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Name: Russ
Status: other
Grade: 12
Location: GA
Country: USA
Date: Spring 2012



Question:
I understand how color affects energy transfer when exposed to light, but can you explain what the rationale for why the interiors of coolers/refrigerators are most often white or metallic colored? Since exposure to light is minimal, how is this advantageous?


Replies:
Interesting question. Right off the top of my head I suspect it is to make what is inside easier to see.

Michael Loop


To make dirt, mold, slime, etc. obvious.

---Nathan A. Unterman


Russ

It may just be a matter of cleanliness. You can tell whether a white (or metallic) surface is clean or not. The efficiency economies scale are not sufficient enough to influence the color inside a refrigerator. Every time you open the door, the cold air will fall out and the refrigerator compressor and coolant will have to start cooling all over again.

Sincere regards, Mike Stewart


Russ,

In this case, what you do not see is what is important. The transfer of heat can happen in several ways. The first is through conduction, in which heat is transferred through touch. If you touch a hot stove, the heat travels (or conducts) from the stove top directly into your fingers. Another means of heat transfer is through convection, in which heat is transferred through air flow. If you hold your finger away from the stove but above it, the air on the stove top heats, rises (convects), touches your finger and heats it. The last form of heat transfer is through radiation. Heat creates “infrared” or light that has a lower frequency than red light. You cannot see it, but if you hold your hand away from the stove such that air is not flowing across it (to the side, for example), you will still feel warmth. The infrared light is absorbed by your skin and causes the molecules in your skin to vibrate. Your finger temperature rises, and you perceive this vibration as heat. The stove is radiating infrared heat and your hand is absorbing it. For a refrigerator, we want to limit all forms of heat flow from the outside to the inside. A silver surface reflects infrared heat and slows the amount of heat transfer from infrared heat. The white color should perform the same function, although to be certain, you should measure the reflectivity of the white surface in infrared.

Kyle Bunch


Russ,

Since some wavelengths of light are quite long. Infrared and radio waves can be anywhere from a few centimeters to meters in length, they are able to penetrate or curve around solid objects. Think for example of how we can receive radio signals inside buildings. Mirrored surfaces can help reflect those waves away from the inside of containers.

Another way that light can penetrate a solid object is by first heating up the walls of the container and then the walls become radiation sources themselves. Think of those movies where they show somebody touching a wall (putting their hand's heat on a wall) and then an infrared detector shows the hand imprint as a glowing red print on the otherwise cool wall. The wall has now become a radiation source. If this heat penetrates to the inside of the container, then heat can be radiated to the contents. Again, a mirrored surface can limit radiated heat from penetrating into the contents.

Greg (Roberto Gregorius) Canisius College


I think it is not a science issue but an aesthetic one. White and metal make dirt or mold more easily visible, and therefore easier to clean/verify clean. People perceive these surfaces as more sanitary.

Hope this helps, Burr Zimmerman


Hi Russ,

The reason for the color of the interior of refrigerators is that white or glossy metal is highly efficient at reflecting incandescent light. The reflection causes light to bounce all around the interior of the box, allowing the customer to better search for the vegetables or orange juice. It allows a manufacturer to place colored labels to easily identify foods.

Food exposure to the light is so minimal, that it would be unlikely that the food would absorb sufficient light to be either advantageous or destructive.

Hope this helps! Peter E. Hughes, Ph.D. Milford, NH


Hi Russ,

I believe the light, reflective colors inside refrigerators serve to make it easier to see around when the door is opened, and to make it easier to notice when something needs to be cleaned. As you have observed, most of the time there is no light on these surfaces, so the color does not make much difference with respect to interior temperatures.

Jerry Gardner


The color of the interior of a refrigerator/cooler is based largely on the simplicity of the color, not on any advantage of one or another color. Remember, when the door is closed the interior walls are all “black” because the interior light is off, so all colors are “created equal”.

Vince Calder


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