ABC's of 80's A/C and Cooling - Part 1
- Thread starter SUMOTOY
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- #42
medtro said:
Not sure that's a correct statement. It *can* have no negative effect on freeway driving, but it *is* is a restriction to airflow vs a smaller one, or one not mounted in direct airflow. Easy to demonstrate, since air and water both share the same properties in terms of flow. Take the grill off, turn the fan on and spray water at the fan, it won't want to go through it, it will go around it. Spray water into the radiator away from the fan, it goes through it.
Confirmed by Flex-a-lite: "... when using an electric fan it is always better to pull the air through the radiator with the fan mounted behind the unit than to push the air through with the fan mounted in front. This is because once the car is up to speed the greatest percentage of air flowing to the radiator will come from the cars movement. Putting a pusher fan in front of the radiator blocks the the incoming air from getting where it needs to go - through the radiator core."
It *is* an obstruction at ram air speeds, it may or may not have a negative effect on cooling. Add more load (heat or towing or altitude) that may not hold true anymore.
My recommendation is to mount a smaller fan out of the direct airflow, that makes a difference to the dash vents with the A/C on. Use the Aux fan to cool the condenser, not the radiator. Using a pusher fan for Auxiliary radiator cooling is not very efficient. Pusher fans tend to be 20% less effective that puller type.
With the 10in fan I used, I mounted it with the lowest part of the shroud at the bottom of the condenser. This leaves less than half the fan exposed to ram air above my TJM. For the task of extending A/C performance in low vehicle speed conditions I targetted, it works well with minimal obstruction to ram air.
Scott Justusson
QSHIPQ Performance Tuning
landtank said:
This is funny - I thought we lost Sumotoy after the "Suspension Travel Upgrades" thread back in April. He was suposedly going to go to his engineer buddies and get a definative answer. I'm guessing the definitive answer was he's wrong, or has no buddies.
Either way, I'm glad the thread came up - gonna go get me a 14" fan tonight.
- Thread starter
- #44
Walking Eagle said:
I look forward to your data on the Fan mod, WE. I'm glad you read the posts and found the advantages to running an aux fan in front of your condenser to decrease dash vent temps. For maximum effectiveness I suggest you read my ABC's of Cooling to get the part numbers for using the existing Medium Pressure Switch circuit.
Scott Justusson
SUMOTOY said:
naw, it just reminded me of the other thred. Mr. T already found the advantages of having a fan infront the condenser. It's not rocket science, just a little thermo and heat transfer. I don't know, since on another thread you talk about using vents to get rid of radiant heat from a turbo, I'm somewhat skeptical of your understanding of cooling. In the end, Toyota used a fan to increase colling capability, and I'm fine with following their lead.
- Thread starter
- #46
Walking Eagle said:
Heat management isn't rocket science, in fact all this is rather simple. That said, I started the ABC thread because several folks here are using A/C compressor feed to trigger the Aux Fan. I believe the medium pressure switch is a better application for triggering, regardless of thoughts as to 'bigger is better' in aux fan application.
In rocket science WE, there are two types of cooling convection and radiant (I'll add no 'conductive' here since we either have a fluid or a heat sink, we're not woried about insulating anything yet). Vents are an excellent way to rid radiant heat from a turbo, or exhaust manifold or supercharger. They are also an excellent way to rid convective heat from the application of more radiator heat transfer. The most effective vent placement will provide excellent convective heat and radiant heat escape.
It would appear that there are a lot of opinions on cooling regarding 80's. Following Toyotas lead, by definition means, following the lead they specifically omitted from US market 80's. With some data and identification, this 'tech list' might even be able to follow current technologies and retrofit these identified improvements to our trucks.
I encourage you to put an aux fan in front of your radiator, following either Toyota or the motivating thread. It appears to be an effective modification.
Scott Justusson
QSHIPQ Performance Tuning
Chicago
FZJ80 Supercharged
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SUMOTOY said:
Exactly how do you believe a vent is allowing more radiant energy to escape the engine compartment? It'll let more air out, but that's convection.
Part of the turbo's radiant energy is going to get bounced back by the hood, part is going to get absorbed by the hood, conduct through the hood, and then go from the hood to the outside air through convection and radiation, and part of it is going to heat the air that then is going to convect out.
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- Thread starter
- #48
Walking Eagle said:
Ok WE. In automotive applications one refers to the *source* of heat and it's venting or insulation/shielding. During engine operations it's the active exchange of fluid (water, antifreeze, R134, air) that causes convection. A hood vent in convection is the active movement of high pressure and high temp air that needs to escape to a lower pressure zone. In radiant heat it is the passive escape of high temp air without an external pressure device (fan, ram air, ducting, scoop)
I'm happy to accomodate you wanting to identify both as convective processies. They aboslutely are. If you would like, I can either identify them as active convection vs passive convection, or any other terms that will help us all differentiate between the two.
It would certainly appear for the placements of vents, we need to, as I'm sure you'd agree. Since there is no 'low pressure' zone caused by fan or vehicle movement in radiant heat release, a passive convection vent might be more efficient in exactly the location where a active convection vent might not or vice versa. And to my exact point, the best vent placement optimizes both active and passive convection (er, car on and car off respectively and simply)
Happy to use whatever terms that will help you with differentiating the two types of venting strategies (pun intended). I believe the terms I used are commonplace and accepted in automotive applications, but happy to be more 'technically' correct.
Scott Justusson
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SUMOTOY said:
It's called forced convection if the fluid motion is caused by a fan, blower, wind ect. It's called free (or natural) covection if the fluid motion is set up by the buoyancy resulting from desity difference cause by the temperature difference with the fluid. Radiant Heat, or Thermal radiation is NOT the passive escape of high temp air.
It's not a matter of being more 'technically' correct. It's either right or wrong. It's either radiant or it's not. What you're talking about is NOT RADIANT HEAT! Doesn't matter if some of your autoshop classmates call it the wrong thing or not. You're wrong - again. Maybe this time you'll have the guts to admit it.
Try wikipedia.org
Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb. Thermal radiation is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation.
The emitted wave frequency of the thermal radiation is a probability distribution depending only on temperature, and for a genuine black body is given by Planck’s law of radiation. Wien's law gives the most likely frequency of the emitted radiation, and the Stefan-Boltzmann law gives the heat intensity.
Convection is the transfer of potential energy, for example heat, by currents within a fluid. Most fluids are liquids, gases, and plasmas, although large solid bodies such as Earth's mantle also behave like a fluid on long time scales and at high pressure and temperature. Thermal convection can arise from temperature differences either within the fluid or between the fluid and its boundary, which maintains a gravitationally unstable density gradient if the temperature gradient increases in the direction of gravity. Other sources of density variations, such as variable composition (for example, salinity), or from the application of an external motive force are also often causes. It is one of the three primary mechanisms of heat transfer, the others being conduction and radiation. Convection occurs in atmospheres, oceans, and planetary mantles.
Free and forced convection
In heat transfer, a distinction is made between free and forced convection.
Free convection is convection in which motion of the fluid arises solely due to the unstable density gradients (for example, the temperature differences existing within the fluid) that can be maintained in the fluid. Example: hot air rising off the surface of a radiator.
The basic premise behind free convection is that heated fluid becomes more buoyant and "rises," while cooler fluid "sinks." Free convection occurs in any liquid or gas which expands or contracts in response to changing temperatures when it is exposed to multiple temperatures in an acceleration field such as gravity or a centrifuge. The local changes in density results in buoyancy forces that cause currents in the fluid. In zero gravity, because buoyancy no longer becomes a factor, free convection does not occur.
Forced convection happens when motion of the fluid is imposed externally (such as by a pump or fan). Example: a fan-powered heater, where a fan blows cool air past a heating element, heating the air. A person blowing on their food to cool it is using forced convection
- Thread starter
- #50
WE said:
Free convection vs force convection it is. Let me restate using that. If you place your hood vents where free convection and forced convection are both optimized, you have the best heat exchange with the 80 off or on (respectively).
A turbo or supercharger or radiator or exhaust manifold that is not ambient temp is a radiant heat source on shutdown. Letting that radiant heat caused by that source, out from under the hood is via either free or forced convection.
Thanks for the clarification WE.
Scott Justusson
Clarification? How about correction. Still can't admit your wrong, eh?
"WE"- I (like many others I'm sure) caught his mistake, and was going to post similar info, but figured it was futile.
"WE"- I (like many others I'm sure) caught his mistake, and was going to post similar info, but figured it was futile.
Information
I appreciate all the info on mods and everyone's expertise but damn..... I feel like I am back in college where I have to read a whole text book to sift through and identify the useful material.. Maybe we should add a section that says---- abridged version or results.....
I appreciate all the info on mods and everyone's expertise but damn..... I feel like I am back in college where I have to read a whole text book to sift through and identify the useful material.. Maybe we should add a section that says---- abridged version or results.....
- Thread starter
- #54
SWCruiser said:I appreciate all the info on mods and everyone's expertise but damn..... I feel like I am back in college where I have to read a whole text book to sift through and identify the useful material.. Maybe we should add a section that says---- abridged version or results.....
Read post 1, then do a search on ABC's of Cooling. You will get 2 other threads. Print post 1 in each. Identified need, identified method of hookup, and identified install. The rest is good chatter I guess.
SJ
- Thread starter
- #55
Walking Eagle said:Well, last time he was wrong he disapeared for 4 months.
You're right, it was futile
WE:
Active and Passive = Forced and Free
Active: using some device to force heated air thru a vent
Forced: using some device to force heated air thru a vent
Passive: The natural effect of radiant heat causing bouyant heated air to rise thru a vent
Free: The natural effect of radiant heat causing buoyant heated air to rise thru a vent
Losing a lot of good information here with some pretty fine technical jargon I'm quite happy to adopt, without having to change any posts. To complete the irony, I suppose we really should technically call a 'radiator' a 'convectionator' too.
Thanks, glad the original post contains the data and information that helps folks understand the need for more active, er, forced convection, on the A/C condenser. I'm hoping step 2 and step 3 can stand up to such intense scrutiny!
WE, once you get your 14in convectionator fan installed, I hoe you can add to LT underhood data.
Scott Justusson
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EDIT: Have to attempt to be nice.
Nice try at a redirect, while trying to make us look dumb.
Nice try at a redirect, while trying to make us look dumb.
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SUMOTOY said:
You are so predictable. You always ask for data. See what you did when the data presented is not in your favor. I don't have to defend any OBDII data. It is what it is, take it however you like.
Oh! I have also done some towing with a 14" electric pusher fan infront through AZ mountains, that is heat and towing and altitude, no overheating, i.e. AC never got shut off automatically by the sensor.
Okay I am done with this thread. Thank you for your education.
- Thread starter
- #59
Walking Eagle said:
As is the nature of all threads, there is a need to shoot messengers, eclipsing the information. WE, again, I will adopt your free convection and forced convection concepts from now on. I believe I didn't need to defend a thing, as before your post I described exactly 'free' and 'forced' convection using 'active' and 'passive'. Further, since I believe this is a very tight technical nuance of terminology, not concept, there doesn't appear to be any discredit, need to correct, or a correction of prior posts. The concept of convection and radiant heat in automobiles has nothing to do with your personal attacks towards me. I deal with 1600 degree glowing turbos almost daily. I know radiant heat well.
I have been known to joke, put up a lot of nerdy posts, and enjoy my 80. I have been attacked several times here, not sure why, maybe because through all this, I see improvements to a very well designed truck. Purists leave it alone, I understand, but attacking me for doing so, seems to be a bit prejudicial.
The irony of this surfacing here, is that the ABC's of Cooling I,II and III were very clear and objective in identifying the need, method, and application of an Aux Fan. Which, prior to these posts, every single one installed used some other method than the one I used. I'm used to discussion and attacks on need, method and application.
What I find somewhat perplexing WE, is your hyper dilegence to grab a technical term as a discreditting device. I'm sure if you shared a beer and any technical discussion, you might find me lacking in engineering terminology, but not application or understanding.
In the meantime, since you obviously found some good in putting an Aux Fan in front of your radiator, I take peace in the fact that the first post of this thread found a mark. I also suspect when I actually get to the hood vent section in ABC IV, I will tread quite carefully as to not use incorrect terminology in addressing it.
Peace
Scott Justusson
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- Thread starter
- #60
medtro said:
Medtro, I read the exact post you directed me to. My summary of the OBDII data presented, In traffic the Aux fan reduced water temps by 5 degrees. If you read my post above, I agree that 'in traffic' you can reduced the temp of your radiator 5 degrees with an aux fan. I also added that above ram air speeds, that fan becomes an obstruction to airflow as well. Is it enough to change your data? I don't know. There is no data "in my favor", there are other documents that may support my opinion on a 14in fan being an obstruction at ram air. I don't want to fight you, only encourage you to present the data during ram air situations.
Ok, I understand that. My question would be, did you try doing any of that towing without the pusher fan on? Did you use the pressure circuit for the fan, or are you manual operation, or did you use the compressor circuit.
You gave a data point, using OBDII. I thank you for an accurate number, and I'm jealous, since I use OBD all the time in my shop to do mods and evaluate them. Don't get mad at me, do some testing in conditions other than when it's already documented a pusher fan is a good thing.
Cheers
Scott Justusson