Multi-stream plate-fin heat exchanger fluid channel arrangement design method

Abstract

The invention provides a fluid channel arrangement design method for a multi-flow plate-fin heat exchanger. The method comprises the following steps that S1, heat loads Q1, Q2,..., Qn of heat exchanger cold and hot channels in the multi-flow plate-fin heat exchanger are determined; s2, the absolute value delta i (i = 1, 2,..., n-1) of the thermal load difference value of each cold and hot channel and the adjacent hot and cold channel obtained in the step S1 is calculated, and delta 1 is made to be equal to Q1 + Q2 + Q3 / 2; delta 2 = Q2 / 2 + Q3 + Q4 / 2; ... delta n-2 = Qn-3 / 2 + Qn-2 + Qn-1 / 2; delta n-1 is equal to Qn-2 / 2 + Qn-1 + Qn; and S3, obtaining the minimum value # imgabs0 # of the sum of the absolute values of the thermal load differences of all the adjacent channels in the step S2, wherein the channel arrangement corresponding to the minimum value # imgabs0 # is the optimal channel arrangement. Compared with the current common Fan Y.N. Isolation type, SucessmannW. And MansourA. Local thermal load channel arrangement design method and the design method based on the heat exchanger performance index computer optimization algorithm, the method has the advantages that the calculation formula is simple, the optimization result is efficient and stable, and the engineering application value is high.

Description

Technical Field

[0001] The invention belongs to the technical field of heat exchangers, and in particular is a method for arranging and designing fluid channels of a multi-stream plate-fin heat exchanger. Background Art

[0002] Plate-fin heat exchangers are usually composed of a sandwich (called a fluid channel) composed of fins, seals and guide vanes between two adjacent partitions. They have a compact structure and are easy to achieve heat exchange between two or more fluids in different flow modes such as co-current, counter-current or cross-current. They are light in weight, small in size, high in heat transfer efficiency and good in economic benefits. They are widely used in air separation, petrochemical industry, power machinery, hydraulic systems, power systems, rail transit systems, atomic energy and defense industries, food and medicine and other industrial production and life fields.

[0003] Fluid channel design is a key issue in the design of multi-stream plate-fin heat exchangers. Whether the channel arrangement is reasonable directly determines the performance and indicators of the plate-fin heat exchanger. The channel arrangement design is not only affected and restricted by the heat and mass exchange conditions in the heat exchanger, but also must be determined before the design calculation. This contradictory requirement causes design difficulties and is a design problem for multi-stream plate-fin heat exchangers.

[0004] At present, there are two methods for designing the channel arrangement of multi-stream heat exchangers: one is to refer to the isolation model proposed by Fan Y.N. (Fan YN, How to design plate-fin heat exchangers, Hydrocarbon Processing, 45 (1966) 211-217) and / or the local heat load balance model proposed by Sucessmann W. and Mansour A. (Suessman W., Mansour A., ​​passage arrangement in plate-fin exchanges, in: Proc. 15th International Congress of Refrigeration, 1979, pp. 421-429), and to optimize the channel arrangement of multi-stream plate-fin heat exchangers manually or with the help of a computer. For this type of design method, the isolation mode proposed by Fan YN can easily cause heat load imbalance between channels, while the local heat load balance mode proposed by Sucessmann W. and Mansour A. In the early stage, the inventors of this article used manual or computer intelligent optimization genetic algorithm to optimize the channel arrangement according to the ZigZag curve corresponding to the Sucessmann and Mansour local heat load. The results showed that the thermal efficiency of the heat exchanger corresponding to the optimal channel arrangement can only reach about 90% of the ideal heat transfer of the heat exchanger with equal wall temperature, and the optimization results are unstable, sometimes good and sometimes bad.

[0005] Another channel arrangement design method for multi-stream heat exchangers analyzes, optimizes and designs the channel arrangement based on the performance indicators of the entire multi-stream heat exchanger, such as the minimum entropy production of the heat exchanger and the uniformity of the temperature field. This type of channel arrangement design method often involves heat exchanger structure and flow heat transfer calculations, involves many parameters, complex formulas, cumbersome calculations, and a large workload, and has no practical engineering value. Summary of the invention

[0006] In view of the shortcomings of the above-mentioned background technology, the present invention proposes a method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger, which solves the problems of unbalanced heat load between channels, low thermal efficiency of the heat exchanger and unstable optimization results, involving many parameters, complex formulas, cumbersome calculations and large workload.

[0007] The technical solution of this application is:

[0008] A method for designing a fluid channel arrangement of a multi-stream plate-fin heat exchanger comprises the following steps:

[0009] S1: Determine the heat load Q1 of the hot and cold channels of the heat exchanger in the multi-stream plate-fin heat exchanger.

[0010] Q2, ..., Q n ;

[0011] S2: Calculate the absolute value of the heat load difference between each hot and cold channel and its adjacent hot and cold channels obtained in step S1, Δ i (i=1, 2, ..., n-1),

[0012] Let Δ1 = |Q1+Q2+Q3 / 2|;

[0013] Δ2=|Q2 / 2+Q3+Q4 / 2|;

[0014] …

[0015] Δ n-2 =|Q n-3 / 2+Q n-2 +Q n-1 / 2|;

[0016] Δ n-1 =|Q n-2 / 2+Q n-1 +Q n |;

[0017] S3: Obtain the minimum value of the sum of the absolute values ​​of the heat load differences of all adjacent channels in step S2 The corresponding channel arrangement is the optimal channel arrangement. The present invention does not involve the heat exchanger structure and flow heat transfer calculation, and only needs to know one parameter of the heat load of the heat exchanger channel to perform analysis and optimization calculation. The calculation formula is simple, the optimization result is efficient and stable, and the engineering practical value is high.

[0018] Furthermore, in step S1, if the cold and hot channels of the heat exchanger are arranged in a single stack, the heat loads of the cold and hot channels of each heat exchanger are Q1, Q2, ..., Q n , where n is the total number of channels of the hot and cold channels of the heat exchanger.

[0019] Furthermore, in step S1, if the hot and cold channels of the heat exchanger are arranged in a stacked arrangement, the two stacked channels are regarded as one channel to calculate the heat load, and the heat load value is the sum of the heat loads of the two stacked channels. The heat loads of the hot and cold channels of each heat exchanger are calculated to be Q1, Q2, ..., Q n , where n is the total number of equivalent channels of the hot and cold channels of the heat exchanger.

[0020] Furthermore, in step S3, the channel arrangement with the smallest absolute value of the heat load difference of all adjacent channels is the best arrangement, that is, The target Δ takes the minimum value.

[0021] Furthermore, the multi-stream plate-fin heat exchanger includes seven fluids, including three hot fluids and four cold fluids. The optimization result is stable. For the complex case of seven hot and cold fluids, the efficiency of the heat exchanger fluctuates between 95% and 97%. When the types of hot and cold fluids are 2 to 4, the efficiency of the heat exchanger under the channel arrangement obtained by the present invention reaches more than 98%.

[0022] Furthermore, the thermal fluid includes high-pressure air A, medium-pressure air B, and low-pressure air C.

[0023] Furthermore, the cold fluid includes low-pressure nitrogen D, low-pressure contaminated nitrogen E, low-pressure oxygen F and medium-pressure liquid oxygen G.

[0024] Furthermore, the hot fluid and the cold fluid flow in opposite directions, thereby enhancing the heat exchange effect.

[0025] Further, the hot fluid flows from top to bottom from the top of the multi-flow plate-fin heat exchanger, and the cold fluid flows from bottom to top from the bottom of the multi-flow plate-fin heat exchanger.

[0026] Further, the hot fluid flows from bottom to top from the bottom of the multi-flow plate-fin heat exchanger, and the cold fluid flows from top to bottom from the top of the multi-flow plate-fin heat exchanger.

[0027] The specific beneficial effects of the present invention include:

[0028] 1. Compared with other existing methods for analyzing, optimizing and designing channel arrangement based on heat exchanger performance indicators such as minimum entropy production of heat exchangers and uniformity of temperature field, the present invention does not involve heat exchanger structure and flow heat transfer calculation. Only one parameter, the heat load of the heat exchanger channel, is needed to perform analysis and optimization calculation. The calculation formula is simple, the optimization results are efficient and stable, and the engineering practical value is high.

[0029] 2. The optimization results are stable. For the complex case of seven cold and hot fluids, the efficiency of the heat exchanger fluctuates between 95% and 97%. When the types of cold and hot fluids are 2 to 4, the efficiency of the heat exchanger under the channel arrangement obtained by the present invention reaches more than 98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0031] Figure 1 It is a schematic diagram of the design steps of the present invention;

[0032] Figure 2 It is a schematic diagram of the arrangement of fluid channels of the multi-stream plate-fin heat exchanger in the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] An embodiment of the present invention is a multi-channel countercurrent plate-fin heat exchanger in which seven fluids participate in heat exchange, wherein No. 1 to No. 3 are hot fluids, namely high-pressure air A, medium-pressure air B, and low-pressure air C, and No. 4 to No. 7 are cold fluids, namely low-pressure nitrogen D, low-pressure dirty nitrogen E, low-pressure oxygen F, and medium-pressure liquid oxygen G, and each hot fluid and each cold fluid flows in its own channel.

[0035] Preferably, the hot fluid and the cold fluid flow in opposite directions to enhance the heat exchange effect, the hot fluid flows from top to bottom from the top to the bottom of the multi-flow plate-fin heat exchanger, and the cold fluid flows from bottom to top from the bottom to the top of the multi-flow plate-fin heat exchanger. Alternatively, the hot fluid flows from bottom to top from the bottom to the top of the multi-flow plate-fin heat exchanger, and the cold fluid flows from top to bottom from the top to the bottom of the multi-flow plate-fin heat exchanger.

[0036] Among the seven fluids:

[0037] The number of channel layers of high pressure air A is n A =8;

[0038] The number of channel layers of medium pressure air B is n B =8;

[0039] The number of channels of low-pressure air C is n C =23;

[0040] The number of channels for low-pressure nitrogen D is n D =34;

[0041] The number of channels of low-pressure polluted nitrogen E is n E =30;

[0042] The number of channels of low-pressure oxygen F is n F =1;

[0043] The number of channels of medium pressure liquid oxygen G is n G =4;

[0044] The heat loads of a single channel are:

[0045] q A =-301.70kW;

[0046] q B =-133.00kW;

[0047] q C =-49.00kW;

[0048] q D =+49.95kW;

[0049] q E =+45.72kW;

[0050] q F = +4.96kW;

[0051] q G =+393.93kW;

[0052] The “+” indicates that the cold fluid absorbs heat, and the “-” indicates that the hot fluid releases heat.

[0053] A method for designing the arrangement of fluid channels in a multi-stream plate-fin heat exchanger, such as Figure 1 As shown, the following steps are included:

[0054] S1: Determine the heat loads Q1, Q2, ..., Q of the hot and cold channels of the multi-stream plate-fin heat exchanger n ;

[0055] There are many actual arrangements of the hot and cold channels of the heat exchanger, such as the following arrangements: EADDCDECDECDEBDECDECDEADEBDGAEDCDEAEGADECDE ADDCDECEDBEDCDECDBGBDBECDECDCDCECECECGDCEDADDBEFCEECDDAEECDECDEBD;

[0056] According to the specific arrangement of the hot and cold channels of the heat exchanger, the heat loads of the hot and cold channels of the heat exchanger are Q1, Q2, ..., Q n Determine as follows: In the above arrangement, if Figure 2 As shown, the first channel is a single stack arrangement of fluid E, so the heat load Q1 of the first channel is equal to the single channel heat load q of fluid E E , that is, Q1=q E =+45.72kW;

[0057] The second channel is a single stack arrangement of fluid A, so the heat load Q2 of the second channel is equal to the single channel heat load q of fluid A. A , that is, Q2 = q A =-301.70kW;

[0058] The third and fourth channels are arranged in a D-fluid cascade arrangement, so the heat load of the third channel is the sum of the heat loads of the two D-cascade channels, that is, Q3 = 2×q D =2×(+49.95kW)=+99.90kW;

[0059] By analogy, the specific values ​​of the heat loads Q1, Q2, ..., Qn of the heat exchanger channels are determined.

[0060] S2: Calculate the absolute value of the heat load difference between each hot and cold channel and its adjacent hot and cold channels obtained in step S1, Δ i (i=1, 2, ..., n-1);

[0061] Δ1=|Q1+Q2+Q3 / 2|=|(+45.72)+(-301.70)+(+99.90 / 2)|=206.03kW;

[0062] Δ2=|Q2 / 2+Q3+Q4 / 2|;

[0063] …

[0064] Δ n-2 =|Q n-3 / 2+Q n-2 +Q n-1 / 2|;

[0065] Δ n-1 =|Q n-2 / 2+Q n-1 +Q n |;

[0066] Substitute the specific values ​​of the heat loads Q1, Q2, ..., Qn of the heat exchanger channels obtained in step S1 into Δ i The above calculation formula, such as Δ1=|Q1+Q2+Q3 / 2|=|(+45.72)+(-301.70)+(+99.90 / 2)|=206.03kW, and so on, determines the absolute value of the heat load difference between each hot and cold channel of the heat exchanger and its adjacent hot and cold channels Δ i (i=1, 2, ..., n-1) specific numerical value.

[0067] S3: Obtain the minimum value of the sum of the absolute values ​​of the heat load differences of all adjacent channels in step S2 manually or with the help of a computer optimization algorithm The corresponding channel arrangement is the optimal channel arrangement.

[0068] In the embodiment of the present invention, there are seven kinds of hot and cold fluids involved in heat exchange, and there are hundreds of heat exchanger channels. In order to improve work efficiency, the above optimization design calculation process is implemented with the help of a computer using a genetic optimization algorithm. According to the channel arrangement chromosome encoding method and constraint conditions introduced in the patent of the inventor's authorized invention entitled "Optimization Design Method for Arrangement of Fluid Channels in Multi-stream Plate-fin Heat Exchangers" and the patent with the authorization announcement number CN102629290B, the absolute value Δ of the difference in heat loads of all adjacent channels in step S3 of the present invention is minimized as the channel arrangement chromosome objective function for optimization, and the best channel arrangement optimization result is obtained as follows:

[0069] DBDECDCDCEECDDADECECEECEECEBGBDEBDECEECDCE

[0070] DAEGBDDADECEGADEAEDCDECECEDAEGADEAEDCDECDCDECDDBDDCEFCEDBDDBDDCD, the corresponding heat exchanger heat transfer is 4407kW, reaching 96.52% of the ideal heat transfer of 4566kW of the heat exchanger with equal wall temperature, which is better than the optimization result of Sucessmann W. and Mansour A. using the minimum deviation of the local heat load ZigZag curve from the zero axis as the channel arrangement chromosome objective function DAEECDECDAEECEFCGCDECDEADEBDBDECDECEDC The heat transfer under DEBDEBDDCEDADCDECDEADCDEAGCDEAGBDECEECDECDEBGCEDAEDCDDCDEBDBDDCEECD is 4157kW (accounting for 91.04% of the ideal heat transfer of 4566kW of equal wall temperature of the heat exchanger), which is 250kW more than that, and 6 percentage points higher. At the same time, the optimization result obtained by the method of the present invention is stable. For the seven cold and hot fluids in this embodiment, the efficiency of the heat exchanger fluctuates between 95% and 97%. When the types of cold and hot fluids are 2 to 4, the efficiency of the heat exchanger under the channel arrangement obtained by the present invention reaches more than 98%. In addition, compared with other current methods for analyzing, optimizing and designing channel arrangement based on heat exchanger performance indicators such as minimum entropy production of heat exchangers and uniformity of temperature fields, the channel arrangement design method of the present invention does not involve heat exchanger structure and flow heat transfer calculation. It only needs to know one parameter of heat exchanger channel heat load to perform analysis and optimization calculation. The formula is simple, the optimization result is stable and efficient, the efficiency of the heat exchanger is more than 96%, and the engineering practical value is high.

[0071] Any details not provided in the present invention are conventional technical means known to those skilled in the art. The above content shows and describes the basic principles, main features and beneficial effects of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for designing the arrangement of fluid channels in a multi-stream plate-fin heat exchanger, characterized in that: The following steps are involved: S1: Determine the heat load Q1 of the hot and cold channels of the heat exchanger in the multi-stream plate-fin heat exchanger. Q2,……,Q n ; S2: Calculate the absolute value of the heat load difference between each hot and cold channel and its adjacent hot and cold channels obtained in step S1, Δ i (i=1, 2, ..., n-1), Let Δ1 = |Q1+Q2+Q3 / 2|; Δ2=|Q2 / 2+Q3+Q4 / 2|; …… Δ n-2 =|Q n-3 / 2+Q n-2 +Q n-1 / 2|; Δ n-1 =|Q n-2 / 2+Q n-1 +Q n |; S3: Obtain the minimum value of the sum of the absolute values ​​of the heat load differences of all adjacent channels in step S2 The corresponding channel arrangement is the optimal channel arrangement.

2. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to claim 1, characterized in that: In step S1, if the cold and hot channels of the heat exchanger are arranged in a single stack, n is the total number of channels of the cold and hot channels of the heat exchanger.

3. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to claim 1, characterized in that: In step S1, if the hot and cold channels of the heat exchanger are arranged in a stacked arrangement, the two stacked channels are regarded as one channel to calculate the heat load, and the heat load value of the hot and cold channels of the heat exchanger is the sum of the heat loads of the two stacked channels, where n is the total number of equivalent channels of the hot and cold channels of the heat exchanger.

4. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to claim 1, characterized in that: In step S3, the channel arrangement with the smallest absolute value of the heat load difference of all adjacent channels is the best arrangement, that is, The target Δ takes the minimum value.

5. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to claim 1, characterized in that: The multi-stream plate-fin heat exchanger includes seven fluids participating in heat exchange, and the seven fluids include three hot fluids and four cold fluids.

6. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to claim 5, characterized in that: The thermal fluid includes high-pressure air A, medium-pressure air B, and low-pressure air C.

7. The method for designing the arrangement of fluid channels in a multi-stream plate-fin heat exchanger according to claim 5, characterized in that: The cold fluid includes low-pressure nitrogen D, low-pressure dirty nitrogen E, low-pressure oxygen F and medium-pressure liquid oxygen G.

8. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to any one of claims 5 to 7, characterized in that: The hot fluid flows in opposite directions to the cold fluid.

9. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to any one of claims 5 to 7, characterized in that: The hot fluid flows from the top to the bottom of the multi-flow plate-fin heat exchanger from top to bottom, and the cold fluid flows from the bottom to the top of the multi-flow plate-fin heat exchanger from bottom to top.

10. The method for designing the arrangement of fluid channels of a multi-stream plate-fin heat exchanger according to any one of claims 5 to 7, characterized in that: The hot fluid flows from bottom to top from the bottom of the multi-flow plate-fin heat exchanger, and the cold fluid flows from top to bottom from the top of the multi-flow plate-fin heat exchanger.

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