Multi-objective optimization of shell and tube heat exchangers

The effectiveness and cost are two important parameters in heat exchanger design. The total cost includes the capital investment for equipment (heat exchanger surface area) and operating cost (for energy expenditures related to pumping). Tube arrangement, tube diameter, tube pitch ratio, tube length, tube number, baffle spacing ratio as well as baffle cut ratio were considered as seven design parameters. For optimal design of a shell and tube heat exchanger, it was first thermally modeled using ε–NTU method while Bell–Delaware procedure was applied to estimate its shell side heat transfer coefficient and pressure drop. Fast and elitist non-dominated sorting genetic algorithm (NSGA-II) with continuous and discrete variables were applied to obtain the maximum effectiveness (heat recovery) and the minimum total cost as two objective functions. The results of optimal designs were a set of multiple optimum solutions, called ‘Pareto optimal solutions’. The sensitivity analysis of change in optimum effectiveness and total cost with change in design parameters of the shell and tube heat exchanger was also performed and the results are reported.     

Heat transfer and pressure drop performance of twisted oval tube heat exchanger

Twisted oval tube heat exchanger is a type of heat exchanger that aims at improving the heat transfer coefficient of the tube side and also decreasing the pressure drop of the shell side. In the present work, tube side and shell side heat transfer and pressure drop performances of a twisted oval tube heat exchanger has been experimentally studied. The tube side study shows that the tube side heat transfer coefficient and pressure drop in a twisted oval tube are both higher than in a smooth round tube. The shell side study shows that the lower the modified Froude number Fr_M, the higher the shell side heat transfer coefficient and pressure drop. In order to comparatively analyze its shell side performance of the heat exchanger, a rod baffle heat exchanger with similar size of the twisted oval tube heat exchanger is designed and its performance is calculated with Gentry's method. The comparative study shows that the heat transfer coefficient of the twisted oval tube heat exchanger is higher and the pressure drop is lower than the rod baffle heat exchanger. In order to evaluate the overall performance of the twisted oval tube heat exchanger, a performance evaluation criterion considering both the tube side and shell side performance of a heat exchanger is proposed and applied. The analyze of the overall performance of the twisted oval tube shows that the twisted oval tube heat exchangers works more effective at low tube side flow rate and high shell side flow rate.     

Economic optimization of shell and tube heat exchanger based on constructal theory

In this paper, the new approach of constructal theory has been employed to design shell and tube heat exchangers. Constructal theory is a new method for optimal design in engineering applications. The purpose of this paper is optimization of shell and tube heat exchangers by reduction of total cost of the exchanger using the constructal theory. The total cost of the heat exchanger is the sum of operational costs and capital costs. The overall heat transfer coefficient of the shell and tube heat exchanger is increased by the use of constructal theory. Therefore, the capital cost required for making the heat transfer surface is reduced. Moreover, the operational energy costs involving pumping in order to overcome frictional pressure loss are minimized in this method. Genetic algorithm is used to optimize the objective function which is a mathematical model for the cost of the shell and tube heat exchanger and is based on constructal theory. The results of this research represent more than 50% reduction in costs of the heat exchanger.     

Optimum Design of Cross-Flow Shell and Tube Heat Exchangers with Low Fin Tubes

This paper presents a simple, efficient, robust, optimum design methodology for the design of a high heat transfer and low pressure drop cross-flow shell and tube heat exchanger with integral low fin tubes. This type of heat exchanger has the potential for application in the design of coolers in hypersonic wind tunnels to cool the air that emerges from the diffuser section of the wind tunnel. The methodology described here allows for the design and optimization of any type of heat exchanger that has constraints on pressure drop, as well as the design of an exchanger for very low pressure drop on the shell side fluid.     

基于前馈-自抗扰算法的换热器动态试验温度控制研究

为了使换热器试验测控系统满足动态换热试验中对温度控制的要求,分析了试验系统中被控温度对象动态模型,设计了前馈-自抗扰温度控制算法。动态换热试验对象为管壳式换热器,试验过程管程流体为强迫对流换热,壳程流体自然对流换热,同时管程流体循环利用,要求控制管程入口温度稳定。控制算法全面利用模型信息,将壳程温度作为管程温度控制中的干扰,为其设计前馈补偿,同时设计自抗扰控制算法,处理模型偏差问题。利用AMESim软件搭建系统模型,在Simulink中设计控制算法,进行了AMESim/Simulink联合仿真,通过对比多种控制算法,验证了在壳程温度变化干扰的换热过程中,使用前馈-自抗扰控制算法能够使管程入口温度波动更小,更快达到稳定。     

Comparative study of mechanical and chemical methods for surface cleaning of a marine shell‐and‐tube heat exchanger

In this article, experimental analysis is done on shell‐and‐tube heat exchanger of a marine vessel for removal of fouling using optimum surface‐cleaning techniques. The main objective is to compare the performance of the heat exchanger before and after maintenance. Two identical deteriorated systems of heat exchangers are taken and real‐time analysis is conducted. The log data are taken before and after undergoing maintenance for the two systems. Two different cleaning techniques are used, namely, chemical cleaning and mechanical cleaning. Detailed calculations are made for the shell‐and‐tube heat exchanger. From the obtained data, comparisons are made for different parameters on the tube side such as friction factor, heat transfer coefficient and pressure drop, as well as total heat transfer rate on the shell side. From the analysis and comparison, it was found that greater heat transfer takes place for the tubes cleaned using the chemical cleaning method than for tubes cleaned by the mechanical cleaning method. Pressure drop is found to be less for chemical cleaning method than mechanical cleaning method. This indicates that the fouling effect is reduced for tubes cleaned by the chemical cleaning method, and furthermore these tubes remain corrosion‐resistant for longer periods of time.     

Analysis of a bayonet tube heat exchanger

This paper details the design, construction and testing of a bayonet tube heat exchanger for use in the process industry and potentially as part of an externally fired combined cycle. Detailed analysis of the system has been undertaken, in particular on the tube side. The data is reported in terms of temperature, pressure, heat gain and heat exchanger effectiveness, over a range of Reynolds numbers and shell side mixture ratios. Much of the heat gained by the tubes is in the annular flow of the bayonet tube. Overall the effectiveness of this system could exceed 70%.     

Twisted bundle heat exchangers performance evaluation by CFD (CJ12/5054)

Shell and tube heat exchanger with single twisted tube bundle in five different twist angles, are studied using computational fluid dynamics (CFD) and compared to the conventional shell and tube heat exchanger with single segmental baffles. Effect of shell-side nozzles configurations on heat exchanger performance is studied as well. Heat transfer rate and pressure drop are the main issues investigated in the paper. The results show that, for the same shell-side flow rate, the heat transfer coefficient of heat exchanger with twisted tube bundle is lower than that of the heat exchanger with segmental baffles while shell-side pressure drop of the former is even much lower than that of the latter. The comparison of heat transfer rate per unit pressure drop versus shell-side mass flow rate shows that heat exchanger with twisted tube bundle in both cases of perpendicular and tangential shell-side nozzles, has significant performance advantages over the segmental baffled heat exchanger. Optimum bundle twist angles for such exchangers are found to be 65 and 55° for all shell side flow rates.     

管壳式换热器管板的结构设计

管壳式换热器中的管板是重要的受压元件，其厚度和结构的正确设计，对换热器的安全性和经济性有着非常重要的影响。由于目前可用的标准和有关资料都过于复杂和保守，甚至有些不够合理，所以笔者根据多年的锅炉设计经验，提出应用最大剪应力强度理论，借鉴锅壳锅炉有关受压元件的强度计算方法，从而为换热器管板的结构设计找出一条捷径。     

连续螺旋折流板换热器动态特性的数值预测和分析

应用有限差分法对以水、油为换热工质的连续螺旋折流板换热器的动态特性进行了数值预测,提出了适用于单壳程多管程换热器的顺流、逆流串联的概念,并通过试验数据进行了校核,证明了计算模型的合理性.同时研究了壳侧流体纵向扩散效应、换热器管壁轴向导热性能及其热容等参数对换热器动态特性的影响规律,为壳管式换热器动态特性的相关研究提供了依据.     

Design and economic optimization of shell and tube heat exchangers using Artificial Bee Colony (ABC) algorithm

In this study, a new shell and tube heat exchanger optimization design approach is developed. Artificial Bee Colony (ABC) has been applied to minimize the total cost of the equipment including capital investment and the sum of discounted annual energy expenditures related to pumping of shell and tube heat exchanger by varying various design variables such as tube length, tube outer diameter, pitch size, baffle spacing, etc. Finally, the results are compared to those obtained by literature approaches. The obtained results indicate that Artificial Bee Colony (ABC) algorithm can be successfully applied for optimal design of shell and tube heat exchangers.     

新型高效紧凑式换热器仿真及热力分析

为了提高新型高效紧凑式换热器设计的功能性,并使其满足热力学性能需求,对绕管的结构参数及桥接布管方式进行设计。采用一种新型的变径变线桥接方式,在体积有限的情况下实现密集的管束布置形式;对该新型换热器设计进行全尺寸流域建模及CFD数值模拟;并将三维建模结果与一维程序计算结果对比,进行可靠性验证。计算结果表明：三维计算的各项热力学性能结果与一维计算仅有较小偏差,总传热系数相对误差仅为3.74%,总传热量相对误差仅为1.04%,验证了该三维计算模型具有较好的准确性;结合温度云图证明了换热区域基本集中在绕管段,为简化复杂换热器的计算提供了思路;该新型高效紧凑式换热器设计实现了管侧双股流可独立运行且同层间不存在无效换热区,整体换热平顺进行,壳侧流阻较小,换热能力保持较好;在工况范围内整机换热体积功率达到4.67 MW。     

An investigation of the performance of compact heat exchanger for latent heat recovery from exhaust flue gases

An experimental and theoretical investigation of the utilization of finned tube compact heat exchanger for a heat recovery steam generator (HRSG) to recover both sensible and latent heat is presented in this paper. The heat transfer and pressure drop characteristics of the fin-and-tube heat exchanger are theoretically studied. A correlation of the combined convection–condensation heat transfer is derived by using the heat and mass transfer analogy models. The experimental results have shown that the Colburn factor (j) and the friction factor (f) for humid air, simulating the exhaust of HRSG, are larger than those for dry air. It has been also found that the f factor difference between humid air and dry air decreases as the air side Reynolds number increases and both the f factor and the j factor for humid air increase with the increase of water vapour concentration. A scheme for the design of compact heat exchanger for HRSGs is presented.     

三叶膨胀管换热器壳程强化传热的数值研究

三叶膨胀管是一种新型强化传热管,针对纵向流换热器特点,设计了三种不同管束结构参数的三叶膨胀管自支撑纵向流换热器。应用FLUENT软件及Realizable k-ε湍流模型,对三种不同结构参数的三叶膨胀管换热器壳程强化传热特性展开了数值模拟,并通过与实验数据的对比,验证了计算模型的可靠性。计算了不同壳程介质流速下,三叶膨胀管换热器壳程的换热系数与压降值,并获得了壳程流体流线以及相应的温度场、速度场和二次流分布图。结果发现,在壳程水流速一致的情况下,管束横向间距越大的三叶膨胀管换热器,壳程拥有更高的综合换热性能和更低的压降值,但相应地,换热系数也更低。流场分析显示,壳程流体流线呈现出三维纵向旋流形态,二次流的出现改变了速度场和温度场分布,二次流的强度随着管束横向间距的减小而增大。     

Optimal geometry and flow arrangement for minimizing the cost of shell‐and‐tube condensers

This paper presents a model for estimating the total cost of shell‐and‐tube heat exchangers (HEs) with condensation in tubes or in the shell, as well as a designing strategy for minimizing this cost. The optimization process is based on a genetic algorithm. The global cost includes the energy cost (i.e. pumping power) and the initial purchase cost of the exchanger. The choice of the best exchanger is based on its annualized total cost. Eleven design variables are optimized. Ten are associated with the HE geometry: tube pitch, tube layout patterns, baffle spacing at the center, baffle spacing at the inlet and outlet, baffle cut, tube‐to‐baffle diametrical clearance, shell‐to‐baffle diametrical clearance, tube bundle outer diameter, shell diameter, and tube outer diameter. The last design variable indicates whether the condensing fluid should flow in the tubes or in the shell. Two case studies are presented and the results obtained show that the procedure can rapidly identify the best design for a given heat transfer process between two fluids, one of which is condensing. Copyright © 2008 John Wiley & Sons, Ltd.     

基于E语言的管壳式换热器设计

管壳式换热器的传统设计过程计算工作量大、效率低。文中在Windows环境中,以E语言为平台,开发管壳式换热器的设计软件,包括工艺设计、热力校核和压降校核,界面友好。计算实例结果表明,所设计换热器的结构和压降都在合理范围内。软件可供工程设计或教学使用,也可为后续换热器的优化设计提供参考。     

Compact potential of exhaust heat exchangers for engine waste heat recovery using metal foams

To improve the practicability of the waste heat recovery system for internal combustion engines, the compact potential of exhaust heat exchangers using metal foams is investigated. In the present study, the performance of compact exhaust heat exchangers is compared with that of a conventional shell and tube heat exchanger in a real test bench. Both heat transfer and pressure drop performance are considered when assessing the performance of heat exchangers because these two factors normally show a trade‐off relationship when designing exhaust heat exchangers. Compared with the conventional heat exchanger, the compact heat exchanger can achieve a similar pressure drop, and at the same time the heat transfer is increased by 30%, whereas the volume and the weight are each reduced by 2/3. The performance of compact heat exchangers with six types of Ni metal foams is also investigated under different mass flow rates and thicknesses of the porous layer. Results show that the optimum compact heat exchanger enhances the comprehensive performance 1.9 times compared with original one. This study shows that metal foams have great potential in realizing a compact exhaust heat exchanger for engine waste heat recovery.     

Convective Heat Transfer and Pressure Drop over Elliptical and Flattened Tube

A numerical study on the effect of the effect of elliptical and flattened tube bundle geometry on the convective heat transfer and pressure drop is presented in this article. The analysis has been carried out to evaluate the performance of these bundle geometries in the design of a compact and effective single phase shell and tube heat exchanger. The temperature, velocity, and pressure drop profiles are obtained from solving the mass, momentum, and energy conservation equations. The comparison is made for inline and staggered bundle with different pitch to diameter ratio and inlet velocity for elliptical and flattened tubes. The pitch to diameter ratio is varied from 1.25 to 2.5 for Reynolds number ranging from 200 to 2000 which is in the laminar flow region. The heat transfer coefficient over the staggered and inline tube bundle decrease with an increase in pitch. The same kind of variation is also observed for the pressure drop in the case of both elliptical and flattened tube bundle. The study shows that the transverse pitch with respect to cross flow affects more than the longitudinal pitch.     

Characteristics of Fluid Flow and Heat Transfer in the Shell Side of the Trapezoidal-like Tilted Baffles Heat Exchanger

Periodic whole cross-section computation models are established for segmental baffle heat exchanger, shutter baffle heat exchanger, and trapezoid-like tilted baffle heat exchanger. The reliability of models is verified by comparing the simulated results to the results obtained from the Bell-Delaware method. Due to the orthogonal assembly of the baffles, the shell side fluid shows the twisty flow of trapezoid-like tilted baffle heat exchanger. The essential mechanism on disturbing flow and heat transfer enhancement is revealed by defining the non-dimensional factor η of the shell side fluid flow direction of heat exchanger and the field synergy principle. The results show that at the same Reynolds number, the shell side fluid convection heat transfer coefficient of trapezoid-like tilted baffle heat exchanger is 12.43%-24.33% and 6.71%-11.51% higher than those of segmental baffle heat exchanger and shutter baffle heat exchanger, respectively. The shell side fluid flow velocity field and the pressure gradient field of trapezoid-like tilted baffle heat exchanger and shutter baffle heat exchanger decreases compared with that of segmental baffle heat exchanger, so the shell side fluid flow resistance and pressure drop is increased; the shell side comprehensive performance of trapezoid-like tilted baffle heat exchanger is 5.85%-9.06% higher than that of segmental baffle heat exchanger, and 15.27%-23.28% higher than that of shutter baffle heat exchanger. In this study, a baffle structure with higher efficiency of the energy utilization for the heat exchanger is provided.     

Comparative design study of a diesel exhaust gas heat exchanger for truck applications with conventional and state of the art heat transfer enhancements

The exhaust gas of heavy duty diesel engines can provide an important heat source that may be used in a number of ways to provide additional power and improve overall engine efficiency. The sizing of a heat exchanger that can manage the heat load and still be of reasonable size and weight without excessive pressure drop is of significant importance especially for truck applications. This is the subject of the present work. To approach the problem, a total of five different configurations are investigated and a comparison of conventional and state of the art heat transfer enhancement technologies is included. Two groups of configurations are examined: (a) a classical shell and tube heat exchanger using staggered cross-flow tube bundles with smooth circular tubes, finned tubes and tubes with dimpled surfaces and (b) a cross-flow plate heat exchanger, initially with finned surfaces on the exhaust gas side and then with 10 ppi and 40 ppi metal foam material substituting for the fins. Calculations were performed, using established heat exchanger design methodologies and recently published data from the literature to size the aforementioned configurations. The solutions provided reduce the overall heat exchanger size, with the plate and fin type consisting of plain fins presenting the minimum pressure drop (up to 98% reduction compared to the other configurations), and the 40 ppi metal foam being the most compact in terms of size and weight. Durability of the solutions is another issue which will be examined in a future investigation. However, coupling of the exhaust heat exchanger after a particulate trap appears to be the most promising solution to avoid clogging from soot accumulation.