Does surface roughness affect emissivity?

The results indicate that the presence of high roughness and high emissivity surfaces increases both the turbulence intensity and the convective heat transfer, which in turn increases both the mass flow rate and air velocity behind the radiator resulting in a higher heat transfer.

What has high emissivity?

The maximum possible emissivity of 1 would imply that incident radiation is completely absorbed, and for a given temperature the object then emits thermal radiation with the maximum strength. Such an object is often called a black body. A high emissivity of a material comes together with a high absorptance.

Why do polished surfaces have low emissivity?

Many metals will form a thin oxide layer which has its own emissivity and is different from the metal. Polishing temporarily removes this oxide layer and lowers the emissivity to that of bare metal.

What is the emissivity of concrete?

Emissivity matters because matt surfaces, such as that of concrete, have a high emissivity level of between 0.85-0.95, making them very good at absorbing and emitting radiant heat.

Does emissivity depend on thickness?

The values of the emissivities apply to materials that are optically thick. This means that the absorptivity at the wavelengths typical of thermal radiation doesn’t depend on the thickness of the material. Very thin materials emit less thermal radiation than thicker materials.

What factors influence the emissivity of a material?

Emissivity is not easy to measure accurately because it depends significantly on many physical and chemical properties, such as temperature, wavelength, angle, oxidation, roughness, heat treatment and so on.

Is black high emissivity?

By definition, a black body in thermal equilibrium has an emissivity ε = 1. A source with a lower emissivity, independent of frequency, is often referred to as a gray body.

Do shiny surfaces have high emissivity?

Any surface above absolute zero will radiate some energy, more than 0% and less than 100%. Emissivity is casually summarized as “shiny things reflect infrared energy and do not radiate well, non-shiny surfaces emit well and do not reflect as much”.

Which surface will have least emissivity?


Materials surface Thermal emissivity
Silver, polished 0.02
Aluminum foil 0.03
Marble, smooth 0.56
Paper, roofing or white 0.88 to 0.86

Why does a basketball bounce higher on a hard surface?

The more energy absorbed by the surface, the less that remains in the ball for it to bounce. This is why you should have seen that when you bounced the basketball on a relatively hard surface it bounced higher (it lost less energy) compared with when it was bounced on a softer surface (where it lost more energy).

How many surfaces do you need to bounce a basketball?

At least two different surfaces to bounce a basketball on, with at least one hard surface and one soft surface (For example, you could use carpet, concrete, grass, linoleum and a basketball court. The surface needs to be flat and next to a wall or other large perpendicular surface.)

What factors affect a basketball’s collision with the ground?

One factor that can affect the basketball’s collision with the ground is the type of surface the ball collides with. When a basketball bounces off of a surface, some of its energy is absorbed by that surface. Some surfaces absorb more energy than others do.

What happens to kinetic energy when a basketball hits the floor?

When a basketball hits a court floor, a part of the kinetic energy gets converted into sound or heat, some of it briefly changes the ball’s shape (flattening it slightly) and a portion is absorbed by the floor surface.