R-134a在三种不同放置方式螺旋管内凝结换热的实验研究

对替代制冷剂R-134a在螺旋管内的对流凝结换热特性进行了实验研究.在制冷剂R-134a的质量流量变化范围为100～400kg/(m2s) 和冷却水的平均温度分别为12℃和22℃的条件下,实验得到了在三种不同放置方式螺旋管内(水平,垂直和倾斜)R-134a的对流凝结换热特性数据.实验结果表明,螺旋管的不同放置方式对R-134a在螺旋管内的凝结换热特性具有重要的影响.通过与已有研究结果的比较,简要分析了螺旋管不同放置方式对R-134a对流凝结换热特性的影响机理.     

R-134a在水平直管和螺旋管内凝结换热特性的实验研究

对替代制冷剂R-134a在水平直管和螺旋管内的凝结换热特性进行了实验研究。在三个不同的冷凝温度（35℃、40℃和45℃）、制冷剂R-1Ma的质量流量变化范围为100-400kg／（m^2·s）和制冷剂的干度范围为0．1-0．8的条件下，实验得到了R-134a在水平直管和螺旋管内的凝结换热系数随R—134a的质量流量和干度的变化关系，并将水平直管和螺旋管内的凝结换热特性数据进行了对比。实验结果表明，R-134a在螺旋管内的凝结换热系数比直管的大4％。13．8％。     

R134a臣卧式螺旋管内流动沸腾换热特性实验研究

对R134a在水平直管和螺旋管内的沸腾换热特性进行了实验研究.在三个不同的蒸发温度(5℃、10℃和20℃),工质R134a的质量流量范围为100～400kg/(m~2·s)和干度范围为0.1～0.8的条件下,实验得到了R134a在水平直管和螺旋管内的沸腾换热系数随其质量流量和干度的变化关系,将水平直管和螺旋管内的沸腾换热特性数据进行了比较,结果显示,在实验条件下,卧式螺旋管的传热系数比直管的平均增加13.7%.     

替代工质水平管内流动凝结换热研究综述

流动凝结传热特性对于制冷系统的性能具有重要意义,是制冷剂筛选中的一个重要参考指标。针对近年来有关新型替代工质的凝结传热进行了调研分析,从实验测量和关联模型两个方面综述了国内外替代制冷剂管内流动凝结换热的研究。对凝结换热关联式的适用性和准确性进行了讨论,对凝结换热系数和压降随各影响因素的变化特性进行了概括。     

R134a制冷剂在微通道中的相变传热特性实验

设计了一个可控制制冷剂流量、压力和温度等实验工况的微通道换热器相变流动与换热的可视化实验平台,对R134a制冷剂流经微通道换热器进行了冷凝换热实验研究.试验测量了小质量流率下的R134a制冷剂在多个饱和状态工况下的冷凝换热性能,涉及质量流量、进出口压力和温度等参数.实验分析了传热系数与雷诺数的关系,与Koyama的关联式预测比较接近.分析了摩擦系数随雷诺数的变化,与H L MO和Wu＆Little方程计算得到的数值相近.     

小通道钎焊板式冷凝器性能仿真与实验研究

本文针对当量直径为1.5 mm的小通道钎焊板式冷凝器的换热和压降特性进行了仿真和实验研究。采用有限体积法建立了一维稳态分布参数模型,对R134a和R1234yf两种制冷剂在板间冷凝换热的性能进行仿真模拟,并对模型进行了实验验证。实验结果表明:本文所建立的仿真模型精度较高,换热性能平均误差为4%,压降平均误差为16%,可用于分析换热器的整体性能。最后用此模型仿真对比了R134a和R1234yf在小通道钎焊板式换热器内的冷凝换热特性,结果显示,在相同工况下,用R1234yf替代R134a,传热系数平均下降9%,压降平均下降8%。     

纯工质水平管内凝结换热研究进展

相对于混合工质,纯工质(单一成分制冷剂)不存在温度滑移、系统泄漏时的成分变化等问题,在制冷设备中得到了广泛应用.研究纯工质水平管内凝结换热特性对其及其混合物在制冷、空调、热泵方面的应用具有重要意义.文章从理论和实验两个方面,综述了国外对纯工质在水平管内流动凝结换热的研究,分析了凝结换热关联式的适用性和局限性,并提出了进一步研究的建议.     

R290和R22在水平细圆管内流动凝结换热的实验研究

实验研究了R290、R22在细圆管中的流动凝结换热特性。实验管内径为1.085 mm,R22的质量流率为200~1200 kg/(m2·s),R290的质量流率为200~650 kg/(m2·s),饱和温度分别为40℃与50℃。实验结果表明,高质量流率时R22在较高干度下换热系数随干度增加缓慢或略有下降,低质量流率时,R290在较小干度下出现换热系数下降。两种制冷剂蒸气相比,相同条件下R290的凝结换热系数高于R22的。本文的实验结果还与现有典型关联式的计算结果作了对比,其中,Wang et al.(2002)关联式对R290的实验数据预测偏差在17.5%之内,Kim et al.(2013)关联式对R22的实验数据预测偏差在18.4%之内。     

R134a与R410A在空调工况下的性能比较

传统制冷剂R22的替代已是大势所趋.本文着重对R22的替代制冷剂R134a与R410A的传热、阻力压降特性进行实验比较研究,认为R410A在传热、阻力压降特性方面比R134a优良,作为R22的替代制冷剂,R410A应比R134a更有竞争力.     

水平微圆管内R22和R410a凝结压降的实验研究

R410a是一种被广泛看好的R22替代物,研究R410a的凝结压降特性对开发适用此种制冷工质的凝结换热设备有重要意义。搭建了微细尺度凝结压降实验台,实验研究了R22和R410a在内径为0.941mm水平不锈钢圆管内饱和温度为40℃、质量流速为200-1000 kg/m^2.s、干度为0.2-0.8时的凝结压降特性。实验结果表明：凝结压降随着质量流速的增大而增大,在较高干度时更加明显。与R22相比,R410a的凝结压降在较低干度和质量流速时与R22相当,在较高干度和较高质量流速时明显低于R22。     

Stress analysis of a strip with a step and a crack

Stress analysis for a strip of which widths are different at the right and left handsides is carried out for before and after occurrence of a crack at a corner of a step. The strip is analyzed as a thin plate bending problem subject to transverse bending and torsion, and as a plane eleastic problem subject to bending in the plane and uniaxial tension. The rational mapping function of a sum of fractional expressions and complex variable method are used. Stress distribution and stress intensity factors are obtained.     

Dispersion of a solute in a Poiseuille flow of a viscoelastic fluid

Gill and Sankarasubramanian's analysis of the dispersion of Newtonian fluids in laminar flow between two parallel walls is extended to the flow of non-Newtonian viscoelastic fluids (known as Phan-Thein-Tanner (PTT)). Using a generalized dispersion model which is valid for all times after the solute injection, the diffusion coefficient K_i(t) is obtained exactly and numerically for linearized and exponential forms of the PTT fluids, respectively. The analysis leads to the novel result for K₁ and K₂(t) (which is a measure of the longitudinal dispersion coefficient of the solute). It is found that the value of K₂(t) depends on the value of Deborah number (De=a measure of the level of elasticity in the fluid) whereas the value of K₁ is constant in both cases. Finally, the effect of the Deborah number on the axial distribution of the mean concentration θ_m is investigated in detail.     

Strength analysis of a split sleeve in a pipe containing a defect

We study the decrease in the strength of a pipe containing an artificial defect. On the basis of the analytic and numerical models, we consider the influence of the structural features of a split sleeve on its load-carrying ability. We also analyze the joint operation of a sleeve and a pipe containing an artificially made axial surface defect. The results of the numerical analysis are compared with the experimental data. Translated from Problemy Prochnosti, No. 2, pp. 102–111, March–April, 2009.     

Interaction between a liquid and a cylindrical body touching a wall

An exact solution is obtained for the problem of interaction between the ideal liquid homogeneously moving at infinity and streamlining a round cylinder touching a solid wall.     

Imaging a point to a line with a single spherical mirror

Methods for imaging a single point source to a line image are discussed, and a design study of single spherical mirror systems that form aberration-free line images is presented. An expression forthe ray density along the line image is derived for such systems in the cases of (i) uniform beam profiles and (ii) Gaussian beam profiles. The resulting ray density profiles are illustrated for single spherical mirror systems over a wide range of design parameters.     

Calculation of a transient in a two-pole network with a thermistor

An analytical expression is derived which describes the variation of the thermistor temperature during a relay-effect transient process following an instantaneous change in the supply voltage in an R — R_T two-pole network.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 3, pp. 465–472, March, 1980.     

Influence lines for bending under a ring load of a free shell,a shell embedded in a soft medium and a shell containing a soft core

Summary Theoretical expressions for stresses and displacements have been derived for bending under a ring load of a free shell, a shell embedded in a soft medium, and a shell containing a soft core. Numerical work has been done for typical cases with anElliot 803 Digital Computer and influence lines are drawn therefrom.

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Einflußlinien für die Biegung einer freien Schale, einer Schale in einer weichen Bettung und einer Schale mit weichem Kern

Zusammenfassung Für die Biegung einer freien Schale, einer weich gebetteten Schale und einer Schale mit weichem Kern unter einer Ringlast werden Ausdrücke für die Spannungen und Verschiebungen hergeleitet. Die Ergebnisse wurden für einige typische Fälle mit einem DigitalrechnerElliot 803 numerisch ausgewertet. Die sich ergebenden Einflußlinien wurden graphisch dargestellt.

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Nomenclature A (),B () Functions of - a, t Mean radius and thickness of the shell - E _S , _S Young's modulus andPoisson's ratio of the shell - G _c , _c Shear modulus andPoisson's ratio of the casting or core - I ₀ (r),I ₁ (r) ModifiedBessel functions of the first kind and order zero and one respectively - K ₀ (r),K ₁ (r) ModifiedBessel functions of the second kind and order zero and one respectively - p Ring load, lb/in - U, W Displacement components in the casing or core in thez andr direction - u, w Displacement components of a middle surface point in the shell - _r , _rz Radial and shearing stress components - Independent variable of infinite integrals - k [3(1–S ²)a ²/t ²]^1/4 With 13 Figures     

聚醚砜四元制膜液体系的相图计算

以Ｆｌｏｒｙ－Ｈｕｇｇｉｎｓ理论为基础，对ＰＥＳ－ＰＧ－ＮＭＰ＿Ｈ２Ｏ＿）聚醚砜丙二醇－Ｎ－甲基－２－哟咯烷酮水）四元制液体系的相图进行了计算，利用三元相图考察Ｈ２Ｏ和ＰＧ对液－液相分离的影响，在三元的理论的基础上提出了低分子量添加剂的卤元改性Ｆｌｏｒｙ－Ｈｕｇｇｉｎｓ理论，并提出了一种获得四元相图的方法，利用四元相图能较争地描述四元体系，利用改性的四元理论，能了地理解该种体系的液－液相分离行为。