Thin-Walled Cylindrical Nickel Electroplated Tubes for Application in Microfluidic Density and Mass Flow Sensors

In this paper, a novel fabrication method is proposed for microfluidic tube with a large diameter, circular cross-section and a thin wall. These properties make the tubes especially suitable for fluid 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 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 m to 1 mm and wall thicknesses from 8 m to 60 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 m, and a wall thickness of 20 m. Density measurements were performed on nitrogen, ethanol, water, isopropyl alcohol (IPA), and various mixtures at 21°C-23°C lab temperature. Mass flow rate was measured up to 30 g/h with less than 30 mbar pressure drop thanks to the large tube diameter.