Arrangement method of annular fins in shell and tube phase change heat accumulator

Abstract

The present invention discloses a method for arranging annular fins in a shell-and-tube phase-change heat accumulator, which has the following characteristics and includes the following steps: Step 1, dividing the shell-and-tube phase-change heat accumulator without fins into regions, recording the complete phase change time of each region, and calculating the average heat storage rate ratio between all regions; Step 2, by discriminating the flow velocity of the heat exchange fluid, determining whether it is necessary to exclude the average heat storage rate ratio of the region where natural convection mainly occurs according to the high or low flow velocity of the heat exchange fluid, obtaining the heat storage rate ratio between regions after flow velocity discrimination, and determining the required fin heat exchange area in each region based on this; Step 3, when the heat exchange fluid flows from top to bottom, taking different optimization directions according to different phase change processes, setting multiple control experimental groups for a single region, selecting the experimental group with the best heat transfer effect in the region as the basis, and conducting optimization experiments on subsequent regions.

Description

Technical Field

[0001] The present invention relates to the field of phase change heat transfer, and in particular to a method for arranging annular fins in a shell and tube type phase change heat accumulator. Background Art

[0002] Phase change energy storage technology utilizes the heat absorbed or released during a material's phase transition to store and release heat. The advantages of this technology include high energy storage density and a nearly constant phase change temperature. However, the disadvantage is the low thermal conductivity of the phase change material, necessitating the use of a phase change heat accumulator to improve the heat transfer efficiency of the phase change process. In industrial applications, shell-and-tube phase change heat accumulators have been widely developed and applied due to their simple yet efficient heat exchange structure. In daily industrial production and daily life, the most commonly used fins for shell-and-tube phase change heat accumulators are annular fins.

[0003] Among existing research and technologies, the exhaustive method for selecting the optimal fin position is relatively simple to implement and has a certain degree of improvement in heat transfer performance. The arithmetic distribution of annular fins is also relatively novel and has significantly improved heat transfer performance. Arranging the annular fins in an exponential distribution along the flow direction of the heat transfer fluid also has good heat transfer performance.

[0004] However, these technologies or methods have some obvious shortcomings. The workload of the exhaustive method is too large, the series or function distribution method is subjective and has poor universality. When the heat transfer material or heat transfer conditions are changed, this type of distribution method is not the optimal fin arrangement, and related research cannot give a specific function or series distribution corresponding to the transformation, and is somewhat speculative. Summary of the Invention

[0005] The present invention is made to solve the above-mentioned problem, and its purpose is to provide a method for arranging annular fins in a shell and tube phase change heat accumulator.

[0006] The present invention provides a method for arranging annular fins in a shell-and-tube phase-change heat accumulator, which has the following characteristics and includes the following steps: Step 1, dividing the shell-and-tube phase-change heat accumulator without fins into regions, recording the complete phase change time of each region, and calculating the average heat storage rate ratio between all regions; Step 2, by discriminating the flow rate of the heat exchange fluid, determining whether it is necessary to exclude the average heat storage rate ratio of the region where natural convection mainly occurs based on the high or low flow rate of the heat exchange fluid, obtaining the heat storage rate ratio between regions after flow rate discrimination, and determining the required fin heat exchange area in each region based on this; Step 3, when the heat exchange fluid flows from top to bottom, adopting different optimization directions according to different phase change processes, setting multiple control experimental groups for a single region, selecting the experimental group with the best heat transfer effect in the region as the basis, and conducting optimization experiments on subsequent regions.

[0007] The method for arranging annular fins in a shell and tube phase change heat accumulator provided by the present invention may also have the following features: wherein, the specific process of step 1 is: performing heat charging and discharging operations on a vertical shell and tube phase change heat accumulator containing phase change material and without fins, dividing the heat accumulator into a plurality of small areas of equal volume, recording the complete phase change time of each small area, and calculating the average heat storage rate ratio between all areas.

[0008] The method for arranging annular fins in a shell-and-tube phase-change heat accumulator provided by the present invention may also have the following features: wherein, the specific process in step 2 is: under a given fin volume and thickness, the flow rate of the heat exchange fluid is judged in combination with the heat exchange conditions on the pipeline side and the phase change material side. When the heat carried by the heat exchange fluid flowing through per unit time is greater than the maximum heat that can be absorbed by the shell-and-tube phase-change heat accumulator equipped with fins per unit time, it is determined to be a high flow rate; otherwise, it is determined to be a low flow rate.

[0009] The method for arranging annular fins in the shell and tube phase change heat accumulator provided by the present invention may also have the following characteristics: when the heat exchange fluid has a high flow rate, the fin heat exchange area required for each area is determined according to the ratio of the average heat storage rates between all areas; when the heat exchange fluid has a low flow rate, the fin heat exchange area required in each area is determined according to the ratio of the average heat storage rates between the areas, and the area where natural convection mainly occurs needs to be eliminated.

[0010] The method for arranging annular fins in a shell and tube phase change heat accumulator provided by the present invention may also have the following characteristics: wherein, in step 3, when the heat exchange fluid flows from top to bottom, different optimization directions are selected according to different phase transitions of the phase change material in the shell and tube phase change heat accumulator.

[0011] The method for arranging annular fins in the shell and tube phase change heat accumulator provided by the present invention may also have the following characteristics: the factor that determines the overall time required for phase change is the area with the slowest phase change, so the basis for selecting different optimization directions is: during the melting process, due to the existence of natural convection, the area with the slowest melting is the bottom area, so the melting process is optimized from bottom to top; during the solidification process, due to the existence of natural convection, the area with the slowest solidification is the top area, so the solidification process is optimized from top to bottom.

[0012] The method for arranging annular fins in a shell and tube phase change heat accumulator provided by the present invention may also have the following features: wherein, the specific process of step 3 is: for a single area, multiple control experimental groups are set up, and fins of corresponding areas are provided for each area according to the proportion of the fin heat exchange area required by each area in the total fin area, and the optimal number of fins or fin length of the area is determined under a given fin area and thickness, and the optimal fin distribution of each area is gradually determined, thereby completing the optimal fin distribution of the entire area.

[0013] Functions and effects of the invention

[0014] According to the method for arranging annular fins in a shell-and-tube phase-change heat accumulator involved in the present invention, the specific process is as follows: Step 1, dividing the shell-and-tube phase-change heat accumulator without fins into regions, recording the complete phase change time of each region, and calculating the average heat storage rate ratio between all regions; Step 2, by discriminating the flow rate of the heat exchange fluid, determining whether it is necessary to exclude the average heat storage rate ratio of the region where natural convection mainly occurs based on the high or low flow rate of the heat exchange fluid, obtaining the heat storage rate ratio between regions after flow rate discrimination, and using this to determine the required fin heat exchange area in each region; Step 3, when the heat exchange fluid flows from top to bottom, adopting different optimization directions according to different phase change processes, setting multiple control experimental groups for a single region, selecting the experimental group with the best heat transfer effect in the region as the basis, and conducting optimization experiments in subsequent regions.

[0015] Therefore, the beneficial effects of the present invention are:

[0016] 1. Due to the existence of natural convection, the heat in the lower area of ​​the phase change material is forced to be carried to the upper area, resulting in extremely uneven phase change process. Due to the lack of heat in the bottom area, the phase change process in this area is further slowed down. Therefore, adding annular fins to this area in the form of an internal heat source can compensate for the heat taken away to a certain extent, achieve uniformity in the melting process, accelerate the phase change rate in this area, and reduce the charging and discharging time in actual application.

[0017] 2. Traditional fin arrangements are somewhat subjective, but this method can objectively give the melting rate of each area and optimize the fin arrangement by adjusting on demand, thereby filling the gaps in phase change while ensuring the uniformity of the entire area, and achieving the maximum phase change rate with the smallest fin volume.

[0018] 3. For each area, by setting up different control experimental groups, the experimental group with the best heat transfer performance in that area is selected, and on this basis, the heat transfer performance of the next area is optimized, and the optimal number and length of fins in that area are selected, which can maximize the heat transfer performance of each area and greatly help improve the overall heat transfer performance of the shell and tube phase change heat accumulator.

[0019] 4. The appropriate addition of annular fins can inhibit the flow of natural convection to a certain extent, reduce the heat exchange between areas, and help build relative independence between adjacent areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of a specific implementation process of a method for arranging annular fins in a shell and tube phase change heat accumulator in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the following embodiments and accompanying drawings specifically illustrate the arrangement method of annular fins in a shell and tube phase change heat accumulator of the present invention.

[0022] In this embodiment, a method for arranging annular fins in a shell and tube phase change heat accumulator is provided.

[0023] Figure 1 It is a schematic diagram of a specific implementation process of the method for arranging annular fins in the shell and tube phase change heat accumulator in this embodiment.

[0024] like Figure 1 As shown, the method for arranging annular fins in the shell and tube phase change heat accumulator involved in this embodiment includes the following steps:

[0025] Step S1, numerical calculation: Divide the finless shell and tube phase change heat storage device into regions, record the complete phase change time of each region, and calculate the average heat storage rate ratio between all regions. The specific process is:

[0026] A vertical shell-and-tube phase-change regenerator (PCR) without fins, containing phase-change material, was charged and discharged. The regenerator was divided into multiple small zones of equal volume. The time it took for each zone to undergo complete phase change was recorded, and the average heat storage rate ratio across all zones was calculated. This average heat storage rate ratio reveals the melting speed of each zone and the equivalent internal heat source required for that zone.

[0027] Step S2, flow rate determination: The flow rate of the heat exchange fluid is determined. Based on the flow rate of the heat exchange fluid, it is determined whether the average heat storage rate ratio of the area where natural convection mainly occurs needs to be eliminated. The heat storage rate ratio between the areas after flow rate determination is obtained, and the required fin heat exchange area in each area is determined based on this. The specific process is as follows:

[0028] Given a given fin volume and thickness, the heat transfer fluid's flow rate is determined based on the heat transfer conditions on both the pipe and phase-change material sides. A high flow rate is determined when the heat carried by the fluid per unit time exceeds the maximum heat that the finned shell-and-tube phase-change heat accumulator can absorb per unit time. Otherwise, a low flow rate is determined. Different flow rates require different optimization paths, so determining the heat transfer fluid's flow rate facilitates more precise placement of the annular fins.

[0029] The amount of heat carried by a heat transfer fluid with a constant flow rate per unit time is constant. At low flow rates, the heat transfer capacity is enhanced in the area where natural convection mainly occurs after fins are added according to the ratio of the average heat storage rate between regions. More heat is absorbed or released from the heat transfer fluid, resulting in the downstream area failing to absorb or release the calculated sufficient amount of heat, resulting in an increase in the duration of the phase change process.

[0030] Therefore, when the heat exchange fluid has a high flow rate, the required fin heat exchange area for each area is determined according to the ratio of the average heat storage rates among all areas. When the heat exchange fluid has a low flow rate, the required fin heat exchange area for each area is determined according to the ratio of the average heat storage rates among the areas, and the areas where natural convection mainly occurs need to be eliminated.

[0031] Since the heat transfer and average heat storage rate in the Fourier heat conduction equation and the Newton cooling equation are both linearly proportional when the temperature is uniformly distributed, the ratio of the average heat storage rates between regions is inversely proportional to the required fin heat transfer area between regions. Determining the fin heat transfer area based on this is more scientific and feasible. Moreover, compared with optimizing the distribution based on the average temperature difference between the phase change material and the heat transfer fluid in the region, optimizing the distribution based on the average liquid phase fraction in the region is more intuitive, simpler, and more accurate. Due to fewer calculation steps, it can effectively reduce calculation and simulation errors.

[0032] Step S3, process optimization: When the heat exchange fluid flows from top to bottom, different optimization directions are adopted according to the different phase transitions of the phase change material in the shell and tube phase change heat accumulator. Multiple control experimental groups are set for a single area. The experimental group with the best heat transfer effect in the area is selected as the basis for optimization experiments in subsequent areas.

[0033] Taking different optimization directions according to the different phase transitions of the phase change material in the shell and tube phase change heat storage device helps to improve the accuracy of the optimization and reduce the impact of the slowest phase change area.

[0034] The factor that determines the overall time required for phase transformation is the area with the slowest phase transformation. Therefore, the basis for selecting different optimization directions is as follows: during the melting process, due to the existence of natural convection, the area with the slowest melting is the bottom area, so the melting process is optimized from bottom to top. During the solidification process, due to the existence of natural convection, the area with the slowest solidification is the top area, so the solidification process is optimized from top to bottom.

[0035] Finally, for a single area, multiple control experimental groups were set up. Each area was assigned a fin of a corresponding area based on the proportion of the required fin heat transfer area to the total fin area. The optimal number of fins or fin length for that area was determined for a given fin area and thickness. By gradually determining the optimal fin distribution for each area, the optimal fin distribution for the entire area could be achieved.

[0036] Functions and Effects of the Embodiments

[0037] According to the method for arranging annular fins in a shell-and-tube phase-change heat accumulator involved in this embodiment, the specific process is as follows: Step 1: Divide the shell-and-tube phase-change heat accumulator without fins into regions, record the complete phase change time of each region, and calculate the average heat storage rate ratio between all regions; Step 2: Determine the flow rate of the heat exchange fluid, and determine whether to exclude the average heat storage rate ratio of the region where natural convection mainly occurs based on the flow rate of the heat exchange fluid. The heat storage rate ratio between regions after flow rate determination is obtained, and the required fin heat exchange area in each region is determined based on this ratio; Step 3: When the heat exchange fluid flows from top to bottom, different optimization directions are adopted according to different phase change processes. Multiple control experimental groups are set for a single region, and the experimental group with the best heat transfer effect in the region is selected as the basis for optimization experiments in subsequent regions.

[0038] Therefore, the beneficial effects of the above embodiment are:

[0039] 1. Due to the existence of natural convection, the heat in the lower area of ​​the phase change material is forced to be carried to the upper area, resulting in extremely uneven phase change process. Due to the lack of heat in the bottom area, the phase change process in this area is further slowed down. Therefore, adding annular fins to this area in the form of an internal heat source can compensate for the heat taken away to a certain extent, achieve uniformity in the melting process, accelerate the phase change rate in this area, and reduce the charging and discharging time in actual application.

[0040] 2. Traditional fin arrangements are somewhat subjective, but this method can objectively give the melting rate of each area and optimize the fin arrangement by adjusting on demand, thereby filling the gaps in phase change while ensuring the uniformity of the entire area, and achieving the maximum phase change rate with the smallest fin volume.

[0041] 3. For each area, by setting up different control experimental groups, the experimental group with the best heat transfer performance in that area is selected, and on this basis, the heat transfer performance of the next area is optimized, and the optimal number and length of fins in that area are selected, which can maximize the heat transfer performance of each area and greatly help improve the overall heat transfer performance of the shell and tube phase change heat accumulator.

[0042] 4. The appropriate addition of annular fins can inhibit the flow of natural convection to a certain extent, reduce the heat exchange between areas, and help build relative independence between adjacent areas.

[0043] The above embodiments are preferred examples of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A method for arranging annular fins in a shell and tube phase change heat accumulator, characterized in that: The following steps are involved: Step 1: Divide the finless shell and tube phase change heat storage device into regions, record the complete phase change time of each region, and calculate the average heat storage rate ratio among all regions; Step 2: Under a given fin volume and thickness, the flow rate of the heat exchange fluid is determined in combination with the heat exchange conditions on the pipe side and the phase change material side. When the heat carried by the heat exchange fluid flowing through per unit time is greater than the maximum heat that can be absorbed by the shell and tube phase change heat accumulator equipped with fins per unit time, it is determined to be a high flow rate; otherwise, it is determined to be a low flow rate. When the heat exchange fluid has a high flow rate, the required fin heat exchange area for each area is determined according to the average heat storage rate ratio among all areas. When the heat exchange fluid has a low flow rate, the average heat storage rate ratio of the area where natural convection mainly occurs needs to be excluded when determining the required fin heat exchange area in each area according to the average heat storage rate ratio among all areas; Step 3: When the heat exchange fluid flows from top to bottom, different optimization directions are adopted according to different phase change processes. Multiple control experimental groups are set for a single area. The experimental group with the best heat transfer effect in the area is selected as the basis for optimization experiments in subsequent areas.

2. The method for arranging annular fins in a shell and tube phase change heat accumulator according to claim 1, characterized in that: in, The specific process of step 1 is: a vertical shell and tube phase change heat accumulator equipped with phase change material and without fins is charged and discharged, and multiple small areas of equal volume are divided, and the complete phase change time of each small area is recorded to calculate the average heat storage rate ratio between all areas.

3. The method for arranging annular fins in a shell and tube phase change heat accumulator according to claim 1, characterized in that: in, In step 3, when the heat exchange fluid flows from top to bottom, different optimization directions are adopted according to different phase transitions of the phase change material in the shell and tube phase change heat accumulator.

4. The method for arranging annular fins in a shell and tube phase change heat accumulator according to claim 1, characterized in that: in, The factor that determines the overall time required for phase transformation is the area where the phase transformation is slowest. Therefore, the basis for taking different optimization directions is: During the melting process, due to the existence of natural convection, the slowest melting area is the bottom area, so the melting process is optimized from bottom to top. During the solidification process, due to the existence of natural convection, the slowest solidifying area is the top area, so the solidification process is optimized from top to bottom.

5. The method for arranging annular fins in a shell and tube phase change heat accumulator according to claim 1, characterized in that: in, The specific process of step 3 is as follows: for a single area, set up multiple control experimental groups, provide fins of corresponding area for each area according to the proportion of the required fin heat exchange area of ​​each area in the total fin area, and determine the optimal number of fins or fin length of the area under a given fin area and thickness, and gradually determine the optimal fin distribution of each area to complete the optimal fin distribution of the entire area.

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