Screen Printed Sensor Design for Thermal Flow Velocity Measurement With Intrinsic Compensation of Thermal Fluid Conductivity

For keeping control of processes in lab-on-chip applications, monitoring the flow velocity inside channels is an important task. One popular approach to this is to consider heat transfer inside the channel as a flow velocity dependent effect, which can be measured by relatively easy means. Additionally, these thermal measurement methods can be designed and applied in a way that the sensors and actuators do not disturb the flow profile. A fabrication technique suitable to fabricate such sensors is screen printing, which combines cost efficient and fast processing with layers thin enough to not alter the fluid flow. In this work, we report on a devised sensor that is fabricated by screen printing and embedded into a 3D printed channel. The sensor layout enables measuring the flow velocity in a microchannel while enabling the user to compensate for the change in thermal conductivity when switching to a different fluid. This design requires calibration only for one fluid, since a simple empirical model is presented to extrapolate the calibration data to fluids with varying thermal properties. The sensor was tested for one calibration fluid and two fluids with differing thermal properties. The flow velocities of these fluids were measured with an error below 5%.