Xiaobin Huang, Liang Zhang, Chun Lu
Development of a portable small gas flow transfer standard based on laminar flow technology

Small gas flow measurement is widely applied in aerospace, environmental monitoring, automotive, medical and other fields. To calibrate the small gas flow, a portable transfer standard device based on laminar flow technology is developed, which includes a gas conditioner, laminar flow elements, a pressure sensor, a temperature sensor and a flow computer. The measurement range of the device is (1 ~ 10000) mL/min with a relative expanded uncertainty of U ≤ 0.3 %, k = 2. The device has the capacity to compensate the medium temperature influencing on the flow rate. It can be utilized to calibrate the gas flow whose pressure does not exceed 0.6 MPa. With a compact dimension and weighing 27 kg, the device is easy to be carried. The consistency of the measurement results of the device under different temperature and pressure conditions is studied, and it is verified that the device can be utilized as a transfer standard for both in-laboratory calibration and on-site calibration for small gas flow.

H. Bissig, M. de Huu
Dynamic vs constant liquid flow calibrations down to 20 nL/min

Calibration of flow devices is important in several areas of pharmaceutical, flow chemistry, HPLC and microfluidic applications, where dosage of process liquids or accurate measurement of the flow rate are important. The process-oriented liquid itself might influence the performance of the flow device. Therefore, the calibration of the flow meter or microfluidic device with the process-oriented liquid is important and performing dynamic flow profile changes to simulate any dosing process gives important insight in the behaviour of these flow devices and their accuracies under non-constant flow conditions. Therefore, METAS has developed facilities with METAS piston provers to address the issue of measuring with process-oriented liquids non-constant flow profiles for flow rates down to 20 nL/min. The stated measurement uncertainties for the constant flow rate and for the dynamic flow profile changes are 1 % and 2 % at 20 nL/min. The piston provers, the new developed capillary beaker for the gravimetric reference method, validation measurements as well as response time characterization with incompressible and compressible liquids are discussed in this paper.

L. Liu, C. Zhou, T. Meng
Research on Methods to Reduce the Influence of Medium Evaporation on Liquid Micro-Flow Facility

Liquid micro-flow facility in our country can achieve ultralow flow measurement as low as 100nL/min. In the detection process of liquid micro-flow facility, evaporation is significant for liquid at low flow rate, and if not controlled, the evaporation of the medium will be the main source of uncertainty for liquid micro-flow facility, so it is necessary to correct the evaporation effect during the test. Evaporation occurs mainly during the collection of liquid in the weighing container inside the balance, the effect of evaporation on flow is analysed, and obtains an evaluation method of the effect of reducing evaporation. The influence of balance drift on evaporation was excluded through experiment, and the research on evaporation under uninhibited conditions, evaporation under evaporation trap and oil film coverage were carried out. In addition, the evaporation studies under oil film coverage plus evaporation trap was also implemented. Finally, it is concluded that both the evaporation trap and the oil film covering can effectively inhibit the evaporation of medium, the optimal anti-evaporation method of the liquid micro-flow facility is to cover the paraffin oil film above 0.15 g/cm², which can reduce the evaporation to 0.3 μg/min, and the uncertainty to 0.12 % (k = 2) at the ultralow flow rate of the facility.

Yinjie Zhuo, Chengxu Tu, Xiang Li, Haohao Xu, Jiaxiang Wang, Weijie Chen, Qingsong Shi, Yexin Lu, Di Xiao, Fubing Bao
Research on standard device of liquid hydrogen flow driven by air pressure

As an important link in the industry chain of hydrogen energy, liquid hydrogen has great potential in civil aviation, shipping, and urban public transportation, and is a also key component in the future large-scaleindustrialization of hydrogen energy. The accuracy of liquid hydrogen flow measurement is crucial in its preparation, storage, transportation, application, and trade settlement during the whole industry chain running. The liquid hydrogen flow standard device is the core equipment to check and calibrate the liquid hydrogen flowmeter, which is the key link to ensure the reliable flow measurement of liquid hydrogen. As a low-temperature fluid with ultra-low viscosity and low density, the non-negligible error would be introduced when the flowmeter is calibrated using other fluids instead such as water, especially in the tiny flow range. Therefore,it is necessary to develop a flow standard device for actual-flow calibration of the liquid hydrogen flowmeters.In this paper, based on the existing research of cryogenic fluid standard devices at home and abroad, a liquid hydrogen flow standard device based on the bi-directional dynamic mass method is designed, using helium to drive the liquid hydrogen in the tank, which can provide the standard flow rate in the small flow range for the calibration and verification of the flowmeter under test. The system is designed to take into account the cryogenic temperature, low viscosity, high flammability and explosivity of the liquid hydrogen, as well as the measurement accuracy. Compared with the cryogenic pump, the high-pressure helium source can provide a more stable and smaller flow rate to achieve the higher accuracy and robustness of the calibration and verification of the flowmeters under the small flow rate of the device. The bi-directional dynamic mass method with reverse drive can avoid the influence of additional pipe capacity on the actual error generated during measurement, effectively reduce the measurement uncertainty of the device and improve the measurement system of the liquid hydrogen flow.

Lianfeng Cheng, Chao Xing, Xiaopeng Li, Fan Chen,HuanchangWei, Tao Meng, Huichao Shi
Control Method And Experimental Verification Of Pipeline Flow Fluctuation Generator

In the actual flow measurement process, flow fluctuations often propagate in the pipeline, which may cause large deviations in the flow measurement results. In order to systematically study the influence of different flow fluctuations on the measurement results of the flowmeter, it is necessary to simulate different controllable flow fluctuations in the pipeline. This paper designs different wave control methods for a vane flow fluctuation generator, and uses LabVIEW programming to control the motor to drive the butterfly valve to swing, forming controllable flow fluctuation of sine wave, frequency conversion sine wave and variable amplitude sine wave in the pipeline. Finally, based on the hot water flow standard facility of National Institute of Metrology (NIM), a real flow experiment is designed to verify the control method of the fluctuation generator. Experimental results show that the proposed control method can control the flow fluctuation generator to generate controllable sine wave， frequency conversion wave and variable amplitude wave , and the flow fluctuation can be propagatedalong the pipeline upstream and downstream.