Intercoolers and other bits

[Snagger]

15 hours ago, Daan said:

I found that the temp drop is virtually independent of ambient temp; thinking of it, a 10 degrees higher ambient temp is going to give 10 degrees higher intake, about ten degrees hotter turbo, and the intercooler has the same delta temp to work with. So the endresult is a 10 degrees higher intake temp into the engine. So whether it is a hot day or a cold day, your intercooler does the same thing.

 

Daan

There won't be such a linear relationship between ambient temperature and compressor output temperature - higher ambient will lead to higher compressor outlet temperature, but not by the same value.  There is likely a complex equation for the relationship, but I don't know it.  What the intercooler achieves is going to depend on several variables, including internal and external flow rates, temperature differentials and actual temperatures.  It's certainly not going to give a flat rate of cooling.  To get a useful comparison of the benefits of intercooler size, we'd need comparable engines and similar conditions (temperature, air density, boost from the compressor and engine rpm).

[ianmayco68]

Got some more figures today , outside temperature was 5.8 c moving, 6.6c stationary in a shed but an open one no doors . 

So accelerating hard to 60mph , in was 88c and out was 8.3c .

 Town style driving 36.8 in and2.6 out that was doing 40mph .

[cackshifter]

That is an impressive amount of cooling

[Bowie69]

Very impressive indeed....

[Peaklander]

Cooling to below ambient, is that possible?

[Anderzander]

Wind chill?

[JohnnoK]

6 hours ago, Peaklander said:

Cooling to below ambient, is that possible?

Not without some sort of assistance from ice or aircon type cooling.

[Peaklander]

Wind chill is supposed to be a "feeling" but in the winter, "cold windy corners" really do seem to hold ice and snow, so I've never been sure that it's purely a feeling.

Wondering if there is some sort of evaporative cooling going on here maybe, particularly if the intercooler is wet and the airflow around it can create the right conditions?

I doubt I'd get many marks at school for that answer though. 

[ianmayco68]

8 hours ago, Peaklander said:

Cooling to below ambient, is that possible?

I’ve wondered this , the day before I switched it on and had 0.8c on the output I actually moved the probe to another socket to see it was working right , all the same readings. But if you notice the outside temperature dropped when moving , and I’m pretty sure it dropped down to as low as 4c but it’s hard to see whilst driving. I’m sure some scientificy type person could explain this , I forgot what I knew years ago when I left school   . 

[landroversforever]

It’s got to be able to as long as ambient is low enough so the cooling capacity of the IC is high enough. Wind chill can easily knock 5/10 degrees off the ambient. 

[Peaklander]

The rate of cooling is higher in forced air - I think the delta raised to power 5/4. That would just speed cooling up but I don't know how the cooling body can get below the temp of the forced air without some other feature coming in to play. Wondering what that might be.

[Bowie69]

Indeed, could have been wet, or you have just neglected to apply error bars to the graphs!

You can't cool to lower than ambient with an air to air intercooler.

[Snagger]

On 3/9/2019 at 3:15 AM, Peaklander said:

Cooling to below ambient, is that possible?

No.

[Snagger]

On 3/9/2019 at 4:33 AM, Anderzander said:

Wind chill?

Also no.  "Wind chill" brings the temperature of a mass towards ambient, so a cold mass would be warmed if the ambient temperature is greater - think of ice cream melting - so it's a misnoma.  The airflow is just stripping away any insulative layer of warmed/cooled air around the body in question.  If you have no airflow around the body, the surrounding air will start to match the temperature of the body and thermal transfer will reduce.  That's why we have fans on radiators.

[Snagger]

On 3/9/2019 at 12:07 PM, ianmayco68 said:

I’ve wondered this , the day before I switched it on and had 0.8c on the output I actually moved the probe to another socket to see it was working right , all the same readings. But if you notice the outside temperature dropped when moving , and I’m pretty sure it dropped down to as low as 4c but it’s hard to see whilst driving. I’m sure some scientificy type person could explain this , I forgot what I knew years ago when I left school   . 

If you reduce the pressure of the air, you'll also reduce temperature (adiabatic cooling).  So, if the position of the intercooler is subject to an air pressure drop when driving, then you would see a corresponding drop in local temperature, and so the air inside the intercooler would also be further cooled.  I wouldn't expect that to be significant in a Land Rover engine bay, but the heat dissipating from the rad and engine while the vehicle is stationary would surround the intercooler, so the lowest temperature while driving is probably the ambient temperature, and the slightly warmer temperature sensed while static is the result of your engine.

There is one thing that would allow cooling below ambient, but it's not the answer to the experiment done and isn't going to be terribly effective in a Land Rover, and that's latent heat.  The evaporation of a fluid on the outside of a heat exchanger could theoretically drop the temperature below that of the surroundings.  That's what sweating does, and works in temperatures well above the human body's 37.something degrees.  But that's rather hypothetical unless you fit a system to spray a readily evaporating fluid as a fine mist to the outside of the heat exchanger.

[Peaklander]

That's why we were speculating that the intercooler might have been wet and thus evaporative cooling coming into play.

[lo-fi]

We need to factor in the pressure loss between one side of the intercooler and the other. As the exiting gas escapes into the lower restriction zone after the cooler, it will lose pressure with a corresponding drop in temp the same as fridge or aircon circuit. 

Cosworth made good use of this on F1 during the turbo era, I seem to recall. Some shenanigans involving boosting up to higher pressure than allowed at the inlet, intercooling, then dropping down to the max permissable under the rules yielding below ambient charge. 

The Guy Lussac law states:

"pressure of a fixed mass of gas at a constant volume is directly proportional to its absolute temperature.

In other words, when temperature increases, pressure increases.
When pressure decreases, temperature decreases." 

Working on a (realistic) 1psi drop across the IC and solving for T2 gives a ~2.5 degree temp drop. Moderate load, the IC seems well able to cool to ambient, then the pressure drop neatly explains the below ambient measurement. 

[ianmayco68]

So the below ambient output temperature is due to the pressure drop in the intercooler , do you think that Allisport mean to do this in there intercooler design to achieve lower temperatures on the output side ? I would think they do , as they are a motorsport company , and is that the difference between the more expensive intercoolers and the cheaper Chinese ones or even standard and front mounted ones ? Also I've seen twin pass intercoolers on eBay does anyone think they would make any difference ?

[Peaklander]

If this is the reason for lower than ambient temperature being achieved (assuming that the recorded reading is correct), I wouldn't have thought that intentionally doing this would be as preferable as maintaining as high a pressure as possible. After all, the objective is higher manifold pressure, meaning more air going in, isn't it? 

[ianmayco68]

I thought that the idea was the cooler the air the denser it is therefore the more oxygen it contains making bigger bangs, equaling more power . So lowering the pressure to achieve lower output temperatures would achieve this .

[Peaklander]

Yes suppose so, otherwise why have an intercooler at all!

[ianmayco68]

It has surprised me how much it cools down the air though , it will be interesting when the weather warms up ( hoping ) to see how much the temperature drop is then .

[lo-fi]

On 3/10/2019 at 3:09 PM, ianmayco68 said:

So the below ambient output temperature is due to the pressure drop in the intercooler , do you think that Allisport mean to do this in there intercooler design to achieve lower temperatures on the output side ? I would think they do , as they are a motorsport company , and is that the difference between the more expensive intercoolers and the cheaper Chinese ones or even standard and front mounted ones ? Also I've seen twin pass intercoolers on eBay does anyone think they would make any difference ?

There are a lot of factors here, all of them interrelated. A larger intercooler should have lower flow resistance which means less pressure loss for a given flow. The turbo has to work less hard to achieve the same manifold pressure. Less work, less heat, denser charge. Also larger surface area for heat exchange so better cooling. From your data, it seems the stock intercooler is a good match though, so going for a bigger IC may not return much of a gain at all. It is only a little diesel, after all. If your readings are accurate and pressure loss is the reason you're seeing that slightly lower temp than ambient, that's likely to be an edge case where the IC was able to cool very close to ambient and the engine was demanding enough flow to maintain a pressure drop. You'd not design for this as the few degrees drop you might see aren't going to compensate for flow loss in creating a restriction. I believe it was only done in F1 as a way to get more air through a restrictor and a boost limit! If you're restricted on pressure and flow area, the only other tools available are temperature and density. It's a cunning solution, but one for a very particular set of circumstances. 

[Sigi_H]

Has there been any progress here? I am really interested in that

[ianmayco68]

Only this far sadly , one of the thermocouples broke and with truck problems and the other project I'm working on , also family life getting in the way I never got back round to it , but I will try and re-fit the thermocouples this week and do some more testing when the lockdown has been lifted .