Simulation on refrigerant flow in adiabatic capillary tube

This paper proposes a new mathematical model to calculate flow characteristics of the adiabatic capillary tube, which is aimed at solving problems existing in some earlier models. The Stocker’s model was modified with consideration of various effects due to sub-cooling, area concentration, and rolling diameter. The new model can be used not only for R22, but also for its substitutes such as R410A and R407C. A comparison of simulation results of the modified model with those in literature showed that the errors are within 10%. The flow characteristics are finally analyzed. __________ Translated from Journal of hydrodynamics, Ser. A, 2006, 21(3): 318-323 [译自: 水动力学研究与进展]     

制冷剂在绝热毛细管内流动的线性特性

虽然制冷剂在毛细管内的流动为非线性的两相临界流,但是在很多特定工况条件下毛细管流量特性表现出良好的线性特性。这类线性特性的存在有利于改进和简化毛细管的设计方法。基于绝热毛细管近似分析解,对这些线性特性从理论上进行了解释和扩展,并用R22、R410A和R407C三种工质的数据进行了验证,结果与理论分析一致。     

液压集成块湍流模型修正及内流特性分析

基于粒子图像测速技术（PIV）建立了带有刀尖角容腔的直角转弯流道流场的数值计算模型,并进行三维流场仿真。通过将数值计算得到的典型涡系结构与实验结果进行对比,考察了工程上常用的7种湍流模型对带有刀尖角容腔直角转弯流场的预测性能。通过定义权重误差K,筛选出S-A模型作为基础湍流模型并对其进行了参数修正。结果表明,当S-A模型Cb1取值从默认值0.1355修正为0.17时,出流方向正对刀尖角容腔模型权重误差值上升25.0％,入流方向正对刀尖角容腔模型权重误差值下降34.7％,修正后的S-A湍流模型对两种直角转弯流场的综合预测精度有所提高。运用筛选修正后的S-A湍流模型分析了4种典型直角转弯流道的内流特性,结果表明圆弧过渡直角转弯流道相比于带有刀尖角容腔的转弯流道具有更小的压力损失。     

基于改进LRN k-ε模型的汽车气动特性研究

针对由Jones和Launder提出的LRN（低雷诺数）k-ε湍流模型对转捩预测不足等问题,引入全应力限制（TSL）方法及流线曲率因子以改进湍动能耗散率及湍流黏性系数,最终获得了一种改进的低雷诺数湍流模型,并将其应用于汽车外部流场计算仿真中,利用ISIS-CFD求解器实现计算。将计算结果与其他常用于汽车外部流场仿真的湍流模型以及风洞试验得到的结果进行了对比分析,结果表明,在同等计算条件下改进LRN k-ε湍流模型能更加准确且高效地模拟车身表面的气流分离以及尾部流场。     

Flow and pressure drop characteristics of R22 in adiabatic capillary tubes

The objective of this study is to present flow and pressure drop characteristics of R22 in adiabatic capillary tubes of inner diameters of 1.2 to 2.0 mm, and tube lengths of 500 to 2000 mm. Distributions of temperature and pressure along capillary tubes and the refrigerant flow rates through the tubes were measured for several condensing temperatures and various degrees of subcooling at the capillary tube inlet. Condensing temperatures of R22 were selected as 40, 45, and 50°C at the capillary tube inlet, and the degree of subcooling was adjusted to 1 to 18°C. Experimental results including mass flow rates and pressure drops of R22 in capillary tubes were provided. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tube was presented considering major parameters which affect the flow and pressure drop characteristics.     

An analysis of sector-shaped thrust bearings operating in the transition regime

The purpose of this study was twofold: (i) to introduce a modified mixing length expression of Reynolds stress in transition and turbulent lubrication theory; (ii) to determine the performance characteristics of sector-shaped thrust bearings when operated in the transition regime taking into account the inertia effects.

A new model of Reynolds stresses for transition-turbulent theory is proposed. The approach relies on Prandtl's mixing length theory and a modified Van Driest mixing length formula which accounts for the effect of the shear stress gradient in thin film lubrication.

The mixing length model is used to analyse turbulent planar and non-planar flows. Turbulent coefficients obtained from the non-planar cases are used to analyse the sector-shaped thrust bearing in the transition region, taking into account the convective inertia forces and centrifugal forces. Bearing performance characteristics such as pressure distribution, load carrying capacity, pressure centre and inlet flow rate are calculated.     

空间柔性结构振动控制用压电主动构件模型与实验研究

利用压电陶瓷的逆压电效应，研制了一种空间柔性结构振动主动控制用的新型压电智能主动构件，该构件具有重量轻、输出位移大、驱动电压低、稳定性高等优点。分析了压电主动构件建模方法中存在的问题，提出了一种修正的机电耦舍导纳模型，通过数值仿真验证了该模型的正确性。结合所研制的主动构件，对主动构件的动静态特性进行了实验研究与分析，揭示了压电主动构件用于空间柔性结构振动主动控制的优良性能。     

不同制冷剂在空调冷凝器内换热性能的比较

通过建立空调换热器分布参数模型,并对模型进行了验证,进而对R22替代制冷剂R32、R410A、R407C和R290在翅片管冷凝器进行了研究,分析了不同迎面风温和风速下冷凝器的流动和传热规律。研究表明:在一定的条件下,无论增加迎面风温或风速,R407C单位面积换热量,压降和质量流量最大;R290和R32压降和循环质量流量均小于R22;R410A虽然压降较小,但循环流量大;R290循环质量流量较R22小40%左右,且R290换热温差较小,换热系数较高。     

Laminar Heat and Fluid Flow Characteristic with a Modified Temperature-Dependent Viscosity Model in a Rectangular Duct

The present study proposes a modified temperature-dependent non-Newtonian viscosity model and investigates the flow characteristics and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The combined effects of temperature dependent viscosity, buoyancy, and secondary flow caused by the second normal stress difference are considered. Calculated Nusselt numbers by the modified temperature-dependent viscosity model give good agreement with the experimental results. The heat transfer enhancement of viscoelastic fluid in a rectangular duct is highly dependent on the secondary flow caused by the magnitude of second normal stress difference.     

A modified model for wet gas flowrate measurement considering entrainment downstream of a cone meter

To develop a reliable wet gas flowrate measurement model, the relationships between pressure drop characteristics and entrainment downstream of the cone are investigated experimentally. The equivalent diameter ratio of the cone is 0.45. The experimental fluids are air and tap water with X_LM in the range of 0–0.3. The two-phase mass flow coefficient and pressure loss ratio are employed to establish the measurement model. The piecewise characteristics of pressure loss ratio are disclosed innovatively, which is explained by the different intensity of entrainment downstream of cone caused by gas-liquid jetting. A simplified method for evaluating the degree of entrainment is proposed to facilitate the establishment of the modified measurement model. Under the present experimental conditions, the relative error of liquid fluctuates within ±20% when X_LM is larger than 0.02, and the relative error of gas flowrate is within ±5%. Compared with the model without piecewise consideration, the relative error of the liquid flowrate of the modified model reduces obviously under low wetness conditions (0.02<X_LM<0.1). The modified measurement model provides a reliable and cost-effective technology for wet gas flowrate measurement.     

基于修正滑移线场模型的倒棱刀具切削力预测

基于材料塑性滑移理论与刀具刃前材料流动状态分析,提出了一种考虑倒棱刀具负前角切削过程下的材料滞流区（死区）和预剪区的修正滑移线场模型,并给出了材料流动剪切应力和刃前切削几何参数的迭代求解方法,揭示了倒棱刃口几何形状与滑移线场几何参数之间的变化规律。将此模型应用于倒棱刀具切削过程,得到了适用于倒棱刀具正交切削力的预测方法。采用有限元仿真和切削试验相结合的方法对所提出的滑移线场模型和切削力预测方法分别进行了验证,模型预测结果与仿真结果和试验测量结果对比误差均在10%以内。研究结果为研究倒棱几何形状对工件材料流动特性和刀具切削性能的影响提供了参考。     

R410A和R22在一种内螺纹强化管管内蒸发性能研究

为了研究单管管内蒸发性能,搭建了管内蒸发性能实验台,用隔膜泵代替了传统压缩机作为系统动力。研究了在冷却水量0.6m3/h,0.8m3/h和1.0m3/h下,9.52mm内螺纹管内10℃蒸发的制冷剂侧换热性能。结果表明,R22和R41OA的总换热系数,换热系数hr和压降均随着制冷剂流量的增加而增加,在小质量流量下,R410A比R22有更好的换热性能,看起来可以替代R22。但当制冷剂流速增大到300～400kg/(s.m2)时,R22的换热系数增加显著,而R410A趋于平缓,所以在大质量流量下,R410A没有R22换热性能好,替代工作仍待研究。     

A proposal for diesel spray model using a TAB breakup model and discrete vortex method

A hybrid model consisting of a modified TAB (Taylor Analogy Breakup) model and DVM (Discrete Vortex Method) is proposed for numerical analysis of the evaporating spray phenomena in diesel engines. The simulation process of the hybrid model is divided into three steps. First, the droplet breakup of injected fuel is analyzed by using the modified TAB model. Second, spray evaporation is calculated based on the theory of Siebers’ liquid length. The liquid length analysis of injected fuel is used to integrate the modified TAB model and DVM. Lastly, both ambient gas flow and inner vortex flow of injected fuel are analyzed by using DVM. An experiment with an evaporative free spray at the early stage of its injection was conducted under in-cylinder like conditions to examine an accuracy of the present hybrid model. The calculated results of the gas jet flow by DVM agree well with the experimental results. The calculated and experimental results all confirm that the ambient gas flow dominates the downstream diesel spray flow.     

新型负载口独立控制阀的设计与仿真研究

针对现有负载口独立控制系统中流量控制技术成本高、应用少等问题，设计了一种带阀后压差补偿的负载口独立控制阀。采用二级结构，将A形半桥应用到主阀的先导控制。研究中，根据阀的结构特点对其进行数学建模，通过合理假设推导出电闭环控制时的传递函数并进行理论分析。通过传统计算的方法对该阀进行结构参数设计，基于阀口迁移理论设计了主阀U形节流槽，采用矩形窗口的先导半桥控制，流量低，压力灵敏度也较大。进一步在AMESim平台上建立电闭环阀的仿真模型，对其动静态特性进行仿真研究。     

基于杆组邻接矩阵的平面机构综合方法

为在平面机构综合中能够求解出包含R副和P副的全部运动链,给出一种基于杆组邻接矩阵的平面机构综合新方法。通过对前期研究提出的杆组邻接矩阵进行修正,构造改进的杆组邻接矩阵。基于改进的杆组邻接矩阵,求解给定杆组的所有装配方式,并同步辨识同构体,获取杆组装配关系的杆组邻接矩阵。根据提出的约束条件,采取逐级构造杆组邻接矩阵方法,求解杆组间的可行连接方式,并同步辨识同构体,从而获取全R副杆组间的连接关系的杆组邻接矩阵。将所有类型杆组代入求得的杆组连接关系矩阵,获取所有类型杆组可构成的全部机构构型,包含主动件和机架变换问题。以平面6杆机构为例,应用该方法首次求出包含R副和P副的所有机构构型为364种,验证了提出的综合方法的有效性和实用性。     

两级旋叶式膨胀机动力特性的理论研究

两级旋叶式膨胀机与传统旋叶式膨胀机在结构上有着明显的差别,能够实现更高的容积膨胀比,适合用于R410A等具有较高膨胀比的制冷系统。本文通过对两级旋叶式膨胀机运动和受力特征的分析,建立了滑片的受力模型,并应用该模型对拟开发的两级旋叶式膨胀机进行动力计算,分析比较了滑片的运动和所受各种力的计算结果,重点讨论了背压对滑片顶部与气缸壁面间接触力的影响,得出将滑片两侧工作腔中高压腔内工质引入背压腔的方法更适合于两级旋叶式膨胀机。     

Effects of lubricant additives on the performance of hydrodynamically lubricated journal bearings

A non-Newtonian rheological model to investigate theoretically the effects of lubricant additives on the steady state performance of hydrodynamically lubricated finite journal bearings is introduced. In this model, the non-Newtonian behavior resulting from blending the lubricant with polymer additives is simulated by Stokes couple stress fluid model. The formed boundary layer at the bearing surface is described through the use of a hypothetical porous medium layer that adheres to the bearing surface. The Brinkman-extended Darcy equations are utilized to model the flow in the porous region. A stress jump boundary condition is applied at the porous media/fluid film interface. A modified form of the Reynolds equation is derived and solved numerically using a finite difference scheme. The effects of bearing geometry, and non-Newtonian behavior of the lubricant on the steady-state performance characteristics such as pressure distribution, load carrying capacity, side leakage flow, and coefficient of friction are presented and discussed. The results showed that lubricant additives significantly increase the load carrying capacity and reduce both the coefficient of friction and the side leakage as compared to the Newtonian lubricants.     

相控阵阵面热设计及流量分配研究

为解决某有源相控阵中T/R组件散热及组件之间温度差异问题,文中针对相控阵阵面布局特点,采取冷板并联、流量均分的热设计方案。运用定性分析与数值计算相结合的方法确定阵面总流量及流量分配,根据流量分配对最长冷板进行了热仿真分析,分析结果表明流量分配满足T/R组件散热要求。对于影响T/R组件之间温度差异的流量分配问题,通过定性分析各冷板通路流阻组成,介绍了如何利用等流阻匹配实现流量均分。最后通过全阵T/R组件温度测试验证了热设计方案满足T/R组件散热及组件之间温度差异要求。     

管内流动沸腾传热关系式对R410A的适应性研究

R410A作为一种替代制冷剂,已经大量用在工业生产中。R410A制冷系统的设计和研发需要进行R410A管内流动沸腾换热计算。目前有很多公式预测两相流流动沸腾换热系数,它们对R410A的适应性需要判断。本文从10篇论文中收集了1268组R410A流动沸腾传热实验数据,用这些数据对27个两相流流动沸腾换热关系式进行了评价,选出了较为精确的R410A管内流动沸腾换热关系式,为R410A管内流动沸腾换热计算的公式选择提供了依据,为提出精确度更高的R410A管内流动沸腾公式提供了参考。     

局部多孔质气浮止推轴承的设计研究

建立了局部多孔质气浮轴承的理论模型,该模型考虑了轴承气膜交界面处的切向速度滑移。利用有限元方法对所建立的模型进行了理论仿真,轴承静态特性的仿真与试验结果取得了较好的一致性,说明经过修改后的雷诺方程可以用来作为局部多孔质气浮轴承研究的理论模型。利用该模型成功计算出不同渗透系数、不同厚度及不同直径的局部多孔质气浮轴承的流量、承载及刚度特性,并给出了相应的变化曲线。根据仿真结论,提出了局部多孔质气浮止推轴承的设计准则。另外,从理论上将该类轴承与全多孔质类型气浮轴的承特性进行了对比,表明局部多孔质气浮轴承有着优良的特性,有很好的应用前景。