螺旋隔板换热器的研究及工业应用

螺旋隔板换热器主要包括两种不同类型的结构形式,即没有中心管的非整体连续的螺旋隔板换热器和有中心管的整体连续的螺旋隔板换热器.本文总结了国内外学者对螺旋隔板换热器所做的主要研究工作,这包括壳程流体的动力学研究、传热与压降性能研究和数值模拟,并介绍了整体连续型螺旋隔板强化管换热器在工业中的应用.最后,对螺旋隔板换热器的下一步研究工作进行了展望.     

光伏散热扁管内部流场的数值模拟

本文将换热器用扁管应用到光伏电池散热中,将光伏电池散失的热量用于提高扁管内流体的温度,实现能源的高效利用.采用fluent软件,对设置在光伏电池板背面以水为介质的扁管通道进行了数值模拟,获得了内部的流场和温度场,并分析了入口流速、入口水温、有无隔板及隔板数目对出口水温的影响,结果表明适当降低入口流速和入口水温、在通道内设置隔板或者增加隔板数目,均可提高出口水温.     

应用数值模拟进行均热炉换热器的节能研究

均热炉应用金属换热器代替传统的非金属陶土换热器,可以提高换热效率,降低均热炉燃气消耗。文章通过数值模拟试验,研究了换热器改造后的流场和温度场,进一步验证了节能改造的可行性。     

螺旋扭曲椭圆管换热器壳程数值模拟

以水为介质,采用k-ε模型,用数值模拟方法研究了5种不同结构的螺旋扭曲椭圆管换热器的管外壳程传热与流阻性能,并和采用椭圆管作为换热部件的换热器进行了比较.研究结果表明,螺旋扭曲椭圆管换热器壳程有较好的强化换热特性,螺旋扭曲椭圆管的几何尺寸和流体流动速度对壳程传热与流阻性能有重要影响.通过数值模拟所获得的规律为螺旋扭曲椭...     

双壳程管壳式换热器的传热和阻力特性

针对弓形折流板管壳式换热器流动死区大,压降高的不足,提出外螺旋折流板内斜百叶折流板的双壳程管壳式换热器结构,外螺旋角为15°～40°,内斜百叶折流板倾角为45°。通过三维数值模拟,研究其传热和阻力特性,获得其局部流场,并与传统弓形折流板换热器进行了对比,同时分析了外壳程螺旋折流板不同倾角对其性能的影响。结果表明:双壳程管壳式换热器的壳侧流场分布均匀,流动死区减小,综合性能高于相同壳径和管束布置的弓形折流板管壳式换热器,外螺旋角为30°时,单位压降下的传热系数平均提高了24. 4%。当外螺旋角为20°时,该换热器具有最好的综合性能。     

熔盐单罐释热过程圆柱形隔板径向尺寸优选

圆柱形隔板在熔盐单罐蓄热器中具有显著的强化传热作用.为获得单罐内圆柱形隔板的最佳径向尺寸,通过数值模拟的方法研究隔板径向尺寸对熔盐单罐蓄热系统释热性能规律的影响,同时分析释热过程中熔盐侧流场变化.结果表明,圆柱形隔板直径为罐体直径的0.6倍时具有最佳的盘管换热器出口温度、单罐释热功率和释热效率,该文研究结果为熔盐单罐蓄...     

连续拼接型螺旋折流板换热器壳程流场与温度场数值研究

针对单弓形折流板换热器壳程压降大、连续型螺旋折流板换热器安装制造成本高的缺点,提出一种连续拼接型螺旋折流板换热器。基于流体力学基本原理与周期性充分发展模型理论,对连续拼接型螺旋折流板换热器壳程流场与温度场进行数值模拟,研究表明：雷诺数在2000~10000范围内,当螺旋角为70°时换热器的综合换热性能最好,且是同尺寸单弓形折流板换热器的15~21倍;利用多元线性回归方法推导出了连续拼接型螺旋折流板换热器壳程对流换热系数与压降的准则数关系式。     

连续拼接型螺旋折流板换热器壳程内流场与温度场模拟研究

针对单弓形折流板换热器壳程压降大、连续型螺旋折流板换热器安装制造成本高的缺点,提出一种连续拼接型螺旋折流板换热器。基于流体力学基本原理与周期性充分发展模型理论,对连续拼接型螺旋折流板换热器壳程流场与温度场进行数值模拟,研究表明:雷诺数在2 000~10 000范围内,当螺旋角为70°时换热器的综合换热性能最好,且是同尺寸单弓形折流板换热器的15~21倍;利用多元线性回归方法推导出了连续拼接型螺旋折流板换热器壳程对流换热系数与压降的准则数关系式。     

螺旋套管换热器传热特性研究

根据螺旋套管换热器的结构特点及传热特性,建立了水一水蒸气的流动与传热的三维几何模型.利用Fluem时不同工况下的螺旋套管进行了数值模拟,得出了湍流状态下螺旋套管内流体的温度场、速度场和压力场;利用搭建的螺旋套管换热器试验台,得出多种工况下的传热系数,为螺旋套管换热器的设计计算提供了依据.同时将试验结果和数值模拟结果进行...     

折流板换热器壳程流场数值模拟与结构优化

基于多孔介质与分布阻力的概念,采用FLUENT软件对单弓形折流板换热器的壳侧流场进行了三维数值模拟,模拟结果与实验结果吻合较好。在此基础上针对折流板换热器壳程压降大、能耗高,存在传热死区等的缺点,提出了壳程流场的改进方案,通过数值模拟可以看到壳程流场改进后不仅具有压降低、场协同性能好、基本无传热死区等特点,而且在一定程度上还提高了管束抗流体诱导振动的性能。     

三分螺旋折流板换热器壳侧二次流的寻踪

对倾斜角20°有34根管子的周向重叠三分螺旋折流板换热器进行了数值模拟研究,通过在三分螺旋折流板换热器壳侧通道内偏心纵向切面和横切面以及六边形纵向切面上速度矢量流场和压力云图的叠加展示,不仅呈现了壳侧总体螺旋速度的周向分量的轨迹,而且从所呈现的轴向和径向速度分量揭示了二次流和相邻折流板V型缺口处逆向泄漏的踪迹.研究结果表明:流体在螺旋通道内在离心力作用下呈现向外扩张的流动趋势,然后在外围高、中心低的压力分布作用下沿着靠近折流板附近的流速较低的区域向心流动返回轴中心,形成单涡型迪恩二次流;二次流增强了流体的掺混,从而有利于强化传热.     

一种新型换热器流动特性的实验研究

螺旋折流板换热器是将折流板布置成与管束有某个倾斜角度 ,流体在壳程沿着螺旋折流板呈螺旋状流动的一种新型换热器。在对几个影响螺旋折流板换热器流动特性的因素进行了实验研究后 ,本文对实验结果进行了论述和分析。     

3D numerical simulation on shell-and-tube heat exchangers with middle-overlapped helical baffles and continuous baffles – Part II: Simulation results of periodic model and comparison between continuous and noncontinuous helical baffles

In this paper, based on the simplified periodic model the performance predictions for heat exchanger with middle-overlapped helical baffles are carried out by 3D simulation for three different helix angles (30°, 40° and 50°), and the commercial codes of GAMBIT 2.3 and FLEUNT 6.3 are adopted in the simulation. It is found that the model average heat transfer coefficient per unit pressure drop of the 40° angle case is the largest, which is in qualitative agreement with the existing literature. The predicted average intersection angle of this case is the smallest, being consistent with the field synergy principle. The performance of periodic model with continuous helical baffle is also compared with that of the noncontinuous middle-overlapped helical baffles. It is found that the heat transfer coefficient per unit pressure drop of the noncontinuous middle-overlapped helical baffles is appreciably larger than that of the continuous helical baffle, indicating that the heat exchanger with noncontinuous middle-overlapped helical baffles has its advantage over the one with continuous helical baffle.     

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。     

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.     

新型蜂窝板式换热器实验与模拟分析

板式换热器在工业生产中广泛应用,采用数值模拟和实验相结合的方法对新型蜂窝板式换热器进行研究。结果表明:数值模拟和实验结果在合理的误差范围内,验证了数值模拟的可靠性。新型板式换热器内部蜂窝结构附近的速度场出现规律的周期性变化,流体湍流强度增加,Nu和阻力系数f随焊孔直径和蜂窝直径的增加而增大,通过对蜂窝板在3 000≤Re≤25 000的数据结果进行关联,得到了蜂窝板流动换热的准则关系式,为蜂窝板式换热器的优化提供了理论依据,并为工业生产提供参考。     

Performance Study of a Circumferential Overlap Trisection Helical Baffle Heat Exchanger at the Shell Side

Using the three-dimensional (3D) modeling software Gambit, a mathematical model of a circumferential overlap trisection helical baffle shell-and-tube heat exchanger (cothSTHX) was developed with 34 tubes and three pulling rods with an equilateral triangle tube layout and a baffle incline angle of 20°. The numerical simulation of flow and thermal performances was performed with the analysis software Fluent. The temperature, pressure, and velocity nephograms are shown for different slices, including spiral, concentric hexagon longitudinal, meridian, eccentric longitudinal, and transverse slices. The nephograms of temperature, pressure, and velocity with superimposed velocity vectors vividly display the important parameters of the cothSTHX. The “Dean vortex secondary flow” is a key mechanism to enhance the heat transfer in heat exchangers, which is clearly depicted to show that the spiral fluid flows outward under the centrifugal force, then flows back to the axis under the radial differential pressure, forming a single vortex in each helix cycle. The structure of circumferential overlap baffles restricts the shortcut leakage flow, and the flow pattern in the cothSTHX is very close to “plug flow” on the unfolded hexagon slices.     

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.     

The effect of baffle shape on the performance of a polymer electrolyte membrane fuel cell with a biometric flow field

Flow field design on the cathode side, inspired by leaf shapes, leads to a high performance, as it achieves a good distribution of reactants. Furthermore, the addition of baffles to the cathode channel also increases the supply of reactants in the cathode catalyst. However, research on the addition of baffles to the cathode channel has still been limited to straight channels and conventional flow fields. Therefore, in this work, a numerical study was conducted to investigate the effect of baffles on the leaf flow field on the performance of a polymer electrolyte membrane fuel cell. The generated 3D model is composed of nine layers with a 25-cm² active area. The beam and chevron shapes of the baffles, which were inserted into the mother channel, were compared. The simulation results revealed that the addition of beam-shaped baffles that are close to each other can increase the current and power densities by up to 18% due to the more uniform distribution of the oxygen mass fraction.     

Numerical and experimental study of a shell and tube heat exchanger for different baffles

In the present work, the shell and tube heat exchanger (STHX) is designed based on The Tubular Exchanger Manufacturers Association standards with hot fluid (water) flowing on the shell side and cold fluid on the tube side. A comparison is made between the Nusselt number and friction factor obtained from numerical and experimental results of segmental baffles (SBs) and helical baffles (HB) with different baffle inclinations. The results show that SB provided a higher Colburn factor (j_s) when compared with HBs STHXs (20°, 30°, 40°, and 50°), but shell side pressure drop is lower for 40° HBs STHXs for the same shell side fluid flow rates.