Why do they polish tanker trucks to a mirror finish?


Why do they polish tanker trucks to a mirror finish?

In: 8

If you’re carrying something temperature-sensitive, you don’t want it heating up on a hot sunny day. It’s going to happen, but a mirror finish reflects a lot of heat that would otherwise get into your cargo.

Reflecting heat and additional visibility. Both at the same time.

Also, for things like milk, easier to sanitize and see if cleaned.

On top of the other good answers here…if something like milk or food-grade liquids are being transported, there is an additional impression of high sanitation\cleanliness that you get with polished stainless steel surfaces. It’s all over the place in food preparation areas because it cleans up and disinfects well (and looks good), so there is a well-deserved sanitary connotation to it.

Anything that needs its temperature to be maintained gets a lot of help (or hindrance) entirely passively just from the optical properties of the surrounding material, e.g. color. We are talking here about minimizing the unwanted heat transfer from thermal radiation — rays of infrared light (different from conduction, which is heat transferred between two materials when they physically touch each other, like the warm air touching the side of the cold tanker). There are two main considerations: (1) reflect the incoming light, e.g. from the sun — a mirrored surface has will have the highest [albedo/reflectance](https://en.wikipedia.org/wiki/Albedo), and white is pretty good too; (2) optimize [thermal emissivity](https://en.wikipedia.org/wiki/Emissivity): the amount of light your tanker emits by virtue of itself being warm — you want high emissivity if you want to keep things cold, so that the things inside will radiate as much excess heat away as possible; and you want low emissivity if you want to keep the things inside warm. An example of the latter are those mylar aluminized emergency blankets. For the former: opaque generic paint. Keep in mind that in either case, once the tanker reaches the same temperature of the outside environment (equilibrium), there’s no more passive heating or cooling that will occur.

In the [simplest theory (Kirchoff’s law of radiation)](https://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation), a good reflector is a good emitter and vice versa. A metal shell is a relatively cheap material that one can wrap around one’s tanker load, or even make the tank out of directly. When the metal is polished, the high albedo and low emissivity is optimal to maintain higher temperatures. However, a polished metal surface is quite expensive to maintain, and heat losses from emissision (being calculable and relatively constant) may not be as crucial to prevent as losses from infrared absorbtion (the sun’s intensity and direction varying all day), so adding a protective clear paint coat, or else just using reflective white paint all over, both of which have very high emissivity may be the more economical choice. (thermal conduction also greatly matters when considering a bare metal surface versus painting — metal obviously tends to be a great conductor — though if the metal is a shell separate from the tank then that won’t matter). (You may have noticed this kind of thing from commercial airliners: American Airlines for decades had distinct polished-metal planes (with a clear paint coating), but the weight of that choice was [in the end tipped by marketing according to an unverifiable comment](https://aviation.stackexchange.com/questions/13824/why-are-commercial-airplanes-painted-at-all)) (Someone may have to help me, as I actually can’t find any data on the use of high-emissivity paints or surfaces in vehicles at all, apart from the Space Shuttle and for specific wavelengths for stealth vehicles).

Of course, real-world surface coatings are a lot more elaborate and have been designed with more complexity to [optimize for passive temperature control in new buildings](https://en.wikipedia.org/wiki/Radiative_cooling#Architecture), for example.

I’m a former heavy truck mechanic that worked on gasoline tankers. I assume that’s the kind of tanker trucks you’re talking about.

The most common reason is that it looks nice. Drivers spend a significant portion of their lives in their trucks. Some of them just like shiny trucks. You see things like that in all big trucks, not just tankers. Some drivers like fancy paint jobs, lots of chrome, lots of lights, etc. Other drivers are okay with plain looking trucks.