The aim of this paper is to develop a theoretical model of a piezoelectric valve-less micropump for liquid delivery with entrapped gas bubbles and evaluate the influence of gas bubbles on the dynamic characteristics of the micropump by using this model. In the model, we consider the vibration of piezoelectric diaphragm, the pressure loss through the nozzle/diffuser and the compressibility of working liquids with entrapped gas bubbles. In order to validate the developed model and make it useful as a design and prediction tool, experimental studies are carried out to investigate the flow rate and dynamic pressure inside the pump chamber when gas bubbles are absent or present in the micropump. The presence of gas bubbles inside the pump chamber is also observed with a high-speed video camera. The outlet flow rate of the micropump with different size of trapped gas bubbles are calculated and compared.

In this work, the influence of viscous heating on the flow performance of a spiral-channel viscous micropump was investigated numerically using finite volume method (FVM). A number of 3D models for the spiral-channel micropump boundary conditions and using different working fluids (Glycerin, and water) were built and analyzed by considering the change of the fluid viscosity as a function of temperature. Results showed that significant temperature rises due to viscous heating are obtained, and the error in calculating the volumetric flow rate by considering viscous heating term is increased with increasing Re .Eu , and reaches 10% for the spiral wall condition and 40% for the single wall condition at Re .Eu = 1.5. Also, it was found that large deviations from the analytical predictions are obtained for high viscous fluids, and that viscous heating and temperature rise in the stationary wall condition is higher than that in the spiral wall condition. As a conclusion, viscous heating in the spiral-channel micropump is too significant to be neglected and affects the temperature, pressure, and velocity distribution of the flow field.

A thermopneumatic valveless micropump with a PDMS-based nozzle/diffuser structure was firstly designed and realized herein by stacking three layers of PDMS on a glass slide. Unlike the conventional peristaltic pumping configuration, the new structure of the micropump consists of only one set of heater on the glass slide, a thermopneumatic actuation chamber, and an actuation diaphragm. Additionally, it includes a flowing channel with nozzle/diffuser structure and inlet/outlet ports. In this valveless microchannel, fluid is driven by asymmetric flow resistance produced from the nozzle and diffuser configuration. The actuation diaphragm between the gas-pneumatic chamber and the flowing channel can bend up and down due to the gas expansion as well as the thermal buckling of the PDMS diaphragm imposed from the heating in the gas-pneumatic actuation chamber.