4 ms·

Ah, gotcha. Feel free to throw out any questions, I'm an expert at this.

avmich 7y ago
If you have two components, which react violently - highly exo-thermally, so that there is a whole system of handling the resulting materials of the reaction - how would you design the point of contact of input substances?
- neltnerb 7y ago
  Assuming all liquid products -- Exothermic reactions are very good to handle using microreactors because the surface area to volume ratio is super high. For instance, if you take a cross section of the reactor and the inner diameter is only a few millimeters then it is quite straightforward to rapidly cool it by simply submerging the tubing in a cooling bath. As to the point of contact, one thing I've done is to build a "coaxial reactor" wherein you have two tubes carrying fluid with one inside the other. The outer "sheath" is one reactant while the inner tube is the second reactant. At the end of the inner tube the two mix via diffusion (low reynolds number) to reduce the speed of the reaction. If that doesn't mix well enough (in reactors at that scale mixing is largely diffusion rather than convection) I've used in-line stainless steel mixers which are basically a convoluted flow path in a little canister that has ports on both sides. I'm not quite sure what you mean by "whole system of handling the resulting materials"; if you're talking about needing to take that into something to handle solids then the above makes slightly less sense. If it's just thermal management, my personal approach would be small diameter tubing in a water bath to rapidly quench it. I think small reactors are much simpler to operate for highly exothermic (or endothermic!) reactions because the heat transfer is so high relative to a bigger reactor. It is also a lot safer because the total amount of chemical in the reactor at a time is a lot less.
  - avmich 7y ago
    Thank you very much, I really appreciate your response! :) Reading about flow reactions, it occured to me that liquid propellant rocket engines sort of satisfy the definition - they often have liquid - sometimes gaseous - components entering the reactor (chamber), where they react, releasing heat, and the products of reaction are passing gasdynamic nozzle with the goal of increasing flow speed. One of the problems is to make sure propellants are reacting well - and the timing is critical, as propellants need to react during millisecond-level periods while they are still in the chamber. So I wondered what methods flow chemistry can offer to rocket injector designers regarding reaching good mixing. This question is important for different scale of engines - both mammoths like Saturn-V's F-1 and tiny reaction control system engines, which these days find their ways into cubesats. Thank you again!
mindcrime 7y ago
1. Are there any good examples of this sort of thing that scale down to level where a DIY'er could experiment with it, and that involve things that aren't crazy dangerous to work with? 2. Is there a canonical text or other reference that you'd recommend on the subject?
- neltnerb 7y ago
  The epoxy gun described below isn't that far off. Yeah, there are a variety of books on microreactors in general. I think my recommendations would be dated. One cool one was talking about fluidics in general including how people used to think it would be simpler to build fluidics-based computers because of the size of vacuum tubes. So they had fluidic versions of things like diodes and amplifiers. Sorry I can't remember the names though, they were mostly good finds at the library.

If you have two components, which react violently - highly exo-thermally, so that there is a whole system of handling the resulting materials of the reaction - how would you design the point of contact of input substances?

neltnerb 7y ago
Assuming all liquid products -- Exothermic reactions are very good to handle using microreactors because the surface area to volume ratio is super high. For instance, if you take a cross section of the reactor and the inner diameter is only a few millimeters then it is quite straightforward to rapidly cool it by simply submerging the tubing in a cooling bath. As to the point of contact, one thing I've done is to build a "coaxial reactor" wherein you have two tubes carrying fluid with one inside the other. The outer "sheath" is one reactant while the inner tube is the second reactant. At the end of the inner tube the two mix via diffusion (low reynolds number) to reduce the speed of the reaction. If that doesn't mix well enough (in reactors at that scale mixing is largely diffusion rather than convection) I've used in-line stainless steel mixers which are basically a convoluted flow path in a little canister that has ports on both sides. I'm not quite sure what you mean by "whole system of handling the resulting materials"; if you're talking about needing to take that into something to handle solids then the above makes slightly less sense. If it's just thermal management, my personal approach would be small diameter tubing in a water bath to rapidly quench it. I think small reactors are much simpler to operate for highly exothermic (or endothermic!) reactions because the heat transfer is so high relative to a bigger reactor. It is also a lot safer because the total amount of chemical in the reactor at a time is a lot less.
- avmich 7y ago
  Thank you very much, I really appreciate your response! :) Reading about flow reactions, it occured to me that liquid propellant rocket engines sort of satisfy the definition - they often have liquid - sometimes gaseous - components entering the reactor (chamber), where they react, releasing heat, and the products of reaction are passing gasdynamic nozzle with the goal of increasing flow speed. One of the problems is to make sure propellants are reacting well - and the timing is critical, as propellants need to react during millisecond-level periods while they are still in the chamber. So I wondered what methods flow chemistry can offer to rocket injector designers regarding reaching good mixing. This question is important for different scale of engines - both mammoths like Saturn-V's F-1 and tiny reaction control system engines, which these days find their ways into cubesats. Thank you again!

mindcrime 7y ago

1. Are there any good examples of this sort of thing that scale down to level where a DIY'er could experiment with it, and that involve things that aren't crazy dangerous to work with? 2. Is there a canonical text or other reference that you'd recommend on the subject?

neltnerb 7y ago
The epoxy gun described below isn't that far off. Yeah, there are a variety of books on microreactors in general. I think my recommendations would be dated. One cool one was talking about fluidics in general including how people used to think it would be simpler to build fluidics-based computers because of the size of vacuum tubes. So they had fluidic versions of things like diodes and amplifiers. Sorry I can't remember the names though, they were mostly good finds at the library.