Thinking out loud: I wonder if Shad's hood and duct design is much more efficient than the NSX-R? It obviously gets rid of the hvac inlet, likely optimizes radiator positioning, and seems like adjoining flows would be fairly seamless.
Efficiency of Radiator Ducts with Air Vents
- Thread starter Hrant
- Start date
Ty, you are reminding me of all the reasons why I almost flunked physics in college 
:tongue:
It seems this thread is has finally caught the attention that I was hoping, but let's loop it with this one that remained unaswered.
I believe there are two issues that seem to be interconnected in here. One, how to make the radiator/shroud inflow/outflow as efficient as possible for cooling purposes; and second how to capitalize on such efficiency while also increasing downforce.
Regarding radiator efficiency (OEM or otherwise; single fan or dual fan with or without shroud), thus far the answer is murky at best. Based on my visuals, my dual Span fans with the shroud offers more rear "open" coverage than the OEM fan and shroud. So if the shroud is viewed as a negative, mine can't be worse than the OEM. So the next question is which of the radiator ducts will help in the efficiency (and all you aero/physics majors can translate that to air flow or whatever)? If 90 degree angles are bad, then that means the DaliRacing and DF ducts are not efficient when compared to the NSX-R, though the DF has the more sealed approach albeit it leaves both sides of the shroud free floating under the hood.
As for downforce, I believe the consensus is a ducted hood with the undertrays improves downforce albeit at the expense of hot air to the vent. Yep, I just have to get used to using the AC more often.
Cheers.
:tongue:It seems this thread is has finally caught the attention that I was hoping, but let's loop it with this one that remained unaswered.
I believe there are two issues that seem to be interconnected in here. One, how to make the radiator/shroud inflow/outflow as efficient as possible for cooling purposes; and second how to capitalize on such efficiency while also increasing downforce.
Regarding radiator efficiency (OEM or otherwise; single fan or dual fan with or without shroud), thus far the answer is murky at best. Based on my visuals, my dual Span fans with the shroud offers more rear "open" coverage than the OEM fan and shroud. So if the shroud is viewed as a negative, mine can't be worse than the OEM. So the next question is which of the radiator ducts will help in the efficiency (and all you aero/physics majors can translate that to air flow or whatever)? If 90 degree angles are bad, then that means the DaliRacing and DF ducts are not efficient when compared to the NSX-R, though the DF has the more sealed approach albeit it leaves both sides of the shroud free floating under the hood.
As for downforce, I believe the consensus is a ducted hood with the undertrays improves downforce albeit at the expense of hot air to the vent. Yep, I just have to get used to using the AC more often.
Cheers.
Get a hot wire type anemometor, most have a hold max setting, some duct tape and some time. This reads velocity and you can measure the cross section area. Depending on how close you are to the fan, you have to account for a non-uniform cross sectional flow profile.
With velocity and area you can calculate cfm, but make sure you average a few readings across the diameter.
The most efficient set up you can do is making sure you are using the full face of the radiator with no stalled regions across the face of the radiator. A flow disruption upstream will be somewhat evened out naturally from the fin and tubes (nsx-r bar). The reason you want the front shroud mated up to the radiator is to get rid of right angle flow at the face; it will double the pressure rise for this transition.
Post radiator at the shroud, is crucial not to have the walls converge at too sharp of angles. A sharp transition will basically stop flow around the periphery of the heat transfer area.
Don't worry I struggled with waves and optics, but I kinda dug thermal and fluids.
With velocity and area you can calculate cfm, but make sure you average a few readings across the diameter.
The most efficient set up you can do is making sure you are using the full face of the radiator with no stalled regions across the face of the radiator. A flow disruption upstream will be somewhat evened out naturally from the fin and tubes (nsx-r bar). The reason you want the front shroud mated up to the radiator is to get rid of right angle flow at the face; it will double the pressure rise for this transition.
Post radiator at the shroud, is crucial not to have the walls converge at too sharp of angles. A sharp transition will basically stop flow around the periphery of the heat transfer area.
Don't worry I struggled with waves and optics, but I kinda dug thermal and fluids.
That design is also a tradeoff. Unless the base of the windshield and the back of the hood merge smoothly, you are going to have a high pressure region there.
I figure a lot of folks on here wouldn't know of the popular "Cowl Induction" from the US muscle car era, but that is why it was a cool feature for awhile for engine air intake location.
The DA "Cowl Exhaust" could be optimized a little more to reduce that high pressure area, but they would really need access to a wind tunnel or some trusted automotive CFD experts.
I think the best design would be a split duct in the hood, with the radiator exhaust flow directed out to the sides of the windshield like Honda does with the HSV:
I know, I know, the HSV is front-engined, so of course any ducts would be located there. But, the HSV shows the latest advancements in ducting, compared to the old JGTC pictures where they also obviously directed the exhaust to the sides of the windshield rather than right over it:
Oh yeah I definitely had no intentions of getting rid of it.
What I don't understand is why it still blows hot air when I set it to reciculate the air instead of drawing it from outside.
It's self evident, that's why there are radiator fans, its why we experience "chill factor'' when air flows over our face and its why hot wire anemometers work. There may be an upper limit to air flow helping efficiency but it's definitely a key factor.
According to stuntman even at > 100mph the air exits NSX radiator at only around 15-20mph , if the enclosed shroud & duct & hood vent can increase this exit velocity (i.e increase mass flow) then I would be very surprised if thermal efficiency did not improve.
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That's curious. Wondering if others with hood vent experience this too? Perhaps , like I have a at present, there's a fault in your heater control valve?
I don't...
I wouldn't rule it out, no idea how I would go about checking something like that though. I'll have to look in to it some more.
My CC was recently rebuilt by briank so that shouldn't be the problem.
Take the front cowl cover off under the windshield and check your recirc damper is closing correctly. IIRC, you should be able to see the damper.
Dave
I'll have to check this too but even if it is closing correctly, I don't think the seal is tight enough to avoid it completely ...... heck all my other cars can't make the seal tight enough not to get the smell or fumes from outside and this with cabin air filters too!
Do tell, explain how the radiator experiences latent heat transfer? Wind chill has nothing to do with a radiator. Your analogy is flawed, outright wrong. Also, convert the exit velocity to mass flow and compare to the mass flow entering; then you are comparing apples to apples. It should be evident that comparing vehicle velocity to hood exit velocity is not linear!
So, please explain in detail how the radiators thermal efficiency was improved by raising mass flow across the fins? I am all ears.:smile: (hint, this is a trick question)
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Oh yeah I definitely had no intentions of getting rid of it.
What I don't understand is why it still blows hot air when I set it to reciculate the air instead of drawing it from outside.
Sparky and I are in agreement. I don't have my manual handy, but I seem to remember a routine for adjusting the heater core hot water valve. Maybe yours is not adjusted properly.
I know, I know, the HSV is front-engined, so of course any ducts would be located there. But, the HSV shows the latest advancements in ducting, compared to the old JGTC pictures where they also obviously directed the exhaust to the sides of the windshield rather than right over it:
Look at where the the engine air intake is, funny scoop thingy on top center. That maybe influenced decision on hood design?
Heading out to garage with beer and stool... thinking...vent hose to fender or bumber area and seal off top of hvac.
Wowie ...... anemometer
What is that in Engelese 101 for laymen, even spell check doesn't recognize the word ........
:wink: We are talking about a weekend hobby with some cheating go fast add-ons to compensate what otherwise we can't with talent :redface::biggrin: So Ty, let's get real and down to earth. Given what we all have to work with re aftermarket available products, what are you actually saying with the options already discussed thus far - I think my post #52 pretty much summarized the issue
Ty B said:
Ty, your latter statement implies a velocity threshold below which increasing velocity will improve radiator performance. So, do you know, or can you estimate, the optimum air velocity for these NSX radiator configurations we're discussing? I don't know that velocity for sure, but I'm of the opinion stuntman's 15-20 mph exit speed is below this threshhold, and that an enclosed duct to hood vent configuration (designed for nice laminar flow) will increase exit velocity, cfm and thus heat transfer from coolant to air flow.
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Hrant, you mentioned NSX-R style radiator shroud in an earlier post. Assuming we're talking about the exit / fan shroud, where did you get hold of yours? [tks again :smile:]
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Sparky, I didn't pick an NSX-R shroud. If I said or referred to an NSX-R shroud as for the front of the radiator or the shroud that holds the fan I misspoke. To my knowledge the fan shroud is the same for all models though the fan shape has changed over the years.
If you are referring to the NSX-R radiator duct, DaliRacing makes one for RHD and LHD. And ProCar makes them too.
If you are referring to the NSX-R radiator duct, DaliRacing makes one for RHD and LHD. And ProCar makes them too.
OK, i thought there may have been a different fan shroud on the NSX-R. Thanks anyway.
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