A novel experimental setup for gas microflows

Abstract

A new experimental setup for flow rate measurement of gases through microsystems is presented. Its principle is based on two complementary techniques, called droplet tracking method and constant-volume method. Experimental data on helium and argon isothermal flows through rectangular microchannels are presented and compared with computational results based on a continuum model with second-order boundary conditions and on the linearized kinetic BGK equation. A very good agreement is found between theory and experiment for both gases, assuming purely diffuse accommodation at the walls. Also, some experimental data for a binary mixture of monatomic gases are presented and compared with kinetic theory based on the McCormack model.

Challenges in Microflow Measurements

“…Over the years a number of transport models have been developed to take into considerations the rarefaction effects in the slip and transition flow regimes. Some of these models include: the first order model (Maxwell, 1879), the second-order model (Deissler, 1964), the second-order model with Deissler boundary conditions modified with Hadjiconstantinou's coefficients (Hadjiconstantinou, 2003) that was recently proposed by Pitakarnnop et al (2010).…”

“…The DT technique is commonly used for measurement of microflows emerging from microchannels (Harley et al, 1995;Zohar et al, 2002;Maurer et al 2003;Colin et al, 2004;Ewart et al, 2006;Pitakarnnop et al, 2010). When the downstream of a capillary is open to atmosphere, the flow measurement can be performed using a soap flowmeter (Celata et al, 2007).…”

“…Studies involving flows in transition and near free molecular regimes require very low downstream pressures. For example, Pitakarnnop et al (2010) and Ewart et al (2006) reported flow measurements at downstream pressures of as low as 1,928 Pa and 1,101 Pa, respectively. At such low pressures, a soap bubble and even a soap liquid droplet would quickly evaporate making measurement impossible.…”

“…The position of the bubble moving in the calibrated part of the capillary is observed visually (Zohar et al, 2002), or with a help of auxiliary instrumentation. The latter includes, the use of opto-electronic sensors (Colin et al, 2004;Pitakarnnop et al, 2010) similar to those used in automated soap flowmeters, or a low power microscope (Harley et al, 1995), or using a high resolution digital camera (Ewart et al, 2006). After measurement, the liquid droplet must be retracted and/or withdrawn from the capillary in order to prepare the system for the next measurement.…”

“…Recently, Pitakarnnop et al (2010) developed a new setup for gas microflows, in which the CV method is applied at both downstream and upstream of the microchannel, which offers a double check and provides the possibility to compare the measured results for the same flow. The system is also equipped with Peltier modules to maintain a constant temperature.…”