Heat Deflection?
03-02-2001, 01:34 PM
#12
Registered User
I talked to my buddy the thermal engineer and here's what he had to say about rubber insulation:
"Rubber that is used for the air inlet tube already has a low heat transfer coefficient. About .03 W/m*K. Where as insulation (i.e. fluffy glass has a value of .035 to .045. Glass matt is around .038.
So, since the air box is plastic and the inlet tube is rubber, adding more rubber insulation around the system will reduce some of the heat going in. Thermal resistance is kA / L. L is the thickness of the material. So,
lets assume that the hose is .1" and the insulation is .1". It will reduce the increase of air temperature, but not by much. A couple of degrees F."
The heat transfer coefficients he estimated are very close to what some of the manufacturers of the insulation are publishing. It would seem that the key benefit would be in blocking off convection heat from the radiator (which was done in the pictures shown) and then blocking radiant heat with foil would be useful too. Even if you could only reduce temps by 10-20 F, that's still worth 1-2% power gains.
In conclusion, just insulation is adding to the strong point of the current intake system (it's low heat transfer from conduction). But blocking the radiator off and putting a foil coating on addresses areas that the stock system doesn't, and would provide greater effect - theoretically of course.
UL
"Rubber that is used for the air inlet tube already has a low heat transfer coefficient. About .03 W/m*K. Where as insulation (i.e. fluffy glass has a value of .035 to .045. Glass matt is around .038.
So, since the air box is plastic and the inlet tube is rubber, adding more rubber insulation around the system will reduce some of the heat going in. Thermal resistance is kA / L. L is the thickness of the material. So,
lets assume that the hose is .1" and the insulation is .1". It will reduce the increase of air temperature, but not by much. A couple of degrees F."
The heat transfer coefficients he estimated are very close to what some of the manufacturers of the insulation are publishing. It would seem that the key benefit would be in blocking off convection heat from the radiator (which was done in the pictures shown) and then blocking radiant heat with foil would be useful too. Even if you could only reduce temps by 10-20 F, that's still worth 1-2% power gains.
In conclusion, just insulation is adding to the strong point of the current intake system (it's low heat transfer from conduction). But blocking the radiator off and putting a foil coating on addresses areas that the stock system doesn't, and would provide greater effect - theoretically of course.
UL
03-02-2001, 03:57 PM
#13
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[QUOTE]Originally posted by ultimate lurker
[B]I talked to my buddy the thermal engineer and here's what he had to say about rubber insulation:
"Rubber that is used for the air inlet tube already has a low heat transfer coefficient.
[B]I talked to my buddy the thermal engineer and here's what he had to say about rubber insulation:
"Rubber that is used for the air inlet tube already has a low heat transfer coefficient.
03-02-2001, 06:05 PM
#14
Registered User
Yes, the incoming air passes over the radiator top tank and almost certainly picks up some convection heat there. As illustrated in the actual install, sealing this off is probably useful. And there is probably some radiated heat that ups the temperature of the airbox too, so the foil would be nice.
As for Peltier devices, don't forget that there are a couple of drawbacks for this application. First, you've got a current draw to deal with and that sucks power - it is probably minor though. More importantly, trying to cool high velocity, high volume airflows with a cold-plate design is not very effective. As an example, I offer a supercharged CRX. We added an intercooler that is based on a cold plate system welded to the intake manifold. It has about 16 sq in of cooling area and circulates a gallon of coolant to a small heat exchanger in the front grill using a 45 gph pump. On a 60 F day, the intake air under full boost approaches 210 F. With the system in operation, water temperature stabilizes at a mere 90-100 F, but we are only able to reduce intake air temps by about 15-20 F maximum. The problem, as verified in simulations, is lack of surface area. If we were blowing the air through a traditional heat exchanger core, we'd be able to reduce temps by another 40-60 F easily. So, the issue with a Peltier is not having enough surface area, even with a heatsink attached. And then you've got to worry abotu intake obstruction, especially critical in a NA engine.
UL
As for Peltier devices, don't forget that there are a couple of drawbacks for this application. First, you've got a current draw to deal with and that sucks power - it is probably minor though. More importantly, trying to cool high velocity, high volume airflows with a cold-plate design is not very effective. As an example, I offer a supercharged CRX. We added an intercooler that is based on a cold plate system welded to the intake manifold. It has about 16 sq in of cooling area and circulates a gallon of coolant to a small heat exchanger in the front grill using a 45 gph pump. On a 60 F day, the intake air under full boost approaches 210 F. With the system in operation, water temperature stabilizes at a mere 90-100 F, but we are only able to reduce intake air temps by about 15-20 F maximum. The problem, as verified in simulations, is lack of surface area. If we were blowing the air through a traditional heat exchanger core, we'd be able to reduce temps by another 40-60 F easily. So, the issue with a Peltier is not having enough surface area, even with a heatsink attached. And then you've got to worry abotu intake obstruction, especially critical in a NA engine.
UL
03-02-2001, 06:40 PM
#15
The Peltier device sure seems like a neat idea (new to me), especially when dealing with the high ambient temperatures in the summer. Is it even reasonable to propose a finned heat sink on the intake side of the airbox so that all intake area passes over it. A 25F drop might not add a lot of power but it would avoid the big power drop (timing retard?) we see when the ambient temps reach 100F. Would you need a different alternator to pull the amps and how much HP would it take to generate it?
03-02-2001, 08:58 PM
#16
Registered User
If you look at the specs in the link listed, I think some of the issues may become apparent.
First, the devices aren't designed to move a lot of heat. The typical unit has what is called a Qmax of about 10-50 watts. That's a measurement of how much heat can be moved with a 0 degree ambient difference between the hot and cold side. The larger the differential, the less heat can be pumped.
For an idea of how much heat 50 watts is put your hand near a 100 watt lightbulb. Now blow 200 CFM of air by that same lightbulb and see how much the temp of the air goes up by (it won't be much). 200 CFM will be hard to come by, but just put your hairdryer on no heat and blow it over the bulb. Even with the miniscule flow (nowhere near 200 CFM) the air temp won't go up much. The reverse is true for trying to cool something. You won't see much effect. Remember, even your typical hair dryer takes 1000-1500 watts and how much does it heat the air?
In the end, if you wanted to try it, you'd need 6-10 of these devices, each drawing 5-6 amps. 30-50 amps is a lot (your brights probably draw 15 amps or so). The capacity of the alternator is probably in the 100-110 amp range. This would give you the ability to lower air temps by 10-20 F (I think, I just did some rough calcs).
We've run some calcs on this before and it just doesn't seem to make much sense, especially given the cost and difficulty. At present, Peltier devices are best used for small device cooling, or maintaining the temps in an insulated compartment, or cooling down a fixed thermal mass. Someday they may be useful for forced air cooling applications.
UL
First, the devices aren't designed to move a lot of heat. The typical unit has what is called a Qmax of about 10-50 watts. That's a measurement of how much heat can be moved with a 0 degree ambient difference between the hot and cold side. The larger the differential, the less heat can be pumped.
For an idea of how much heat 50 watts is put your hand near a 100 watt lightbulb. Now blow 200 CFM of air by that same lightbulb and see how much the temp of the air goes up by (it won't be much). 200 CFM will be hard to come by, but just put your hairdryer on no heat and blow it over the bulb. Even with the miniscule flow (nowhere near 200 CFM) the air temp won't go up much. The reverse is true for trying to cool something. You won't see much effect. Remember, even your typical hair dryer takes 1000-1500 watts and how much does it heat the air?
In the end, if you wanted to try it, you'd need 6-10 of these devices, each drawing 5-6 amps. 30-50 amps is a lot (your brights probably draw 15 amps or so). The capacity of the alternator is probably in the 100-110 amp range. This would give you the ability to lower air temps by 10-20 F (I think, I just did some rough calcs).
We've run some calcs on this before and it just doesn't seem to make much sense, especially given the cost and difficulty. At present, Peltier devices are best used for small device cooling, or maintaining the temps in an insulated compartment, or cooling down a fixed thermal mass. Someday they may be useful for forced air cooling applications.
UL
03-02-2001, 09:38 PM
#17
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[QUOTE]Originally posted by ultimate lurker
[B]If you look at the specs in the link listed, I think some of the issues may become apparent.
First, the devices aren't designed to move a lot of heat.
[B]If you look at the specs in the link listed, I think some of the issues may become apparent.
First, the devices aren't designed to move a lot of heat.
03-02-2001, 09:57 PM
#18
Banned
Am I the only one who thinks that this whole approach is....ummm....majorly flawed?
No, I have no "physics" based reason, but I just simply cannot imagine that this would make any noticeable difference in anything. Plastic is not a good conductor of heat...so why would you think that this tape would make any difference? And a difference you can FEEL?!
I'm sorry, I'm just not buying it.
No, I have no "physics" based reason, but I just simply cannot imagine that this would make any noticeable difference in anything. Plastic is not a good conductor of heat...so why would you think that this tape would make any difference? And a difference you can FEEL?!
I'm sorry, I'm just not buying it.
03-03-2001, 06:33 AM
#19
Registered User
Greg,
As the comment from the thermal engineer stated, just rubber insulation isn't going to have a major effect, because that's where the strength of the stock system is. But sealing off the radiator and adding reflective surfaces will help, the radiator being the most relevant. It's much like the BYS intake plate in theory, just a lot cheaper.
UL
As the comment from the thermal engineer stated, just rubber insulation isn't going to have a major effect, because that's where the strength of the stock system is. But sealing off the radiator and adding reflective surfaces will help, the radiator being the most relevant. It's much like the BYS intake plate in theory, just a lot cheaper.
UL