The fluid flow behavior model in medical devices has been adjusted.

The article has been published in the journal Physics of Fluids. The work was carried out with the support of the Ministry of Science and Higher Education of Russia.

Studying heat and mass transfer processes at small spatial scales enhances our understanding of the mechanisms responsible for fluid movement in microchannels. This knowledge is essential for developing devices such as biochips for DNA analysis, cell separation devices, protein and biomolecule analysis, and drug testing. It is also crucial for creating chemical microreactors with channels less than one millimeter in diameter. These are used in pharmaceuticals for the efficient synthesis of chemical compounds and conducting complex reactions.

The primary challenge of flows at small scales is the high resistance from solid walls, which complicates fluid movement. One of the tasks is to increase the flow rate and optimize its mixing. This is typically achieved mechanically using pumps, a process known as forced convection. However, from the perspective of energy and resource conservation, it is more efficient to utilize natural convection, where fluid movement is induced by density inhomogeneities. The application of an external force sets the fluid in motion, promotes intense mixing, and accelerates chemical reactions.

One of the most convenient devices for research is the Hele-Shaw cell, a thin gap filled with liquid between two parallel plates. It allows for advanced optical observation methods of flow during experiments and simplifies the procedure for solving equations. The ability to control the flow is crucial for technological devices, which is why inertial forces acting on the liquid in a rotating Hele-Shaw reactor are used as the energy source to maintain convection. Unlike gravitational forces, these can be easily controlled in experiments.

According to established theory, the Coriolis force (one of the forces arising in rotating systems) can only exist in three-dimensional fluid flows. Scientists from Perm Polytechnic have disproved this assertion by demonstrating that it also contributes to two-dimensional flows when the fluid is heterogeneous in density. The influence of this force was observed in experiments with the rotation of solution systems in the Hele-Shaw reactor. However, the previously used theoretical model inadequately described the process under such conditions and required further development.

“It was previously believed that the Coriolis force does not contribute to two-dimensional convection. Accounting for this new effect makes the model's predictions accurate. Firstly, the conditions for the onset of convection are defined more precisely. Secondly, the flow characteristics that arise only under the action of the Coriolis force now have a theoretical explanation and can be modeled in numerical experiments. For instance, the theory did not predict the presence of spiral flows in Hele-Shaw flows, although this phenomenon was observed experimentally,” comments Dmitry Bratsun, head of the Department of Applied Physics at PNIPU, Doctor of Physical and Mathematical Sciences.

“Another important property of the Coriolis effect is its stabilizing influence on the fluid. We discovered that with this force present, the onset of convection is slowed down, and the already developed motion remains orderly for a longer time and space. The scenario in which the system transitions from an equilibrium state to chaos significantly differs from previous predictions. We can say that we have corrected a fundamental inaccuracy in the equations of two-dimensional convection, which has important implications for both the theory itself and for devices that manage flows at small scales,” adds Vladimir Utoshkin, assistant professor at the Department of Applied Physics at PNIPU.

The research conducted by PNIPU scientists has identified a factor influencing fluid movement in two-dimensional cavities. The results are applicable in medicine, pharmaceuticals, and other fields related to microfluidic devices.