Subject: Dwell time | Posts 48+

olbetec wrote:

You must free yourselves from the idea that this convective heat transfer has something to do with time!

Given that real liquid cooling systems also involve thermal resistance [Kelvin per Watt], which cannot be reduced arbitrarily, doesn't the time component inevitably come into play?

You want to increase the effectiveness or performance of your LED lighting system. You have two LED light sources of the same type. You want to operate the LEDs in a purely cross-flow configuration (meaning side by side, not one behind the other, otherwise it would be a mixed cross-flow...). Question: Is parallel wiring or series wiring better?
The heat transfer area remains the same; only the convective heat transfer and the pressure loss are different.
First of all, regarding point 1:
The heat transfer rate (Q') is calculated as Q' = k * A * Tm, where:
k = heat transfer coefficient,
A = heat transfer area,
Tm = mean temperature difference.
Parallel oder Seriell bestimmt die Strömungsgeschwindigkeit bei gegebenem Massenstrom und damit auch den Wärmedurchgangskoeffizienten. Dieser ist zusammengesetzt aus dem inneren Wärmeübergangskoeffizienten (unterschiedlich), der Wärmeleitung durch die Wandung (bleibt gleich) und dem äußeren Wärmeübergangskoeffizienten (abhängig von Fahrtgeschwindigkeit, bleibt für den Vergleich natürlich gleich). Der innere Wärmeübergangskoeffizient wird über die Nusseltzahl berechnet, welche wiederum eine Funktion der Reynoldszahl (abhängig von der Strömungsgeschwindigkeit) und der Prandtl-Zahl (Stoffgröße, also konstant) und der Geometrien (konstant also) ist. Man erkennt also die Abhängigkeit von der Strömungsgeschwindigkeit. So unTime cannot be found here.Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.
Given a specific mass flow rate, the power of the heat sink is fixed. The resulting temperatures depend only on the operating characteristics (i.e., the design and current carrying capacity of the heat sink) (see diagrams from the VDI Heat Atlas).
Regarding point 2: The pressure loss is relevant for the delivery rate. It's lower in a parallel configuration and higher in a series configuration. (I will continue working on this tomorrow.)
Stay cheerful.
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

olbetec wrote:

Therefore, one can recognize the dependence on the flow velocity. And time is nowhere to be found here...

In my opinion, it is contained within the concept of time: half the flow velocity (in the case of 2 parallel identical liquid crystal devices) equals double the residence time in the liquid crystal device.

The same result could be achieved, for example, by doubling the width of the cooling system in a single intercooler (doubling the number of charge air ducts).


EDIT
Perhaps we're just talking past each other.

It is easy to imagine that the power transmitted via a liquid-filled cable increases with the internal and external flow velocity, and I do not dispute this.

The question is only how much of the transferred (cooling) power does each gram of charge air receive?
If the transmitted power only increases by 50%, for example, when doubling the LL (charge air) flow rate, then the cooling capacity per gram of charge air decreases to 1.5 / 2 = 75% of its initial value.

Result: Higher LLT (low-level temperature), even though the LLK (low-level cooler) provides more cooling capacity – but not enough to keep up with the increasing LL (low-level) current draw.
Conversely, the cooling performance per gram of charge air decreases when the mass flow rate of the charge air through the intercooler decreases, or when the charge air remains in the intercooler for a longer period.

This essentially corresponds to my logs as well: with a practically constant LD (load density), the LLT (local lambda temperature) increases with engine speed or LL mass flow.

I should be more illustrative...
You have two identical micro hydropower (MHP) units, each with a power output of 20 kW, operating at a flow rate of X when connected in parallel.
Then, in a series configuration, you have double the flow rate, okay, but perhaps only 98% of that due to the higher pressure loss: 98% * 2 * X...
This increases the internal heat transfer coefficient by perhaps 10%, meaning that at the higher flow rate, you might be able to transfer approximately 21 kW per cooling unit.
And based on the equation provided above, with a constant value of A, this inevitably leads to higher average temperature differences. And that's what you were trying to achieve...
Stay cheerful.
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

olbetec wrote:

Therefore, based on the equation provided above and with a constant value of A, higher average temperature differences inevitably result.

And that is what you wanted to achieve...
Für den 1. LLK in der Reihe mag das gelten. Aber der 2 LLK bekommt ja schon vorgekühlte Ladeluft, so daß sein mittleres Delta T erheblich niedriger liegen wird als beim 1. LLK -> geringere Kühlleistung des 2. LLKBitte gib mir den deutschen Text, den du übersetzt haben möchtest.

With 2 parallel intercoolers, the delta T of both intercoolers is maximized -> resulting in the best cooling performance per gram of charge air}, with the lowest overall pressure loss.

Okay, hier ist die Übersetzung:

"Is that correct?"

Ja das stimmt. Aber bei der Nachrechnung der LLK in Parallelschaltung oder Reihenschaltung wird bei der Berechnung der Temperaturdifferenzen der gesamte Wärmetauscher betrachtet und ihr geht ja von dem gleichen Massenstrom aus. Also ist bei der Parallelschaltung bezogen auf die Durchströmte LLK-Lauflänge ein erheblich größeres Temperaturgefälle bei niedrigen Strömungsgeschwindigkeiten zu erzeugen als bei Serienschaltung. Also kann man das nicht so vereinfacht betrachten...Es bleibt einem also nicht erspart, einmal eine Beispielrechnung durchzuführen, um zu einer Aussage zu kommen. DeUnfortunately, my stomach isn't helping much in this situation...
Stay cheerful.
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

olbetec wrote:

However, when recalculating the latent heat capacity (LLC) in parallel or series configurations, the entire heat exchanger is considered when calculating the temperature differences

. So, from a thermal point of view, it's roughly this question.
"Should I build the larger liquid crystal display (LCD) panel twice as long or twice as wide compared to the original product?"
I have to admit that only through this reformulation would the decision (for minimal LLT at the output) not be as easy for me, instinctively.

EDIT:
The VDI Heat Atlas would certainly be interesting, but with a price of around 600 euros and a target audience of engineers (and similar professions), it's not really my thing.

Quote:

The VDI heat atlas would certainly be interesting, but with a price of around 600 euros and a target audience of engineers (and similar professions), it's not really my thing

.
What's the point of libraries? You can just copy the relevant pages or see below...
On the left and bottom are the dimensionless temperature changes, on the right and top are the heat capacity flow ratios, and Theta represents the constant dimensionless temperature differences (see also the second image). At the bottom (unfortunately cut off in the image) is written: (T2'' - T2') / (T1' - T2').
Carefully recalculated.
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

olbetec wrote:

What's the point of libraries...? You can copy the relevant pages there, or see below...

"Thank you!"

Let's see how much of this I'll be able to understand...

In my opinion, the following steps are necessary to verify a Large Language Model (LLM):
To calculate the heat capacity flows or the thermal conductivity of the cooling liquid: measure the air temperature at the inlet (okay, using the outside air temperature from the onboard computer) and outlet, and determine the volumetric flow rate through reverse calculation. On the low-temperature side, you essentially have all the data readily available except for the compressor discharge temperature (the inlet temperature of the cooling liquid).
Then, estimate the heat transfer capacity of the parallel double latent heat exchanger based on the change in the internal heat transfer coefficient (k*A), and recalculate the achievable average temperature differences by referring back to the diagram. For a series-connected double latent heat exchanger, only double the value of A.
Stay cheerful.
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Okay, so I have a gas refrigerator in my T3 van. It has both intake and exhaust vents. Because the pipes for these are longer than originally intended, I installed a fan in the intake vent (to prevent the flame from going out) - and then wondered why the stainless steel exhaust pipe got much hotter than before. Now I know why, thanks guys!

PS: I'll soon be installing a digital intercooler temperature gauge in my ALH. I plan to switch to an ARL radiator and want to know how much of a difference it actually makes afterward. I'll let you know what I find out.

Hello everyone,

I recently had a second LLK implanted in my AFN.
The renovation took a while, and then I went on vacation.
After the first test drive, it almost seemed like he had less power than before!
Okay, it's been 4 weeks since I last drove, and I couldn't really tell if there was more or less power.
Question:

I've attached two pictures.
Can the experts among you tell me if this is a good idea, or should I leave out the original LLK (likely referring to a specific product or component)?

Thank you in advance!
Best regards,
DJ.

The increased volume of the air intake system results in a longer turbo spool-up time. This might make it feel subjectively slower. You could potentially reduce this by removing the original intercooler. However, who said that this would increase power? At most, the engine control unit won't restrict performance as much in warm weather. The main reason for tuning the intercooler is to reduce thermal stress and enable higher boost pressures for further tuning, thus preventing the system from being prematurely limited in warm weather.Stay cheerful.
OlBe
"A decrease of 20,000 kPa in the low-pressure temperature reduces the engine's compressor performance by approximately 6%, which should result in about a 1% increase in usable pressure. That must be quite an impressive pop meter..."

Hi,

So, I had already noticed significant fluctuations in the outside temperature before.
For example, at 20°C it didn't run as well as it did at 10°C; there was a really significant difference!
'Then I thought, if I install a second air conditioner and it cools the air down even further, would you notice an even bigger difference?'

But that wasn't the only reason I installed a larger radiator.
Sure, I'm planning to run a higher LD soon, and I'll also be adding a 12mm pump piston.
Then I've done everything that can be done .


Regards,
DJ.

@ Ulf:

Can you explain that to me in more detail?

What is the purpose of actually connecting two LLKs in series?
Double boost pressure loss compared to a single turbocharger, and the second turbocharger is less effective because the intake air is already pre-cooled, resulting in a smaller temperature difference with the ambient air.

If I were to do it, I would connect the intercoolers in parallel: this would halve the pressure loss and improve overall performance because the hot intake air would flow into both intercoolers.


Wouldn't it be better if the air was already a bit cooler before it enters the second LLK?
Pressure loss? I still have 1.2 bar - just like before -> so there's no pressure loss.
Response behavior is the same.

Regards,
DJ.

dj1 wrote:

Wouldn't it be better if the air was already a bit cooler before it enters the second LLK?

Then it will come out colder, but the effectiveness of the LLK is wasted: the higher the inlet temperature, the more heat is extracted from the LL.

Quote:

Pressure loss? I still have 1.2 bar - just like before -> so there is no pressure loss. Response behavior is the same.

Lucky you! If you installed the LD sensor behind the second LLK (likely referring to a specific component), then the LD (presumably light intensity) will naturally be regulated for that location.

Assuming that each of your valves causes a pressure drop of 0.1 bar at its maximum flow rate (Pmax).
Previously, your charger had to deliver 1.3 bar at the compressor outlet, and now it's delivering 1.4 bar.

In a parallel configuration, it should theoretically only need to provide about 1.25 bar. And an increase or decrease of 0.15 bar in the target pressure is quite a lot for a TDI turbocharger .