Alternative To Mineral Oil

You don't mention your application, but there are several perfluorocarbons that have low vapor pressure and viscosity. I suggest you take a look at Fluorinerts by 3M.

We manufacture oils for ammonia refrigeration systems that surpass whats currently being made. I looked into this same style of application. One of the things you might want to research is different nano technology. One that I found is nano diamonds. They are rather expensive, but a small amount go a long ways for adding lubrication in extreme low temp areas.

Also, if I were you I would look at the oils that are used for cryogenic applications. These will work at the temps you listed and being wax free they should also help with the thermal absorption that you are looking for as well.

This reply is for both Welderman and Enersol,

First my application. Many here will remember what I do with our experiments with high altitude balloons. We 99% of the time do these flights for young people groups, as an example like Boy Scouts. As seen here in a flight we did for several hundred a few years ago. a you tube video of the news story of the flight can be seen here,

http://youtu.be/HJ0IT4ZwtSo

Or the view from 118,000 feet.

OK, we have been working on a special flight that is a long duration flight. These flights normally only last 3 hours or so because the balloon keeps rising until it can not expand any more and it pops and the payload comes down on a parachute.

We have developed a balloon that will reach altitude and then vent out some of the lifting gas until it reaches a neutral bouyancy and floats there.

Thing is tho after sun down, it looses the energy from the sun and the lifting gas looses about 10% of it's lifting capacity, and the system begins to sink. If we drop 10% of the weight we can remain aloft. Anything that can be dropped can act s a ballast drop. from sand, to alcahol, to paper leaflets, etc.

I thought of taking this Ballast one step further. Make it not only a dropable weight, but to make it useful at thermal management too.

Because at these altitudes it gets cold, and I mean really cold especially at night it can get as bad as 70 below C.

The thought is we launch at sundown, so we already then have a 24 hour flight before we would need to do the first 10% drop of ballast.

We pre heat the oil to the upper limit of either the oil or the electric components. so it has the first night of as toasty as possible.

The next day we have surplus solar energy both direct and via excess power from the solar panels that we can dump this into the oil to try to keep it warmer.

we have a solenoid valve that will gravity drop ballast when needed.

So the electronics is in the oil.

So there we go thats the application.

oil needs to not boil in vacuum.

of course needs to be a insulator, we do have 12 volts dc running in the oil.

and needs to remain relatively flowable through a 3/8 inch orifice solenoid valve, when cold, Hopefully with the energy from the electronics of the payload and solar panels as well as direct solar gain we hope to keep it at least at 0 deg C, but still need to plan on that not working and the oil get as cold as 50, 60 or even 70 below C.

So Enersol, or anyone else, have anything suitable?

Joe

Based on the information you have provided, I would not rule out the fluorinerts such as FC-40. It has low vapor pressure (287 Pa) and pours well at low temperature. It's an excellent dielectric and you can operate electronics submerged in it. It's very dense (but so am I) which will limit the volume you can take on board. I suggest you check it out.

Looks very promising, I contacted 3M about it and what i plan on doing with it. no where on their site did i see any pricing for it tho. and one E-Bay auction sure made some serious sticker shock!

Joe

No doubt, this stuff IS expensive. But the good news is that it is dense, so you shouldn't need a lot of it. I got some FC-77 on Ebay for a very reasonable price. It was used, but I filtered it and it served my purpose nicely. According to some charts I've seen, at any temperature FC-40 is about 1/100 the viscocity of mineral oil.

77 looks like it goes even colder!

I hope you are not using the mineral oil as ballast....Ha!

Why not simply use an onboard (small) compressor of the lightest possible weight, to store and deploy enough gas to maintain neutral bouyancy during the 24-hour period? Peel and stick PV should be coming out soon as boasted by results of Stanford University tests.

If that was possible, we would, but we are limited to weight per air regulations. The whole payload must weigh less than 6 pounds.

So any type of compressor, or storage tank would be far too heavy.

And what is wrong with mineral oil as ballast? other than it flows, but too slowly,

Why not use dry sand? Too hard to control? OK, then try something like cutting the mineral oil with kerosine? After all, it is just another hydrocarbon...

the kerosene I'll check out. two things it has to not do,

Biol in a vacuum, and freeze t 70 below c

From what i found Kerosene freezes at only 20 below C so thats a no-go

In the interest of those who suggested silicone oils, you might have better luck with those. Many of the hydrocarbon oils, even olefin oils of C10-C12 cut will probably either vapor-boil or freeze under your conditions.

I still think nice dry sand that is microscopically "rounded" compared to angular sands, would run out from a cone-shaped bin with a electric operated shutter flap in a controlled way.

The only problem with sand is indeed getting it dry enough and keeping it that way.

next to impossible really.

Sand may be difficult. I don't know how much ballast you intend to drop, but I drop lead shot into shot shells with accuracy and repeatability of a small fraction of an ounce (about 1/1000oz). It flows nicely under all kinds of atmospheric conditions.

Let's make that steel shot and save a bird.

I like the idea though.

Now they will fly over a high tension power line, drop ballast, and the steel rain, will short out the system, causing a blackout in at least 7 states.

And on the way down the shot will enter the intake of a passenger jet loaded with vacationers. The engines will flame out, steel shot will blast through the redundant controls and the airplane will crash into the power lines, causing death and destruction over a wide area. Due to the drought conditions millions of acres of grassland, homes and Bambi will suffer the consequences of a major firestorm.

OK, lead shot, just this once.

OK, OK, then try the silicone oil, at least all it will do is lube a goose or two.

In my part of the country, more birds are shot with steel shot than lead. I wouldn't worry about shot falling on power lines from 100,000 feet up. It will be so dispersed that nearest other piece of shot is likely to be a mile or two away. Also, OP has not told us how much weight he needs to discharge and any volume restrictions. The ballast could be ceramic or even plastic spheres. You must be aware that the engines on jet aircraft are designed and tested to digest large birds. Teflon spheres might be considered mandatory lubricant.

Dropping ounces at a time once a day. so not much at all.