CFD技术在板翅式换热器设计中的应用

回顾了计算流体动力学 ( CFD)几年来的发展现状 ,并且介绍了计算流体动力学 ( CFD)技术应用的领域、CFD软件的一般结构以及各种商业软件的特点 ,同时阐明了 CFD技术在板翅式换热器设计应用方面的优越性 ,并指出了我国在 CFD技术研究领域与国际先进水平的差距及进一步开展 CFD研究的方向     

CFD在换热器局部结构优化设计的应用

本文利用CFD模拟手段对电加热水箱换热器流动传热特性进行三维数值计算,通过对流场和温度场的分析,改进原设计中不利于热量传递的结构特征.在保证水箱基本结构尺寸不变的前提下,对箱体内两块折流板的位置及其几何形状进行多种结构模型的数值模拟和比较分析,实现了基于CFD数值模拟结果进行换热器局部结构优化设计的工程应用.     

(火积)耗散理论在换热器设计中的应用

本文首先说明(火积)耗散理论避免了最小熵产原理和傅里叶定律间的矛盾,显示了其在处理导热问题上的优越性.然后利用热力学(火积)和熵的关系,推出了换热器中由流体阻力引起的(火积)耗散表达式.     

基于模型的制冷翅片管换热器数字化设计技术

文中对翅片管换热器水侧和空气侧传热和流动过程进行深入研究,并开发了换热器辅助设计系统,建立了湿空气物性快速计算模型.并在此基础上,采用集总参数模型设计合理的算法,进行翅片管换热器设计计算.根据计算所得排数和其他结构参数,调用基于ObjectARX的AutoCAD二次开发程序绘制换热器二维工程图.     

铝基MOF合成及其在除湿换热器中的应用

提出一种铝基MOF的新型合成方式,用金属铝代替铝盐作为MOF铝离子来源,制备可直接涂覆于金属基表面的MOF浆料。经XRD表征浆料的主要成分为MIL-96(Al)和MIL-100(Al),该材料在20°C下吸附量可达到0.38 g/g。利用喷涂法制备MOF–金属基样片,样片动态吸附测试表明各相对湿度下吸附过程均与LDF模型良好拟合且相对湿度越高吸附速率越快;经50个吸附–脱附循环样片的吸水性能无衰减。制备MOF除湿换热器(MCHE)并分析了入口风速和热水温度的影响,在多个工况下MCHE均表现出优于硅胶除湿换热器2³倍的除湿能力。     

微通道换热器在制冷空调系统中的应用分析

2010年6月1日实施的新能耗标准进一步推动了制冷空调行业的升级,微通道换热器以其体积小、重量轻、结构紧凑、耐高压、热阻低、换热效果好等特点开始逐步在汽车制冷空调系统、家用和商用制冷空调系统中得以应用.然而,国内在该领域的研究比国外起步晚,理论和实验研究都比较缺乏.文中对微通道换热器在制冷空调系统中的应用研究进行了总结...     

微管壳式换热器在能量转换循环中的应用

目前，超临界二氧化碳(S-CO₂)布雷顿循环普遍采用印刷电路板换热器(PCHE)来保证其相对其他能量转换循环的紧凑性优势。PCHE芯体为整体结构，若内部出现泄漏或结垢等问题，很难进行维护与检修。本文提出了一种微管壳式换热器(MSTE)，其结构与传统管壳式换热器类似，但其管径缩小至微通道级。由于MSTE的流道横截面积占总截面积之比较PCHE大，在典型的回热器与冷却器设计工况下，相对PCHE而言，采用MSTE可将体积与质量均减小30%以上。灵敏性分析结果显示，采用本文设计的MSTE结构的回热器与冷却器，回热器冷热流道入口温度升高20℃左右，压缩机入口温度变化均不超过1℃，说明该种结构换热器的换热能力足够支撑能量转换循环的一般工况波动。     

多孔介质模型在管壳式换热器数值模拟中的应用

本文详细讨论了多孔介质模型在管壳式换热器数值模拟中的应用,开发了一套能自动生成多孔介质特性参数的通用程序。该程序主要基于三维交错网格及SIMPLE算法,然后运用该模型,采用改进的κ-ε模型和壁面函数法,对换热器壳侧的湍流流动进行了数值模拟。计算结果与换热器冷态实验结果符合良好,表明该模型和计算方法是切实可行的。     

气体轴承换热器节流气孔结构的应用设计研究

本文通过研究气体轴承换热器气体轴承的工作原理,设计出三种不同的气体轴承节流气孔方案,并对这三种气体轴承节流气孔的设计方案进行了实验对比分析。作为气体轴承换热器的核心结构,气体轴承节流气孔的优化设计对减小气体轴承换热器体积和换热面积、提高换热效率有着重要意义。     

Application of He's variational iteration method to nonlinear heat transfer equations

Instead of finding a small parameter for solving nonlinear problems through perturbation method, a new analytical method called He's variational iteration method (VIM) is introduced to be applied to solve nonlinear heat transfer equations in this Letter. In this research, variational iteration method is used to solve an unsteady nonlinear convective-radiative equation and a nonlinear convective-radiative-conduction equation containing two small parameters of ε₁ and ε₂ and evaluate the efficiency of straight fins. VIM can apply to the nonlinear equations with boundary or initial conditions defined in different points just with developing the correction functional using the extra parameters such as Cn, as used in this Letter.     

Application of variational iteration method and homotopy–perturbation method for nonlinear heat diffusion and heat transfer equations

Perturbation methods depend on a small parameter which is difficult to be found for real-life nonlinear problems. To overcome this shortcoming, two new but powerful analytical methods are introduced to solve nonlinear heat transfer problems in this Letter; one is He's variational iteration method (VIM) and the other is the homotopy–perturbation method (HPM). Nonlinear convective–radiative cooling equations are used as examples to illustrate the simple solution procedures. These methods are useful and practical for solving the nonlinear heat diffusion equation, which is associated with variable thermal conductivity condition. Comparison of the results obtained by both methods with exact solutions reveals that both methods are tremendously effective.     

The application of He's variational iteration method to nonlinear equations arising in heat transfer

In this Letter, we purpose to solve nonlinear equations arising in heat transfer through the He's variational iteration method (VIM) and show that it is strongly and simply capable of solving a large class of linear or nonlinear differential equations without the tangible restriction of sensitivity to the degree of the nonlinear term and also is very user friend because it reduces the size of calculations besides, its iterations are direct and straightforward. VIM can apply to the nonlinear equations with boundary or initial conditions defined in different points just with developing the correction functional using the extra parameters such as cn$c_n$, as used in this Letter.     

Characterization of heat recirculation effects on the stabilization of edge flames in the near-wake of a mixing layer

A fundamental study aimed at investigating the stabilization characteristics of edge flames established in the near-wake of two merging streams, one containing fuel and the other oxidizer, is presented, with the main focus placed on the effects of the thermal interaction between the flame and the splitter plate. To this end, a diffusive-thermal model characterized by constant gas density and transport coefficients is used for conditions at which flame liftoff is likely to occur. It is assumed that the incoming streams are of equal strain rates, that the fuel and oxidizer are supplied in stoichiometric proportion, and that the mass diffusivities of the reactants are equal, such that the resulting combustion field is symmetric with respect to the centerline extending from the splitter plate. The results indicate that the plate has a negligible effect on the edge flame unless the tip of the plate intrudes into the preheat zone of the curved premixed flame segment forming the edge flame. In an overall adiabatic system, the heat conducted from the flame to the plate is completely recirculated back to the reactants via the lateral surfaces of the plate, thus supporting an excess enthalpy flame in the near-wake. The average output heat flux, defined as the total heat output through the lateral surfaces of the plate divided by the characteristic length associated with the temperature variation along the plate, is identified as an appropriate measure to characterize the heat recirculation efficiency.     

升膜式板式换热器的换热性能研究

升膜蒸发是在换热器表面形成一层薄液膜,薄膜蒸发能够强化换热。文中研究采用光滑铜板的板式升膜蒸发器,以去离子水作为介质,在不同进水流量、不同加热量(热流密度)下,测定换热器某些点的局部换热系数,计算出总的换热系数,研究影响板式换热器升膜蒸发的因素和变化趋势。     

盘状螺旋管换热器的实验研究

介绍了一种适用于小流量大温升的新型盘状螺旋管换热器,具有结构简单、质轻,体积小的特点;利用相关的实验研究,获得其换热性能和流动阻力特性。实验结果表明,其在小流量下仍具有较高的传热系数,适合于做热泵热水器的水冷换热器。     

影响风机盘管换热器传热性能的因素分析

从设计和生产工艺两方面阐述了影响风机盘管换热器传热性能的主要因素,针对风机盘管机组在运行中换热器的常见问题,分析原因并提出了相应的解决措施。     

液化天然气(LNG)冷藏车冷量回收换热器的设计

液化天然气(LNG)用做优质"绿色"汽车燃料的同时,还具有大量的冷能,该冷能可回收用于冷藏车制冷,LNG冷藏车是一种节能环保型汽车。在LNG冷藏车冷量回收系统中,传统的方式是将LNG在换热器中直接气化,并向空气释放冷量,但这种方式中的换热器表面易结霜,对其性能造成很大危害。文中提出了采用热管技术回收LNG冷量并用于冷藏车制冷的方法;设计了新型的热管式LNG冷量回收换热器,该新型换热器具有高效、紧凑等特点。     

Gain ripple minimization in fiber Raman amplifiers based on variational method

In this paper, the variational method is employed for minimizing the gain ripple of multi-wavelength fiber Raman amplifiers. The variance of gain spectrum of the fiber Raman amplifier is regarded as the cost function, restriction on total pump power and average gain is given as the constraints of the minimization problem. It is shown that the minimization problem with any necessary constraints on the pump powers, average gain and signal to noise ratio, is reduced to a two-point boundary value problem. The method gives the entire possible local and global solutions. The method is applied to different examples of fiber Raman amplifiers with different lengths from 25 km to 100 km and different numbers of pumps from 4 to 20 to determine the pump powers and wavelengths for minimum gain ripple. It was obtained for a 100 km fiber Raman amplifier the gain ripple can be about 0.1 dB with on-off gain more than 20 dB.     

组合式热管换热器在热泵系统中的试验研究

采用组合式热管换热器作为生活浊水余热热泵热水器的热管蒸发器,并在试验台上进行了不同污水进口温度和不同污水流量的可视化试验,通过分析试验结果,发现组合式热管上升管和下降管的温差很大的现象,这与热管特性相矛盾。采用理论分析和实验相结合的方法,研究了热管中产生温差的原因。它主要是由于下降管压力损失较大,使热管工质在热管蒸发器中的滞留引起。