汽轮机凝汽器冷却水流量的在线测量方法研究

凝汽器冷却水流量对汽轮机运行经济性和安全性产生很大的影响,冷却水流量的在线测量目前尚无成熟的方法。提出借助于冷却水管路与凝汽器之间的连接弯管对冷却水流量进行在线测量。首先对流体在弯管内流动的自由涡流理论和强制涡流理论进行了分析,给出了弯管的理想流量与弯管内外压差之间的关系式。然后借助于数值模拟软件FLUNT,对流体在弯管前后以及弯管中流动过程中的速度和压力分布进行了数值模拟,指出弯管前后流体的速度和压力分布的不均匀性比较小。最后,以某300MW汽轮机为例,研究通过弯管流量与弯管内外压差之间的关系。结果表明,尽管进入凝汽器的冷却水弯管前后直管段均较短,但其流量系数随流量变化基本不变。从而证明可以借助于冷却水管路弯管内外压差实现对冷却水流量的在线测量。     

A method for the evaluation and magnified representation of two-dimensional contouring error

The method of evaluating two-dimensional contouring error between the reference trajectory and the trajectory measured with a cross-grid encoder and magnifying the error is widely used. However, this method has a problem in that the inner cornering error is discontinuously magnified and represented and thus is not accurately detected. Several methods have been proposed to solve this problem, but they have limitations, such as the requirement that an offset value be set or the imposition of conditions on the reference trajectory. Therefore, by calculating errors in the inward direction from a longer trajectory to a shorter trajectory, this paper proposes a new method to continuously magnify and represent the inner cornering error including the corner vertex without the need to set an offset or the imposition of conditions on the reference trajectory. The proposed method was applied to the measurement results at an actual machining center. Consequently, the inner cornering error was continuously magnified and represented, and the error at a corner was accurately calculated using the proposed method.     

A new mass & time primary standard for natural gas in China and the uncertainty evaluation

A new mass-time primary standard for high pressure natural gas, which is based on electromagnetic balance and hydraulic fast-acting valves, was set up at the beginning of 2017 in Chengdu, China. The full load of the electromagnetic balance is 3 tons and the measurement uncertainty of mass is better than 1.0g(k = 2). The opening and closing time of the hydraulic fast-acting valves can achieve 33 ms±3 ms.The operation pressure and flowrate range of the facility is (4–60)bar.a and (5–410)m³/h respectively. In accordance with the preliminary tests, the estimate uncertainty of sonic nozzles calibration is between 0.10% and 0.12%(k = 2). The operation principle, testing results and the uncertainty evaluation are presented in the paper as well as some improving ideas.     

A naphthalene sublimation study on heat/mass transfer for flow over a flat plate

It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburnj-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburnj-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.     

相序检测的极速算法

醉提出了一种相序检测的新算法，该算法运算极快，使相序检测的速度提高了1000至10000倍，可广泛运用于数字化检测之中。     

科里奥利颗粒料质量流量计流量公式理论分析

本文通过对科里奥利固体颗粒料质量流量计的结构分析，认为该流量计无法获取实时的质量流量，并对公开的瞬时流量计算公式进行了理论分析，说明其理论上的缺陷，给出了详细的推证过程和更为精确的理论计算方法和措施。     

Modification of the equation for mass flow rate (mass) measurement of liquid with account of dynamic influencing factors

The paper introduces theoretical foundations for the method of transferring units of mass and volume of liquid in the flow, mass and volumetric liquid flow rates using the indirect measurement method. The equation for measuring the mass flow rate (mass) was modified in terms of assessing the dynamic influencing factors caused by transient processes: liquid flow rate fluctuations and turbulent pulsations, unevenness of the liquid velocity profile in the nozzle exit of the diverter. The modified equation was derived from the continuity equation in physical and mathematical modeling of hydrodynamic processes of liquid flow in the nozzle exit of the diverter using mathematical statistics methods. The main uncertainty sources of calibration units with weighing devices were identified. The results of the approbation of the method of transferring units of mass and volume of liquid in the flow, mass and volumetric liquid flow rates were obtained on calibration units with weighing devices in a wide range of geometric and operating parameters. A comparison of the expanded measurement uncertainty of the calibration unit with weighing devices when transferring units of mass and volume of liquid in the flow, mass and volumetric liquid flow rates, determined using the method of indirect measurements and comparison testing with a transfer standard, was performed.     

A study of signal noise reduction of the mass air flow sensor using the flow conditioner on the air induction system of heavy-duty truck

The mass air flow meter is a critical sensor that works based on thermal hot wire technology, used to determine the fuel to be injected into the cylinder and calculate the fuel-air ratio. In order to measure the airflow rate accurately, the flow should be uniform and smooth upstream of the sensor. The flow disturbance with a short straight length upstream of the flow meter results in the noise of the sensor signal. This noise causes unstable mass flow measurement on the system. Flow conditioners can be used to smooth the velocity profile of the flow. In this study, experimental and numerical methods were used to characterize the performance and operating accuracy of the mass flow meter used in heavy-duty truck applications. The flow conditioners were implemented to smooth the velocity profile around the mass flow meter that was disrupted by bends. The flow structures with and without flow conditioner were examined using Particle Image Velocimetry (PIV) to measure the time-averaged velocity. As well as the validated computational fluid dynamics (CFD) model provides data to understand the flow uniformity effect of the conditioner on the mass airflow (MAF) sensor. The optimization study was performed using a full factorial design of experiment (DOE) for flow conditioner design. A robust methodology was developed for the flow conditioner characteristics and mass airflow sensor implementation on the air induction system.     

A modified fractional step method of keeping a constant mass flow rate in fully developed channel and pipe flows

The objective of this paper is to present a modified fractional step method of keeping a constant mass flow rate in spatially periodic flows, because original fractional step methods do not precisely keep the mass flow rate constant in time. In the modified method, the mean and fluctuating pseudo-pressure gradients are separately obtained at each time step. This method is successfully applied to channel and pipe flows and shown to be suitable for maintaining a constant mass flow rate in time.     

Review of techniques for the mass flow rate measurement of pneumatically conveyed solids

An accurate, reliable, on-line, continuous and non-invasive measurement of solids’ mass flow rate in pneumatic conveying pipelines has been a technically challenging area, which becomes increasingly significant to achieve efficient utilization of energy and raw materials and to reduce waste. Energy and environmental regulation and legislation, and efficiency and waste reduction are two most powerful drivers in the academic research and industrial applications for solids’ mass flow meters. In this paper, a review is presented on the recent measurement techniques of solids’ mass flow rate measurement in pneumatic conveying systems. On basic principle and configuration of each technique, performances and limitations of these techniques in industrial applications are analyzed and compared from different views to demonstrate the recent developments in the field and the possible approaches which may provide solutions to the solids’ mass flow measurement problem.     

Measurement of mass flow rate and evaluation of heat transfer coefficient for high-pressure pneumatic components during charge and discharge processes

Both the mass flow rate and heat transfer characteristics are significant factors to the flow behavior of the high-pressure air; however, they are not easy to be obtained by analytical model during discharge and charge processes. In this paper, the mass flow rate characteristics of high-pressure pneumatic components (HPPC) are measured by a compounding approach; two components under test with the same geometry and dimension are needed to be connected in series. Both the effective cross-section area and critical pressure ratio of HPPC are determined accurately, and only the pressure variation and the steady-state temperature of air in the chamber are utilized. The compared results between experimental and simulation data show that the accuracy of the measured effective cross-section area and critical pressure ratio of the HPPC is high when the sonic and adiabatic releasing time is less than 2 s. And then, a new combined method of calculating the heat transfer coefficient during discharging and charging processes for the high-pressure air is proposed. The computational fluid dynamics (CFD) method is used to illustrate the intensity of heat exchange between the high-pressure air inside the chamber and outer atmosphere. The dynamic flow behavior is analyzed based on the tested flow rate characteristics of HPPC, mixed heat transfer theory and numerical results. The results show that the heat-transfer coefficient during charge process is much greater than discharge process, and the forced convection heat exchange happened owing to the strong “air agitation” during the charge process. The experimental results also validate that the proposed method of calculating the transient heat transfer coefficient is more reasonable to describe the heat transfer behavior. The findings may also have general implication in the development of the design and analysis of the high-pressure pneumatic system.     

大批量定制合作伙伴的小波网络综合评价方法

为客观地综合评价合作伙伴,建立了大批量定制环境下合作伙伴的评价指标体系.在此基础上提出了一种基于小波网络的合作伙伴多指标综合评价方法,并结合案例,对大批量定制企业合作伙伴的选择进行了较为客观的评价.最后,给出了该方法与层次分析法和前馈神经网络法的对比.仿真实验表明,该方法不仅能够模拟专家对合作伙伴进行综合评价,避免评价过程中的人为失误,还具有比前馈神经网络法更好的质量和更高的效率.     

A study on the analysis of O-ring under uniform squeeze rate and internal pressure by photoelastic experimental hybrid method

There are three kinds of loading conditions applied to the O-ring, The first loading condition is the case in which uniform squeeze rates are applied to the upper side and the lower side of the O-ring (the strain condition). The second loading condition is the case in which uniform squeeze rates are applied to the upper side and the lower side of the Oring and other squeeze rates are applied to the front side of the O-ring. The third loading condition is the case in which uniform squeeze rates are applied to the upper side and the lower side of the O-ring, other squeeze rates are applied to the front side of the O-ring, and internal pressures are applied to another front side of the O-ring(loading condition is the combination of stress condition and the strain condition). In this research, a new photoelastic experimental hybrid method under the third loading condition was developed and it was verified. The stresses of the O-ring under the third loading condition were analyzed by the new photoelastic experimental hybrid method developed in this research. The internal pressures applied to the O-ring were 0.98 MPa, 1.96 MPa, 2.94 MPa and 3.92 MPa. This paper was recommended for publication in revised form by Associate Editor Jooho Choi Jai-Sug Hawong received a B.S. degree in Mechanical Engineering from Yeungnam University in 1974. Then he received his M.S. degree and Ph.D. degree from Yeungnam University in Korea in 1976 and from Kanto Gakuin University in Japan in 1990, respectively. Prof. Hawong is currently a professor at the school of Mechanical Engineering at Yeungnam University, in Gyeongsan city, Korea. He is currently serving as an vise-president of Korea Society Mechanical Engineering. Prof. Hawong’s research interests are the areas of static and dynamic fracture mechanics, stress analysis, experimental mechanics for stress analysis and composite material etc.     

A two-dimension velocity field measurement method for the thermal smoke basing on the optical flow technology

The confine and heat are remarkable features in building fire research, as well as is a barrier for flow velocity profiles measurement, which the general method is unsuitable for this experimental environment. Therefore, this paper develops a measurement method for the acquisition of the thermal smoke flow velocity profiles in the fire building experiment. Firstly, we utilize the smoke itself particle distribution to replace the manual track particles in which reduce the complexity of the measurement method for fire experiments system. Secondly, we optimize the non-uniform distribution of smoke soot particle and utility the smoke stratification characteristics basing on the optical flow technology. The four optimized methods were compared to acquire reasonable smoke velocity distributions. Finally, we take advantage of filter post-process method to smooth the smoke velocity profiles in the main transportation direction. Moreover, a series of experiments and simulations show the feasibility of this image-based method in which the pre-process, optical calculation and smooth methods were established to denote reasonably the smoke flow velocity gradient and inclined upward trend nearby the corridor open. Meanwhile, it is not only in acquiring two-dimension smoke field velocity, while also can fulfill the other particle flow movement.     

A novel method for the evaluation of stress-optic coefficient of commercial float glass

The measurement of residual stress in float glass is important in glass industries as they affect their cutting quality. Photoelasticity can be used for residual stress analysis of float glass as they exhibit stress induced birefringence. Stress measurement using photoelasticity necessitates the knowledge of the stress-optic coefficient of float glass. Carrier fringe method in conjunction with digital photoelasticity is used for the photoelastic calibration of float glass. The conventional method of photoelastic calibration is improved to calibrate float glass with residual stress which eliminates the need for annealing them. The new method developed is self consistent as the results are verified by the reconstruction of the composite fringe pattern. The use of the improved method is recommended for calibration of float glass as it takes into account the residual stress in glass sample apart from its potential for automation.     

Numerical analysis for prediction of flow rate of the motor cooling fan

In this study, we analyzed the three dimensional unsteady flow around a motor cooling fan using the vortex panel method. For a popular type of motor cooling fan that has thin blades, we predicted the flow rate through numerical analysis without experimental data, such as the free stream velocity, which is a boundary condition of the flow field. We also calculated the flow rate for various cooling fan geometries and rotating speeds. For these fans, the numerical results showed flow rates within 3% of the experimental results. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

吸附管/气相色谱/质谱法分析纵火案的纵火剂残留物

用吸附管(AT)/气相色谱(GC)/质谱(MS)法检测纵火残留物中轻质矿物油是通过吸附管动态吸附检材中可挥发的有机物,然后通过热脱附将挥发物送至GC及GC/MS中检测。它既适用于轻组分的碳氢化合物,如汽油,也适用于较高分子的碳氢化合物,如柴油和煤油。用沸石预处理样品克服了样品中水分对鉴定的干扰。用本方法能够得到比过去所使用的溶剂提取法或顶空法(HS)更高的吸附效率和灵敏度,解决以往由于残留物中热解产物干扰所造成的GC图形混乱复杂,难以准确分析鉴定的问题。用本方法分析纵火或火灾案件中常见的残留物——轻质矿物油,具有快速、灵敏、准确和简便等特点,可广泛用于公安、司法和保险等各个领域。     

An improved model for the frequency estimate of mass-loaded plates by a combined use of equivalent center mass and stiffness factors

In this paper, an improved model is developed to determine the frequency of vibrating plates carrying multiple masses at various positions. By virtue of an equivalent-center method, the frequencies of the plates carrying multiple masses can be predicted by using merely the data obtained earlier for the same plate with each corresponding mass component. Further accounting the change of the strain energy into the model and by introducing respective stiffness ratios, one can obtain a quick and better estimation of the loaded plates with various boundary conditions. The proposed model is validated through experimentation of a rectangular clamped plate carrying concentrated masses. Analytical and experimental results for the plate system are compared and discussed. It is found that the change in the strain energy should be incorporated in the model, especially for cases of large masses placed on a thin plate, in order to predict well the natural frequency of the amalgamated system from those of the component systems. The excellent performance of the proposed model is due to the fact that the effects of both the different masses and their locations on the frequency have been accounted for, implicitly, in the respective equivalent center mass and stiffness factors. Although the model considered is rather simple, the proposed methodology can be extended to plates with other geometry and configurations.     

核能海水淡化源蒸汽质量流量的测量与新的密度补偿式

本采用汽液两相流均相流动的模型,分析了涡街流量计在核能海水淡化源汽的捏流量测量中的适用性,并结合低压和蒸汽的热物理性质,论述了涡街流量计测量低压饱和蒸汽质量流量的误差一蒸汽干度之间关系。给出了一个用于低压饱和蒸汽质量流量测量的变系数密度补偿式和该补偿式的特色。