130mpg Plug in Escape Hybrid delievered! - Page 4 - GreenHybrid

wwest · #31 (**permalink**) 08-12-2007, 09:34 AM

Quote:

Originally Posted by gpsman1

This is probably not the place for a physics lesson, but yes, due to the laws of thermodynamics any object will eventually equalize to the exact same temperature as its surroundings. If it is -10 degrees in the air, any water, ice, metal, plastics, oranges, whatever, will eventually reach -10 degrees also.

In an orange grove, for example, the fruit has sugar, and sugar lowers the freezing point to less than 32'F ( 0'C ). I don't know exactly, but let's say, 28'F. As long as the oranges are 29'F, they won't be harmed.

Pure water ( or tap water for practical purposes ) does freeze at 32'F.
As long as water is in the process of freezing, it will stay at 32'F.
If the surface of the orange has 90% ice and 10% water, the surface will stay 32'F. Once the entire surface freezes, ( all the liquid is now solid ) the ice will start to cool to ambient air temperature.

So the key to protecting fruit groves is to keep the sprinklers going all night. As long as there is some liquid water on the surface of the fruit, the ice under the surface will stay at 32'F. And there is about 4'F of "buffer" (28'F) before the fruit gets damaged.

This is based on the principle of heat of fusion.
ALSO... as water goes from liquid to solid, it actually GIVES OFF HEAT!
So making ice, actually makes heat from the oranges' point of view.

Ice giving off heat? Sound impossible? Then think of the reverse.
Do you have to put heat into ice (or an orange ) to melt it into water?
Then the reverse must be true. ( and it is true )
You get heat out of water when you change it to solid ice.

You actually get 335 Joules or 80 calories PER GRAM of water changed to ice. You only get 4.18 J or 1 calorie changing 33'F water to 32'F water.

You also only get about the same, 1 calorie per gram changing 31'F ice to 30'F ice. It is the change of state that is important, to both orange groves, and energy storage devices. Just like your air conditioner that constantly changes liquid to gas, and makes the air cool in your home, and then moves the gas outside, and makes it back into liquid, and dumps heat outdoors, in the process.

Changing water into ice on the surface of the orange, actually dumps heat into the orange!!!

NOT disagreeing with any of the above.

But.

I'm pretty sure that in the early spring as the fruit trees are beginning to "bud" out, and an overnight freeze is coming, farmers in our area (nearby, actually, on the "dry" side), the farmers spray the orchard with a mist, the mist freezes on the buds and then provides a protection "insulation".

Clearly the water, in initally giving up its heat and freezing, protects the bud. But it is my understanding that even once frozen it now acts as an insulation keeping the COLD night time atmosphere away from the bud.

wwest · #32 (**permalink**) 08-12-2007, 09:42 AM

Quote:

Originally Posted by gpsman1

BUT that does NOT make it bad! It is opportunistic in nature.

If you are on a cross desert hike, and there is only 1 water hole every 25 miles, you might have to drink when you are not thirsty, to be "more efficient" than your partner who only drinks when he is thirsty, and skips a watering hole here and there.

-John

I'm pretty sure, almost certain sure, that if I could disable the regenerative braking on the hwy in our '03 Prius it would improve FE. Seattle to Portland there is virtually no opportunity for "free" energy, but the hybrid battery is continually used to regain cruise control speed, so the only choice is to recharge it via the ICE, a VERY lossy "loop".

DavidH · #33 (**permalink**) 08-12-2007, 09:57 AM

Ice can certainly be colder than the freezing point. All the way down to absolute zero.

Ice water is at freezing. A good way to check thermometer calibration is to submerse the sensing bulb in stirred ice water (distilled).

SPL · #34 (**permalink**) 08-12-2007, 02:45 PM

Ice is a good thermal insulator. That is, it doesn't allow the fruit's heat energy to pass through (escape) easily. Its mass also adds a thermal "reservoir" that has to be cooled down along with the fruit itself. That's why it helps protect fruit from frostbite. But the temperature of the ice coating the fruit will slowly drop, and if it falls below the freezing point of the fruit, the damage will occur.

Stan

gpsman1 · #35 (**permalink**) 08-12-2007, 04:56 PM

And the coldest time is usually that last hour right before dawn.
The ice coating may buy you that extra hour of safety.
I'm sure everyone agrees, it's only going to help in those very borderline cases. Get a 25'F night and you might as well not bother with the effort.

mamorgan2 · #36 (**permalink**) 08-16-2007, 07:49 AM

Sorry to take this away from a freezing fruit discussion

...

There was a point hit on before about plug-in hybrids being better environmentally. It seems to me that the argument has always been that it is better because the most electricity they use is all being produced in one place (and, therefore, the by-products like carbon can be better controlled) and there is more of potential to produce the electricity there in a renewable manner (wind, solar, etc.). My first question is why do people only mention wind and solar? I've read one or two articles about producing electricity through the capture of tidal energy. I don't know the physics behind it, but it seems to have the capability of harnessing a lot more energy. Granted, that may not help areas that are far from oceans, but I think it would help a lot.
Also, I don't know that much about nuclear power generation, but it seems to me that everyone who is for it is VERY adamant about it. Why do they prefer nuclear over wind, solar, or tidal?

DavidH · #37 (**permalink**) 08-16-2007, 08:10 AM

We also have geothermal, but that can be dirty.

wwest · #38 (**permalink**) 08-16-2007, 08:43 AM

Wind doesn't always blow, sometimes for days.

Sun doesn't always shine, sometimes for days. Weeks or months if you live in Seattle.

Tidal effects are on a 28 day cycle.

You don't have to be against any of the above in order to be "for" nuclear.

DavidH · #39 (**permalink**) 08-16-2007, 08:50 AM

I think Seattle gets a lot of hydro power

KenG · #40 (**permalink**) 08-16-2007, 11:17 AM

Mark,

I'm going to reply to your question on electric sources in several posts, since there are several interesting issues. I'm sure I'll stir the nest a little here but I work in the power industry so I know some things about it.

First, efficiency. Plug in hybrids have increased potential for carbon reduction because only about 50 - 60% of our electricity is produced by processes that directly emit CO2 and that number should go down. (ALL electrical generation indirectly produces a small amount of CO2 due to infrastructure needs.) The fossil fuel electrical generation is produced by processes that are 40 to 60% thermally efficient in comparison to a conventional ICE powered car that is probably less than 20% thermally efficient. Therefore, even with battery charge/discharge losses, carbon is reduced with electrical plug ins.

If, over the next 50 years or so, we get the carbon based electrical generation down to 20% or so of the total and we move to plug in cars, CO2 will be greatly reduced.