CN114608372B - Inducing structure of supercritical pressure fluid double main vortex field in rectangular heat exchange channel - Google Patents
Inducing structure of supercritical pressure fluid double main vortex field in rectangular heat exchange channel Download PDFInfo
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- 239000012530 fluid Substances 0.000 title claims abstract description 68
- 230000001939 inductive effect Effects 0.000 title claims description 8
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- 230000004907 flux Effects 0.000 claims abstract description 14
- 230000006698 induction Effects 0.000 claims abstract description 11
- 230000002708 enhancing effect Effects 0.000 claims description 7
- 238000013461 design Methods 0.000 abstract description 10
- 230000008569 process Effects 0.000 abstract description 8
- 238000010586 diagram Methods 0.000 description 11
- 238000005516 engineering process Methods 0.000 description 10
- 238000010438 heat treatment Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 7
- 238000012546 transfer Methods 0.000 description 6
- 230000009471 action Effects 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 230000000704 physical effect Effects 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
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- 239000002887 superconductor Substances 0.000 description 2
- 230000006978 adaptation Effects 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000008094 contradictory effect Effects 0.000 description 1
- 230000000779 depleting effect Effects 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 238000009284 supercritical water oxidation Methods 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 230000035900 sweating Effects 0.000 description 1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F1/00—Tubular elements; Assemblies of tubular elements
- F28F1/02—Tubular elements of cross-section which is non-circular
- F28F1/04—Tubular elements of cross-section which is non-circular polygonal, e.g. rectangular
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F1/00—Tubular elements; Assemblies of tubular elements
- F28F1/10—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses
- F28F1/40—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only inside the tubular element
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
- F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
- F28F13/08—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by varying the cross-section of the flow channels
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Abstract
The invention provides an induction structure of a double main vortex field of supercritical pressure fluid in a rectangular heat exchange channel, wherein a triangular longitudinal rib with a certain length is arranged on the upper wall in the rectangular heat exchange channel along the length direction of the upper wall, the rectangular heat exchange channel is a rectangular heat exchange channel with mm grade and high heat flux density, the fluid in the rectangular heat exchange channel is under the supercritical pressure, and the double main vortex field structure in the rectangular heat exchange channel is induced and enhanced by the triangular longitudinal rib, so that the low-temperature fluid in the rectangular heat exchange channel is closer to the heated wall surface of the rectangular heat exchange channel, and the heat exchange capability of the fluid near the heated wall surface of the rectangular heat exchange channel is improved. Even when the heat flux density reaches 1MW/m 2, the local heat convection coefficient can be improved by about 24% by designing triangular longitudinal ribs in a lower wall heated square tube with the hydraulic diameter of 2 mm. Meanwhile, for the mm-level heat exchange channel in the industrial field, the design method provided by the invention is easy to process and convenient to realize engineering application.
Description
Technical Field
The invention relates to the technical field of flow control and enhanced heat exchange, in particular to an induction structure of a double main vortex field of supercritical pressure fluid in a rectangular heat exchange channel.
Background
Because of unique physical parameters, supercritical pressure fluid is widely applied in industry, and mainly relates to the fields of ground nuclear power stations, transcritical carbon dioxide air conditioners, sweating cooling of supercritical water oxidation technology wall surfaces, cooling of superconductors by supercritical low-temperature fluid and the like. In the above applications, the hydraulic diameter of the pipes involved is wide, without depleting the pipes on the order of mm or even finer. Meanwhile, the rectangular heat exchange channel is widely applied in the industrial field, and relates to the fields of superconductor cooling, aircraft heat protection, heat exchanger design, air conditioning system pipeline design, reactor heat protection design and the like. In summary, the flow heat exchange process of the supercritical pressure fluid in the rectangular channel is a common basic physical process in the related field. In order to widen the application range of a related system using supercritical pressure fluid as a working medium and improve the heat exchange performance of the system, so as to absorb more heat with smaller mass flow of the working medium, a person skilled in the art needs to study the reinforced heat exchange technology of the supercritical pressure fluid in a rectangular heat exchange channel, and the reinforced heat exchange technology is particularly suitable for a micro channel.
In the industrial field, in order to promote the convective heat transfer of the working medium in the pipeline, a fin-added mode is generally adopted to promote the heat transfer. Patent application publication number 1451937A provides a design method of a discontinuous double-inclined inner rib reinforced heat exchange tube. By arranging a series of discontinuous double-inclined inner rib structures which are inclined in two directions and form a certain included angle with the axial direction along the flow direction in the pipeline, longitudinal vortex flow and other forms of radial flow are induced near the inner wall surface. Patent application publication number 106017194a provides a method of designing a heat exchanger with the ability to induce longitudinal vortex. Longitudinal vortex is generated by arranging a series of vortex generators with streamline edges on the surface of the heat exchanger, so that the heat exchange capacity is improved. But for some special application environments, the design of the heat exchange channel faces more limitations and is more unique. On the one hand, the hydraulic diameter of the pipeline is smaller in the relevant application background, which is about mm magnitude or even smaller, such as the design of a working medium heat exchange channel in an air conditioner. This makes a more complex enhanced heat exchange design similar to that of the related patents described above difficult to implement. On the other hand, because the working medium in the heat exchange channel is under the supercritical pressure, the physical property change of the supercritical pressure fluid is obvious, and the flow heat exchange process of the working medium in the channel is unique. For example, a double primary vortex structure may be formed at the inlet of the heated channels, which may allow for improved heat exchange within the tubes. Therefore, when the circulating working medium is supercritical pressure fluid, the reinforced heat exchange scheme of the rectangular pipeline needs to be designed by combining the special properties of the supercritical pressure fluid, and not all reinforced heat exchange measures can be applied.
Under supercritical pressure, the existing researches are mostly based on the working condition of low heat flux density, and the pipeline is a uniform heat exchange circular pipe. The adopted reinforced heat exchange scheme is mainly to carry out reinforced heat exchange design through a spiral wire structure, and the mechanism is that a spiral flow structure is generated in a circular channel through the induction of a spiral wire, so that on one hand, the exchange between fluids in a cross section is reinforced, and on the other hand, the turbulent energy is promoted, so that the heat exchange is promoted. In some applications, the heat exchange channels need to withstand relatively high heat flux densities, as in nuclear reactor applications. This makes it difficult to apply the prior art directly to the above-mentioned research fields. Meanwhile, the processing difficulty of the reinforced heat exchange technology adopting the spiral wire structure is relatively high.
For the micro-channel of the mm level, the prior art has larger processing difficulty and high realization cost, and the discontinuous double-inclined inner rib structure is difficult to be directly applied to the application field of the heat exchange pipeline of the mm level. Meanwhile, the reinforced heat exchange technology based on the complex vortex generator in the prior art does not consider the flow field structure formed by supercritical pressure fluid spontaneously inside the rectangular channel, and the applicability of the reinforced heat exchange technology needs to be further examined.
In addition, under certain working conditions, the high-temperature side heat exchange channel can face a non-uniform heated working condition, and the rectangular channel is a preferential scheme due to the relatively large heated area. The flow field inside the channels has its own uniqueness, as the flow within rectangular channels is affected by the reynolds stresses which are unevenly distributed in the circumferential direction. The design of convective heat transfer needs to consider the influence of the self flow field structure inside the rectangular channel. However, for partial inner rib structures, such as reinforced heat exchange technology based on bottom wall trapezoidal longitudinal ribs, the influence of the physical parameters of the strong nonlinear change of the supercritical pressure fluid on the flow field structure and the heat exchange process is not considered, and the heat exchange cannot be reinforced. Therefore, the applicability of the inner rib structure in the prior reinforced heat exchange technology to the reinforced heat exchange of the supercritical fluid in the rectangular channel is further questionable.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention aims to provide an induction structure of a double main vortex field of supercritical pressure fluid in a rectangular heat exchange channel.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
On the one hand, the invention provides a reinforced heat exchange method of supercritical pressure fluid in a rectangular heat exchange channel, wherein the rectangular heat exchange channel is a micro-mm-level rectangular heat exchange channel with high heat flux density, the internal pressure of the rectangular heat exchange channel is higher than the critical pressure of corresponding fluid, the fluid in the rectangular heat exchange channel is under the supercritical pressure, and the low-temperature fluid in the rectangular heat exchange channel is closer to the heated wall surface of the rectangular heat exchange channel by inducing and reinforcing a double-main vortex field structure in the rectangular heat exchange channel, so that the heat exchange capability of the fluid near the heated wall surface of the rectangular heat exchange channel is improved.
Furthermore, as a preferred scheme of the invention, the upper wall in the rectangular heat exchange channel is provided with a triangular longitudinal rib with a certain length along the length direction, and when supercritical pressure fluid in the rectangular heat exchange channel flows through the triangular longitudinal rib, the triangular longitudinal rib can induce and strengthen the double main vortex field structure in the rectangular heat exchange channel.
Further, as a preferred embodiment of the present invention, the triangular longitudinal rib is provided at the center of the upper wall in the rectangular heat exchange channel.
Further, as a preferable scheme of the invention, the bottom surface of the triangular longitudinal rib is overlapped with the upper wall in the rectangular heat exchange channel and is in an inverted triangle structure.
Further, as a preferable aspect of the present invention, the triangular longitudinal ribs have a cross section of isosceles triangle.
Further, as a preferable scheme of the invention, the heated wall surface of the rectangular heat exchange channel is the lower wall surface of the rectangular heat exchange channel.
On the other hand, the invention provides a double-main vortex field induction structure for supercritical pressure fluid in a rectangular heat exchange channel, wherein the induction structure improves heat exchange capacity by utilizing the reinforced heat exchange method for supercritical pressure fluid in the rectangular heat exchange channel, and triangular longitudinal ribs with certain length are arranged on the upper wall in the rectangular heat exchange channel along the length direction of the upper wall.
Also, as a preferred embodiment of the above-described induction structure, the triangular longitudinal rib is provided at the center of the upper wall in the rectangular heat exchange channel.
Similarly, as a preferable scheme of the induction structure, the bottom surface of the triangular longitudinal rib is overlapped with the upper wall in the rectangular heat exchange channel, and is in an inverted triangle structure.
Also, as a preferable mode of the above-mentioned inducing structure, the triangular longitudinal ribs have a cross section of isosceles triangle.
Also, as a preferable mode of the induction structure, the heated wall surface of the rectangular heat exchange channel is a lower wall surface of the rectangular heat exchange channel.
Compared with the prior art, the invention has the following advantages:
The invention provides an intensified heat exchange method of supercritical pressure fluid in a rectangular heat exchange channel, which is used for enhancing a double-main-vortex structure in the rectangular heat exchange channel and improving the heat exchange effect of supercritical pressure working media. According to the invention, through reasonably designing the inner rib structure in the rectangular heat exchange channel, the generation of the double main vortex structure in the rectangular heat exchange channel is induced, the double main vortex structure in the rectangular heat exchange channel can be maintained at a longer distance, the double main vortex structure beneficial to heat exchange in the rectangular heat exchange channel is enhanced, and the flow heat exchange process in the channel is enhanced, so that the heat exchange performance of working media in the channel is improved.
Drawings
FIG. 1 is a schematic diagram of heat exchange of supercritical pressure fluid in a rectangular heat exchange channel with one side heated according to an embodiment of the present invention;
FIG. 2 is a schematic cross-sectional view of a rectangular heat exchange channel provided with triangular longitudinal ribs in an embodiment of the invention
Fig. 3 is a schematic flow field diagram of a single-sided heated rectangular smooth heat exchange channel (no rib structure is provided in the channel) at x=0.20m according to an embodiment of the present invention;
Fig. 4 is a schematic flow field diagram of a single-sided heated rectangular smooth heat exchange tube (without rib structure in the channel) at x=0.45m according to an embodiment of the present invention;
fig. 5 is a schematic flow field diagram of a single-sided heated rectangular heat exchange channel with triangular longitudinal ribs at x=0.45m according to an embodiment of the invention;
FIG. 6 is a schematic diagram showing the effect of triangular longitudinal ribs on the wall temperature of the bottom heating surface of a single-sided heated rectangular heat exchange channel according to an embodiment of the present invention;
FIG. 7 is a schematic diagram showing the influence of triangular longitudinal ribs on the heat exchange coefficient in a single-sided heated rectangular heat exchange channel according to an embodiment of the present invention;
FIG. 8 is a schematic view of heat flux density distribution of a uniformly heated rectangular smooth heat exchange channel (without rib structures in the channel) according to an embodiment of the present invention;
Fig. 9 is a schematic flow field diagram of a rectangular smooth heat exchange channel (without rib structure in the channel) with uniform heat exposure at x=0.05m according to an embodiment of the present invention;
fig. 10 is a schematic flow field diagram of a rectangular smooth heat exchange channel (without rib structure in the channel) with uniform heat exposure at x=0.30m according to an embodiment of the present invention;
Fig. 11 is a schematic view of a flow field at x=0.30m in a uniformly heated rectangular heat exchange channel with triangular longitudinal ribs according to an embodiment of the present invention;
FIG. 12 is a schematic view showing the effect of triangular longitudinal ribs on the temperature of the upper and lower walls of a uniformly heated rectangular heat exchange channel according to an embodiment of the present invention;
FIG. 13 is a schematic view showing the effect of triangular longitudinal ribs on the bottom wall-to-flow heat transfer coefficient of a uniformly heated rectangular heat exchange channel in accordance with an embodiment of the present invention;
The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that all directional indicators (such as up, down, left, right, front, and rear … …) in the embodiments of the present invention are merely used to explain the relative positional relationship, movement, etc. between the components in a particular posture (as shown in the drawings), and if the particular posture is changed, the directional indicator is changed accordingly.
Furthermore, descriptions such as those referred to as "first," "second," and the like, are provided for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implying an order of magnitude of the indicated technical features in the present disclosure. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.
In the present invention, unless specifically stated and limited otherwise, the terms "connected," "affixed," and the like are to be construed broadly, and for example, "affixed" may be a fixed connection, a removable connection, or an integral body; the device can be mechanically connected, electrically connected, physically connected or wirelessly connected; either directly or indirectly, through intermediaries, or both, may be in communication with each other or in interaction with each other, unless expressly defined otherwise. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
In addition, the technical solutions of the embodiments of the present invention may be combined with each other, but it is necessary to be based on the fact that those skilled in the art can implement the technical solutions, and when the technical solutions are contradictory or cannot be implemented, the combination of the technical solutions should be considered as not existing, and not falling within the scope of protection claimed by the present invention.
The embodiment of the invention provides a reinforced heat exchange method for supercritical pressure fluid in a rectangular heat exchange channel. Referring to fig. 1, the rectangular heat exchange channel is a micro-mm-level rectangular heat exchange channel with high heat flux, the internal pressure of the rectangular heat exchange channel is higher than the critical pressure of the corresponding fluid, and the fluid in the rectangular heat exchange channel is under the supercritical pressure. In this embodiment, by inducing and enhancing the double-main vortex field structure in the rectangular heat exchange channel, the low-temperature fluid in the rectangular heat exchange channel is closer to the heated wall surface of the rectangular heat exchange channel, so that the heat exchange capability of the fluid near the heated wall surface of the rectangular heat exchange channel is improved. The rectangular heat exchange channel is a micro-millimeter level, and particularly is a micro-millimeter rectangular heat exchange pipeline with a hydraulic diameter of millimeter level or even finer.
In one embodiment of the present invention, referring to FIG. 2, a double primary vortex field structure within a rectangular heat exchange channel is induced and enhanced by adding triangular longitudinal ribs within a fine rectangular heat exchange tube having a hydraulic diameter on the order of mm or even finer.
In one embodiment of the invention, triangular longitudinal ribs with certain length are arranged on the upper wall in a micro rectangular heat exchange pipeline with the hydraulic diameter of mm or even finer along the length direction of the micro rectangular heat exchange pipeline, and when supercritical pressure fluid in the rectangular heat exchange channel flows through the triangular longitudinal ribs, the triangular longitudinal ribs can induce and strengthen a double main vortex field structure in the rectangular heat exchange channel. Compared with the complex structures such as the transverse inclined rib, the spiral wire and the like, the upper wall triangular longitudinal rib structure is easier to process.
In an embodiment of the invention, the triangular longitudinal ribs extend from the inlet of the rectangular heat exchange tube to the outlet of the rectangular heat exchange channel, i.e. the length of the triangular longitudinal ribs is the same as the length of the rectangular heat exchange tube. Of course, in practical application, the length of the triangular longitudinal ribs can be reasonably designed, the whole section of the triangular longitudinal ribs can be continuously designed, the triangular longitudinal ribs can be sectionally designed, and the distribution form is not limited.
In one embodiment of the invention, the triangular longitudinal ribs are arranged in the centre of the upper wall in the rectangular heat exchange channels.
In one embodiment of the present invention, the bottom surface of the triangular longitudinal rib coincides with the upper wall in the rectangular heat exchange channel, and has an inverted triangle structure.
In one embodiment of the invention, the triangular longitudinal ribs have a cross section of isosceles triangle.
In an embodiment of the present invention, the heated wall surface of the rectangular heat exchange channel is a lower wall surface of the rectangular heat exchange channel, that is, single-sided heating is adopted. In practical application, the heating device is not limited to single-sided heating, and can be double-sided heating and multi-sided uniform heating.
In the above embodiments, the triangular longitudinal ribs are disposed on the upper wall in the micro rectangular heat exchange tube, and the secondary flow is enhanced under the action of the triangular longitudinal ribs, and the double main vortex structure in the cross section of the rectangular heat exchange tube is maintained for a longer distance. Due to the effect of the double main vortex structure, low-temperature fluid at the core of the rectangular heat exchange pipeline is extruded to the vicinity of the heated wall surface, so that heat exchange in the vicinity of the heated wall surface of the rectangular heat exchange pipeline is improved, and the temperature of the rectangular heat exchange pipeline is reduced.
In an embodiment of the present invention, referring to fig. 2, the heat exchange channels in the micro rectangular heat exchange tube 1 are square heat exchange channels 2, the side length c of the square heat exchange channels 2 is 2mm, the vertical wall thickness δ of the micro rectangular heat exchange tube 1 is 1mm, the left and right wall thickness a of the micro rectangular heat exchange tube 1 is 0.5mm, the height H of the micro rectangular heat exchange tube 1 is 4mm, and the width b of the micro rectangular heat exchange tube 1 is 3mm. The center of the upper wall in the rectangular heat exchange pipeline 1 is provided with a triangular longitudinal rib 3 along the length direction of the upper wall, the cross section of the triangular longitudinal rib is isosceles triangle, and the bottom surface of the triangular longitudinal rib is overlapped with the upper wall in the rectangular heat exchange channel and is in an inverted triangle structure. The triangular longitudinal ribs extend from the inlet of the square heat exchange tube to the outlet of the square heat exchange tube. The height h of the triangular longitudinal ribs is 0.4mm, and the width of the bottoms of the triangular longitudinal ribs is 0.24mm, wherein the heated wall surface of the rectangular heat exchange channel is the lower wall surface of the rectangular heat exchange channel. In order to enhance the heat exchange of the supercritical pressure working medium in the bottom heated channel, and simultaneously consider the reinforced heat exchange potential of the double main vortex structure spontaneously formed at the front section of the pipeline, a triangular longitudinal rib is designed on the upper wall of the heat exchange channel so as to induce the double main vortex structure to generate and further prolong the continuous distance of the double main vortex structure in the heat exchange channel. Referring to fig. 5, 6 and 7, fig. 5 is a schematic view of a flow field at x=0.45 m in a single-sided heated rectangular heat exchange channel provided with triangular longitudinal ribs in the present embodiment; FIG. 6 is a schematic diagram showing the effect of triangular longitudinal ribs on the wall temperature of the bottom heating surface of a single-sided heated rectangular heat exchange channel in the embodiment; FIG. 7 is a schematic view showing the influence of triangular longitudinal ribs on the heat exchange coefficient in a single-sided heated rectangular heat exchange channel in the present embodiment; it can be seen from fig. 5 that the double main vortex structure still dominates the channel cross section. This shows that the present invention induces the generation of a double main vortex structure and significantly extends its sustained distance within the channel. As can be seen from fig. 6, the double main vortex structure is induced and prolonged in its range of action due to the triangular rib structure, which reduces the wall temperature of the tube, especially at the rear end of the heat exchange channel. Under the condition of 1MW/m 2 heat flow density, the wall temperature can be reduced by about 40K, and the mechanical property of the corresponding material can be improved. As can be seen from fig. 7, since the triangular rib structure induces and extends the range of the double main vortex structure, the low temperature fluid in the center of the pipe is pressed to the vicinity of the lower wall, thereby enhancing heat exchange at the lower wall. At a heat flux density of 1MW/m 2, at x=0.45 m, the convective heat transfer coefficient near the center of the lower wall can be improved by about 24%.
The heat exchange channels in the micro rectangular heat exchange pipeline in an embodiment of the invention are square heat exchange channels, the square heat exchange channels are shown in fig. 8, but triangular longitudinal ribs are not arranged in the square heat exchange channels. The side length c of the square heat exchange channel is 2mm, the upper and lower wall thicknesses of the micro rectangular heat exchange channel are 1mm, the left and right wall thicknesses of the micro rectangular heat exchange channel are 0.5mm, the height H of the micro rectangular heat exchange channel is 4mm, the width b of the micro rectangular heat exchange channel is 3mm, and the heated wall surface of the rectangular heat exchange channel is the lower wall surface of the rectangular heat exchange channel. The rectangular heat exchange pipeline starts to be heated at x=0.15m, and referring to fig. 3 and 4, fig. 3 is a schematic diagram of a flow field structure at x=0.20m in a single-sided heated rectangular smooth heat exchange channel (rib structure is not arranged in the channel) in this embodiment, and as can be seen from fig. 3, the flow field structure is affected by physical properties of a supercritical fluid, and at this time, the cross section of the heat exchange channel is occupied by a double main vortex structure. The structure can promote the mixing between the fluids on the cross section and enable the low-temperature fluid at the core of the pipeline to approach the heated lower wall, thereby promoting the heat exchange in the pipeline. Fig. 4 is a schematic view of the flow field structure at x=0.45m in the single-sided heated rectangular smooth heat exchange tube (no rib structure is provided in the channel) in this embodiment, and it can be seen from fig. 4 that the double main vortex structure has been resolved.
In an embodiment of the present invention, referring to fig. 2, the heat exchange channels in the micro rectangular heat exchange tube are square heat exchange channels, the side length c of the square heat exchange channels is 2mm, the upper and lower wall thicknesses of the micro rectangular heat exchange tube are 1mm, the left and right wall thicknesses of the micro rectangular heat exchange tube are 0.5mm, the height H of the micro rectangular heat exchange tube is 4mm, and the width b of the micro rectangular heat exchange tube is 3mm. The center of the upper wall in the rectangular heat exchange pipeline is provided with a triangular longitudinal rib along the length direction of the upper wall, the cross section of the triangular longitudinal rib is isosceles triangle, and the bottom surface of the triangular longitudinal rib is overlapped with the upper wall in the rectangular heat exchange channel to form an inverted triangle structure. The triangular longitudinal ribs extend from the inlet of the square heat exchange tube to the outlet of the square heat exchange tube. The height h of the triangular longitudinal ribs is 0.4mm, and the width of the bottoms of the triangular longitudinal ribs is 0.24mm, wherein the heated wall surfaces of the rectangular heat exchange channels are all the side wall surfaces of the rectangular heat exchange channels, namely the heat exchange channels with the rectangular heat exchange channels heated uniformly. The supercritical pressure fluid flows through the rectangular heat exchange channel, heat is transferred to the supercritical pressure fluid from the periphery of the rectangular heat exchange channel through each side wall, and the supercritical pressure fluid is supercritical pressure CO 2. Referring to fig. 11, 12 and 13, fig. 11 is a flow field schematic diagram at x=0.30m in the uniformly heated rectangular heat exchange channels provided with triangular longitudinal ribs in the present embodiment; FIG. 12 is a schematic view showing the effect of triangular longitudinal ribs on the wall temperature of the bottom heating surface of a uniformly heated rectangular heat exchange channel in the present embodiment; FIG. 13 is a schematic view showing the influence of triangular longitudinal ribs on the heat exchange coefficient in a uniformly heated rectangular heat exchange channel in the present embodiment; it can be seen from fig. 11 that the double main vortex structure still dominates the channel cross section. This shows that the present invention induces the generation of a double main vortex structure and significantly extends its dominant distance within the channel. As can be seen from fig. 12, the double main vortex structure is induced and prolonged in its range of action due to the triangular rib structure, which reduces the wall temperature of the tube, especially at the rear end of the heat exchange channel. At a heat flux density of 250kW/m 2, the wall temperature can be reduced by about 90K at maximum. As can be seen from fig. 13, since the triangular rib structure induces and extends the range of the double main vortex structure, the low temperature fluid in the center of the pipe is pressed to the vicinity of the lower wall, thereby enhancing heat exchange at the lower wall. In this embodiment, the convective heat transfer coefficient near the center of the lower wall can be increased by about 22% under uniform heat flux conditions. The heat convection coefficient is improved more at the right angle position near the wall surface.
The heat exchange channels in the micro rectangular heat exchange pipeline in an embodiment of the invention are square heat exchange channels, the square heat exchange channels are shown in fig. 8, but triangular longitudinal ribs are not arranged in the square heat exchange channels. The side length c of the square heat exchange channel is 2mm, the upper and lower wall thicknesses of the micro rectangular heat exchange channel are 1mm, the left and right wall thicknesses of the micro rectangular heat exchange channel are 0.5mm, the height H of the micro rectangular heat exchange channel is 4mm, the width b of the micro rectangular heat exchange channel is 3mm, wherein the heated wall surfaces of the rectangular heat exchange channel are all side wall surfaces of the rectangular heat exchange channel, namely the rectangular heat exchange channel is uniformly heated. The supercritical pressure fluid flows through the rectangular heat exchange channel, heat is transferred to the supercritical pressure fluid from the periphery of the rectangular heat exchange channel through each side wall, and the supercritical pressure fluid is supercritical pressure CO 2. Referring to fig. 9 and 10, fig. 9 is a schematic view of a flow field structure at x=0.05m in a rectangular smooth heat exchange channel (no rib structure is arranged in the channel) heated uniformly in this embodiment, and it can be seen from fig. 9 that the flow field structure is affected by the physical properties of the fluid under the supercritical pressure, and the cross section of the heat exchange channel is occupied by a double main vortex structure. The structure can promote the mixing between the fluids on the cross section, and the low-temperature fluid at the core of the pipeline is close to the heated lower wall, thereby being beneficial to promoting the heat exchange in the pipeline. Fig. 10 is a schematic view of the flow field structure at x=0.30m in the uniformly heated rectangular smooth heat exchange tube (no rib structure is provided in the channel) in this embodiment, and it can be seen from fig. 10 that the double main vortex structure has been resolved.
On the other hand, referring to fig. 2, the present invention provides a structure for inducing a double main vortex field of supercritical pressure fluid in a rectangular heat exchange channel, which improves heat exchange capacity by using the method for enhancing heat exchange of supercritical pressure fluid in a rectangular heat exchange channel provided in the above embodiment, and a triangular longitudinal rib with a certain length is provided on an upper wall in the rectangular heat exchange channel along a length direction thereof. The structure optimization arrangement of the rectangular heat exchange channels and the triangular longitudinal ribs is described in detail in the previous embodiments, and is not described herein.
For the supercritical pressure fluid, the triangular longitudinal ribs arranged on the upper wall in the micro rectangular heat exchange pipeline can enable the double main vortex structure to maintain a longer distance, and heat exchange of the supercritical pressure fluid is improved. Compared with a smooth rectangular pipeline, the double-main-vortex structure in the pipeline is induced and enhanced, so that the convection heat exchange coefficient at the rear part of the pipeline is improved by about 20%. While other configurations of the inner rib structure are not necessarily capable of inducing the generation of a double main vortex structure and enhancing heat exchange within the duct. If the bottom trapezoid longitudinal inner rib is arranged, the structure cannot strengthen the double main vortex structure, and the heat exchange of supercritical pressure fluid is not improved, but the heat exchange of supercritical pressure working medium in the rectangular pipeline is restrained.
Compared with the prior reinforced heat exchange technology of supercritical fluid in a circular tube, such as a spiral wire technology, the invention can be suitable for the working condition with high heat flux density, and the heat flux density can reach MW/m 2 level.
In summary, the triangular longitudinal rib structure arranged in the micro rectangular heat exchange channel can induce the generation of the double main vortex structure in the rectangular heat exchange channel, and the continuous distance of the double main vortex structure is wider, so that the convective heat exchange performance of the supercritical pressure working medium is enhanced, and the wall temperature of the high temperature side of the heat exchange channel is reduced. In the rectangular heat exchange channel, when the pressure is 8MPa and the heat flux density is 1MW/m 2, the local wall temperature can be reduced by 40K, and the mechanical property of the corresponding material can be improved. Meanwhile, the triangular longitudinal rib structure is easy to process and convenient to realize.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the invention without departing from the principles thereof are intended to be within the scope of the invention as set forth in the following claims.
Claims (5)
1. The intensified heat exchange method of the supercritical pressure fluid in the rectangular heat exchange channel is characterized in that the rectangular heat exchange channel is a micro-mm-level rectangular heat exchange channel with high heat flux density, the heated wall surface of the rectangular heat exchange channel is the lower wall surface of the rectangular heat exchange channel, the internal pressure of the rectangular heat exchange channel is higher than the critical pressure of the corresponding fluid, the fluid in the rectangular heat exchange channel is under the supercritical pressure, a triangular longitudinal rib with a certain length is arranged on the upper wall in the rectangular heat exchange channel along the length direction of the upper wall, the bottom surface of the triangular longitudinal rib coincides with the upper wall in the rectangular heat exchange channel and is in an inverted triangle structure, when the supercritical pressure fluid in the rectangular heat exchange channel flows through the triangular longitudinal rib, the triangular longitudinal rib can induce and strengthen the double-main vortex field structure in the rectangular heat exchange channel, and the double-main vortex field structure in the rectangular heat exchange channel is induced and strengthened, so that the low-temperature fluid in the rectangular heat exchange channel is closer to the heated wall surface of the rectangular heat exchange channel, and the heat exchange capacity of the fluid near the heated wall surface of the rectangular heat exchange channel is improved.
2. The method of enhancing heat exchange of supercritical pressure fluid in a rectangular heat exchange channel according to claim 1, wherein the triangular longitudinal rib is provided in the center of the upper wall in the rectangular heat exchange channel.
3. The enhanced heat exchange method of supercritical pressure fluid in a rectangular heat exchange channel according to claim 1 or 2, wherein the cross section of the triangular longitudinal rib is isosceles triangle.
4. The induction structure of the double main vortex fields of the supercritical pressure fluid in the rectangular heat exchange channel is characterized in that the induction structure improves heat exchange capacity by using the reinforced heat exchange method of the supercritical pressure fluid in the rectangular heat exchange channel as claimed in claim 1.
5. The structure for inducing a double primary vortex field of a supercritical pressure fluid in a rectangular heat exchange channel according to claim 4 wherein the triangular longitudinal rib is centrally disposed in the upper wall of the rectangular heat exchange channel.
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