Heat on heat shield. Friction or compression?

In summary, the conversation touches on the concept of atmospheric heating caused by a reentry vehicle compressing air in front of it. NASA heat shield experts explain that while most of the heat is generated through compression, some also comes from the friction of the air. This friction is important in transferring heat to the surface, and can be further understood through the concepts of viscous dissipation and boundary layer. The conversation also mentions the role of friction in making the concept of atmospheric heating easier to understand.
  • #1
thenewmans
168
1
I always thought of a reentry vehicle compressing the air in front of it. And that would cause a lot of heat kind of like filling my tires. But I keep hearing friction even from NASA heat shield experts. OK, I guess maybe 10% of the heat is friction. I always assumed they said that to make the concept easier. But I’ve heard it so much recently that I’m starting to think I’m wrong. Or maybe they’re the same thing in a way that I hadn’t understood yet. Can you straiten me out?
 
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  • #2
The jargon is atmospheric heating, and its explanation is
When fluid flow slows down its kinetic energyis converted to heat; in high speed flows, tremendous energy is represented by the mean motion of the flow. As the flow is slowed to near zero speed, its temperature increases, the gradient in the speed in a direction normal to the surface allows small scale mass transport effects to dissipate the temperature in the outward direction and thus the temperature at the surface is less than the stagnation temperature; the actual temperature is referred to as the recovery temperature. [ ... ]
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  • #3
Both are contributors. The heat is mostly generated through the compression but there is some that comes from viscous dissipation as well (or what you might call "friction"). The "friction" plays a great role in transferring that heat to the surface, however.
 
  • #4
That's what I love about PF. Thanks guys. I did found some good stuff on "viscous dissipation"
 

Related to Heat on heat shield. Friction or compression?

1. What is a heat shield and why is it important?

A heat shield is a protective barrier designed to prevent heat from damaging or penetrating the surface it is protecting. It is important because it helps to maintain the integrity of the object by reducing the effects of high temperatures.

2. How does heat affect a heat shield?

Heat can cause damage to a heat shield through either friction or compression. Friction occurs when the heat shield rubs against another object, causing wear and tear. Compression occurs when the heat shield is subjected to intense pressure, which can cause it to deform or break.

3. What materials are commonly used in heat shields?

The materials used in heat shields vary depending on the specific application, but some common materials include ceramics, metals, and composites. These materials are chosen for their ability to withstand high temperatures and their insulating properties.

4. How do scientists test the effectiveness of a heat shield?

Scientists use a variety of methods to test the effectiveness of a heat shield, including subjecting it to extreme temperatures and pressures in controlled environments. They also use simulations and computer models to predict how the heat shield will perform in different scenarios.

5. Are there any new technologies being developed for heat shields?

Yes, there are constantly new technologies being developed for heat shields, such as new materials and designs. Some scientists are also exploring the use of active cooling systems, which would use a coolant to actively cool the heat shield and prevent it from reaching high temperatures in the first place.

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