The proposed technique is a novel, efficient, frugal and noninvasive approach to imaging fluidic flow through a packed powder bed yielding high spatial and temporal resolution. This technique is advantageous as the flow cells are cost effective, reusable, small and easily handled illustrating the dominant aspect of frugal science. Tapping the powders and confirming powder compaction is key to producing a reproducible diagnostic tool.
To begin prepare the microfluidic flow cell by covering the outlet with perafoam to seal one end of the channel so that the empty flow cell may be packed with polymeric powder. Tape the metric paper ruler directly beneath the flow channel. Wave the microfluidic flow cell with the perafoam and the ruler attached.
The mass of the flow cell is the unpacked flow cell mass. Use a plastic pipette to transfer the powder. While introducing the powder into the channel tap the flow cell at least five times to compact the powder.
Continue packing until the powder reaches the beginning of the opening of the flow channel. Remove the powder present on the outer surface of the flow cell with a wipe soaked in alcohol. Once the powders are packed, visually inspect the flow cell for loosely packed powder.
If the powder within the flow cell appears loosely packed, tap the flow cell five more times. If the powder packing appears consistent and compact, weigh the flow cell to measure the mass of the polymeric powder. To prevent flooding the camera detector with too much light, cover the light table with an opaque material such as a 3D printed cover in a black polylactic acid filament.
Ensure that the material has an opening that is the size of the microchannel to allow light to illuminate the powder. To ensure that the camera on the mobile device can capture the contrast between the wet and dry powder, use the light table at a low to medium light intensity. Align the camera on the mobile device directly above the light table.
Confirm that the camera is perpendicular to the top of the light table. After focusing the camera on the mobile device, select the record button. Add 125 microliters of fluid to the open inlet of the microchannel using a pipette.
Record the flow for two minutes or until all the powder is wetted visibly. Transfer the video file from the mobile device to the computer for easy access. Once the software is installed, open the tracker software.
From the file menu select open file to load the transferred video file on the desktop of the computer. To define the starting frame and the step size, click the clip settings icon. Then click on the calibration tool followed by new and select calibration stick.
To zoom in on the ruler in the video, right click on the area to magnify and select zoom in from the list. Once appropriately magnified, define the beginning and end of one millimeter on the ruler taped to the microchannel and type 1 mm to define the distance. Click on the coordinate access tool.
Set the origin for the x and y axis using the starting frame while doing the step. To create a point mass click on create. Then select point mouse.
Use shift plus control to change the size of the rectangle. The initial point is where the inlet and the channel connect. Click on search next a couple of times to verify that the software is analyzing the correct area.
If the software is functioning properly, click on search and wait for the software to finish analyzing the video. The open red circles on the plot represent the exact time and distance of the compiled information. In the interval from one to two seconds, the distance traveled by the fluid has doubled.
During the interval from two to five seconds, the distance that the fluid has traveled also doubled. From five to 10 seconds, the fluid is still moving quickly. However, after 15 seconds the flow rate is slowing to a rate of approximately two millimeters every five seconds.
The most important thing to remember when attending this procedure is to compact your powders. The procedure can be performed for ceramic and metallic powders and has high potential for geological field studies to track flow in pack pattern systems. This technique paved the way for researchers to explore chemically modified surfaces as well as fluids loaded with nanoparticles to observe particle attachment.
