Practical methodology for in situ measurement of micro flow rates using laser diode absorption sensors

A laser diode-based flowmeter based on the infrared absorption method that can measure in situ micro flow rates from 0.2 to 20 ml h−1 was developed. A 1450 nm laser absorbed in water was irradiated to form a heated spot at 0 mm, and the temperature was measured upstream and downstream of the heated spot. The flow rate was measured by the temperature difference obtained by two diode lasers and photodetectors upstream and downstream of the heated spot. We measured the temperature profile of the flow rate by changing the temperature measurement position and the heating laser energy upstream and downstream of the heated spot, and compared the measurements with the simulation results. As the flow rate increased, the temperature profile shifted downstream, and the measured temperature upstream and downstream were analyzed according to the flow rate. The flow measurement range was adjusted according to the temperature measurement position. Increasing the energy of the heating laser also improved the measurement accuracy in the lower flow range. The developed flowmeter was calibrated by the gravimetric method, and the deviation and measurement uncertainty according to the flow rate were obtained. The maximum measurement uncertainty was 6.8% at a 1 ml h−1 flow rate, and the minimum measurement uncertainty was 1.78% at 8 ml h−1. Thus, it was confirmed that the flow rate can be measured through the temperature difference gauged using a simple diode laser set. Using the laser diode-based flowmeter developed in this study, one can measure the flow rate in situ without injecting contaminants, such as particles, for measurements without cutting the piping. In addition, it can be manufactured in a miniaturized form at a low cost, and thus, it can be used for multi-drug infusion analysis, semiconductor process monitoring, etc.