Battery on the ground

When I studied chemistry they told me taht H2SO4 and water were soluble in each other in all proportions, also that a solution cosisted of two substances that would not separate merely due to differences in density. Has any of this changed?

Engineman

the water in strata due to chilling it. Ionic flow must take place for battery operation to take place. Without the acid mixed in evenly, only small areas of the plates can conduct electrons.

Some of those are thermoclines, regions where temperature (hence density) changes rapidly in a short range of depth. These also occur in some freshwater lakes during the summer, are visible with sonar.

There are continuous inputs (e.g., rivers) and ouputs (evaporation) of fresh water to and from the ocean which prevent it from ever reaching equilibrium with respect to solutes, unlike electrolyte which is thoroughly mixed before filling a battery.

Similarly, as a result of localized inputs and outputs of heat, most bodies of water are also not in thermal equilibrium, as any swimmer can attest. It seems reasonable that the same could be true of a battery sitting undisturbed on a large heat sink (a concrete floor) while air temp is fluctuating.

And the same thing "cant" happen in an undisturbed battery. ...lew...

A-MEN!

Batteries are too small to support much of a thermocline. It takes at least a lake to get anything that will last more than an hour or two.

Joe Gwinn

I didn't see any mention of a thermocline. What's been proposed is a temperature gradient in a battery cell that's packed with enough stuff to inhibit convection when set on a relatively good conductor that's at a different temperature than the ambient air.

Lew Hartwick mentioned the thermocline.

But anyway, what's the thermal conductivity of the metal battery plates, and of the electrolyte? It has to be 1000 times greater than air, and unless the battery is *huge*, thermal equilibrium will soon be achieved.

Joe Gwinn

I don't see that in Lew's posts, perhaps I missed one.

The heat capacity of a concrete slab and the earth below it is huge compared to the battery, and it may take days to reach equilibrium with the air. In the meantime, if the weather is trending warmer, the bottom of the battery is cooled below ambient by the slab. I have no idea whether the effect is actually large enough to discharge an otherwise healthy battery, but I don't think the possibility can be dismissed without either an experiment or some very messy calculations.

In any case, I find the notion more plausible than *'s assertion that, "Electrons WOULD leak through the porous case to ground - eventually discharging the battery."

Not to any significant extent, because the battery is only about a foot deep at most.

I think the stratification is due to electrochemical action as David Harmon suggested.

Have you noticed this while wading in a foot of water, or swimming on the surface over deeper water on a calm day?

The thermal conductivity of water is not much different than that of concrete -- roughly 0.5 W /(m*K). HDPE is also in the same ballpark.

Air is about 24 times less. A battery sitting on concrete surrounded by air of different temperature will behave thermally about like a block of concrete sitting on the concrete.

It's easier to notice on the scale of a couple feet in open water. But one of my favorite places to swim has several ledges covered with rockweed or bladderwrack; at half tide when the seaweed is floating on the surface it inhibits convection and steepens the temperature gradient near the surface. A few extra degrees feels pretty good when the water temperature is in the low to mid 60's.

I would expect the plates in a battery to have much the same effect on convection within the cells.

If one were inclined to calculate what the temp gradient might be, treating the battery as a block, and ignoring convection, seems like a reasonable first pass to me.