Shear rates investigation in a scraped surface heat exchanger

The electrodiffusion technique was performed in order to investigate the shear rate on a scraped surface heat exchanger. Microelectrodes were placed inside: the walls of the outer cylinder; the inlet and outlet bowls; the rotor and the blades. Highly viscous Newtonian fluid (Emkarox HV45 solutions) and non-Newtonian model fluid (aqueous solutions of CMC) were used. The electrodiffusion method allowed us to measure wall shear rates. Maximum shear rate was observed at the scraping surface and caused by blades scraping, high shear rate was also measured on the leading edge of the blades. In the other parts of the exchanger, shear rate remained low but the development of Taylor vortices completely modified the scraped surface heat exchangers behaviour inside the surface of the bowls. A dimensionless representation of the friction factor was established for the inner and outer wall surface of the exchanger.     

一次原表面型换热器传热性能的数值模拟

应用计算流体力学CFD(Computational Fluid Dynamics)方法,以周期性的单元控制体为模型,对一次原表面错流型换热器内三维稳态层流流场进行了数值模拟,分析了不同流动条件下控制体的传热和阻力特性,并与实验值进行了对比,结果表明,数值模拟结果与实验值符合得较好.在对速度场和温度场分析的基础上,研究了结构参数对传热性能的影响关系,为该类换热器的设计提供了可行性的方法和依据.     

板翅式换热器综合考虑传热、流动与结构的优化设计

给出一种针对一侧装翅片 (或肋片 )而另一侧不装翅片的板翅式换热器的优化设计新方法。这里综合应用了给定换热器结构材料而使得换热量最大的两侧换热表面的最佳匹配准则和使可用能损失率最小的最佳运行参数准则。利用两个准则间的关系 ,采用迭代的方式完成换热器的优化设计。这样的设计方法能使换热器的设计达到材料省、换热效果好及运行费用低的目的 ,且能在设计阶段实现。     

Determination of heterogeneities in a scraped surface heat exchanger using electrochemical sensors

An experimental investigation of a scaled-down model of an industrial exchanger, using an electrochemical technique, was undertaken in order to show the presence of hydrodynamic heterogeneities at low axial Reynolds number. Heterogeneities were revealed in the bowls with respect to the generalised Taylor number as the result of the perturbations added to the flow by blade rotation at both ends of the exchanger. Shear heterogeneities associated to flow visualisations were correlated to temperature heterogeneities observed in the bowls. Shear fluctuations were revealed in the scraped part describing two distinctive zones at low rotation speed caused by varying viscosity in the flow field. A complex spiral flow was observed by flow visualisation characterising a mass transfer evolution comprised between these two distinctive zones at low Taylor number.     

Development of a catalytic combustor with heat exchanger

Catalytic combustion is thought to be a considerable improvement on the traditional one under specific conditions. Due to its special features, catalytic combustion has two strong points compared to flame: no NO_x emission and high reaction efficiency. However, the preheating process of catalytic combustion is an obstacle that deteriorates profitability in operation. So the HTHE (High Temperature Heat Exchanger) is adapted to the system to reinforce the preheating process, and we show that the catalytic combustion is maintained steadily without exceptional heat injection. As a result, the stability on the catalytic surface is the most important operational factor. To achieve it, both mixture gas property and temperature distribution should be controlled.     

Experimental and numerical analysis of heat transfer including viscous dissipation in a scraped surface heat exchanger

Viscous dissipation plays an important role in the dynamics of fluids with strongly temperature-dependent viscosity because of the coupling between the energy and momentum equations. The heat generated by viscous friction causes a local temperature increase in the high shearing zone with a consequent decrease of the viscosity which may dramatically change the temperature and velocity distribution. These processes are mainly controlled by the Brinkman number, the rotating velocity and the thermal boundary conditions. This work analyses forced convection heat transfer including the viscous dissipation in a scraped surface heat exchanger (SSHE). In this study the increase of the temperature due to the viscous dissipation is analysed both experimentally and numerically for Newtonian and non-Newtonian fluids. Heat transfer simulations including viscous dissipation were carried out by means of the CFD code of the software Fluent, version 6.3, with solving momentum and energy equations. Two thermal boundary conditions were considered: pseudo-adiabatic wall and constant temperature on the stator wall exchange. In the case of Newtonian fluid (pure HV45), for both considered thermal boundary conditions, an important increase of the temperature was obtained. In the case of non-Newtonian shear thinning fluid (2 wt% CMC solution), viscous dissipation is neglected. The developed numerical model agrees well with experimental results. The validated numerical model was then used to study the effect of index and consistency behaviour of shear thinning fluid using power-law rheological behaviour on the viscous dissipation, and correlation using dimensionless analysis expressed with different dimensionless process numbers is proposed for Newtonian and non-Newtonian shear thinning fluid.     

防垢涂层对热交换器表面性能的影响

通过调整工艺用化学镀的方法制备了具有不同结构形态的防垢涂层。X射线衍射结果表明,这些涂层的结构形态分别为非晶、混合晶及纳米晶。进一步的界面张力分析表明,这些镀层均不润湿水,具有较低的表面自由能,且不同结构形态的涂层表面自由能与涂层结构形态之间没有线性的对应关系。与没有镀层的不锈钢相比,这些具有低表面自由能的涂层表面,生垢速度要远远小于普通无涂层不锈钢管的换热表面。在热稳定性方面,纳米相的析出改善了涂层的热稳定性。该结论为涂层在热交换器防垢方面的应用提供了理论基础。     

一次表面换热器瞬态响应特性的数值模拟

根据一次表面热交换器（PSHE）的结构和流动特点，利用能量守恒定律，导出它的瞬态温度变化物理模型和数学方程式.研究工作流体温度和流量发生阶跃变化时PSHE出口温度的响应特性，分析指出一次表面换热器板片各几何参数以及通道形状对其温度响应特性的影响次序是：板片厚度δ最强，宽度W和数目n次之，波纹通道形状最弱.比较研究表明，由于PSHE的固体壁面时间常数远小于板翅式和管壳式换热器，因此这种轻质结构换热器的响应特性明显优于常规热交换器，非常适用于那些要求工况经常变动、能够提供的场地和空间又十分有限的化工联合装置.     

热管式通风换热器热回收的实验研究

针对普通住宅日常通风换气的特点设计出一台小型热虹吸管式通风换热器的样机,并利用热虹吸管换热器对房间通风系统中的冷量(热量)进行热回收实验研究。通过实验测试了该换热器在不同风量和新、排风温差条件下的热回收效率,以及新、排风的压力损失随风速的变化情况。实验结果表明,新风的温降(升)随着新、排风温差的增大而增大,随着风量的增大而减小;该样机的最大热回收效率在夏季可达70%,冬季为63%,新、排风的最大阻力损失仅为25 Pa,节能效果显著。     

间壁换热分解开采天然气水合物的实验模拟

在自制3.5 L带内置换热器的可视化反应釜中,进行了不同间壁换热温度（84.8、72.2、50.5、30.9℃）的定容分解开采丙烷水合物实验模拟。分解初始时釜内气体压力迅速上升,随着分解的进行,压力增加的幅度逐渐减小,最后压力保持一定值。因此,将水合物分解过程分为释放气体阶段和分解尾声阶段。在释放气体阶段,气体大量产出,釜内压力迅速升高;在分解尾声阶段,釜内压力趋于平缓。计算得到总分解过程平均分解速率介于0.16～0.46 mol·min^-1·m^-2之间、总分解过程的能量效率介于1.33～3.74之间;释放气体阶段分解速率介于0.27～2.56 mol·min^-1·m^-2之间、水合物分解的能量效率介于2.25～5.58之间。与相关文献比较,间壁换热分解水合物的能量效率有很大程度提高。在实际应用中,存在一个最佳间壁换热分解温度,既提高水合物分解速率又提高能量效率。     

基于扩张状态观测器的换热器动态面控制

针对带有延时、大惯性换热器温度控制问题,设计基于扩张状态观测器（ESO）动态面控制器。换热器温度控制是非线性的、时变的和不确定的动态过程,采用扩张状态观测器不仅可以获取系统不可测状态还能实时估计系统动态;采用动态面控制律,实现对温度的精确快速跟踪。利用Lyapunov函数证明控制系统的稳定性。通过对经典PID控制方法、动态矩阵控制方法和基于扩张状态观测器的动态面控制方法进行比较,仿真结果表明基于扩张状态观测器的动态面控制方法具有更优越的控制效果和鲁棒性能,且在被控系统设定值和扰动发生变化时具有更好的动态响应性能。     

空心环管壳式换热器的应用

介绍 ４０ ｋｔ／ａ硫铁矿制酸转化系统的技改和应用空心环管壳式换热器（下称新型换热器）的运行情况：传热系数提高,换热面积由 ２ ３４５ ｍ２减少到 １２７９ ｍ２,节约设备投资约 ３３万元,压力降大幅度降低,从 １５ ８００ Ｐａ减到 ８ １３０ Ｐａ,生产能耗减少,每年节省电费 ３５． ２万元。     

热管式固相粉末换热系统传热分析

介绍了一种新型分离热管式固相粉末换热系统的工作原理,并对其传热情况进行了分析.这种新型的分离热管式固相粉末换热系统已得到实际应用,用来加热高炉喷煤用的空气和煤粉的混合物,运行效果良好,增加了高炉的喷煤量,减少了焦炭用量.利用分离式热管作为以固相粉末为换热介质时的传热元件是完全可行的.     

Enhanced heat transfer in a heat exchanger square-duct with discrete V-finned tape inserts☆

The article presents an experimental and numerical study on thermal performance enhancement in a constant heat-fluxed square-duct inserted diagonal y with 45° discrete V-finned tapes (DFT). The experiments were carried out by varying the airflow rate through the tested square duct with DFT inserts for Reynolds number from 4000 to 25000. The effect of the DFT with V-tip pointing upstream at various relative fin heights and pitches on heat transfer and pressure drop characteristics was experimentally investigated. Both the heat transfer and pressure drop were presented in terms of Nusselt number and friction factor respectively. Several V-finned tape characteristics were introduced such as fin-to duct-height ratio or blockage ratio (RB=e/H=0.075, 0.1, 0.15 and 0.2), fin pitch to duct height ratio (RP=P/H=0.5, 1.0, 1.5 and 2.0) and fin attack angle,α=45°. The experimental results reveal that the heat transfer and friction factor values with DFT inserts increase with the increment of RB but the decrease of RP. The inserted square-duct at RB=0.2 and RP=0.5 provides the highest heat transfer and friction factor while the one with RB=0.1 and RP=1.5 yields the highest thermal performance. Also, a numerical simulation was conducted to investigate the flow structure and heat transfer mechanism inside the tested duct with DFT inserts.     

并流多通道管壳式换热器壳程传热性能

对并流多通道进出口(MPC)轴流管壳式换热器壳程传热性能进行数值模拟,分别研究了管排数N,Re,不同开孔率的挡板对壳程进口段的局部传热系数分布、局部平均Nu的分布、换热器的平均Nu等特性的影响。结果表明:在无挡板条件下,随着N的减小,壳程传热系数分布不均现象得到有效的遏制,N=7时基本上无传热死区。挡板的存在,不但使得进口段的局部传热系数分布更加均匀,而且能够提高换热器的整体传热Nu。不同参数的挡板之间,挡板1的作用最为明显,可以使得Nu提高10%—12%。     

Hydrodynamics and heat transfer characteristics of a novel heat exchanger with delta-winglet vortex generators

The effects of vortex generators on heat transfer and pressure drop of a novel heat exchanger are investigated using computational fluid dynamics (CFD) method. The Reynolds numbers based on fin collar outside diameter varied from 600 to 2600, the attack angle from 10° to 50°, and the aspect ratio from 1 to 4. The numerical results are also analyzed from the view point of field synergy principle, according to which the reduction of the intersection between velocity and temperature gradient is the basic mechanism for augmentation of heat transfer. The results indicate that the enhanced configurations produce the longitudinal vortices and accelerate the flow, which result in significant augmentations of heat transfer with modest pressure drop penalties. It was found that the delta-winglet vortex generator with an attack angle of 20°and an aspect ratio of 2 provides the best integrated performance over the range of Reynolds number computed. The Colburn j-factor of the optimal configuration is shown to increase by 35.1–45.2% with a corresponding increase of 19.3–34.5% in the friction factor.     

管翅式换热器离子交换树脂涂层

采用浸渍法将离子交换树脂（IER）浸渍于饱和氯化锂或氯化镁溶液中,并依次经过滤、洗涤及干燥得改性离子交换树脂。经粉碎后的改性离子交换树脂粉与固体粉末涂料混合成喷涂料,对管翅式换热器铝箔表面进行静电喷涂、热固化得吸湿涂层。XRD分析表明,改性前后树脂结构没有发生根本性改变;SEM表明,吸湿涂层能够均匀紧密地分散在铝箔表面,涂层厚达120 mm;EDS显示出吸湿涂层各成分组成及含量;TG曲线表明,吸湿涂层失重主要集中在30～150℃及400～600℃区域,前者与吸附剂脱附有关,后者与涂料及树脂粉热分解有关;静态和动态吸附曲线显示,吸湿涂层经改性后,其吸湿性能明显提高;吸湿涂层重复性测试显示,涂层具有较高吸附及脱附稳定性。     

具有相变的三介质换热器的分析

具有混合能源的暖通空调与制冷（heating, ventilation, air conditioning & refrigerating, HVAC&R）系统通常需要在3种或多种流体之间传递热量。三介质换热器能满足多流体换热需求,在该领域具有应用前景,其优化具有重要意义。对于具有相变的三介质换热器,现有的热阻定义不能很好地发挥作用,而最新提出的理论提供了另一种方法。本文采用分布参数法建立了翅片管三介质换热器的仿真模型,并用实验结果进行了验证。此外,还推导了三介质换热器中基于耗散的的热阻。根据传热量和理论,分析了不同结构和空气流量下的三介质换热器的换热性能。结果表明,采用基于耗散的热阻作为评价标准与采用传热量为评价标准相比,改变管路排布方式获得的优化结果不同,改变管径或风量获得的优化结果相同。以基于耗散的热阻为标准,考虑不同流体侧之间的传热和压降的匹配,以获得最佳的管路排布方式。本文的实验结果有利于制冷空调系统中三介质换热器的优化以及理论新应用领域的拓展。