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.     

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.     

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。     

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.     

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.     

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…     

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.     

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.     

Thermodynamic optimization of design variables and heat exchangers layout in HRSGs for CCGT,using genetic algorithm

The heat recovery steam generator (HRSG) is one of the few equipments that are custom made for combined cycle power plants, and any change in its design affects all performance parameters of a steam cycle directly. Thus providing an optimization tool to optimize its design parameters and the layout of its heat exchangers is of great importance. A new method is introduced for modeling a steam cycle in advanced combined cycles by organizing non-linear equations and their simultaneous solutions by use of the hybrid Newton methods in this article. Thereafter, optimal thermodynamic performance conditions for HRSGs are calculated with the help of the genetic algorithm. In the conclusion, the results obtained for different types of HRSGs are compared. The results show that the use of several pressure levels in HRSGs increases the power production in the steam cycle, and similarly, reheating is very beneficial in three pressure heat recovery steam generators.     

Optimal design of plate-and-frame heat exchangers for efficient heat recovery in process industries

The developments in design theory of plate heat exchangers, as a tool to increase heat recovery and efficiency of energy usage, are discussed. The optimal design of a multi-pass plate-and-frame heat exchanger with mixed grouping of plates is considered. The optimizing variables include the number of passes for both streams, the numbers of plates with different corrugation geometries in each pass, and the plate type and size. To estimate the value of the objective function in a space of optimizing variables the mathematical model of a plate heat exchanger is developed. To account for the multi-pass arrangement, the heat exchanger is presented as a number of plate packs with co- and counter-current directions of streams, for which the system of algebraic equations in matrix form is readily obtainable. To account for the thermal and hydraulic performance of channels between plates with different geometrical forms of corrugations, the exponents and coefficients in formulas to calculate the heat transfer coefficients and friction factors are used as model parameters. These parameters are reported for a number of industrially manufactured plates. The described approach is implemented in software for plate heat exchangers calculation.     

A generalized multifluid optimal pressure for heat exchangers operating with supercritical fluid

Distinct thermophysical properties encountered in supercritical fluids operating near the critical point have made them strong candidates for working fluids in various engineering applications. Particularly due to the existence of heat capacity maxima near the critical point, heat transfer involving supercritical fluids and their employment in power generation systems have received special attention. In this paper, the existence of optimal operating pressures that maximize the global conductance of supercritical heat exchangers is demonstrated. Analysis of the behavior of the isobaric specific heat along the heat transfer process shows that optimal performance is achieved when the average isobaric specific heat is maximized. Consequently, optimal pressure maps can be created to assist heat exchanger design for various combinations of inlet temperatures and heat transfer rates. Furthermore, it is demonstrated that simple dimensionless groups can correlate—with a mean absolute error (MAE) of 0.0332—the optimal operating pressures of up to 122 different fluids. In addition, it is shown that the correlation is even stronger closer to the critical point and for separate classes of fluids, where MAE can be as low as 0.0103 for triatomic substances.     

Identifying optimal cleaning cycles for heat exchangers subject to fouling and ageing

Fouling of heat exchangers causes reduced heat transfer and other penalties. Regular cleaning represents one widely used fouling mitigation strategy, where the schedule of cleaning actions can be optimised to minimise the cost of fouling. This paper investigates, for the first time, the situation where there are two cleaning methods available so that the mode of cleaning has to be selected as well as the cleaning interval. Ageing is assumed to convert the initial deposit, labelled ‘gel’, into a harder and more conductive form, labelled ‘coke’, which cannot be removed by one of the cleaning methods. The second method can remove both the gel layer and the coke layer, but costs more and requires the unit to be off-line longer for cleaning. Experimental data demonstrating the effects of ageing are presented. The industrial application is the comparison of cleaning-in-place methods with off-line mechanical cleaning. A process model is constructed for an isolated counter-current heat exchanger subject to fouling, where ageing is described by a simple two-layer model. Solutions generated by an NLP-based approach prove to be superior to a simpler heuristic. A series of case studies demonstrate that combinations of chemical and mechanical cleaning can be superior to mechanical cleaning alone for certain combinations of parameters.     

Constructal multi-scale design of compact micro-tube heat sinks and heat exchangers

A constructal multi-scale design approach is examined for micro-tube heat sinks and heat exchangers. Heat transfer per unit volume is increased by considering the use of additional micro-tubes placed in the intersticial regions of a circular tube array. Three constructs are considered in the proposed analysis. As the system complexity increases, the heat transfer rate increases, and exceeds the theoretical value for a volume of similar size, composed of parallel plates. Approximate solutions for the diameter of the principal construct are obtained for each case using Bejan's intersection of asymptotes method. Exact analytical methods are applied to determine the relative increase in heat dissipation per unit volume as compared with systems containing parallel plates.     

Predictor-corrector algorithm for solving quasi-separated-flow and transient distributed-parameter model for heat exchangers

The successive sub〈stitution (SS) method is a suitable approach to solving the transient distributed-parameter model for heat exchangers. However, this method must be enhanced because its convergence heavily depends on the iterative initial pressure. When the iterative initial pressure is improperly assigned, the calculated flow rates become negative values, causing the state parameters to exhibit negative values as well. Therefore, a predictor-corrector algorithm (PCA) is proposed to improve the convergence of the SS method. A predictor is developed to determine an appropriate iterative initial pressure. Total fluid mass is adopted as the convergence criterion of pressure iteration instead of outlet flow rate as is done in the SS method. Convergence analysis and case study of the PCA and SS method are conducted, which show that the PCA has better convergence than the SS method under the same working conditions.