A Experimental Study on the design of Inlet and Outlet in the Valveless Micropump
Date Issued
2010
Date
2010
Author(s)
Tsai, Wen-Hui
Abstract
Nowadays, optimizing the performance of microfluidic elements has been gradually mature. Some researchers started to focus on the integration of microfluidic units .The concept of “systemization” has been greatly emphasized in the recent years.
For a micropump, the inlet and outlet are quietly essential since they build the bridge of a actuating source (micropump) to other functional kits. But there were few studies on the design of inlet and outlet..Therefore, by varying the geometrical design of the inlet and outlet , the pumping performance was firstly systematically analyzed. Furthermore, by the establishment of flow visualization system, the flow patterns inside the valveless micropump were clearly discovered in order to have more detailed explanation of the flow mechanism.
First, the concept of “reassembly” was applied to the fabrication of the micropump. In order to reduce the variance resulted from combination of the different PZT actuators and the substrates of micro-channel, the same piece of PZT actuator was fixed by a screw-fixing design in each experiments. Also, the relationship between the flow rate and the back pressure were conducted. The results showed that the flow rate was in positive correlation with the back pressure. Besides, the trends of the flow rate and the back pressure coincided with the developing trend of pumping efficiency. And, the best pumping efficiency also occurred at the resonance frequency.
The several designs of radius (R) of inlet and outlet were varied to analyze the pumping efficiency. The results showed that when the ratio of tinlet and outlet radius to the vibrating chamber radius (R/Rch)≧0.64, there were two operating frequency regions: the first region(located in 10Hz~50Hz)and the second region(located in 50Hz~600Hz), and the maximum flow rate of the second region is up to 10 times greater than that in the first region. This phenomenon has never been discovered in the previous literatures of valveless micropumps. The results showed that the optimal radiusfor the inlet and outlet was 1.2 times of the chamber. And for a smaller or bigger radius, the pumping efficiency would decrease. In addition, the flow visualization analysis showed that the best pumping efficiency happened as the vortex pairs of inlet and outlet region and the vortex pair in the vibrating chamber near the outlet diffuser reached maximum. Therefore, when designing the size and geometry of inlet and outlet, both the flow resistance and the development of vortex pairs should be considered.
Next, one to several buffers were serially connected to the micropump in order to discuss its influence on the pumping efficiency The design of buffers can really enhance the performance of micropump (especially, the design of each buffer serially connecting on the both sides of the chamber is optimal. ). In the same channel, when the number of buffers are anti-symmetrical, the flow rate curve and maximum flow rate were quietly similar; in other words, the position of buffers had no influence in this case. When the number of serial buffers increased, the shape of flow rate curve became trapezoid-liked. The frequency of the high flow rate region can be chosen widely.
Consequently, “varying the size of inlet and outlet” and “buffers serially connecting to a vibrating chamber” both could decrease the flow resistance and provided enough space to make the vortex inside chamber develop well. Hence, the micropump performance was obviously enhanced. So, when the two ways of enhancing performance were put together, the coupling effect should be considered carefully due to its property of non-linear superposition. Finally, moving the tube position of micropump along the symmetric axe made no difference in pumping efficiency.
Subjects
reassemble PZT valveless micropump
size of inlet and outlet buffer
vortex pair
tube position
Type
thesis
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