Re: Wind Chill on machinery

Posted by ScottyHOMEy on December 10, 2009 at 09:53:32 from (71.241.220.190):

In Reply to: Re: Wind Chill on machinery posted by JMOR on December 10, 2009 at 08:15:13:

Yep. We humans are equipped for evaporative cooling (you left that one out, but I figure it was included in the . . .) and that's what the windchill factor takes in.

To jdemaris's point, a radiator by design will indeed carry heat away from the source even in still air, but only up to a point. I'm not enough of an engineer to say whether it is strictly convection or conduction or some combination of the two, but the idea is that the fine fins serve to increase the area for the heat exchange between the source and the coolant (ambient air being the coolant). Perhaps others have had the experience, but I had a car a few years back that began to overheat on upgrades, even in mild weather. The problem was that the fins had corroded so from road salt that there was little left except the tubing in the core to transfer the heat away. Lesson? The tubes themselves are not sufficient -- they need the added surface area of the fins for the radiator to work.

The same principle is at work in lots of places. Theres a reason for fans pulling or driving air over radiators in things like refrigerators and air conditioners. A radiator in still air, a staionary app like an air conditioner, or an idling vehicle, will build an envelope of heat around the cooling surfaces, eventually rising to near the temperature of the internal coolant, and no longer have a cooling effect. Some of it can be attributed to marginal design. But the concept is evident in a vehicle with an electric fan. It will idle quietly up to a point. But if the still air allows that envelope of warm air in the fins of the radiator to reach the point where they stop cooling, an aquastat will detect the rising temp of the internal coolant, and you'll eventually hear the howl of the fan as it kicks in to draw more air to restore the cooling effect. Agree or disagree, there is no denying the effectiveness of that design or, on the flip side, the effectiveness of radiator shutters or curtains on the front of a big rig (or a tractor) to inhibit the flow of air to maintain a higher operating temperature.

In the extreme on both ends, is the heat pump concept for heating and cooling homes. There are upper and lower extremes of temp at which they are efficient. As design has improved those temps are getting more and more extreme, but there is a physical limit beyond which the exchange of heat is not sufficient to provide the heating or cooling desired.

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