十字滑环载荷与失效原因的有限元分析

十字滑环是涡旋式压缩机动涡旋防自转的功能性零件,十字滑环直接影响涡旋式压缩机动静涡旋的啮合。为了研究十字滑环的载荷和应力分布,本文通过理论分析十字滑环凸键处所受应力,并采用Unigraphics NX10.0对十字滑环凸键的应力分布进行有限元分析,结合以往的可靠性试验,发现十字滑环的危险位置在其环臂上。进一步对十字滑环受载时的变形作出分析,得出十字滑环环臂位置是在周期性的弯曲应力作用下疲劳失效的结论。研究结果对压缩机十字滑环的失效原因分析以及设计优化提供有力的理论支撑。     

蒸汽压缩/喷射制冷系统喷射器设计及节能分析

蒸汽压缩/喷射制冷系统是一种有效的节能系统,可以减少节流膨胀损失,降低压缩机压力比,提高制冷系统效率。选择5种计算工况对蒸汽压缩/喷射制冷系统进行计算,研究喷射器结构与蒸发温度和冷凝温度的变化规律,并与普通蒸汽压缩系统对比,从制冷量、压缩机耗功、性能系数三个角度分析新系统的节能效果。计算结果表明蒸汽压缩/喷射制冷系统在低温工况条件下节能效果最优,制冷量最大可提高29%,压缩机耗功最大可降低65%,COP值最大可提高63%。     

滚动转子压缩机摩擦噪声数值模拟及试验研究

为了解空调转子压缩机摩擦噪声的产生机理,开展油润滑条件下压缩机各个摩擦副摩擦系数的试验研究。采用销-盘试验机测量不同转速下各个摩擦副的摩擦系数。建立全尺寸转子压缩机摩擦噪声的有限元模型,运用复特征值分析方法研究压缩机摩擦噪声的产生机理。结果表明：在一定相对转速范围内,摩擦系数随相对滑动速度增大而减小,即存在摩擦系数相对于滑动速度曲线显现负斜率特性,这个负斜率特性可能是引起压缩机摩擦噪声一个原因。     

滚动转子压缩机摩擦噪声数值模拟及试验研究

为了解空调转子压缩机摩擦噪声的产生机理,开展油润滑条件下压缩机各个摩擦副摩擦系数的试验研究。采用销-盘试验机测量不同转速下各个摩擦副的摩擦系数。建立全尺寸转子压缩机摩擦噪声的有限元模型,运用复特征值分析方法研究压缩机摩擦噪声的产生机理。结果表明：在一定相对转速范围内,摩擦系数随相对滑动速度增大而减小,即存在摩擦系数相对于滑动速度曲线显现负斜率特性,这个负斜率特性可能是引起压缩机摩擦噪声一个原因。     

高温压缩机变转速的复叠式热泵系统性能实验研究

为研究变转速压缩机对复叠式热泵系统的影响,本文搭建了高温压缩机变转速的复叠式热泵实验台。通过实验研究了不同运行工况下系统排气温度、中间温度、制热量、功率及COP随高温压缩机转速的变化规律。结果表明:在冷凝温度为46℃,蒸发温度为-35℃～-10℃时,压缩机运行安全可靠;在冷凝温度为46℃,蒸发温度为-25℃,高温压缩机转速从1 200 r/min增至6 000 r/min,制热量提升了129. 7%,低温压缩机功率减少43.4%; COP随高温压缩机转速的增加呈先增大后减小的趋势,存在最大COP和对应的最佳高温压缩机转速。     

跨临界二氧化碳压缩机热力性能仿真与分析

针对跨临界二氧化碳半封闭式往复式活塞压缩机建立了一个通用数学模型,既包括热力学模块,也包括机械模块。热力学模块主要描述气缸内部的气体压缩过程。机械模块包括运动学模型和曲轴连杆机构模型,考虑了轴承上的功耗损失。采用一台压缩机样机对模型进行了不同运行工况下的实验验证,结果显示压缩机流量和耗功的最大误差分别不超过5%和8%。通过仿真分析了变结构和变工况条件下的压缩机性能,结果表明:在不同的运行工况下,存在最佳缸径行程比;容积效率和等熵效率都随着转速的增加而下降;吸排气阀门内径存在最佳值;对于容积效率的影响,吸气阀间隙比排气阀间隙更大,活塞与汽缸间隙比活塞环与汽缸间隙更大。     

R410A回热循环的热力分析

R410A是一种新型环保的制冷剂,针对R410A回热循环方面的性能加以分析。将不采用回热循环时的单位容积制冷量、单位容积压缩机耗功、COP与回热循环后的参数做比较,得出单位容积制冷量、单位容积压缩机耗功、COP随回热蒸发温度及回热过冷度变化时的变化情况,对R410A是否采用回热循环及在什么情况下采用回热循环具有一定意义。     

土壤源VRF空调系统冬季运行特性实验研究

以土壤源VRF空调系统为研究对象,利用土壤源VRF实验台对其冬季运行特性进行了实验研究,分析在不同开机率时,小时制热量、小时耗功量、机组COP随部分负荷率的变化规律。结果表明:小时制热量与小时耗功量随开机率的升高基本呈现增大趋势,且耗功量对开机率的变化更为敏感;不论室内机的开启率为何值,小时制热量随部分负荷率的增大而增大,小时耗功量、机组COP随部分负荷率的增加呈现下凹、上凸的变化趋势,即土壤源VRF空调机组在部分负荷运行条件下具有较为良好的节能性。     

A11VO190轴向柱塞泵滑靴副摩擦特性的研究简

 为了分析A11VO190恒功率轴向柱塞泵滑靴副的摩擦特性,建立了剩余压紧力滑靴的数学模型.在考虑由热膨胀引起的热楔力和由阶梯结构引起的动压效应的基础上,根据空间力系平衡原理,利用软件Matlab计算滑靴在排油区的动态特性,得到滑靴在斜盘不同位置的油膜厚度.在此基础上推导出滑靴副摩擦功率损失和泄漏功率损失的计算公式,并对比不同负载压力和主轴转速对油膜厚度和功率损失的影响.结果表明：负载压力增大,油膜厚度减小,功率损失增加;转速增大,油膜厚度增大,功率损失也随之增加．     

机房空调室内外机间配管长度对机房空调性能影响的研究

以名义制冷量为71.4kW的制冷机组为对象,研究室内外机管长在水平和垂直方向变化时,系统制冷量、压缩机耗功的变化情况,从而为需要配置长配管的系统管长的确定提供参考.计算结果表明,压缩机耗功随着配管长度的增加而增加,系统制冷量变化与管道的水平或垂直方向有关.     

驱动轴承内嵌式涡旋压缩机特性分析

对驱动轴承内嵌于动涡旋齿中的涡旋式压缩机的几何特性进行了研究分析，引入了涡旋型线始端展角和终端展角，使吸气容积、吸气角、排气容积、排气角、内容积比等几何参数计算式的应用更为方便，它不仅适用于涡旋型线为整数圈的情况，而且也适用于涡旋型线为非整数圈的情况。将动涡旋的驱动轴承安置于涡旋齿中，可以在结构设计上达到减少气体力和动涡旋离心惯性力对动涡旋产生的倾覆力矩的目的，从而改善了驱动轴承的受力状况。延长了使用寿命。     

The effect of scroll wraps on the performance of scroll compressors

A number of geometrical curves have been used to form the wraps of scroll compressors. When the suction pressure, pressure ratio, scroll wrap height and thickness, and suction volume are constant, the effect of the involute curves of a cricle, square and line segment on the performances of the scroll compressor, such as geometrical parameters, leakage line length and various gas forces acting on the orbiting scroll are analysed in this paper. The effects of these scroll wraps on the performance of the scroll compressor vary as the suction volume changes. The results in this paper should be considered in scroll compressor design.     

Dynamic model for the orbiting scroll based on the pressures in scroll chambers – Part II: Investigations on scroll compressors and model validation

This two-part study proposes a dynamic model for the orbiting scroll based on the pressures in scroll chambers. Part II investigates scroll compressors by using the dynamic model developed in this work to predicate the dynamic characteristics of the scroll compressors and the dynamic model is validated by comparing the predicted results with the experimental results of the powers of two air scroll compressors. This study utilizes two air scroll compressors and ten virtual scroll compressors to investigate the pressure distribution on the wrap surfaces of orbiting scrolls, the component forces and moments of orbiting scrolls, the overturning moment of the scroll mechanism, and the theoretical driving power of scroll compressors. The effects of scroll type (such as modified-wrap scroll, truncated-wrap scroll, single-wrap scroll, multi-wrap scroll, odd-wrap scroll, and even-wrap scroll) on the dynamic performance of the scroll compressor based on the pressures in scroll chambers are also analyzed.     

Analysis of thrust bearing in high-side shell type scroll compressor

A thrust bearing of a scroll compressor plays an important role in reliability and efficiency of the scroll compressor. In the case of high-side shell type scroll compressors, the back pressure mechanism without tip-seals is adopted for the sealing in the axial direction between a fixed scroll and an orbiting scroll. Therefore, the lower surface of the fixed scroll becomes a thrust bearing, and the shape and boundary conditions of the thrust bearing are changed successively during one cyclic motion of the orbiting scroll. In this study, the pressure distribution on the thrust bearing is analyzed numerically with real bearing shapes and boundary conditions using the Finite Element Method, and then Newton's method is applied to solve three-degrees-of-freedom motion of the orbiting scroll using the theoretical gas forces. From the results of this analysis, the “overturning coefficient and thrust load map” is proposed to ensure the normal operation of the thrust bearing in the high-side shell type scroll compressors.     

Deformations of Working Elements in Oil Free Scroll Vacuum Pumps

The mechanical and thermal causes of deformations of the orbiting and the fixed elements of oil free vacuum pumps are considered. Basic data for deformation calculation are geometric dimensions of the pump and dependence of working chamber volume on the orbiting scroll element rotation angle. Gas temperature and pressure values in each vacuum pump chamber are obtained with the help of a working process mathematical model. Deformation calculation is carried out by the finite element method realized in the software ANSYS. It is shown that deformations caused by pressure‐induced mechanical forces do not have considerable influence on the change of radial clearances between the scrolls. They may not be taken into account for pumping characteristics calculation. Thermal‐induced deformations are much greater, and the change of the clearances due to this cause may be 25 % and even larger.     

Experimental investigation on convective heat transfer mechanism in a scroll compressor

This paper describes an experimental study on the convective heat transfer inside the scroll compressor. An experimental refrigeration system is composed with extensive instrumentations in the compressor that is operated at variable speeds. The 13 thermocouples installed inside the compressor monitor the temperatures of the scroll wrap during compression process of refrigerant. The temperature and the pressure of refrigerant at suction, and the pressure at discharge ports are measured, and applied to the numerical simulation as the operating condition parameters. The temperature measured at the discharge port is used to verify the simulation result with relevant heat transfer coefficient. This paper describes the effect of motion of the orbiting scroll on the convective heat transfer in the scroll wraps. Separate experiments are performed to investigate the heat transfer in such a peculiar physical condition. With this experimental result, the effect of the oscillation of the wall on the heat transfer is quantitatively analyzed and applied to the simulation of compression process in scroll compressor. The whole consecutive compression processes in the scroll compressor is simulated in detail by solving equations of mass and energy balance for the refrigerant. The modified heat transfer coefficient correlation considering the effect of motion of the orbiting scroll predicts the discharge temperature better than other typical heat transfer coefficients.     

Design, Construction and Calibration of a Triaxial Dynamometer for Measuring Forces and Moments Applied on Tillage Implements in Field Conditions

In this research, a dynamometer was designed, constructed and calibrated to measure the forces and moments applied on tillage implements. This dynamometer is able to measure the three orthogonal forces acting on the implement and the three moments acting around the orthogonal axes, up to a maximum force of 20 kN and a maximum moment of 20 kN m. The dynamometer uses two extended octagonal ring transducers mounted in a back-to-back arrangement with their axes at right angles and has a tubular torque meter for torque measurement. For mechanical design of the dynamometer frame and its units, the finite element method and CATIA software were used. The device was machined from the solid part and high tensile steel. The forces and moments acting on the dynamometer were measured by using the strain gauge bridges on two extended octagonal ring transducers and on the torque meter tube. The results of data analysis, including forces applied on the dynamometer, the designing method of rings and torque meter tubes, the mounting arrangement of load cell parts on each other, the mounting method of load cell on frame and the position of strain gauge on load cell, in other words, the position of different parts of the dynamometer relative to each other has been explained in this paper. Calibration of the measurement unit was done by a calibration system which was designed for static calibration of the triaxial dynamometer. The results of calibration of the measurement unit showed that the designed and constructed dynamometer has appropriate precision, sensitivity and good repeatability for measuring the desired forces and moments. The results showed a high degree of linearity between output voltage of bridges and applied forces and moments. The interaction effects of the applied forces and moments were very negligible.     

Dynamic model for the orbiting scroll based on the pressures in scroll chambers–Part I: Analytical modeling

This two-part work proposes a dynamic model for the orbiting scroll based on the pressures in the scroll chambers. In Part I, the scroll mechanism and characteristic polygon of the scroll compressor are defined, the geometry of the multi-wrap compressor is described, the modification and construction methods for one multi-wrap scroll are presented, and the dynamic model is developed. Thereafter, the overturning moment and theoretical driving power of the scroll mechanism are discussed. This dynamic model can predict the pressure distribution on wrap surfaces as well as the variations of the axial force, tangential force, radial force, overturning moment, self-rotation moment, and resistance moment. This dynamic model provides better understanding of scroll compressors and other types of scroll machines. The investigations on scroll compressors using this model and the model verification are reported in Part II.     

Moving Water Droplets Over Nanoscaled (Super) hydrophobic Wettability Contrasts: Experimental Test of a Simple Model Describing Driving Forces

Applying advanced nanolithography techniques, various arrays of nanopillars on top of Si‐wafers are fabricated with all geometric parameters on the nanoscale. Additional chemical functionalization together with control over areal pillar density, height, and diameter allows the preparation of superhydrophobic surfaces exhibiting a wide range of contact angles (CA). Further improvement of this approach enables the production of step‐like wettability contrasts involving various CB–CB (Cassie‐Baxter) and CB–S (Smooth substrate)‐transitions. Such samples in combination with a high‐speed camera allow studying under optimized conditions quantitatively additional driving forces acting on a water droplet due to CA gradients. Experimentally it turns out that the maximum driving force on the droplet is well predicted by a simple model assuming circularly‐shaped base lines during the passage of a step‐like gradient of wettability. The provided study permits a comparison between maximum retention forces when tilting the substrate up to a critical angle and the presently determines maximum driving forces acting on a droplet due to a step‐like CA gradient. Both situations can be nicely described by a joint linear relation between normalized forces and CA hysteresis values with a slope close to theoretical values.     

Scroll profiles in scroll compressors: General criteria and error sensitivity

General criteria for scroll profiles that include the evolute, orbiting movement, differential, and integrative conditions are proposed. The profile error sensitivity is defined based on the composite meshing error and meshing clearances of the scroll profiles. A case study on regular polygon involutes as scroll profiles indicates that the general criteria are satisfied when the edge number of the two involutes of a regular polygon is equal to the common multiple of the doubled number of scroll wraps on one scroll. The profile error sensitivity of the involutes of a base circle is shown to be controlled by the radial machining error, which is extremely low. The involute of a base circle is the ideal profile for a scroll compressor because it contains low error sensitivity and more stable dynamic characteristics.