Experimental Performance Comparison of Shell-Side Heat Transfer for Shell-and-Tube Heat Exchangers with Different Helical Baffles

In this study, experiments were carried out to study the effects of baffle overlap proportion on the shell-side flow resistance and heat transfer performance of the shell-and-tube heat exchangers with helical baffles (STHXsHB). Three STHXsHB with an overlap proportion of 10% and helix angles of 20°, 30°, and 40° were tested. Comparisons were made of the experimental data of the STHXsHB with the same helix angles but 50% overlap proportion. The theory of entransy dissipation was employed to evaluate the irreversible loss in STHXsHB with different helix angles and overlap proportions. The results indicated that both the baffle overlap proportion and the helix angle have a great effect on the shell-side flow resistance and heat transfer. For a given helix angle, the comprehensive performance of STHXsHB with small overlap proportion is always better than that with large overlap proportion at the same mass flow rate or Reynolds number on the shell side. However, for the same heat transfer area, working conditions, and helix angle, the STHXsHB with large baffle overlap proportion has less irreversibility in the heat exchange process, according to the theory of entransy dissipation. In addition, experimental results demonstrated that the configuration of the relatively large helix angle and baffle overlap proportion is the preferred alternative in STHXsHB.     

Troubleshooting Shell-and-Tube Heat Exchangers

A newly developed methodology for the design of multistream plate-fin heat exchangers in the optimization of heat exchanger networks is described in detail. The designed heat exchanger consists of several block sections with intermediate entry and exit points along its length, and these sections are determined by the composite curves in the Pinch technology. The requirements of heat transfer and pressure drop are fulfilled through proper surface selection. The methodology was applied to an industrial case study, and the detailed design parameters are given. The example confirms the validity of the suggested methodology.     

Synthesis of Cost-Optimal Shell-and-Tube Heat Exchangers

Abstract

Synthesis of cost-optimal shell-and-tube heat exchangers is a difficult task since it involves a large number of parameters. An attempt is made in this article to simplify the process of choosing the parameter values that will minimize the cost of any heat exchanger satisfying a given heat duty and a particular set of constraints. The simplification is based on decoupling of the geometric and the thermal aspects of the problem. The concept of curves for cost-optimal design is introduced and is shown to simplify the synthesis process for shell-and-tube heat exchangers.     

Computer Techniques to Analyze Shell-and-Tube Heat Exchangers

This paper outlines computer analyses to predict thermal-hydraulics, flow-induced vibration, and fretting-wear damage in shell-and-tube heat exchangers. The analytical techniques are briefly described and the results arc illustrated by example. It is concluded that computer techniques can do much to improve the reliability and performance of heat exchangers.     

Tube Vibration and Flow Distribution in Shell-and-Tube Heat Exchangers

Avoiding flow-induced vibration damage is a major concern to the designers and operators of shell-and-tube heat exchangers. This paper discusses the characteristics of tube vibration as determined from a research program featuring tests of an industrial-size exchanger. The state of the art in understanding and predicting tube vibration and shell-side flow distribution is briefly reviewed. Finally, research needs are identified and discussed.     

Heat Transfer Enhancement in Shell-and-Tube Heat Exchangers Using Porous Media

A numerical simulation has been carried out to investigate the heat transfer enhancement in a shell-and-tube heat exchanger using a porous medium inside its shell and tubes, separately. A three-dimensional geometry with k-? turbulent model is used to predict the heat transfer and pressure drop characteristics of the flow. The effects of porosity and dimensions of these media on the heat exchanger's thermal performance and pressure drop are analyzed. Inside the shell, the entire tube bundle is wrapped by the porous medium, whereas inside the tubes the porous media are located in two different ways: (1) at the center of the tubes, and (2) attached to the inner wall of the tubes. The results showed that this method can improve the heat transfer at the expense of higher pressure drop. Evaluating the method showed that using porous media inside the shell, with particular dimension and porosity can increase the heat transfer rate better than pressure drop. Using this method inside the tubes leads to two diverse results: In the first configuration, pressure loss prevails over the heat transfer augmentation and it causes energy loss, whereas in the second configuration a great performance enhancement is observed.     

Exergetic Optimization of Shell-and-Tube Heat Exchangers Using NSGA-II

In this article, a multi-objective exergy-based optimization through a genetic algorithm method is conducted to study and improve the performance of shell-and-tube type heat recovery heat exchangers, by considering two key parameters, such as exergy efficiency and cost. The total cost includes the capital investment for equipment (heat exchanger surface area) and operating cost (energy expenditures related to pumping). The design parameters of this study are chosen as tube arrangement, tube diameters, tube pitch ratio, tube length, tube number, baffle spacing ratio, and baffle cut ratio. In addition, for optimal design of a shell-and-tube heat exchanger, the method and Bell–Delaware procedure are followed to estimate its pressure drop and heat transfer coefficient. A fast and elitist nondominated sorting genetic algorithm (NSGA-II) with continuous and discrete variables is applied to obtain maximum exergy efficiency with minimum exergy destruction and minimum total cost as two objective functions. The results of optimal designs are a set of multiple optimum solutions, called “Pareto optimal solutions.” The results clearly reveal the conflict between two objective functions and also any geometrical changes that increase the exergy efficiency (decrease the exergy destruction) lead to an increase in the total cost and vice versa. In addition, optimization of the heat exchanger based on exergy analysis revealed that irreversibility like pressure drop and high temperature differences between the hot and cold stream play a key role in exergy destruction. Therefore, increasing the component efficiency of a shell-and-tube heat exchanger increases the cost of heat exchanger. Finally, the sensitivity analysis of change in optimum exergy efficiency, exergy destruction, and total cost with change in decision variables of the shell-and-tube heat exchanger is also performed.     

Thermal-Hydraulic Characteristics of Helical Baffle Shell-and-Tube Heat Exchangers

Abstract

Shell-and-tube heat exchangers are frequently used in several industrial applications. A model was developed using engineering equations solver software to predict the performance of various baffle configurations of shell-and-tube heat exchangers. The model is based on the Bell-Delaware method for the segmental baffle, while mathematical correlations for the helical baffle are provided for design and analysis purpose. The accuracy of the present model is validated against the experimental data available in the literature. The results showed that helical baffles offer much higher performance compared to the segmental baffled heat exchanger. It was found that the performance of the helical baffle increases with increasing baffle angle until it reaches an optimum value; it then starts to decrease at an angle of 42°.     

A Comparative Assessment of RODbaffle Shell-and-Tube Heat Exchangers

The shell-and-tube heat exchanger (SBE), with its tubes held in plate baffles to produce cross flow of the shell-side fluid, has recently been modified to produce a RODbaffle heat exchanger (RBE) free from tube failure due to vibration. The results showed slightly enhanced heat transfer coefficients with significant reductions in pressure loss, leading to reduced cost of exchangers and in some instances smaller exchangers.     

Flow-Induced Vibration in Shell-and-Tube Heat Exchangers with Double-Segmental Baffles

One of the techniques used by designers of shell-and-tube heat exchangers when they encounter a potential flow-induced vibration problem is to shift from a tube bundle with segmental baffles to one with double-segmental baffles. This results in a split of the flow into either half of the shell with lower velocities and makes it possible to reduce the unsupported tube span length while keeping below a given allowable pressure drop. Tests were performed as a part of a systematic study of water flow-induced vibration in industrial-size heat exchangers. Results for nine different double-segmental baffled bundle configurations are presented. Comparison of the results with those for similar segmental baffled bundles shows that higher flows can be tolerated without developing damaging flow-induced vibration.     

Review of Improvements on Shell-and-Tube Heat Exchangers With Helical Baffles

Helical baffles are employed increasingly in shell-and-tube heat exchangers (helixchangers) for their significant advantages in reducing pressure drop, vibration, and fouling while maintaining a higher heat transfer performance. In order to make good use of helical baffles, serial improvements have been made by many researchers. In this paper, a general review is provided of developments and improvements on helixchangers, which includes the discontinuous helical baffles, continuous or combined helical baffles, and the combined multiple shell-pass helixchangers. Extensive results from experiments and numerical simulations indicate that these helixchangers have better flow and heat transfer performance than the conventional segmental baffled heat exchangers. Based on these new improvements, the conventional heat exchangers with segmental baffles might be replaced by helixchangers in industrial applications to save energy, reduce cost, and prolong the service life and operation time.     

Temperature Distribution and Heat Exchange in Multipass Shell-and-Tube Exchangers with Baffles

A model predicting the temperature distribution and the mean temperature difference in multipass shell-and-tube heat exchangers with baffles is presented. The exchanger is treated as a cascade of cells with mixing taking place in each fluid. From the computed results, design rules are deduced to enable the choice of the construction that leads to the highest efficiency.

The effect of leakage currents on exchanger effectiveness is ignored in this analysis and is treated separately in another paper.     

Influence of Scaling on the Performance of Shell-and-Tube Heat Exchangers

Fouling in shell-and-tube heat exchangers was modeled by combining Hasson's ionic diffusion model for scaling from CaCO₃ solutions with a model for predicting the temperature distribution developed by Gaddis and Schlünder. Using the computed results, clean heat exchanger design rules were tested for fouling conditions. The effects of fouling on the efficiency of heat exchanger configurations were determined.     

改进粒子群算法在管壳式换热器优化设计中的应用

以管壳式换热器每年的总费用作为目标函数,采用含随机扰动算子的改进粒子群算法(IPOS)对其进行了优化.在优化设计模型中,采用Bell-Delaware法描述壳侧流体,优化变量选择管程数、换热管内径和外径及间距、管布置方式、封头类型、流体分配方式、密封条数、壳程压降和管程压降.对采用IPOS算法得到的优化结果与相关文献的结果进行了比较.结果表明:IPOS算法具有全局收敛、计算精度高、稳定性好的特点,并能获得约束条件下管壳式换热器的最优设计方案.     

Particulate Fouling and Challenges of Metal Foam Heat Exchangers

ABSTRACT

In recent years, open-cell metal foam has gained attention for utilization for exhaust gas recirculation coolers due to its large surface area and porous structure. Theoretically, the porous foam structure would have better transfer heat through conduction and convection processes. However, the exhaust gases that enter the cooler would carry particulate matter, which may deposit within the foam structure. The existing fouling studies cannot explain the underlying mechanisms of particulate deposition thoroughly within the foam structure. This study reviews the particulate fouling of heat exchangers, particularly in the exhaust gas recirculation system. Some past approaches to investigate fouling, particle transport, and deposition in the metal foam heat exchangers for many different applications are also included. In addition, this study also includes the challenges that lie ahead in implementing the metal foam heat exchangers in the industries.     

Helical Baffles in Shell-and-Tube Heat Exchangers,Part I: Experimental Verification

Performance of heat exchangers with helical baffles, or helixchangers, is discussed using the results of tests conducted on units with uarious baffle geometries. An optimum helix angle is identified at which the conversion efficiency for converting pressure drop to heat transfer on the shell side of helixchangers is maximized. Designs for standard industry applications are optimized using the analysis of test results.     

板式换热器颗粒污垢特性的实验研究

以纳米氧化镁颗粒溶液为实验工质,进行了板式换热器颗粒污垢特性的实验研究,分析了颗粒质量浓度、颗粒粒径、流速和低温介质温度对颗粒污垢热阻的影响.结果表明:板式换热器颗粒污垢无明显诱导期存在,结垢速率和污垢热阻渐进值均随颗粒质量浓度的增大而增大,且增大幅度逐渐减小;颗粒粒径对污垢热阻的影响较明显,在相同质量浓度下,颗粒粒径越小,结垢速率越快,且污垢热阻越大;流速对污垢热阻的影响较为复杂,高流速下的结垢速率略大于低流速下,且高流速下达到稳定时的污垢热阻渐进值小于低流速下;低温介质温度对颗粒污垢热阻的影响不明显.     

污水换热器污垢生长特性试验研究

污水换热器污垢是影响污水冷热源应用的主要因素.了解污垢的形成规律是污水换热器应用与研究的基本要求.基于工程现场实验,通过热阻法测定污水换热器管程内污垢的热阻变化模型Rf(θ)=8×10-4[1-exP(-θ/188)].提出了污垢形成过程有效热阻与有效总传热系数的概念.并通过热阻模型提出了渐进型污垢形成过程的压降模型△(△p)=A-Bexp[-t/t0).为进一步的研究与应用提供了理论基础.     

Shell-and-Tube Heat Exchanger Geometry Modification: An Efficient Way to Mitigate Fouling

Abstract

Crude oil fouling of a shell-and-tube heat exchanger sized according to TEMA standard is compared to a No-Foul design under industrial operating conditions. For similar operating conditions, TEMA and No-Foul heat exchangers have the same behavior regarding fouling. Since the No-Foul one has less tubes by design for the same heat duty, shear stress is increased. Consequently, the No-Foul heat exchanger is less prone to fouling at the same throughput. Impact of tube bundle geometry is then investigated. Helically finned tubes are compared to plain tubes in the No-Foul heat exchanger. Under similar operating conditions, fouling rates measured are up to an order of magnitude lower than plain tubes (respectively 10^?11 and 10^?10 m² K/J). However, pressure drop across the tube-side in both No-Foul plain and finned setup are increased in comparison to the TEMA heat-exchanger.