Why Asymmetry in radiator

Roscal · 08-17-2002, 03:03 PM

Look at this radiator (BM Opel Corsa). The 2 rooms (inlet and outlet) are asymmetric. I think it's about the loss of load (pressure drop) in the radiator, water comes in the small inlet (right on the pic) to go to the big outlet (Passage of a small section to one bigger (more tubes) so less loss of load )

Someone could confirm or not this explanation? Has someone realized some flow tests in the two differents directions (small-->big and big-->small) to have a comparison?

Limeygreg · 08-17-2002, 04:41 PM

Interesting.

It may be that because of the delta T between the delivery temp and the air temp is greater on the inlet side compared to the outlet side (as heat has already been extracted). We are talking heater core here with engine block coolant at just below 200F.

The greater the delta T the more efficient the heat transfer, so as the delta T is highest on the inlet side it needs less radiator core because thermal transfer is high. When the coolant gets to the other side it is cooler, the delat T is less and so the heater core has a larger area to increse the effective heat transfer to the air.

That's my $0.02 for what it's worth.

Of course, in our application this "deliberate lopsidedness" to increse thermal heat transfer efficiency is undoubtidly negligable due to the low coolant temperature that a CPU liquid cooling system runs at.

redleader · 08-17-2002, 04:52 PM

Probably because one line is going to a 3/4 in part and the other is leaving a 5/8 in one. These are heatercores, they make the cabin a little more comfortable. Performance is basically a nonissue. Size and cost are.

Limeygreg · 08-17-2002, 05:05 PM

That's what I get for being in this "most efficient water cooling mode" with WB channels, resricitve flows and radiator sizing - I MISS THE MOST OBVIOUS ANSWER

Sounds good though.

Roscal · 08-17-2002, 05:10 PM

Another explanation :
Hot water goes in the larger tank to increase the efficiency of the radiator. Heat transfer is dependent on temperature difference, thus, the most efficient part of the radiator is where the temp difference is greatest. So by making the most surface area available when the water is hottest, you get rid of more heat than having the input and output the same size. As the water cools down heat transfer drops and this becomes a problem when the heat transferrate drops to a point where it cant remove enough heat from the water before the water leaves the radiator.

BillA · 08-17-2002, 06:01 PM

bassakwards fellahs

think heating air, NOT dumping heat

they are equalizing the heat transferred by making the hotter inlet portion smaller

uniform air temp is the goal

Limeygreg · 08-17-2002, 11:44 PM

That's what I said didn't I ???

Smaller inlet surface area coz the water is hotter, larger outlet surface area coz the water is cooler.

Yep, I just read my first post again and that's what I said alright.

Thank you BillA for confirming my reasoning, I knew reading all that info on thermal stuff (technical term

) was sinking in.

BillA · 08-17-2002, 11:51 PM

indeed you did
I shoulda read more closely

JimS · 08-18-2002, 03:47 PM

What makes you think the inlet is the smaller opening, I thought it was the opposite?

Limeygreg · 08-18-2002, 06:15 PM

I don't believe I was talking about the size of the inlet, I was talking about the size of the core and how it is divided. The inlet and outlet tubes look like they are the same size to me, but I don't have the core in front of me to measure it - maybe Roscal would like to confirm their size.

redleader · 08-18-2002, 07:42 PM

I don't see how having one inlet bigger changes anything. The same amount going in and out right ?

The only thing I can think of is the inlet velocity would be lower, but thats just in the pipe, channel fluid velocity shouldn't be affected.

redleader · 08-19-2002, 12:49 AM

Nevermind, I just looked more closely at the picture. Please ignore what I posted above.

Roscal · 08-19-2002, 04:23 AM

I sent a mail to a firm which use the same asymmetry on its radiators (not for cars) so there is a good reason to do that.
I'm expecting the answer

JimS · 08-19-2002, 07:26 AM

Cool Roscal, I would like to know as well. I know that my heater core and most that I have seen have different size inlets and outlets. There obviously is a reason for this. I always thought the inlet was larger to keep maximum water and pressure inside the radiator, eliminating air in there.

08-17-2002, 03:03 PM	#1
Roscal Cooling Savant Join Date: Apr 2002 Location: North of France Posts: 198	Why Asymmetry in radiator Look at this radiator (BM Opel Corsa). The 2 rooms (inlet and outlet) are asymmetric. I think it's about the loss of load (pressure drop) in the radiator, water comes in the small inlet (right on the pic) to go to the big outlet (Passage of a small section to one bigger (more tubes) so less loss of load ) Someone could confirm or not this explanation? Has someone realized some flow tests in the two differents directions (small-->big and big-->small) to have a comparison? Last edited by Roscal; 08-17-2002 at 04:23 PM.

08-18-2002, 06:15 PM	#10
Limeygreg Cooling Neophyte Join Date: Aug 2002 Location: Los Angeles, CA. Posts: 20	I don't believe I was talking about the size of the inlet, I was talking about the size of the core and how it is divided. The inlet and outlet tubes look like they are the same size to me, but I don't have the core in front of me to measure it - maybe Roscal would like to confirm their size. Last edited by Limeygreg; 08-19-2002 at 12:03 AM.

08-17-2002, 04:41 PM	#2
Limeygreg Cooling Neophyte Join Date: Aug 2002 Location: Los Angeles, CA. Posts: 20	Interesting. It may be that because of the delta T between the delivery temp and the air temp is greater on the inlet side compared to the outlet side (as heat has already been extracted). We are talking heater core here with engine block coolant at just below 200F. The greater the delta T the more efficient the heat transfer, so as the delta T is highest on the inlet side it needs less radiator core because thermal transfer is high. When the coolant gets to the other side it is cooler, the delat T is less and so the heater core has a larger area to increse the effective heat transfer to the air. That's my $0.02 for what it's worth. Of course, in our application this "deliberate lopsidedness" to increse thermal heat transfer efficiency is undoubtidly negligable due to the low coolant temperature that a CPU liquid cooling system runs at.

08-17-2002, 04:52 PM	#3
redleader Thermophile Join Date: Jun 2001 Location: The deserts of Tucson, Az Posts: 1,264	Probably because one line is going to a 3/4 in part and the other is leaving a 5/8 in one. These are heatercores, they make the cabin a little more comfortable. Performance is basically a nonissue. Size and cost are.

08-17-2002, 05:05 PM	#4
Limeygreg Cooling Neophyte Join Date: Aug 2002 Location: Los Angeles, CA. Posts: 20	That's what I get for being in this "most efficient water cooling mode" with WB channels, resricitve flows and radiator sizing - I MISS THE MOST OBVIOUS ANSWER Sounds good though.

08-17-2002, 05:10 PM	#5
Roscal Cooling Savant Join Date: Apr 2002 Location: North of France Posts: 198	Another explanation : Hot water goes in the larger tank to increase the efficiency of the radiator. Heat transfer is dependent on temperature difference, thus, the most efficient part of the radiator is where the temp difference is greatest. So by making the most surface area available when the water is hottest, you get rid of more heat than having the input and output the same size. As the water cools down heat transfer drops and this becomes a problem when the heat transferrate drops to a point where it cant remove enough heat from the water before the water leaves the radiator.

08-17-2002, 06:01 PM	#6
BillA CoolingWorks Tech Guy Formerly "Unregistered" Join Date: Dec 2000 Location: Posts: 2,371.493,106 Posts: 4,440	bassakwards fellahs think heating air, NOT dumping heat they are equalizing the heat transferred by making the hotter inlet portion smaller uniform air temp is the goal

08-17-2002, 11:44 PM	#7
Limeygreg Cooling Neophyte Join Date: Aug 2002 Location: Los Angeles, CA. Posts: 20	That's what I said didn't I ??? Smaller inlet surface area coz the water is hotter, larger outlet surface area coz the water is cooler. Yep, I just read my first post again and that's what I said alright. Thank you BillA for confirming my reasoning, I knew reading all that info on thermal stuff (technical term ) was sinking in.

08-17-2002, 11:51 PM	#8
BillA CoolingWorks Tech Guy Formerly "Unregistered" Join Date: Dec 2000 Location: Posts: 2,371.493,106 Posts: 4,440	indeed you did I shoulda read more closely

08-18-2002, 03:47 PM	#9
JimS Cooling Savant Join Date: Jun 2001 Location: Connecticut Posts: 140	What makes you think the inlet is the smaller opening, I thought it was the opposite?

08-18-2002, 07:42 PM	#11
redleader Thermophile Join Date: Jun 2001 Location: The deserts of Tucson, Az Posts: 1,264	I don't see how having one inlet bigger changes anything. The same amount going in and out right ? The only thing I can think of is the inlet velocity would be lower, but thats just in the pipe, channel fluid velocity shouldn't be affected.

08-19-2002, 12:49 AM	#12
redleader Thermophile Join Date: Jun 2001 Location: The deserts of Tucson, Az Posts: 1,264	Nevermind, I just looked more closely at the picture. Please ignore what I posted above.

08-19-2002, 04:23 AM	#13
Roscal Cooling Savant Join Date: Apr 2002 Location: North of France Posts: 198	I sent a mail to a firm which use the same asymmetry on its radiators (not for cars) so there is a good reason to do that. I'm expecting the answer

08-19-2002, 07:26 AM	#14
JimS Cooling Savant Join Date: Jun 2001 Location: Connecticut Posts: 140	Cool Roscal, I would like to know as well. I know that my heater core and most that I have seen have different size inlets and outlets. There obviously is a reason for this. I always thought the inlet was larger to keep maximum water and pressure inside the radiator, eliminating air in there.

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