压差效应对焊接密封型称重传感器输出稳定性的影响

本文主要讨论了温度变化引起的压差效应对焊接密封型称重传感器零点输出和稳定性的影响。通过设计的对比实验,验证了焊接密封型称重传感器的零点输出会受到传感器内外压差变化的影响。这些影响包括传感器零点输出误差的变化以及传感器需要更长的零点输出稳定时间。同时,理论分析表明本文实验中采用的密封型传感器的内外压差每增加1k Pa,传感器输出变化大约0.014%FS。本文的研究结果对今后提高焊接密封型称重传感器的精度和稳定性具有一定的参考价值。

机械通风环境中的压差控制

在受控环境中,具备机械通风条件是利用压差效应的基础,但受控环境的通风量(换气次数)与控制压差的大小无绝对的相关性。在调控压差的工作中,需在相关标准及法规文件中的压差管控要求基础上满足受控环境中的特殊工艺要求,并采取“两者取其高”原则,分别评测受控环境的静态和动态工况下的控制情况。因此,压差调控的技能水平是决定受控环境内压差效应作用的重要因素。该研究阐明了通风环境中压差的产生原理及影响压差的关键因素,为压差调控工作提供参考。

深水压力试验中水下设备压力设计

在深水条件下的压差效应会对海底管道系统水压试验中的水下设备造成影响。结合水下阀门、水下连接器的密封特点,介绍了确定水下设备水压试验压力的指导性要求。引入API 17TR11—2015《Pressure Effects on Subsea Hardware during Flowline Pressure Testing in Deep Water》,介绍了5种深水压力试验水下设备压差效应情况。结合API 17TR12—2015《Consideration of External Pressure in the Design and Pressure Rating of Subsea Equipment》,介绍了承受外压情况下水下设备的评估流程。针对南海某深水气田项目,应用上述原则进行了水下阀门和连接器的压力等级设计计算。

微流量测量方法及其技术的发展

归纳了近五年来基于MEMS技术的微流量传感器结构及性能参数。根据国际上热门的研究方法推断微流量测量技术可能的发展方向与研究趋势,即集成两种或两种以上的测量方法,实现优势互补,提高测量精度或扩大量程比。最后基于现有的技术基础,提出了融合科氏效应与差压效应的微流量测量方法,阐述了传感器的工作原理与理论基础,并对其可行性进行了分析与论证。

The twoscale asymptotic error analysis for piezoelectric problems in the quasi-periodic structure

Applications for piezoelectric effect have grown rapidly, and piezoelectric materials play important roles in countless areas of modem life. By means of twoscale method and coupled boundary layer, some new kinds of twoscale asymptotic expansions for solutions to the electrical potential and the displacement in quasi-periodic structure under coupled piezoelectric effect are derived, and the homogenization constants of piezoelectric materials are presented. The coupled twoscale relation between the electrical potential and the displacement is set up, and some improved asymptotic error estimates are analyzed.

Aerodynamic effects of impeller-diffuser axial misalignment in low-flow-coefficient centrifugal compressor

A numerical investigation on the aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor is conducted through three-dimensional CFD analysis.The results show that the flow,especially near the diffuser inlet,is influenced by the axial misalignment obviously.When the impeller offsets to one side,the pressure at diffuser inlet close to this side will descend,and the vortex in the cavity on the other side will partially enter the diffuser and then result in the back flow.The performances of the stage and its components also change with the impeller-diffuser axial misalignment.There exists an optimum offset making the efficiency maximum at a given operating point.Furthermore,the effect of impeller-diffuser axial misalignment on the axial thrust is pronounced.The axial thrust is nearly increased linearly with the increase of axial misalignment.The aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor behaves more remarkably at the large flow rate.To alleviate the aerodynamic effects of impeller-diffuser misalignment,a rounding in the meridional plane at the diffuser inlet can be applied.

Ultrafast photoinduced strain in super-tetragonal PbTiO ferroelectric films

The ultrafast photoinduced strain(UPS)resulting from the coupling of piezoelectric and photovoltaic effects in ferroelectric has been focused in the last decade,endowing them with extensive applications including ultrafast optical memories,sensors and actuators with strain engineering.The mechanism of screening of the depolarization field by photoinduced carriers is generally accepted for UPS in ferroelectrics,while the thermal component of the strain is usually diluted as the offset and has not been systematically confronted,leading to unnecessary confusion.Herein,both the positive and negative thermal expansion effects in composite ferroelectric epitaxial films are investigated by use of high-repetition-rate ultrafast X-ray diffraction,along with the piezoelectric and photovoltaic effects.The coupling of the positive/negative thermal effects and the piezoelectric/photovoltaic effects in ultrafast strain is evidenced and can be regulated.The opposite lattice responses due to different thermal effects of the samples with different axial ratios are observed.The maximum UPS is up to 0.24%,comparable to that of conventional ferroelectric.The interaction between the thermal and ferroelectric effects in the induced strain could promote the diversified applications with the coupling of light,heat and electricity.