Sciencemadness Discussion Board

A very cheap way to evaporate solutions

Hexabromobenzene - 24-1-2026 at 17:43

Evaporation in open trays.

Evaporating large quantities of aqueous solutions is very expensive due to the consumption of electricity, gas, or wood. To save money, I've long used evaporation in trays at room temperature. I use 20 x 20 cm square polypropylene containers. Sometimes I stack them into a large battery of 10-15 for evaporating larger quantities. In any case, evaporation takes a very long time, about a month.

To increase the speed of evaporation, I discovered a new method. I blow a computer cooler fan over the solution. It consumes only 2 watts of power. However, effective evaporation occurs up to 40 cm from the cooler. One computer cooler can be used for two containers. The evaporation rate increases tenfold due to the blower. Using a more powerful fan does not increase the evaporation rate.

During evaporation, the container cools down. At a room temperature of 23 degrees Celsius and 35% humidity, the container cools to 17 degrees Celsius (minus 6 degrees Celsius) with a fan, and only by minus 1-2 degrees Celsius without. The cooler the container, the higher the evaporation rate.

This method is highly seasonal. Evaporation is most effective in the summer during droughts or in the winter when the room is heated. This method is ideal for dilute solutions. Concentrated solutions can be evaporated further by heating.

You can easily achieve evaporation rates of up to 1 liter per day in a dilute solution.

This method can even evaporate sulfuric acid to around 50-60%.

This method does not produce aerosols, which can be problematic. It also creates large crystals that are easy to separate from the liquid.


[Edited on 25-1-2026 by Hexabromobenzene]

Sulaiman - 24-1-2026 at 20:58

your home must be a lot cleaner than mine because
I get 'dust' in/on any liquid left uncovered, even worse with airflow.

In uk winters I put solutions to be evaporated in beakers covered with filter paper
on top of one of my central heating radiators.

Hexabromobenzene - 24-1-2026 at 22:20

Insects are also a problem. However, you can create a closed system using racks with coolers and a fabric filter. You can place this in direct sunlight to increase efficiency. Polypropylene shouldn't be exposed to direct sunlight.

bnull - 25-1-2026 at 03:22

I've been using a fan from a dead ATX supply for more than a month. It is practically silent, works fine, no dust, insects or cat fur. The part of the tray closest to the fan tends to evaporate first. The tray must be in front of the upright fan and its rim below the level of the fan. I tried putting the fan above the tray but the result wasn't that good.

Edit: One issue I found was the formation of a crust on the surface of the liquid. Inspecting the trays every 2 hours should do.

[Edited on 25-1-2026 by bnull]

fx-991ex - 25-1-2026 at 13:57

work very well in dry winter month with a fan and large surface area but on humid summer not very well.

MrDoctor - 25-1-2026 at 14:21

better solution is, dont blow at the solution, but suck. turn that fan the other way around, better yet use a tiny ducted fan or centrifugal blower fan.
i used to have a fume extractor setup before i made my fumehood, it was pretty interesting quickly evaporating something like DCM in front of the thing would leave it completely full of snow if i put it too close and it went well below zero C from the DCM evaporating so fast.

I believe strong suction should produce fairly laminar flow directed towards the intake which is why particulates are so unlikely to land on the surface being drawn across. Otherwise acheiving this with actual laminar filtered air in positive-flow, is not a simple feat, for refference things like H13 air purifiers are designed around 0.3uM which is about the bottom end for biological life, not neccesarily, for air particulates, they get rid of mold and organic allergens, other inorganic particulates can make their way through. It may or may not be a big deal since we are talking about stuff that fills the air anywhere you go, this is the stuff that causes certain precision processes like hard drive repair or chip manufacturing fail consistently.

I would recommend setting up some sort of box with filters on the walls, and the fan drawing air out through the lid or one of the adjacent walls. a centrifugal fan might be better, and then you can duct the flow out a window or something rather than dispersing solvent fumes all around your environment.
10-20W ducted fans are common, but investing in a proper fume extraction setup might be worth your while, and this would be a good alternate use for a fume extractor.

chloric1 - 25-1-2026 at 17:45

Quote: Originally posted by fx-991ex  
work very well in dry winter month with a fan and large surface area but on humid summer not very well.


I had a cheap $14 fax mounted on a 1 gallon polypropylene container and I put 800 ml of dilute cupric nitrate and evaporated for 3 days last July with the following weather conditions; daytime highs 30-32 ℃ with nighttime lows roughly of 23 ℃ with 68-72% relative humidity. I got it down to under 200 millimeters in that time and put in a desiccator over NaOH until mid September to get 120-130 grams of copper nitrate. To be honest, concentrated sulfuric acid would have been better.

Hexabromobenzene - 4-2-2026 at 07:11

Experiments have shown that 80mm computer fans with 1 and 2 watts (0.15 and 0.3 A) are sufficient for two and three 20 x 20 cm trays, respectively. A 120mm fan with the same wattage produces a weaker wind. A 120mm fan with 7 watts (0.9 A) seemed excessive and produced a loud noise without increasing the cooling effect. I was unable to cool the trays below 17 degrees Celsius from 22-23 degrees Celsius. Perhaps evaporation will be more effective in the summer heat.

The rate of evaporation is proportional to the tray cooling delta. It was also noted that cooling drops sharply when the density of the potash solution reaches 1.3 and sulfuric acid also reaches about 1.3.

[Edited on 4-2-2026 by Hexabromobenzene]

fx-991ex - 4-2-2026 at 08:25

The top of refrigerator are often pretty warm too, i guess setting a fan up there would speed things up too.

Hexabromobenzene - 4-2-2026 at 09:22

Yes, heating can be very helpful. It's a shame that polypropylene can't be heated by direct sunlight. During a summer heat wave, the room temperature reached 35 degrees Celsius. This evaporated the potash to dry. It's likely possible to evaporate sulfuric acid to 70-80% under this condition.

pesco - 4-2-2026 at 10:21

Excellent idea with a fan. I'll add fan soon to mine stuff.

Since I glued tons of aquariums I made "evaporator" with glass. basically am aquarium with the top to prevent rain dripping inside. The top is sloping towards the back, so any condensation drips outside the box. Front is removable, sort of a slid in mechanism. Hard to explain. I'll take photos when I have a chance. Both front and back walls do not go all the way to the top crating a gap through which wind is roaming freely. The draft does same job as the fan. All , walls, but the front, which is exposed to the Sun, are painted black. Best result I got when I matted the glass with sand and painted the outside of glass. The black paint greatly increases temperature and speeds up evaporation.
I don't have much problems with tiny debris or bugs, but if I get something "dirt" sensitive I cover the slits with fine nylon mesh.
Usually I place inside liquids in PET containers like 2L or 5L bottles with top cut at widest section. Sometimes rectangular PP containers. PP, unlike LDPE or HDPE is pretty UV resistant and fact that glass is filtering majority of UV, the containers last long time without entitlement.
I had good source of HDPE and I fabricated containers. Using old oven to melt the HDPE, then formed sheets, which I welded using hot air soldering station. With walls 6mm thick and dark colour only the surface gets brittle not compromising the whole structure. These containers/trays are 7 years old and no hint of weakened structure.


Just to mention. Using same principle, part out of boredom and part out of curiosity I glued prototype distilled water factory.
Box like above, just without the "draft slits". Kind of fish tank with sloping lid and where it drips was collection vessel. The front aquarium filled with water, evaporated and condensed water collected in another "fish tank" behind it in a shade.
Works very well. Pretty productive during heatwaves, but not very fast in other weather conditions. However if you have space, several such "factories" placed in a corner of a garden can provide you with plenty of distilled water.

Most beautiful thing - this is TOTALLY passive system.

Only think you have to buy is glass cutter (few paunds/dollars) and silicone - pennies. Glass is free. Just find glazing shop. They always have plenty of windows that they are disposing off and every time I asked they were happy for me to take any I wanted.. All the double glazed windows/doors are 4mm or 6mm thick. Just got to be careful as some are toughened glass and you can't cut those.

Varungh - 6-2-2026 at 05:27

Quote: Originally posted by Hexabromobenzene  
Yes, heating can be very helpful. It's a shame that polypropylene can't be heated by direct sunlight. During a summer heat wave, the room temperature reached 35 degrees Celsius. This evaporated the potash to dry. It's likely possible to evaporate sulfuric acid to 70-80% under this condition.


35°C is rather cold stuff. At my place, it will be 45°C(approx) in about 2 months.
I am curious as to what that can dehydrate

6dthjd1 - 6-2-2026 at 22:04

wouldn't vaccum evaportation work?

bnull - 7-2-2026 at 02:42

Yes, but fan evaporation is simpler, cheaper, and even absolute beginners can do it.