Free Suspended Thin-Walled Nickel Electroplated Tubes for Microfluidic Density and Mass Flow Sensors

In this paper, a novel fabrication method is proposed for microfluidic tubes with a large diameter, circular cross-section, and thin wall. These properties make the tubes especially suitable for density sensors and Coriolis mass flow sensors, because of the resulting low tube mass, low-pressure drop, and low pressure-dependence of the tube shape. A demonstrator sensor was fabricated and the first measurement results of fluid density and mass flow are presented. The low-cost fabrication method is based on electroplating technology and results in tubes with a near-perfect circular cross-section. Diameters ranging from 120
$\mu \text{m}$
to 1 mm and wall thicknesses from
$8~\mu \text{m}$
to 60
$\mu \text{m}$
have been achieved. For the demonstrator sensor presented in this paper a freely suspended tube was realized with a total length of 37 mm, a diameter of 600
$\mu \text{m}$
, and a wall thickness of 20
$\mu \text{m}$
. Density measurements were performed using various gases, liquids, and liquid mixtures at 21°C to 23°C lab temperature. The accuracy of the measured densities of gases such as nitrogen, argon, and helium is 5%. For liquids including DI water, isopropyl alcohol (IPA), and their various mixtures an accuracy of 0.5% was obtained. Preliminary mass flow rate measurements were performed with water and isopropyl alcohol up to 30 g/h with less than 30 mbar pressure drop thanks to the large tube diameter. [2021-0179]