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Calcium chloride hexahydrate and metals (newbie)

Howdy,
Apologies in advance if this is the wrong place to post this.
I'm working on a machanical experiment that requires a dense, nontoxic
and reasonably inexpensive fluid. The melting point and price of
calcium chloride hexahydrate, appears to make it a tolerable
candidate. (I was brought to this material based on the knowledge that
salts have been broadly used for valve cooling in piston engines.)
Within the experiment we will be passing our selected fluid in mixture
with a (also preferably as inert as possible) gas through a
pressurized heat exchanger.
I'm not a chemist. My question stems from concerns for toxicity and
corrosion. I am looking to achieve a minimum of risk from exposure,
and a low corrosion rate in the design of the heat exchanger. A
pressure explosion is considered a possibility, and we are using
safety precautions. But from a chemistry standpoint I am concerned
about reactions causing toxicity levels significantly beyond those
experienced in a typical mechanical engineering lab. My questions
are:
1. First, is there something else out there that is liquid at around
30C that is significantly denser than water and more inert than
calcium chloride hexahydrate?
2. How hazerdous is calcium chloride hexahydrate? Does it do anything
nasty when combined with common metals? (copper, aluminum, iron) How
about water?
3. What gas should I use?
4. What materials should I use for the heat exchanger?
My current design is to use helium gas, calcium chloride hexahydrate
as a fluid, and an aluminum heat exchanger. Ultimately my question
boils down down to: is there anything chemistry related here that
would put me in the running for a darwin award?
Thanks in advance!
Reply to
shrike
Loading thread data ...
Dear shr...:
Might also try sci.engr.mech
Mineral oil. Silicone oil.
Right. A sort of "heat pipe" like is used in cooling processors today.
Mixed? If so, the gas bubbles will block your heat exchange surfaces, and you'll have a big "fail". Also, departitioning the two afterwards will be problematic.
... those whom make a career (in some cases) of blowing stuff up.
My list above is not complete, but a start.
You'll have signficant corrosion with any salt.
Darwin, not as described so far, no. Sad (expensive) surprises on material choices though.
David A. Smith
Reply to
dlzc
Does OP mean by "dense" density or viscosity ?
Toxicity of calcium chloride is neglible. BTW Kitchen salt is toxic too, eating about 200g will kill you. Where are any salts, there corrosion can occur.
I am afraid mostly less inert and much more toxic.
Its level of hazard and corrosion support is comparable to kitchen salt. OTOH aluminium is quite resistant to corrosion, maybe unless very long term scenario.
From inertness point of view I think nitrogen is adequate. Unless there is real need of bigger helium thermal conductivity and diffusion coefficient.
Aluminium seems to be good choice.
Reply to
Poutnik
Dense, as in density. We are trying to improve performance of a system that is known to work using water and air. The fluid and gas are contained in a closed cycle. The density of the fluid serves a mechanical function. If it varporizes, performance is reduced.
Operating temperatures are expected to be between 100F and 200F, but the machine is expected to be exposed to ambient temperatures prior to startup and shutdown. I'm predisposed to expect outliers, and it is possible that we will see higher performance at even higher temperature/pressure.
It would seem that going with a calcium chloride brine would probably be the best solution.
Again, forgive my stupidity, I'm drawing on 8th grade science a few decades old. If I heat a calcium chloride brine, it will form its various hydrates as crystals when temperature decreases, correct?
However, those hydrate crystals would still be water soluable if the brine was in constant motion right? I understand that the ability of the solution to hold the salt decreases as the temperature drops. So provided I set the ratio of salt to water relative to the 100% solubility rate at the lowest expected temperature, I should have no accumulated crystalization in the lines. Sound about right?
Thanks in advance!
Reply to
shrike
Dear shr...:
...
Water carries more heat per pound that most other economically viable choices. It also departitions from gas easily. Salt solutions don't.
Air is very cheap on Earth.
Aluminum is out. Maybe SS, Carpenter-20, perhaps titanium.
The carrier is water in a salt solution. As you heat water, it tends to make things *less* soluble. Witness "scaling" problems in most heat exchangers.
Nope. Motion does not change how much water is present in solution.
Below some point.
Sounds like a miracle of tuning, likely to freeze up with expensive repairs when you look away or take a small snack.
Sounds like someone is trying to reinvent infernal combustion engine cooling.
David A. Smith
Reply to
dlzc
You are mistaken. Decreasing solubility with temperature is very exceptional.
Scaling is different issue. One encounters thermal decomposition of calcium bicarbonate Ca2+ + 2 HCO3- -> CaCO3 (scale/limestone ) + H2O + CO2
Concerning Calcium chloride, solubility is given by this table Temp g CaCl2/100g water Deg C
0 59.5 10 64.7 20 74.5 30 100 40 128 50 - 60 137 70 - 80 147 90 154 100 159
See
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more
Reply to
Poutnik
Dear Poutnik:
Thanks.
Let's also add this:
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chloride solution carries 64% the heat per unit mass, per degree, than plain water does. At only 25% more dense, this is still a net reduction in cooling / heating capacity.
Thanks. Engine cooling or CPU cooling, would you guess?
David A. Smith
Reply to
dlzc
Furthermore heat capacity [J/kg/K] and density has to be counted together with thermal conductivity and viscosity,
Reply to
Poutnik
I also miss a little why is the need being denser than water....
Glycol could be a good choice.
It is not corrosive and fits better than water for upper temperature limit, even if viscosity, thermal capacity and conductivity is lower.
But I am not sure if fits OP toxicity constrains. How much non-toxic it should be ? ( as all stuff is toxic with proper doses )
Reply to
Poutnik
Dear Poutnik:
The OP may be equating "denser" with more heat capacity per unit volume and/or per unit degree. Remember he said "eighth grade" schooling, and that isn't a bad guess for limited education.
The most efficient heat exchange is a phase change from liquid to vapor at the target temperature. If a gravity field is present, and this is planned for in the fluid flow system. Like "heat pipes".
David A. Smith
Reply to
dlzc
Remember the law of Dulong and Petit. The specific heat of a substance per molecule is the same per molecule multiplied by the degrees of freedom. Thus, specific heat goes up as the molecular or atomic wight goes down. Thus solid lithium has about the same specific heat as water. This gets modified by quantum effects.
Water with MW of 18 compared to atomic weight 7 for Li also has additional degrees of freedom from molecular rotation and vibration that increases specific heat higher than can be expected from MW alone.
So what do you look for to find a high specific heat substance? Low atomic number atoms and the opportunity for the molecules to vibrate and rotate. My guess is that methane may fit the bill.
Bill
Reply to
Salmon Egg
The thing we want to heat is not the fluid but the gas, in order to displace the fluid. More like a barometer or a thermometer or air- over-hydraulic system than a refrigeration system really. I shouldn't have said "heat exchanger", as that presumable got verybody thinking about a coil.
Incidentally, what do they use in thermometers now instead of mercury?
Reply to
shrike
Not exactly, but thanks for the attempt to clarify. The behaviors of the two I wish to maintain, are that the gas expands quickly and contracts quickly with temperature changes, and the fluid acts pretty much like hydraulic oil, but is as heavy as possible, yet remains stable across a wide range of temperatures. The specific gravity of the fluid does have a role, but that role is ancillary to the question: "How best not to end up sucking in a cloud of toxic gas, should this thing convert the test shed to a pile of toothpicks?"
Incidentally, in consideration of the fact that one can now make more money forging college textbooks than they can selling drugs, I generally refer to my education as "alternately sourced" rather than "limited". :-)
Thanks!
Reply to
shrike
Dear shr...:
OK, then you are limited to non-ideal gases. Something like freons and such, near their boiling point.
Water and air are your safest material choices. Should be suitable for proof-of concept.
By now, everything I learned in school is out-of-date. We all get to continually learn. Poutnik keeps teaching me stuff even in this thread.
You are still holding on to the belief that the liquid needs to hold lots of heat, and I don't think you are challenging that in your mind. I think you simply need good thermal conductivity, essentially no heat capacity (since heating liquid is not your intent... heating gas is), and the ability to stay intimate with all the cool gas during heating.
This recommendation still stands.
David A. Smith
Reply to
dlzc
I am familiar with that, not yet fully forgotten my graduate lessons from physical and quantum chemistry.
Yes, methane will have definitely good heat capacity, but I guess it will not probably fit all OP requirements.
Reply to
Poutnik

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