Intercooler: How Much Does It Really Heat Up?

Hello,

The supercharger's performance is determined by the volumetric flow rate multiplied by the pressure increase.

Taking into account the density and heat capacity of the air, this results in a temperature increase of approximately 75K per bar of boost pressure - without any external heat input or removal.

Now, the loader on the compressor side doesn't just produce useful work.
The compressor performance maps indicate efficiency peaks around 75%, assuming an average efficiency of 73% across all operating conditions.

So, if 73% of the energy fed into the compressor is converted into compression, where does the remaining 27% go?

Normally, this loss of power is converted into useless heat... and where does that heat go in the charger?
I suspect it's due to the heat in the intake air, in addition to the heat generated by compression.

A 100% / 73% ratio results in a loss factor of approximately 1.37, which would need to be added to the temperature increase caused by compression to calculate the actual temperature increase.

So, 75K / bar * 1.37 = 103K at 1 bar... that's already quite a lot for the VP-TDIs .

At a power level of 96 kW with a boost pressure of 1.3 bar, the total output is already around 134 kW, plus the respective ambient temperature.
That means that at an air temperature of 30°C, the charge air exits the turbocharger at approximately 164°C.

Is this generally correct, or have I made a mistake in my thinking or calculation somewhere?

What is the basis for the efficiency, i.e., what is the reference value?

75% of the power comes from the exhaust gases?
or something else?

CU Gremlin.

Gremlin wrote:

What is the basis for the efficiency, i.e., what is the reference size? 75% of the power that is introduced through the exhaust?

AFAIK, the identification fields in question only refer to the compressor side.

Mass flow (towards the motor) - Pressure ratio (inlet / outlet) - Compressor speed - Impeller blades (these shell-like shapes).

The reference value should therefore be the power or energy that enters the compressor through the charging shaft.
Regardless of the efficiency of the exhaust gases -> turbine on the hot side...

I found something that might provide an answer.

http://members.aon.at/dihaider/Ladeluftkuehlung.html
(by the way, the whole website is quite informative...)

. . . but what does this "k" with the value 1.4 mean?

Hi!

To verify your assumption, simply install a temperature sensor in the intake manifold. You can find various kits with digital displays at any electronics retailer.

Best regards,

SeatArosa1.7SDI wrote:

To verify your assumption, simply install a temperature sensor in the intake manifold.

I actually didn't want to put in so much effort just to measure things that are already known, and in the process, get more or less inaccurate results.

@ulf:

Quote:

. . . but what does this "k" with the value 1.4 icon_question.gif

mean?

k=1.4 indicates that a polytropic exponent of 1.4 is being used, which implies an adiabatic process.
This assumption is largely correct, provided that the processes occur very quickly, such that there is practically no heat exchange with the surroundings.

Regards,
Alex.

donalexo wrote:

k=1.4 means that a polytropic exponent of 1.4 is being used in this calculation, which implies an adiabatic process.

Thank you, Alex .
But now, my initial invoice doesn't seem to be correct anymore.

Haider assumes a compressor efficiency of 75%.
So, based on the rated power, a "loss factor" of 33% is included.

During adiabatic compression, the temperature increases by approximately 75K per bar.
If the additional 33% power loss also contributes to the temperature of the intake air (which it has nowhere else to go), then, in my opinion, this results in a temperature increase of 75K / 0.75 = 100K per bar.

At 1 bar of boost pressure and an intake temperature of 20°C, the charge air would have to exit the intercooler at 120°C.
The Haider diagram, however, only indicates a temperature of approximately 105°C for this.

How is this explained, or where do the missing 15K of warming go?

Does it go into the potentially heated exhaust as a loss...?

Best regards,
Uwe

Uwe wrote:

Do they go into the potentially heated exhaust gas as a loss...?

Hm... by what means?

a) regarding the charger housing -> this would only work if the intake air was hotter than the exhaust gases -> therefore, it's not a viable option.

b) through the charge air cooler into the engine -> then those 15K would have to be measurable in the charge air cooler at the turbocharger outlet - but that's exactly where they are "missing" . . .

Where do those 33% of efficiency losses go? I don't know either .

Best regards,
Uwe