CurtPalme.com Home Theater Forum

**Curt Palme** · Posted: Fri Oct 19, 2007 2:49 pm Post subject: Why glycol?

OK, stupid question time. What properties does glycol have that water or mineral oils (or Koolaid!) don't?

What would happen if you used something like baby oil in place of the glycol?

Just something that's been bugging me for years, and today someone emailed me the same question, so I thought I'd post.

nuttall_chris · Posted: Fri Oct 19, 2007 2:58 pm Post subject:

Water expands when frozen (glycol doesn't). Most of the projectors are rated for storage temperatures below the freezing point of water. Expanding frozen water would break the tube face on AC sets and possible rupture the bellows on LC sets.

Also on LC sets the lenses/C-elements have been designed to work with glycol which has a higher index of refraction than water.

As for other substances....mineral oils, baby oil, Koolaid...don't know.

Chris

Z-Photo · Posted: Fri Oct 19, 2007 4:02 pm Post subject:

glycol is non-flammable-

Baby oil - not so much.

jask · Joined: 17 Mar 2006 Posts: 10187 Location: kamloops BC

I think it is actually the optical refraction that would be the most correct answer Very Happy

edit: the purpose is to as closely match the index of refraction in all the materials of the optical path..

drice1234 · Joined: 07 Oct 2006 Posts: 1309 Location: Allen, Texas

**kal** · Posted: Fri Oct 19, 2007 8:10 pm Post subject:

Having spent the last 2-3 weeks trying different fluids for cooling my beer taps and lines and doing a lot of research on it, it also has to do with heat transfer coefficients and efficiency. Glycol's really good and consistent in this way - you don't get hot/cold spots (and it also has a much lower freezer point/much high boiling point).

Water just doesn't work that well for cooling. One of the reasons why you don't have water in your car radiator either.

Kal

jask · Joined: 17 Mar 2006 Posts: 10187 Location: kamloops BC

this is a list of the indices of refraction for a few materials (no cool-aid, but you could just keep adding sugar till you hit the target gravity..)
acrylic glass 1.49
crown glass 1.52 (optical glass)

water 1.33 (@20C)
alcohol 1.36 grain
alcohol 1.32 wood
glycerine 1.47
turpentine 1.47
veg oil 1.47
lab oil 1.515 microscope oil

Glycol has the added bonus of being a very good conductor of heat,
if the tube face ever cracked a non-flamable fluid would make the choice of glycol over oil much easier!! I found a link to a patent that used siloxane polymers (silicone liquid) with a matched index for CRT projection lens groups...

ecrabb · Posted: Fri Oct 19, 2007 8:16 pm Post subject:

I think it's all of the above.

Compared to water, ethylene glycol/glycerol has:
- lower surface tension (better interface between materials, fewer bubbles)
- a lower freezing point
- a higher boiling point
- an index of refraction closer to typical lens materials
- better thermal conductivity (like Kal mentioned - this and the freeze/boil points are why ethylene glycol is a good automotive coolant)

If you do some googling, you can find some patents from people working on some cool polymer-based coolants with similar properties to glycol, but non-corrosive and non-conductive. Wouldn't that have been cool (sorry, bad pun)? Too bad they were working on that stuff right before CRT's started their precipitous popularity decline. Stupid digitals.

SC

bengalfan · Joined: 17 Mar 2006 Posts: 157 Location: Moline, Ohio

Ethylene glycol (a type of alcohol) has a very good coefficient of exansion (0.00099), excellant clarity, and a very low refrative index (1.406) . It also has a high flash point of ~ 120°+ F and bp of 275° C. this is important, means it can absorb alot of heat w/o expansion (or at least minimal).
It appears that Barco also used some glycerol blended into the et-glycol, probably as a humectant.

Mineral oils (baby oils) are alkanes, part of the early cracking process of petroleums. As such, the flash point would be in the dangerous area (fire and projector, bad), plus with all the impurities the clarity would not be good, and the coef of expansion is not very good at all. It does expand with heat, but I don't know at what level.

Water - gets hot quickly and POP, there goes that nice lens.

So save the oil to slather up your honey and keep it away from the projector. Very Happy

Van

(finally something I can write about!)

stefuel · Posted: Fri Oct 19, 2007 9:36 pm Post subject:

God you guys crack me up with all your slide-rules, flash point and refractive index's. I've tried straight medical grade distilled water and it works just fine. In fact the sharpest image you'll ever get out of a LC. The only thing I can't say is how long before corrosion occurs.

lucht · Guest

Fujifrontier · Joined: 20 Oct 2007 Posts: 354 Location: San Antonio, Texas

*ahem*

Good evening, sirs Smile

I was actually the person who asked Curt the question earlier, and he responded lightning-quick, which I appreciate greatly.

The reason I'm asking is because on another forum they were talking about Magnavox RPTVs, whose CRTs like to grow the algae/deposits; and one of the members said you could just refill the CRT chamber with mineral oil. I thought it unlikely... and was wondering what other (safe) substitutes could be used, 'cos I admit I had a bit of sticker shock from the price of pure glycol.

How hot do the tubes normally run? How many containers of glycol would I need; the $46 isn't for a set of 3 bottles, is it?

Tom.W · Joined: 09 Mar 2006 Posts: 6635

You might want to read this thread also..

https://www.curtpalme.com/forum_archived/viewtopic.php@t=6894.html

mr_ro_co · Joined: 08 May 2006 Posts: 1643 Location: Santa Fe NM

Isn't it propylene glycol (usually mixed with some water and glycerin), not ethylene glycol, that's used in crt projectors?

I had to take apart the entire chassis on my 9500 Ultra to clean up a major glycol leak that occurred in shipping. The stuff I was cleaning up looked and smelled just like the stuff that runs in HVAC chilled water and condenser water systems, which is typically propylene glycol. My understanding was ethylene glycol is used in applications that involve much higher temperatures (such as a car radiator).

Z-Photo · Posted: Sat Oct 20, 2007 1:48 pm Post subject:

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Just talked with Mat electronics and they have 500 16oz bottles of Teck Spray CRT coolent coming in next week. It was on back order. Still $5.50 a bottle if ordering 10 or more.

http://www.matelectronics.com/acatalog/Mat_Electronics_Chemicals___Tech_Spray_59.html

Here's the MSDS sheet for Teck Spray. 25 % glycerin and 75% ethylene glycol

http://www.mcminone.com/content/ProductData/MSDS/20-4275.pdf

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Just recieved the back ordered Tech spray glycol/glycerin mix today from Mat electronics Thumbs Up

jask · Joined: 17 Mar 2006 Posts: 10187 Location: kamloops BC

Tom.W · Joined: 09 Mar 2006 Posts: 6635

15 pounds UPS ground $15.44. Got 10 16oz bottles.

ILOVEMYTHEATRE · Joined: 23 Jan 2007 Posts: 6 Location: NHILL, VIC AUSTRALIA

Well ,read all the tech stuff posted and it all sounds like I should not have had used baby oil , but its been in my sony D50 for the past 6 years with no ill effects .The projectors been runnning with ambient room temperature around "35 degrees C " (or around 95 degrees F for our US friends) besides it smells nice too Tried it in my frie Very Happy

nds 1252 but the rubber groment swelled up