Albedo of Stainless Finishes

Please describe the insulation on the obverse side of the <...stainless...panels...> for the forum to consider, as this feature will affect greatly the ability to withstand heating and the <...value of the heat reflected...>.

There is no insulation.

I don't know if this helps...

I have a stainless steel refrigerator with a matte finish. When I take a picture with a thermal camera, it's like a mirror reflection. Light wavelength is 0.4-0.7 microns. Heat radiation wavelength is approximately 5-20 microns, 10 to 30 times as large. The heat radiation doesn't even see the matte finish.

Optical <-----------------------------------------Thermal

That’s interesting, when I was looking, light and heat reflection is tied together in the links that I saw.

the 5-10 microns… can you expand on that… as in is that the light wave???

Here are my thoughts...

the 5-10 microns… can you expand on that… as in is that the light wave???

Optical -------------------------------Thermal

The intent was to show that a matte finish at optical wavelengths is a "smooth finish" at the much larger thermal emission wavelengths.

If you plot radiation given off by a hot body, Wien's law says the peak will be inversely proportional to temperature.

"

where T is the absolute temperature and b is a constant of proportionality called Wien's displacement constant, equal to 2.897771955...×10⁻³ m⋅K,^[1][2] or b ≈ 2898 μm⋅K."

https://en.wikipedia.org/wiki/Wien%27s_displacement_law

https://pressbooks.online.ucf.edu/app/uploads/sites/163/2020/03/CNX_UPhysics_39_01_BBradcurve-1.jpg

It seems that the surface finish does affect Albedo. Albedo is the energy reflected divided by the total incident energy.

Here is a listing of the Albedo of various materials. Stainless steel is not listed, but several other metals are.

"polished silver - 0.88-0.93 (S)
white gypsum - 0.85 [D]
fresh snow - 0.75-0.78 [M]
mirror - 0.72-0.85 (S)
matte silver - 0.7 [D-S]
polished aluminum - 0.65-0.75 (S)
polished chrome - 0.6-0.7 (S)
matte aluminum - 0.55-0.6 [D-S]
white paper sheet - 0.6-0.7 [D-S]
melting snow (clean) - 0.6-0.62 [M]
matte chrome - 0.5 [D-S]"

https://forum.corona-renderer.com/index.php?topic=2359.0

In all the cases listed, matte finish decreases the albedo. I assume these values of albedo are for optical wavelengths and the value for "matte" finish would be closer to the "polished" value for the larger thermal wavelengths inside the oven.

Wow,… a class in physical metallurgy all over again…

I must have been sick that day when we covered that.

heres a little tidbit… aluminum needs to be masked (a plastic cover) when using a laser to cut aluminum… because when the laser melts the aluminum (and that’s all it does), before the air blast blows it away that puddle of melted aluminum is like a mirror and will reflect the laser back at the machine or individual and harm it.

masked aluminum will somewhat somewhat that as opposed to unmasked aluminum.

Here is a research paper on exactly your question. You might want to consider aluminum as an alternative to steel. Aluminum reflects infrared better than any steel.

It’s for food production, so stainless, too much caustic during washdown, and it has to be sanitary. so no aluminum.

Thanks, I’ll look through the link.

I'm speculating here but the very slight roughness of a 2B finish might degrade the uniformity of the reflected heat, thus making hot and cold spots. This might increase if the sheet metal creates concave pockets as it heats. The rougher finish of RA32 should scatter both the emissivity and reflectance of the infrared heat regardless of any curvature making for a more uniform heating.

It’s interesting having designed design USDA 3A food processing equipment for over 30 years.

I needed the USDA field inspector in my shop to inspect equipment before delivery. Even though they prefer polished material. Looking at 2B under a microscope, 2B is more sanitary, because the surface is smoother. (32Ra aka is more sanitary #4 finish) electro polish is even worse… because it’s nothing more than it removing the ferrous and non reflective material and leave the chromium.

“ Surprisingly, #4 finished stainless steel is more dull than stainless steel with a 2B finish. It appears more flat, less reflective, but even. Because of the grained finish, light scratches can often be reclaimed by using a very light-grit finishing pad.”

From the link

Material Emissivity

Value

Stainless Steel: type 303, oxidized 0.74 - 0.87

Stainless Steel: type 303, 304: 8Cri 18Ni light

silvery, rough brown, after heating 0.36 - 0.44

Stainless Steel: type 303, After 42 hours of

heating at 527oC

0.62 - 0.73

Stainless Steel: type 310 - 25Cr, 20Ni, Brown,

splotched, oxidized from furnace service 0.90 - 0.97

Stainless Steel: type 310, rolled 0.56 - 0.81

Stainless Steel: type 316, polished 0.28 - 0.66

Stainless Steel: type 321 0.27 - 0.32

Stainless Steel: type 321, polished 0.18 - 0.49

Stainless Steel: type 321, with BK oxide 0.66 - 0.76

Stainless Steel: type 347, oxidized 0.87 - 0.91

Stainless Steel: type 350 0.18 - 0.27

Stainless Steel: type 350, polished 0.11 - 0.35

Stainless Steel: type 17-7 PH 0.44-0.51

Stainless Steel: type 17-7 PH, polished 0.09 - 0.16

Stainless Steel: type C1020, oxidized 0.87 - 0.91

Stainless Steel: type PH-15-7 MO 0.07 - 0.19

Stainless Steel: Allegheny metal No. 4,

polished 0.13

Stainless Steel: Allegheny metal No. 66,

polished 0.11

..."The Ra for a 2B finish is typically between 0.3 µm (12 µin) and 1 µm (40 µin), depending on the gauge of the metal."...

https://astropak.com/surface-roughness-average-ra/

I'm not getting involved in the Surface debate as its out of my scope but I am amazed that an industrial Oven is being built / used without Isulation material ! especially considering increasing energy costs.
Also the use of a Insulated Stainless Material would add strength to the construction and less surface deflection. Depending on how thick or thin the panels are, they could distort due to the heat and that would affect the surface reflection, which was the original question being asked !
Just my 2 cents..

It’s an infrared oven for cooking beef patties. Since it’s a meat product and not a bakery product, being open and uninsulated it’s more sanitary.

As far as heat, it’s indirect heat to the panels where the heat is directed right to the patties.

the infrared heaters are above the patties about 6” , so it’s the patties and the stainless conveyor belt that is getting the heat. Now the belt is water cooled at a section.

is it hot, yes, but the heat is not direct. I just want the reclaim the heat by reflected as much as I can off the panels and back to the product.

and the panels are just hung, made out of 14 gauge 304 SS. As far as distortion, no not really, if any it’ll be nominal. And because they are hung, it so all the panels can be removed and washed.

the design is actually quite open, where you can look and see the infrared heaters, as well as the patties the Patty flippers, and the grease being dropped off and diverted and reclaimed.

Hi Phoenix, thanks for clearing up the oven function. I was thinking along the lines of a conventional baking oven and not a conveyor belt type cooking Burgers ! (Beef Patties)
Can you not design the Infra Red lights to concentrate the light / heat directly onto the Burgers so you don't need to depend on secondary heat reflections, that way you could avoid unnecessary costs for surface treatment of your panels.
Infra red lights can be controlled / directed to hit predetermined areas.. when I worked for Hella in Germany I had a project using infra red LED's to turn on cargo room lighting when a person came within a specified area.
Also when working for LAM Research in Austria I had a Infra red lamp used for heating chemicals that had over 1500 LED's on a 12 inch disk..
Also, presumably, some of the fat / grease from the burgers will land on the panels which will reduce the reflections anyway, irrespective of what surface finish is used so the secondary heating will affect the cooking levels in the individual burgers depending on the condition of the reflective panels. Clean panels will result in in a quicker cooking time than dirty panels covered in fat / grease etc. so there will be no consistency in the preparation time.

the IR burns are directed onto the pattys.

… to digress further, there are multiple gas fired (NG) IR heaters mounted on multiple carts where the heaters are cantilevered over the conveyor belts 4-6 inches above the pattys..

I’m not going to go into too much details, just due to how the grease drippings are removed.

The burners are mounted on carts so the carts can be removed during wash-down so the ceramics doesn’t get wet. As well as maintained,

So the majority of the heat is focused on the pattys, but there is residual heat coming off the fire box (et al) where the ceramics are in as well as reflected from the stainless belts being heated up. (These belts are also cooled down with a water spray after the pattys are dumped.

it’s warm (hot) in the environment where these ovens are. I’m just curious if I can make the ovens more efficient.

OK now I get the full picture, you are not using IR LED's you are using the heat from a gas-fired heater to generate the IR level !
I would guess the efficiency level will depend on a number of factors being optimized, distance from heat source to Patty, temperature required to cook the Patty to the desired depth, thickness of the Patty, time spent travelling in heating zone, ambient temp. in the cooking zone, Temp. of the Patty at start, (frozen / Fresh ?)
It will be interesting to know when you have finished how much weight you gained tasting all those prototype patties !!

There are variable details that I did not mention… but what you mentioned, have been addressed. I apologize for that.

thank you for your input.