I've been giving a good bit of thought about how to separate the water before it gets into my compressor tank. I'm currently planning on running it through an automotive air conditioning evaporator core and then into something similar to what I've found on the web called a "franzinator" which separates the water from the air by giving the air flow a sharp turn after leaving a small pipe into a larger pipe. I've got a blower for the core, but haven't actually put it all together just yet. Time and budget constraints.... The franzinator works by creating a pressure drop and a sharp turn. The pressure drop cools the air and the sharp turn flings the water away, where it falls down, and as the air flow going up is slower in the larger pipe, each component goes their separate ways. I'm sure that the evaporator will reduce the air temperature significantly, and there will also be a temperature drop in the franzinator. Is there a way I can figure out if there will be a freezing problem, or am I overthinking this issue, which happens all the time? There's not a whole lot on the web about this sort of arrangement, least not the combination I have in mind, so I wanted to see if anyone has any experience with this sort of thing or has used either part of this system, and if so, how it worked for you.
Even if you intercool and remove any liquid water, the compressed air is still warmer than ambient and at 100 percent relative humidity. As it cools down the line it condenses more liquid water. Don't confuse "wet" with "moist". One is liquid, one is vapor. One you can mechanically filter, the other you can't.
The only way to make dry air is with a phase-change heat transfer, such as a refrigerated dryer, ice bath, or regenerated dessicant.
Simply widening of the pipe, does not necessarily create a pressure drop of significance. That's a flaw in your reasoning. But even without it, cooling compressed air to ambient will probably precipitate some moisture, so your plan is solid. Just use a moisture separator (filter) with a drain.
Have a filter the output of the tank, for sure. I have a thing about rust inside a pressure vessel. I was sure that the idea would work, but wasn't sure how well. Neither item by itself would remove the moisture, and I have most of the materials floating around the house. Plus this is a fun little project for me; I just wanted to make sure it would be worth the effort. I figure that when the tank is full of hot air, it will cool off and eventually kick on again at quiet times, something my wife finds annoying. If the tank is full of cool air, it holds more useful air and won't kick on a again a couple times after I'm done using it.
I -think- I've rust proofed several tanks by sloshing LPS-3 mixed with kerosine around in them. A week hanging up in the sun dried out the solvents. I did have to explain the bright red 60 gallon tank hanging from a tree. (It's a bird feeder...)
There are several anti-rust chemicals that perform well. I've tried LPS-3, Rustlick 631, and Sprayon 711. Boeshield T-9 may be better. MSC had LPS-3 at a local store and I bought a few gallons.
The evidence that it works is no discoloration of the condensate from the air tanks and no rust, odor or oil sheen on the water from the solar heater, which had rusted through. I re-treated an air compressor when a little rust started to show after 20 years.
The big stationary tanks are easier to drain if you connect a short air hose whip to the drain fitting to bring the valve out where it's accessible. It's easier if you can crack open the drain valve with one hand and restrain the clear container with the other. Once the water is gone you'll get a blast of air.
Simplified chemistry lesson: If a gas is much warmer than its boiling point, air for example, Pressure X Volume / Temperature = a constant. PV/T=nR. Double the (absolute) temperature and the (absolute, not gauge) pressure will double. Let it expand to twice the volume and its pressure and temperature will drop. After it warms back up the pressure will be half what it was before.
If it's near or below its boiling point, like water, the vapor pressure depends only on temperature. When you try to compress water vapor it simply condenses (less simply, it also warms up). The air in the tank has as much water vapor in it as saturated outside air at the same temperature, the rest is liquid. If the tank warms up some liquid will evaporate, if it cools some vapor will condense.
When the compressed air passes through a regulator its pressure drops, it cools and its volume increases. The water vapor that was at 100% relative humidity now expands into the larger volume and the relative humidity decreases, unless there is liquid water in the line. This means that the easy way to dry compressed air is to increase the tank pressure and let it expand more to the regulated output pressure.
Carl, if you cool the air to a little above room temp in the evaporator core before it enters the tank, some of the water will condense but you will still have air saturated with water vapor going into the tank, and a little water will still condense in the tank as the air cools the rest of the way. The evaporator would remove much more water if it was in a bucket of ice water or a refrigerator. I don't know if you can take out enough to keep the tank dry but it's easy to try and a good excuse for an extra beer cooler.
I don't want the bother and expense of drying air to mainly run air tools, so I use a STA-DRI in-line dessicator for painting and plasma cutting and dry the calcium chloride out in a vacuum oven when it turns color.
Those of you with air compressors in their shop[, Ho w many times have you inspected the inside of your air reciever? My comp is 20 years old and I've never looked inside. I always have a little air bleeding out of the drain on the bottom of the tank. I always shutoff the compressor when I leave the shop and let the tank go to zero psi out the drain. I have an air dryer on the tank outlet if I need it.