New Generation of Liquid Flow Sensors for the Nanoliter through Milliliter per Minute Range with extremly small Internal Volume

摘要

Accurate measurement and control of tiny liquid flows of the order of nanoliters through milliliters per minute is becoming more and more important for a lot of applications in the life science, analysis (e.g. HPLC), biotech, synthesis (of e.g. pharmaceuticals) and nanotechnology markets. Accompanying demands to flow sensors suited for this low flow range are an extremely small internal volume, the use of for instance PEEK and fused silica as wetted material for the flow sensor tube (instead of stainless steel), and a modular set-up of the instruments, so they can be easily exchanged and adapted to a new need. For example, the separation column at the detector side of analytical equipment is sometimes made of the material fused silica with an internal diameter typically of the order of 100 μm. In some cases, it is necessary to measure the. very small - flow at the detector side to improve the accuracy of the analysis. In this application, the internal diameter and wetted material of the flow sensor tube should preferably be the same as those of the separation column, to avoid disturbances in the flow and to minimise the internal volume. Up to now, none of today's commercially available flow sensors is equipped with the above mentioned features. In this paper, a new generation of liquid flow sensors is presented that is capable of meeting the requirements as imposed by the life science, analysis, biotech and other markets. First, the sensor structure and basic operating principle are described, followed by a description of the occurring heat transfer, the necessary electronic circuitry and the resulting output voltage for a certain flow range. Some measurement results will be presented and discussed, and finally some conclusions are drawn.