Intake piping- heat soak concerns

Silicone Vs stainless / aluminium / rubber... what is the best material for minimizing heat soak into the intake system?


I looked up some specific heats capacities of metals, and found the following:
Aluminum 0.91 kJ/kg K
Carbon Steel 0.49 kJ/kg K
Silicon (metal) 0.71 kJ/kg K

Problem is these specific heats are by weight... ie it takes 0.91kJ to heat 1Kg of aluminium by 1 degree kelvin (ie 1 degree celsius). Obviously intake pipes made of aluminium will weight more than silicone, but less than carbon steel (or a stainless alloy). Herein lies the problem.

What have you heard about heat soak when choosing material for your intake system?

 

I like silicone. Easiest to get on and off. That counts more for me than any possible advantage or disadvantage heat soak wise...

 

I'm pretty much sold on the silicone accordian hose replacements at Z1. Airflow gains alone are worth it.
Was tossing up between going with silicone for the TB/ intercooler holses, or go the stainless / aluminium style.

I agree that too many hose clamps and additional pipes in the intake are a mess, and difficult to work with. trying to weigh up the options though.

 

Thinking outside the box - or was it pipe - lol

Think of it combined with other compounds though e.g. surround the piping with water for heat soaking

It takes 16,000,000 Joules/watts (16000KJ) to convert 1 Litre of water to 100c !!! - one of the best latent heat of vaporisation compounds around!

but weight is the factor with 1L being approximately 1 Kg

I mean you can move it and replace it being a fluid whereas a block of metal will not flow away to somewhere else to cool down.

Also don't forget conversely that air is a great insulator with technically no weight - it all comes down to application and purpose I guess

I only mention this because you used the word heat sink -
Just food for extra thought even if application is tedious?

Cheers

 

I'm not breaking any power records rob, but I guess my aim is to get the most out of what I have- what I currently have for the intake piping is stock, and in pretty bad shape.
At my level, going coated aluminum is probably overkill, likewise any silicone I use will be fixed with t bolt clamps.
It stands to reason that heat travels from hot to cold objects (one of the laws of thermodynamics), so even with high end coatings, heat soak will occur over time. So the idea is to choose a material which has the best ability to insulate against heat- ie a high kj/kg per celsius value.
As with anything, im chasing cost versus return. Ive got a few temp probes I can setup as a test if needed, might be a good exercise to review.

 

I would think that you want low specific heat capacities if its soak that you're worried about, that way the temperature of the pipes corresponds to a lesser amount of thermal energy. Really you have quite a small surface area/volume ratio inside the piping so heat transfer isn't going to be significant on an average build.
If you want an improvement an don't want soft silicone the whole way alloy wrapped in some heat tape is probably your best bet along with reducing under bonnet temps through ventilation and exhaust wraps.

 

Over analyzing is what I'm best at. Its just a shame I'm no expert on this - so everyone should take my ramblings as uneducated, not gospel.

Going ceramic coatings to reduce heat soak is an all or nothing in my opinion. The heat exists in the system, so i think insulating one component just moves the heat load to another part of the system.

As for the low specific heat Fists, I'm not entirely sure.
On one front, you want a material which resists heat soak form the engine bay ambient temps, while also having the ability to remove heat out of the intake air, back into the engine bay efficiently. i.e. resist radiant and conductive heat, into the intake charge, while promoting convection via airflow out of the piping.

A higher specific heat will resist sudden changes in IAT's, as it will hold heat and remove it from the system gradually. Low specific heat will have the material fluctuating significantly in temp.

I'm guessing there is probably a couple of hundred bucks of coatings on top of the purchase price of any off the shelf intake pipes for the Z32. Silicone seems cheap enough, easy to install, and readily available.

Before I take the jump, I might look into logging some IAT's using a cheap digital readout probe I have. Ideally I'd have one before the FMIC, and one after. Might make this the next little project.

 

While the material will change 'temperature' more the energy change will be less and hence less temperature change in the air charge. Higher specific heat also leads to higher thermal conductance and radiance which means a greater ability to transfer the heat its carrying into the air charge.
As for using the piping as part of the charge cooling system I would be checking your bay temps as Rob mentioned; your compressor outlet runs past the exh manifold so you'd want that insulated and if your air charge is still hotter than the bay after its been through the intercooler then you probably want a better intercooler

 

Good insight, thanks. It's good to hear from people with a better understanding of it than me, so thanks.
I've got the intercooler front sorted- running a big plazmaman FMIC. I'll do some testing and see what I come up with.

 

Some data will be good, I know a bit of the theory but no practical experience. Do you have any way of data logging? you're probably really only interested in the numbers under heavy load.
It will all depend what you want out of the car too, when you want the power to be available just for a sprint or for long hauls

 

I have lots of open road, 2 eyes (hopefully a passenger's) and a notepad. I have a cheap 5v powered digital readout and thermocouple which is used for monitoring PC case temps, so should be good enough for me. For 5 bucks a pop, I could fill the engine bay with them if needed, and run them off batteries.

I've also got a datalogger thing I bought from magicmike in a group buy 3 years back, but to be honest, I have not even removed it from its pack
I should look into that...

 

So my guessing wasn't too far off, considering the air inlet for the engine bay is through the 80* radiator its going to be hard to get cool. Some proper quarter panel vent would awesome if someone made them.
Any record of the difference in charge temp between standard/ceramic pipes or did you do it while changing other things?

Keep us posted Mitch, might try and do some measurements myself once everything's back together

 

I would guess that due to the volume and the speed of the air, in a relatively large (2-2.5") pipe, the heat transfer between the two is between minimal and insignificant. A smooth large pipe wont transfer any noticeable temperature.

If the heat transfer did actually take place to a reasonable degree, then the pipes should be much cooler than what they air. Considering the mass of airflow through them is considerable, the pipe will be flowing hundreds of liters of air per second. To heat that amount of air from only a short, smooth wide pipe wall it would need to be white hot.

 

This above

This above - +1

and ......... there is also certainly merit in exhaust wraps helping out indirectly given there effectiveness in reducing heat radiation to other components - one of the biggest problems though that is often neglected, is really the block itself (being the largest area of heat) and the heat radiation transferring to these other components by conductivity or heat radiation.
I wonder if anyone has ever come up with a solution for the block itself like ceramic coatings / thermal paints etc - lol - its not like you can wrap it up with exhaust tape with ease - As you know aluminium for example will absorb heat from a radiation source and therefore interfere with its operating efficiency whereas CF or Silicon are more resistant to this absorption.
Has anyone heard of this (block external heat radiation)being addressed before? I am assuming that any solution would not be able to change the characteristics of the expansion of the block itself in an adverse way to be effective. I know that professional high end racing teams have addressed this specifically in some way with heat shielding materials but clearly the motor specs are somewhat vastly different to the VG30DETT in design and materials and so any consideration would have to be effective and viable.

Looking at the block and these other large heated components can assist is bringing down the ambient temperatures and thus allow better cooling of these other components indirectly - as you can probably appreciate - it all adds up.

The information to your question is somewhat limited in any worthy input I could offer that you don't know already, so I am just trying to look at it from different perspectives - because it all adds up - especially when you have massive large heat sources like blocks and exhausts emitting large quantities of heat radiation nearby. Its a bit like pushing shit up a mountain

JC

 

You can also increase cooling by adding heat pipes (re first post) or heat-sink wrap around fins or clamp on heat-sink fins to any effected parts that you want to cool if they are metal and round, typically you can also add heat-sink fins to any flat metal parts, your really just limited to the space and weight considerations available. It's surprising how effective they can be even with limited airflow.

JC