Abstract

Abstract

Measurement of Hydraulic Resistance for Microfluidic Channels Nathan Xu (SEAS ‘19, SAS ‘19), Siddharth Challani, Minsoo Kim, Mark Allen

Dept. of Mechanical Engineering and Applied Mechanics & Dept.of Electrical and Systems Engineering, University of Pennsylvania Vagelos Integrated Program in Energy Research (VIPER)

Experimental Design for Hydraulic Resistance Measurement

Abstract We developed a method to measure the hydraulic resistance of microchannels created using a microelectromechanical systems (MEMS) method. While water flows in the microchannel at a given pressure, we can more easily measure the flow rate of the system by looking at the flow rate of water in the glass capillary tube with a much larger diameter of 0.5 mm. We calculate the hydraulic resistance of a microchannel from the linear relationship between the flow rate and the pressure drop. Polymethylmethacrylate (PDMS) channels with various geometries and interior designs (i.e., nanopatterned channel walls) are fabricated and their hydraulic resistances are measured. The measurement results are comparable to the calculations based on Hagen-Poiseuille’s theory. This method could be potentially used to characterize novel microfluidics that utilize embedded nanostructures for drag reduction.

In our experiment, we record the amount of time it takes the meniscus of the liquid in the glass tube to travel one centimeter at a specific pressure (ΔP). This time is converted to the volumetric flow rate (Q) of the water in the microchannel (since the geometry of the glass capillary channel is known). Then we change the pressure and repeat. Although there are other resistances in the testing system such as in the connecting tubes and the capillary tube, the resistance in the microchannel is so much greater that all other resistances are negligible. Then, hydraulic resistance can be defined by RH, measured = ΔP/Q. We compare the measured resistances to the calculated resistances based on Hagen-Poiseuille’s law.

Conclusion •  We developed a system to test hydraulic resistance in microchannels. This

newly developed system will be utilized to characterize various microchannels with various geometries and interior designs (i.e., nanopatterned channel walls)

Future work •  Improve testing contraption by replacing the source of pressure with a gas

device that can be finely adjusted •  Use a more accurate pressure gauge •  Test hydraulic resistance in different types nanopatterns in microchannel •  Test microchannels of different materials with different properties

Contact information: nathanxu@seas.upenn.edu, (585) 733-1243

Fabrication of Microfluidic Channels using PDMS molding

.

18µm

30nm Titanium(adhesivelayer)Spu9eredCopper

Titanium(protec=velayer)

Photoresist(PR)

Photoresist(PR)

500μm

700nm

300nm

30nm

Siliconsubstrate

(a) (d)

PR(b)

Hagen-Poiseuille’s law:

Abstract

Introduction -  Microfluidic systems enables

rapid chemical/biological analysis with even small volumes of a sample

-  High hydraulic resistance may limit applications

à Characterization setup is required

(news.Stanford.edu)*

N2

Syringe tube

Microchannel

ΔP

Q (m3/s)

*Max. limit of gauge: 10 psi = 70 kPa

Pressure gauge

RH, theory

Lw

h

(Actual setup)

(Photolithography)

-  PDMS: Representative material for microfluidic systems; biocompatible, soft, easy-to-fabricate, inert, and non-toxic

PR(c)

(Dispensing PDMS & Heat cure)

(PDMS de-molding)

(Seed layer deposition, PR spin coat) (e)

Glass

Oxygenplasma

(f)

Glass

(PDMS-glass bonding)

Measurement Results

-  Measured hydraulic resistance of microchannels (h = 17.5 µm) with different cross-sectional geometries (e.g., width-to-height ratio, nanopatterned vs. smooth interior)

(Surface treatment)

RH, theory

*Orenstein,David.2006.’Microfluidic’chipsmayacceleratebiomedicalresearch.[Internet]Stanford(CA):StanfordUniversity[Cited2016Oct15].Availablefromh9p://news.stanford.edu/news/2006/january18/fluidics-011806.html

0.0E+00

2.0E+15

4.0E+15

6.0E+15

8.0E+15

1.0E+16

1.2E+16

1.4E+16

1.6E+16

1.8E+16

10 20 30 40 50 60 70

Channel Width (µm)

Flow Rate vs Channel Width

17.5umtheory 16.5umTheory 18.5umTheory