Study on the key parameters influencing the near-wall electroviscous effect in thermal micro-liquid flow measurement

When measuring micro-liquid flow in microchannels, thermal micro-liquid flowmeters are subject to the influence of the electroviscous effect induced by the near-wall electric double layer, resulting in distortion of the flow field and temperature field distribution, ultimately leading to a decline in measurement accuracy. In response to this problem, a microscale fluid–thermal–electric–ion coupling multi-physics field model was established. De-ionized water and electrolyte solutions were employed as analysis subjects. The influence mechanisms of ionic type, ion concentration, and channel height on micro-liquid flow and heat transfer characteristics were systematically investigated. The final results indicate that due to the difference in the main types of ions contained in the solution, the impact of the electroviscous effect in potassium chloride solution is greater than that in sodium chloride solution because of the high mobility of K+. Furthermore, when the channel flow is less than 10 nl/min and the ion concentration is greater than 10−3 mol/m3, the electroviscous effect significantly impedes fluid motion and causes shifts in the flow velocity and thermal field. Moreover, with the increase in the microchannel height, the decrease in the flow velocity in the microchannel leads to a more significant electroviscous effect near the wall surface, thereby causing the change of the temperature gradient. All the aforementioned parameters affect the measurement accuracy of the thermal micro-liquid flowmeters. This research provides theoretical support for enhancing the measurement accuracy of thermal micro-liquid flowmeters in complex ionic environments and the flow control ability of microfluidic systems.