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Brians256 09-13-2002 07:35 PM

Coolant
 
Thanks to all those members in the forum talking about coolants! You got me sparked to write a quick article on coolant selection and maintenance. Now, I just need to make sure that it is well proof-read by some other staff members and that it gets approved and posted by Joe.

bigben2k 09-17-2002 09:32 AM

It would be nice if you could clear up the "unknowns".

You state to check the pH level of antifreeze. Do you have an easy suggestion for checking that pH?

Otherwise, you did a great job, and answered some of my questions. Thanks!

pHaestus 09-17-2002 12:20 PM

red cabbage makes a tolerable indicator:

http://www.cchem.berkeley.edu/demola.../CabbIndic.htm

You can make your own pH meter but I bet its costly and a pain to calibrate. I think some saltwater aquarium users have them, and you can probably get litmus paper at the pet store too.

the pKa of ethylene glycol is 14.22, so it is basically completely present as C2H4(OH)2
(my weird notation to show that the OH on the alcohol groups are present and not O-)

Can just calculate pH using henderson-hasselbalch eqn:

pH = pKa + log (A-/HA )

oops too many unknowns; better just measure :)

Brians256 09-17-2002 12:30 PM

How would I measure the pH? I'd just go to the local store and get some litmus paper, to be honest. They have it in the gardening section of the local megastore (Fred Meyers) to measure soil pH. Or, I'd get it from a hobby store or from an online chem supply house.

The pH that I'd want to maintain would be above 9.0 for antifreeze. As for the pH of water wetter coolants, I don't know for sure what the initial pH of a 1:32 (water:ww) liquid is. I also don't know for sure if there are any buffering chemicals in WW. That being said, my first guess is to keep it at pH 9.0 or above.

Being lazy, I plan on changing the coolant fairly frequently (about every 4 months). That's probably MUCH more than I need, but it really isn't that expensive to do a coolant flush. I do have an "inspection port" to monitor the color and transparency, too. If the coolant becomes cloudy or discolored, it'd be an immediate alarm bell to do a flush. I'll also do a quick inspection of the heater core and waterblock when I do my flushes. That way I can increase or decrease the frequency of my changes if things look good.

Besides, this way the feral cats and possums get a quick waterdish treat every 4 months! :D Keeps their population down.

P.S. Just kidding about the waterdish, but it is a tempting thought.

Bignuts 09-17-2002 01:34 PM

the swimming pool guys have pH down to a science
 
You can get multiple indicators for a wide range of pH at any swimming pool supplier, and they dont require you to buy in bulk.

Also, you can use a multimeter to check for pH:

http://www.venturers.org/NextGenTech/pages/Coolant.html

down near the bottom of that page.

bigben2k 09-17-2002 01:52 PM

Nice link!

Here's the relevant info:
You can also use an ordinary digital volt meter for the same purpose. With the engine off, touch the voltmeter positive test lead to the radiator or engine (making sure you get good metal-to-metal contact). Then open the radiator cap and insert the negative test lead into the coolant. A reading of up to 0.2 volts is considered acceptable and indicates the presence of reserve alkalinity in the coolant. If the coolant reads 0.3 to 0.6 volts, it is borderline and should be recycled or replaced. A reading of 0.7 volts or more would tell you the coolant is overdue for a change.

Based on this, I might be able to build a monitoring ciruit...

I can't help but wonder where this voltage comes from though. Anyone?

Brians256 09-17-2002 04:02 PM

Where does the voltage come from? Good question! My first thought was that it came from the ongoing galvanic corrosion. The voltage you got was because the dissimilar metals were forming a nice battery effect, and the effect became more pronounced as more charge carriers became available. But, I'm not sure of that. Wouldn't the electrical potential be there even if the solution had no charge carriers?

BTW: the chelating agent should trap the charge carriers. That's what it is for.

bigben2k 09-17-2002 04:18 PM

I guess...

If it is a galvanic induced voltage, then I may not want to build a circuit that induces a voltage, which may accelerate the process. I could build something with a needle indicator, stuck to a 5 1/4 plate, with a push button to check the pH.

All we'd have to do, is press the button once in a while, to check the pH. It could be PSU or battery powered. It could be built around a 1/2 inch copper tee, like the overclocker flow sensor (without the cork plug, thank you!).

Brians256 09-17-2002 04:23 PM

A voltmeter circuit wouldn't induce voltage, though. It measures voltage by involving a high-impedance parallel circuit that reponds to the existing voltage.

bigben2k 09-17-2002 04:51 PM

True, but I need to amplify this reading so that it'll show up on the needle indicator. I'll give it a whirl, and see what happens.

utabintarbo 10-16-2002 01:37 PM

bump
 
Any progress?

bigben2k 10-16-2002 02:18 PM

LOL! no, I ordered the wrong parts. This is going to have to wait until my next order, but thanks for the reminder!

Alchemy 10-30-2002 02:05 AM

Quote:

Originally posted by pHaestus
the pKa of ethylene glycol is 14.22, so it is basically completely present as C2H4(OH)2
(my weird notation to show that the OH on the alcohol groups are present and not O-)

Can just calculate pH using henderson-hasselbalch eqn:

pH = pKa + log (A-/HA )

oops too many unknowns; better just measure :)

It's not difficult to solve.

Assuming you use a 50% volumetric solution of ethylene glycol and water, and assuming volumetric additivity [edit-spelling] (probably off by 5-10% right there) you'd have a solution of 0.0180 molar ethylene glycol.

If the pKa is 14.22

Ka = 10^-14.22 = 6.0256 x 10^-15

Ka = [OH]*[C2H40H] / [C2H4(OH)2]

The concentrations of C2H4OH and OH- are equal and the concentration of C2H4(OH)2 doesn't change, so you can solve for them given the inital concentration of C2H4(OH)2.

6.0256 x 10^-15 ~ [OH-]^2 / 0.0180

Solving for the concentration of OH- gives 1.04 x 10^-8.

pOH = - log (1.04 x 10^-8) = 7.98

pH = 14-7.98 = 6.01

So if you have a 50% ethlyene glycol solution in water, you should have a pH of approximately 6.0.

If, after mixing the additives, you still have a pH below what you want, you might be able to add base to boost the pH, checking periodically with litmus paper.

If one of those additives is a buffer, though, you're doing your coolant a disservice.

Alchemy

pHaestus 10-30-2002 03:54 AM

So you just added something strongly basic to water (pK = 14), and the pH dropped? Reasonableness?

(I think you want to remove a proton when writing a reaction for the dissociation and not release an OH-)

HOC2H40H <--> -OC2H4OH + H+ (logKa1 = -14)

Not so simple in real world though.

Consider the equilibrium between copper ions and aluminum ions and the glycol as well (that will affect the speciation of the glycol). I dont have stability constants for such at fingertips; dont know what concentrations for metals is "normal".

Another complication with neutral/alkaline pH:

Don't forget to consider the solubility of CO2.

CO2(g) <-->CO2(l)
CO2(l) + H2O <--> H2CO3*
H2CO3* <--> H+ + HCO3^- (logKa1 = -6.3)
HCO3- <--> H+ + CO3^2- (log Ka2 = -10.3)

You'll find quite a lot of total dissolved CO2 (H2CO3* + HCO3- + CO3^2-) at pH 8 or higher. You can solve the above by considering that the relationship between CO2(g) and CO2(l) is related to Pco2 and the Henry's Law constant for CO2.

Not going to be able to solve this without an iterative approach. Mineql is a free download and not too bad (DOS but works mostly in XP/2k)

EagleShadow 11-13-2002 03:20 PM

Quote:

Originally posted by Brians256
Where does the voltage come from? Good question! My first thought was that it came from the ongoing galvanic corrosion. The voltage you got was because the dissimilar metals were forming a nice battery effect, and the effect became more pronounced as more charge carriers became available. But, I'm not sure of that. Wouldn't the electrical potential be there even if the solution had no charge carriers?

BTW: the chelating agent should trap the charge carriers. That's what it is for.

Guess they never did the water in a beaker with Iron and copper rods with ya in science class eh.

When you take Basic water and place it in a beaker. Take Iron Rod on 1 side. Copper on other. You can actually create electricity.

It boils down to the atomic substructure of one metal to the other. The water just acts like a bridge.

Put simply. Water and metals always makes battery's. Just most cases it's just not enough electric value to be of any problem.
( Been a while since I was in that class so pardon me for not remember'n all the details. ) " I just had my 10 year Reunion "

Brians256 11-14-2002 03:11 PM

Unfortunately, my High School chemistry class was a total joke. The chemistry that I did learn (outside of class) was in the field of applied energetic exothermic reactions. I made fun stuff like black gunpowder, nitrocellulose, Cupric Azide, thermite, Nitrogen Tri-iodide, and basic coloring agents (such as magnesium for white and strontium for red).

Now, if the teacher had possessed some modicum of enthusiasm and/or the students were actually interested and motivated to learn (you can't just blame it on the teacher).... who knows what we could have learned?

Public school stinks because it's just a sad application of the lowest-common-denominator principle. Take the laziest and least talented person in the room (sometimes, although rarely, it's the teacher), and move the class at that person's speed.

punish3r 11-27-2002 01:07 AM

Ph Meter
 
Hi all, I know I'm new here, but thought I might be able to help with your Ph predicament. I've been working on a computer for the last three weeks or so that I'm turning into an electronics workstation, currently I've got an oscilloscope (Dave Jones' DSO Mk3) a DMM (PCMCIA card Ines i218) a frequency counter, a function generator and, the reason I'm posting this here, a home built Ph meter.

The meter is actually designed to plug into the DMM and provide a voltage reading (0.01v = 1pH @ 24 deg C) with about a 0.1 +/- pH accuracy. The whole setup cost me about $70 US, but fifty of that was the probe itself. The other twenty was wrapped up in casing the main circuit, buying more etchant, buying the PCB materials, and actual component cost. All in all a cheap beastie considering that pH add-on probes for Fluke DMM's start at one hundred US and go up from there. But I digress.

I'm using a Cole-Parmer U-59001-65 General Purpose pH electrode. Mainly because it's no maintenance, has a top reading of 80 deg C, is designed for permanent/semi-permanent submersion, and looks pretty cool ;) I haven't bought a digital camera yet, so if you want to see the probe, go to
Cole-Parmer's Website

The circuit itself is actually a very simple design.

http://home.attbi.com/~punish3r/Ph_meter_schematic.jpg

This was built with exacting measurements in mind, so the calibration is a bit long, but I'll put it here in case anyone is interested. Anyway. As far a design, it's basically an electronic representation of a mathematic equation. At 24 deg C, the equation for the slope is Y=-0.017X+7 so, to obtain the output in tenths of volts (just for a cleaner reading from the A/D DMM) the equation would be 10Y=-0.17X+70

The first chip (LM351) turns the probe output into a high impedance signal, the second chip (First half of LM353) controls the slope by taking the LM351 output and multiplies it by -0.17, and the third chip (second half of the LM353) while acting as a summing amplifier, controls the Y-intercept by adding 70mV to the signal.

Like I said before, the calibration is long, but makes sense as long as you understand the math. Start by shorting the inputs together, and adjust the offest on the LM351 to read 0mV at its output. Now, unshort the inputs, connect the probe, and place your probe in a pH standard, and measure the voltage at the output of the LM351. Multiply this voltage by 0.17, and now measure the voltage at the output of the first half of the LM353. Adjust the slope pot until you get the voltage (0.17 * X) INVERTED. i.e. if your reading at the first chip was Z adjust until you get -Z at the second chip. Finally, check the final output and adjust the Y-intercept pot until your voltage reading and the pH of the solution are matched. Remember, the way this circuit works (1pH = 0.01v) so if your standard is 10.1 pH your voltage reading will be 0.101v
Finally, check the meter by using it in other liquids that you know the pH of, just to verify proper calibration.
A few notes on the components used. The key on this circuit is accuracy. That's why the slope and y-intercept pots are both 15 turn. Yes, you can use a normal 3/4 or 1 turn, but I would recommend against it. Even with the x10 boost in voltage, the amounts we're dealing with are still so tiny, that a slight bump on the board might change the value of the pots enough to mess up your reading. On the chips, it's what I had on hand. If you can conceive of a better opamp to use, by all means do. The 351 and 353 are not application specific, so I'm sure there is a more 'refined' chip out there for this circuit.

As an afterthought, I have found digital pH meters around the net for about $60 US. The reasons I spent more than that are that one, I like building this stuff, and two, with a homebuilt design like this, you can build a second circuit to read the voltage, make it out of any kind of readout you want (LED, LCD, LPT input, etc) and get it that much more custom/closer to the way you like displays to be. Anyway. I know this was a bit long of a post, but I hope it helps.

The PÜNiSH3R

pHaestus 11-27-2002 08:24 AM

Nice post Punisher!

Try www.labx.com for pH electrodes. There is a complete Corning pH meter/electrode setup for $27 on their auction list at the moment, and similar will always be around.

Brians256 12-01-2002 12:48 AM

Nice! Real component analog work is uncommon these days.

punish3r 12-01-2002 09:28 PM

I just figure what's the point in having to manually program a PIC to do something that two IC's that cost less than a dollar can do without an A/D conversion? Anyway, I suck at high-level programming. Lots better with hardware than I am with software. That's why I used to be Automatic_Jack. Anyway, getting off subject here.

Uncle_Dave 08-12-2007 04:25 PM

Re: Coolant
 
The red cabbage caught my eye.


How did the PH meter work out?


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