Numerical investigation on the multi-objective optimization of a shell-and-tube heat exchanger with helical baffles

An improved method combining numerical simulation with multi-objective genetic algorithm (MOGA) was applied to study the flow and heat transfer characteristics of shell-and-tube heat exchanger with helical baffles (STHXsHB). It overcomes the dependence on empirical correlations. The helix angle and overlapped degree of helical baffles were chosen as optimization parameters, while the overall heat transfer coefficient K and pressure drop ΔP of STHXsHB were optimized by MOGA. The results showed that both overall heat transfer coefficient K and pressure drop ΔP varied adversely with the helix angles. The pressure drop ΔP was favorably affected by the overlapped degrees. The overall heat transfer coefficient K did not vary significantly with the overlapped degree. Three optimum configurations were obtained by the MOGA to maximize the overall heat transfer coefficient K and minimize the shell-side pressure drop ΔP. Compared with the original heat exchanger, the overall heat transfer coefficient K increased averagely by 28.3%, while the average pressure drop reduced averagely by 19.37%.     

Computation of thermal properties of CMSP shell and tube heat exchanger using different types of helical baffles

This paper investigates the flow and thermal properties of a combined multiple shell pass (CMSP)-shell and tube heat exchanger (STHE) with the provision of unilateral ladder-type helical baffle (ULHB) and continuous helical baffle (HB) in the outer shell pass of the heat exchanger. Two CMSP-STHEs with ULHB and HB, respectively, are compared with the traditional STHE having segmental baffles (SG-STHE) using the computational fluid dynamics method. The computational outcomes are validated with the empirical correlations of the Kern and Esso method. The Reynolds-averaged Navier–Stokes-based standard k–ω turbulence model accurately predicts the heat transfer (HT) rate and pressure drop. The computed results of HT rate, pressure drop, and logarithmic mean temperature difference corresponding to various mass flow rates (m) for three STHEs are presented. The results show that the overall HT rate of CMSP (ULHB)-STHE and the CMSP (HB)-STHE at the same mass flow rate are nearly 28.3% and 14.8% larger than that of traditional SG-STHE, respectively. Furthermore, the overall area-weighted average pressure drop (ΔP) of CMSP (HB)-STHE is smaller than that of SG-STHE by 26.5% at the same mass flow rate (m) and for CMSP (ULHB)-STHE it is larger by 2% than that of traditional STHE. Based on the above results, it is concluded that the CMSP (ULHB)-STHE is a suitable replacement for the conventional SG-STHEs.     

Experimental determination of shell side heat transfer coefficient and pressure drop for an oil cooler shell-and-tube heat exchanger with three different tube bundles

In this paper, the heat transfer coefficient and pressure drop on the shell side of a shell-and-tube heat exchanger have been experimentally obtained for three different types of copper tubes (smooth, corrugated and with micro-fins). Also, experimental data has been compared with theoretical data available. Correlations have been suggested for both pressure drop and Nusselt number for the three tube types. A shell-and-tube heat exchanger of an oil cooler used in a power transformer has been modeled and built for this experimental work in order to investigate the effect of surface configuration on the shell side heat transfer as well as the pressure drop of the three types of tube bundles. The bundles with the same geometry, configuration, number of baffles and length, but with different external tube surfaces inside the same shell were used for the experiment. Corrugated and micro-fin tubes have shown degradation of performance at a Reynolds number below a certain value (Re < 400). At a higher Reynolds number the performance of the heat exchanger greatly improved for micro-finned tubes.     

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.     

Numerical Analysis of a Small Size Baffled Shell-and-Tube Heat Exchanger Using Different Nano-Fluids

In this study, numerical simulation was used to investigate the effect of adding different nano-particles into the fluid on the performance of a baffled shell-and-tube heat exchanger. A three-dimensional modeling approach was followed to analyze the effect of different nano-fluids, at various volume fractions, as applied in a baffled shell-and-tube heat exchanger. Once finished with validating the grid independency and results, we proceeded to obtain heat transfer rate, pressure drop, outlet shell temperature and exchanger effectiveness for different volume fractions and particle size of different nano-fluids. The studied nano-particles in the present work included Al₂O₃, CuO, Fe₂O₃, Cu, Fe, SiO₂, and Au, with water and ethylene glycol employed as base fluids. With constant mass flow rate for all cases, the results indicated that, the addition of nano-particles had reduced the heat transfer coefficient, pressure drop and the rate of heat transfer through the shell, even though it had increased outlet shell temperature. In other words, considering a constant heat transfer rate, the presence of nano-fluids in a baffled shell-and-tube heat exchanger is likely to be associated with increased outlet shell temperature. Another consequence presents that using ethylene glycol as base fluid leads to higher effectiveness compared with water as a base fluid in exchanger.     

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.     

Enhancement of shell side forced convective heat transfer in the shell tube‐type heat exchanger using thin plate‐type supports

The shell side heat transfer and pressure drop in counterflowing water were experimentally investigated on the basis of the overall heat transfer coefficient. The investigation was intended to identify ways to get higher performance for the cooler in a BWR nuclear power plant. The following three conclusions were reached in the study. (1) Predicted performance of the heat exchanger, using the overall heat transfer coefficient based on the outside area of the tube K_o, indicated an enhancement by 92% compared with the measured performance of the conventional segmental baffle‐type heat exchanger. (2) The tube side pressure drop ΔP_t=20 kPa and the shell side pressure drop ΔP_s=70 kPa were obtained, and were within the allowable value ΔP_a=80 kPa. The shell side pressure drop of the low‐pressure drop spacer could be decreased by 20% as compared with that of the standard spacer. (3) The enhancement constant of the shell side heat transfer using the low‐pressure drop spacer was about 1.2 times as large as that of the standard spacer, regardless of the pumping power. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(5): 455–471, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10097     

Optimization of high-pressure shell-and-tube heat exchanger for syngas cooling in an IGCC

This work investigates the flow field and the heat transfer characteristics of a shell-and-tube heat exchanger for the cooling of syngas. Finite volume method based on FLUENT software was used and the RNG k–ε turbulence model was adopted for modeling turbulent flow. The porosity rate, the distribution of the resistance and the distribution of the heat source are introduced to FLUENT by coupling the user defined function. The pressure drop, the temperature distribution and the variation of local heat transfer are studied under the effects of the syngas components and the operating pressure, and the effect of the arrangement of the baffles on the heat transfer is studied. The results show that higher operation pressure can improve the heat transfer, however brings bigger pressure drop. The components of the syngas significantly affect the pressure drop and the heat transfer. The arrangement of the baffles influences the fluid flow.     

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.     

Most Frequently Used Heat Exchangers from Pioneering Research to Worldwide Applications

Heat exchangers contribute significantly to many energy conversion processes. Applications range from power production, petroleum refining and chemicals, paper and pharmaceutical production, to aviation and transportation industries. A large percentage of world market for heat exchangers is served by the industry workhorse, the shell-and-tube heat exchanger. Recent developments in other exchanger geometries have penetrated in various industry applications; however, the shell-and-tube exchanger by far remains the industry choice where reliability and maintainability are vital. Over the years, significant research and development efforts are devoted to better understand the shell-side geometry. New geometries are introduced for performance enhancement and to improve reliability. The pioneering work published by J. Nemcansky et al. in the Trans. Institute of Chemical Engineers in May, 1990, on helical baffles paved the way to a major shift from a conventional understanding of baffles in a shell-and-tube heat exchanger. Helical baffles serve as guide vanes for shell-side flow as compared to creating flow channels with conventional segmented baffles. In the past decade, ABB Lummus Heat Transfer has extended the understanding of the helical baffle geometry through extensive testing and development. CFD flow simulation studies have further confirmed the helical baffle advantage. Industry feedback on operating Helixchanger® heat exchangers—the shell-and-tube heat exchangers with helical baffles—has demonstrated low fouling characteristics as well as a higher conversion of shell-side pressure drop to heat transfer. In this paper, the characteristics of this novel Helixchanger heat exchanger are discussed. Examples from early installations in the power industry to the major applications in the petro-chemical and refining industries are presented, illustrating the advantages in reducing fouling and increasing reliability while achieving lower total life cycle costs.     

管壳式换热器壳侧强化传热与管束支撑方式的研究进展

从管壳式换热器壳侧管束支撑方式和强化传热的角度,综述了从弓形折流板换热器、折流杆式换热器到螺旋折流板式换热器的研究进展,特别介绍了一种适合正三角形布管的三分螺旋折流板换热器的新型结构,并指出非连续折流板螺旋换热器中相邻折流板形成的三角区的泄漏是方向指向上游的有益流动,而目前常用的螺旋折流板轴向搭接方案则开启了一条指向下游的旁通捷径,将影响绕行主流正常流动和传热。     

Thermal performance augmentation using water based Al2O3-gamma nanofluid in a horizontal shell and tube heat exchanger under forced circulation

Shell and tube heat exchanger is one of the most prevalent heat exchangers with a wide variety of industrial applications, i.e., power plants, chemical processes, marine industries, HVAC systems, cooling of hydraulic fluid and engine oil in heavy duty diesel engines and the like specifically where a need to heat or cool a large fluid volume exist and also higher-pressure use. In the present study, the effect of using Al₂O₃-water nanofluid on thermal performance of a commercial shell and tube heat exchanger with segmental baffles is assessed experimentally. For this purpose, Al₂O₃-gamma nanoparticles with 15 nm mean diameter (99.5% purity) and Sodium Dodecyl Benzene Sulphonate (SDBS) as surfactant are used to make aqueous Al₂O₃ nanofluid at three various volume fractions of nanoparticles (φ = 0.03, 0.14 and 0.3%). Indeed, in this paper the effect of some parameters of hot working fluid such as Reynolds number and volume concentration of nanoparticles on heat transfer characteristics, friction factor and thermal performance factor of a shell and tube heat exchanger under laminar flow regime is investigated. The results indicate a substantial increment in Nusselt number as well as the overall heat transfer coefficient of heat exchanger by enhancement of Reynolds number and it can be seen that, at a certain Reynolds number, heat transfer characteristics of heat exchanger increase as the nanoparticles volume concentration increases. Outcomes of the heat transfer evaluation demonstrate that applying nanofluids instead of base fluid lead to increment of Nusselt number up to 9.7, 20.9 and 29.8% at 0.03, 0.14 and 0.3 vol%, respectively. Likewise it is seen that at mentioned nanoparticles volume fractions, overall heat transfer coefficient of heat exchanger enhances around 5.4, 10.3 and 19.1%, respectively. In term of pressure drop, a little penalty is found by using nanofluid in the test section. Eventually a thermal performance assessment on the heat exchanger was conducted. According to the analysis results, utilizing nanofluid at minimum and maximum nanoparticles volume fractions (φ = 0.03 and 0.3%) results in average augmentation of around 6.5% and 18.9% in thermal performance factor (η) of the heat exchanger compared to the base liquid, respectively.     

On the recirculation of ammonia-lithium nitrate in adiabatic absorbers for chillers

This paper presents a numerical model of single-effect absorption cycles with ammonia-lithium nitrate solution as the working pair and incorporating an adiabatic absorber. It is based on UA-ΔT_lm models for separate regions of plate-type heat exchangers and it assumes an approach factor to adiabatic equilibrium. The results are offered as a function of external temperatures. A loop circuit with a heat exchanger upstream the absorber produces subcooling for facilitating absorption process. The effect of the mass flow rate recirculated through the absorber is studied. Results show a diminishing return effect. The value at which the recirculation mass flow yields a reasonable performance is between 4 and 6 times the solution mass flow. With a heat transfer area 6 times smaller than with a conventional diabatic shell-and-tube type absorber, the adiabatic absorber configured with a plate heat exchanger yields a 2% smaller maximum COP and a 15–20% smaller cooling power.     

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.     

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。     

Use of segmental baffle in shell and tube heat exchanger for nano emulsions

Among the heat exchangers (HE), the shell and tube type is being widely used in different applications like oil, chemical, and power plant Industries. The incorporation of segmental baffles (SB) improves the HE capacity from higher temperature fluid to lower temperature fluid. Nanofluids can be effectively used to enhance the heat transfer rate. In this study, numerical simulations have been carried out in a shell and tube heat exchanger (STHX). Among HE design methods, Tubular Exchanger Manufacturers Association (TEMA) standard is being used for better design by many researchers. In this paper, the computational fluid dynamics analysis was carried out with Al₂O₃, CuO, and SiO₂ nanofluids amid 1, 3, and 5 vol. % with water emulsion to enhance the heat transfer coefficient of STHX. The nanofluid has been used in the cold fluid of the HE and on the other side hot water is used. From the results, it is noticed that with the increase of Nanofluids, the value of heat transfer coefficients is found to be increasing. The overall heat transfer coefficient has been enhanced for Al₂O₃, CuO, and SiO₂ about 10.41%, 12.27%, and 9.56%, respectively, at 0.22 kg/s for the 5 vol. % addition. It is also depicted that the pressure drop is increasing with the incorporation of nanofluids.     

Numerical investigation on the thermohydraulic performance of a shell-and-double concentric tube heat exchanger using nanofluid under the turbulent flow regime

The heat transfer characteristics of water-based Al₂O₃ nanofluid flowing through the annulus-side of a shell-and-double concentric tube heat exchanger (SDCTHEX) are investigated numerically. The temperature-dependent thermophysical properties of the nanofluid and pure water were used. The heat exchanger is analyzed considering conjugate heat transfer from hot oil flowing in the shell and the inner tube to the nanofluid flowing in the annulus formed between the concentric tubes. The overall performance is assessed based on the thermohydraulic performance. The overall thermohydraulic performance of the SDCTHEX, expressed in terms of the ratio of the overall heat transfer rate to the overall pressure drop with the nanofluid flowing in the annulus, is lower than that obtained with water when compared at constant hot fluid mass flow rates and at different inner tube diameters.     

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.     

半圆柱空间异形孔板换热器热工水力性能的数值模拟

为研究半圆柱空间异形孔板换热器的流动与传热特性,建立换热器简化物理模型,运用ANSYS软件建立CFD模型进行数值模拟,分析了开孔形状与板间距的影响,并对比了半圆柱空间异形孔板换热器与弓形板换热器的联系与区别。研究结果表明：半圆柱异形孔板换热器壳侧流体呈纵向流动,壳侧流体通过孔隙形成射流冲刷管壁,具有强化传热作用;板间距一定,开孔面积相近时,开孔形状对壳侧压降的影响较小,对换热性能的影响稍大;板间距越小壳侧换热系数越高但其综合性能指标越小;圆头三角孔板换热器在板间距30 mm时的壳侧换热系数比40及50 mm方案分别高5.62%,10.06%,综合性能指标低1.44%,2.07%;异形孔板换热器的综合性能指标比弓形折流板换热器平均约高27.89%。     

The effects of nanofluid on thermophysical properties and heat transfer characteristics of a plate heat exchanger

Improving heat exchanger's performance by increasing the overall heat transfer as well as minimising pressure drop is one of the promising fields of research to focus on. Nanofluids with higher thermal conductivity and better thermophysical properties can be applied in heat exchanger to increase the heat transfer rate. In the present study SiO₂, TiO₂ and Al₂O₃ are applied in a plate heat exchanger and the effects on thermophysical properties and heat transfer characteristics are compared with the base fluid. Since it is desired to minimize the pressure drop, the influence of nanofluid application on pressure drop and entropy generation is investigated. It is concluded that the thermal conductivity, heat transfer coefficient and heat transfer rate of the fluid increase by adding the nanoparticles and TiO₂ and Al₂O₃ result in higher thermophysical properties in comparison with SiO₂. The highest overall heat transfer coefficient was achieved by Al₂O₃ nanofluid, which was 308.69 W/m².K in 0.2% nanoparticle concentration. The related heat transfer rate was improved around 30% compared to SiO₂ nanofluid. In terms of pressure drop, SiO₂ shows the lowest pressure drop, and it was around 50% smaller than the pressure drop in case of using TiO₂ and Al₂O₃.