Date:         Sun, 13 Dec 2009 07:49:21 -0800
Reply-To:     Rocket J Squirrel <camping.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Rocket J Squirrel <camping.elliott@GMAIL.COM>
Subject:      Re: About coolant
Comments: To: Keith Hughes <keithahughes@Q.COM>
In-Reply-To:  <BLU0-SMTP32EF9A930385EA86F37F72DA8A0@phx.gbl>
Content-Type: text/plain; charset=UTF-8; format=flowed

Well, that certainly complicates things.

--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR


On 12/12/2009 5:28 PM Keith Hughes wrote:

>> Date:  Sat, 12 Dec 2009 12:20:09 -0800
>> From: Jim Arnott <jrasite@EONI.COM>
>> Subject: Re: About coolant
>>
>> Short answer: yes. Water transfer heat better than glycol.
>>
>> Longer answer: When I worked in aerospace about a century ago, one of
>> my first assignments was process control for the heat treat area. We
>> solution heat treated a bunch of aluminum. (Solution heat treat:
>> <http://www.azom.com/Details.asp?ArticleID=2540
>> > This was done to soften the material for forming. To reduce
>> residual stress, we used a quenchant of 20% polyalkalene glycol. This
>> provided a slower quench than water. Quenching in water would have
>> resulted in much more residual stress and distortion. Slower quench =
>> slower heat transfer.
>>
>> Numbers here:
>> http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html
>> http://www.engineeringtoolbox.com/overall-heat-transfer-coefficients-d_284.html
>>
>>
>> Water is about 14% more efficient at 220 deg F.
>>
>> Jim
>
> Uhm, well, you forgot the last half of the "longer answer"; Yes pure
> *liquid* water has a higher specific heat than does glycol or
> glycol/water mixtures. However, the glycol raises the boiling point
> significantly, and *that* is the key parameter. When the cooling water
> reaches the boiling point (i.e. when the system temperature results in a
> system pressure greater than the reservoir cap bypass valve setpoint -
> when water begins to dump into the overflow) then the dissolved gases
> will begin to come out of solution. This causes two major problems,
> both of which increase with additional temperature rise; cavitation in
> the water pump, which reduces fluid flow, and a water/vapor mixture
> (foam if you will) at the heat transfer interfaces (water/metal contact
> point in the water jackets and radiator). Both of these result in a
> dramatic reduction in cooling efficiency. So yes, as long as the
> cooling water remains below boiling, pure water is better (for cooling,
> not, certainly for corrosion) than water/glycol. In real life
> operation, in hot climes, pure water is almost always the wrong choice
> for a vehicle, like the stock Vanagon, with a pretty marginal cooling
> system.
>
> Keith Hughes
> '86 Westy Tiico (Marvin) in Phoenix
>