Hi All - starting account to be able to comment & question wrt Mooch

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Baditude

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    Welcome to the forum.

    Mooch stays pretty busy these days, but you can contact him by targeting his screen name with @Mooch.

    You can also comment and question others on ECF. There are many knowledgable and experienced veterans here who can also answer questions that you may have. Battery specific questions are best asked here: Batteries and Chargers
     

    PapaBear

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    Sep 14, 2018
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      In my 9-5, I deal with feeding reactants and humidity to a high current/power application. I've got some thoughts wrt the whole concept of using rice to desiccate electronics.

      No pun intended, but rice should (and indeed Mooch proved that it does) slow the process of desiccation of electronics. Here's the why:

      Water in electronics can only move out of the electronics in two ways, fluid flow and vapor flow. There are no other pathways. Fluid flow generally will not happen. As a matter of fact, it almost never happens unless there is a significant amount of water. As in pooled water.

      Why do I say this? Well, I'm going to dive into physics a bit, but, it's the best way to explain this. Most electronics and electrical components are either coated in a polymer (plastic) or surrounded by polymer components. Most polymers are hydrophobic - meaning that water beads up on them. Picture droplets of water on a Teflon pan. Once you have managed to wet out hydrophobic surfaces that are in close proximity (i.e. a small capillary tube), the energy required to make water move through these small tubes is very significant. So water will only flow when physically forced to move.

      I'll continue with the vapor movement explanation in a bit.
       
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      PapaBear

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      Sep 14, 2018
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        Per my previous post, small amounts of liquid water won't move. Therefore, the only practical way to desiccate electronics is vapor movement. However, vapor movement is governed by 2 things. Although rice would seem to be a potential desiccant, it works very poorly. Vapor movement is described by Fick's law - molar flux is proportional to the concentration gradient.

        Let's unpack that. Gasses try to achieve an equal concentration everywhere. If you have a wet piece of electronics buried in rice, the local water vapor pressure will tend to equalize. The real effect on this is an initial movement of water vapor to the rice skin. But once a tiny bit of humidity is absorbed, the rice acts like a sponge barrier and slows the passage of water vapor out of the vicinity of the electronics. Clearly rice is not the best answer.

        An alternate solution that will bear much better results is to use heat to accelerate the desiccation process. Let's assume that the electronics is at a room temperature of 70F. There will be a very small amount of water vapor that is in the immediate vicinity of the water droplets. That vapor will have a pressure of about .37 PSI. The surrounding air will have a lower vapor pressure of .37 PSI * the relative humidity of the surrounding air (typically 30% - 70% RH). If we take a nice round number of 50% RH, the surrounding pressure is approximately .185 PSI. The differential pressure of .185 PSI is enough to cause the water vapor to move into the surrounding air.

        However, if heat is applied, the vapor pressure in the vicinity of the water droplet will drastically increase. As an example, at 120F, the vapor pressure will increase to 1.69 PSI. The differential pressure is now approximately 1.5 PSI. That's approximately 8 times the motive power to move the water vapor. Of course this can also be improved by blowing a fan over the warm piece of electronics.

        Please note that I am suggesting a very moderate temperature. Most consumer polymers *CANNOT* handle high temperatures. Some polymers like polypropylene start to soften at approximately 140F.
         

        r77r7r

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          TL;DR issue?

          Short version, if you need to dry electronics: put it in a container, heat the container to 120F and blow air over the top. That will beat all other methods by a long shot.
          So, throw it in a shoe box with a hair dryer?
          Welcome to the forum.
           

          stols001

          Moved On
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          May 30, 2017
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            Welcome @PapaBear I actually have a piece of electronics that I deeply want to be sure dries out completely and it's been sitting a few days but I'd love for it to be dryer! I really like this thing and cannot replace it. I've gutted it as far as I can.

            Can you please phrase for me your method in language useful for clumsy idiots? It sounds interesting from what I can tell. I don't necessarily need a "why" it works, I'm gonna assume based on what you are saying, this works. (I also have little to lose at this point). I need like a how to and yeah probably using household items LIKE a blowdryer, etc. and also "how long". Etc.

            Also, welcome to ECF.
            Anna
             

            r77r7r

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          • Feb 15, 2011
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              Welcome @PapaBear I actually have a piece of electronics that I deeply want to be sure dries out completely and it's been sitting a few days but I'd love for it to be dryer! I really like this thing and cannot replace it. I've gutted it as far as I can.

              Can you please phrase for me your method in language useful for clumsy idiots? It sounds interesting from what I can tell. I don't necessarily need a "why" it works, I'm gonna assume based on what you are saying, this works. (I also have little to lose at this point). I need like a how to and yeah probably using household items LIKE a blowdryer, etc. and also "how long". Etc.

              Also, welcome to ECF.
              Anna
              Seen some guy Put something in a box and poke a hole in it and point a hairdryer in and leave it for a few hours. I imagine airflow is a priority over heat. We used to dry atties using a pc fan or home aircleaner or ac/heating vent.
              But, u didn't ask me :).
               

              uthinkofsomething

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                I'm just a simple unfrozen caveman vaper, but I seem to have heard that water evaporates more quickly when air is cold. If the rice doesn't work, which I have heard previous to this thread, mayhapst I would set something wet in front of my air conditioner, which also removes humidity from the air.
                Heat may work better to get the moisture OUT of the device though.
                 
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                PapaBear

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                Sep 14, 2018
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                  Easiest way to do this would be to pop the piece of electronics in a shoebox with 2 holes. 1 hole should be exactly the size of the hair dryer. You'll need a thermometer to make sure the temperature inside the box doesn't get too hot (just poke the thermometer through the lid). Try to keep the temperature under 120F. Remember that several plastics start to go soft at 140F.
                   
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                  PapaBear

                  Full Member
                  Sep 14, 2018
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                    I'm just a simple unfrozen caveman vaper, but I seem to have heard that water evaporates more quickly when air is cold. If the rice doesn't work, which I have heard previous to this thread, mayhapst I would set something wet in front of my air conditioner, which also removes humidity from the air.
                    Heat may work better to get the moisture OUT of the device though.

                    The reason why an air conditioner helps to dry things is because it actually dehumidifies the air that it is chilling.

                    The speed that water evaporates at depends on the relative humidity of the ambient air (this is effectively the ambient water vapor pressure), the vapor pressure of water (which goes up with temperature) and the movement of air across the water's surface.

                    Bottom line, it is much easier to evaporate water at higher temperatures.
                     
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