CN113175838B

CN113175838B - Heat exchanger with composite flow-around structure

Info

Publication number: CN113175838B
Application number: CN202110559461.2A
Authority: CN
Inventors: 谢纬安; 樊登柱; 包雅媛; 瞿磊; 李守娟; 施蒋彬
Original assignee: Nantong Vocational College
Current assignee: Nantong Vocational College
Priority date: 2021-05-21
Filing date: 2021-05-21
Publication date: 2022-07-22
Anticipated expiration: 2041-05-21
Also published as: CN113175838A

Abstract

The invention discloses a heat exchanger with a composite flow-around structure, which comprises collecting pipes arranged on two sides and a micro-channel flat pipe layer group used for communicating the collecting pipes, wherein the micro-channel flat pipe layer group comprises a first micro-channel flat pipe, a second micro-channel flat pipe and a third micro-channel flat pipe; the micro-channel flat tube layer group also comprises a plurality of straight fins, and the straight fins and three adjacent layers of micro-channel flat tubes form a flow winding structure unit; in the bypass structure unit, the first micro-channel flat tube and the second micro-channel flat tube are encircled to form a first air side channel, the second micro-channel flat tube and the third micro-channel flat tube are encircled to form a second air side channel, and a bypass part is arranged in the first air side channel. The second microchannel flat tube forms first strand of streaming, and streaming spare forms second strand of streaming, and two strand of streaming interact form compound streaming, can initiate the swirl that has less swirl scale ratio LRv, help improving convection heat exchange efficiency.

Description

Heat exchanger with composite flow-around structure

Technical Field

The invention belongs to the technical field of heat exchangers, and particularly relates to a heat exchanger with a composite bypass structure.

Background

With the development of the air conditioner heat exchanger technology, the micro-channel heat exchanger has the advantages of high heat transfer efficiency, small volume, light weight, small refrigerant filling amount, compact structure and the like, and becomes a hot spot for research and attention of the industrial high-efficiency heat exchanger. The design research about the microchannel parallel flow heat exchanger focuses on three aspects of fin structure parameters, collecting pipe connection distribution form and flat pipe microchannel mechanism: in the aspect of fin structure parameters, the heat transfer at the air side is enhanced by optimizing the profile of the fin and the size parameters of the louver fin; in the aspect of the connection and distribution form of the collecting pipes, the structure of the heat exchanger is optimized and the heat transfer is enhanced by changing the direct connection mode of the collecting pipes and the flat pipes and the structural characteristics of the collecting pipes; in the aspect of a flat tube micro-channel mechanism, the uniformity of refrigerant distribution is promoted through a novel micro-channel structural design.

However, because of the structural limitation of the micro-channel flat tube on the micro-channel heat exchanger, the heat exchange performance of the existing micro-channel flat tube is poor. In the prior art including chinese patent CN207635921U, the structure of the micro-channel flat tube is improved, and the micro-channel flat tube is designed to be bent, so as to increase the turbulent flow strength of the passing fluid and strengthen the heat exchange.

However, the blunt body formed by only depending on the special-shaped structure of the micro-channel flat tube has limited streaming strength, the promotion degree of the heat exchange effect is not high, and the heat exchange efficiency of the whole heat exchanger has a further promotion space.

Disclosure of Invention

The invention provides a heat exchanger with a composite streaming structure, aiming at further increasing the passive streaming effect of fluid, enhancing the instability of flow, strengthening the convection heat transfer effect and improving the working efficiency of the heat exchanger.

During the development process, the vortex scale ratio LRv has a certain correlation with local convective heat transfer while characterizing the vortex morphology. Here LRv is the concept proposed by the inventor for the first time, and its calculation formula is: LRv ═ Lv/Hv, where Lv is the swirl flow direction length and Hv is the swirl height, as shown in fig. 13. Experiments show that the smaller the vortex scale ratio LRv is, the better the local convective heat transfer effect is; while the swirl scale ratio LRv is closely related to the flow structure as well as the reynolds number. Therefore, the invention improves the structure of the heat exchanger to generate the vortex with the vortex scale smaller than LRv in the heat exchanger, thereby obtaining the heat exchanger with higher heat exchange efficiency.

In order to achieve the technical effects, the invention adopts the following technical scheme:

the heat exchanger with the composite bypass structure comprises

Collecting pipes arranged at two sides of the heat exchanger main body;

the micro-channel flat tube layer group comprises a first micro-channel flat tube, a second micro-channel flat tube and a third micro-channel flat tube which are sequentially adjacent from top to bottom, the second micro-channel flat tube comprises a first horizontal section, a second horizontal section and a connecting section, and the first horizontal section and the second horizontal section are arranged in a staggered mode and are connected through the connecting section;

each micro-channel flat tube layer group also comprises a plurality of straight fins, and the straight fins divide the micro-channel flat tube layer group into a plurality of flow winding structure units; in each flow-bypassing structural unit, the first micro-channel flat tube and the second micro-channel flat tube enclose a first air side channel, and the second micro-channel flat tube and the third micro-channel flat tube enclose a second air side channel; a bypass is provided in the first air-side passage, and a second bypass is provided in the second air-side passage.

In some embodiments, the connecting section is vertically arranged, and the second microchannel flat tube composed of the first horizontal section, the second horizontal section and the connecting section is stepped.

In some embodiments, the distance between the first microchannel flat tube and the second horizontal segment is twice the distance between the first microchannel flat tube and the first horizontal segment.

In some embodiments, the distance between the first flat microchannel tube and the first horizontal segment is the same as the distance between the third flat microchannel tube and the second horizontal segment.

In some embodiments, the flow-around member is disposed on an extension of the first horizontal segment.

In some embodiments, the distance between the bypass flow element and the connecting segment is not less than the distance between the first microchannel flat tube and the second horizontal segment.

In some embodiments, the distance between the flow-around element and the connecting segment is equal to the distance between the first microchannel flat tube and the second horizontal segment.

In some embodiments, the second flow winding member is the same shape as the flow winding member, and the positions of the second flow winding member and the flow winding member correspond to each other.

In some embodiments, the flow-around component is a circular tube having a diameter equal to the distance between the first microchannel flat tube and the first horizontal segment.

In some embodiments, the flow-surrounding member is in communication with the manifold.

The beneficial effects of the invention are: in each flow-bypassing structural unit, a first bypass flow is formed by the induction of a second micro-channel flat tube in a multi-section structure shape, a second bypass flow is formed by the induction of a bypass flow piece, and two bypass flows interact to form a composite bypass flow, so that a vortex with a smaller vortex scale ratio of LRv can be initiated, the damage to a wall surface flow boundary layer is facilitated, and the heat convection of the heat exchanger is improved.

Drawings

FIG. 1 is a schematic overall structure of one embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a portion of a bypass flow structure unit according to an embodiment of the present invention;

FIG. 3 is a schematic view of the arrangement of the flow-around elements in one embodiment of the invention;

FIG. 4 is a schematic view of an embodiment of the present invention with a different number of streams around the core;

FIG. 5 is a schematic diagram of an embodiment of the present invention with different positions of flow-around elements;

FIG. 6 is a schematic diagram of an embodiment of the present invention with different dimensions of the flow-surrounding members;

FIG. 7 is a schematic view of an embodiment of the invention with different flow-around element shapes;

FIG. 8 is a schematic view of an alternative flow-around element configuration of the present invention;

FIG. 9 is a schematic of a composite flow field of examples 1-7 of the present invention and a comparative example;

FIG. 10 is the time-averaged Knoop numbers of inventive examples 1-7 and comparative examples;

FIG. 11 is a schematic view of a composite flow field of examples 5, 8-11 of the present invention;

FIG. 12 shows the time-averaged Knoop numbers of examples 5 and 8 to 11 according to the invention;

FIG. 13 is a physics model of a vortex in accordance with the present invention;

in the figure: 100 collecting main, 200 microchannel flat tube group, 210 first microchannel flat tube, 220 second microchannel flat tube, 230 third microchannel flat tube, 221 first horizontal segment, 222 second horizontal segment, 223 linkage segment, 240 straight fin, 251 first air side passageway, 252 second air side passageway, 260 is around flowing the piece.

Detailed Description

The technical scheme of the invention is further explained by combining the drawings in the specification.

Example 1

As shown in FIGS. 1 and 3, a heat exchanger with a composite bypass structure comprises

Collecting pipes 100 arranged at two sides of the heat exchanger main body;

the microchannel flat tube layer set 200 comprises a first microchannel flat tube 210, a second microchannel flat tube 220 and a third microchannel flat tube 230 which are sequentially adjacent from top to bottom, the second microchannel flat tube 220 comprises a first horizontal section 221, a second horizontal section 222 and a connecting section 223, and the first horizontal section 221 and the second horizontal section 222 are arranged in a staggered manner and connected through the connecting section 223;

each micro-channel flat tube layer group 200 also comprises a plurality of straight fins 240, and the straight fins 240 divide the micro-channel flat tube layer group 200 into a plurality of flow winding structure units; in each flow-around structure unit, the first micro-channel flat tube 210 and the second micro-channel flat tube 220 enclose a first air side channel 251, and the second micro-channel flat tube 220 and the third micro-channel flat tube 230 enclose a second air side channel 252; a tubular bypass member 260 is provided in each of the first air-side passage 251 and the second air-side passage 252, and the positions of the bypass members 260 correspond to each other. The connecting section 223 is vertically arranged, and the second microchannel flat tube 220 composed of the first horizontal section 221, the second horizontal section 222 and the connecting section 223 is step-shaped.

The distance between the first microchannel flat tube 210 and the second horizontal segment 222 is twice the distance between the first microchannel flat tube 210 and the first horizontal segment 221, and the distance between the first microchannel flat tube 210 and the first horizontal segment 221 is equal to the distance between the third microchannel flat tube 230 and the second horizontal segment 222, that is, the two horizontal segments forming the second microchannel flat tube 220 are respectively located on the trisection line of the distance between the first microchannel flat tube 210 and the third microchannel flat tube 230.

The bypass 260 is disposed on an extension of the first horizontal segment 221, and a distance from the connection segment 223 is equal to a distance between the first microchannel flat tube 210 and the first horizontal segment 221, that is, Xc/S ═ 1, where Xc is a distance between the bypass 260 and the connection segment 223, and S is a distance between the first microchannel flat tube 210 and the first horizontal segment 221. The diameter D of the bypass 260 is 0.4 times the distance between the first microchannel flat tube 210 and the first horizontal section 221, i.e., D is 0.4S.

A first medium (which may be a gas or a fluid) is input from the header 100 on one side of the heat exchanger, flows through the plurality of microchannel flat tube layer sets 200, and is output from the header 100 on the other side. When a first medium flows through the interior of the microchannel flat tube layer group 200, a second medium (usually air) passes through the exterior of the microchannel flat tube layer group 200 along the direction perpendicular to the flow direction of the first medium, and takes away heat transferred by the first medium through the microchannel flat tube, so as to form heat exchange. In each of the bypass structural units of this embodiment, the air current that the step-like second microchannel flat tube 220 induction passes forms the first bypass, and the air current that the circular tube shape is around flow piece 260 induction and is formed the second bypass, and two bypass interactions form compound bypass, strengthen the instability of air current, improve convection and heat exchange efficiency from this.

As shown in fig. 4 to 6, the number, position and dimension conditions of the flow-around members 260 can be modified according to actual conditions, and the technical effect of improving the heat exchange efficiency can also be achieved.

Of course, the bypass 260 can be set to be square, triangular or other shapes as shown in fig. 7 and fig. 8, and it can also form blunt body bypass, but the bypass 260 with other shapes can generate a larger resistance to fluid while inducing bypass, which affects the flow velocity of the fluid passing through, and thus affects the passing rate of the fluid and the heat exchange efficiency of the heat exchanger, and round tubes are the shape of the bypass 260 which is theoretically most suitable.

The flow-surrounding member 260 is communicated with the collecting pipe 100, and the flow-surrounding member 260 can provide an additional channel for the refrigerant in the collecting pipe 100 while inducing to form flow surrounding, so that the flow of the refrigerant is increased, the distribution uniformity of the refrigerant is improved, and the heat exchange efficiency is further improved. Of course, in other embodiments, the bypass member 260 may only play a role of generating bypass, but is not communicated with the header 100, and this is an alternative arrangement and should not be construed as limiting the technical solution.

Example 2

The general structure is the same as that of embodiment 1, except that the distance between the flow-around piece 260 and the connecting section 223 is twice as long as the distance between the first microchannel flat tube 210 and the first horizontal section 221, that is, Xc/S is 2. That is, the distance between the bypass 260 and the connecting segment 223 is equal to the distance between the first microchannel flat tube 210 and the second horizontal segment 222.

Example 3

The general structure is the same as that of embodiment 1, except that the distance between the flow-around member 260 and the connecting section 223 is four times as long as the distance between the first microchannel flat tube 210 and the first horizontal section 221, i.e., Xc/S is 4.

Example 4

The general structure is the same as that of embodiment 1, except that the distance between the flow-surrounding member 260 and the connecting segment 223 is six times the distance between the first microchannel flat tube 210 and the first horizontal segment 221, that is, Xc/S is 6.

Example 5

The general structure is the same as that of embodiment 1, except that the distance between the flow-around piece 260 and the connecting section 223 is eight times as long as the distance between the first microchannel flat tube 210 and the first horizontal section 221, that is, Xc/S is 8.

Example 6

The general structure is the same as that of embodiment 1, except that the distance between the winding member 260 and the connecting section 223 is ten times that between the first microchannel flat tube 210 and the first horizontal section 221, that is, Xc/S is 10.

Example 7

The general structure is the same as that of embodiment 1, except that the distance between the flow-around piece 260 and the connecting section 223 is twelve times the distance between the first microchannel flat tube 210 and the first horizontal section 221, that is, Xc/S is 12.

Comparative example

The heat exchanger is similar in construction to embodiment 1, but only stepped second microchannel flat tubes 220 are provided in the bypass flow structure unit, and no bypass 260 is provided in both the first air-side channel 251 and the second air-side channel 252.

Example 8

The general structure is the same as that of embodiment 5, except that the diameter of the flow-surrounding member 260 is 0.2 times the distance between the first microchannel flat tubes 210 and the first horizontal section 221, i.e., D is 0.2S.

Example 9

The general structure is the same as that of embodiment 5, except that the diameter of the flow-around piece 260 is 0.6 times the distance between the first microchannel flat tube 210 and the first horizontal section 221, i.e., D is 0.6S.

Example 10

The general structure is the same as that of embodiment 5, except that the diameter of the flow-surrounding member 260 is 0.8 times the distance between the first microchannel flat tubes 210 and the first horizontal section 221, i.e., D is 0.8S.

Example 11

The general structure is the same as that of embodiment 5, except that the diameter of the flow-surrounding member 260 is equal to the distance between the first microchannel flat tube 210 and the first horizontal section 221, i.e., D ═ 1.0S.

Analysis of test results of position of streaming part

The above examples 1 to 7 and comparative example were subjected to the same conditions for testing, and the flow field test results are shown in fig. 9. It can be seen from the above that, compared with the single step bypass generated in the comparative example, the composite bypass generated in examples 1 to 7 has obvious effect, and can effectively control the reattachment point position of the main bypass return zone of the step bypass, and the additional bypass 260 can inhibit the development of the separation shear layer of the main bypass return zone of the step bypass, so that the main return zone forms fluid reattachment in advance near the insertion position of the bypass 260, which is most obvious in example 2. Meanwhile, the flow instability of downstream air can be further enhanced by additionally arranging the flow-surrounding part 260, the wake flow of the flow-surrounding generated by the flow-surrounding part 260 interacts with the step surface boundary to initiate a series of vortex motions, so that the convective heat transfer at the air side is more favorably strengthened, the good convective heat transfer effect can be ensured even if the length of the downstream flow channel of the step is greatly reduced, and the design range of the length of the flow channel (namely the width of the microchannel flat tube) is expanded.

The time-averaged Knoop number results are shown in FIG. 10. It can be seen that the single step streaming of the comparative example shows a characteristic of a single peak in the knoop number curve, which peak is caused by reattachment of the separated flow. In the embodiments 1-7, under the working condition that the flow surrounding piece 260 is additionally arranged to generate the composite flow surrounding,

are greater than the single step bypass, with the peaks of example 1(Xc/S ═ 1) and example 2(Xc/S ═ 2) being significantly greater than the other examples; and when Xc/S is more than or equal to 4,

the peak value of (a) shows a small tendency of increasing first and then decreasing, and a large value appears when Xc/S is equal to 8.

The location of the peak formation is directly related to the location of the flow wrap 260, both near the location of the insertion of the flow wrap 260, and compared to a proportional single step flow wrap, the peaks in the other embodiments are generated in advance, except for the late peak occurrence in example 7(Xc/S ═ 12), indicating that the location of the flow wrap 260 provides control over the area of peak formation and significant control over the heat transfer of the flow.

In embodiment 1 and embodiment 2 of fig. 9, the swirl scale ratio of the main return swirl is smaller than LRv, and the time-averaged knoop number of the two embodiments in fig. 10 also has a significantly larger peak value near the flow-bypassing member 260, which shows that the heat exchange efficiency near the flow-bypassing member 260 is significantly improved; turning to examples 4 and 5 in FIG. 9, which produce near-wall vortices having smaller vortex scales than LRv in the region near the duct wall downstream of the flow-wrap 260, both of these examples have a higher heat exchange efficiency in the region downstream of the flow-wrap 260 in FIG. 10. Therefore, the distance between the flow-around member 260 and the connecting segment 223 can be changed according to actual needs to change the action region for improving the heat exchange efficiency.

Analysis of test results of the diameter of the flow surrounding part

The above example 5 and examples 8-11 were subjected to the same conditions for testing, and the flow field test results are shown in fig. 11. It can be seen that the diameter of the bypass 260 has little effect on the main recirculation zone, with significant effect on the cylindrical bypass wake and downstream flow pattern. Along with the increase of the diameter of the flow surrounding piece 260, the position of the reattachment point of the main backflow area gradually moves upstream, the vortex scale behind the flow surrounding piece 260 is continuously increased, and the flow instability of the downstream of the flow channel is firstly enhanced and then weakened.

In embodiment 8, D is 0.2S, the main recirculation zone extends to some extent downstream from the insertion position of the flow-surrounding member 260, and the reattachment position thereof is downstream from the insertion position of the flow-surrounding member 260, and no obvious vortex is formed near the downstream wall surface; in example 5, D is 0.4S, reattachment is formed in the main return area near the insertion position of the flow-surrounding member 260, and the fluctuation range of the downstream fluid is increased; in example 9, where D is 0.6S, the change in flow pattern mainly consists in further enhancement of the alternately formed vortices near the downstream flow channel wall and the main flow fluctuation; in the embodiment 10, D is 0.8S, the blockage ratio of the flow channel is increased, the acceleration effect of the fluid when the fluid passes through the bypass flow member 260 is remarkable, and a large-scale backflow area is formed by connecting a plurality of unseparated vortices near the downstream bottom surface; in the embodiment 11, D is 1.0S, the fluid acceleration effect is further enhanced, and a large-scale top surface secondary backflow area formed by a single backflow vortex is formed at the downstream.

The time-averaged knoevenagel number results are shown in fig. 12. It can be seen that different diameter flow-around elements 260 are built-in

The peak value is larger than the working condition of the non-bypass member. The peak value increases with the increase of the diameter of the bypass 260, and is increased by more than one time compared with the peak value of the working condition without the bypass when D is 1.0S. Except for embodiment 8, D is 0.2S, and the peak positions are advanced in the bypass-free condition under other conditions. The heat transfer of the downstream wall surface is reduced along with the increase of D, and the heat transfer is reduced after X/S is more than or equal to 35

Substantially in agreement.

As can be seen in fig. 11, the vortex scale ratio LRv of the main return vortex becomes progressively smaller as the diameter of the flow-winding member 260 increases, and the time-averaged knoop number main peak in fig. 12 increases progressively. When D is 0.6S in example 9, near-wall vortices with a small vortex size ratio are formed downstream of the flow-around element 260, and the reaction is that the local heat transfer downstream of the flow-around element 260 is optimal in fig. 12.

It will be apparent to those skilled in the art that various modifications to the above embodiments can be made without departing from the general spirit and concept of the invention. All falling within the scope of protection of the present invention. The protection scheme of the invention is subject to the appended claims.

Claims

1. The heat exchanger with the composite bypass structure is characterized by comprising

Collecting pipes (100) arranged at two sides of the heat exchanger main body;

the micro-channel flat tube layer group (200) is used for communicating the collecting pipe (100), and the micro-channel flat tube layer group (200) comprises a first micro-channel flat tube (210), a second micro-channel flat tube (220) and a third micro-channel flat tube (230) which are sequentially adjacent from top to bottom; in the direction perpendicular to the self-extending length direction, the second micro-channel flat tube (220) comprises a first horizontal section (221), a second horizontal section (222) and a connecting section (223), wherein the first horizontal section (221) and the second horizontal section (222) are arranged in a staggered mode and are connected through the connecting section (223);

each micro-channel flat tube layer group (200) further comprises a plurality of straight fins (240), and the straight fins (240) divide the micro-channel flat tube layer group (200) into a plurality of flow-around structural units; in each bypass structure unit, the first microchannel flat tube (210) and the second microchannel flat tube (220) enclose a first air side channel (251), and the second microchannel flat tube (220) and the third microchannel flat tube (230) enclose a second air side channel (252); a bypass pipe (260) is provided in the first air-side passage (251), and a second bypass pipe is provided in the second air-side passage (252); and the bypass pipe (260) and the second bypass pipe are parallel to the extending length direction of the second microchannel flat pipe (220).

2. The heat exchanger with the composite bypass structure according to claim 1, wherein the connecting section (223) is vertically arranged, and the second microchannel flat tube (220) composed of the first horizontal section (221), the second horizontal section (222) and the connecting section (223) is stepped.

3. The heat exchanger with the composite bypass structure according to claim 1, wherein a distance between the first microchannel flat tube (210) and the second horizontal section (222) is twice a distance between the first microchannel flat tube (210) and the first horizontal section (221).

4. The heat exchanger with the composite bypass structure according to claim 3, wherein the distance between the first microchannel flat tube (210) and the first horizontal section (221) is equal to the distance between the third microchannel flat tube (230) and the second horizontal section (222).

5. The heat exchanger with a composite bypass structure according to claim 1, characterized in that the bypass pipe (260) is disposed on an extension line of the first horizontal section (221).

6. The heat exchanger with the composite bypass structure according to claim 5, characterized in that the distance between the bypass pipe (260) and the connecting section (223) is not smaller than the distance between the first microchannel flat pipe (210) and the second horizontal section (222).

7. The heat exchanger with the composite bypass structure according to claim 5, characterized in that the bypass pipe (260) is at the same distance from the connecting section (223) as the distance between the first microchannel flat pipe (210) and the second horizontal section (222).

8. The heat exchanger with a composite bypass structure according to any one of claims 1 to 7, characterized in that the diameter of the bypass pipe (260) is equal to the distance between the first microchannel flat pipe (210) and the first horizontal section (221).