage, which affects the reliability of the compressor.

Description of drawings

Fig. 1 is a schematic diagram of a centrifugal compressor according to an embodiment of the present invention;

Figure 2 is an enlarged view of area B in Figure 1;

Fig. 3 is a second schematic diagram of a centrifugal compressor according to an embodiment of the present invention;

Fig. 4 is a schematic diagram III of a centrifugal compressor according to an embodiment of the present invention;

Fig. 5 is a schematic diagram of the vane structure on the surface of the flow plate of the reflux device according to the embodiment of the present invention;

Fig. 6 is a sectional view along A-A in Fig. 5;

Fig. 7 is a sectional structural schematic diagram of the cooling channel of the flow plate of the reflux device according to the embodiment of the present invention;

Fig. 8 is a schematic diagram of the cross-sectional structure of the cooling channel of the flow plate of the reflux device according to the embodiment of the present invention;

Fig. 9 is a comparison diagram of the temperature and entropy of the refrigeration cycle according to the embodiment of the present invention.

Among them, centrifugal compressor-10; impeller-100; first-stage impeller-110; second-stage impeller-120; Air port-600; main branch-610; auxiliary branch-620; first auxiliary branch-622; second auxiliary branch-624; third auxiliary branch-626; air outlet-700; first air outlet- 710; second air outlet-720; third air outlet-730; cooling channel-800; first cooling channel-810; second cooling channel-820; third cooling channel-830; first air inlet-812; Second air inlet-822; third air inlet-832; channel unit-840; plug hole-850; branch channel-860; flow vane-900; flow hole-910; fastening screw hole- 920.

detailed description

In order to make the object, technical solution and technical effect of the present invention clearer, specific embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Referring to FIG. 1 , the present invention provides a centrifugal compressor 10 , including at least two stages of impellers 100 , a diffuser 200 , a reflux flow plate 300 and a reflux 400 . The diffuser 200 , the reflux flow plate 300 and the reflux 400 form a stage channel 500 communicating between the two impellers 100 . The centrifugal compressor 10 also includes a supplementary air passage. The air supply channel includes an air supply port 600 , an air outlet 700 and a cooling channel 800 . The cooling channel 800 is disposed inside at least one of the diffuser 200 , the flow plate 300 of the reflux device and the reflux device 400 . The gas outlet 700 communicates with the stage channel 500 . The supplementary medium enters from the gas supply port 600 , flows through the cooling channel 800 , and finally flows out through the gas outlet 700 into the stage channel 500 and mixes with the gas in the stage channel 500 .

By opening the air supply channel, the refrigerant supplemented from the air supply port 600 circulates in the air supply channel for a long time before being mixed with the refrigerant compressed in the previous stage in the stage flow channel 500, which prolongs the subsequent replenishment time. The heat exchange time between the refrigerant and the refrigerant compressed by the previous stage. The design of the supplementary air channel increases the heat exchange process and heat exchange area, so that the heat exchange between the subsequent added refrigerant and the refrigerant compressed by the previous stage in the stage flow channel 500 is more sufficient, which greatly reduces the impact on the previous stage. The cooling rate of the compressed refrigerant. The temperature of the mixed gas entering the subsequent compression is lower, reducing the energy consumption of the compressor and improving the efficiency of the refrigerant. At the same time, sufficient heat exchange can fully absorb heat and vaporize the liquid components in the refrigerant entering from the air supply port 600, avoiding the existence of liquid droplets in the refrigerant entering the subsequent compression process, and the phenomenon of "gas supplementation with liquid" occurs. However, liquid impact is formed on the flow channel 500 of the next stage and the impeller 100 of the next stage, which affects the reliability of the compressor.

Preferably, the diffuser 200 , the reflux flow plate 300 and the reflux 400 are all provided with a cooling channel 800 . The cooling channel 800 inside the reflux device 400 is a first cooling channel 810 . The cooling channel 800 located in the flow plate 300 of the reflux device 400 is the second cooling channel 820 . The cooling passage 800 inside the diffuser 200 is a third cooling passage 830 . Preferably, the air outlet 700 includes a first air outlet 710 , a second air outlet 720 and a third air outlet 730 . The first air outlet 710 communicates with the first cooling channel 810 . The second air outlet 720 communicates with the second cooling channel 820 . The third air outlet 730 communicates with the third cooling channel 830 . Setting independent gas outlets 700 for the cooling channels 800 in each component can make the gas coming out of each component enter the stage flow channel 500 to mix with the gas in the stage flow channel 500 and enter the next stage impeller. This process is repeated until the compression is complete, and the high-pressure refrigerant gas is discharged to the outside of the compressor. It is equivalent to the gas supply section with three internal flow channels. Through such a segmented gas supply method, the change of the flow line of the refrigerant gas in the stage flow channel 500 is reduced as much as possible, and the resistance loss and extra power consumption are reduced. The refrigerant gas entering the stage channel 500 from the gas outlet 700 can continue to cool the compressed refrigerant gas again, thereby reducing the temperature of the gas entering the subsequent stage of compression to a greater extent and improving the refrigeration efficiency of the compressor.

Please also refer to FIG. 3 , the air supply port 600 includes a main branch 610 and a plurality of auxiliary branches 620 communicating with each other. The first cooling channel 810 , the second cooling channel 820 and the third cooling channel 830 communicate with at least one secondary branch 620 respectively. The sub-branches 620 connected to the same cooling channel 800 can be opened or closed independently. According to the actual needs of compressor operation, one or more sub-branches 620 can be selectively opened separately, so as to ensure that the superheat of the compressor intake can be controlled in a suitable state, reduce the energy consumption of the compressor, and improve the cooling efficiency .

Optionally, flow vanes 900 are disposed between the flow return plate 300 and the diffuser 200 . Optionally, a flow vane 900 is also arranged between the flow plate 300 of the reflux device and the reflux device 400 . A flow hole 910 is disposed in the flow vane 900 . The flow hole 910 may be used to communicate the air supply port 600 with the second cooling channel 820 and/or the third cooling channel 830 . Optionally, the air supply port 600 is communicated with the second cooling channel 820 and/or the third cooling channel 830 by passing a pipeline through the flow hole 910 .

Please also refer to FIG. 4 , optionally, the sub-branch 620 includes a first sub-branch 622 , a second sub-branch 624 and a third sub-branch 626 . The first cooling channel 810 has a first air inlet 812 . The second cooling channel 820 has a second air inlet 822 . The third cooling channel 830 has a third air inlet 832 . The first secondary branch 622 communicates with the main branch 610 and the third air inlet 832 through the flow hole 910 on the flow vane 900 between the reflux flow plate 300 and the flow flow vane 900 between the reflux 400 and the diffuser 200 in turn. . The second sub-branch 624 is located in the flow plate 300 of the reflux device, and is used to communicate with the first sub-branch 622 and the second air inlet 822 . The third auxiliary branch 624 directly communicates with the main branch 610 and the first air inlet 812 .

Please refer to Figure 5 and Figure 6 together. A plurality of flow vanes 900 that function as diffusers are arranged annularly on both sides of the reflux flow plate 300 . Like the diffuser 200 and the refluxer 400, the refluxer flow plate 300 is also a rotating part. In order to shorten the pipeline flow at the air supply port 600 and reduce the resistance along the way, the second air inlet 822 and the second air outlet 720 are preferably "Up and down" arrangement. The second air inlet 822 is located at the upper flow vane 900 , and the air outlet 700 is located at the lower part of the reflux flow plate 300 . Fastening screw holes 920 are provided on the flow vane 900 on both sides for fixing the flow plate 300 and the flow vane 900 of the reflux device. The second air inlet 822 runs through the flow vanes 900 on both sides, and part of the gas coming from the right recirculator continues to flow to the left and enters the diffuser 200 of the previous stage impeller 100, and the other part flows into the recirculator pass through. The second cooling passage 820 inside the flow plate 300 continues to flow in the second cooling passage 820. After completing the entire internal process, it flows out from the second air outlet 720 on the lower side of the reflux flow plate 300 and enters the stage on one side. In the runner 500.

Preferably, the first air inlet 812 and the first air outlet 710 are arranged along two radial ends of the reflux device 400 . The second air inlet 822 and the second air outlet 720 are arranged along two radial ends of the reflux flow plate 300 . The third air inlet 832 and the third air outlet 730 are arranged along two radial ends of the diffuser 500 .

Preferably, the first gas outlet 710 , the second gas outlet 720 and the third gas outlet 730 are arranged at intervals along the gas flow direction in the stage channel 500 . The way of setting intervals can make the gas coming out of each gas outlet 700 enter the stage flow channel 500 from different positions in the stage flow channel 500 , reducing the influence of supplementary gas on the original gas flow in the stage flow channel 500 .

Please also refer to FIG. 2 , there is an included angle θ between the gas outlet 700 and the stage channel 500 . The size of the included angle θ is consistent with the size of the included angle between the air outlet 700 and the cooling channel 800 . By adjusting the size of the included angle θ, the angle between the flow direction of the gas when it flows out from the gas outlet 700 and the direction of the air flow in the step flow channel 500 can be reduced to reduce the direct impact of supplementary gas on the flow in the step flow channel 500, thereby reducing additional Airflow resistance and compression work. Preferably, the included angle θ is less than 60°.

Please refer to FIG. 7 and FIG. 8 , the cooling channel 800 may be an annular channel distributed in a ring. Preferably, at least one layer of annular passages is provided inside the diffuser 200 , the flow plate 300 of the reflux device and the reflux device 400 . When the cooling passage is a multi-layer annular passage, the annular passages of each layer are communicated with each other, so that the gas entering it can circulate continuously. The multi-layer annular channel structure can have more heat exchange processes and heat exchange lengths, thereby also having a larger heat exchange area and better heat exchange effect.

Optionally, the single-layer annular channel in the cooling channel 800 includes two branch channels 860 arranged in parallel. The supplementary medium, such as refrigerant gas, flows evenly in two directions through the two parallel branch channels 860 after entering the annular channel from the inlet port, and exchanges heat with the refrigerant gas compressed in the previous stage in the stage channel 500 .

The annular channel may include a plurality of channel units 840 and plug holes 850 . A plurality of channel units 840 are sequentially connected in a ring shape. The plug hole 850 is located at the junction of the channel unit 840 away from the center of the annular channel.

Specifically, the second cooling passage 820 in the reflux flow plate 300 is taken as an example for description. The second cooling channel 820 consists of several channel units 840 machined out of a cross-sectional diameter Φ. The plug holes 850 are evenly distributed along the circumference of the flow plate 300 of the reflux device, so that the cooling channel 800 can have good sealing performance. Increasing the number n of the channel unit 840 and the plug hole 850 and reducing the angle β between the branch channel 860 and the center line of the plug hole 850 can increase the length of the annular channel, and increase the cross-sectional diameter Φ of the channel unit 840 at the same time. Increase the heat exchange area between the supplementary refrigerant gas and the compressed gas in the previous stage. The number n of the plug holes 850 is preferably 3-12. The angle β between the centerline of the channel unit 840 and the centerline of the plug hole 850 is preferably 10°-60°. The cross-sectional diameter Φ of the channel unit 840 is preferably 0.3-0.6 times the thickness of the reflux flow plate 300 . Through the control of parameters, the heat exchange space is improved, and the heat exchange process and area are greatly increased, thereby reducing the superheat of the post-compression intake air and improving energy efficiency, and at the same time effectively avoiding the phenomenon of "gas supplementation with liquid".

Similarly, the reflux 400 on both sides of the reflux flow plate 300 and the cooling channel 800 in the diffuser 200 also adopt this structural form.

The design of the cooling channel 800 not only ensures that the limited space is reasonably used to fully exchange heat for the gas in the stage channel 500 , but also ensures a good sealing effect in the stage channel 500 . Based on the internal channel of the stage flow channel 500, make full use of the advantage of the middle position of the reflux flow plate 300, maximize the use of the limited space of the stage flow channel 500, increase the heat exchange area, and do not change the operating parameters such as cooling capacity and pressure ratio In this way, the overheating loss can be effectively reduced, the energy consumption of the compressor can be further reduced, and the cooling efficiency can be improved.

The following will take the two-stage compression as an example to illustrate the process of supplementing air in detail. Please refer to Fig. 1, the stage flow channel 500 between the first stage compression and the second stage compression is composed of a fixed static element diffuser 200, a reflux flow plate 300 and a reflux 400, the first stage compression and the second stage compression are respectively Work is done by the high-speed rotation of the impeller 100 in the flow passage of the first-stage impeller 110 and the second-stage impeller 120 . The refrigerant in the gas-liquid mixed state from the flasher enters the gas supply port 600 from the outside, and enters the inside of the reflux device 400, and then is divided into two paths. All the way into the first cooling channel 810 in the reflux device 400 to flow continuously, so as to exchange heat with the first-stage compressed exhaust gas in the side-stage flow channel 500, reduce the temperature of the first-stage exhaust gas, and finally flow in from the first air outlet 710 The other path flows from the flow hole 910 in the flow vane 900 into the reflux flow plate 300, and then divides into two paths again. All the way into the second cooling passage 820 in the flow plate 300 of the reflux device and flows continuously, thereby exchanging heat with the first-stage compressed exhaust gas in the two-stage flow passages 500 on both sides, reducing the exhaust gas temperature of the first stage, and finally from the first stage The second air outlet 720 flows into the stage flow channel 500; the other path continues to flow continuously from the flow hole 910 in the flow vane 900 to the third cooling channel 830 in the diffuser 200, thereby connecting with one side stage flow channel The first-stage compressed exhaust gas in 500 performs heat exchange, lowers the temperature of the first-stage exhaust gas, and finally flows into the first-stage flow channel 500 from the third air outlet 730 . The refrigerant gas that flows out from each gas outlet and is fully mixed with the first-stage compressed exhaust gas for heat exchange basically does not have liquid entrainment, and the mixed gas is sucked by the second-stage impeller 120 and compressed again, and finally discharged to the outside of the compressor, so It also avoids adverse effects such as the impact of the "liquid hammer" phenomenon on the pneumatic components inside the compressor.

The first-stage compressed exhaust mentioned above is the refrigerant gas that enters the first-stage flow channel 500 after the first-stage impeller 110 rotates at a high speed to perform work and is compressed.

Please refer to Figure 9, the starting point of the two-stage compression before cooling is 2a, and the starting point of the two-stage compression becomes 2b after cooling. At this time, the temperature of the mixed gas has been reduced to a certain extent, and is closer to the ideal dry saturation state. The power consumption of the two-stage compression is reduced by ΔWc, and the refrigeration coefficient ε is also improved while keeping the cooling capacity q _o unchanged, thus improving the refrigeration efficiency of the compressor.

The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. a kind of centrifugal compressor (10), including at least both stage impellers (100), diffuser (200), return channel cross flowing plate (300) And return channel (400), the diffuser (200), the return channel cross flowing plate (300) and the return channel (400) forms connection Level runner (500) between the both stage impellers (100), it is characterised in that the centrifugal compressor (10) is also led to including tonifying Qi Road, the air supply passage include gas supplementing opening (600), gas outlet (700) and cooling duct (800), and the cooling duct (800) sets Be placed in the diffuser (200), the return channel crosses flowing plate (300) and the return channel (400) at least one inside, The gas outlet (700) connects with the level runner (500), and supplement medium enters from the gas supplementing opening (600), flows through described cold But passage (800), via the gas outlet (700) exit into the level runner (500) and with the level runner (500) Gas mixing.

2. centrifugal compressor (10) according to claim 1, it is characterised in that

The cooling duct (800) includes the first cooling duct (810) in the return channel, positioned at the return channel mistake The second cooling duct (820) in flowing plate (300) and the 3rd cooling duct (830) in the diffuser (200)；

The gas outlet (700) includes the first gas outlet (710), the second gas outlet (720) and the 3rd gas outlet (730)；

First gas outlet (710) connects (810) with first cooling duct, second gas outlet (720) with it is described Second cooling duct (820) connects, and the 3rd gas outlet (730) connects with the 3rd cooling duct (830).

3. centrifugal compressor (10) according to claim 2, it is characterised in that the gas supplementing opening (600) includes mutually interconnecting Logical main branch (610) and multiple sub-branchs (620), first cooling duct (810), second cooling duct (820) And the 3rd cooling duct (830) connects with least one sub-branch (620) respectively.

4. centrifugal compressor (10) according to claim 3, it is characterised in that the return channel crosses flowing plate (300) and institute State and excessively stream blade (900) is provided between diffuser (200) and the return channel (400), set in the excessively stream blade (900) Have a flowing hole (910), the flowing hole (910) be used to connecting the gas supplementing opening (600) and second cooling duct (820) and 3rd cooling duct (830).

5. centrifugal compressor (10) according to claim 4, it is characterised in that it is secondary that the sub-branch (620) includes first Branch road (622), the second sub-branch (624) and the 3rd sub-branch (626), first cooling duct (810) have the first air inlet Mouthful (812), second cooling duct (820) have the second air inlet (822), and the 3rd cooling duct (830) is with the Three air inlets (832)；

First sub-branch (622) passes sequentially through the return channel and crosses flowing plate (300) and the return channel (400) and the expansion The flowing hole (910) on excessively stream blade (900) between depressor (200) connects the main branch (610) and the described 3rd Air inlet (832)；

Second sub-branch (624) is located at the return channel and crossed in flowing plate (300), for connecting first sub-branch (622) with second air inlet (822)；

3rd sub-branch (626) directly connects the main branch (610) and first air inlet (812).

6. centrifugal compressor according to claim 5, it is characterised in that

First air inlet (812) is set with radial direction both ends of first gas outlet (710) along the return channel (400)；

Second air inlet (822) crosses the radial direction both ends of flowing plate (300) with second gas outlet (720) along the return channel Set；

3rd air inlet (832) is set with radial direction both ends of the 3rd gas outlet (730) along the diffuser (500).

7. centrifugal compressor (10) according to claim 5, it is characterised in that be connected to the identical cooling duct (800) closure or openness that can be independent between the sub-branch (620).

8. centrifugal compressor (10) according to claim 1, it is characterised in that the gas outlet (700) and the level stream There is angle, the angle is less than 60 ° between road (500).

9. centrifugal compressor (10) according to claim 2, it is characterised in that first gas outlet (710), described The gas flow of second gas outlet (720) and the 3rd gas outlet (730) along the level runner (500) is arranged at intervals.

10. centrifugal compressor (10) according to claim 2, it is characterised in that the horizontal stroke of second cooling duct (820) Diameter of section is 0.3-0.6 times that the return channel crosses flowing plate (300) thickness.