In this decade, paper-based microfluidics
has gained more interest
in the research due to the vast applications in medical diagnosis,
environmental monitoring, food safety analysis, etc. In this work,
we presented a set of experiments to understand the physics of the
capillary flow phenomenon through paper strips. Here, using the wicking
phenomenon of the liquid in porous media, experimentally, we find
out the capillary height of the liquid in filter paper at different
time intervals. It was found that the Lucas–Washburn (L–W)
model, as well as the evaporation model, fails to predict the capillary
rise accurately. However, the detailed numerical solution shows a
better similarity with the experimental results. We have also shown
the different regimes of the wicking phenomenon using scaling analysis
of the modified L–W model. The capillary rise method was applied
to detect the added water content in milk. We used milk as a liquid
food and found the added water content from the change in the capillary
height at different concentrations of milk. Finally, results obtained
from the paper-based device were verified with the commercially available
lactometer data.