Experimental Studies on Thermal Performance and Flow Resistance of Heat Exchangers with Helical Baffles

In this study, the shell-side heat transfer performance and flow resistance of the shell-and-tube heat exchangers with third-symmetrical, quarter-symmetrical, quarter-unsymmetrical helical baffles and segmental baffles were experimentally obtained. Except for the baffles, these heat exchangers had the same geometrical configuration and number of tubes. Cold and hot water were used as working fluids in the shell and the tube side, respectively. The experiments were done with the cold water volumetric flow rate ranging between 3 and 7 m³/h and the hot water volumetric flow rate constant at 5.5 m³/h. The results show that the heat exchanger with segmental baffles has higher shell-side heat transfer performance and flow resistance than those with helical baffles. Among the three helical baffles used, the third-symmetrical helical baffle offers the highest shell-side heat transfer performance and flow resistance. The quarter-unsymmetrical helical baffle offers the lowest shell-side flow resistance. Its performance of shell-side heat transfer is also the lowest one but close to that of the quarter-symmetrical helical baffle, so the quarter-unsymmetrical helical baffle provides the best conversion efficiency in all heat exchangers mentioned. Compared with the segmental baffle, the shell-side Nusselt numbers that the third-symmetrical, the quarter-symmetrical, and the quarter-unsymmetrical helical baffle offer decrease on the average by about 26%, 37%, and 38%, respectively, and the corresponding shell-side Euler numbers they provide decrease on the average by about 33%, 49%, and 55%, respectively. Thus, the relative shell-side conversion efficiencies increase by about 9%, 25%, and 39% on the average, respectively.     

Numerical Investigation of the Effect of Baffle Orientation on Heat Transfer and Pressure Drop in a Shell and Tube Heat Exchanger With Leakage Flows

The commercial CFD code FLUENT is used to investigate the effect of baffle orientation and of viscosity of the working fluid on the heat transfer and pressure drop in a shell-and-tube heat exchanger in the domain of turbulent flow. The shell-and-tube heat exchanger considered follows the TEMA standards and consists of 76 plane tubes with fixed outside diameter, which are arranged in a triangular pitch. Two baffle orientations as well as leakage flows are considered. In order to determine the effect of viscosity on heat transfer and pressure drop, simulations are performed for the working fluids air, water, and engine oil with Prandtl numbers in the range of 0.7 to 206. For each baffle orientation and working fluid, simulations are performed using different flow velocities at the inlet nozzle. Heat transfer and pressure drop are reported in order to describe the performance of vertically and horizontally baffled shell-and-tube heat exchangers. The heat transfer coefficient is described as modified shell-side Nusselt number, which is defined similar to the VDI method.     

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°.     

Computational Fluid Dynamics Analysis of a Heat Exchanger Provided with Helical Baffles

Abstract

In the article, a three-dimensional numerical solution of two real shell-and-tube heat exchangers, with different types of baffles, segmental, and pseudohelical, is presented, through the use of commercial codes, in order to evaluate the influence of the baffles type on heat exchanger performance. The parameters to be evaluated, which influence the efficiency of the thermal exchange and the maintenance and pumping costs, are the pressure drops, the heat transfer coefficient, and the fouling resistance. The fluid dynamic study of the shell-and-tube heat exchanger is conducted under stationary flow conditions. In the article, furthermore, the results of the thermohydraulic analysis, performed under stationary flow conditions, more "helical baffles" exchangers, with different baffles helix angle, are presented. Exchangers with pseudohelical baffles inclined by 7°, 20°, 30°, 40°, 45°, and 50° are analyzed. The simulations are carried out considering a real fluid, approximately incompressible, under laminar flow conditions. Finally, to verify the correctness of the results, they are compared with correlations in the literature.     

Modeling and Prediction of Shell-Side Fouling in Shell-and-Tube Heat Exchangers

Fouling is a challenging, longstanding, and costly problem affecting a variety of heat transfer applications in industry. Mathematical models that aim at capturing and predicting fouling trends in shell-and-tube heat exchangers typically focus on fouling inside the tubes, while fouling on the shell side has generally been neglected. However, fouling deposition on the shell side may be significant in practice, impairing heat transfer, increasing pressure drops, and modifying flow paths. In this paper, a new model formulation is presented that enables capturing fouling on the shell side of shell-and-tube heat exchangers including the effect of occlusion of the shell-side clearances. It is demonstrated by means of an industrial case study in a crude oil refinery application. The model, implemented in an advanced simulation environment, is fitted to plant data. It is shown to capture the complex thermal and hydraulic interactions between fouling growth inside and outside of the tubes, the effect of fouling on the occlusion of the shell-side construction clearances, and to unveil the impact on shell-side flow patterns, heat transfer coefficient, pressure drops, and overall exchanger performance. The model is shown to predict the fouling behavior in a seamless dynamic simulation of both deposition and cleaning operations, with excellent results.     

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.     

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.     

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.     

连续型螺旋折流板换热器结构及性能研究

连续型螺旋折流板换热器一直受限于加工工艺而未能得到广泛应用,本文提出采用加装中芯管的方法,实现了连续型折流板的加工,并给出了连续型折流板螺旋升角和螺旋包络面的计算方法。利用Fluent软件,与现今应用较广泛的1／4椭圆形折流板换热器的流动和换热特性进行模拟比较。结果表明,连续型折流板换热器换热能力提高了近一倍,综合性能系数也提高了近30％,虽然1／4椭圆折流板压力降较小,但其折流板的漏流,也严重降低了传热能力。为在工程中推广应用连续型螺旋折流板换热器,本文提供了理论依据和技术支撑。     

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.     

Configuration optimization of shell-and-tube heat exchangers with helical baffles using multi-objective genetic algorithm based on fluid-structure interaction

The configuration parameters of helical angle and overlapped degree of shell-and-tube heat exchangers with helical baffles have been discussed for the thermal-structural comprehensive performance. Based on fluid-structure interaction theory, a method on configuration optimization of shell-and-tube heat exchangers with helical baffles is introduced using second-order polynomial regression response surface combined with Multi-objective Genetic Algorithm. The results show that the heat transfer coefficient per unit pressure drop of shell-and-tube heat exchangers with helical baffles increases firstly and then decreases with the increase of helical angle, and decreases with the increase of overlapped degree under certain shell-inlet velocity. And the performance of flow and heat transfer is more sensitive to helical angle compared with overlapped degree. The maximum shear stress increases with helical angle, but it is almost unaffected by overlapped degree for mechanical properties of helical baffles. The objectives of optimization are the heat transfer coefficient per unit pressure drop maximizing and maximum shear stress minimizing with scope of allowable stress, and three optimal structures are obtained. The optimal results indicate that the heat transfer coefficient per unit pressure drop increases averagely by 14.1%, the maximum shear stress decreases averagely by 4.1%, which provides theoretical guidance for industrial design of shell-and-tube heat exchangers with helical baffles.     

Modeling for Shell-Side Heat Transfer Coefficient and Pressure Drop of Helical Baffle Heat Exchangers

This study has suitably modified the existing heat transfer and pressure drop correction factors of the modified Bell–Delaware method used for heat exchangers with segmental baffles, taking into consideration the helical baffle geometry. These correction factors are presented in parametric formulas based on the Taborek presented procedure for segmental baffles. These formulas are functions of the geometrical and physical parameters of discontinuous helical baffles. In addition, the parametric formulas are presented graphically based on the Stehlik method. The correction design method proposed by Stehlik for the helical baffle is presented in detail and a theoretical model for shell-side heat transfer and pressure drop is developed. In general, the results show that the present model matches more closely with the graphically proposed correction factors of Stehlik. In order to calculate the shell-side heat transfer coefficient and pressure drop using the present method, a computational code has been developed by the authors. In addition, in order to examine the validity, the results of the code for a case study are compared with the results obtained from EXPRESS software and experimental formulas presented by Zhang. The results of comparison show that the proposed method is accurate and can be used by designers confidently.     

Heat transfer and entropy analysis of three different types of heat exchangers operated with nanofluids

The development of nanotechnology has witnessed an emergence of new generation of heat transfer fluids known as nanofluids. Nanofluids are used as coolants which provide excellent thermal performance in shell and tube heat exchangers. However, the viscosity of these fluids increases with the addition of nanoparticles. Furthermore, the performance of these heat exchangers is influenced by the arrangement of baffles. Thus, in this paper, the study focuses on the heat transfer and entropy analysis of segmental, 25° and 50 helical baffles shell and tube heat exchangers. Heat transfer rate of the 25 helical baffles heat exchanger found to be the highest among the three heat exchangers studied in this research. Study indicates that shell and tube heat exchanger with 50° helical baffles exhibits lowest entropy generation among three different heat exchangers.     

Design optimization of shell-and-tube heat exchanger using particle swarm optimization technique

Shell-and-tube heat exchangers (STHEs) are the most common type of heat exchangers that find widespread use in numerous industrial applications. Cost minimization of these heat exchangers is a key objective for both designer and users. Heat exchanger design involves complex processes, including selection of geometrical parameters and operating parameters. The traditional design approach for shell-and-tube heat exchangers involves rating a large number of different exchanger geometries to identify those that satisfy a given heat duty and a set of geometric and operational constraints. However, this approach is time-consuming and does not assure an optimal solution. Hence the present study explores the use of a non-traditional optimization technique; called particle swarm optimization (PSO), for design optimization of shell-and-tube heat exchangers from economic view point. Minimization of total annual cost is considered as an objective function. Three design variables such as shell internal diameter, outer tube diameter and baffle spacing are considered for optimization. Two tube layouts viz. triangle and square are also considered for optimization. Four different case studies are presented to demonstrate the effectiveness and accuracy of the proposed algorithm. The results of optimization using PSO technique are compared with those obtained by using genetic algorithm (GA).     

Numerical simulation on the performance of trisection helical baffle heat exchangers with small baffle incline angles

ABSTRACT

Numerical simulation was conducted on oil–water heat transfer in five circumferential overlap trisection helical baffle shell–and–tube heat exchangers (cothSTHXs) with 16 tubes and incline angles of 12°, 16°, 20°, 24°, and 28° and a segmental baffle heat exchanger of the identical tube layout for comparison under laminar flow calculation conditions. The local images represent shell-side flow patterns, and heat transfer properties are presented showing the detailed “secondary vortex flow” and “shortcut leakage flow” patterns to explain the different characteristics of the six schemes. The simulation curves of the heat transfer coefficient and pressure drop are compared with those of the experimental ones, with satisfactory agreement. The average values of the shell-side heat transfer coefficient and the comprehensive index h_o/Δp_o of the 12° helical scheme are respectively 47% and 51% higher than those of the segmental baffle scheme with about the same pressure drop.     

The Effect of a Number of Baffles on the Performance of Shell-and-Tube Heat Exchangers

The number of baffles has an impact on the thermal-hydraulic performance of a shell-and-tube heat exchanger (STHX), thus a model was developed using Engineering Equations Solver software to solve the governing equations. The program uses Kern, Bell-Delaware, and flow-stream analysis (Wills Johnston) methods to predict both the heat-transfer coefficient and pressure drop on the shell side of an STHX. It was found that Bell-Delaware method is the most accurate method when compared with the experimental results. The effect of a number of baffles, mass flow rate, tube layout, fluid properties and baffle cut were investigated. The analysis revealed that an increase in the number of baffles increases both the heat-transfer coefficient and pressure drop on the shell-side. Increasing the mass flow rate, the heat transfer coefficient increases; however, the pressure drop increases at a higher rate. For a large number of baffles, the pressure drop decreases with an increase in the baffle cut. It also shows that the heat transfer coefficient increases at a higher rate with the square tube layout, whereas the rotated square and triangular layouts have approximately the same behavior.     

Effect of helical baffles and water-based Al2O3, CuO,and SiO2 nanoparticles in the enhancement of thermal performance for shell and tube heat exchanger

In this study, Shell and tube heat exchanger (STHX) with 22% cut segmental baffles and helical baffles with 20°, 30°, 40° inclination angles are considered for three-dimensional CFD analysis using the ANSYS FLUENT tool to investigate the performance of STHX. OHTC and comprehensive performance index are higher for 40° helical baffles when compared to segmental baffle and 20°, 30° helical baffle heat exchangers with water as working fluid. Hence, further investigations are carried out for 40° helical baffle heat exchangers. Numerical investigations are extended with nanofluids (Al₂O₃, CuO, and SiO₂) at 1%, 3%, and 5% volume concentrations for each nanofluid. Under the same mass flow rates, 40° helical baffles with Al₂O₃ nanofluid as working fluid provided better heat transfer rates when compared to the other two nanofluids and base fluid. Also, the authors noticed that the 5% volume (vol) concentration nanofluids provided better heat transfer enhancements when compared to 1%, 3% volume concentrations, and base fluid. Enhancements (10.33%–8.24%) from lower to the higher mass flow rate in 40° HB with Al₂O₃ nanofluid at 5% volume concentration are observed when compared to water as base fluid.     

Design of shell-and-tube heat exchangers when the fouling depends on local temperature and velocity

Shell-and-tube heat exchangers are normally designed on the basis of a uniform and constant fouling resistance that is specified in advance by the exchanger user. The design process is then one of determining the best exchanger that will achieve the thermal duty within the specified pressure drop constraints. It has been shown in previous papers [Designing shell-and-tube heat exchangers with velocity-dependant fouling, 34th US National Heat Transfer Conference, 20–22 August 2000, Pittsburg, PA; Designing shell-and-tube heat exchangers with velocity-dependant fouling, 2nd Int. Conf. on Petroleum and Gas Phase Behavior and Fouling, 27–31 August 2000, Copenhagen] that this approach can be extended to the design of exchangers where the design fouling resistance depends on velocity. The current paper briefly reviews the main findings of the previous papers and goes on to treat the case where the fouling depends also on the local temperatures. The Ebert–Panchal [Analysis of Exxon crude-oil, slip-stream coking data, Engineering Foundation Conference on Fouling Mitigation of Heat Exchangers, 18–23 June 1995, California] form of fouling rate equation is used to evaluate this fouling dependence. When allowing for temperature effects, it becomes difficult to divorce the design from the way the exchanger will be operated up to the point when the design fouling is achieved. However, rational ways of separating the design from the operation are proposed.     

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.     

The RODbaffle Heat Exchanger

The RODbaffle exchanger offers a solution to the vexing problem of tube failures in shell-and-tube exchangers resulting from tube vibration. Additional benefits are good heat transfer rates, low pressure drop, and lower fouling rates. The ratio of heat transfer rate to pressure drop can be more than double that of the conventional plate-type baffle in a comparable application.