Study On Pressure Drop And Filling Dynamics Of Fluids In Microchannels

Since the 21st century,the most important goal of chemical industry is to achieve high-efficiency controllable and green energy-saving industrial processes.Micro-chemical technology has become a frontier and hot spot in the chemical engineering industry due to its small size and high mass transfer performance.In this thesis,the pressure drop of fluids in a microchannel was studied,and the filling dynamics of fluids in a single microchannel and a symmetric bifurcation microchannel were explored experimentally by using a high-speed camera.The main contents are as follows:The pressure drop of Newtonian and non-Newtonian fluids in microchannels was measured by pressure sensors.The effects of flow rate,Reynolds number,and viscosity of fluid on the pressure drop of single-phase flow in microchannels were investigated and compared with traditional prediction models.The rheological properties of fluids in the microchannel were studied based on the pressure drop.The results showed that the pressure drop of Newtonian fluid is in good agreement with the prediction formula proposed by Cornish.The pressure drop of non-Newtonian fluid,however,deviated from the traditional theoretical model.The relationship between the apparent viscosity and the characterized shear rate in a specific microchannel based on the pressure drop data was completely different from the rheological curve measured by conventional rheometers.The main reason was the limitation of conventional rheometers and heterogeneous distribution of shear rates at the radial direction for non-Newtonian fluids flowing in the microchannel.The filling process of glycerol aqueous solution with different viscosity in a single microchannel was observed by a high-speed camera.The filling process was divided into two stages,the first stage satisfied the linear relationship between L and T,and the filling rate was affected by the inertial force and the capillary pressure.In the second stage,L and T satisfied the power-law relationship,and the exponent n was not a fixed value,due to the change of the contact angle.The results showed that when Ca was much larger than 10^-4,the advancing angle of gas-liquid solid contact angle fluctuated with time,and the fluctuation range was within 2°.The filling phenomenon of low viscosity and high viscosity fluid in symmetric bifurcation microchannel was studied.The effects of viscosity,flow rate and surfactant of fluids on the uniformity of filling process in symmetric bifurcation microchannel were investigated.Non-uniformity phenomenon of fluid filling in the symmetric bifurcation microchannel has been observed.The filling of the low-viscosity fluid in the microchannel was evenly distributed in the early stage,and the inhomogeneity degree increased with time.For high-viscosity fluid,fluid distribution was not uniform at low Ca;while as Ca increased,the fluid propagated at the same speed in the branch microchannel,and a symmetrically distributed pattern appeared.After the surfactant was added,the fluid was evenly distributed in two bifurcated microchannels,and the gas-liquid solid advancing angle was relatively stable and smaller than the gas-liquid solid advancing angle without the added surfactant.