Investigation on Performance of PVDF Actuated Micropump with Compliant Diaphragm

Abstract

Micropumps are promising devices which play an important role in microfluidic systems, which are widely used in biomedical fields, automobile applications, electronic cooling systems, chemical analysis, etc. Past research work has presented different types of micropump based on working principle, different actuator, valves, and different combination of micropumps. Based on the available literature, the piezoelectric actuation is extensively used for micropump. In the present work, Polyvinylidene Fluoride (PVDF) piezo polymer is used for micropump actuation. The diaphragm is the key element of the reciprocating type of micropump. The flexible thin circular or rectangular plane diaphragms are used in most of the micropumps. Some of the general characteristics considered during diaphragm selection are stability, reliability, low hysteresis, size, weight, biocompatibility, and fabrication technique. Diaphragm with maximum deflection is required, which improves the micropump performance. In this context, we have designed a compliant diaphragm based on compliance/flexure mechanism, in which three flexures are connected parallel to the actuating area of the diaphragm. The compliant diaphragm design is based on some of the important parameters like material, type of flexure, number of flexures, and perforations. Based on the resilience, three materials are considered for a compliant diaphragm, i.e., stainless steel, beryllium copper, and brass. The better deflection is obtained for brass material three flexure rectangle compliant diaphragm with minimum stress concentration. Further, the deflection can be improved by a decrease in the mass and stiffness of diaphragm. Therefore different perforation patterns are used in the diaphragm actuation area. In the present work, the concept of single and bi-layer PVDF film is used to actuate the compliant diaphragms and plane diaphragm. The diaphragm deflection is improved with an increase in the PVDF film thickness, three different thickness single layer PVDF filmsare considered for the study. The effect of diaphragm deflection is better for bi-layer stacks (PESP configuration) with stacking done using lower thickness PVDF films of equal thickness. The analysis is carried out using COMSOL Multi-physics. To predict the behavior of the micropump with compliant diaphragms and perforated compliant diaphragm, Simulink analytical micropump model is used. The main objective of using compliant diaphragm and perforation pattern compliant diaphragm is to improve the performance of micropump with low operating voltage. In the present study, a new type of compliant diaphragms for micropump is designed, fabricated, and experimentally investigated. From the current work, it could be concluded that the use of flexures in diaphragm has improved the diaphragm deflection, i.e., twice that of the plane diaphragm at the same operating voltage. Further, the perforation patterns in diaphragm actuation area have given better deflection compared to the compliant diaphragm. The concept of stacking of PVDF film is done to achieve better performance of micropump. The micropump character, namely discharges and pressure difference with the plane diaphragm, compliant diaphragm, and perforation compliant diaphragm is investigated. The discharge obtained for compliant diaphragm micropump is twice that of the plane diaphragm micropump at same operating voltage. Better discharge is achieved by using a bi-layer actuator in micropump. The discharge obtained in the plane diaphragm micropump is 14.3 ml/hr. The maximum discharge obtained in the compliant diaphragm micropump and perforated compliant diaphragm micropump is 47.3ml/hr and 49.8ml/hr at 140V respectively.