Session: 11-10-01: Multiphase Flow Applications

Paper Number: 173767

A Novel Method for Measuring Pressure Profile Along Microchannels 

The pressure profile along a channel is typically measured using pressure taps. The diameter of pressure taps should be significantly smaller than that of the channel to minimize its impact on the flow and associated errors in pressure measurement. As channels scale down to sub-millimeter scale, it becomes increasingly challenging to fabricate taps small enough to measure the pressure without significantly affecting the flow.

Microchannel pressure taps that are made via microfabrication and silicon-based technologies are limited by the two-dimensional nature of microfabrication. Traditionally these taps are placed normal to and in plane with the channel resulting in a tap that extends the entire height of the channel. This design is easy to implement and works well with existing microfluidic practices. When polydimethylsiloxane (PDMS), a commonly used soft polymer, is fusion bonded to the channel to act as a cap, a punch tool can be used to create a hole through which a tube can be fitted to access the pressure tap. Much work has been done to optimize the tap geometry [1] for this method. However, a limitation of this and similar methods is they can cause flow disturbances affecting downstream measurements because these taps span the height of the channel wall.

To tackle the above issue, we have developed a new method for fabricating pressure taps that adhere more closely to macroscale design principles. Instead of using SU-8 alone, we employ deep reactive ion etching (DRIE) through a silicon substrate in conjunction with SU-8 geometry to create 25 µm diameter taps in a 300 µm × 300 µm channel. This approach decouples tap size from channel height and allows tap diameters as small as 5 µm, limited only by the minimum feature size of the SU-8 pattern.

This method introduces new pressure tap interfacing challenges since existing PDMS punching procedures no longer apply. We intend to address this by using a printed circuit board (PCB) stack originally proposed by van Erp et al [2]. While the method proposed by Erp et al. focused on fluid routing, which we intend to use to deliver fluid to the proposed microchannel device, we also propose that similar PCB channels can be used to route the pressure taps to outlets that provide external access to the pressure taps.

With the proposed method and device, we will measure the pressure profile along the microchannel for a wide range of Renyolds numbers. The pressure measurements will be used to derive the friction factor and compare them with existing models. The measurements will also provide insights into the flow characteristics in microchannels, which can aid the design for future microchannel devices for chip cooling.  

 

References

[1] Rodrigues, T., & Galindo-rosales, F. J. (2019). Towards an Optimal Pressure Tap Design for Fluid-Flow Characterisation at Microscales. 13. https://doi.org/10.3390/ma12071086

[2] van Erp, R., Soleimanzadeh, R., Nela, L., Kampitsis, G., & Matioli, E. (2020). Co-designing electronics with microfluidics for more sustainable cooling. Nature, 585(7824), 211–216. https://doi.org/10.1038/s41586-020-2666-1

Presenting Author: Henry Gagliardi University of Maryland, College Park

Presenting Author Biography: Henry is a M.S. student at the University of Maryland. He received his undergraduate degree from the Rochester Institute of Technology in 2022 after which he worked for Texas Instruments as a ceramic packaging engineer for their Digital Micromirror Devices (DMDs).

Authors:

Henry Gagliardi University of Maryland, College Park
Lingnan Lin University of Maryland, College Park