looks amazing.

 

so coat the dp

 

 

No, It's better not to coat the DP.

This is what Kane is saying I believe.

 

I'm not so sure about this.

Lowering the post turbine exhaust gas temperature results in a reduction in energy, a lowering in fluid velocity, and an increase in density. I don't see why you wouldn't want the fluid to have as much energy as possible (very hot and fast) on both sides of the turbine. The faster it moves through the system, the quicker it will spool the turbine. Any reduction in post turbine heat will result in additional back pressure, decreasing the performance of the turbine.

Perhaps you can explain your point with more clarity?

 

The coating keeps the heat inside the pipe instead of allowing it to radiate into the engine bay, etc. There is no heat loss there. The outside of the downpipe, manifold, etc. will be warm to the touch.

 

*straps on benchracer suite*

From what i've seen, the actual differences between coated and uncoated downpipes are probably insignificant. The basic theory sounds good that "if you cool the gases post turbine, it will lower the pressure in the same amount of downpipe space thereby creating a larger pressure differential from pre to post turbine" However, I have some questions about this. If the gases touching the downpipe surface inside the pipe cool, their velocity requirements will lower and then there will be turbulence generated from the shear between the higher temp gases in the center of the pipe and the cooler gases towards the outside. I wonder if these turbulences could raise the pressure required to push all the gases through the pipe? In this case a coating inside the pipe would be more beneficial because it would insulate the gases from cooling allowing all of the gases to travel at the same velocity. However the opposite could be true too, maybe shear friction in gases is less then of uni-temperature gases pushing against the downpipe as they expand.

...just some thoughts...

 

I've been talking about this one topic for a long while now between my engineering friends over at honeywell (though not the turbocharger division) and also an engineer at Turbonetics, and a few other engineers that work with fluid dynamics of HVAC systems almost daily. The hard part is that it's not just water and the temperature variations are unknown as well as all the gases and %'s. The change in density of the water vs. the other compounds to the temperature change. There just isn't enough data that I could get to pull together a conclusion. The turbulence generated can also help to pull the gases away from the blades as was shown by earlier turbocharged F1 engines where turbulence was purposely created.

I'd ask you for some CFD's but we both know that the variations between real world would be too great. I would like to know the truth myself and what I presented was actually my theory more than anything else. I don't think the back pressure generated would be significant. Heck the whole retaining or not retaining probably has no significant value at all. If anything the only value would be to prevent fatigue of the metal due to constant cooling and heating Vs. a decelerated rate of temperature change of the downpipe.

 

I'll do a CFD analysis. I'll use air as my medium, running a full compressible simulation. One simulation will allow the air to cool as it exits, and another won't. Should be pretty simple to run. The model will be a simple centrifugal pump.

 

Thanks

Let me know what you used for the rate of temp. change/specific heat of the metal, volume, the length, and initial temp, outside ambient temp.