低功率确定弯管流量计测量蒸汽流量标定数据的实验及其应用

本文介绍弯管流量计确定标定数据的实验方法,尝试新的计算方法,得到较精确的标定数据.     

LNG energy transfer uncertainty–sensitivity to composition and temperature changes

Determining and reducing the measurement uncertainty of LNG energy transfer in custody transfer operations is considered extremely important and challenging for industry. The European Metrology Research Programme (EMRP) for Liquefied Natural Gas (LNG) has been focused on reducing the uncertainty in the evaluation of LNG energy transfers by improving existing measurement methods, validating new measurement methods and development of new traceable calibration systems. Part of this project was to produce realistic measurement uncertainty budgets and to determine the sensitivity of the overall LNG energy transfer uncertainty to changes in the composition and temperature of different LNG cargoes.This paper provides details on the development of an uncertainty budget and the results from the sensitivity study. It was found that the uncertainty in the LNG energy transfer ranged from 0.56% to 0.77% when using the uncertainty budget for 461 LNG cargoes. The variation was mainly due to the difference in the LNG composition and its associated uncertainty.     

Influence of upstream disturbances on performance of an LDV-based cryogenic flow meter standard – CFD modelling and preliminary measurements with air

Increasing trade of liquefied natural gas (LNG) imposes stringent requirements for accurate flow rate measurement of this high energy content fluid. To satisfy this demand, a flow meter has been developed by CEASAME Exadebit which is based on velocity measurement behind a contraction nozzle using Laser Doppler Velocimetry technique (LDV). For this instrument, a calibration factor is defined relating the measured velocity to the flow rate. This calibration factor depends on the Reynolds number and it can be sensitive to the velocity profile behind the nozzle outlet and to presence of upstream flow disturbances such as bends, valves, etc. when the meter is installed on-site. In this paper, CFD modelling, using OpenFoam software, was employed to analyse the sensitivity of the calibration factor to flow disturbances for two types of disturbing elements; a U-bend and half-plate orifice. The CFD model was validated by comparison with experimental data for the calibration factor and velocity profiles obtained from preliminary LDV measurements with air. Two measurement setups were considered where the velocity is measured either in one point at the nozzle axis or integrated along a line across the nozzle diameter. The results show that the considered disturbing elements cause deviations in the calibration factor in the order of tenths of percent and that the maximal sensitivity of the line-setup to these disturbances is approximately half of the maximal sensitivity of the point-setup. On the other hand, it was shown that the line-setup is more sensitive to the LDV positioning than the point-setup.     

微通道中液氮的流动沸腾——换热特性分析

对微通道中液氮流动沸腾换热特性进行试验研究和分析。给出典型的沸腾曲线,分析壁温、干度和换热系数沿微通道管程的变化规律,考察热流密度、质量流量和压力对流动沸腾换热的影响。将126个试验数据点与四个换热关联式比较,并对微通道中流动沸腾换热机理进行分析。结果表明,在多数情况下干度和热流密度对沸腾换热系数的影响较小,换热系数主要决定于质量流量和压力,随两者增加而增加,换热以对流蒸发为主导机理。KLIMENKO关联式预测效果最好,TRAN微通道关联式次之,对常规管道得到广泛使用的CHEN关联式和SHAH关联式都远远高估了试验值。基于两相流压降和换热特性分析,推知微通道中的两相流流型不同于常规管道：在低干度情况下,流型以弥散泡状流为主;而在高干度情况下,流型以由雾状汽芯和不规则液膜组成的环状流为主。     

微细通道内液氮流动沸腾的流型特性

采用高速摄像,得到内径为1.931 mm、1.042 mm、0.531 mm的竖直上升圆管内液氮流动沸腾的主要流型为泡状流、弹状流、搅拌流和环状流;并且在1.042 mm、0.531 mm管内发现受限气泡流。并绘制流型图,分析表面张力,压力和管径对流型转变的影响。表面张力是影响流型转变的重要物性参数,相对于空气—水的流型图,对应的弹状流/搅拌流,搅拌流/环状流流型转变线向较低的气体表观速度方向移动;而泡状流/弹状流的转变线向较高的气体表观速度方向移动。压力越高,相应的流型转变曲线向较低的气体表观速度方向移动。管径对流型转变有重要影响,随着管径的减小,相应的流型转变线向较低的气体表观速度方向移动。试验结果与通用的流型转变理论模型作比较,发现理论模型的预测结果与试验结果相差较大。     

Experimental studies on cryogenic recycling of printed circuit board

Printed circuit board (PCB) recycling is an important challenge for today’s industry. This paper presents results from a study of cryogenic decomposition as a potential alternative recycling method for obsolete printed circuit board scraps. In this method liquid nitrogen is employed as a cryogen to form an environment as low as 77 K for PCB treatment. In order to test the effect of thermal stress set-up during the rapid cryogenic treatment, impact tests were used to simulate the current shredding process. The treated PCB scraps were investigated under a monocular microscope with a 200X magnitude for micro-crack effect observation. Fatigue behavior of the boards was also examined by repeating the cryogenic treatment. The experimental results, as analyzed, demonstrated no obvious support to this alternative PCB recycling method. The energy absorbed during the impact tests for the cryogenically treated boards is insignificantly different from those without the treatment.     

微通道中液氮的流动沸腾——两相流动压降分析

对液氮在直径为0.531 mm,加热长度为250mm的圆管中的流动沸腾压降和传热特性进行研究.作为第一部分,主要对微通道中液氮的两相流动压降进行试验研究与分析.结果表明:在核态沸腾起始时,质量流量迅速降低,而压降突然增大,并伴随着明显的温度滞后,幅度约为4.0～5.0 K.由于压降很大,在微通道内液氮的两相流动中会出现闪蒸,从而对质量干度产生重要影响.最后,利用均相模型和三个两相流动模型(L-M模型,Chisholm B系数模型和Friedel模型)对微通道沿程压降进行分析和比较.不同于常规通道的是,均相模型可以很好地预测压降试验结果,而三个两相流动模型的预测偏差较大,这是由于在微小通道中的高速流动情况下,汽相和液相混合比较均匀;同时液氮的液汽密度比很小,这也有利于均相模型的预测.     

Ultrasonic pulse-Doppler flow meter application for hydraulic power plants

At hydraulic power stations, Pitot tubes have commonly been used to measure flow rates in steel penstocks for performance testing of hydraulic turbines. Due to the difficulties of Pitot tube installation, transit-time ultrasonic flow meters are becoming a popular replacement, but their accuracy is sensitive to velocity profiles that depend on Reynolds numbers and pipe surface roughness. Ultrasonic pulse Doppler flow meters have recently gained favor as suitable tools to measure flow rates in steel penstocks because they can measure instantaneous velocity profiles directly. Field tests were conducted at an actual hydraulic power plant using an ultrasonic pulse Doppler flow meter, and it was found capable of measuring velocity profiles in a large steel penstock with a diameter of over one meter and Reynolds number of more than five million. Furthermore, two ultrasonic transducers were placed on the pipe surface to validate the multi-line measurement of asymmetric flow. Each transducer recorded the velocity profile simultaneously from the pipe centerline to its far wall during plant operation. Velocity profiles were obtained from three-minute measurements to improve the accuracy of flow rate measurements.     

热量表检定的现状和发展

本文介绍了热量表检定工作的现状,阐述各种检表方式以及优缺点,并结合热量表,交流热量表关于检定的思考和体会.     

Calibration procedures and uncertainty analysis for a thermal mass gas flowmeter of a new generation

This paper deals with the differences between traditional and new technology gas meters, and focuses specifically on the calibration procedure and uncertainty evaluation of CTTMFs (Capillary Type Thermal Mass Flow Meter). In particular, measurements performed on a sample set of commercial CTTMFs for natural gas in domestic/residential (G4) applications allowed to evaluate the modifications to calibration procedures required by the new generation, digital, gas flow meters. Indeed, traditionally natural gas is metered by means of volumetric measurement techniques, while the modern, static gas flow meters (thermal and ultrasonic ones) are based on electronic flow sensors. This implies that the gas volume through the meter is measured by sampling the flow rate at selected time points and integrating the flow rate in time. The measurement time becomes therefore an important parameter, thus requiring a thorough rethinking of the calibration procedure. In order to analyse the effects of the various parameters, a series of ad-hoc calibrations were performed. Specifically, one set of calibrations was performed with constant totalized volume, while the other required a constant measurement time. In order to highlight the novelties that will have to be implemented in ordinary calibration procedures to get the best of the new technologies, the two procedures as performed on a sample set CTTMFs will be compared; the theoretical (generic) evaluation of the associated uncertainty will also be presented. Measurements were carried out at the test facility of INRIM, the Italian National Metrology Institute.     

液氮低温切削加工对高强度钢加工表面的效果

介绍了高强度钢材料的应用现状,以及其切削加工特性;探讨了高强度钢材料的切削加工问题和35CrMnSiA的化学成分与力学性能。针对干切削和冷却液浇注切削的不足,通过对采用液氮低温切削加工高强度钢零件方法的研究,设计了低温液氮切削与干切削和冷却液浇注切削的对比试验。试验结果表明,这种方法能提高了工件表面的精度,延长了刀具的使用寿命,可省去冷却液和废液,有利于实现清洁生产模式,符合绿色制造的要求。     

Flow instability due to cryogenic cavitation in the downstream of orifice

Flow instability in LRE (liquid rocket engine) occurs due to various reasons such as flow interactions with valve, orifice and venturi, etc. The inception of cavitation, especially in the propellant feeding system, is the primary cause of mass and pressure oscillations because of the cyclic formation and depletion of cavitation. Meanwhile, the main propellant in a liquid rocket engine is the cryogenic fluid, which properties are very sensitive to temperature variation. And the change of propellant properties to temperature variation by thermodynamic effect needs to be properly taken into account in the flow analysis in order to understand basic mechanisms for cryogenic cavitation. The present study focuses on the formation of cryogenic cavitation by using the IDM model suggested by Shyy and coworkers. The flow instability was also numerically investigated in the downstream of orifice with a developed numerical code. Calculation results show that cryogenic cavitation can be a primary source of flow instability, leading to mass fluctuations accompanied by pressure oscillations. The prediction of cavitation in cryogenic fluid is of vital importance in designing a feeding system of an LRE. This paper was recommended for publication in revised form by Associate Editor Jun Sang Park Changjin Lee received his B.S. and M.S. degrees in Aeronautical Engineering from Seoul National University in 1983 and 1985. He then went on to receive his Ph.D. degree from University of Illinois at Urbana- Champaign in 1992. Dr. Lee is currently a Professor at the department of Aerospace Engineering at Konkuk University in SEOUL, Korea. His research interests are in the area of combustion instabilities of hybrid, liquid rocket and jet propulsions. Tae-Seong Roh received his B.S. and M.S. degrees in Aeronautical Engineering from Seoul National University in 1984 and 1986. He then went on to receive his Ph.D. degree from Pennsylvania State University in 1995. Dr. Roh is currently a Professor at the department of Aerospace Engineering at Inha University in Incheon, Korea. His research interests are in the area of combustion instabilities, rocket and jet propulsions, interior ballistics, and gas turbine engine defect diagnostics.