CN105115347B - Flow-guiding plug-in device in heat exchange tube - Google Patents

Abstract

The invention discloses a drainage type insertion device in a heat exchange tube, which comprises an insert unit and a support rod. The flow channels are respectively arranged at the upper and lower ends of the drainage section in the horizontal direction to form a stepped structure; the support rod is arranged along the axial direction of the heat exchange tube, and the insert unit is installed on the On the support rod, wherein, the distance between the insert unit and the wall of the heat exchange tube is H, 0<H≤0.15D, and D is the inner diameter of the heat exchange tube. The insert unit of the present invention generates a longitudinal vortex through turbulence in a certain arrangement mode, which increases heat transfer without excessively increasing resistance. The new insertion device integrated in one body has a good ability to enhance heat transfer.

Description

A drainage type insertion device in a heat exchange tube

technical field

The invention belongs to the field of heat exchange tube turbulence technology and devices, and more specifically relates to a drainage type insertion device in a heat exchange tube.

Background technique

There are generally two types of tube-side enhanced heat transfer technologies: one is surface-based enhanced heat transfer technology, such as spiral grooved tubes, zoom tubes, corrugated tubes and other common special-shaped tubes, which are formed by different surface structures near the tube wall. The fluid is disturbed and disrupts the development of the boundary layer to achieve the purpose of enhancing heat transfer. The other is fluid-based enhanced heat transfer technology, such as twisted ribbons, worm rods, spiral coils and other common tube inserts, which disturb the fluid area by themselves, so that the temperature of the fluid area is as uniform as possible to achieve the purpose of enhancing heat transfer . The disturbance of the latter to the boundary layer will be weaker than that of the former, so the pressure loss will be smaller, so there will be better comprehensive performance of heat transfer enhancement.

The design of traditional inserts is generally based on the following ideas: while causing strong disturbances, the resistance will not increase excessively. The fundamental purpose of disturbance is to make the temperature in the tube more uniform, so as to achieve the purpose of enhancing heat transfer. However, while the insert greatly improves the heat transfer capacity, the price paid is a large pressure drop along the way. Therefore, the comprehensive performance of enhanced heat transfer is limited. At the same time, some inserts have higher enhanced heat transfer capacity in theory, but are difficult to process and support in practice, so the application range is limited.

Contents of the invention

In view of the above defects or improvement needs of the prior art, the present invention provides a drainage type insertion device in the heat exchange tube, in which, based on the consideration of the purpose of turbulence, on the basis of the traditional insert, it is proposed that the drainage method is more intuitive The mixing between fluids of different temperatures can be greatly promoted, so that the heat exchange tube can obtain a more ideal heat exchange capacity. At the same time, the new insertion device is easy to process and welded on the support rod, and it is easier to be applied in practice.

In order to achieve the above object, the present invention proposes a drainage type insertion device in a heat exchange tube, which is characterized in that it includes a support rod and a plurality of insert units, wherein:

The support rod is arranged inside the heat exchange tube and arranged along the axial direction of the heat exchange tube;

The insert unit includes a drainage section and two horizontal flow channels, the drainage section is arranged obliquely, and the two horizontal flow channels are respectively arranged at the upper and lower ends of the drainage section along the horizontal direction, and are connected to the upper and lower ends of the drainage section. The included angles are all obtuse angles; the insert unit is welded on the support rod through the horizontal flow channel; the distance between the insert unit and the wall of the heat exchange tube is H, where 0< H≤0.15D, D is the inner diameter of the heat exchange tube.

As a further preference, there are 24 insert units, and every two insert units are arranged symmetrically on both sides of the support rod to form a set of flow disturbance units, each set of flow disturbance units along the The support rods are arranged in a row.

As a further preference, there are 24 insert units, and every two insert units are arranged symmetrically on both sides of the support rod to form a set of flow disturbance units, each set of flow disturbance units along the The support rods are arranged in a fork row.

As a further preference, the cross-sectional shape of the drainage section is rectangular, semicircular or circular.

As a further preference, the inclination angle of the drainage section is preferably 45°.

As a further preference, the cross-sectional shape of the horizontal channel is rectangular or arc-shaped.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

1. In the present invention, each insert unit is designed to be composed of a drainage section and a horizontal flow channel, wherein the drainage section guides the fluid in the core flow region to the vicinity of the wall surface, and the horizontal flow channel constrains the guided fluid to scour near the pipe wall, Thereby enhancing heat transfer. The insert unit is fixed by the support rod and does not contact the wall of the heat exchange tube, thereby reducing the disturbance to the wall velocity boundary layer, the flow resistance will not increase excessively, and the heat transfer is significantly improved.

2. Compared with traditional inserts (such as twisted bands), the present invention has smaller fluid contact area and less flow resistance. At the same time, the present invention can also form a longitudinal vortex in a fork row arrangement, so that it has enhanced A good flow structure that does not increase the resistance too much while exchanging heat.

Description of drawings

Fig. 1 (a) is a schematic diagram of the arrangement of the fork row of the insert unit of the present invention;

Figure 1(b) is a schematic diagram of the arrangement of insert units in a row according to the present invention;

Fig. 1 (c) is a structural schematic diagram of the drainage section of the insert of the present invention;

Figure 2 is the temperature distribution diagram of different cross-sections in the fork row and in-row arrangement;

Fig. 3 is the velocity vector diagram of cross-section z=18mm for the arrangement of forks;

Fig. 4 is the velocity vector diagram of section z=18mm in the arrangement mode along the row;

Fig. 5 is the longitudinal vortex at the cross-section z=18mm of the cross-row arrangement;

Fig. 6 is the temperature distribution diagram at the cross-section z=18mm of the cross-row arrangement;

Figure 7 shows the variation of heat transfer coefficient Nu with Re for light pipes and different arrangements;

Figure 8 shows the variation of resistance coefficient f of light pipes and different arrangements with Re;

Fig. 9 shows the variation of PEC, the comprehensive performance evaluation index of enhanced heat transfer with Re, in different arrangements.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not constitute a conflict with each other.

The present invention proposes a drainage type insertion device in the heat exchange tube, the drainage insertion device is installed in the heat exchange tube 4, which includes an insert unit and a support rod 3, wherein: the insert unit includes a drainage section 1 and two A horizontal flow channel 2, the drainage section 1 is arranged obliquely, and the two horizontal flow channels 2 are respectively arranged at the upper and lower ends of the drainage section 1 along the horizontal direction, and the included angle with the drainage section is an obtuse angle; The support rod 3 is arranged along the axial direction of the heat exchange tube, which is used to weld the insert unit and the support, and the insert unit is welded on the support rod 3 through the horizontal flow channel 2, wherein the insert The distance between the highest point of the drainage section in the unit and the wall of the heat exchange tube is H. A suitable H can prevent the drainage section from being too close to the wall surface and cause excessive resistance increase, and at the same time ensure that the horizontal channel restricts the fluid to the wall surface. For strong scouring, too large H will make the horizontal channel too far away from the wall, and the scouring effect of the fluid on the wall is not strong enough, which in turn affects the improvement of heat exchange capacity. According to the test, the present invention finds that when 0<H≤0.15D ( D is the inner diameter of the heat exchange tube), and its heat exchange capacity is better.

The above-mentioned drainage section can be in the form of a groove or a tube, and its size and cross-sectional shape can be varied, and the angle of inclination can also be changed, and the cross-sectional shape can be rectangular, semicircular, circular or other optimized shapes. The shape and size of the horizontal flow channel can also be optimized according to the specific heat exchange tube, which can be rectangular, fan-shaped, etc., and its cross-sectional shape is rectangular or arc-shaped, etc. Equivalents or modifications to slots, tubes, or horizontal flow paths are also considered consistent with the principles of the invention. There are multiple insert units, which are installed along the support rod 3 according to the requirements of heat exchange capacity, working conditions, arrangement pitch and length of heat exchange tubes. , the insert units can be arranged on the support bar in a straight row, a fork row, or in other ways, and one, two or more insert units can be arranged on each pitch.

The following will describe and demonstrate the present invention in more detail through a calculation example, but the example is only for illustrative purposes, and the specific implementation of the present invention is not limited by the example.

Example:

In this embodiment, a circular tube with an inner diameter of 18 mm and a length of 500 mm is used for the heat exchange tube. The boundary conditions of fully developed inlet velocity and inlet temperature are given at the inlet, the constant heat flow condition of 2000 W/ ^m2 is given on the wall, and the outlet is free. Flow, the surface of the insertion device is insulated, and the distance between the horizontal flow channel and the pipe wall is 2mm. Using the insertion device model shown in Figure 1, every two insert units are symmetrically arranged on both sides of the support rod 3 to form a group of turbulence units, and the pitch between each two groups of turbulence units is p=30mm , according to the arrangement pitch and the length of the heat exchange tubes, there are altogether 12 sets of turbulence units, and a total of 24 insert units. The actual needs are selected and limited, and the increase in the number of turbulence units arranged will improve the heat exchange capacity, but it will also cause an appropriate increase in resistance. Each group of turbulence units is arranged on each pitch, and the selected arrangement pitch is 30mm, which can allow the fluid to enter the next group of turbulence units after the previous group of turbulence units produces wall scour and the longitudinal vortex decays, making the disturbance And the flushing continues to recover, and the heat transfer effect of the spoiler is good. The drainage section of the insert unit adopts a rectangular chute, the drainage length l=5.6mm, the height h=1mm, the groove width w=3mm, and the inclination angle x=45°; this example adopts a rectangular horizontal flow channel, and the horizontal flow channel Dimension a=b=2mm. The material thickness of the insertion device is 1mm, and the insert units in the spoiler unit are welded on the square support rod 3 with a cross-section of 3*3mm according to the arrangement of parallel row and fork row.

Figure 2 is a comparison of the temperature field on different axial sections for the fork row and the parallel row arrangement. It can be seen from the figure that the fork row can make the temperature more uniform faster. The starting point of the position parameter z of the model in this embodiment along the axial direction of the heat exchange tube is -50mm. It can be observed in the figure that when z=82mm, there is no high temperature zone at the wall of the fork row model, because this distribution form can be faster The disturbance to the high-temperature thermal boundary layer near the wall makes it gradually disappear; therefore, the temperature is more uniform than that of the parallel model, and the thermal boundary layer is thinner, while the parallel model has two high-temperature regions near the wall, which disappear slowly , according to the core flow enhanced heat transfer theory, the heat transfer of the fork row model will be better.

Fig. 3 and Fig. 4 are the velocity vector diagrams of cross-section z=18mm in fork row and parallel arrangement. Figure 3 and Figure 4 illustrate that the drainage insertion device can make the fluid have a large component velocity in the cross-sectional direction under the drainage effect of the drainage section, so that the fluid can strongly scour the wall. From the temperature field diagram in Figure 2, it can be seen that in the two wall areas subjected to scouring, the fluid temperature is relatively low, the temperature gradient is larger, and the heat transfer performance is good. At the same time, by comparing the two arrangements, it can be seen that the fork row can also form multiple pairs of longitudinal vortices in the direction perpendicular to the drainage direction of the insert. Under the disturbance of these multiple pairs of longitudinal vortices, the boundary layer in the longitudinal vortex area is disturbed, and the thermal boundary layer Thin, good heat transfer capacity. However, the parallel arrangement does not form a strong longitudinal vortex in the direction perpendicular to the drainage, so the local heat transfer capacity in the area without inserts is not as good as that of the fork arrangement, and the temperature in the tube is not as uniform as that of the fork arrangement.

Figure 5 and Figure 6 respectively show the longitudinal vortex and temperature field at the cross-section z=18mm in the fork row mode. As in the above analysis, fork rows can form multiple pairs of longitudinal vortices, and Figure 6 shows more clearly that there are multiple pairs of high-intensity longitudinal vortices on the wall. Under their action, the temperature in these areas is more uniform, and the heat transfer capacity improve.

The calculation results of the heat transfer and resistance characteristics of this example are shown in Figures 7-9. It can be seen from Figure 7 that no matter what the arrangement is, the drainage insert can greatly improve the heat exchange capacity of the heat exchange tube, and Nu increases with the increase of Reynolds number Re. By comparison, the heat exchange capacity of the fork row is 24.2%-37.1% higher than that of the straight row, which is 4.22-4.87 times that of the bare tube. Figure 8 shows that when the heat transfer of the fork row is 24.2%-37.1% higher than that of the straight row, the resistance is only increased by 6.2%-11.1%. As shown in Figure 9, the PEC of the fork row is 25.1%-32.9% larger than the PEC of the straight row, indicating that the drainage insert can achieve better comprehensive performance by using the fork row arrangement. The PEC of the cross row arrangement can reach 1.96-2.09 under the simulated Reynolds number, which shows that the drainage insertion device can effectively improve the comprehensive performance of the heat exchange tube under laminar flow conditions.

Generally speaking, the present invention integrates the functions of drainage, turbulence, and longitudinal vortex generation, while traditional tube inserts only rely on one or two points to enhance heat transfer. The new drainage type insertion device makes the flow and heat transfer in the tube It has the following characteristics: under the action of the drainage section, the fluid of the core flow is guided to the wall surface, and the two fluids of different temperatures are mixed to increase the heat transfer; at the end of the drainage section, the fluid velocity is very high, and in the horizontal flow channel Under the constraint, the wall surface of this part is strongly washed by the fluid, the boundary layer is destroyed, and the local heat transfer capacity is improved; under the turbulence of the drainage section, a longitudinal vortex is formed, and the longitudinal vortex makes the temperature of the fluid in the area where the vortex is located more uniform. The temperature gradient becomes larger and the local heat transfer capacity increases.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (6)

1. A drainage type insertion device in a heat exchange tube, characterized in that it includes a support rod (3) and a plurality of insert units, wherein: The support rod (3) is arranged inside the heat exchange tube and arranged along the axial direction of the heat exchange tube; The insert unit includes a drainage section (1) and two horizontal flow channels (2), the drainage section (1) is a three-dimensional structure and is arranged obliquely, and the two horizontal flow channels (2) are respectively arranged in the horizontal direction The upper and lower ends of the drainage section (1) and the included angle with the drainage section (1) are both obtuse angles, so that the fluid in the core flow area in the heat exchange tube is guided to the heat exchange tube through the drainage section (1). Near the wall of the heat pipe, the guided fluid is constrained to scour near the pipe wall through a horizontal flow channel (2), thereby enhancing heat exchange; the insert unit is welded to the support rod (3) through a horizontal flow channel (2) ) above; the distance between the insert unit and the wall of the heat exchange tube is H, where 0<H≤0.15D, and D is the inner diameter of the heat exchange tube. 2. The drainage type insertion device in a heat exchange tube according to claim 1, wherein there are 24 insert units, and every two insert units are symmetrically arranged on the support rod (3 ) to form a group of turbulence units, and each group of turbulence units is arranged in a row along the support rod (3). 3. The drainage type insertion device in a heat exchange tube according to claim 1, wherein there are 24 insert units, and every two insert units are symmetrically arranged on the support rod (3 ) to form a group of turbulence units, and each group of turbulence units is arranged in a forked row along the support rod (3). 4. A drainage type insertion device in a heat exchange tube according to any one of claims 1-3, characterized in that, the section shape of the drainage section (1) is rectangle, semicircle or circle. 5. The drainage type insertion device in the heat exchange tube according to claim 4, characterized in that, the inclination angle of the drainage section (1) is 45°. 6 . The drainage type insertion device in the heat exchange tube according to claim 5 , characterized in that, the cross-sectional shape of the horizontal flow channel ( 2 ) is rectangular or arc-shaped. 7 .