Study Of Microfluidic Flow Distributing Based On Phase Change Control

Micro Total Analysis System (μ-TAS) has many advantages, such as rapid response, low consumption, convenient using and so on, so it has aroused a wide range of applications. Microfluid should be controlled effectively by a lot of micro valves in μ-TAS when it is under working state, therefore, the micro valve plays a great role in μ-TAS.This paper studied the phase change process of water and the impact of supercooling on it. Combining the principle of traditional micro flowing valve and micro phase change valve, we proposed a microfluidic distributing valve, which could be implemented three operating modes-proportional shunt, single-channel closed, dual-channel closed. The mold of the microfluidic chip was fabricated through lithography process, the PDMS chips were fabricated through molding method and the temperature sensor (PT100) was embedded in the chip.Three-level thermoelectric cooling system was designed for the actual need of ice valve controlling. In order to improve the accuracy of the system, the PT100temperature sensor was placed on the surface of the secondary cooling device. This cooling system could lower the temperature of the chip to-20℃, and has high stability and accuracy. The temperature accuracy of this system could achieve0.1℃. In order to observe working process of the ice valve, the cooling device was conducted on the left side of the micro channel. A integration platform, which include microfluidic chip, PT100temperature sensor, three-level cooling device and clamping device, was designed to ensure the close contact of the microfluidic chip and the cooling system. This platform has great versatility, so it could be used for different experiments through change the chips.The temperature change of the micro channel in the phase change process of water, which was measured by the temperature sensor(PT100), proved that supercooling cause the phase change process of water to be instantaneous. Through accurately controlling the fluid curing and melting volume in specific area, it could be implemented three operating modes-proportional shunt, single-channel closed, dual-channel closed.With changing micro valve from closed to open, the flow velocity change of water in the sub-channel was measured by Micro-PIV technology. The result shows that the micro valve has a good distributing effect in proportional shunt mode. In order to verify the effect of ice storage pool, two groups of experiment were done. The ice valve without ice storage pool closed in5s and opened in5s as well. The ice valve with ice storage pool closed in1.5s and open in2s. So the ice storage could reduce the closing and opening time of the micro ice valve. Except that, it enhances the stability of ice valve.