组合式多壳程螺旋折流板管壳式换热器数值模拟研究

本文采用数值模拟方法对内壳程为非连续螺旋折流板的组合式螺旋折流板和单壳程弓形折流板管壳式换热器壳侧流动换热特性进行对比研究,结果表明:相同壳程质量流量和相同换热量条件下,组合式两壳程螺旋折流板换热器的压损比弓形折流板换热器降低14.6%;相同壳程质量流量条件下,组合式两壳程螺旋折流板换热器单位压降下换热量比弓形折流板换热器提高10.8%.     

螺旋折流板换热器流动与换热特性的试验分析

对螺旋折流板换热器的流动及换热特性进行了试验研究与分析.结果表明,当保持螺旋周期为定值时,在相同流量下和相同壳径下,螺旋折流板换热器的壳侧压降随螺旋角增大而减小,且远低于弓形折流板的管壳式换热器;壳径减 小时,压降增加明显.相同Re下,螺旋折流板换热器的壳侧换热系数低于弓形折流板,在螺旋角为40°时达到最大值.相同流量下,螺旋折流板管壳式换热器单位压降和单位泵功下的换热系数均高于弓形折流板管壳式换热器.     

双壳程连续螺旋折流板换热器的数值模拟

本文提出了一种新型的双壳程连续螺旋折流板换热器。采用数值模拟方法对双壳程、单壳程连续螺折流板换热器,以及弓形折流板换热器壳侧流动与传热持性进行了对比研究。结果表明,同质量流量和对流换热系数近似相等的情况下,双壳程连续螺旋折流板换热器壳程压降比弓形折流板换热器低17.7%～23.5%,同质量流量和壳程压降近似相等的情况下,其对流换热系数比单壳程连续螺旋折流板换热器高7.1%～12.6%。     

周向重叠三分螺旋折流板换热器壳侧性能试验研究

对倾斜角为20°、24°、28°和32°的单头以及32°的双头周向重叠三分螺旋折流板换热器和弓形折流板换热器的传热和压降性能进行了测试,换热器采用公共壳体和可更换管芯结构。采用壳侧轴向雷诺数和轴向欧拉数分别作为反映壳侧流量和阻力系数的无因次参数。试验结果显示在试验范围内周向重叠三分螺旋折流板换热器壳侧换热系数、壳侧压降和综合性能指标都随着倾斜角增大而减小;倾斜角20°方案的性能指标最佳,其平均壳侧努塞尔数和轴向欧拉数与弓形折流板方案的数值之比分别为1.123和0.45;双头螺旋折流板方案的换热系数和压降都大于同样倾斜角的单头螺旋折流板方案,但两者的综合性能较接近。     

新型铝叠片油冷却器的结构及传热性能研究

对三种不同结构的新型弓形折流板铝叠片油冷却器的传热和流阻进行研究,并与螺纹管弓形折流板油冷却器进行对比,结果表明:铝叠片油冷却器换热效果明显优于螺纹管油冷却器,且铝叠片油冷却器生产成本低、质量轻、结构紧凑。对弓形折流板铝叠片油冷却器分析中可得:油冷却器的壳程压降随着折流板间距和铝叠片间距的增大而降低。折流板间距为130mm铝叠片间距为2.0mm的2号油冷却器综合性能更佳,3号单位体积换热量大其结构更紧凑、经济性好。     

弓形折流板换热器中折流板对换热器性能的影响

本文采用Bell-Delaware换热器设计方法研究了传统弓形折流板换热器加热轻油时在不同管束排列角度下,改变换热器壳侧折流板间距以及改变折流板的窗口高度对管壳式换热器的壳体内径、换热管数目、壳侧换热系数及壳侧压降的影响.     

双螺旋与中间搭接螺旋折流板换热器性能研究

采用数值模拟方法研究了40°螺旋角时螺旋折流板换热器双螺旋和中间搭接两种折流板布置形式对壳程性能与螺旋流动的影响,并与30°和40°螺旋角时单螺旋连续搭接结构的进行了对比.结果表明,40°螺旋角时双螺旋和中间搭接结构会强化壳程流体的螺旋流动,使同流量下壳程换热系数与压降增加,但同压降下的换热系数显著下降且均低于30°螺...     

折边螺旋折流板电加热器换热强化

对倾斜角为20°、25°、30°单头及30°双头"斜日字"单元环形布管方式的周向重叠三分折边螺旋折流板电加热器方案进行了热力性能模拟,并与相同布管方式板间距为200、250 mm的弓形折流板电加热器方案进行了数值模拟结果对比。结果表明,倾斜角为25°的折边螺旋折流板方案的换热系数较高,综合指标最高,同时加热管表面平均温度较低。而弓形折流板方案中板间距越大,其换热系数和压降越低,平均温度越高。与板间距200 mm的弓形折流板方案S200相比,三分折边螺旋折流板方案H25°的传热系数与综合性能指标h.△p~(-1/3)分别提高了18.3%和29.8%,同时压降及加热管表面平均温度分别下降了24.3%和45.6 K。     

三分螺旋折流板换热器壳侧传热特性研究

本文给出了三分螺旋折流板换热器几何参数的关系式,并分析了倾斜角为10°、15°、20°扇形、15°椭圆、20°扇形搭接的三分螺旋折流板换热器和弓形折流板换热器的传热和压降性能测试实验结果。结果显示20°扇形折流板方案的壳侧换热系数较高且压降较低,其性能指标h_o/△p_o~(1/3)平均值比弓形折流板换热器的值高26%;20°扇形搭接方案与螺距相仿的15°扇形方案的性能大致相当;15°扇形方案比螺距较小的15°椭圆方案的性能更高。结果表明对换热器的性能起决定作用的不是折流板的倾斜角而是当量螺旋角。     

阶梯式螺旋折流板换热器流动与传热特性研究

针对现有的螺旋折流板换热器加工较为复杂,并且非连续型螺旋折流板的相邻折流板间存在漏流的问题,提出了一种新型阶梯式螺旋折流板换热器。通过数值模拟的方法对阶梯式螺旋折流板换热器和弓形折流板换热器进行对比,研究其壳程流动与传热特性。结果表明,阶梯式螺旋折流板换热器能够使壳侧流体呈近似螺旋状流动,综合性能优于弓形折流板换热器,速度分布更加均匀。     

Numerical research of stream analysis on helical baffles heat exchangers

In this paper, the numerical simulations for a helical baffles heat exchanger and a segmental baffles heat exchanger with component clearance are performed to reveal the features of leakage streams and their effect on heat exchanger performance. Helical baffles heat exchanger models with four different angles and segmental baffles heat exchanger model were established and calculated via Gambit and Fluent software. The results reveal that the heat exchanger with a 40° helix angle shows the best comprehensive heat transfer performance in turbulent state, and the heat exchanger with a 50° helix angle shows better comprehensive heat transfer performance in laminar flow state. The leakage streams proportion of the helical baffles heat exchanger varies from 5.5% to 6.1%, compared with the leakage streams proportion changes from 16.6% to 21.0% in the segmental baffles heat exchanger. In both turbulent flow state and laminar flow state, with the rise of shell-side Reynolds number, the main spiral stream B proportion decreases and the leakage streams proportion increases in the segmental baffles heat exchanger, while the stream B proportion increases and the leakage streams proportion decreases in helical baffles heat exchanger. The proportion of stream B increases with the increase of the helix angle β and the proportions of leakage streams decrease with the increase of β. The proportion of the tube-baffle leakage stream A increases in radial direction. Both the proportion of stream A and that of the baffle-shell leakage stream E fluctuate in the intermediate zone in axial direction; the stream A proportion decreases at the inlet and outlet zone, while the stream E proportion increases at the inlet and decreases at the outlet zone. The results of this paper could be of great significance in the optimal design and manufacture of the helical baffles heat exchanger.     

变角度百叶窗翅片的数值模拟和性能分析

为研究变角度百叶窗结构对平行流蒸发器换热性能的影响,文中建立了一种均匀角度百叶窗和两种变角度百叶窗的计算模型;采用fluent软件数值模拟了空气侧的传热和流动过程,得到了百叶窗翅片的速度场、温度场及压力场;将数值模拟结果与相关文献实验关联式结果进行对比,验证了数值模拟的可行性,分析了迎面风速对换热和压降特性的影响;并利用公式j/f1/3,比较了三种翅片的综合性能,发现变角度百叶窗翅片综合性能优于均匀角度百叶窗翅片。     

螺旋隔板花瓣管换热器的传热强化研究

比较了螺旋用板花瓣管和螺旋隔板低肋管润滑油冷却器和空气冷却器的传热性能,实验结果表明,无论是作为油冷却器,还是作为空气冷却器,螺旋隔板花瓣换热器的综合传热性能明显优于螺旋隔板低肋管换热器,且螺旋隔板花瓣换热器还能节省３０％以上的铜管重量．     

螺旋折流板换热器层流流动与换热的数值模拟

应用多孔介质和分布阻力模型对一螺旋折流板管壳式换热器的壳侧层流流动与换热进行了三维数值模拟,并与该换热器的实验研究结果进行了对比分析,符合程度良好.证明了该方法能有效地模拟螺旋折流板换热器的流动和换热特性.     

Performance Analysis of a New Water-based Microcooling System

In the electronic industry, dissipating the heat load becomes a critical factor for highly developed designs. These require higher power transfer in a more compact size. In the current study, a new microcooling system was developed and tested. It utilizes the enhancement in heat transfer characteristics associated with implementing a vortex promoter in the evaporator segment of a water-based heat pipe. The test evaporator was a cavity of 4-mm diameter and 23-mm length in an electrically heated aluminum block. A helical coil (of various diameters, namely 500, 300, and 250 μm) was introduced to the evaporator segment to act as a vortex promoter. Configurations of a new microcooling system based on a modified heat pipe technology were built and tested. The presented system proves to work efficiently in situations where a closed-loop thermosyphon encounters film boiling limitation. The most efficient configuration has a flow modifier diameter about one-tenth of the evaporator chamber gap, while the diameter of the return line was three-quarters of the evaporator gap. This configuration shows a stable operation characteristic and possesses high thermal efficiency. The maximum heat flux obtained by such a configuration was 305 W/cm² when it runs at 103°C saturated temperature and 0.01°C/W thermal resistance. A uniform temperature distribution along the system was noticed.     

刮膜蒸发器内非牛顿流体流场特性数值模拟

刮膜蒸发器是通过旋转刮板强制成膜,可实现高黏度非牛顿流体类物料平稳蒸发的新型高效蒸发器.蒸发器内流体的流动、分布与传输机制直接决定了蒸发器的蒸发效率与功耗.不同于现有研究主要基于牛顿流体开展,本文针对不同黏度的非牛顿流体,建立蒸发器三维计算流体动力学模型,系统研究了蒸发器内的流场分布特性和成膜机理.结果表明:低黏非牛顿流体的流场分布特性和牛顿流体类似,物料可在壁面形成均匀且连续的液膜;随着黏度的增加,液膜的均匀性和连续性逐渐变差.通过对流场分布与传输形式的研究,结合液膜分布、速度分布、剪应变率分布,以及黏度分布进行对比分析发现,蒸发器内部结构与运行状态形成的剪切场与黏度分布是蒸发器良好成膜的关键.此外,提出对刮板前缘进行弯折可辅助高黏流体液膜铺展,并对最佳弯折角度进行探索.本研究为刮膜蒸发器的设计和应用提供了理论指导与依据.     

刮膜蒸发器内非牛顿流体流场特性数值模拟

刮膜蒸发器是通过旋转刮板强制成膜,可实现高黏度非牛顿流体类物料平稳蒸发的新型高效蒸发器.蒸发器内流体的流动、分布与传输机制直接决定了蒸发器的蒸发效率与功耗.不同于现有研究主要基于牛顿流体开展,本文针对不同黏度的非牛顿流体,建立蒸发器三维计算流体动力学模型,系统研究了蒸发器内的流场分布特性和成膜机理.结果表明:低黏非牛顿流体的流场分布特性和牛顿流体类似,物料可在壁面形成均匀且连续的液膜;随着黏度的增加,液膜的均匀性和连续性逐渐变差.通过对流场分布与传输形式的研究,结合液膜分布、速度分布、剪应变率分布,以及黏度分布进行对比分析发现,蒸发器内部结构与运行状态形成的剪切场与黏度分布是蒸发器良好成膜的关键.此外,提出对刮板前缘进行弯折可辅助高黏流体液膜铺展,并对最佳弯折角度进行探索.本研究为刮膜蒸发器的设计和应用提供了理论指导与依据.     

符号回归在换热关联式求解中的应用

本文利用符号回归分析换热器的实验数据,以寻找更高精度的换热关联式。为改进MATLAB环境下的遗传规划工具箱GPLAB的性能,增入了四种新功能:个体简化、常数优化、单亲交叉、新生操作。利用改进后的GPLAB对连续螺旋折流板管壳式换热器壳程传热的实验数据进行了符号回归,得到的换热关联式的预测精度高且稳健度强。     

Ghost rods adopting the role of withdrawn baffles in batch mixer designs

In batch mixers the stirring of a fluid is known to be particularly effective when the motion of the stirring rods form nontrivial braids. This motion is desirable as it generates (predictable) exponential stretching of material lines. Additionally, it has also been recognized that flow structures themselves (such as periodic islands) may adopt the role of proxy or “ghost” stirring rods. For a number of designs (which form nontrivial braids), we investigate the prevalence of ghost rods that effectively replace stationary stirring rods (baffles) as the latter are removed from the batch mixer. We show (for the case of Stokes flow) that designs with fewer baffles have comparable material stretch factors to corresponding designs with all baffles present.     

Averaging Versus Chaos in Turbulent Transport?

In this paper we analyze the transport of passive tracers by deterministic stationary incompressible flows which can be decomposed over an infinite number of spatial scales without separation between them. It appears that a low order dynamical system related to local Peclet numbers can be extracted from these flows and it controls their transport properties. Its analysis shows that these flows are strongly self-averaging and super-diffusive: the delay (r) for any finite number of passive tracers initially close to separate till a distance r is almost surely anomalously fast ( (r) r^2–, with > 0). This strong self-averaging property is such that the dissipative power of the flow compensates its convective power at every scale. However as the circulation increases in the eddies the transport behavior of the flow may (discontinuously) bifurcate and become ruled by deterministic chaos: the self-averaging property collapses and advection dominates dissipation. When the flow is anisotropic a new formula describing turbulent conductivity is identified.