CN110395488B

CN110395488B - Grid particle composite bed stacking method

Info

Publication number: CN110395488B
Application number: CN201910691080.2A
Authority: CN
Inventors: 王秋旺; 王晶钰; 杨剑
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2019-07-30
Filing date: 2019-07-30
Publication date: 2020-07-14
Anticipated expiration: 2039-07-30
Also published as: CN110395488A

Abstract

The invention relates to a grid particle composite bed stacking method, which comprises the steps of pre-assembling an upper layer of positioning grids and a lower layer of positioning grids with spherical particles to form a spherical layer whole body, then filling the spherical layer whole body into a container layer by layer at the top of the container, and automatically forming an ordered stacking structure when the grids and the particles fall down and the relative positions of the grids and the particles are unchanged. The grid particle composite bed stacking method provided by the invention can realize various different ordered stacking modes and various gradient ordered stacking structures, and compared with the grid particle composite bed, the heat transfer performance is possibly further improved by reasonably designing the stacking structures under the condition of maintaining the same horizontal heat transfer characteristic.

Description

Grid particle composite bed stacking method

Technical Field

The invention belongs to the field of porous medium flow heat transfer, and relates to a method for realizing an ordered packed bed of composite particles.

Background

The particle accumulation bed is widely applied to catalytic reactors, high-temperature gas cooled reactors, particle energy storage and other industries. Among the particle stacking beds, disordered stacking is the most common one, because this stacking is randomly generated, and has the advantage of low cost compared to other stacking. However, it has been found that since the particles are randomly distributed in the disordered packed bed, the flow paths of the fluid are complicated and varied, so that the flow resistance is high, and high pressure drop loss is caused. In addition, non-uniformity of the packing structure can cause non-uniformity of flow heat transfer, which on the one hand reduces the heat transfer characteristics of the packed bed and on the other hand also affects the safe operation of the reactor. Thus, although widely used, random packed beds are not the most efficient way to pack them.

In recent years more and more scholars have been concerned with ordered packed beds. Due to the regularity of the stacked structure, the flow heat transfer characteristics in the ordered structure show a periodic and symmetrical rule, and the nonuniformity is greatly reduced. Meanwhile, in the research on the ordered accumulation beds in different forms, the result shows that the ordered accumulation beds in different forms have different flowing heat transfer characteristics, and compared with the disordered accumulation bed, some ordered accumulation beds can greatly reduce the pressure drop and some ordered accumulation beds can further improve the heat exchange capacity. By reasonably selecting the form of the packed bed, the comprehensive flow heat transfer performance can be optimized. The ordered stacking bed has certain difficulty in industrial implementation, and a laboratory often adopts technologies such as 3D printing to construct a small-sized ordered stacking bed, but the cost of the method is too high to be paid.

Calis et al proposed a composite stacked structure [ patent No.: US20020038066a1], which is a random arrangement with a high degree of order. The specific implementation method is that the grid channels are filled in the container, the whole container is divided into a plurality of parallel single channels, and then the particles are filled, so that the particles randomly fall into each single channel to form a plurality of parallel sub-channel stacked beds. The shape of each sub-channel may be square or trigonometric, etc. Generally, each sub-channel has a small diameter-to-diameter ratio (1-2), and the purpose is to increase the degree of order of particle arrangement in the channel by utilizing the constraint of the wall surface of the sub-channel, so that the pressure drop in the whole container is reduced. Although the composite stacking structure proposed by Calis et al can improve the order degree of particle arrangement and reduce the pressure drop, the structure has close relation with the shape and the diameter-to-particle ratio of a single channel; after the pipe diameter particle diameter ratio in the single channel is increased, the stacking structure can not be guaranteed to be orderly controllable.

From several forms of the existing packed beds, the packed bed with high order degree is beneficial to the flow heat transfer process, but the completely ordered packed bed is difficult to realize, and the composite packed bed with the next order degree cannot be absolutely ordered. Therefore, a method for constructing a controllable ordered structure is lacked at present.

Disclosure of Invention

In order to overcome the defects of the traditional disordered, ordered and composite stacking bed, the invention provides a method for realizing a grid particle composite stacking structure, namely, various ordered stacking structures can be realized through a reasonable arrangement mode of grids and particles, and the structural design can be flexibly carried out according to the actual requirements.

The technical scheme of the invention is realized as follows: a method for stacking grid-type particle composite bed is characterized in that an upper layer of grid-type spacer grid and a lower layer of grid-type spacer grid are preassembled with spherical particles to form a spherical layer whole, then the spherical layer whole is filled into a container layer by layer at the top of the container, and when the grid-type spacer grid and the particles fall down, the relative positions of the grid-type spacer grid and the particles are unchanged, so that an ordered stacking structure can be automatically formed. When the spacer grid and the ball layer are filled at intervals, the stacking beds with different stacking modes or the same stacking mode but different particle distances can be formed by adjusting the characteristic sizes of the spacer grid and the spacer grid. The joint surface of the upper and lower layers of location grids is positioned at the maximum diameter position of the spherical particles, and the location holes are provided with spherical grooves which have opposite directions and are matched with the spherical particles in size and are used for fixing the positions of the particles. The upper and lower location grids are respectively provided with a circular truncated cone pit and a circular truncated cone boss which form an interference fit relationship, and after the upper and lower location grids are assembled with the spherical particles, the relative positions of the particles and the location grids are determined. The method is particularly suitable for use in the case of inclined filling of containers. The stacking method is not only suitable for the case that the container is a square tube, but also can be used for stacking according to the original mode only by cutting the grid frame, filling particles at the positions with complete positioning holes when the container is a round tube or other shapes.

By adopting the technical scheme, a series of grid particle composite stacking structures can be designed. The invention has the beneficial effects that:

1. the implementation method of the ordered stacking structure is provided, so that the structure is controllable and feasible;

2. the proposed composite bed stacking method can realize different ordered stacking modes and ordered stacking structures with various gradients;

3. taking an in-line stacking structure designed by the method as an example, the flowing heat transfer characteristic of the stacking structure is calculated and compared with the heat transfer characteristic of the grid particle composite stacking bed with a square pipe as a single channel proposed by Calis et al. The results show that the heat transfer characteristics of the in-line stacked structure provided by the invention are slightly higher than the heat transfer performance of the grid particle composite stacked bed with the highest heat transfer coefficient, so that the structure with better performance can be obtained by reasonable design.

Drawings

FIG. 1(a) is a three-dimensional schematic of an in-line packing structure;

FIG. 1(b) is a three-dimensional schematic view of a staggered stack configuration;

FIG. 2 is a three-dimensional schematic view of the spacer grid and ball layer when unassembled;

FIG. 3 is a two-dimensional schematic view of section A-1 shown in FIG. 2;

FIG. 4 is a three-dimensional schematic view of section A-2 shown in FIG. 2;

figure 5(a) is a cross-sectional schematic view of a support lattice (including the location of balls in an in-line stacked configuration);

FIG. 5(b) is a cross-sectional schematic view of the support lattice (including the location of the balls in a staggered packing configuration);

FIG. 6(a) is a schematic representation of feature sizes in an in-line build-up structure;

FIG. 6(b) is a schematic of feature sizes in a staggered stack configuration;

FIG. 7(a) is a circular variation of the in-line stacked configuration shown in FIG. 6 (a);

fig. 7(b) is a circular variation of the staggered stack configuration shown in fig. 6 (b).

In the figure: 1-a lower spacer grid; 2-spherical particles, 3-upper spacer grid; 4-a support grid; 5-positioning holes on the positioning grid; 6-spherical grooves on the spacer grid; 7-a truncated cone-shaped boss on the lower-layer location grid; 8-a circular truncated cone-shaped pit on the upper-layer location grid frame; 9-support holes in the support lattice; 10-unsupported holes in the support lattice.

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

Detailed Description

The drawings illustrate specific embodiments of the invention.

As shown in fig. 1, the present invention provides a method for realizing ordered particle packed bed, which can realize different ordered packing modes, not only a single one, but also two more typical ordered structures, namely a particle-in-line packed structure and a particle-staggered packed structure, are shown in fig. 1(a) and fig. 1 (b). The method for realizing the ordered packed bed provided by the invention comprises the following steps: firstly, a plurality of spherical particles 2 are clamped by a lower layer positioning grid 1 and an upper layer positioning grid 3 to form a spherical layer whole, and then the spherical layer whole is put into a container from the top so as to freely fall to the bottommost end under the action of gravity; then putting a support grid 4 at the top of the container, and enabling the support grid to freely fall onto the lower-layer particles; and putting down the ball layer assembled by the positioning grids from the top of the container, and repeating the steps to finally form the grid-particle composite ordered packed bed. It can be seen that the stacking method proposed by the present invention makes it possible to automatically realize an ordered stacking bed by preassembling the spacer grid with spherical particles. In addition, in this structure, different packing patterns can be achieved by adjusting the parameter sizes in the spacer grids and the support grids.

Fig. 2, 3 and 4 are three-dimensional schematic diagrams and two cross-sectional schematic diagrams of the spacer grid and the ball layer when the spacer grid and the ball layer are not assembled. As can be seen, the upper and lower spacer grids are provided with positioning holes 5, each positioning hole 5 is provided with a spherical groove 6 matched with the size of the spherical particles, the directions are opposite, and the combination surface is just positioned at the maximum diameter of the sphere so as to fix the particles. In addition, a circular truncated cone-shaped boss 7 is arranged on the lower-layer spacer grid, an inverted circular truncated cone-shaped pit 8 is arranged on the upper-layer spacer grid, an interference fit relation is formed between the upper-layer spacer grid and the lower-layer spacer grid, when the spherical particles and the upper-layer spacer grid and the lower-layer spacer grid are assembled, the spherical particles, the upper-layer spacer grid and the lower-layer spacer grid form a whole, and; even when the container is inclined, the relative positions of the particles and the positioning grids can still be ensured to be unchanged.

Fig. 5 is a cross-sectional view of the support lattice 4, with the maximum profile of the spherical particles in an in-line packed configuration also shown in fig. 5(a) with dashed lines and in a staggered packed configuration shown in fig. 5 (b). Referring to fig. 5(a), during the falling of the support lattice 4 from the top of the container, the support lattice does not fall any more after the bottom surfaces of the support holes 9 of the support lattice come into contact with the spherical particles. When the ball layer assembled by the spacer grid and the spherical particles is put into the top of the container again and the ball layer is the same as the first ball layer, a new ball layer is supported by the upper end surfaces of the supporting holes 9, thereby automatically forming the in-line stacking structure. In the in-line stacking structure, the upper layer particles and the lower layer particles are both in contact with the supported holes 9, and the unsupported holes 10 are only used as fluid passages.

Referring to fig. 5(b), when the positions of the alignment holes in the second layer of spacer grids are exactly crossed with the positions of the alignment holes in the first layer of spacer grids, the second layer of balls will exactly fall into the support holes 10 of the support grids 4, forming a staggered stacking structure. The spherical profile shown in fig. 5(b) more than that shown in fig. 5(a) is the profile of the second layer sphere. In the staggered stacked structure, the lower layer particles are in contact with the lower end faces of the non-support holes 10, and the upper layer particles are in contact with the upper end faces of the support holes 9.

FIG. 6(a) and FIG. 6(b) are each cisSchematic representation of grid characteristic parameters in row packing and staggered packing. How to change the packing structure by the adjustment of the parameter sizes in the spacer grids and the spacer grids will be described with reference to fig. 6(a) and (b). Referring to FIG. 6, the upper and lower positioning grids have the same dimensions in cross-section, and the width of the grid bars is w₁The inner side length of the positioning hole is w₃The distance between two positioning holes is w₂The upper and lower spacer grids may have different heights, respectively h₂And h₁(ii) a The width of the grid bars in the support grid is w₅The inner side length of the supporting hole is w₄The inner side length of the unsupported hole is w₆Height of h₄(ii) a The distance between the top end of the upper positioning grid frame and the bottom end of the support grid frame is h₃. The width w of the grid bars is such that the location holes of the upper and lower location grids need to retain particles₁And the length w of the inner edge of the positioning hole₃Sum (2 w)₁+w₃) Need to be larger than the particle diameter d_pAt the same time w₃Is less than d_p(ii) a To ensure sufficient flow space for the fluid, w₃Slightly smaller than d_pThen the method is finished; w is a₂For adjusting the spacing between particles in the same layer of spheres. In the parallel stacking structure, the upper end surface and the lower end surface of the support holes in the support grillwork are respectively tangent with the upper sphere layer and the lower sphere layer, and the characteristic parameters of the support grillwork also satisfy the following relations:

in the staggered stacking structure, the lower end surfaces of the non-support holes in the support grillwork are tangent to the lower layer balls, the upper end surfaces of the support holes are tangent to the upper layer balls, and the characteristic parameters of the structure are in the following relationship:

it is worth mentioning that the stacking structure designed by the method is not limited to the same parameter for each layer, and the lattice parameter varying along the axial direction can be designed according to the axial flow heat transfer condition. In addition, the method for realizing the composite ordered stacking bed is not only suitable for the condition that the containers are square tubes, but also can be used for containers with other shapes only by cutting the lattice frames according to the shapes of the containers, filling particles into complete lattice frame positioning holes and finishing the arrangement of a layer of balls and a layer of partition lattice frames. To be more intuitive, fig. 7(a) and (b) show an in-line stacking structure and a staggered stacking structure formed in a round tube, respectively.

The invention also uses a numerical simulation method to study the flow heat transfer characteristics of the grid particle composite packed structure and compares the characteristics with those of the grid particle composite packed bed proposed by Calis et al. Here, the structure proposed by Calis et al was chosen as the comparison target because the structure with a single-pass tube diameter to diameter ratio of 1(N1) had the highest overall heat transfer performance. Meanwhile, as the invention provides a plurality of implementation schemes of the ordered packed bed, the closest structure to the structure of N1 is selected for comparison. The thicknesses of the upper and lower positioning grids in the selected structure are both 1mm, and the thickness of the support grid is zero (corresponding to the mutual contact of the upper and lower layer balls); the particle diameter was kept the same as that of N1.

It was calculated that the on-way average main flow velocity of the patented structure was found to be higher than N1, indicating that the fluid scours the solid surface more strongly, which is beneficial for improving the convective heat transfer coefficient. The dimensionless convective heat transfer coefficient Nu of these two structures at different inlet velocities is shown in the table below, and it can be seen that Nu is indeed improved for the patented structure proposed by the present invention compared to the conventional structure.

Inlet velocity v (m/s)	Reynolds number Re_p	Nu with structure of the invention	Nu of N1
				1	685	27.44	27.46
2	1370	47.15	42.10
				3	2054	64.40	54.32

In addition, if the stacking mode or the grid parameters of the ordered stacking bed provided by the invention are changed, the heat transfer performance is expected to be further improved. In conclusion, the invention not only provides a method for realizing the ordered stacking bed, but also provides possibility for further improving the flow heat transfer characteristic of the traditional ordered stacking bed.

Claims

1. A grid particle composite bed stacking method is characterized in that an upper layer of location grids and a lower layer of location grids and spherical particles are preassembled to form a spherical layer whole, then the spherical layer whole is filled into a container layer by layer at the top of the container, and when the grids and the particles fall down, the relative positions of the grids and the particles are not changed, so that an ordered stacking structure can be automatically formed;

after each ball layer is placed, a support grid is placed from the top of the container, so that the support grid falls onto the particles at the lower layer, another ball layer assembled by using a positioning grid is placed from the top of the container, and the grid particle composite ordered packed bed is formed repeatedly in this way;

and when the support grids and the ball layers are filled at intervals, the stacking bed with an in-line stacking structure or a staggered stacking structure can be formed by adjusting the characteristic sizes of the positioning grids and the support grids, or the stacking bed with the same stacking mode but different particle distances can be formed.

2. The method of claim 1, wherein the lattice particle composite bed packing method comprises: the joint surface of the upper and lower layers of the location grids is positioned at the maximum diameter of the spherical particles, and the location holes of the location grids are provided with spherical grooves which have opposite directions and are matched with the spherical particles in size and are used for fixing the positions of the particles.

3. The method of claim 1, wherein the lattice particle composite bed packing method comprises: the upper and lower location grids are respectively provided with a circular truncated cone pit and a circular truncated cone boss which form an interference fit relationship, and after the upper and lower location grids are assembled with the spherical particles, the relative positions of the particles and the location grids are determined.

4. The method of claim 1, wherein the lattice particle composite bed packing method comprises: the method is suitable for the case of oblique filling of containers.

5. The method of claim 1, wherein the lattice particle composite bed packing method comprises: the container is a square tube.

6. The method of claim 1, wherein the lattice particle composite bed packing method comprises: the container is a round tube or other shapes, the grid needs to be cut, and particles are filled at the position with complete positioning holes.

7. A grid particle composite packed bed is characterized in that: produced using the grid particle composite bed packing method of any of claims 1-6.