Optimal design of plate-fin heat exchangers by a hybrid evolutionary algorithm

This study explores the first application of a Genetic Algorithm hybrid with Particle Swarm Optimization (GAHPSO) for design optimization of a plate-fin heat exchanger. A total number of seven design parameters are considered as the optimization variables and the constraints are handled by penalty function method. The effectiveness and accuracy of the proposed algorithm is demonstrated through an illustrative example. Comparing the results with the corresponding results using GA and PSO reveals that the GAHPSO can converge to optimum solution with higher accuracy.     

Optimization of plate-fin heat exchangers by an improved harmony search algorithm

This study explores the use of a proposed variant of harmony search algorithm for design optimization of plate-fin heat exchangers. The algorithm deals with a large number of continuous and discrete variables. To handle the constraints in the optimization problem, a self-adaptive penalty function scheme is used. The efficiency and accuracy of the proposed method are demonstrated through an illustrative example taken from previous studies. Numerical results indicate that the presented approach can generate optimum solutions with higher accuracy when compared to Genetic algorithms (GAs), Particle Swarm Optimization (PSO) and GA hybrids with PSO (GAHPSO).     

An imperialist competitive algorithm approach for multi-objective optimization of direct coupling photovoltaic-electrolyzer systems

In the context of sustainable clean hydrogen production pathways, photovoltaic-electrolyzer systems are one of the most promising alternatives for acquiring hydrogen from renewable energy sources.     

An approach for the optimum design of heat exchangers

In this paper, an approach for the optimum design of heat exchangers has been presented. Traditional design method of heat exchangers involves many trials in order to meet design specifications. This can be avoided through the present design method, which takes the minimization of annual total cost as a design objective. In alternative optimum design methods, such as Lagrange multiplier method, by changing one variable at a time and using a trial–error or a graphical method, optimum results are obtained in a long time. In the present design optimization problem, the total annual cost has been taken as the objective function and heat balance, and rate equation have been taken as equal constraint. The method using the penalty function transforms the constrained problem into a single unconstrained problem. To solve the optimal problem, the method of steepest descent has been used. Initial design variables include the tube‐inside coefficient of heat transfer, tube‐outside coefficient of heat transfer, temperature difference and outside tube area of heat transfer. The changes in variables are considered simultaneously to reach an optimum solution. The results show that the present approach is a powerful tool for optimum design of heat exchangers and is expected to be beneficial to energy industry. Copyright © 2004 John Wiley & Sons, Ltd.     

Second law based optimisation of crossflow plate-fin heat exchanger design using genetic algorithm

A genetic algorithm based optimisation technique has been developed for crossflow plate-fin heat exchangers using offset-strip fins. The algorithm takes care of large number of continuous as well as discrete variables in the presence of given constraints. The optimisation program aims at minimising the number of entropy generation units for a specified heat duty under given space restrictions. The results have also been obtained and validated through graphical contours of the objective function in the feasible design space. The effect of variation of heat exchanger dimensions on the optimum solution has also been presented.     

Numerical study of flow patterns of compact plate-fin heat exchangers and generation of design data for offset and wavy fins

Thermo-hydraulic design of compact heat exchangers (CHEs) is strongly dependent upon the predicted/measured dimensionless performance (Colburn factor j and Fanning friction factor f vs. Reynolds number Re) of heat transfer surfaces. Also, air (gas) flow maldistribution in the headers, caused by the orientation of inlet and outlet nozzles in the heat exchanger, affects the exchanger performance. Three typical compact plate-fin heat exchangers have been analyzed using Fluent software for quantification of flow maldistribution effects with ideal and real cases. The headers have modified by providing suitable baffle plates for improvement in flow distribution. Three offset strip fin and 16 wavy fin geometries used in the compact plate-fin heat exchangers have also been analyzed numerically. The j and f vs. Re design data are generated using CFD analysis only for turbulent flow region. For the validation of the numerical analysis conducted in the present study, a rectangular fin geometry having same dimensions as that of the wavy fin has been analyzed. The results of the wavy fin have been compared with the analytical results of a rectangular fin and found good agreement. Similarly, the numerical results of offset strip fin are compared with the correlations available in the open literature and found good agreement with most of the earlier findings.     

板翅式换热器翅片及隔板动态特性分析

基于板翅式换热器翅片的非稳态导热方程，计算分析了翅片的动态特性，认为翅片的不稳定传热过程相对于换热器其它过程特征时间无限小，因此可以不考虑翅片的动态特性，从而简化了板翅式换热器动态模型，通过分析换热器动态过渡过程表明：隔板的热容对板翅式换热器的动态特性的影响是不容忽略的。     

An alternate algorithm for the analysis of multistream plate fin heat exchangers

A new algorithm has been developed for the analysis of multistream heat exchangers. The numerical technique involves partitioning of the exchanger in both axial and normal directions. Conservation equations written for each segment are solved using an iterative procedure. In the axial direction, the exchanger is successively partitioned to 2^k segments, the final value of k being determined by the point where further partitioning has only marginal effect. In the normal direction, the exchanger is divided into a stack of overlapping two-stream exchangers interacting through their common streams. The algorithm has been tested against published results and good agreement has been observed.     

Fin efficiency and mechanisms of heat exchange through fins in multi-stream plate-fin heat exchangers: development and application of a rating algorithm

The basic heat balance equations for separating surface and passage in a multi-stream plate-fin heat exchanger are derived based on a formalism proposed earlier [Prasad, International Journal of Heat and Mass Transfer 1996, 39(2), 419–428]. An algorithm is developed for rating heat exchangers based on the equations, and incorporated into an existing computer code called STACK [Prasad, Heat Transfer Engineering, 1991, 12(4), 58–70]. The program is used to analyse some typical heat exchangers. It was found that though transverse conduction could be present in some and absent in some passages, it tended to play an increasingly important role as fin effectiveness increased. Of the three mechanisms of heat exchange identified, Mechanism 1 and Mechanism 3 dominated at low fin effectiveness, whereas Mechanism 2 tended to dominate at high fin effectiveness. It was found that the developed method reliably predicted heat transfer in special situations such as the presence of dummy passages, where other methods were known to fail.     

Optimal configuration design for plate heat exchangers

A screening method is presented for selecting optimal configurations for plate heat exchangers. The optimization problem is formulated as the minimization of the heat transfer area, subject to constraints on the number of channels, pressure drops, flow velocities and thermal effectiveness, as well as the exchanger thermal and hydraulic models. The configuration is defined by six parameters, which are as follows: number of channels, numbers of passes on each side, fluid locations, feed relative location and type of channel flow. The proposed method relies on a structured search procedure where the constraints are successively applied to eliminate infeasible and sub-optimal solutions. The method can be also used for enumerating the feasible region of the problem; thus any objective function can be used. Examples show that the screening method is able to successfully determine the set of optimal configurations with a very reduced number of exchanger evaluations. Approximately 5% of the pressure drop and velocity calculations and 1% of the thermal simulations are required when compared to an exhaustive enumeration procedure. An optimization example is presented with a detailed sensitivity analysis that illustrates the application and performance of the screening method.     

Computer Implementation of the Passage Arrangement for Plate-Fin Heat Exchangers According to Local Balance Principle

INTRODUCTIONPlate-finheatexchangersarewidelyusedinmanyindllstries,incIudingcryogenics,electroniccooling,automobiles,etc.Theneedforsmallsize,lightweight,high-performanceofheatexchangershasresultedintherapiddevelopmentinboththeirproductiontech-nologyanddesignmethodology.Figure1showsatyp-icalsketchofanaluminumplate-finheatexchanger.Itconsistsofapackageofmanysmoothandcorru-gatedplates,whichformthepassagesfortheprocessfluids.Itusuallyhasalargenumberofseparatedpas-sagesandallowtheheatexchangeb…     

Fluid flow analysis and extension of rapid design algorithm for helical baffle heat exchangers

“Shell-and-tube heat exchanger with helical baffles” is one of the new technologies used to improve the performance of common heat exchangers with segmental baffles. In this paper, after a short introduction of the technology, investigations of fluid flow pattern are carried out. By creating different arrangements of the helical baffles, the comparison between these types of baffles and the segmental one has been performed. Then, by using derived pressure drop relationship and the rapid design algorithm, some equations for both turbulent and laminar regimes are developed which relate pressure drop to heat transfer coefficient and heat transfer area. With the help of these relationships a straightforward design procedure has been developed.     

Thermal design of multi-stream heat exchangers

The thermal design of multi-stream heat exchangers of the plate and fin type is presented. Although originally used in low temperature processes, their application is extrapolated to above temperature processes and it is shown that, conceptually, multi-stream exchangers could replace whole heat recovery networks. The approach is based on the use of temperature vs. enthalpy diagrams or composite curves, which show how a multi-stream exchanger can be subdivided into block sections that correspond to enthalpy intervals and indicate the entry and exit points of the streams. A design methodology for plate and fin exchangers in countercurrent arrangement, characterized by the maximization of allowable pressure as a design objective is extended to the design of multi-fluid exchangers. The methodology uses a thermo-hydraulic model which relates pressure drop, heat transfer coefficient and exchanger volume. The potential applicability of the methodology is demonstrated on a case study.     

Neural networks analysis of thermal characteristics on plate-fin heat exchangers with limited experimental data

In this paper, an application of artificial neural networks (ANNs) was presented to predict the pressure drop and heat transfer characteristics in the plate-fin heat exchangers (PFHEs). First, the thermal performances of five different PFHEs were evaluated experimentally. The Colburn factor j and friction factor f to different type fins were obtained under various experimental conditions. Then, a feed-forward neural network based on back propagation algorithm was developed to model the thermal performance of the PFHEs. The ANNs was trained using the experimental data to predict j and f factors in PFHEs. Different network configurations were also examined for searching a better network for prediction. The predicted values were found to be in good agreement with the actual values from the experiments with mean squared errors (MSE) less than 1.5% for j factor and 1% for f factor, respectively. This demonstrated that the neural network presented can help the engineers and manufacturers predict the thermal characteristics of new type fins in PFHEs under various operating conditions.     

Accuracy of one-dimensional design procedures for finned-tube heat exchangers

In design procedures for finned-tube heat exchangers a common simplification is assuming that the temperature distribution is one-dimensional. In this way, the heat exchanger can be schematized as a thermal circuit with three thermal resistances in series: internal convection to the tube, conduction through the tube wall, and external convection through the fin assembly. The aim of this work is to quantitatively evaluate the accuracy of one-dimensional schematizations in the context of finned-tube heat exchangers utilized in air-conditioning applications. To this purpose, first three-dimensional benchmark results are obtained employing an in-house FEM code. Afterwards, a simplified two-dimensional model is proposed and validated through a comparison with the three-dimensional results. Finally, the simplified two-dimensional model and the commercial software COMSOL Multiphysics are used to conduct a parametric study aimed at assessing the accuracy of one-dimensional schematizations. The main conclusion is that the accuracy of one-dimensional design procedures is quite acceptable for practical purposes, since it leads to errors in the estimation of heat flow rates that are always less than 2%.     

French rules for the design of fixed-tubesheet heat exchangers

Since 1981 new rules have been applied in France (CODAP) for heat exchanger mechanical design, which have been elaborated under the responsibility of the author. The purpose of this paper is to present the rules relative to the fixed-tubesheet heat exchangers and compare them with the rules provided by the Tubular Exchanger Manufacturing Association (TEMA).

The tubesheet is replaced by an equivalent solid plate for which the effective elastic constants are given by original curves depending on the ligament efficiency and on the ratio of tubesheet thickness to tube pitch.

The connection of the tubesheet with the shell and the head is simulated by considering the tubesheet as being elastically clamped at its periphery: this allows one to treat, in a continuous way, simply supported and clamped tubesheets and to avoid arbitrary choices by the designer between those two extreme cases.

The method enables the calculation of the maximum stresses in the tube-sheet, tubes, shell and head, which are limited to allowable stresses established according to the stress category concept of ASME VIII, division 2.

These rules lead generally to thinner tubesheets than those arising from TEMA whilst still providing more overall safety due to a better representation of the tubesheet behaviour.     

The combined effects of longitudinal heat conduction,flow nonuniformity and temperature nonuniformity in crossflow plate-fin heat exchangers

An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effects of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distribution is carried out using a finite element method. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in fluid flow. Using these models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance variations are quite significant in some typical applications.     

An online adaptive optimal control strategy for complex building chilled water systems involving intermediate heat exchangers

This paper presents an adaptive optimal control strategy for online control of complex chilled water systems involving intermediate heat exchangers to enhance operation and energy performances. This optimal control strategy determines the optimal settings of the heat exchanger outlet water temperature (hot side) and the required operating number of heat exchangers and pumps in order to minimize the total energy consumption of pumps under varying working conditions. Adaptive method is utilized to update the key parameters of the proposed models online. A simulated virtual platform representing a chilled water system in a super high-rise building was established to validate and evaluate the proposed optimal strategy. Test results show that the strategy has enhanced control robustness and reliability, particularly in avoiding deficit flow problem. Significant energy of chilled water pumps is saved when compared with conventional methods.     

Numerical study of horizontal ground heat exchangers for design optimization

Despite ground source heat pump has been proven as highly efficient, high initial cost discourages homeowners and small-medium enterprises to opt for such systems. Horizontal ground heat exchangers offer relatively low-cost solution that may help promoting these systems usage worldwide. This study examines ways to optimize the designs for horizontal ground heat exchangers by using different layouts and pipe materials. CFD simulation of three dimensional models was performed to achieve this objective. All cases tested are able to yield comparable heat exchange rate for an equal trench length. However, the effective period differs one from the other. Additional initial and overhead costs are worthy as slinky ground heat exchangers prolongs heat transfer process when compared against straight configuration. Pipe materials with superior thermal conductivity also promote longer high efficiency operation. An improvement of 16% is reported when copper pipe is used instead of the conventional HDPE pipes. Effective period can be extended by 14% when ground heat exchangers are installed in vertical orientation. Thermal interference in slinky configuration is prevalent during initial operation. In a long run, the effect is observed to be minimal except in vertical orientation. However, it is avoidable beforehand at design stage.