Two Sides to metallurgy

By Tim Buyle (**)

Date 10-18-2002 08:35

This is due to the rolling proces.

By dee

Date 10-18-2002 18:06

Buffalo,
To add specificity to other posts, the complete story is that Mrs Reynolds herself, of Reynolds Aluminum, was actually a distinguished philosopher in compliment to her husbands industrial talents. His process, accepted and adopted by others as a standard because reportedly Reynolds held the licenses to the patented rolling equipment, intentionally, at her insistance, made one side shiney and the other dull as a representation of the balance of opposing forces, much like the Yin and Yang.
Some contention does, however, exist, attributing it directly and solely to her husband as a symbolic representation of life both before and after what we today might describe as his "Sam-Kinnisonian" marrage... at least that's what the letter carrier from the series "Cheers" on TV once said; the source is sufficient to permit you to be able to sleep again rather than stay awake in worry about such perplexing complexities, and may even earn you a beer next time at the pub if you promise not to bring up any other similar trivia. It's merely a good natured poke at fun; please take no ofense and recognize this as a smiley-face.

Regards,
d

By buffalo (*)

Date 10-19-2002 15:42

COOL!

By Ken Dougherty (**)

Date 10-20-2002 18:21

d,
You got way too much time on your hands! (The post was fun and appreciated however.)
Ken

By buffalo (*)

Date 10-21-2002 23:27

Well said, oh Great Metallurgic One!

By Niekie3 (***)

Date 10-20-2002 20:09

If you are referring to Al cooking foil, then it is this:

1) The shiny side reflects heat.
2) The "matt" surface tends to absorb heat.

This means that if you place your roast in the oven, you need to place the shiny side of the foil to the inside. This allows a great heat transfer to the inside where the shiny surface then tends to "capture" the heat should your oven's temperature reduce.

Happy cooking!

Regards
Niekie

By DGXL

Date 10-22-2002 00:30

Who knew Aluminum foil could be so complex.

By G.S.Crisi (****)

Date 10-25-2002 18:46

Great, Niekie! Now I know why the very few times I tried to roast a turkey in the oven it came a mess out of it (the turkey, not the oven). It was because I wrapped the turkey with the bright face of the aluminum foil on the outside. Next Christmas I know what I should do.
Now, from a metallurgical point of view, I'd like that someone explains me the following:
1) Why is one side bright and the other dull? Is it just because of the grain size (smaller at the bright side and coarser at the dull one?).
Or is there another reason?
2) How do they do to at the rolling mill to get that difference?
Giovanni S. Crisi
Sao Paulo - Brazil

By buffalo (*)

Date 10-26-2002 00:32

Yo Gio, Me thinks its because shiney aluminum particles are more expensive than the dull type. And because of some corporate strategy to save money and invariably increase their "bottom line" at the expense of denying us the luxury of having our foil shiney on both sides, we are confused, and our turkeys come out a mess.
Insidently, I didn't know there existed the American observance of Thanksgiving in Brazil. I sure do hope your turkeys are juicier than they are in the States!
Salutations Mettalurgic Brother,
-Buffalo

By Niekie3 (***)

Date 10-26-2002 10:08

I am only taking a guess, but I can only think that it has to do with the finish on the calender rolls they use when rolling the Al. The rolls that work on the shiny side must have a mirror finish while those on the dull side must have an etched finish.

I certainly can not believe that it is due to differences in grain size. How could one possibly achieve this on such a thin material? In fact, due to the coarse grained nature of most Al, I will be surprised if the light gauge foil in any case has more than a single grain in the through-thickness direction. This is however again an assumption on my side.

Good luck with the turkey next time round.

Regards
Niekie

By dee

Date 10-26-2002 20:51

On this more serious muse I have wondered how they cleaned the foil, or if any cleaning was required after manufacturing, before it is sold for use in contact with food.

The dull side of the foil looks as if it was chemically or electrically etched, as in an anodizing process, and I would suspect a spray of lye would achieve about the same thing except for the uniformity of the finish... it makes sense, then, that one roller should have the etched finish. It also seems to me a textured roller would provide some different performance characteristics in contrast to a mirror-smooth one.
To satisfy my curiosity I did cover two thermocouples with as uniform a cover as I could devise within limits of practicality and at 350oF was unable to detect any difference in temperature between the shiny and dull one. My test proved my suspicion that my equipment is far too inaccurate to serve the purpose, with smallest graduations in 20oF increments, and the thermocouple technology itself leaving something to be desired...
...perhaps the real issue is the type of heat we are trying to control here, radiation, conduction or convection. My couples are radiation shielded, and perhaps food should be as well. (see theory of convection oven operation)

My theory is that the shiny side's inability to radiate cancels the dull side's ability to absorb. If reduced to an equation I believe the proper term for the mathmatical process would be a reciprocal... but then again this would also perhaps disprove the accepted theory of CO2 on global warming?

There is more info at the EPA site on that accepted theory and its frankly beyond my level of present interest. In any event I would have been ahead of the game if I left understanding this to my first remark allready.

Finally, the turkey flopped because of something other than inside-out aluminum foil... my instruments are standard Gemline units built for calibrating thermostats for ovens, irons and other heat appliances and are much more accurate than the appliances themselves. The result of which side is outside is neglegible in real terms; on that point I rest assured despite the Rube Golberg nature of my test procedure.

Regards
d

By Niekie3 (***)

Date 10-27-2002 18:12

You are just so ahead of me on this one. I have never tested the theory myself! Just goes to show that the old adage "an ounce of experimentation is worth a ton of theory" rings true.

Just a comment on your experimental method though. In an oven, you will not find a difference in temperature unless you are measuring the rate of temperature increase and decrease. (Even a thermocouple in insulation will EVENTUALLY reach the same temperature as the inside of the oven.)

If you have some more time, it would be interesting to test the theory by measuring the rate of temperature increase, or possibly measuring the temperature when placed on an open "hot plate" where there is a surface where temperature loss can occur.

Just a thought.

Regards
Niekie

By dee

Date 10-29-2002 03:00

Niekie,
We agree on practical application of foil for cooking, but I was thrown where you drew my attention to heat transfer. I beleive the practicality lies in the retention ability--- the radiant insulation--- of the polished surface through superior reflection of IR energy radiating from the food, but without regard for absorption factor of outside finish.

I am of course making some presumptions about a finish's ability to radiate being proportional to its ability to absorb. Please note that I avoided thermodynamics quite effectively while studying physics and do not claim advice of any authority or reference.

My tests equipment is useless for this purpose; it reacts too slow and lacks the resolution to find any slight difference in performance.
Parenthetically, you are probably aware that a thermocouple actually measures the DIFFERENCE in temperature between the coupled and free ends, and to obtain any accuracy at all the indicator gauge should be built with a compensator bimetal designed to correct for variations in ambient temperature... there is a lot to go wrong.
Please trust that I did use two matched meters simultaneously to determine any difference in rate of change in real-time. The oven was a small portable (GeneralElectric T 93 type chassis) chosen for its two symetrically placed points from which identical tests can be made in relation to the heat elements as well as the top, bottom, front and sides of the oven and had many opportunities to find any difference.
In modern computer parlance you might say I did apply a great deal of "artificial intelligence" to find the answer :-)

I believe the best practical purpose for cooking with foil is merely to protect the delicate surface of the food from intense radiation causing it to burn, and as an anti-spatter device to protect the oven.

There is a real difference in the heat both absorbed and radiated from an object which depends on the surface finish and color, which you can proove with merely a coat of black and silver paint, some heat, and the back of your hand as a sensor. On that point we agree.
I lost you, though, on the hot-plate suggestion. I do have tables around somewhere (graphs actually) comparing surface finishes (textures) properties of CONDUCTION; the wrinkles will invalidate the experiment.

I wonder, though, if a can of spray paint or a roll of foil can be made to recoup it's expense as a convenient means of insulating a weldment during pre/post-heat techniques in some way or another- through savings in fuel gas and time.
I'd like to direct the museing toward something practical and appropriate to our main subject; to hone and sharpen our foible, if a foible it must be.

Regards
d

By pipewelder_1999 (****)

Date 10-29-2002 11:33

I have to get my two cents in. Regardless of what I wrap an object in, given enough time in the oven, eventually all objects become the same temp. If my oven is 400 def F, all other things are 400 degrees or does a turkey in foil generate its own energy? I think this is kinda what d said but I'm not sure.

It is my opinion that the prime purpose of the foil is to keep moisture in. I guess if you wrapped your turkey tight enough, you could get the "pressure cooker" effect. However with the increase in pressure, there would be an increase in temp which would cause the ovens thermostat to stop/slow down the heat source from the heat generated from the turkey.

Of course this is only my opinion and is based on 30 + holidays. Regardless of the wrapping medium, ALWAYS watch the little plastic red thing!

I have questions aboout hot water freezing faster but I am afraid my entire 2 hours of heat transfer training will be devastated by the concepts that may arise.

Gerald Austin
Iuka, Miss (Physics Capitol of the South!)

By dee

Date 10-29-2002 17:31

A little adjustment is called for in the pressure cooker effect;

The temperature of the oven is not changed by a rise in pressure, but rather, the point at which the latent heat of evaporation begins to cool the subject turkey; it is unable to exceed the boiling point of the water within it. The increase in pressure effectively raises the cooking temperature above 212oF boiling point of water. This in no way should change the temperature of the oven surrounding it. Parenthetically, rapid depressurization also ruptures cell walls as fluid inside suddenly turns to steam, and yields results similar (but not identical) to hours of slow cooking, but we digress.

In any event, unless the foil were wrapped around the turkey tightly enough to bring it to critical mass, or it were spiced so as to create some kind of chemical reaction, there would be at no time any heat generated by the turkey.
What I was thinking of is akin to the effect "greenhouse gasses" have on global temperature... IR energy passes "in" more easily than it passes "out"... it absorbs more heat than it radiates so the temperature rises over time.
My test, by the way, was to draw appropriate conclusions from simultaneous observation of two identical measuring devices within two identical (except for surface finish) containers placed symetrically within a symetrically shaped oven... it's been poorly described which led to some confusion.

My hang-up here is trying to pass radiated heat through a foil intermediary. Radiated heat must first raise the temperature of the foil before the foil can serve to radiate it through to the other side. Shiny side out: it's reflected off the outside but radiated inside more efficiently... shiny side in: its absorbed from the outside well, but radiated inside only poorly. The precise and complex dynamics of radiated, convected and even to some degree conducted heat begin to exceed my level of interest where they start to require this kind of level of concentration from me.

I did read that Niekie presumed the turkey would be warmer than the oven at some point along the heat-up and cool-down cycles imposed by the thermostat (typical variations are between 25oF to 70oF oven air temp without consideration for effects of RADIATED energy) but I am skeptical; the internal temperature of fully cooked poultry (which is higher than for beef, veal, or pork) is typically less than 200oF which permits very little prospect for SIGNIFICANT heat loss through radiation in a 350o oven.

I stand on my presumtion that the prime benefit of the foil is to shield against radiation, but give you the point that it's role in raising the humidity of the area directly surrounding the turkey is significant.

Bone Appletight
d

BTW I believe we are applying the same formulae used in freeze-drying and other industrial and cryogneic processes when we pop that bird in a pressure cooker.

By pipewelder_1999 (****)

Date 10-29-2002 17:34

I was right. Devastated!

By dee

Date 10-29-2002 18:17

Perhaps we could market a black anodized (one side) cooking foil? when we solicit sponsorship from Emeril or some other cooking personality we can ask him to settle this question.

By Niekie3 (***)

Date 10-29-2002 18:53

I believe this rather culinary post raised the bar on all future thermodynamics questions on this board. Who would have believed it!

Niekie

By Jay Krout (*)

Date 10-30-2002 02:32

This is why the ones that come from Venus does the turkey, the one from Mars watches the football game, the one from Venus just does it, the one from Mars analyzes it first, then does it, and I myself who comes from Mars gets too hungry analyzing the football game to analyze the aluminum foil before cookin the turkey. NANU NANU :) J Krout

By jwright650 (*****)

Date 10-30-2002 12:36

Well, we only have 29 days to get this all sorted out before the turkey goes in the oven this year! All this reading has made me hungry.
John Wright

By GRoberts (***)

Date 10-30-2002 15:42

I have heard the theory that hot water freezes faster than cold water. I believe the explanation is relatively simple. (However it is just my theory, and I have not tried it out.) The hot water raises the temperature of your freezer, turning on the compressor at the preset temperature. Thus, in a little while the freezer actually becomes colder than if you had placed cold water in the freezer. The hot water may acually take longer to get down to the freezing point, but since there is much more energy required to be removed to convert the water to ice than to reduce the waters temperature 32F (0C), the previously hot water that is in a colder freezer now has the advantage.

By bspeirs (*)

Date 11-18-2002 02:48

Hot water freezing faster than cold water - lots of ways to skin this question.

1: shallow pan - lots of hot water evaporates. Less left over to freeze, and the main heat removal is required in the change of phase.

2: "Faster" may not be the most appropriate word. If you have ever wondered why Mr. Farenheit chose 32F as the freezing point of fresh water....

Turns out he did'nt want to. He tried to pick the freezing point, but water does not alway freeze at the same point. It pretty much melts at the same point, but depending on the amount of dissolved gas, thermal history, and type, size, quantity of particulates, there is a substantial amount of sub-cooling that may occur. Experiments done in a labs have shown that liquid water can exist for long periods of time (months) at around -20 F. If the surface is 'appropriately' disturbed, the water can freeze instantaneously. Millisecond type time frame, not like watching frost creep accross the window.

Two stories. Fellow from Shell was in one of the Former Soviet Union countries, beside a river that was very wide - hundreds of meters. Running water when he went to sleep - being used as an ice walkway when he woke up.

2nd one - more related to welding.
A steam pipeline (design pressure 2500 psi, 650 F, 12.75 OD, about 3/4" thick; material is quenched and tempered - impact properties exceed A333 - SMYS = 65 ksi; UTS = 80 ksi, 30% elongation) was constructed. Steam was not introduced, but the line was protected by a double block and bleed valve system.

One day, as the temperature dropped to close to -40 C, a large - say 36" x 8" - chunk blew out of the line. Really blew - ripped through the insulation, and was later found a few hundred feet away in the bush.

Then a few more chunks blew out. This continued for about 4 days- a chunk or so every hour or two. Very interesting for a non-commissioned line. One would have thought that the first hole should depressure the entire line. All failures were in the pipe body proper, not at a weld. (Did have a fracture that was arrested at a circ weld - much relief by the welding crew, since you know there was going to be a good investigation)

Also very interesting to note that the ambient temperature had been below 0C (32F) for about 2-3 months, but never below the -20C mark.

Turns out a valve had leaked, and essentially dry steam had filled part of the line. Published reports (around 1950) indicate that filtered water will subcool more than unfiltered; heated water further than unheated - de-areated dry steam fulfills those requirements nicely.

Best theory to date is that the line filled with condensed steam. When the temperature dropped the water subcooled, but did did not freeze, until ambient dropped to -35. As the water instantly transformed to ice, there was a volume increase. The probable place to initiate the formation of ice is where the pipe-shoes penetrate the insulation and act as a cold-finger. Due to the speed of tranformation, and the ice being unable to squeeze down the line between shoes - the pipe swelled, then burst. Interesting couple of days.

Long story short - most of what we were taught to belive in elementary school about water does not really apply - it melts at 32 F, not freezes; pressure on ice by your skate blade does not melt it - its the friction, ... there are guys with PHD's who are still studying water properties. Kind of boggles the mind.

By billvanderhoof (****)

Date 11-18-2002 06:10

The farenheit scale zero point is the temperature of fresh water ice melting in a saturated salt solution (think icecream maker). The 100 degree point was, I understand, mr. Farenheit's own temperature (he probably wasn't feeling well that day since everybody else's temperature runs a little less). Celsius zero is the freezing point of fresh water but avoids the supercooling problem by specifying a mixture of water and ice. As far as I know supercooled water cannot exist in contact with ice.
Bill

By TimGary (****)

Date 10-30-2002 19:04

Just out of curiosity, I contacted the nice folks at Reynolds Aluminum and asked them about it.
Thier reply is:
"In the final rolling pass of household aluminum foil, two layers are rolled together.
The sides that contact the rolling mills are shiny, mirroring the surface
finish of the roll. The side in contact with the other piece of foil is
matte."
When asked what the intended purpose of having one shiny side, if any, the reply is:
"There is no real purpose - its just the way it worked out when the process was developed more than 50 years ago. Unfortunately there's no one around from that time to ask."
Go figure...
Tim

By RonG

Date 11-02-2002 16:24

YEA BUT!
Isn't the reason the hot water freezes faster because it contains less dissolved gases? Which in turn makes it less cloudy.

Never tried to prove the theory but I have heard many versions of it.

By dee

Date 11-02-2002 19:45

Like I said, blame it on Mrs Reynolds...

By bzzzzzzzzzz (**)

Date 11-18-2002 00:20

I don't feel bad about silly 85 amp wire welder questions any more.