How Abrasive is Water?

Why don't you just get some, "water found in cooling towers and heat exchangers" for your tests?

I fear that you are over thinking this.

Is this your first time developing a coating for this industry?

There are several areas that you should be aware of that should provide you with that information. ASTM standards and the AAMA standards are two that you can research. If you are a coating manufacture you should access to each of these standards. If your an application person then you will need to contact your coating supplier for this info or purchase from the two fore mentioned parties.

It is basically going to be demineralised/deionised water. Easiest way to get some is go an buy demineralised/deionised water that you would have used to top up car batteries.

Since cooling towers pick up whatever is in the local atmosphere there is no obvious way that you can simulate it. I've seen cooling towers loaded with sodium chloride (not good!) - the site was near the coast. In addition, you will probably get some precipitation of calcium and/or magnesium carbonate crystals, despite having chemicals present to prevent/minimize it. I would venture to say that the suspended particles in cooling water will depend very much on which way the wind is blowing. As lyn says, try to get some real-life cooling tower to play with.

the water supply that will feed your cooling tower will provide you with a few clues. the cooling tower works off of evaporation principles. as the water evaporates it will leave behind solids that were previously dissolved in the supply water. when starting a fresh cycle there will be few solids present...or should be few the longer the tower is in service the more these solids will accumulate in your sump. this of course does not take in account the bleed off rate the drain is set for or any chemical treatment that is holding solids in suspension. so depending on the region the tower is being used in and the quality of the water supplied to the tower will always be factors. not to mention the overall quality of the ambient air being drawn through the tower. dirty city air contains quite a bit of particulate matter that will end up being deposited in the sump as well. these combined solids will be drawn into the circulation pump and will shower the inside of the tower as long as the tower has power and a demand load. so to answer your question. I'd start with a water quality report on your supply water, looking at the elements that make up your dissolved solids.

About as abrasive as a wet kiss....

You should be more concerned with the periodic maintenance cleaning, and chemicals used to treat water....as well as the materials used to construct the wet surfaces...

We need to set-up a test of the coating's resistance to abrasion.

Do you perhaps mean corrosion?

What type of cooling tower and heat exchanger is this for? Don't some of them use a mixture of anti-freeze, other chemical additives (anti-corrosion, fluid enhancers, colouring, etc) or perhaps even high pressure which could directly effect the cooling tower surfaces.

What is the application and do you know the actual composition of the fluid (it may not even be water depending on the application)?

Not knowing much about chemicals or abrasives, my approach would be to make up a sample of the particulates in the air at a typical site, along with a sample of the water in that same area. I would go for a worst condition senario to develop the coating. The ability of a coating to resist an abrasive would depend on the surface finish of both the inside of the pipes and the cooling tower. A smooth finish would be less affected than a rough finish. I would think a coating containing teflon or another slippery and durable material would be what you would be looking at.

Water is not in itself abrasive. It is non-dissolving contaminants that may make it so.