Multi-stream Plate-fin Heat Exchangers Research Articles

Optimal design of the first stage of the plate-fin heat exchanger for the EAST cryogenic system

The size of the heat exchanger is an important factor determining the dimensions of the cold box in helium cryogenic systems. In this paper, a counter-flow multi-stream plate-fin heat exchanger is optimized by means of a spatial interpolation method coupled with a hybrid genetic algorithm. Compared with empirical correlations, this spatial interpolation algorithm based on a kriging model can be adopted to more precisely predict the Colburn heat transfer factors and Fanning friction factors of offset-strip fins. Moreover, strict computational fluid dynamics simulations can be carried out to predict the heat transfer and friction performance in the absence of reliable experimental data. Within the constraints of heat exchange requirements, maximum allowable pressure drop, existing manufacturing techniques and structural strength, a mathematical model of an optimized design with discrete and continuous variables based on a hybrid genetic algorithm is established in order to minimize the volume. The results show that for the first-stage heat exchanger in the EAST refrigerator, the structural size could be decreased from the original 2.200 × 0.600 × 0.627 (m3) to the optimized 1.854 × 0.420 × 0.340 (m3), with a large reduction in volume. The current work demonstrates that the proposed method could be a useful tool to achieve optimization in an actual engineering project during the practical design process.

Design optimisation of multi-stream plate fin heat exchangers with multiple fin types

For multi-stream plate fin heat exchanger design, one needs to consider the optimal combination of fin categories and detailed geometries of fin types. Due to the complexity of the design problem for multi-stream plate fin heat exchangers, a major limitation of existing technology is the lack of a general design methodology that can consider mix-and-match fin type selection and imposed constraints simultaneously to take advantage of different fin characteristics. In this work, a new design method is proposed to consider the possibility of mix-and-match fin types. Multi-stream plate fin heat exchangers with mix-and-match fin types is considered as a network of two-stream plate fin heat exchangers. A mixed integer nonlinear programming (MINLP) model is converted into a nonlinear programming (NLP) model, and solved in combination of enumeration for a few remaining binary variables. The objective is to minimise the total capital cost. Case studies are carried out to validate the effectiveness of new proposed design methodology and demonstrate the benefits of mix-and-match fin type combinations in the overall design methodology.

Development and validation of a direct passage arrangement method for multistream plate fin heat exchangers

Passage arrangement quality significantly affects the performance of multistream plate fin heat exchanger (MPFHEs) because a bad arrangement may result in uneven temperature difference field and pressure field between passages and thus reduce the thermal efficiency. However, it is very difficult to design an effective passage arrangement owing to large numbers of possible passage arrangement patterns and complex heat transfer processes between the passages in a MPFHE. This work develops a direct passage arrangement method for MPFHEs to address this problem. In this method, an improvement of passage arrangement with good synergistic heat transfer effect is first proposed. The determination of passage quantity for each fluid is suggested to be proportional to its design heat load. Next, based on the results of the checking calculation, the fin and heat exchanger structure parameters should be adjusted until the constraints including thermal effectiveness, length deviation and pressure drops have been satisfied. Afterwards, the passages are arranged directly by a symmetry arrangement method. To evaluate the effectiveness of this method, three different industrial cases are performed and compared with the existing optimization designs by three evaluation means. The validation results indicate that this method performs better than the complex optimization methods.

A thermal design method for the performance optimization of multi-stream plate-fin heat exchangers

An optimization design method based on field synergy principle is developed for Multi-stream plate-fin heat exchangers (MPHEs) with a segmented differential model. The heat exchanger is divided into a number of sub-exchangers along the main stream, and each sub-exchanger consists of N passages along the height of the exchanger. Compared with the traditional heat exchanger design, this method allows temperature and pressure fields to be obtained via coupling calculation with consideration of variable physical properties and the axial heat loss of the heat exchanger. Finally, the heat exchanger is optimally designed using a temperature-difference uniformity optimization factor based on field synergy principle. This design model can provide an accurate temperature field and pressure field, because the stream properties are determined by the mean temperature and pressure of each local sub-exchanger. Optimum results indicate that the temperature distribution on the cross section of the heat exchanger is relatively uniform and that the temperature difference of heat transfer for each stream is always a small value. These characteristics prove the feasibility and effectiveness of this design model. In this paper, a case of five stream plate-fin heat exchangers for an ethylene plant is designed under a practical cold box operating condition with the proposed model, the structure and heat transfer of which are optimally determined. The design model and optimization method proposed in this work can provide theoretical and technical support to the optimization design of MPHEs.

Property Impacts on Plate-fin Multi-stream Heat Exchanger (Cold Box) Design in CO2 Cryogenic Process: Part I. Heat Exchanger Modeling and Sensitivity Study

The multi-stream plate-fin heat exchanger is one of the most important components in the CO2 cryogenic system. Appropriate design methodology and in-depth analysis of property on the heat exchanger are of importance. This paper, as part I of the two-paper series, presented the design procedure for the multi-stream plate-fin heat exchanger in CO2 cryogenic process. Sensitivity study was also conducted to analyze the impacts of thermos-physical properties including density, viscosity, heat capacity and thermal conductivity. The results show that thermal conductivity has the most significant impact and it should be prioritized to develop a more accurate thermal conductivity model for the heat exchanger design. In addition, viscosity has least significant impact but the higher uncertainty range of viscosity may lead to a higher possible deviation in volume design.

Experimental investigations and validation of two dimensional model for multistream plate fin heat exchangers

Experimental investigations are carried out using a specially developed three-layer plate fin heat exchanger (PFHE), with helium as the working fluid cooled to cryogenic temperatures using liquid nitrogen (LN2) as a coolant. These results are used for validation of an already proposed and reported numerical model based on finite volume analysis for multistream (MS) plate fin heat exchangers (PFHE) for cryogenic applications (Goyal et al., 2014). The results from the experiments are presented and a reasonable agreement is observed with the already reported numerical model.

Effect of inlet flow maldistribution on the passage arrangement design of multi-stream plate-fin heat exchanger

Inlet flow maldistribution has deteriorative influence on the thermal performance of multi-stream plate-fin heat exchanger, which affects the design of passage arrangement. In this paper, the optimization design of passage arrangement considering inlet flow maldistribution is investigated. A thermal model based on integral mean temperature difference is developed for evaluating the coupling effects of inlet flow distribution and passage arrangement on the total heat transfer rate of multi-stream plate-fin heat exchanger, the model is validated with ±6.71% root-mean-square errors of heat transfer rate under uniform flow with 20 groups of simulation data of Aspen Plate Fin Exchanger (Single)®. Then three representative one-dimensional inlet mass flow distributions are adopted to characterize the inlet flow maldistribution. Passage arrangement under these flow maldistributions are optimized using hybrid particle swarm algorithm. By carrying out the optimization, the total heat transfer rate increased 2.50% and 4.52% under different inlet flow maldistributions of Flow A; and increased by 2.58–3.98% under different inlet flow maldistributions of Flow A of Flow B simultaneously.

Study on Entropy Generation of Multi-Stream Plate Fin Heat Exchanger with use of Changing Variables Thermodynamic and Fluids Flow Rate between Plates and Provide an Optimal Model

Background/Objectives: In this study we have investigated entropy generation of multi-stream plate fin heat exchanger with use of changing variables thermodynamic and fluids flow rate between plates and provide an optimal model. Methods/Statistical Analysis: For optimizing the plate thermal exchanger, we get the help of a toolbox (genetic algorithm) which has come with MATLAB software. So it is suitable to point to the logic and essence of this optimization method. Between the optimization methods, genetic algorithm, inspired by nature is one of the most advanced ones with disconnected variables. This algorithm is based on natural progress. Findings: The results of calculation were obtained without any change in geometric parameters that was used by air separation unit in APC, thermal exchange coefficient factors are as follows, 1545, 833, 1519, 706 and 2030 ; and pressure drop of each of the exchanger feeding fluid is calculated approximately 10.8, 19.0, 12.1, 19.9, 18.6, in KPa Pascal. Also overall pressure drop in suggested plate heat exchanger with simple fins was calculated 80.5 K.Pa which is less than desired figure of air separation unit in petrochemical company but instead, output temperature of passing fluids between plates is reduced. Application/Improvements: Optimization was done by using the principal of entropy generation minimization, Entropy Generation Minimization (EGM).

A combined method for surface selection and layer pattern optimization of a multistream plate-fin heat exchanger

In the design of multistream plate-fin heat exchangers (MPFHEs), surface selection and layer pattern optimization have been investigated as two independent problems and still remain at the empirical stage, which becomes an obstacle for optimizing the performance of MPFHEs. A combined method of the equipartition of entropy production and the balance of local heat load is proposed in the present research to consider these two problems simultaneously, by means of which the decrease of heat transfer performance and the increase of pressure drop caused by inappropriate surface selection and layer pattern could be reduced to a large extent. The temperature difference and pressure drop are introduced into the optimization model in the forms of specific entropy generation rates of the heat transfer and fluid friction. These parameters are adopted as a dual-objective function in the optimization to associate the surface selection with the layer pattern. This combined method starts from the design of layer numbers and fin structures, includes the layer pattern arrangement and finally employs multi-objective optimization to achieve an optimal production. This method conforms to the actual design process and provides good robustness and high efficiency for a main heat exchanger in air separation plants, which is a beneficial approach for the design of MPFHEs.

Development of experimental test facilities for validation of multistream plate finheat exchanger design codes

Compact plate-fin heat exchangers (PFHE) having very high effectiveness (>0.95) are key equipment of modern helium liquefaction/refrigeration systems. Effectiveness (e) of these heat exchangers strongly influences the overall system performance. Apart from basic fluid film resistances, various secondary parameters such as axial heat conduction (AHC) through the heat exchanger metal matrix, parasitic heat in-leak from surroundings, variation in fluid/metal properties and flow mal-distribution etc need to be considered while sizing/rating such high effectiveness PFHE. Need of multiple streams in a single heat exchanger further complicates thermal designs. In-house codes are developed at BARC/IIT Bombay for rating of such high effectiveness PFHEs. For experimental performance evaluation of PFHEs, their characterization at various operating conditions and validation of in-house developed numerical codes, a dedicated closed loop experimental test facility is developed. Development of the dedicated closed loop experimental test facility is presented in this paper along with initial test results.

Available online Design and simulation of multistream plate-fin heat exchangers – Single-phase streams

Widely known cryogenic processes, such as LNG, ethylene or air separation plants, make use of plate-fin heat exchangers (PFHEs) because of their compactness and ability to exchange heat simultaneously between the different streams that flow through it. However, this ability to simultaneously exchange heat makes their design and simulation a complex task. An accurate model that is able to predict their performance (i.e. simulate PFHEs) for different operating conditions is needed to be able to optimise the operation of plants that make use of PFHEs. However, little research has addressed this subject. In the present work, several methodologies are proposed for the design and simulation of PFHEs for single-phase streams. In this work, a design methodology is proposed that addresses the shortcomings of previous methodologies. For the simulation of PFHEs, a superstructure approach is used and the PFHE is represented as a network of two-stream heat exchangers. Two different methodologies are proposed for the simulation of PFHEs: one model makes use of detailed geometry data to make thermal-hydraulic calculations (i.e. heat transfer coefficient and pressure drop calculations); the other model regresses a number of parameters based on available operational data and then makes use of these parameters to estimate the heat exchange between streams. The benefits of using the design and simulation methodologies proposed are illustrated with an example taken from the open literature. The results show that all of the models are able to predict with good accuracy the outlet temperatures and thermal-hydraulic behaviour of these exchangers.

Optimisation of fin selection and thermal design of counter-current plate-fin heat exchangers

A major challenge in designing optimal multi-stream plate-fin heat exchangers is the large number of combinations of standardised fin geometries for various fin types to choose from, which adds discrete aspects to an already complicated design problem. In this work, a new design algorithm is proposed to address this issue. By treating basic fin geometries such as plate spacing, fin pitch, fin length and fin thickness as continuous variables for all the fin types, different fin types are characterised based on the work published by different researchers. Then by taking into account thermal hydraulic performance of different fin types, optimal fin types and their corresponding design parameters can be obtained simultaneously by minimising the total volume of heat exchanger. The design parameters can be rounded to the nearest standardised fin parts for a feasible design. A case study with a comparison of published results is carried out to demonstrate the effectiveness of the method.

Experimental investigation on the thermal performance of multi-stream plate-fin heat exchanger based on genetic algorithm layer pattern design

Efficient approaches are imperative for the design of the layer pattern of multi-stream plate-fin heat exchangers (MPFHE) to obtain enhanced thermal performance. This paper presents few layer pattern criterion models to determine optimal stacking pattern. These models were developed by employing a genetic algorithm with binary chromosome ring representing alternatively placed hot and cold layer fluid streams. The method of dual fitness alternating optimization functions was used for conducting local heat energy balance and single layer thermal load difference. The zigzag pattern weighted deviation of the cumulative heat load σ was evaluated for the layer pattern. An experimental study was conducted on layer pattern to test the optimality of the stacking pattern. The experimental data and HTFS MUSE simulation results were found to be in agreement. The optimized results showed that the smallest value of σ was in the range of 0.05–0.20, and that the average thermal efficiency of exchanger was higher than 98%. From these results it was concluded that the performance of MPFHE in relation to heat transfer and fluid flow was effectively improved by the optimization design of the genetic algorithm (GA) layer pattern.

Passage arrangement optimization of multi-stream plate-fin heat exchangers

Passage arrangement quality is of great significance for the heat transfer performance of multi-stream plate-fin heat exchangers. In the present paper, a passage arrangement method is presented on the basis of minimizing the cumulative heat load to bring convenience for passage arrangements and to improve the heat transfer performance. The passage arrangement results are compared with that of the previous research, indicating 2.9% reduction of the mean square error of the cumulative heat load. For further improvement of the passage arrangement quality, the temperature profiles of the heat exchangers are obtained by applying the distributed-parameter model, based on which a further scheme for optimization is proposed. By carrying out the optimization, the outlet temperature inhomogeneity of the air stream, the waste nitrogen stream and the nitrogen stream are reduced by 7.8%, 4.1% and 82.0% respectively, indicating better heat transfer performance.

Passage arrangement design for multi-stream plate-fin heat exchanger under multiple operating conditions

As the development of heat exchangers from two streams and single operating condition to multi-stream and multiple operating conditions, passage arrangement becomes a key problem for heat exchanger design. In this paper, a new passage arrangement design method for multiple operating conditions is developed for multi-stream plate-fin heat exchangers. The integral-mean temperature differences method (IMTD) is expanded from three-stream to multi-stream plate-fin heat exchanger, and then the correlation model among heat transfer rate, passage arrangement and fin design parameters is constructed based on IMTD. Upon the maximum heat transfer rate under each operating condition, the passage arrangement coefficient of each condition and the passage arrangement design space of multiple operating conditions are calculated. As passage arrangements being design variables, the passage arrangement under multiple operating conditions is designed using hybrid particle swarm algorithm. Effectiveness of the passage arrangement design approach is verified through optimization design of a 24 streams heat exchanger, and the results show that the heat exchanger obtained by the proposed algorithm exhibit comfort heat transfer rates under multiple operating conditions. Finally, the method is used to design the passage arrangement of main heat exchanger in 80,000Nm3 air separation unit.

Two dimensional model for multistream plate fin heat exchangers

A model based on finite volume analysis is presented here for multistream plate fin heat exchangers for cryogenic applications. The heat exchanger core is discretised in both the axial and transverse directions. The model accounts for effects of secondary parameters like axial heat conduction through the heat exchanger metal matrix, parasitic heat in-leak from surroundings, and effects of variable fluid properties/metal matrix conductivity. Since the fins are discretised in the transverse direction, the use of a fin efficiency is eliminated and the effects of transverse heat conduction/stacking pattern can be taken care of. The model is validated against results obtained using commercially available software and a good agreement is observed. Results from the developed code are discussed for sample heat exchangers.

An effective layer pattern optimization model for multi-stream plate-fin heat exchanger using genetic algorithm

For multi-stream plate-fin heat exchangers (MPFHEs), a crucial factor affecting performance is the layer pattern used to distribute hot and cold streams. However, for the design of MPFHE layer pattern, so far it still remains at semi-qualitative, empirical or trial-and-error stage, lacking efficient approaches to obtain the optimum. In this paper, an effective layer pattern optimization model using genetic algorithm (GA) is developed in detail. It includes the chromosome of binary string that represents hot and cold layers alternatively arranged, the dual fitness functions that act on chromosome individuals alternatively, the constraint that requires the spacing layers between hot and cold streams to be no less than 1 and no greater than 2, the selection of optimization tool and the corresponding setting of GA parameters. When used to optimize the layer pattern of actual MPFHE, this model exhibits well. The average thermal efficiency of exchanger reaches up to 98% of that obtained under the ideal common wall temperature assumption. Furthermore, the study of this paper make it clear the association of previous classical deviation from ideal of layer pattern zigzag curve with MPFHE thermal performance, which is not a strict monotonic decreasing relation as people thought to be, but a multiple vs. multiple relation.

Thermal Design of Multistream Plate Fin Heat Exchangers—A State-of-the-Art Review

Multistream plate fin heat exchangers have replaced two-stream heat exchangers in diverse applications due to their compactness, capacity of handling multiple fluid streams in a single unit, and possibilities of having intermediate entry and exit of the streams. Unique features of such heat exchangers like direct/indirect crossover in temperatures due to several thermal communications among the fluid streams and the dependence of the thermal performance on “stacking pattern” have no equivalent in two-stream modules. As a consequence, an extension of the commonly used design/simulation techniques like ϵ-NTU or the LMTD method, applicable for two-stream exchangers, fails miserably in the case of multistream units. Though several techniques have been suggested over the years, in reality, no universally accepted methodology exists for the “thermal design” of multistream plate fin heat exchangers to date. In this communication, a state-of-the-art review of the thermal design of multistream plate fin heat exchanger is provided. Reported techniques based on heuristics, extension of the analysis applicable for two-stream heat exchangers, differential analysis, network analysis, and rigorous numerical solutions are briefly reviewed. Advantages and limitations of such techniques are also critically judged. The method of “area splitting” and “successive partitioning” proposed by the present research group is also elaborated. Apart from the basic design methodology, the techniques adopted for accounting for variable fluid properties, axial heat conduction in the solid matrix, and thermal communication with the environment have been discussed. Further, the suggested methodologies for optimizing the thermal design are reviewed. Finally, comments have been made indicating the future need of research in this topic.

Optimum stacking pattern for multi-stream plate-fin heat exchanger through a genetic algorithm

A methodology has been developed to determine optimal stacking pattern of multi-stream plate-fin heat exchangers using a genetic algorithm. This investigation tries to find out the stacking pattern, which gives the maximum heat load for a given number of fluid streams with some specified properties, mass flow rate and entry temperature. The method of area splitting and successive partitioning has been used for the estimation of heat load. Several direct and indirect checks have been made to test the optimality of the stacking pattern. These include exhaustive search, checking the pattern of cumulative heat load and plate temperature profile along a plane normal to the exchanger. The solutions obtained through the developed algorithm exhibit excellent conformity to all of these criteria.

Application of process decomposition in multi-stream plate fin heat exchangers design to use in heat recovery networks

Application of multi-stream heat exchangers in heat recovery networks has a lot of advantages as low initial and operation costs, high thermal performance, low volume and weight. However, the main question arises encountering a real problem is: How many multi-stream plate fin heat exchangers are required for a specific process unit? Current work presents the financial drawbacks and thermal malfunction of the exchanger that may be appeared as a consequence of using a single heat exchanger in the process units consisted of several gaseous and liquid streams. Based on the design method, process limitations and physical properties, a new method of process decomposition will be introduced. In order to minimize the financial drawbacks due to increase of external utilities as a consequence of stream zoning, new stream zonal transfer will be presented. The applicability of the method is demonstrated on a case study.