板式换热器构型的最佳选择的筛选方法-毕业论文外文翻译.docx

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1、外文翻译英文原文： A SCREENING METHOD FOR THE OPTIMAL SELECTION OF PLATE HEAT EXCHANGER CONFIGURATIONSJ.M.Pinto and J.A.W.GutDepartment of Chemical Engineering,University of So Paulo, USPAbstract - An optimization method for determining the best configuration(s) of gasketed plate heat exchangers is presented

2、. The objective is to select the configuration(s) with the minimum heat transfer area that still satisfies constraints on the number of channels, the pressure drop of both fluids, the channel flow velocities and the exchanger thermal effectiveness. The configuration of the exchanger is defined by si

3、x parameters, which are as follows: the number of channels, the numbers of passes on each side, the fluid locations, the feed positions and the type of flow in the channels. The resulting configuration optimization problem is formulated as the minimization of the exchanger heat transfer area and a s

4、creening procedure is proposed for its solution. In this procedure, subsets of constraints are successively applied to eliminate infeasible and nonoptimal solutions. Examples show that the optimization method is able to successfully determine a set of optimal configurations with a minimum number of

5、exchanger evaluations. Approximately 5 % of the pressure drop and channel velocity calculations and 1 % of the thermal simulations are required for the solution. Keywords: plate heat exchanger, heat exchanger configuration, optimization, screening method.INTRODUCTIONThe plate heat exchanger (PHE) co

6、nsists of a pack of gasketed corrugated metal plates, pressed together in a frame. The fluids flow through a series of parallel flow channels and exchange heat through the thin corrugated metal plates. The gasket design and the closed ports of the plates determine the fluid flow arrangement, which c

7、an be parallel, in series or one of several possible combinations of the two. The flow distribution, number of plates, type of gaskets and feed locations characterize the exchanger configuration.CONFIGURATION CHARACTERIZATIONTo characterize the PHE configuration, six distinct parameters are used: NC

8、, PI, PII, f , Yh and Yf, which are described as follows:NC : Number of ChannelsPI and PII : Number of Passes on Sides I and IIf : Feed Connection Relative LocationYh : Hot Fluid LocationYf : Type of Flow in Channels.This binary parameter defines the type of flow inside the channels, which can be st

9、raight or crossed depending on the gasket type (Fig. 1). The crossed flow avoids the formation of stagnation areas, but the straight flow type is easier to assemble. It is not possible to use both types together. If Yf = 1, then the flow is crossed in all channels. If Yf = 0, the flow is straight in

10、 all channels.The six parameters can represent any regular configuration and an example of configurations for a nine-plate PHE is shown in Fig. (2). For any given number of channels, NC, the five remaining parameters have a finite set of allowable values, which limits the number of possible configur

11、ations, as shown in Fig. (3). The disperse pattern is due to the variation in the number of integer factors of NCI and NCII. For the range of number of channels between 2 and 500 there are 284,976 different configurations.Equivalent ConfigurationsFor a given value of number of channels and a fixed t

12、ype of flow, the existence of equivalent configurations (that have the same thermal effectiveness and pressure drops) is possible. Identification of equivalent configurations is important to avoid unnecessary exchanger evaluations. The equivalence of two or more configurations occurs due to the prop

13、erty of flow reversibility (Pignotti & Tamborenea, 1988), to the presence of single pass or to geometrical similarity (the configuration can be freely rotated or mirrored).A methodology to detect equivalent configurations is shown in Tab. (1). For each set of NC, PI, PII and Yf there are groups of v

14、alues for parameter f that result in equivalent configurations. In the case of even-numbered NC, there may be equivalency between Yh = 0 and Yh = 1 because sides I and II have the same number of channels and therefore can have the same numbers of passes. Consider for instance the exchanger shown in

15、Fig. (2), which is arranged for f = 1 and Yh = 1; according to Tab. (1), changing the sides of the fluids (Yh = 1 Yh = 0) will yield a different although equivalent configuration.CONFIGURATION OPTIMIZATIONThe configuration optimization problem is formulated as the minimization of the number of chann

16、els, NC, which is equivalent to minimizing the exchanger heat transfer area or its fixed cost (Eq. 1). There are constraints on the number of channels (NC), fluid pressure drops (DPhot, DPcold), channel flow velocities (vhot, vcold) and exchanger effectiveness (E), as shown in Constraints (2a) to (2

17、f). The optimization model is also subject to the PHE model, necessary for calculation of the aforementioned variables (Constraint 3).subject toConstraint (2a) on the number of channels is related to the available number of plates and exchanger capacity. The minimum values for fluid pressure drop av

18、oid large variations between the average fluid pressures that can bend the plates. Lower bounds on channel flow velocities avoid the formation of preferential paths or stagnation areas inside the channels.The thermal and hydraulic modeling of the PHE (Constraint 3) was developed by Gut and Pinto (20

19、01). The rigorous thermal model accounts for the variation in the overall heat transfer coefficient in the exchanger and consists of a system of differential and algebraic nonlinear equations, which can be solved by numerical methods. Assuming the heat transfer coefficient invariable, the rigorous m

20、odel can be reduced to the so-called simplified thermal model, which consists of a system of linear ordinary differential equations and has an analytical solution. Since there is little difference between the main simulation results achieved by rigorous and simplified thermal models, the latter will

21、 be used for the optimization, keeping the former for final verification of the results.The Screening MethodThe proposed optimization procedure is based on the screening method, also employed by Daichendt and Grossmann (1994) for heat exchanger network optimization. In this procedure, constraints ar

22、e successively used to remove infeasible and nonoptimal solutions of a MINLP problem, thus reducing its size and complexity.In the optimization of a PHE configuration, the Constraint on the number of channels (2a) defines the initial set, IS, of possible configurations, formed by combinations of the

23、 five remaining parameters. An exhaustive enumeration procedure could be used to obtain the optimal configurations within this set; however, this procedure requires a large computational effort due to the large number of thermal simulations needed.Since it is possible to calculate (DP, v) prior to t

24、he thermal simulation using average values for the fluid temperatures, the constraints on pressure drops and channel velocities (Constraints 2b to 2e) can be used to eliminate all infeasible elements in set IS. Therefore, a reduced set of configurations, RS, is generated. It is important to note tha

25、t to obtain set RS it is not necessary to calculate (DP, v) for all the configurations in IS because of the following:A1) parameter f has no influence over (DP, v), A2) (DP, v) is independent for sides I and II. Thus, for a given NC, the calculations are made only once for each allowable number of p

26、asses, A3) for a given NC, DP is proportional to the number of passes; therefore, if DP DPmax is verified, any configuration with a larger number of passes also results in an infeasible solution, A4) for an even-numbered NC, sides I and II have the same number of channels and therefore the same allo

27、wable numbers of passes. In this case, (DP, v) will have the same value for Yh = 1 and Yh = 0. Once set RS is obtained, the effectiveness Constraint (2f) is used to select the optimal set of configurations, OS. However, it is not necessary to thermally simulate all elements in RS because of the foll

28、owing:B1) there are equivalent configurations with the same effectiveness; thus only one needs to be simulated, B2) if a search is conducted in increasing order of NC, when the optimal set is found, all remaining configurations with higher values of NC can be neglected. Since the influence of parame

29、ter Yf on the convective coefficients and friction factor is usually unknown, this parameter may be fixed prior to optimization, thus reducing the number of possible configurations by 50 %. Moreover, it is not possible to change the type of flow in an existing exchanger.Based on these principles, a

30、screening algorithm is developed for the solution of the PHE configuration problem. The steps of the screening algorithm are as follows. For this algorithm, Yf must have a given value (Yf = 0 or 1). If there is available data on the influence of Yf on the heat exchange and friction correlations, thi

31、s algorithm can be used once for each case and the results compared.1. The required data for plate (corrugation pattern, dimensions, area enlargement factor and thermal conductivity), hot and cold fluids (flow rate, inlet temperature, fouling factor and correlations for friction factor, convective h

32、eat transfer coefficients and physical properties) and constraints (lower and upper bounds for Constraints (2a) to (2f) are read. 2. Initialization: RS = , NC(k) = NCmin , k = 1. 3. All allowable numbers of passes for sides I and II (PIi, PIIj) are obtained for NCk. 4. Verification of constraints on

33、 pressure drop and channel flow velocities: 4.1 The (DP, v) pair is calculated for the cold fluid located on side I for each one of the numbers of passes PIi (in increasing order). If the constraints of (DP, v) are satisfied, the cold-fluid/sideI-pass pair is selected. If DPmax is exceeded, there is

34、 no need to evaluate larger numbers of passes. This procedure is applied to the cold fluid located on side II for all the numbers of passes, PIIj, thereby selecting the cold-fluid/sideII-pass pairs. 4.2 The same procedure as that in step 4.1 is applied to the hot fluid, obtaining the hot-fluid/sideI

35、-pass and hot-fluid/sideII-pass pairs. 5. The selected pairs of cold-fluid/sideI-pass and hot-fluid/sideII-pass are combined to generate all possible configurations with Yh = 0. Each combination results in four configurations since f has four values equivalent to (DP, v). The same procedure is appli

36、ed to the selected hot-fluid/sideI-pass and cold-fluid/sideII-pass pairs, yielding configurations with Yh = 1. All generated configurations are stored in RS. 6. If NC(k) = NCmax, then proceed to step 7. Otherwise, NC(k+1) = NC(k) + 1, k = k + 1 and return to step 3. 7. Set RS is now complete. It con

37、tains all the configurations that satisfy the constraints on pressure drop and channel velocity for both sides. Now the optimal set, OS, must be obtained. 8. The configurations in RS with the minimum value of NC are selected. 9. The equivalent configurations are detected and grouped using the method

38、ology shown in Tab. (1). 10. The simplified thermal model (the overall heat transfer coefficient is constant) is used to simulate one of the configurations in each group, obtaining the corresponding thermal effectiveness. 11. If one or more groups of equivalent configurations satisfy the effectivene

39、ss constraint, they are stored in set OS and there is no need to simulate other elements of RS. Otherwise, proceed to the next value of NC in set RS and return to step 9. 12. The rigorous thermal model is used to simulate the nonequivalent elements in OS to verify the effectiveness results. In case

40、of discrepancy (|Esimplified Erigorous| / Erigorous e ), the rigorous model should be used in the previous simulations after step 8. Otherwise, the optimal solution is achieved. OPTIMIZATION RESULTSIt was verified that the number of channels per pass has a strong effect on the pressure drop, and con

41、sequently, about 98 % of the elements in IS are eliminated in the first part of the screening (steps 1 through 8). Compared to an exhaustive enumeration procedure, the screening method demands approximately 5 % of the required evaluations of (DP, v). Further, to obtain set OS only a few elements are

42、 thermally simulated (approximately 1 % of the elements in IS or 20 % of the elements in RS).As an example to show the efficiency of the screening method, consider the selection of a configuration for a process-water (26.0 kg/s, 67 C) / cooling-water (62.5 kg/s, 22 C) PHE with 1.4 m chevron plates w

43、ith crossed channel flow (Yf = 1). The constraint bounds are shown in Constraints (4a) to (4f).In this problem, IS has 26,240 elements and only 1.8 % of the (DP, v) calculations and 0.06 % of the simulations were necessary for the solution of the problem by the screening method. The comparative perf

44、ormance of the screening and enumeration methods is shown in Fig. (4). The set RS obtained contains 84 configurations, ranging from NC = 43 to NC = 144, with pass arrangements of 1/2, 2/3 and 2/4 for hot fluid/cold fluid. The problem solution consists of two pairs of equivalent configurations, all w

45、ith 120 channels, two passes for the hot fluid and three passes for the cold fluid, as shown in Tab. (2). The required CPU time in a DEC-Unix workstation for the simulations of the simplified model was under 1 min, and 5 min were necessary to validate the results using the rigorous model (the deviat

46、ions in E were under 1 %).CONCLUSIONSThe configuration of a gasketed plate heat exchanger (PHE) was represented by a set of six distinct parameters and a methodology to detect equivalent configurations was presented. The problem of optimizing the PHE configuration was formulated as the minimization

47、of the heat transfer area, subject to constraints on the number of channels, the pressure drop and channel flow velocities for hot and cold fluids and the exchanger thermal effectiveness as well as the PHE simulation model. Since it is not possible to derive a mathematical model of the PHE that is e

48、xplicitly a function of the configuration parameters, a mixed-integer nonlinear programming (MINLP) approach could not be used. A screening procedure was then proposed to solve the optimization problem. In this procedure, subsets of the constraints were successively used to eliminate infeasible and

49、nonoptimal elements from the set defined by the bounds on the number of channels. An algorithm was developed to perform the screening with minimum computational effort. Examples show that this algorithm can successfully select a group of optimal configurations (rather than a single solution) for a given application using a very reduced number of thermal simulations.中文翻译：板式换热器构型的最佳选择的筛选方法J.M.Pinto和J.A.W.GutUSP圣保罗大学化学