Cylindrical tubes with large diameters and thin walls for application in microfluidic density and mass flow sensors

Abstract

In the past, numerous density and flow sensors have been presented for a large variety of applications. Over time, with emerging new applications monitoring of very small flow rates, and detection of fluid composition have become even more important.Almost three decades ago, the first micromachined density and Coriolis mass flow sensor was introduced. This sensor was based on a freely suspended vibrating channel. Over the years, to improve the performance of the microfluidic sensor, different fabrication methods based on silicon micromachining techniques were proposed. All these fabrication methods lead to a freely suspended channel with a non-circular cross-sectional shape, and a limited range of wall thicknesses and cross-sectional areas, which leads to a limited flow range and pressure dependency of the sensor. To overcome these drawbacks, this research aims to improve the range of channel diameters of a circular shape and a relatively thin, chemically inert channel wall.This research is divided into three different sections. The first part of the research focuses on a literature review to investigate all the different fabrication methods already used to realize a freely suspended channel. The second part of the research focuses on fabricating freely suspended tubes based on the three most promising potential fabrication methods that do not require the frequently used silicon micromachining techniques. In this section, each fabrication method is further investigated and discussed in detail to find out the possibility of achieving such a tube with a circular cross-sectional shape and a high ratio of the diameter to wall thickness. In the third section, each tube that has been realized is tested in practice and the measurement results are compared to a numerical model. This numerical model has been made to model the mechanical behavior of the tube when a medium is flowing through the tube. The results show a significant improvement in the range of the mass flow and dependency of the performance of the sensor on the input pressure. Furthermore, a demonstrator is proposed with an integrated optical readout which improves the stability of the output signal regarding the mass flow rate.