[sucrose]

I have to make a lot of a particular solution for use in a machine. The solution is made from a powdered compound dissolved in water. For simplicity, lets say it's sucrose dissolved in water. Currently I have to make it in batches, where I measure ten liters of distilled water then weigh and add 21kg of sucrose.

My goal is to build a system that uses the compound's properties to automatically supply the machine, with the solution at the correct strength, without having to measure anything. The solubility of sucrose in water is 2.1g/ml at 25C which is the level I need my solution to be.

I'm thinking of building a tank that is fed by a distilled water supply line. The supply line would maintain a certain level of water and a submersible heater would keep the tank at 25C. I'd dump (without weighing) sucrose directly into the tank until I see a thick layer of sucrose form at the bottom, then I'd have a line that draws from the tank to supply the machine. If I see the layer of sucrose getting thin in the tank, I'd just dump another bag or two until it builds up.

How could I ensure that the solution that leaves the tank in the draw line is at the correct strength?

I'm thinking the temperature would prevent the solution from being too strong and a screen on the draw line would prevent undissolved sucrose from entering the draw line.

How can I prevent too weak of a solution from entering the draw line? And, do I need to agitate or cycle the tank water to facilitate the solubility or will osmosis automatically facilitate this?

[Enthalpy]

Hi Sucrose,

I wonder how slow dissolution becomes when the concentration approaches the limit, and how you will know that the solutions has attained (= is close enough to) the limit. A different temperature, where the solubility is bigger, and amounts measured prior to mixing, let operate farther to the limit and possibly gain time.

You will have to store the solution at +25°C too, as a temperature change would let the solute precipitate.

Checking the solution's concentration afterwards doesn't look much simpler than weighing the compounds before. Some water pumps offer an exact displacement volume. The regulation loop may need knowledge not available within your company but easily found at a contractor, a university... And if your amounts suffice, maybe you can ask your suppliers to fill exactly 21kg powder per bag and 10kg water per containers?

Don't forget the ease of cleaning your machine. Heaters on the outer side of the tank's wall may simplify this, a good design of the stirring element too. I also wonder how quickly the filter will clog, since it would necessarily operate from an over-saturated solution. Discontinuous operation, where the excess solute is allowed to sediment before filtering the solution out, would help but looks lengthy.