Using Peltier dehumidifer for lenses etc

I have one too, used to keep the humidity down inside a wardrobe. It would be interesting to see how it performed in a small box (around

I brought a jar of indicating silica gel granules back with me after my spell in Fiji (where you can watch the mould growing on the walls, and is death to anything ferrous, optical or made of leather !!).

The granules are blue but change to pink when they have absorbed H20, then they can be recharged back to blue in a warm oven. I keep a pot of these granules in a plastic tub along with my camera lenses and tightly fitted lid.

Indicating silica gel must be available in this country, I would have thought ?.

It is:

I would probably do that rather than using the Peltier, although if the lens was kept in a warm dry place for a long period of time before putting in a sealed container with the gel it would probably help by having it dry to start with.

Theo

Drying is done in stages, each stage using a different amount of energy, and having a different "quality of drying".

If the lens was dripping water, you could use a "first stage" drying method. Maybe the Peltier would work, but a Peltier is one of the more inefficient phase change solutions (vapour to liquid or solid collection). A pool of liquid water has a partial pressure ppH2O over it, so it does not constitute being really dry.

The desiccant is a "finisher", to remove the vapour or most of it.

For some drying jobs, even a desiccant isn't enough. Perhaps you resort to a first stage vacuum pump and then for a couple days, a mercury diffusion pump.

Some things in chemistry are quite intolerant of the presence of water, and an explosion can result from improper prep. You look through your range of techniques, for the "appropriate" one.

You would not dry a soaking wet blanket with silica gel, because it would take a metric ton of packets to do it :-) Hanging the blanket on the line in the Sun, is a cheap source of energy for phase change, and removes the bulk of the moisture. If you have a clothes dryer, it can then take "less time" to finish the blanket. Then, if you wanted to place the blanket in a desiccator, it doesn't take quite as many packets of silica gel.

A molecular sieve (which is a synthetic zeolite), seems to be the most recent addition to the desiccant family. It can reduce the dew point of the sample to -70C or so, and is better than silica gel. Lots of things are better than silica gel, but silica gel is a very practical thing for most consumer usage. There are a ton of synthetic zeolites, for various purposes such as sequestering Hydrogen gas and releasing it slowly. It has a large surface area. F-gas removal for refrigerators, is done with zeolite filled cylinders (sucks up the F-gas).

A number of desiccants recharge in an oven. Some at 200C. The one I used in the lab at work, we recharged that one at 500C, but that was to ensure organic residues were burned off. That uses an electric oven with fire brick liner, thin ceramic dishes filled with desiccant. Once a recharge cycle is done, you leave the oven alone and DONT OPEN THE DOOR until the next morning. It needs a solid eight hours to be safe to open. Leave a PostIt note for your colleagues so no one opens the door. The desiccant still has drying power, while left in the oven to cool off.

A Google, does not seem to list all the desiccants, so good luck with that. Some desiccants for example, are clays, just like kitty-litter for soaking up petrol, is a clay of some sort. And the clay can be dried in an oven, at some temp.

Paul

I’ve used a small Petlier dehumidifier in the cooler months, with a small heater, our motorhome while on our drive for years. I use a temperature sensor to ensure the air temp kept is high enough via the heater so the dehumidifier can work.

As to your problem, I assume the rangefinder isn’t sealed?

I’d be tempted to try an airing cupboard, if you have on.

The heat should be enough to both turn the moisture to vapour and increase the pressure to expel some of the vapour. The dehumidifier can then deal with it. Not all will be removed but some will. Put the unit in a ‘Tupperware’ box before you start, lid off. After 24 hours in the cupboard, open the door, pop the lid on and remove. Let it cool. When cool, return to airing cupboard, remove lid, leave 24 hours.

Repeat several times.

Essentially, you are trying to expel ‘warm moist’ air and replace it with dry air. The Tupperware acts as an airlock.