Rice doesn't help dry anything!

It's time to put this myth to rest. Using rice to help dry batteries or a mod that got wet doesn't help at all. In fact, it slows down evaporation of any water that is inside.

I set up a 24 hour test using paper towel sheets with enough water added to bring their weight to 18 gms. I then put these wet folded paper towels in four places; a slightly ventilated box in rice, a slightly ventilated box 3 feet in front of a fan on low, a bare folded paper towel in still air, and a bare folded paper towel 3 feet in front of a fan on low. The complete results are in the table but two are presented here...
  • Amount of water that evaporated from the box in the rice after 24 hours = 2 gms
  • Amount of water that evaporated from the box in front of the fan after 24 hours = 10 gms
Five times more water evaporated from the box that was in front of the fan. It's clear that burying anything in rice just slows down the evaporation of any water that's present. This makes sense though. Rice can't vacuum up water. It can only absorb any water that evaporates and touches the surface of the rice. Even then though rice is a lousy absorber of atmospheric water.

Since the device that is wet is buried in rice, with no air movement, the humidity level quicky rises up to 100% next to any water that is present inside the device. This significantly slows down any evaporation that could take place.

Adding air movement blows away the layer of very humid air above any water, allowing the water to evaporate much faster.

Some of you might have tried using rice and found that you could turn on your mod a day or two later and it worked. But did you open up your mod to see if the water had actually evaporated? How can we know that the rice did anything?

Bottom Line: If you have a mod that got wet, do not turn it on. Remove the batteries (if possible), shake out any water you can, and then place it in front of a fan. Rotate it every couple of hours to try to get any blowing air into any seams or ventilation holes. It should be pretty dry internally in 24 hours.

Please don't bury it in rice!

[edit] I'm sure there will be those who feel this test was invalid for one reason or another. It's backed up by every good test like this I found online but I strongly encourage anyone who feels I erred to do their own tests. I would love to see the results!

[edit] For those who are concerned that the paper towels "lock in" the water, keeping it from evaporating:

Pictures of the setups:

Comments

Oh i assumed that the rice only worked with chinese built mods being as after u we t to sleep some chinese would come for the rice and fix the mod as payment for the rice? Thats not how it worked?
 
Have you given any thought to testing silica packets? I have read they should be used over rice.

Thanks for the informative research. I'll admit I have put a fair share of phones into rice beds with mixed results. Hadn't tried a mod yet, though I would be hesitant to put a regulated mod into that. Bigger crevices than a phone. I like Sonic's idea for the new blog category "Mooch Busters" ;)
 
I have some indicating silica gel coming but all these different substances can only absorb moisture that has evaporated to outside of the case of the device. If the moisture is already out, why try to trap it in a container long enough for the substance to eventually absorb it? Just blow it away so the humidity immeduately surrounding the device is lowered and evaporation is easier. :)

But I will give the silica gel a full test.
 
The IMRBatteries sale, eh? :)
Check my blog index for the link to all my test results. The test report for the HD4 is there.
 
I think the silica gel might work better than you suggest even though I agree that no matter what the water has to get out the mod and evaporate. But the silica will make the air drier therefore speeding up evaporation inside the matter by the drier air pulling the moisture faster. Just my 2 cents, and thanks for the testing on rice because I assumed that would work but now I know it's an urban myth perpetuated by The lying media that tries to bring down dear leader
 
Silica gel can only bring the humidity down to 45%-55% though and absorbs incredibly slow. It's only made to absorb trace amounts of moisture vapor left inside a sealed box or the tiniest of air leaks.

Blowing the humid air away from the openings of a mod will always work faster than having the 100% humidity at the openings waiting for it to be absorbed, which only happens if it hits a piece of gel.

The testing I did using a pound of baked new gel was only a small bit better than rice and much worse than using a fan on low nearby.
 
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.

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.

The only practical way to desiccate electronics is vapor movement. However, vapor movement is governed by 2 things; local vapor pressure and movement of gasses. 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 (and silica gel) 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.

TL;DR

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.
 
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