riff_raff: You have an interesting point as usual.
However, I find it a little difficult to believe that the air exiting the radiators would carry as much as 250 kW of energy, why I amused myself by cracking some numbers.
Water's capacity to pick-up or give-away energy, can be popularized as 70W per Liter per minute of flow and Temperature difference in degree C. To give away 250 kW through the radiator, it would require 90 Lpm of water-flow at a temperature-drop through the same radiator of 40 C.
Are you sure that you are not confusing the cooling numbers with the exhaust flow?
"I spent most of my money on wine and women...I wasted the rest"
I would disagree with your numbers slightly, 250kW (14,234 Btu/min) would require about 62L/min (136 lbm/min) of water with a deltaT of 40degC, assuming a specific heat of 1.088 Btu/lbm-degF for water at 100degC.
But otherwise you are correct, a racing engine probably rejects about 10% to 12% of the fuel LHV (approx. 18,200 Btu/lb) content through the coolant. Which for an 800hp F1 engine would be about 180kW at 40% BTE. Thanks for the correction. I probably screwed up converting from HP to kW.
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
Yo riff_raff,
Strange this, 62 Lpm at a deltaT of 40K(C), should with my metric calculations give some 180 kW?
But anyway, 180 kW dissipated through the air is the combined heat of 240 toasters.
Now I understand better what a mess a piece of paper stuck on the radiator can cause.
"I spent most of my money on wine and women...I wasted the rest"
riff_raff,
I double-checked my lazy-dog calc's in SI-units just to make sure, here we go:
Heat capacitivity of water, between 20 and 100C, is 4.18 kJ/kg*K, or 4180 Ws per liter and degree C, if you assume a density of 1 kg per liter. Then divide 4180 with 60 seconds and you will end up with a conveyed thermal power of 69.7 W per Lpm and degree C of deltaT.
Conclusively, if you want to loose 250 000 W through the cooling system with a temperature difference of 40C in and out, of 40 C, you need 250 000/(69.7 * 40) = 89.7 Lpm.
"I spent most of my money on wine and women...I wasted the rest"
Sorry to revive an old thread but can somebody please explain why the device on the radiator of this kart works? Do the horizantal fins stop some of the flow from "spilling" up the radiator, never actually passing threw it?
A fluid flow (whether compressible or not) will always take the path of least resistance. Since the radiator core is canted aft significantly, and thus the radiator fin airflow duct inlets are at a divergent angle to the ambient airstream, the relative inertia of the air mass will cause the airflow to naturally want to spill over the top and sides of the core instead of passing through it.
Normally with race cars, there is an inlet and exhaust duct that creates a condition of high air pressure ahead of the core, and lower air pressure behind the core. That way you have the natural airflow conditions from high pressure to low pressure, required by the laws of physics. Since most of those karts in the photo simply have a heat exchanger hung out in the airflow, with no ducting, the most efficient positioning for that radiator should be perpendicular to the airflow, in an area that has little turbulence. That would create the maximum dynamic pressure ahead of the core, and the lowest flow losses through the core.
As for the horizontal fins in question, they simply cause the airflow to stagnate ahead of the core. Creating a crude form of duct that slows the airflow and increases its local pressure.
Regards,
Terry
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
