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The development of microfluidic technology is becoming more and more mature. It has the advantages of small sample consumption, heat and mass transfer, large surface area, small space scale, and small time scale. It is widely used in microchemical reactors, chip laboratories, bioengineering and other fields. The distribution, dynamics and stability of the phase state in the microfluidic system are controlled by the surface tension and viscous force, and it is very important for the dynamic online measurement of the surface tension and viscosity of the microfluidic system. However, traditional interfacial tension and viscosity measurement methods are difficult to achieve on-line measurement of physical properties, which takes a long time and requires more samples, which has always been a problem in the field of petrochemicals.
To solve the above problems, the heat and mass transfer research center is based on the fluid dynamics of Taylor flow in microchannels. The relationship between the liquid film thickness and the surface tension and viscous force of the fluid is expressed by the Taylor relation and a new online measurement is proposed. The system, through the liquid film thickness measurement of the Taylor flow, can perform reliable physical calculations for gas/liquid, liquid/liquid systems, and more complex fluid systems including non-Newtonian fluids and biological fluids.
For the first time in the country, the research team realized the measurement of the liquid film thickness at the air-liquid interface in the microchannel. The liquid film thickness is measured by a laser confocal displacement meter (LFDM, accuracy ±0.3μm, response time 640μs). The schematic diagram of the experimental setup is shown in Figure 1. The position of the target surface is determined by adjusting the displacement of the objective with the tuning fork, and the two phases at the gas-liquid interface The refractive index is different and the reflection intensity reaches the highest. The liquid film thickness measurement first determines the position of the inner wall surface of the glass tube, and then determines the position of the gas-liquid interface. Data Acquisition Use LabVIEW software to monitor and control the data acquisition process and perform preliminary processing of the acquisition results. The data acquisition frequency is 5 kS/s and the resolution is 16 bits.
Based on Taylor fluid dynamics, the relationship between surface tension and viscosity with liquid film thickness is derived:
Based on the measurement results of the liquid film thickness and the above theoretical relationship, the surface tension and viscosity of three different pure liquids (water, ethanol, and FC-72 refrigerants) and liquid mixtures and surfactant-containing aqueous solutions were measured. Get reliable measurement results.
The on-line measuring system is characterized by fast and convenient measurement accuracy, and can not only reliably measure the physical properties of gas/liquid, liquid/liquid systems and more complex fluid systems including non-Newtonian fluids and biological fluids, but also at higher flow rates. Both surface tension and viscosity measurements can be obtained simultaneously. At present, the research team is developing and improving the system for simultaneous measurement of surface tension and viscosity, and has developed non-Newtonian fluid rheometers for biomedical applications.
The research has applied for two invention patents, and the results are published in the Review of scientific instrument, the top journal of instrument measurement. The research work has been funded by the National "Young Thousand Talent Plan" fund and the National Natural Science Foundation.
(Original title: Institute has invented a device for rapid measurement of viscosity and surface tension)
New measuring system for measuring viscosity and surface tension has been proposed
[China Instrument Network Instrument Research and Development] The Institute of Engineering Thermophysics of the Chinese Academy of Sciences has made important progress in the microfluidic research field recently. It has proposed a new on-line measurement system for measuring viscosity and surface tension, and has independently designed a measuring device.
Experimental device schematic