Car Exhaust Heat: Convectional or Radiated?

[itstillruns]

Hey everyone, a recent argument came up between two people which had to do with the temperature of a car hood.

Basically, the argument was what kind of heat would an exhaust manifold mainly use to get the hood of a car hot, convectional or radiated heat.

The exhaust manifold is made of stainless steel but is ceramic coated, id say it gets around 800 Fahrenheit. I do not believe it emits any light at that temp.

Thanks in advance!

 

[K^2]

Anything at any temperature emits radiation. At 800F, not enough of it is in visible range to be visible. In IR, however, 800F positively glows.

Whether that's enough to be dominant mode of heat transfer, however, I'm not sure. There are ways to estimate how much heat is actually radiated, but I'm not sure how to estimate convective transfer under car's hood.

 

[itstillruns]

Thanks for the 1st reply, I understand that at almost every temp things emit radiation, even if if the value is extremely small.

The argument was mainly if a clear heat-shield could be used to prevent the hood from getting as hot.

 

[K^2]

Oh, whatever you end up using is most likely not transparent in wavelengths that are being radiated. Clear plastics tend to be opaque in IR.

 

[sardar]

I would say that the heat from a car exhaust manifold is primarily convectional heat. This is because the hot gases from the exhaust flow over the surface of the hood, transferring their heat energy to it through convection. This is similar to how a hot air balloon rises due to the hot air underneath it.

While it is true that the exhaust manifold may also emit some radiated heat, this is likely a smaller factor compared to the convectional heat transfer. Radiated heat is a form of energy that is transferred through electromagnetic waves, and can be felt as warmth on the skin. However, at the temperature of 800 degrees Fahrenheit, the majority of the heat energy is likely being transferred through convection.

Additionally, the fact that the exhaust manifold is ceramic coated may affect the amount of radiated heat it emits. Ceramic coatings are known for their high heat resistance and low thermal conductivity, meaning that they are effective at trapping heat and preventing it from radiating outwards. This further supports the idea that convection is the primary method of heat transfer in this scenario.

Overall, while some radiated heat may contribute to the heating of the car hood, it is likely that convection is the dominant mechanism for transferring heat from the exhaust manifold to the hood.