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Water collection techniques at very low flow rates including strong capillary effects
Flow Measurement and Instrumentation ( IF 2.2 ) Pub Date : 2020-06-01 , DOI: 10.1016/j.flowmeasinst.2020.101744
Hugo Bissig , Martin Tschannen , Marc de Huu

Abstract Milli-, micro- and nano-flow calibrations are important in several areas of pharmaceutical, flow chemistry and health care applications where volumetric dosage or delivery at given flow rates are crucial for the process. After developing a facility for the micro-flow range, METAS has developed a facility for flow rates from 50 nL/min up to 400 mL/min. The continuous collection of the flowing water into a beaker on a balance without having droplet formation for a continuous increase of the weighing values is a challenge (dynamic gravimetric method). This technique is often used to determine the flow rate over several orders of magnitude. In this paper, we describe the newly developed METAS piston provers and focus on the water collection techniques used for the flow rate determination of very low flow rates going as low as 50 nL/min by means of the dynamic gravimetric method. One water collection technique is to immerse the outlet needle into the water in the beaker. To reduce evaporation either a saturated environment is created or a layer of oil is added on top of the water. Another water collection technique is applied at the METAS facilities, where the outlet needle is positioned just over glass filters on top of the beaker to collect the water by means of a constant water bridge obtained independently of the flow rate. These two techniques are investigated for comparing the stability of the flow rate determination and the influence of the capillary forces acting due to the water or water-oil surface on the outlet needle and on the water bridge between the outlet needle and glass filters. The technique applied at METAS with the water bridge between outlet needle and glass filter reveals to be more stable for the flow rate determination and corrections due to capillary forces acting on the outlet needle can be neglected compared to the water collection technique with the immersed needle.

中文翻译:

极低流速下的集水技术,包括强大的毛细管效应

摘要 毫微流、微流和纳流校准在制药、流动化学和医疗保健应用的多个领域中很重要,在这些应用中,体积剂量或给定流速下的输送对过程至关重要。在开发了微流量范围的设备后,METAS 开发了流量从 50 nL/min 到 400 mL/min 的设备。将流动的水连续收集到天平上的烧杯中而不会形成液滴以连续增加称量值是一项挑战(动态重量法)。这种技术通常用于确定几个数量级的流速。在本文中,我们介绍了新开发的 METAS 活塞式校准器,并重点介绍了用于通过动态重量法测定低至 50 nL/min 的极低流速的水收集技术。一种水收集技术是将出口针浸入烧杯中的水中。为了减少蒸发,要么创建饱和环境,要么在水面上添加一层油。另一种水收集技术应用于 METAS 设施,其中出口针位于烧杯顶部的玻璃过滤器正上方,通过独立于流速的恒定水桥收集水。研究这两种技术是为了比较流速测定的稳定性和毛细管力的影响,这是由于出口针上的水或水-油表面以及出口针和玻璃过滤器之间的水桥产生的。与浸入式针头的集水技术相比,在出口针头和玻璃过滤器之间采用水桥的 METAS 技术表明,由于作用在出口针头上的毛细力可以忽略流速测定和校正更稳定。
更新日期:2020-06-01
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