折流板换热器壳程流体流动与传热特性数值模拟

根据流体动力学和计算传热学理论,建立了折流板管壳式换热器计算模型,运用CFD技术对换热器壳程流体的流动与传热问题进行了三维数值模拟,得到了不同壳程进口雷诺数Re条件下换热器壳程流体的流场和温度场。对数值模拟结果进行分析,以总传热系数h．壳程总压降△p以及单位压力损失下的传热系数h／Ap作为换热器性能的衡量标准,分析了不同折流板间距和不同折流板圆缺高度时管壳式换热器壳程总传热系数h、总压降△p以及h／Ap随壳程进口雷诺数的变化规律。结果表明：随着壳程进口流速的增大,换热器壳程总传热系数和总压降增大、h／Ap减小：在壳程流体流量不变的情况下,结合单位压力损失下的传热系数h／Ap,适当减小折流板间距或减小折流板圆缺高度。可提高换热器的换热性能。     

曲面弓形折流板换热器壳程压力降的数值模拟

采用Fluent软件数值模拟了一种新型折流板换热器——曲面弓形折流板换热器壳侧流体的流动状态,计算了壳程压力降,并与普通弓形折流板换热器进行了比较。结果发现:在流量一定的情况下,曲面弓形折流板换热器的壳程压力降明显低于普通弓形折流板换热器的壳程压力降,而且随着曲面折流板曲率半径和折流板圆缺口高度的减小,曲面弓形折流板换热器的壳程压力降降低的百分比增大。     

小孔混流折流板换热器壳程传热性能研究

传统弓形折流板换热器在折流板背流侧存在“流动死区”,会减小壳程传热效率。为降低“流动死区”的影响,提出小孔混流折流板结构,并建立小孔型混流折流板换热器有限元模型,研究小孔位置和数量对换热器壳程传热性能的影响。结果发现,壳程流体在折流板小孔处会形成射流,增强了附近流体的湍流程度,减小了“流动死区”的范围,提高了壳程传热效率。在研究范围内,随着折流板小孔位置向缺口处移动,壳程强化传热能力先增强、后减少。壳程强化传热能力最强的小孔位置靠近折流板缺口,相比没有小孔的传统折流板换热器,此时的努塞尔数提高了17.02%,压力降减少了3.58%。同时还发现,折流板小孔数目越多,虽然壳程流体的流动阻力越小,但换热效率变化不是单调的,意味着折流板的小孔布孔方案存在优化设计空间。     

密封条对六分螺旋折流板换热器壳程侧换热影响

针对两种不同剪裁方式(60°、90°)布置的六分螺旋折流板,建立无密封条和存在密封条的换热器壳程侧模型;采用CFD分析软件借助数值模拟的方法,研究密封条及密封条结构改变对换热器壳程侧流动和传热的影响。结果表明:密封条的存在能够有效的提高壳程侧的换热系数,对90°扇形剪裁方式布置的六分螺旋折流板换热器壳程的影响较60°明显;在壳程侧换热系数增加的同时,壳程压降也随之增大。密封条宽度与间隙比值越大,壳程侧的换热系数越高;当比值为94.1%时,壳程单位压降换热系数较无密封条时增加(8.05~17.8)%。     

大小孔折流板换热器壳程场协同分析

根据大小孔折流板换热器壳程结构和流动特点,利用有限元软件ANSYS-Fluent建立了大小孔折流板换热器周期性单元流道模型,通过对该模型的分析,揭示了大小孔折流板换热器内部流道的压力、温度、速度和角度场的分布规律。从角度场的分析得知：随着雷诺数的增大,大小孔折流板换热器壳程角度场的平均协同角逐渐降低,其传热效果越好;而当大孔直径和板间距较小时,大小孔折流板换热器壳程的场协同度较好,具有更好的传热性能。     

管壳式换热器壳程流体流动与传热数值模拟

利用ANSYS参数化建模方法建立了管壳式换热器的参数化模型,在ANSYS FLUENT 13.0模拟软件中对管壳式换热器的壳程流体的流动与传热进行了数值模拟计算,得到了不同折流板间距及入口流速的情况下换热器壳程流体温度场、速度场和压力场,分析了折流板间距及入口流速对换热效率和流体诱导振动的影响,对换热器结构优化设计提出了改进措施。     

螺旋折流板换热器壳程传热性能的研究

主要对18°,25°,30°螺旋角的螺旋折流板换热器壳程传热性能进行了测定与研究,同时又进行了18°,25°,30°螺旋角的螺旋折流板换热器与传统的弓形折流板换热器壳程传热性能的比较。即从试验中得出了螺旋角为30°的螺旋折流板换热器的传热效率最高,又得出18°,25°,30°不同螺旋角度的螺旋折流板换热器的壳程传热效率都比传统的弓形折流板换热器壳程传热效率高。     

开孔折流板对列管式换热器传热性能的影响研究

针对由传统弓形折流板结构带来的壳程流动死区,从而引起的流动阻力大、传热效率低等问题,本文对折流板进行开孔,通过数值模拟的方法研究开孔折流板结构对列管式翅片换热器壳侧流体流动、传热及阻力性能的影响。研究发现,折流板开孔后,壳程流动死区明显减小,壳程传热系数及压降同比开孔前降低了;综合换热性能同比开孔前提升了。壳程压降随开孔率及板间距的增大而减小,壳程努塞尔数Nu随板间距的增大逐渐增大。从综合换热性能及场协同的角度分析发现,开孔率x=0.229、折流板间距H=85 mm的列管式换热器综合传热性能最佳。     

倾斜折流栅式换热器壳程热力特性研究

为提升常规斜向流换热器的壳程传热性能,提出了一种倾斜折流栅式换热器。采用CFD分析软件FLUENT,标准k-ε模型方程对两种斜向流换热器的壳程热力特性进行了数值研究,并运用场协同原理分析了斜向流换热器的强化传热机理。结果表明:随着折流栅倾斜角的降低,壳程传热系数、压降、综合性能升高,但随着倾斜角的继续降低,如在(60~70)°范围内,壳程传热系数和综合性能基本保持不变;倾斜折流栅式换热器能够提高壳程局部纵向流场的流速,增加壳程流体整体的斜向流程度和速度场与温度场的协同性,强化换热。倾斜角为70°时,倾斜折流栅式换热器较常规斜向流换热器壳程传热系数和综合性能分别提高(7.54~7.66)%和(6.29~6.45)%。研究结果为斜向流换热器的结构优化和推广应用提供了理论依据。     

板壳式换热器壳程传热性能分析

针对一种波纹板式换热器,改变其板束放置方式和折流板切口方向建立4种不同结构实验模型。利用Fluent分析壳程流体传热性能,得出板束竖直放置—折流板水平切口模型换热器压降ΔP最小;忽略压降损失时板束竖直放置—折流板垂直切口模型换热器的对流传热系数ho最高;在综合考虑的情况下,前者ho/ΔP最高,传热性能比其他模型增高40%以上,该实验对同类产品设计研究可提供理论参考。     

Numerical simulation of fluid flow and heat transfer in a plasma spray gun

A computational fluid dynamics (CFD) simulation for analyzing fluid flow patterns in a plasma spray gun is presented in this study. It is coupled with a heat transfer simulation of the plasma spray gun. Based on CFD and heat transfer theory, the numerical model of the nozzle in the plasma spray gun is developed, and the coupled simulation of the flow fluid and heat transfer is carried out with the semi-implicit method for pressure-linked equations (SIMPLE) method. Local turbulence, which will lead to appearance of a static-water region, is found at the front corner of the cooling channel in the nozzle. The locations insufficiently cooled are found in the wall near the heat source and in the gasket in the rear of the nozzle. Then, cooling processes with different parameters of cooling water are analyzed. The optimal velocity and direction of cooling water, which efficiently cool the nozzle and improve the service life of the plasma jet, are obtained .     

Numerical simulation of fluid flow and heat transfer in a plasma spray gun

A computational fluid dynamics (CFD) simulation for analyzing fluid flow patterns in a plasma spray gun is presented in this study. It is coupled with a heat transfer simulation of the plasma spray gun. Based on CFD and heat transfer theory, the numerical model of the nozzle in the plasma spray gun is developed, and the coupled simulation of the flow fluid and heat transfer is carried out with the semi-implicit method for pressure-linked equations (SIMPLE) method. Local turbulence, which will lead to appearance of a static-water region, is found at the front corner of the cooling channel in the nozzle. The locations insufficiently cooled are found in the wall near the heat source and in the gasket in the rear of the nozzle. Then, cooling processes with different parameters of cooling water are analyzed. The optimal velocity and direction of cooling water, which efficiently cool the nozzle and improve the service life of the plasma jet, are obtained .     

异型管在热管换热器中传热数值模拟研究

针对热管换热器中热管具有高效传热特性,在诸多领域有着极其重要的应用。应用fluent计算软件对三种不同形状的热管的传热性能进行研究,并研究三角形热管与四边形热管混排的传热性,并比较它们之间的传热效果。分析得出:圆形热管的传热系数从前排到后排近似符合抛物线分布;三角形热管的热管系数从前排到后排维持高的传热系数不变,在此热管换热器中三角形热管的综合传热性能最好,能起到强化传热的效果;正方形热管和正方形与三角形热管从前排到后排传热系数近似符合指数分布。     

翅片热板散热器的传热数值模拟研究

采用有限元法,应用ANSYS软件的热分析功能对翅片热板散热器的传热性能进行了数值模拟,并计算出该散热器表面的瞬态温度变化曲线,与实验测试结果吻合得较好.最后的研究结果表明:所研制的新型功率电子元器件翅片热板散热器散热性能良好,具有良好的启动性能和等温性能.     

Characteristics of fluid flow and heat transfer in a fluidized heat exchanger with circulating solid particles

The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000.     

波纹管内流动与换热的数值模拟研究

利用计算流体力学软件Fluent,采用数值模拟方法究了幅值不同的两种波纹管传热状况,发现幅值为4mm的波纹管的传热状况优于幅值3mm波纹管的传热状况,这是由前者管内湍流强度高于后者所致.同时,回归了两波纹管的换热准则方程,为波纹管的校核计算及工程应用提供依据.     

双波纹板束传热与流动的数值模拟

应用数值分析Fluent软件对新开发的一种用于气—气换热的双波纹板管换热器板束的传热与流动进行数值模拟。板束叠放采用对顶和平行两种形式,分别模拟计算出不同流量和温度下两种模型的传热系数和湍流强度并进行对比分析。研究结果表明:同样条件下,热通道对顶叠放模型的换热系数是平行叠放的1.2倍,湍流强度比平行叠放模型提高了一倍;随着热侧流量和进口温度的不断升高,总换热系数逐渐增大,但其对冷侧对流系数和压降影响微小。     

Numerical investigation of fluid flow and heat transfer characteristics in a helically-finned tube

In order to investigate the characteristics of flow and heat transfer rate in a Helically-finned tub (HFT), we used continuity, momentum and energy equations under a steady, three-dimensional and incompressible fluid flow assumptions. For the performance metrics, we considered the Darcy friction factor, Colburn j-factor, volume goodness factor and area goodness factor of the HFT. We could also evaluate the effect of geometry parameters on the results of local pressure coefficient, fluid vorticity and Nusselt number of the HFT. We carried out the CFD calculation for a range of laminar flow (Re = 100) and turbulent flow (Re = 2000 and 10000). In a laminar and turbulent flow regime, the friction factor increases with increasing the each geometric parameter. While the Colburn j-factor decreases as increasing these geometric parameters. Consequently, the thermal performance of HFT is poorer than that of single straight circular tube type because of having a small volume and area goodness factor as increasing the Reynolds numbers.     

Large-eddy simulation of fluid flow and heat transfer in a mixing tee junction

The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold fluids was often used as thermal load in previous analysis of thermal fatigue failure, thereby the influences of the amplitude and frequency of temperature fluctuation on thermal fatigue failure were neglected. Based on the mechanism of flow and heat transfer which induces thermal fatigue, the turbulent mixing of hot and cold water in a tee junction is simulated with FLUENT platform by using the Large-eddy simulation(LES) turbulent flow model with the sub-grid scale(SGS) model of Smagorinsky-Lilly(SL) to capture the amplitude and frequency of temperature fluctuation. In a simulation case, hot water with temperature of 343.48 K and velocity of 0.15 m/s enters the horizontal main duct with the side length of 100 mm, while cold water with temperature of 296.78 K and velocity of 0.3 m/s enters the vertical branch duct with the side length of 50 mm. The numerical results show that the mean and fluctuating temperatures are in good agreement with the previous experimental data, which describes numerical simulation with high reliability and accuracy; the power spectrum density(PSD) on top wall is higher than that on bottom wall(as the frequency less than 1 Hz), while the PSD on bottom wall is relatively higher than that on top wall (as the frequency of 1-10Hz). The temperature fluctuations in full mixing region of the tee junction can be accurately captured by LES and can provide the theoretical basis for the thermal stress and thermal fatigue analyses.     

缩放管内脉动流动对流换热的数值模拟研究

通过数值模拟计算,研究在不同脉动频率、脉动振幅下的管内流体脉动对缩放管的传热和阻力的影响。研究结果表明:管内流体脉动能够强化缩放管的传热效果,相比稳态时,传热被强化了约为16%;管内流体脉动在一定条件下,也会增大缩放管的沿程阻力。