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     

不同螺旋角螺旋折流板换热器传热性能对比实验

对螺旋角为8°、12°、18°、30°、40°的螺旋折流板换热器进行了壳程传热性能和压力降测试,得到了相应结构下的总传热系数和压力降。然后通过对试验数据的整理分析,并进行曲线回归,得到了不同螺旋角的螺旋折流板换热器换热系数和压降经验计算公式。研究表明,实验条件下,30°螺旋角的螺旋折流板换热器的单位压降传热系数要优于8°、12°、18°、40°螺旋角的螺旋折流板换热器的传热系数。     

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%。     

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.     

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.     

Numerical Analysis of Baffle Cut on Shell Side Heat Exchanger Performance with Inclined Baffles

In this work, an attempt has been made to decrease the pressure drop and to increase the heat transfer rate in a shell and tube heat exchanger (STHX) by tilting the baffle angle and by varying the baffle cut. The process of solving the simulation includes modeling, meshing, and analyzing the geometry of the STHX by using Pro-E, hypermesh, and computational fluid dynamics package of ANSYS Fluent, respectively. The objective of this study is to find a suitable baffle inclination and baffle cut for the efficient performance of the STHX. The baffle inclinations of 25°, 30°, 35°, and 40° were considered for three different baffle cuts of 25%, 30%, and 35% of shell inside diameter and the results were compared with segmental baffle of inclination angle 0°. The shell side flow with different inclination angles and baffle cuts results in a significant variation in heat transfer rate and pressure drop in the STHX. The results provide a clear idea that the heat transfer rate is maximum in inclined baffle heat exchanger compared to that of segmental baffle heat exchanger. Further it is found that the STHX with the configuration of 35º baffle inclination angle and baffle cut of 30% of shell inside diameter provides higher heat transfer rate with minimum pressure drop compared to all other configurations.     

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。     

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.     

折弯弓形折流板换热器流动换热性能研究

为了提高折流板换热器的换热性能,改变了折流板换热器的折弯夹角和折流板间距,利用ANSYS Fluent对换热器壳程流体流动与换热过程进行模拟,分析了不同折流板折弯夹角α (110°,135°,170°和180°)、折流板间距（250,300和350 mm)和雷诺数（10 000,20 000和50 000）对换热器壳程压力、速度和温度的影响。结果表明：增大雷诺数对改善流动死区有很大的作用,雷诺数为50 000时的流动死区相对于雷诺数为10 000时面积减小较大;随着夹角α的减小,折流板背流侧的流动死区面积逐渐减小、换热器的表面传热系数和进出口压降力越大,夹角α为110°时出口温度最小、进出口压降最大,夹角α为135°时PEC最大且换热器综合性能最优;折流板间距增大,压力变化梯度减小,压差变化幅度减小,壳程出口温度变化不成正比关系,间距为300 mm时出口温度最低。     

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.     

Numerical research on heat transfer and flow resistance performance of specially‐shaped rod baffle heat exchangers

In order to overcome the disadvantages of heat transfer performance in the shell side of the common circular cross section rod baffle heat exchanger with a low Reynolds number, a numerical simulation on fluid flow and heat transfer in the shell side with different types of rod baffles is carried out. The rod baffles include the circular cross section, trigonal cross section, and rhombic cross section. The influence of heat transfer enhancement and flow resistance reduction affected by baffles is summarized. It is indicated that the trigonal and rhombic cross section rod baffles present the better performance of heat transfer enhancement and flow resistance reduction. With the rhombic cross section rod baffles in the shell side, the higher heat transfer coefficient and overall property in the shell side are achieved when Re is lower, and the heat transfer coefficient in the shell side is 10% higher than that of a circular cross section rod baffle at the same Reynolds number. The trigonal and rhombic cross section rod baffles in the shell side give more optional structure forms for expanding the application scope of rod baffle heat exchangers. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20388     

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。     

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.     

Enhancement of heat transfer from a flat surface in a channel flow by attachment of rectangular blocks

Enhancement of the heat transfer from a flat surface in a channel flow by attachment of rectangular cross‐sectional blocks has been investigated as a function of Reynolds number (Re), arrangement of the blocks with respect to the main flow direction as well as each other, and the numbers (spacing) of the blocks. The channel had a cross‐sectional area of 80×160 mm² (i.e. an aspect (width‐to‐height) ratio of 2). Re, based on the hydraulic diameter of the channel (D_e) and bulk mean velocity (u), changed in the range of 6670–40000. The blocks were positioned both transverse and parallel with respect to the main flow direction. The parallel blocks were arranged in both in‐line and staggered orientation with respect to each other. The effect of the blocks on the flow pressure drop was also measured. The results indicated that the heat transfer could be enhanced or reduced depending on the spacing between the blocks and their positioning and arrangement. For a given pressure drop, the best heat transfer enhancement by the blocks over that from a smooth surface (without blocks) was obtained when the blocks were positioned parallel to the flow and arranged in a staggered manner with respect to each other. Copyright © 2001 John Wiley & Sons, Ltd.     

Fluid flow and heat transfer investigations in shell and dimple heat exchangers

Heat transfer and pressure drop characteristics are investigated here using experimental and analytical techniques for a dimple plate heat exchanger. The analysis uses the log mean temperature difference method (LMTD) in all its calculations. Whilest the shell side flow highly resembles the flow over a rough or wavy plate, the tube side passage in these represents the flow over short hexagonal tube banks with the flowing across the sectional areas between the hexagons having the shape of a benzene ring. Local and global experimental measurements are carried out around the heat exchanger. Furthermore, analytical models for both sides of the heat exchanger were obtained from the literature. Reasonable cross match between experimental and analytical results could be obtained. Copyright © 2005 John Wiley & Sons, Ltd.     

Characterization of sodium flow over hexagonal fuel subassemblies

Steady flow of liquid sodium over a bundle of heat generating hexagonal subassemblies has been investigated. The cross flow pressure drop and heat transfer are characterized using the general purpose CFD code STAR-CD. Analysis has been carried out for both laminar and turbulent regimes of interest to liquid metal fast reactors. Turbulence has been modeled using low Reynolds number (Re) k-ε model. The estimated pressure drop and heat transfer coefficients are compared against that of a straight parallel plate channel. It is seen that in the low Reynolds number range, the pressure drop for the hexagonal path is nearly equal to that of the parallel plate channel for the same length. However, in the high Reynolds number range, the pressure drop of the hexagonal path is much higher than that in the parallel plate channel, the ratio being 2 at Re = 2000 while it is 3.6 at Re = 20,000. Two competing factors, viz., (i) jet impingement/flow development effect and (ii) flow separation effect are found to influence the average Nusselt number (Nu). In the laminar regime, the latter effect dominates leading to a decrease of the Nusselt number with an increase in the Reynolds number. However, in the turbulent regime, the former effect dominates leading to an increase in the Nusselt number with Reynolds number. The Nusselt number in the hexagonal path is about twice that of the parallel plate channel due to under development of velocity/temperature profiles and the recirculation associated with the hexagonal path due to the changes in flow direction. Detailed correlations for both the pressure drop and the average Nusselt number have been proposed.     

螺旋折流板换热器的研究与进展

本文介绍了螺旋折流板换热器的几何形状和流动原理,对其传热及压力降的研究现状进行了总结,与弓形折流板换热器相比,螺旋折流板换热器的最大优点降低阻力,增加传热系数。未来的研究重点是流动换热机理以及影响流动换热机理的因素。     

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.     

Influence of inclination angle,attack angle,and arrangement of rectangular vortex generators on heat transfer performance

We have studied the enhancement of heat transfer by vortex generators. Experiments were performed on rectangular‐type vortex generators mounted on a parallel‐plate heater, and the heat transfer coefficient of the heater surface and pressure drop in the duct were measured. These measurements indicated that a rectangular vortex generator (called a double‐inclined winglet), with inclination angle of the vortex generator surface to the heater surface (β) at 60°, and the attack angle to the flow direction (γ) at 45°, maximizes the local Nusselt number of the heater surface. It was also found that a group of double‐inclined winglets has an optimal arrangement in a winglet array, longitudinal pitch and transverse pitch, that maximizes the ratio [Colburn's dimensionless heat transfer coefficient J_H]/[friction factor f]. The results of numerical calculations showed that the double‐inclined winglet was superior to the conventional rectangular vortex generator in heat transfer. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(3): 253–267, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10089     

Heat transfer enhancement in a parallel plate duct by an oscillating thin plate insertion

Various arrangements were considered for two thin plates, oscillated by a flow in a parallel plate duct, with a view to enhancing the heat transfer along the duct. Heat transfer and pressure distributions were measured at varying the clearances from the wall and various plate separations. The maximum and mean Nusselt numbers have a Reynolds number dependence of Re^0.8, and were, respectively, 2.3 and 1.6 times as large as those in fully developed turbulent flow, for air with Reynolds number ranging from 9,000 to 37,500. Full-field infrared imaging, a relatively new technique, was used to obtain the temporal and spatial temperature profiles on the wall surface. Isotherm contours of the infrared images correspond well to the heat transfer characteristics and flow. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25 (8): 554–567, 1996