CN113776207A

CN113776207A - A shell-and-tube phase change heat storage device with conical spiral coil structure

Info

Publication number: CN113776207A
Application number: CN202110653840.8A
Authority: CN
Inventors: 胡定华; 林肯; 林伯
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2021-06-11
Filing date: 2021-06-11
Publication date: 2021-12-10
Anticipated expiration: 2041-06-11
Also published as: CN113776207B

Abstract

The invention discloses a shell-and-tube type phase change heat storage device with a conical spiral coil structure, comprising a heat exchange tube group, a phase change heat storage material and a heat storage device shell; the heat exchange tube group comprises an inlet header pipe, an outlet header pipe and Conical helical coil; Conical helical coil is a coiled pipe structure in which the centerline of the pipe rotates from outside to inside on a conical surface; multiple groups of conical helical coils are arranged at equal intervals and coaxially; each group of helical disks The inlet of the tube is on the outside of the spiral, and the outlet is on the inside of the spiral; the inlet and outlet of these spiral coils are respectively connected to form a heat exchange tube group; the heat exchange tube group is immersed in the phase change heat storage material, and is stored by The device shell is wrapped to form a phase change heat storage device with a conical spiral coil structure. The device utilizes the fluid rotation process to promote the heat storage process, and has the advantages of compact structure and high heat storage efficiency.

Description

Shell-and-tube phase-change heat storage device with conical spiral coil pipe structure

Technical Field

The invention belongs to the field of phase change heat storage, and particularly relates to a shell-and-tube phase change heat storage device with a conical spiral coil structure.

Background

The solar power generation technology is a clean and pollution-free energy technology, but because the solar energy is periodically fluctuated in the daytime in the collection process, the stable operation of the power generation process is influenced, and the solar power generation technology is not suitable for directly using the solar energy for power generation. To solve this problem, a phase change heat storage device is often used to store the collected solar energy in the form of thermal energy and stably supply it to a power generation device.

The shell-and-tube phase-change heat storage device is a classic phase-change heat storage device and has mature processing and manufacturing experience. Conventional phase change thermal storage devices, such as the phase change thermal storage device of patent No. 201010119607.3, use heat exchange tube bundles that spread out on a flat surface to store heat. Along with the progress of heat accumulation process, the temperature of the fluid flowing in the phase-change heat accumulation device is gradually reduced, the heat accumulation effect of the heat exchange tube bundle in the phase-change heat accumulation device is gradually reduced, and a large amount of phase-change heat accumulation materials at the tail end of the heat exchange tube bundle can not participate in the heat accumulation process.

In order to solve the problem, patent No. 201621087825.2 proposes a pitch-gradient spiral coil heat accumulator, which reduces the thickness of a phase-change heat accumulation layer at the end of a heat exchange tube bundle, promotes the melting of a phase-change heat accumulation material, but correspondingly increases the length of the heat exchange tube bundle and consumes more metal materials.

Disclosure of Invention

The invention aims to provide a shell-and-tube phase-change heat storage device with a conical spiral coil structure, so as to achieve the purpose of reducing consumption of heat-conducting metal materials and phase-change heat storage materials on the premise of meeting the phase-change heat storage requirements.

The technical solution for realizing the purpose of the invention is as follows:

a shell-and-tube phase-change heat storage device with a conical spiral coil structure comprises a phase-change heat storage device shell, a heat exchange tube set and a phase-change heat storage material, wherein the heat exchange tube set is arranged in the phase-change heat storage device shell;

the heat exchange tube group comprises a group of inlet main pipes, a group of outlet main pipes and a plurality of groups of conical spiral coil pipes; the conical spiral coil is of a coil structure with a pipe center line rotating on a conical surface from outside to inside circle by circle, and the conical spiral coils are coaxially arranged at equal intervals; the bending radius of the conical spiral coil is gradually reduced to improve the turbulence of the fluid.

A method for determining key parameters of a shell-and-tube phase-change heat storage device with a conical spiral coil structure comprises the following steps:

step 1, calculating heat transfer coefficient h of fluid in phase change heat storage device_liqHeat transfer coefficient h of heat exchange tube wall_pipAnd heat transfer coefficient h of phase change heat storage material_PCM；

Step 2, calculating heat transfer coefficients h (r) of coils with different bending radii:

wherein r is the coil bend radius; n is a coil correction coefficient;

step 3, establishing the following equation based on the heat storage power requirement and the conical spiral shape requirement to determine the lengths l (r) of the coils with different bending radii and establish corresponding conical spiral coil structures;

wherein q is the heat storage power, dT is the temperature difference between the input fluid and the phase change heat storage material, and d₂Is the outer diameter of the heat exchange tube.

Compared with the prior art, the invention has the following remarkable advantages:

(1) by the conical spiral coil pipe structure, the invention consumes less metal heat conduction materials and phase change heat storage materials on the premise of meeting the phase change heat storage requirement, and has a more compact structure.

(2) Through the structure of the conical spiral coil pipe, the length of the central low-bending-radius part of the spiral coil pipe is effectively improved. And the heat transfer coefficient of the central low-bending radius part of the spiral coil is higher, so that the heat storage efficiency of the phase change heat storage device is effectively improved by prolonging the part.

Drawings

Fig. 1 is an assembly view of a phase change thermal storage device.

Fig. 2(a-c) are schematic isometric, side and top views, respectively, of a conical helical coil structure.

Fig. 3 is a structural view of a heat exchange tube group.

FIG. 4 is a plot of coil correction coefficients for a 20 ℃ heat transfer differential.

Detailed Description

The invention is further described with reference to the following figures and embodiments.

Referring to fig. 1, fig. 2(a-c) and fig. 3, the shell-and-tube phase-change heat storage device with a conical spiral coil structure according to the present invention includes a heat exchange tube set 1, a phase-change heat storage material 2 and a phase-change heat storage device housing 3.

The heat exchange tube set 1 comprises an inlet header pipe 4, an outlet header pipe 5 and a plurality of sets of conical spiral coils (in this embodiment, two types of conical

spiral coils

6 and 7 are adopted). The conical

spiral coils

6 and 7 are a coil structure (as shown in fig. 2) in which the central line of the pipe rotates from outside to inside on the conical surface one by one, and the bending radius of the coil structure is gradually reduced to be consistent with the outer diameter of the pipe. The surfaces of the inlet manifold 4 and the outlet manifold 5 are provided with openings, and the conical

spiral coils

6 and 7 are inserted into the openings on the surfaces of the inlet manifold 4 and the outlet manifold 5 and are tightly connected. The inlet header pipe 4 and the outlet header pipe 5 are connected with the conical

spiral coils

6 and 7 to form the heat exchange group 1 (as shown in figure 3). The inlet of each set of spiral coils is arranged at the outer side of the spiral, and the outlet is arranged at the inner side of the spiral. The heat exchange tube group is immersed in the phase change heat storage material and is wrapped by the heat storage device shell to form the phase change heat storage device with the conical spiral coil structure. The phase change heat storage device shell 3 is a cylindrical barrel, and a heat exchange tube group hole 8 is formed in the top of the barrel. The conical

spiral coil pipes

6 and 7 are nested in structure, and the conical top of the conical spiral coil pipe 7 is coincided with the conical bottom of the conical spiral coil pipe 6.

Further, after the heat exchange tube group 1 is verified to have good tightness through a water pressure test, the heat exchange tube group 1 is placed in the phase change heat storage device shell 3 and fixed, and the phase change heat storage material which is melted into a liquid state is filled in the phase change heat storage device shell 3 until the phase change heat storage material passes through the conical

spiral coils

6 and 7. The shell 3 of the closed phase-change heat storage device forms a shell-and-tube phase-change heat storage device with a conical spiral coil structure.

The heat exchange tube set 1 is made of aluminum, copper or stainless steel. The bottom of the phase change heat storage device shell is provided with a heat exchange tube bundle positioning and supporting structure, the top of the phase change heat storage device shell is provided with a heat exchange tube bundle opening, and the phase change heat storage device shell is made of aluminum, copper or stainless steel. The phase-change heat storage material 2 is paraffin, fatty acid or molten salt, or corresponding materials are selected according to the phase-change temperature requirement.

The phase change heat storage function of the device is mainly realized by the heat exchange tube group 1 and the phase change heat storage material together. The hot fluid is input into the device from the inlet of the heat exchange tube group 1 and is in heat transfer with the phase change heat storage material with lower temperature in the device, so that the heat is stored in the form of latent heat of the phase change heat storage material.

In traditional shell-and-tube phase change heat storage device, along with the fluid flows from the input to the output, the difference in temperature between fluid and the phase change heat storage material reduces gradually for phase change heat storage device's heat accumulation effect weakens gradually from the input to the output. In the shell-and-tube phase-change heat storage device with the conical spiral coil pipe structure, the bending radius of the pipeline is gradually reduced from the input end to the output end, the turbulence degree of the fluid is gradually improved, and the heat exchange process between the fluid and the phase-change heat storage material is promoted. Because the influence of the reduction of the heat transfer temperature difference and the improvement of the fluid turbulence degree is simultaneously received, the heat storage effect of the phase change heat storage device is not greatly changed from the input end to the output end, and the compactness of the phase change heat storage device is favorably improved.

step 1, calculating heat transfer coefficients h of all parts in the phase change heat storage device_liq，h_pipAnd h_PCM：

Wherein h is_liq、h_pip、h_PCMRespectively representing the heat transfer coefficient of the fluid, the heat transfer coefficient of the heat exchange tube wall and the heat transfer coefficient of the phase change heat storage material; d₁、d₂E is the inner diameter and the outer diameter of the heat exchange tube and the thickness of the phase change heat storage material layer respectively; mu.s_liq、c_liq、v_liq、ρ_liqHydrodynamic viscosity, isobaric specific heat capacity, linear flow rate and density; lambda [ alpha ]_liq、λ_pip、λ_PCMThe heat conductivity coefficients of the fluid, the heat exchange tube and the phase change heat storage material are respectively.

wherein r is the coil bend radius; n is coil correction coefficient, which is composed of coil bending radius r and coil external diameter d₂The ratio determination can be obtained through numerical simulation or experimental calculation.

Step 3, determining the lengths l (r) of the coils with different bending radii according to the following equation and establishing corresponding conical spiral coil structures;

wherein q is the heat storage power, and dT is the temperature difference between the input fluid and the phase change heat storage material. The two equations of the equation respectively and correspondingly meet the requirements of heat storage power and conical spiral shape.

And 4, adjusting the outer diameter of the heat exchange tube, recalculating l (r) and establishing a conical spiral structure. And comparing conical spiral structures with different heat exchange tube outer diameters, and selecting the lowest quality of the device as a final design result.

Examples

The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

Step 1, calculating the heat transfer coefficients of all parts respectively:

a copper tube with the outer diameter of 6mm and the inner diameter of 5mm is selected as a heat exchange tube, and the heat transfer coefficient is 728 kW/(m)²K); deionized water as fluid working medium, input temperature of 80 deg.C, input flow rate of 0.8m/s, and heat transfer coefficient of 73.9W/(m)²K); no. 58 refined paraffin is a phase change heat storage material, the thickness is 5mm, and the heat transfer coefficient is 52.4W/(m)²·K)。

And 2, obtaining a coil correction coefficient n shown in the following figure 4 through numerical simulation.

And 3, calculating to obtain the maximum bending radius of the conical spiral coil pipe of 50mm, the minimum bending radius of 20mm, the spiral stage interval of 10mm, the whole conical spiral comprises 4 revolutions, and the distance between the conical spiral coil pipes is 40 mm.

Step 4, in order to meet the requirements of the conical spiral coil, the radius of the shell of the phase change heat storage device is designed to be 60mm, the height of the shell is 160mm, the wall thickness of the shell is 1mm, and the shell is made of aluminum; designing the inlet main pipe and the outlet main pipe to be red copper heat exchange pipes with the diameter of 8mm, and welding and sealing the bottoms of the pipes; the minimum filling height of the phase change heat storage material is designed to be 130mm so as to ensure that the phase change heat storage material is completely immersed in the conical spiral coil; the maximum filling height is 150mm to prevent the phase change heat storage material from overflowing during melting.

The total weight of the phase change heat storage device is about 2.2kg, the volume is about 1.8L, after continuous heat storage for 1800s, the number 58 refined paraffin filled in the device as the phase change heat storage material is melted by more than 60%, and the heat storage capacity can reach 150 kJ.

Claims

1. A shell-and-tube type phase-change heat storage device with a conical spiral coil structure, comprising a phase-change heat-storage device shell and a heat exchange tube group arranged in the phase-change heat-storage device shell, a phase-change heat-storage material; is characterized by,

The heat exchange tube group includes a group of inlet header pipes, a group of outlet header pipes and multiple groups of conical helical coils; the conical helical coil is a coiled pipe structure in which the center line of the pipe rotates from outside to inside on a conical surface, and the conical The spiral coils are arranged coaxially at equal intervals; the bending radius of the conical spiral coils is gradually reduced to improve the turbulence of the fluid.

2 . The shell-and-tube phase change heat storage device with a conical spiral coil structure according to claim 1 , wherein the heat exchange tube group and the shell of the phase change heat storage device are made of aluminum, copper or stainless steel. 3 .

3 . The shell-and-tube phase change heat storage device with a conical spiral coil structure according to claim 1 , wherein the phase change heat storage material is paraffin, fatty acid or molten salt. 4 .

4 . The shell-and-tube type phase change heat storage device with a conical spiral coil structure according to claim 1 , wherein the multiple groups of conical spiral coil tubes are in a nested relationship in structure. 5 .

5. The shell-and-tube type heat storage device with conical helical coil structure according to claim 1, is characterized in that, the length l (r) of different bending radius coils of conical helical coil satisfies the following formula:

where the heat transfer coefficient

h _liq , h _pip , h _PCM are fluid heat transfer coefficient, heat transfer coefficient of heat exchange tube wall and heat transfer coefficient of phase change heat storage material respectively; r is the bending radius of the coil; n is the correction coefficient of the coil; q is the heat storage Power, dT is the temperature difference between the input fluid and the phase change heat storage material.

6. A method for determining key parameters of a shell-and-tube phase-change heat storage device with a conical spiral coil structure, characterized in that it comprises the following steps:

Step 1. Calculate the fluid heat transfer coefficient h _liq in the phase change heat storage device, the heat transfer coefficient h _pip of the heat exchange tube wall and the heat transfer coefficient h _PCM of the phase change heat storage material;

Step 2. Calculate the heat transfer coefficient h(r) of the coils with different bending radii:

Among them, r is the bending radius of the coil; n is the correction coefficient of the coil;

Step 3. Based on the thermal storage power requirements and the requirements of the conical spiral shape, the following equations are established to determine the length l(r) of the coils with different bending radii and establish the corresponding conical spiral coil structures;

Where q is the heat storage power, dT is the temperature difference between the input fluid and the phase change heat storage material, and d ₂ is the outer diameter of the heat exchange tube.

7. The method for determining key parameters according to claim 5, wherein in step 1, the fluid heat transfer coefficient h _liq , the heat transfer coefficient h _pip of the heat exchange tube wall and the phase change heat storage material heat transfer coefficient h _PCM are respectively:

where d ₁ and e are the inner diameter of the heat exchange tube and the thickness of the phase-change heat storage material layer, respectively; μ _liq , c _liq , v _liq , and ρ _liq are the hydrodynamic viscosity, isobaric specific heat capacity, linear velocity and density, respectively; λ _liq , λ liq , respectively _pip and λ _PCM are the thermal conductivity of the fluid, the heat exchange tube and the phase change heat storage material, respectively.