Fabrication, Characterization, and Computational Modeling of a Piezoelectrically Actuated Microvalve for Liquid Flow Control

Abstract

Liquid-compatible piezoelectric microvalves have been modeled, fabricated, and characterized. The microvalve was designed for proportional flow control of liquid propellant for integrated spacecraft micropropulsion. The microvalve consists of a custom-designed piezoelectric stack actuator bonded onto silicon valve components with the entire assembly contained within a stainless steel housing. The valve seat configuration includes narrow-edge seating rings and tensile-stressed silicon tethers that enable the normally closed and leak-tight operation. A concentric series of narrow rings simulates a "knife-edge" seal by greatly reducing the valve contact area, thereby increasing the seating pressure and consequently reducing leak. Leak testing of the microvalve, conducted using a Helium leak detector, showed a leak rate of approximately 3/spl times/10/sup -6/ scc/s for Helium gas. During operation, the valve flow rate was measured using an external Mass Flow Meter (MFM) with a measurement resolution of approximately 10/sup -2/ scc/s. The measured forward flow rate for deionized (DI) water is approximately 64 mg/min at an inlet pressure of 20 psi and an applied voltage of 50 V. The mechanical resonance frequency of the microvalve structure was measured at 11.1 kHz. The measured dynamic power consumption of the microvalve is approximately 60 mW when operated at 50 Hz. The measured static power consumption is approximately 2.5 mW at 20 V. Computational modeling of liquid flow within the piezoelectrically actuated microvalve has also been performed. The commercial computational fluid dynamics (CFD) code FLUENT was utilized for solving the continuity and momentum equations. The pressure drop between the inlet and outlet ports was determined as a function of the inlet mass flow rate, and a pressure drop coefficient was determined for each valve plate deflection value. The model-predicted values were compared to the experimental data, and confirmed the sensitivity of the results to the value of the deflection.