Thermal insulation and positive pressure

[Qbomb]

I was having a discussion about thermal insulation (high temperature) and I thought that positive pressure (meaning the heat is being blown onto the insulation) would reduce how effective the insulation was.

Say a 1/2" of insulation reduced temperature from 1000 degrees F to 500 degrees F. The question is if the heat was being blown (say with a fan) onto the insulation would it only reduce the insulation to say 600 degrees F?

I hope that made sense.

If this does make sense to someone is there a formula to figure it out?

 

[cjl]

That depends. You're basically talking about forced convection, which will reduce the thermal resistance of the air-surface interface. However, in most insulation, the air-surface interface already can transfer heat much more effectively than the insulation itself (the insulation has a higher thermal resistance than the air-insulation interface). If that is the case, it won't make much of a difference. However, if the air-surface interface has a thermal resistance that is significant relative to the thermal resistance of the insulation, the forced convection will increase the rate of heat transfer and probably the temperature of the opposite side of the insulation. In general, the more effective the insulation is, the less difference the forced convection would make.

 

[Qbomb]

Yes I am talking about forced convection against an insulation. One difference that i should have mentioned, was that in the original discussion I had, we were trying to trap the heat inside and not let it escape. Therefore making the 'cold side' of the insulation the air-surface interface.

So we were discussing if 1/2" of insulation with no forced convection dropped the temp from hot side being 1000 degrees F to cold side being 500 degrees F, what would the change be with forced convection. So say 10 psi of forced convection would make the hot side 1000 degrees F (or possibly hotter?) and the insulation would only reduce the cold side to x degrees F (550 degrees F or something like that).

Any thoughts cjl?...or anyone else out there.

 

[cjl]

As I said, it depends. In most cases, with decent insulation, the change will be pretty minimal. One way to tell would be to measure the temperature of the hot side surface relative to the air. If the surface is 1000F and the air is 1200F (and the cold side is 500F), then forced convection will make a significant difference, since it will make the surface temperature rise to become much closer to the air temperature of 1200F. However, if the air is 1020F and the surface is 1000F, the forced convection really won't make much of a difference.

 

[sardar]

I would like to clarify that thermal insulation and positive pressure are two separate factors that affect the effectiveness of insulation. Thermal insulation refers to the material's ability to resist heat transfer, while positive pressure refers to the force of air or gas being pushed into a space.

In terms of insulation, it is important to understand that the effectiveness of insulation is measured by its R-value, which is a measure of its thermal resistance. The higher the R-value, the more effective the insulation is at resisting heat transfer. In the scenario described, if the insulation has an R-value that can reduce the temperature from 1000 degrees F to 500 degrees F, then it will still have the same effect regardless of whether there is positive pressure or not.

Positive pressure, on the other hand, can affect the overall temperature of a space by introducing outside air or gas that may be at a different temperature. However, it does not directly impact the effectiveness of the insulation. In fact, positive pressure can even help improve the insulation's performance by reducing air infiltration and preventing heat loss through leakage.

In terms of a formula, there are various equations that can be used to calculate the thermal resistance and heat transfer in a system, but the specific formula would depend on the materials and conditions involved. It is important to consider all factors, including the type and thickness of insulation, the temperature and pressure differentials, and any external influences such as positive pressure, in order to accurately assess the overall performance of the insulation.