0.001 deg C / watt

[Circlotron]

I was driving along the freeway the other day at a steady 100 kph in my 1400 kg car for a trip of about 20 km, and seeing it was a hot day just over 40 deg C, before I left home I attached a battery and multimeter to the LM35 temperature sensor that is permanently attached to the engine cooling water outlet that leads to the radiator. I wanted to keep an eye on things and also to see what it would get to on such a hot day.

For most of the way the temp sat on 87 deg +/- 0.5 deg. There was about 20 kilowatts continually being dumped out the radiator to the air.

Where it gets interesting is that the water would not get cooled right down to ambient by the time it exits the bottom of the radiator, but lets be conservative and say it gets down to 60 deg C. That's 20 deg above ambient for 20kW, so we would have a thermal resistance of 0.001 deg per watt. That's some heatsink!

[Tube_Dude]

Originally posted by Circlotron
That's 20 deg above ambient for 20kW, so we would have a thermal resistance of 0.001 deg per watt. That's some heatsink!

Good for a 1 KW "radiator water cooled" class A amplifier!!!

[rwagter]

Nice, but the "natural convection" is helped along with:
1.- a fan
2.- carspeed of 100 kph

unless you'd strap the amplifier on top of your car and use it only when driving fast this c/w needs a bigggg fan

[UrSv]

And WHO said Class A amps were akward in car audio?

[millwood]

or you can remotely mount your amp in some places with really cold windchill (International Falls, ND). How about -11,000 degrees windchill?

[tschrama]

How did you come up with the 20KW figure? Are you sure that's the energy dissipated by the radiotor?

Regards,
Thijs

[rwagter]

20KW might be conservative.

I have no idea what the effivienty of a car is, but a volkswagen golf 1.6 has a 74KW motor (nice that DIN-standard)

[phase_accurate]

but a volkswagen golf 1.6 has a 74KW motor

Keep in mind that this is not dissipation but mechanical power on the shaft.
The efficieny of a car's engine is about 20%, so your Golf's power dissipation would come up to 300 kW approx.

Fortunately the engine's full power is only needed on a short term basis (acceleration etc).

Apart from the radiator, some heat is also released by the exhaust and the engine's surface.

Regards

Charles

[roddyama]

For a gasoline engine, you can roughly figure 25% efficiency, that's power to the shaft. Approximately, a silmilar amount of power goes through the cooling system. The rest is lost in friction, radiant heat, and heat through the exhaust system.

[rwagter]

So we can conclude that there is a possibility for an even bigger amp there