In situ measurement of micro flow rate using near infrared absorption method

A novel technique is presented for measuring micro flow rate using the near infrared (NIR) absorption method. The principle of this method is based on the temperature dependency of the NIR absorption band of water (O-H band, ν₁ + ν₃). We obtained the water temperature in the tube in situ condition using NIR absorption method. A calibration curve between temperature and the NIR absorption intensity in the range of 1500 nm - 1700 nm wavelength was obtained. For measuring flow rate in the tube, the tiny spot of water in the tube was heated using NIR laser (1450 nm) through the lens which was absorbed into the water. The temperature profiles along the tube were obtained using the NIR absorption method via laser heating for different flow rates. The simulation results of the temperature profiles were well matched with the experimental results of it for different flow rates. We found that the conduction affected the temperature more when the flow was low in the upstream and the convection more affected when the flow rate was high in the downstream through the heat transfer analysis. The flow rates were obtained from the temperature difference between the room temperature and the obtained temperature from the NIR method. The calibration curves between the flow rate and temperature obtained from the NIR absorption method was obtained in the two flow rates (1-20 mL/h and 40-100 mL/h). The error and uncertainty of the NIR absorption method for measuring flow rate were approximately 1.2% and 1% at the 1-100 mL/min flow rate, respectively. Thus, we confirmed that the NIR absorption method quantitatively measures the flow rate with respect to the in situ condition for the first time. This method is used for various applications including biomedical and chemical processing without causing any contamination owing to the flow meter installation.