Microreactors - Science topic

Characterizing the degree of mixing is essential in processes involving multiphase systems, chemical reactions, and material blending. Here are some common methods used to quantify mixing quality:

In my opinion, this is one of the technologies of the future. If such solutions, i.e. portable nuclear fission reactors (battery microreactors) could be developed, refined and implemented for mass production, it could revolutionize the energy sector. This may be one of the important factors in creating innovative, pro-ecological solutions as part of the future pro-environmental transformation of the energy sector.

Regards,

Dariusz Prokopowicz

Just a general comment. Consider the traditional first-order kinetic of reaction occurs in the micro-channels, so we can write the rate of reaction:

-dC/dt = kC where k = k0*exp(-Ea/(RT)); Ea is the activation energy, k0 is the pre-exponential factor.

Recall the basic chemistry knowledge that the activation energy is determined by the chemistry, e.g., nature of chemicals and catalysts used. It's independent of the mixing condition. The pre-exponential factor is of course depends on the mixing intensity - i.e., better mixing leads to a higher collision rate that leads to a faster reaction rate. In this way, a microreactor might outperform the conventional macro reactor due to a more intense mixing in the former, thus increasing the k0 value.

Prajakta Gajbhiye, In my opinion, you cannot "incorperate" E(t) into any mass balance equation. However, you can try to modify the mass balance taking into account, apart from longitudinal dispersion, e.g. radial dispersion. The model can also be extended with the dynamics of the catalyst grain. But that's just a guess.

I think,.you try.with paint remover solvents. Commonly used solvents include mineral spirits, turpentine, denatured alcohol, linseed oil, xylene, lacquer thinner, acetone and methyl ethyl ketone (MEK).

hi,

Microreactor systems is the assembly of various working instruments shrunk down to micrometer scales for its ease of use in the field with enhanced efficiency and reduced cost. For example, micro pcr. Assuming the size to be in few mm, it contains microreaction chamber embedded with heater, fluid pumps, optical sensors and the signal conditioning and processing electronics hardware. Continuous flow would be any generic fluid flow that you must have observed in your surrounding environment. For example, a garden water pipe made of flexible material. The water flowing out of the pipe is continuous if you keep open the water tap. In the same scenario if you press the pipe at an arbitrary point by your feet and immediately remove it, it will cause the water coming out of the pipe to be with a discontinuity. If you repeat the same process, you will end up with a water flow coming out of the pipe having intermittent flow characteristics. If we apply the same logic to the fluids that have microliter volumes, it becomes microfluidics. Microfluidics is a generic word to describe the study and applications of characteristic nature of fluids at microliter volumes.

All the above explanation is superficial.

Regards

I think what you are seeing in your experiments is a wicking phenomenon. That is, the curvature of the moving interface generates a favorable capillary pressure drop to drive the flow preferentially near the sidewalls of your channel. High curvature near the side walls of the channels relative to the mid region of the channel generates a capillary pressure, for the same reason why liquid climbs up (wets) a glass slide dip into a pool of liquid.

I am not sure I fully understand the pocket formation of dry spots. It may be an example of what is referred to as "pearling". That is the thin film region on the middle of the channel undergoes a instability that breaks the flow in the mid channel into drops. The pearling effect has been studied extensively.

There is quite a lot of work on using wicking to generate passive flow in micro-channels (Google "wicking in microchannels"). Just as water wicks a paper sheet ( see Lucus -Washburn eqn), researchers have used used porous material at either end of a microchannel to generate passive flow in a microchannel. Hope this helps.

Dear Ghasem,

I haven't checked it without flushing. I should do it next time. For the case of contamination or algae, I should do further investigation.

Thank you

Yes, invest in some glass house of the height you want and keep it at the temperature you want, with water base and your samples on a platform on that base covered with glass. So, your samples, culture, whatever, will be at a platform in the water in the house, covered with glass. The platform will not be covering the water base completely, but partially, so the water can condense the air within the chamber. So, in a circular base, the platform can be a hexagonal glass plate, on some small stand, made from, anything, from bottle caps to some other lid.

Some home-made ones that are available at home as well:

When the Re number is very low, diffusion becomes the main player in assuring inter-diffusion, i.e. mixing. Although diffusion processes can be quite slow when considered from the macro-scale point-of-view, in a microfluidic channel the small sizes make the mixing time much shorter, moreover diffusion can provide for a reliable and predictable tool. One can precisely calculate the time and spatial distribution of chemicals in a solution, by knowing the initial concentrations, channel geometry, flow rate and diffusion coefficient. Even more, given the laminar flow regime, in the steady state the spatial distribution remains constant and offers a picture of the time evolution of the mixing process.

This is a question of molecular dimensions with respect to channel size. If the molecular sizes remain small with respect to channel dimensions, there is no reason to assume a change in reaction mechanism and kinetics.

Vivekananda, is there a third member to the reaction from A to B? It is possible that the intrinsic addition of this member is what is causing the mass balance error. What I mean is, if the reaction is of the form:

A + C ----> B

it could be possible that C is not explicit present in the domain, but is being modeled by a coefficient that is multiplied to A.