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post #1 of (permalink) Old 09-22-2001, 07:11 AM Thread Starter
CJDave
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Why electric fans?

[img]/wwwthreads_images/icons/tongue.gif[/img] As you may have noticed, autos now use electric fans on the sideways-engine models. Obviously, the use of electric fans came because they could no longer include the fan in the accessory drive group on the crank pulley end of the engine. However, there IS another good reason to use an electric fan, DESPITE the fact that reliability is a questionmark, and current draw is fairly high. FUEL MILEAGE is improved by using an electric fan setup over clutch fans or direct-drive fans. Because the HORSEPOWER REQUIRED to drive a fan blade goes up as the CUBE OF THE DIFFERENCE IN SPEED....like when you double the RPM, the new HP required is 2 X 2 X 2 or EIGHT TIMES the original HP. When a clutch fan locks in on a grade at 3500 engine RPM, can you IMAGINE what the HP requirement is? The blade has to be such that it cools at 1500 RPM, so it has a lot of bite. At 3500 RPM, it is a HUGE power-robber. In industrial applications I have to add one gallon of diesel per hour if the engine has a direct-drive fan. However, we DO have the luxury in stationary applications of knowing exactly what the constant engine RPM will be and the fans are chosed specifically for that speed so no extra HP is consumed.....theoretically.....beyond what it takes to do the job. In the automotive world, consessions must be made to cover all possible conditions, so fans have to be made for the worst possible scenario, and that means BIG blades. Even though electric fans are actually driven by the alternator; and the alternator puts more drag on the engine because of it, you have the advantage of running the fans at constant, optimum RPM at all times, and no overspeeding has to occur to waste HP. So the overall HP input to the system is actually less with electric fans. One thing about it; when an elctric fan is OFF, it's off, no drag is present; and when it is on, it is immediately at optimum efficiency, regardless of engine RPM.[img]/wwwthreads_images/icons/tongue.gif[/img]


CJDave
A Jeep Skunkworks run by Moonguys[img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/tongue.gif[/img][img]/wwwthreads_images/icons/laugh.gif[/img], buildin' the ultimate SNOJEEP!
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